Detecting Subclinical Biventricular Impairment in Scleroderma Patients by Use of Pulsed-Wave Tissue Doppler Imaging

Systemic scleroderma is a disease that is characterized by excessive fibroblastic activity and collagen deposition in various organs, including the heart. We sought to evaluate the limits of biventricular function as derived noninvasively from pulsed-wave tissue Doppler imaging (TDI) of tricuspid and mitral annular motion in patients who had scleroderma.We enrolled 24 patients with scleroderma (study group; mean age, 49 ± 11 yr; 20 women) and 24 healthy participants (control group; mean age, 51 ± 9 yr; 19 women). Persons with cardiovascular risk factors were excluded. We obtained images by conventional echocardiography and by pulsed-wave TDI, measuring the respective peak systolic velocities (S, Sm) and peak early (E, Em) and late (A, Am) diastolic velocities. Mean Sm, mean Em, and mean Am were averages of the 4 measured sites (anterior, inferior, lateral, and septal). We calculated noninvasive estimates of left ventricular (LV) filling pressure by dividing E velocities (from the mitral inflow) by Em velocities (E/Em ratios).Biventricular regional Sm, regional LV myocardial Em, and ratios of myocardial Em/atrial component velocity (Em/Am) for the LV, and mean Sm, mean Em, and mean Em/mean Am ratios for the LV were significantly lower in the study group. The E/Em ratio was higher in the study group (7.3 ± 2.6 vs 5.2 ± 1.0, P = 0.01). Global LV systolic and diastolic function did not differ between the groups.Tissue Doppler imaging complements conventional echocardiography in detecting subclinical biventricular impairment in patients with scleroderma who have normal global measurements.Key words: Case-control studies, diastole/physiology, echocardiography/methods, heart diseases/ultrasonography, heart ventricles/ultrasonography, scleroderma, systemic/complications/diagnosis/physiopathology, sensitivity and specificity, systole/physiology, ultrasonography, Doppler, pulsed/methods, ventricular dysfunction/ultrasonographySystemic sclerosis is a connective-tissue disease that is clinically characterized by variable involvement of the skin and the visceral organs.¹ Involvement of the heart is one of the most frequent complications that has been reported in several clinical investigations and autopsy studies.^1–3 When scleroderma involves the heart, fibrosis due to collagen deposition replaces damaged muscle cells with fibrous ones, which leads to atrial and ventricular arrhythmias, conduction disturbances, and right ventricular (RV) and left ventricular (LV) systolic and diastolic dysfunction.⁴ Cardiac involvement can exist without symptoms; once it becomes clinically apparent, the affected patient''s prognosis is poor.^5–7Pulsed-wave tissue Doppler imaging (PW TDI) is a recently developed ultrasonographic technique that enables quantitative analysis of global and regional myocardial function. It has been shown that early diagnosis of ventricular dysfunction is possible by the use of newer techniques such as PW TDI.^8,9 Previous investigators who used tissue Doppler echocardiography reported reduced systolic myocardial function of the LV¹⁰ and significant improvement after patients were treated with nifedipine,¹¹ while others¹² detected no alteration in the systolic function of patients who had scleroderma. Several investigators have reported LV diastolic dysfunction after using conventional echocardiography or TDI.^12–15 Right ventricular diastolic impairment has also been reported.^15–17 In our study, we sought to investigate RV and LV function by both conventional echocardiography and PW TDI.     

Feasibility of Temporary Biventricular Pacing after Off-Pump Coronary Artery Bypass Grafting in Patients with Reduced Left Ventricular Function

In selected patients undergoing cardiac surgery, our research group previously showed that optimized temporary biventricular pacing can increase cardiac output one hour after weaning from cardiopulmonary bypass. Whether pacing is effective after beating-heart surgery is unknown. Accordingly, in this study we examined the feasibility of temporary biventricular pacing after off-pump coronary artery bypass grafting.The effects of optimized pacing on cardiac output were measured with an electromagnetic aortic flow probe at the conclusion of surgery in 5 patients with a preoperative mean left ventricular ejection fraction of 0.26 (range, 0.15–0.35). Atrioventricular (7) and interventricular (9) delay settings were optimized in randomized order.Cardiac output with optimized biventricular pacing was 4.2 ± 0.7 L/min; in sinus rhythm, it was 3.8 ± 0.5 L/min. Atrial pacing at a matched heart rate resulted in cardiac output intermediate to that of sinus rhythm and biventricular pacing (4 ± 0.6 L/min). Optimization of atrioventricular and interventricular delay, in comparison with nominal settings, trended toward increased flow.This study shows that temporary biventricular pacing is feasible in patients with preoperative left ventricular dysfunction who are undergoing off-pump coronary artery bypass grafting. Further study of the possible clinical benefits of this intervention is warranted.Key words: Arrhythmias, cardiac/therapy; cardiac pacing, artificial/methods; cardiac output, low/therapy; heart failure/therapy; stroke volume; ventricular dysfunction, left/complications/prevention & controlCardiac resynchronization therapy in the form of biventricular pacing (BiVP) results in long-term improvements in left ventricular (LV) function and in heart-failure morbidity and mortality rates.^1–4 Consequently, it has become the standard of care for select patients with advanced congestive heart failure (CHF), reduced LV function, and intraventricular conduction delay (IVCD).⁵ Biventricular pacing acutely raises stroke volume and maximal first derivative of pressure (dP/dt_max) and reduces intraventricular dyssynchrony, without increasing myocardial oxygen consumption.^6,7 Accordingly, considerable interest has developed in regard to the acute hemodynamic effects of temporary BiVP in patients at risk of low-output states after cardiopulmonary bypass (CPB).^8–24 In patients with reduced preoperative LV function and IVCD, we recently reported a 10% to 13% increase in intraoperative cardiac output when BiVP was performed after weaning those patients from CPB.²⁴ It was also shown that the benefit of BiVP was amplified by the optimization of pacemaker settings such as atrioventricular delay (AVD) and interventricular delay (VVD). Whether these effects extend to patients who undergo surgery without CPB and cardioplegic arrest is unclear. Accordingly, we evaluated the effects of temporary BiVP on cardiac output in patients undergoing off-pump coronary artery bypass grafting (CABG). We compared optimized BiVP to right atrial pacing (AAI) and to sinus rhythm.     

Posterobasal Left Ventricular Aneurysms: Surgical Treatment and Long-Term Outcomes

This retrospective study analyzes short- and long-term outcomes in 18 patients who underwent repair of posterobasal left ventricular aneurysm from January 1993 through December 2009. As concomitant procedures, mitral reconstruction was performed in 4 patients, ventricular septal defect repair in 2 patients, and coronary artery bypass grafting in 17 patients. In regard to surgical technique, 10 patients underwent patch repair and 8 underwent closure by linear suture.The in-hospital mortality rate was 11% (2 patients). An intra-aortic balloon pump was placed postoperatively in 1 patient. One patient underwent reoperation for mediastinitis and 2 for bleeding. The 1-, 5-, and 10-year survival rates were 82%, 76%, and 52%, respectively.Posterobasal left ventricular aneurysm repair can be performed with low short-term mortality rates and good long-term outcomes. It must be judged whether a linear repair or patch repair is better, in accordance with aneurysm size and the concomitant operative procedure, if any.Key words: Aneurysm, left ventricular; aneurysmectomy; cardiac surgical procedures/mortality; heart aneurysm/mortality/surgery; heart ventricle/surgery; myocardial infarction; retrospective studiesPosterior left ventricular (LV) aneurysms are less common than anterior aneurysms.^1–3 Their prevalence in large series has usually been reported as less than 10%.^2–4 The posterobasal part of the heart is supplied by the left circumflex coronary artery and by terminal branches of the right coronary artery.⁵ Pathologic states of these branches cause inferoposterior or posterolateral LV aneurysm.³ Posterior aneurysms can be accompanied by various degrees of mitral insufficiency⁶ and by ventricular septal defects (VSD).⁷ A 2004 study reported mitral insufficiency of grade 2/4 or higher in all 13 patients who underwent repair of aneurysm due to posterior myocardial infarction (MI).⁶ Our study investigates operative results among patients who underwent surgery for posterior LV aneurysm. Our surgical approach is discussed in terms of short- and long-term outcomes.     

Atypical Transient Stress-Induced Cardiomyopathies with an Inverted Takotsubo Pattern in Sepsis and in the Postpartal State

Several cases of inverted Takotsubo cardiomyopathy—a variant form with hyperdynamic left ventricular apex and akinesia of the left ventricular base and mid-portion—have been reported recently, especially in association with cerebrovascular accidents and catecholamine cardiomyopathies. Herein, we describe 2 cases of inverted Takotsubo cardiomyopathy: one that occurred in a middle-aged woman who had a septic condition, and another in a young woman who was in the postpartal state. Such cases have not been reported previously.Key words: Cardiomyopathies/physiopathology/therapy/ultrasonography, coronary angiography, echocardiography, heart ventricles/physiopathology/radiography, postpartum period, sepsis, ventricular dysfunction/diagnosis/physiopathology, ventricular dysfunction, leftStress-induced cardiomyopathy is characterized by a transient abnormality of left ventricular (LV) apical wall motion, electrocardiographic changes, and minimal cardiac enzyme release. The condition mimics acute coronary syndrome in patients who have no angiographic stenosis upon coronary angiography. Recently, atypical stress-induced cardiomyopathies without involvement of the LV apex have been reported.¹ Most of the cases were transient midventricular ballooning syndrome with midventricular akinesia and normal wall motion of the LV base and apex,^1–3 and some were the “inverted Takotsubo pattern” cardiomyopathy that is characterized by a hyperdynamic LV apex and akinesia of the LV base and mid-portion.^4–6 Here, we describe 2 cases of inverted Takotsubo cardiomyopathy, one of which occurred in a middle-aged woman with a septic condition and one in a young woman who was in the postpartal state.     

Pathophysiology of the Syndrome: Biventricular Takotsubo Cardiomyopathy: Case Report and General Discussion

In recent years, our understanding of the physiologic mechanisms of transient takotsubo cardiomyopathy has improved because of the growing use of emergent heart catheterization in patients who present with severe ischemic syndromes. However, even this procedure has revealed only that, in most patients with takotsubo syndrome, the sudden onset of ventricular dysfunction is not due to fixed coronary artery occlusions. We present a case of transient takotsubo cardiomyopathy with an exceptional feature—uneven impairment of both right and left ventricular function, or biventricular takotsubo—and we discuss a novel, comprehensive theory that we have devised to explain the pathophysiology of this syndrome''s many manifestations.Key words: Acetylcholine/diagnostic use, angina pectoris, variant, coronary endothelial dysfunction, coronary vasospasm/physiopathology, takotsubo cardiomyopathy/classification/diagnosis/physiopathology, ventricular dysfunction, left/etiology/diagnosis, ventricular dysfunction, right/etiology/diagnosisOnly during the last 2 decades have Japanese authors^1,2 specifically categorized transient takotsubo cardiomyopathy (TTC) as an entity in itself. Before that time, TTC was often called “acute myocardial infarction with normal coronary arteries.”³ Its prevalence is probably as low today as in the remote past. However, acute coronary artery syndromes are now studied aggressively with emergent heart catheterization, which documents better than any previous means the transience of the myopathy and the presence of apparently normal coronary arteries. These circumstances have stimulated the quest to generate a pathophysiologic concept broad enough to encompass the full clinical spectrum of TCC.Apical ballooning (resulting in a systolic takotsubo or “octopus trap”) is the most frequent and emblematic feature of TTC. The use of this term has successfully promoted awareness of the disease in the cardiology community at large, but it has also impeded clinicians'' understanding of the breadth of this entity''s clinical manifestations. Our persistently inadequate knowledge of the nature and spectrum of TTC seems to warrant an update on the subject.Here, we present a case of right ventricular (in union with left ventricular) TTC. In addition, we discuss a pathophysiologic theory that our group has recently proposed, which might explain the newly discovered and broad spectrum of TTC clinical manifestations.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:Synergistic regulation of nonbinary molecular switches by protonation and light

We report a molecular switching ensemble whose states may be regulated in synergistic fashion by both protonation and photoirradiation. This allows hierarchical control in both a kinetic and thermodynamic sense. These pseudorotaxane-based molecular devices exploit the so-called Texas-sized molecular box (cyclo[2]-(2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene); 1⁴⁺, studied as its tetrakis-PF₆ ⁻ salt) as the wheel component. Anions of azobenzene-4,4′-dicarboxylic acid (2H⁺•2) or 4,4′-stilbenedicarboxylic acid (2H⁺•3) serve as the threading rod elements. The various forms of 2 and 3 (neutral, monoprotonated, and diprotonated) interact differently with 1⁴⁺, as do the photoinduced cis or trans forms of these classic photoactive guests. The net result is a multimodal molecular switch that can be regulated in synergistic fashion through protonation/deprotonation and photoirradiation. The degree of guest protonation is the dominating control factor, with light acting as a secondary regulatory stimulus. The present dual input strategy provides a complement to more traditional orthogonal stimulus-based approaches to molecular switching and allows for the creation of nonbinary stimulus-responsive functional materials.

Multifactor regulation of biomolecular machines is essential to their ability to carry out various biological functions (1 –11). Construction of artificial molecular devices with multifactor regulation features may allow us to understand and simulate biological systems more effectively (12 –31). However, creating and controlling such synthetic constructs remains challenging (16, 32 –37). Most known systems involving multifactor regulation, including most so-called molecular switches and logic devices (38 –43), have been predicated on an orthogonal strategy wherein the different control factors that determine the distribution of accessible states do not affect one another (20, 44 –56). However, in principle, a greater level of control can be achieved by using two separate regulatory inputs that operate in synergistic fashion. Ideally, this could lead to hierarchical control where different states are specifically accessed by means of appropriately selected nonorthogonal inputs. However, to our knowledge, only a limited number of reports detailing controlled hierarchical systems have appeared (57). Furthermore, the balance between specific effects (e.g., kinetics vs. thermodynamics) under conditions of stimulus regulation is still far from fully understood (54). There is thus a need for new systems that can provide further insights into the underlying design determinants. Here we report a set of pseudorotaxane molecular shuttles that act as multimodal chemical switches subject to hierarchical control.     

Syncope from Dynamic Left Ventricular Outflow Tract Obstruction Simulating Hypertrophic Cardiomyopathy in a Patient with Primary AL-Type Amyloid Heart Disease

Dynamic left ventricular outflow tract (LVOT) obstruction is seen classically in hypertrophic cardiomyopathy. Cardiac amyloidosis can present with asymmetric hypertrophy that resembles hypertrophic cardiomyopathy, and, in some cases, with dynamic LVOT obstruction. The occurrence of syncope in such patients is not uncommon. The syncope is usually thought to be related to mechanisms other than LVOT obstruction, such as arrhythmias, conduction disturbances, orthostatic hypotension, or vasovagal effects associated with neuropathy.Herein, we report the case of a patient who had immunocyte-derived (primary AL-type) cardiac amyloidosis with the echocardiographic appearance of hypertrophic cardiomyopathy and evidence of LVOT obstruction that caused syncope. We were able to provoke and identify dynamic LVOT obstruction that produced presyncopal symptoms similar to those that typically occur in such patients spontaneously. Dynamic LVOT obstruction as a cause of syncope should be considered in patients who have cardiac amyloidosis and echocardiographic evidence of hypertrophic cardiomyopathy.Key words: Amyloidosis/classification/diagnosis/etiology/mortality/pathology/therapy, cardiomyopathies/complications/diagnosis, cardiomyopathy, hypertrophic/diagnosis, diagnosis, differential, echocardiography, heart failure/etiology, prognosis, syncope/etiology/physiopathology, ventricular outflow obstruction/etiologyThe estimated age-adjusted incidence of immunocyte-derived (primary AL-type) amyloidosis is approximately 3,000 cases annually in the United States.¹ Cardiac involvement is frequent and is the cause of death in at least 50% of affected patients.² The most common echocardiographic findings include granular myocardial appearance, thickened ventricular walls, small cavities, the spectrum of diastolic dysfunction (from impaired relaxation to restrictive physiology), and, in advanced stages, systolic dysfunction.^3–5 In a small percentage of patients (3%–5%), myocardial infiltration by amyloid has been reported to simulate hypertrophic cardiomyopathy (HCM) with asymmetric septal hypertrophy.^6,7Despite evidence of left ventricular outflow tract (LVOT) obstruction that is identified by documenting systolic anterior motion of the mitral valve,⁸ early systolic aortic valve closure,⁹ increase in LVOT flow velocity by continuous-wave Doppler echocardiography,¹⁰ and deterioration of hemodynamics after treatment with vasodilators,¹¹ the occurrence of syncope in these patients has been attributed to mechanisms other than LVOT obstruction.¹²We report here the case of a patient who had primary AL-type cardiac amyloidosis and syncope with echocardiographic evidence of HCM. We were able to provoke and identify dynamic LVOT obstruction that produced presyncopal symptoms similar to those that typically occur in such patients spontaneously.     

Cardiac myosin binding protein C regulates postnatal myocyte cytokinesis

Homozygous cardiac myosin binding protein C-deficient (Mybpc^t/t) mice develop dramatic cardiac dilation shortly after birth; heart size increases almost twofold. We have investigated the mechanism of cardiac enlargement in these hearts. Throughout embryogenesis myocytes undergo cell division while maintaining the capacity to pump blood by rapidly disassembling and reforming myofibrillar components of the sarcomere throughout cell cycle progression. Shortly after birth, myocyte cell division ceases. Cardiac MYBPC is a thick filament protein that regulates sarcomere organization and rigidity. We demonstrate that many Mybpc^t/t myocytes undergo an additional round of cell division within 10 d postbirth compared with their wild-type counterparts, leading to increased numbers of mononuclear myocytes. Short-hairpin RNA knockdown of Mybpc3 mRNA in wild-type mice similarly extended the postnatal window of myocyte proliferation. However, adult Mybpc^t/t myocytes are unable to fully regenerate the myocardium after injury. MYBPC has unexpected inhibitory functions during postnatal myocyte cytokinesis and cell cycle progression. We suggest that human patients with homozygous MYBPC3-null mutations develop dilated cardiomyopathy, coupled with myocyte hyperplasia (increased cell number), as observed in Mybpc^t/t mice. Human patients, with heterozygous truncating MYBPC3 mutations, like mice with similar mutations, have hypertrophic cardiomyopathy. However, the mechanism leading to hypertrophic cardiomyopathy in heterozygous MYBPC3^+/− individuals is myocyte hypertrophy (increased cell size), whereas the mechanism leading to cardiac dilation in homozygous Mybpc3^−/− mice is primarily myocyte hyperplasia.Dilated cardiomyopathy (DCM) leads to heart failure and is a leading cause of morbidity and mortality (1, 2). DCM is generally diagnosed as left ventricular (LV) dilation with associated reduction in cardiac contraction measured as impaired fractional shortening (3). Hearts from affected individuals frequently demonstrate myocyte elongation, myocyte death, and fibrosis, in addition to LV dilation. DCM results from a variety of environmental factors, such as viral infection and alcohol abuse, as well as from mutations in a number of genes including titin, lamin A/C, cardiac actin, cardiac myosin heavy chain, and phospholamban (reviewed in refs. 4–6). Whether all of these DCM-inducing factors activate the same or different cellular pathways to produce similar clinical features remains uncertain. The mechanisms by which mutations in the cardiac myosin binding protein C (MYBPC3) gene and other sarcomere protein genes lead to cardiac dilatation are under investigation.MYBPC is a thick filament accessory protein component of the striated muscle sarcomere A band that constitutes 2–4% of the myofibril (discussed in ref. 7). Although there are four Mybpc genes in the mammalian genome, only cardiac Mybpc (Mybpc3) is expressed in embryonic, neonatal, and adult hearts (8, 9). Cardiac MYBPC interacts with at least four sarcomere components: myosin heavy chain, actin, myosin light chain 2, and titin (10–12). More than 400 cardiac MYBPC3 gene mutations have been identified in patients as a cause of hypertrophic cardiomyopathy (HCM), an autosomal dominant disorder resulting from defective sarcomeres (for reviews, see refs. 12, 13). Due to an ancient founder mutation, 4% of the population of India carries a truncating MYBPC3 mutation (14, 15). The majority of cardiac MYBPC3 mutations are predicted to encode truncated proteins that lack portions of either the carboxyl myosin and/or titin binding domains (7, 13). These truncating MYBPC3 mutations are thought to cause cardiac hypertrophy by inducing myocyte hypertrophy (increased cell size), rather than myocyte hyperplasia.We and other researchers have created mice that carry a mutant cardiac Mybpc3 gene to create murine HCM models (16–18). Heterozygous mice, designated Mybpc^t/+, like humans bearing the same mutation, develop adult onset HCM. Homozygous MYBPC3 mutations are a much rarer cause of human DCM than autosomal dominant mutations in other sarcomere protein genes. However, homozygous Mybpc^t/t mice that express two mutant alleles and no wild-type cardiac Mybpc3 develop LV dilation by 3 d postbirth and have all of the features of DCM, including LV chamber dilation, albeit mildly impaired fractional shortening (16). Unlike most humans with DCM, homozygous mutant cardiac Mybpc^t/t mice have normal survival despite their cardiac disease. Other homozygous null cardiac Mybpc3 mice develop an identical phenotype (7, 17, 18). Hence, for the studies described here, we assume that the phenotype of the Mybpc^t/t mice is due to lack of MYBPC protein, rather than to small amounts of truncated protein. Recently, two groups have demonstrated that delivery of MYBPC to Mybpc3-null hearts restores cardiac function and morphology (19, 20). Here, we have begun to dissect the mechanism by which homozygous Mybpc^t/t hearts develop DCM.Because Mybpc^t/t mice begin LV dilation within a few days postbirth (16), we hypothesized that this reflected abnormal development of neonatal myocytes. During fetal and early perinatal development in wild-type hearts, cardiomyocytes divide rapidly, producing hyperplastic cardiac growth (21). However, at 10 d postbirth, cardiomyocytes cease to divide and all subsequent increases in myocardial mass result from myocyte hypertrophy (22). Despite the importance of this phenomenon, little is known about the molecular basis for the transition from hyperplasic to hypertrophic-based myocardial growth. We hypothesized that abnormal cardiomyocyte growth, either hyperplastic or hypertrophic, in the perinatal period accounted for the LV dilation of Mybpc^t/t mouse hearts. To address this question, we have counted and measured cardiomyocytes from Mybpc^t/t and wild-type mice. We have also studied the consequences of reducing MYBPC levels by injecting Mybpc3-specific shRNA at birth. Neonatal cardiomyocytes lacking cardiac MYBPC, due to Mybpc3-specific shRNA knockdown, undergo an additional round of cytokinesis. We conclude that dramatic reductions in the amount of cardiac MYBPC leads to aberrant cell cycle regulation at the G1/S checkpoint, resulting in at least one extra round of myocyte division and DCM.     

Molecular basis of force-pCa relation in MYL2 cardiomyopathy mice: Role of the super-relaxed state of myosin

In this study, we investigated the role of the super-relaxed (SRX) state of myosin in the structure–function relationship of sarcomeres in the hearts of mouse models of cardiomyopathy-bearing mutations in the human ventricular regulatory light chain (RLC, MYL2 gene). Skinned papillary muscles from hypertrophic (HCM–D166V) and dilated (DCM–D94A) cardiomyopathy models were subjected to small-angle X-ray diffraction simultaneously with isometric force measurements to obtain the interfilament lattice spacing and equatorial intensity ratios (I₁₁/I₁₀) together with the force-pCa relationship over a full range of [Ca²⁺] and at a sarcomere length of 2.1 μm. In parallel, we studied the effect of mutations on the ATP-dependent myosin energetic states. Compared with wild-type (WT) and DCM–D94A mice, HCM–D166V significantly increased the Ca²⁺ sensitivity of force and left shifted the I₁₁/I₁₀-pCa relationship, indicating an apparent movement of HCM–D166V cross-bridges closer to actin-containing thin filaments, thereby allowing for their premature Ca²⁺ activation. The HCM–D166V model also disrupted the SRX state and promoted an SRX-to-DRX (super-relaxed to disordered relaxed) transition that correlated with an HCM-linked phenotype of hypercontractility. While this dysregulation of SRX ↔ DRX equilibrium was consistent with repositioning of myosin motors closer to the thin filaments and with increased force-pCa dependence for HCM–D166V, the DCM–D94A model favored the energy-conserving SRX state, but the structure/function–pCa data were similar to WT. Our results suggest that the mutation-induced redistribution of myosin energetic states is one of the key mechanisms contributing to the development of complex clinical phenotypes associated with human HCM–D166V and DCM–D94A mutations.

Inherited cardiomyopathies are a class of heart diseases caused by variations in multiple genetic loci, mostly originating from point mutations in sarcomeric proteins (1). The majority of hypertrophic cardiomyopathy (HCM)–causing mutations reside in human β-cardiac myosin (∼35%) and cardiac myosin-binding protein C (∼35%); however, according to recent genetic studies, mutations in the human cardiac regulatory light chain (RLC, MYL2 gene) are more common than previously reported, and they are often associated with adverse clinical outcomes (reviewed in refs. 2 and 3). In this study, we focused on the D166V (aspartate166 → valine)-RLC mutation shown to result in HCM (4) and the D94A (aspartate94 → alanine)–RLC mutation associated with dilated cardiomyopathy (DCM) in patients (5). Two “humanized” mouse models were explored, expressing human ventricular HCM–D166V and DCM–D94A MYL2 variants in mice (6, 7), and they served as model systems for investigating the mechanisms underlying human HCM and DCM.The myosin RLC is a major subunit of striated-muscle myosin and a modulator of Ca²⁺ and tropomyosin–troponin-regulated cardiac muscle contraction (8). Together with the myosin essential light chain (ELC), the RLC binds to the lever arm domain of the myosin head, suggesting important roles for both light chains in maintaining the structural and functional integrity of the lever arm during the power stroke and sarcomere shortening (9, 10). Structurally, the RLC belongs to the EF-hand calcium-binding protein family and contains a homologous helix–loop–helix region composed of a 12-amino-acid Ca²⁺-binding loop flanked by two perpendicular α-helices (EF-hand motif) (8). The human cardiac RLC also contains a highly conserved N-terminal phosphorylatable serine (Ser-15), a target of cardiac myosin light chain kinase (11). Our previous investigations implied that both properties of the RLC, Ca²⁺ binding and Ser-15 phosphorylation, determine the role that RLC plays in cardiac muscle contraction in healthy and cardiomyopathic muscle (12, 13). The phosphorylation of cardiac RLC was shown to directly modulate the Ca²⁺-dependent force development and the kinetics of attachment and detachment of cycling myosin cross-bridges (14–16), and RLC phosphorylation-mediated sensitization to calcium was attributed to the switch between the OFF and ON conformations of myosin motors and a movement of myosin heads toward the thin filaments (17, 18).Considering the importance of myosin RLC for the actin–myosin interaction and force production in the heart, it is not surprising that genetic mutations in MYL2 can result in structural and functional alterations and lead to cardiomyopathy in humans. To better understand the interplay between the mutation-induced molecular insult and heart dysfunction, we examined the effect of HCM–D166V and DCM–D94A mutations expressed in mouse models of HCM and DCM (6, 7) on sarcomeric structure, force production, and myosin energetic states using left ventricular (LV) papillary muscles (PM) from the hearts of mutant versus wild-type (WT) mice expressing a nonmutated human ventricular RLC. Importantly, we monitored the structural determinants of muscle contraction simultaneously with force development over the full range of Ca²⁺-activated force from relaxed through submaximal to maximum Ca²⁺ activation.Small-angle X-ray diffraction is the technique of choice to obtain structural information concerning the sarcomere under physiological or disease-like conditions. The equatorial diffraction patterns yield two structural parameters, the interfilament lattice spacing (d₁₀) that is proportional to the center-to-center distance between two adjacent thick and thin filaments (19) and the equatorial intensity ratio (I₁₁/I₁₀). I₁₁/I₁₀ is the ratio of the integrated intensity of the 1,1 equatorial reflections originating from the myosin and actin filaments to the 1,0 equatorial reflections arising from the myosin-containing thick filaments. These two parameters have been extensively used to characterize the normal sarcomere structure, but they also enable the assessment of the effects of various mutations in sarcomeric proteins on the proximity of myosin heads to actin, providing insights into the structural basis of disease phenotypes (18, 20, 21). I₁₁/I₁₀ reveals information about the proximity of myosin heads to the actin-containing thin filaments and is directly proportional to the number of attached cross-bridges in both cardiac (22) and skeletal (23) muscles. A relatively high value of I₁₁/I₁₀ indicates that myosin heads are more closely associated with the actin filaments, and a low value depicts myosin heads more closely associated with the thick filament backbone, apparently reflecting the formation of the “interacting-heads motif” (IHM) (22, 24). The IHM is thought to be, but not yet proven, the structural basis of the recently discovered super-relaxed (SRX) state of myosin (25, 26) that is considered central to modulating sarcomeric force production and energy utilization in cardiac muscle (27–29). The SRX is an energy-conserving state in which myosin cross-bridges cycle with a highly inhibited ATP turnover rate (25, 26). It has 10- to 100-fold slower ATPase than the already known non-actin–bound, disordered relaxed (DRX) state in which myosin heads protrude into the interfilament space but are restricted from binding to actin compared with SRX heads that are neatly ordered around the thick filament backbone (30). Structurally, the SRX state is associated with the IHM, comprised of the primary head–head interaction site of the “blocked” head and the converter domain of the “free” head, with both heads locked into the thick filament backbone, thus inhibiting ATP hydrolysis and withdrawing both heads from thin filament interaction and force production (1, 28, 31). This asymmetric IHM formation is presumed to define the SRX state of thick filaments in the heart (22) and could explain the structural origin of the slow (250 to 300 s) versus fast (<30 s) ATP turnover time in cardiac muscle (30, 31).Under resting conditions, myosin heads can exist in a wide range of structural states and proximities to actin filaments, each associated with different rates of energy consumption (1). The relaxation phase of the cardiac cycle is critically important for normal heart function, and the disruption of IHM structures may contribute to energetically compromised myocardium and inefficient heart performance (24, 27, 29). The SRX conformation is supported by protein–protein interactions of myosin heads with the ELC and RLC that serve as scaffolding proteins, and mutations in these structural components of the IHM may lead to destabilization of SRX and unbalanced SRX ↔ DRX equilibrium. We thus tested whether the SRX state is affected by the two pathogenic variants of RLC and explored the mutation-specific redistribution of myosin energetic states in the hearts of HCM–D166V and DCM–D94A versus WT mice.     

Thermodynamics of formation of coffinite,USiO4

Coffinite, USiO₄, is an important U(IV) mineral, but its thermodynamic properties are not well-constrained. In this work, two different coffinite samples were synthesized under hydrothermal conditions and purified from a mixture of products. The enthalpy of formation was obtained by high-temperature oxide melt solution calorimetry. Coffinite is energetically metastable with respect to a mixture of UO₂ (uraninite) and SiO₂ (quartz) by 25.6 ± 3.9 kJ/mol. Its standard enthalpy of formation from the elements at 25 °C is −1,970.0 ± 4.2 kJ/mol. Decomposition of the two samples was characterized by X-ray diffraction and by thermogravimetry and differential scanning calorimetry coupled with mass spectrometric analysis of evolved gases. Coffinite slowly decomposes to U₃O₈ and SiO₂ starting around 450 °C in air and thus has poor thermal stability in the ambient environment. The energetic metastability explains why coffinite cannot be synthesized directly from uraninite and quartz but can be made by low-temperature precipitation in aqueous and hydrothermal environments. These thermochemical constraints are in accord with observations of the occurrence of coffinite in nature and are relevant to spent nuclear fuel corrosion.In many countries with nuclear energy programs, spent nuclear fuel (SNF) and/or vitrified high-level radioactive waste will be disposed in an underground geological repository. Demonstrating the long-term (10⁶–10⁹ y) safety of such a repository system is a major challenge. The potential release of radionuclides into the environment strongly depends on the availability of water and the subsequent corrosion of the waste form as well as the formation of secondary phases, which control the radionuclide solubility. Coffinite (1), USiO₄, is expected to be an important alteration product of SNF in contact with silica-enriched groundwater under reducing conditions (2–8). It is also found, accompanied by thorium orthosilicate and uranothorite, in igneous and metamorphic rocks and ore minerals from uranium and thorium sedimentary deposits (2, 4, 5, 8–16). Under reducing conditions in the repository system, the uranium solubility (very low) in aqueous solutions is typically derived from the solubility product of UO₂. Stable U(IV) minerals, which could form as secondary phases, would impart lower uranium solubility to such systems. Thus, knowledge of coffinite thermodynamics is needed to constrain the solubility of U(IV) in natural environments and would be useful in repository assessment.In natural uranium deposits such as Oklo (Gabon) (4, 7, 11, 12, 14, 17, 18) and Cigar Lake (Canada) (5, 13, 15), coffinite has been suggested to coexist with uraninite, based on electron probe microanalysis (EPMA) (4, 5, 7, 11, 13, 17, 19, 20) and transmission electron microscopy (TEM) (8, 15). However, it is not clear whether such apparent replacement of uraninite by a coffinite-like phase is a direct solid-state process or occurs mediated by dissolution and reprecipitation.The precipitation of USiO₄ as a secondary phase should be favored in contact with silica-rich groundwater (21) [silica concentration >10⁻⁴ mol/L (22, 23)]. Natural coffinite samples are often fine-grained (4, 5, 8, 11, 13, 15, 24), due to the long exposure to alpha-decay event irradiation (4, 6, 25, 26) and are associated with other minerals and organic matter (6, 8, 12, 18, 27, 28). Hence the determination of accurate thermodynamic data from natural samples is not straightforward. However, the synthesis of pure coffinite also has challenges. It appears not to form by reacting the oxides under dry high-temperature conditions (24, 29). Synthesis from aqueous solutions usually produces UO₂ and amorphous SiO₂ impurities, with coffinite sometimes being only a minor phase (24, 30–35). It is not clear whether these difficulties arise from kinetic factors (slow reaction rates) or reflect intrinsic thermodynamic instability (33). Thus, there are only a few reported estimates of thermodynamic properties of coffinite (22, 36–40) and some of them are inconsistent. To resolve these uncertainties, we directly investigated the energetics of synthetic coffinite by high-temperature oxide melt solution calorimetry to obtain a reliable enthalpy of formation and explored its thermal decomposition.     

Sleep spindles are generated in the absence of T-type calcium channel-mediated low-threshold burst firing of thalamocortical neurons

T-type Ca²⁺ channels in thalamocortical (TC) neurons have long been considered to play a critical role in the genesis of sleep spindles, one of several TC oscillations. A classical model for TC oscillations states that reciprocal interaction between synaptically connected GABAergic thalamic reticular nucleus (TRN) neurons and glutamatergic TC neurons generates oscillations through T-type channel-mediated low-threshold burst firings of neurons in the two nuclei. These oscillations are then transmitted from TC neurons to cortical neurons, contributing to the network of TC oscillations. Unexpectedly, however, we found that both WT and KO mice for Ca_V3.1, the gene for T-type Ca²⁺ channels in TC neurons, exhibit typical waxing-and-waning sleep spindle waves at a similar occurrence and with similar amplitudes and episode durations during non-rapid eye movement sleep. Single-unit recording in parallel with electroencephalography in vivo confirmed a complete lack of burst firing in the mutant TC neurons. Of particular interest, the tonic spike frequency in TC neurons was significantly increased during spindle periods compared with nonspindle periods in both genotypes. In contrast, no significant change in burst firing frequency between spindle and nonspindle periods was noted in the WT mice. Furthermore, spindle-like oscillations were readily generated within intrathalamic circuits composed solely of TRN and TC neurons in vitro in both the KO mutant and WT mice. Our findings call into question the essential role of low-threshold burst firings in TC neurons and suggest that tonic firing is important for the generation and propagation of spindle oscillations in the TC circuit.Sleep spindles are one type of several rhythmic brain waves detected by electroencephalography (EEG) during normal non-rapid eye movement (NREM) sleep. A spindle consists of characteristic waxing-and-waning field potentials grouped into 7- to 14-Hz oscillations that last for 1–3 s and recur once every 5–10 s in the thalamus and the cortex (1–3). Spindles are also visible under anesthesia, particularly with barbiturates but also with ketamine-xylazine combinations (4, 5). These oscillations are generated in the thalamus as a result of synaptic interactions between inhibitory [i.e., thalamic reticular nucleus (TRN)] neurons and excitatory thalamocortical (TC) neurons, and are propagated to the cortex. Corticothalamic projections back to the thalamus complete the cortico-thalamo-cortical loop.In vivo data suggest that TRN neurons are spindle pacemakers, because spindles can be generated in deafferented TRN neurons (6) but disappear in TC regions after disconnection from TRN neurons (7). However, in vitro data suggest that an intact TC-TRN network is a necessity, because spindles are abolished after disconnection of TC and TRN neurons (8).Two distinct firing patterns, tonic and burst, are displayed by both TRN and TC neurons. Burst firing is mediated by low-threshold T-type Ca²⁺ channels (9). Of the three subtypes of T-type channels, Ca_V3.1 is expressed exclusively in TC regions, whereas Ca_V3.2 and Ca_V3.3 are abundant in TRN regions (10). T-type channels in TC neurons have been proposed to be a critical component in the generation of physiological and pathological TC oscillations, such as sleep rhythms (1, 11, 12) and the spike-wave discharges (SWDs) of absence seizures (11, 13, 14). One generally accepted hypothesis proposes that inhibitory inputs from TRN neurons de-inactivate T-type Ca²⁺ channels in TC neurons, leading to induction of burst firings in TC neurons, which in return excite reciprocally connected TRN neurons. These thalamic oscillations are then transmitted from TC neurons to cortical neurons. This model proposes that T-type channel-mediated burst firing in TC neurons underlies sleep spindles and other sleep rhythms within TC circuits (1, 11).There have long been doubts regarding the extent to which TC T-type Ca²⁺ channels contribute to the heterogeneity of TC oscillations during NREM sleep, which consists of multiple EEG components including slow waves (<1 Hz), delta waves (1–4 Hz), and sleep spindles (7–14 Hz). T-type channels have received particular attention in the genesis of spindles and delta waves, both of which are thought to originate from thalamic neurons (8), although cortically generated delta waves also have been found in cats with thalamic lesions (15). A role for TC T-type channels in sleep has been demonstrated in two studies, one using mice with a global deletion (16) and the other using mice with a thalamus-restricted deletion (17) of Ca_V3.1 T-type channels. Both mice exhibited reduced delta waves with intact slow waves (16, 17). Fragmented sleep was observed in both mice, indicating that this sleep phenotype in the global Ca_V3.1^−/− mice is related to a defect in TC neurons. The effect of the mutation on spindle rhythms was unclear, however (16).In the present study, we examined the role of low-threshold burst firing in sleep spindles expressed in TC neurons using mice lacking Ca_V3.1 T-type Ca²⁺ channels. We observed intact sleep spindles in Ca_V3.1^−/− mice during NREM sleep. Our findings suggest that the classical view of the roles of T-type channels and burst firing in TC neurons with respect to the generation of spindle oscillations may need to be revised.     

Netrin-4 regulates thalamocortical axon branching in an activity-dependent fashion

Axon branching is remodeled by sensory-evoked and spontaneous neuronal activity. However, the underlying molecular mechanism is largely unknown. Here, we demonstrate that the netrin family member netrin-4 (NTN4) contributes to activity-dependent thalamocortical (TC) axon branching. In the postnatal developmental stages of rodents, ntn4 expression was abundant in and around the TC recipient layers of sensory cortices. Neuronal activity dramatically altered the ntn4 expression level in the cortex in vitro and in vivo. TC axon branching was promoted by exogenous NTN4 and suppressed by depletion of the endogenous protein. Moreover, unc-5 homolog B (Unc5B), which strongly bound to NTN4, was expressed in the sensory thalamus, and knockdown of Unc5B in thalamic cells markedly reduced TC axon branching. These results suggest that NTN4 acts as a positive regulator for TC axon branching through activity-dependent expression.Axon branching is an essential process to determine the final pattern of neuronal connections. Previous studies have demonstrated that axon branching is controlled not only by axon guidance-related molecules (1–6) but also by neuronal activity, such as firing and synaptic activity (7–10). However, how neuronal activity is converted into the molecular signals that underlie axon branching is still largely unknown.The thalamocortical (TC) projection is a well-characterized system in which to address this issue. TC axons originating from sensory thalamic nuclei form elaborate arbors, primarily in layer 4 of the neocortex (11). Lamina-specific axon branching occurs from the onset of development and is universal in the mammalian cortex (12–17), indicating that a rigid developmental program is predominant for laminar specificity. TC axon branching is also known to be modified by neuronal activity. In the visual system, geniculocortical axon arbors can be remodeled drastically by manipulating visual experience and cortical-cell activity (18–22). A similar feature has been demonstrated in the somatosensory system. In mutant mice in which synaptic transmission or downstream signaling mechanisms are disrupted, TC axon arbors are affected primarily along the tangential axis whereas their laminar pattern is not obviously influenced (23–26). We have also shown in vitro that the loss of firing and synaptic activities substantially suppresses TC axon branching in the target layer (27). All of these findings imply the existence of a target-derived, branch-promoting molecule whose expression is regulated by neuronal activity. In this study, we attempted to identify this hypothetical molecule and to reveal the molecular mechanism of its action.     

Predictive Value of Brain Natriuretic Peptides in Patients on Peritoneal Dialysis: Results from the ADEMEX Trial

Background and objectives: Natriuretic peptides have been suggested to be of value in risk stratification in dialysis patients. Data in patients on peritoneal dialysis remain limited.Design, setting, participants, & measurements: Patients of the ADEMEX trial (ADEquacy of peritoneal dialysis in MEXico) were randomized to a control group [standard 4 × 2L continuous ambulatory peritoneal dialysis (CAPD); n = 484] and an intervention group (CAPD with a target creatinine clearance ≥60L/wk/1.73 m²; n = 481). Natriuretic peptides were measured at baseline and correlated with other parameters as well as evaluated for effects on patient outcomes.Results: Control group and intervention group were comparable at baseline with respect to all measured parameters. Baseline values of natriuretic peptides were elevated and correlated significantly with levels of residual renal function but not with body size or diabetes. Baseline values of N-terminal fragment of B-type natriuretic peptide (NT-proBNP) but not proANP(1–30), proANP(31–67), or proANP(1–98) were independently highly predictive of overall survival and cardiovascular mortality. Volume removal was also significantly correlated with patient survival.Conclusions. NT-proBNP have a significant predictive value for survival of CAPD patients and may be of value in guiding risk stratification and potentially targeted therapeutic interventions.Plasma levels of cardiac natriuretic peptides are elevated in patients with chronic kidney disease, owing to impairment of renal function, hypertension, hypervolemia, and/or concomitant heart disease (1–7). Atrial natriuretic peptide (ANP) and particularly brain natriuretic peptide (BNP) levels are linked independently to left ventricular mass (3–5,8–16) and function (3,6–17) and predict total and cardiovascular mortality (1,3,8,10,12,18) as well as cardiac events (12,19). ANP and BNP decrease significantly during hemodialysis treatment but increase again during the interdialytic interval (1,2,4,6,7,14,17,20–23). Levels in patients on peritoneal dialysis (PD) have been found to be lower than in patients on hemodialysis (11,24–26), but the correlations with left ventricular function and structure are maintained in both types of dialysis modalities (11,15,27,28).The high mortality of patients on peritoneal dialysis and the failure of dialytic interventions to alter this mortality (29,30) necessitate renewed attention into novel methods of stratification and identification of patients at highest risk to be targeted for specific interventions. Cardiac natriuretic peptides are increasingly considered to fulfill this role in nonrenal patients. Evaluations of cardiac natriuretic peptides in patients on PD have been limited by small numbers (3,9,11,12,15,24–26) and only one study examined correlations between natriuretic peptide levels and outcomes (12). The PD population enrolled in the ADEMEX trial offered us the opportunity to evaluate cardiac natriuretic peptides and their value in predicting outcomes in the largest clinical trial ever performed on PD (29,30). It is hoped that such an evaluation would identify patients at risk even in the absence of overt clinical disease and hence facilitate or encourage interventions with salutary outcomes.     

Effects of lymphocyte profile on development of EBV-induced lymphoma subtypes in humanized mice

Epstein-Barr virus (EBV) infection causes both Hodgkin’s lymphoma (HL) and non-Hodgkin’s lymphoma (NHL). The present study reveals that EBV-induced HL and NHL are intriguingly associated with a repopulated immune cell profile in humanized mice. Newborn immunodeficient NSG mice were engrafted with human cord blood CD34⁺ hematopoietic stem cells (HSCs) for a 8- or 15-wk reconstitution period (denoted ^8whN and ^15whN, respectively), resulting in human B-cell and T-cell predominance in peripheral blood cells, respectively. Further, novel humanized mice were established via engraftment of hCD34⁺ HSCs together with nonautologous fetal liver-derived mesenchymal stem cells (MSCs) or MSCs expressing an active notch ligand DLK1, resulting in mice skewed with human B or T cells, respectively. After EBV infection, whereas NHL developed more frequently in B-cell–predominant humanized mice, HL was seen in T-cell–predominant mice (P = 0.0013). Whereas human splenocytes from NHL-bearing mice were positive for EBV-associated NHL markers (hBCL2⁺, hCD20⁺, hKi67⁺, hCD20⁺/EBNA1⁺, and EBER⁺) but negative for HL markers (LMP1⁻, EBNA2⁻, and hCD30⁻), most HL-like tumors were characterized by the presence of malignant Hodgkin’s Reed–Sternberg (HRS)-like cells, lacunar RS (hCD30⁺, hCD15⁺, IgJ⁻, EBER⁺/hCD30⁺, EBNA1⁺/hCD30⁺, LMP⁺/EBNA2⁻, hCD68⁺, hBCL2⁻, hCD20^-/weak, Phospho STAT6⁺), and mummified RS cells. This study reveals that immune cell composition plays an important role in the development of EBV-induced B-cell lymphoma.Epstein Barr virus (EBV) infects human B lymphocytes and epithelial cells in >90% of the human population (1, 2). EBV infection is widely associated with the development of diverse human disorders that include Hodgkin’s lymphoma (HL) and non-Hodgkin’s lymphomas (NHL), including diffused large B-cell lymphoma (DLBCL), follicular B-cell lymphoma (FBCL), endemic Burkitt’s lymphoma (BL), and hemophagocytic lymphohistiocytosis (HLH) (3).HL is a malignant lymphoid neoplasm most prevalent in adolescents and young adults (4–6). Hodgkin/Reed–Sternberg (HRS) cells are the sole malignant cells of HL. HRS cells are characterized by CD30⁺/CD15⁺/BCL6⁻/CD20^+/− markers and appear large and multinucleated owing to multiple nuclear divisions without cytokinesis. Although HRS cells are malignant in the body, surrounding inflammatory cells greatly outnumber them. These reactive nonmalignant inflammatory cells, including lymphocytes, histiocytes, eosinophils, fibroblasts, neutrophils, and plasma cells, compose the vast majority of the tumor mass. The presence of HRS cells in the context of this inflammatory cellular background is a critical hallmark of the HL diagnosis (4). Approximately 50% of HL cases are EBV-associated (EBVaHL) (7–11). EBV-positive HRS cells express EBV latent membrane protein (LMP) 1 (LMP1), LMP2A, LMP2B, and EBV nuclear antigen (EBNA) 1 (EBNA1), but lack EBNA2 (latency II marker) (12). LMP1 is consistently expressed in all EBV-associated cases of classical HL (13, 14). LMP1 mimics activated CD40 receptors, induces NF-κB, and allows cells to become malignant while escaping apoptosis (15).The etiologic role of EBV in numerous disorders has been studied in humanized mouse models in diverse experimental conditions. Humanized mouse models recapitulate key characteristics of EBV infection-associated disease pathogenesis (16–24). Different settings have given rise to quite distinct phenotypes, including B-cell type NHL (DLBCL, FBCL, and unspecified B-cell lymphomas), natural killer/T cell lymphoma (NKTCL), nonmalignant lymphoproliferative disorder (LPD), extremely rare HL, HLH, and arthritis (16–24). Despite considerable efforts (16–24), EBVaHL has not been properly produced in the humanized mouse setting model, owing to inappropriate animal models and a lack of in-depth analyses. After an initial report of infected humanized mice, HRS-like cells appeared to be extremely rare in the spleens of infected humanized mice; however, the findings were inconclusive (18). Here we report direct evidence of EBVaHL or HL-like neoplasms in multiple humanized mice in which T cells were predominant over B cells. Our study demonstrates that EBV-infected humanized mice display additional EBV-associated pathogenesis, including DLBCL and hemophagocytic lymphohistiocytosis (16, 17).     

Right Ventricle-Sparing Left Ventricular Resection and Replacement with a Continuous-Flow Rotary Blood Pump: An In Vivo Experiment

Despite recent advances in left ventricular assist device and total artificial heart technologies, these devices are still so large that they pose a significant problem in small patients with refractory heart failure. Excising the left ventricle while preserving the right ventricle—and then replacing the left ventricle with a mechanical pump—has been proposed as an alternative approach to this problem. We conducted a pilot study to evaluate possible surgical techniques and the hemodynamic effects of right ventricle-sparing left ventricular resection and replacement with a continuous-flow rotary blood pump in a healthy bovine model.Key words: Animals, blood pump, centrifugal, heart, artificial, heart-assist devices, heart failure, congestive, heart transplantation, heart ventricles, prosthesis fitting, prosthesis implantationLeft ventricular assist devices (LVADs) have proved useful both in supporting patients who have chronic refractory heart failure until an appropriate donor heart can be obtained and in enabling patients who manifest acute decompensation to become, over time, better candidates for cardiac transplantation.¹ Similarly, the pneumatically actuated total artificial heart has been shown to benefit these same patients.¹ More recently, LVADs have been implanted as permanent, or destination, therapy in patients who were deemed not to be transplantation candidates. Despite substantial advances in LVAD and total artificial heart technology over the past several years, these devices are still so large that they pose a significant problem in small patients with refractory heart failure.^1-4 Surgically excising the left ventricle (LV) and placing an LVAD-like pump in the left atrial-to-aortic position might mitigate some of the difficulties associated with size constraints by removing the markedly enlarged LV and, as an added benefit, might eliminate a potential source of emboli and right ventricular (RV) dysrhythmias.In our previous studies,^2,3 we demonstrated in a bovine model the feasibility of long-term LV replacement with a pulsatile, pneumatically actuated volume-displacement pump. After LV excision and replacement, the calf maintained normal RV function and systemic hemodynamics for 4 days. In the current pilot study, we attempted to repeat this experiment with a continuous-flow rotary pump. By exploiting some of the advantages of the newer rotary pumps, namely smaller size and better wear resistance, we hoped to demonstrate the viability of a potentially beneficial treatment option for some patients with end-stage heart failure.     

The spontaneous emergence of conventions: An experimental study of cultural evolution

How do shared conventions emerge in complex decentralized social systems? This question engages fields as diverse as linguistics, sociology, and cognitive science. Previous empirical attempts to solve this puzzle all presuppose that formal or informal institutions, such as incentives for global agreement, coordinated leadership, or aggregated information about the population, are needed to facilitate a solution. Evolutionary theories of social conventions, by contrast, hypothesize that such institutions are not necessary in order for social conventions to form. However, empirical tests of this hypothesis have been hindered by the difficulties of evaluating the real-time creation of new collective behaviors in large decentralized populations. Here, we present experimental results—replicated at several scales—that demonstrate the spontaneous creation of universally adopted social conventions and show how simple changes in a population’s network structure can direct the dynamics of norm formation, driving human populations with no ambition for large scale coordination to rapidly evolve shared social conventions.Social conventions are the foundation for social and economic life (1–7), However, it remains a central question in the social, behavioral, and cognitive sciences to understand how these patterns of collective behavior can emerge from seemingly arbitrary initial conditions (2–4, 8, 9). Large populations frequently manage to coordinate on shared conventions despite a continuously evolving stream of alternatives to choose from and no a priori differences in the expected value of the options (1, 3, 4, 10). For instance, populations are able to produce linguistic conventions on accepted names for children and pets (11), on common names for colors (12), and on popular terms for novel cultural artifacts, such as referring to junk email as “SPAM” (13, 14). Similarly, economic conventions, such as bartering systems (2), beliefs about fairness (3), and consensus regarding the exchangeability of goods and services (15), emerge with clear and widespread agreement within economic communities yet vary broadly across them (3, 16).Prominent theories of social conventions suggest that institutional mechanisms—such as centralized authority (14), incentives for collective agreement (15), social leadership (16), or aggregated information (17)—can explain global coordination. However, these theories do not explain whether, or how, it is possible for conventions to emerge when social institutions are not already in place to guide the process. A compelling alternative approach comes from theories of social evolution (2, 18–20). Social evolutionary theories maintain that networks of locally interacting individuals can spontaneously self-organize to produce global coordination (21, 22). Although there is widespread interest in this approach to social norms (6, 7, 14, 18, 23–26), the complexity of the social process has prevented systematic empirical insight into the thesis that these local dynamics are sufficient to explain universally adopted conventions (27, 28).Several difficulties have limited prior empirical research in this area. The most notable of these limitations is scale. Although compelling experiments have successfully shown the creation of new social conventions in dyadic and small group interactions (29–31), the results in small group settings can be qualitatively different from the dynamics in larger groups (Model), indicating that small group experiments are insufficient for demonstrating whether or how new conventions endogenously form in larger populations (32, 33). Important progress on this issue has been made using network-based laboratory experiments on larger groups (15, 24). However, this research has been restricted to studying coordination among players presented with two or three options with known payoffs. Natural convention formation, by contrast, is significantly complicated by the capacity of individuals to continuously innovate, which endogenously expands the “ecology” of alternatives under evaluation (23, 29, 31). Moreover, prior experimental studies have typically assumed the existence of either an explicit reward for universal coordination (15) or a mechanism that aggregates and reports the collective state of the population (17, 24), which has made it impossible to evaluate the hypothesis that global coordination is the result of purely local incentives.More recently, data science approaches to studying norms have addressed many of these issues by analyzing behavior change in large online networks (34). However, these observational studies are limited by familiar problems of identification that arise from the inability to eliminate the confounding influences of institutional mechanisms. As a result, previous empirical research has been unable to identify the collective dynamics through which social conventions can spontaneously emerge (8, 34–36).We addressed these issues by adopting a web-based experimental approach. We studied the effects of social network structure on the spontaneous evolution of social conventions in populations without any resources to facilitate global coordination (9, 37). Participants in our study were rewarded for coordinating locally, however they had neither incentives nor information for achieving large scale agreement. Further, to eliminate any preexisting bias in the evolutionary process, we studied the emergence of arbitrary linguistic conventions, in which none of the options had any a priori value or advantage over the others (3, 23). In particular, we considered the prototypical problem of whether purely local interactions can trigger the emergence of a universal naming convention (38, 39).     

Recent Advances in Archaeological Science Techniques Special Feature: A Neandertal dietary conundrum: Insights provided by tooth enamel Zn isotopes from Gabasa,Spain

The characterization of Neandertals’ diets has mostly relied on nitrogen isotope analyses of bone and tooth collagen. However, few nitrogen isotope data have been recovered from bones or teeth from Iberia due to poor collagen preservation at Paleolithic sites in the region. Zinc isotopes have been shown to be a reliable method for reconstructing trophic levels in the absence of organic matter preservation. Here, we present the results of zinc (Zn), strontium (Sr), carbon (C), and oxygen (O) isotope and trace element ratio analysis measured in dental enamel on a Pleistocene food web in Gabasa, Spain, to characterize the diet and ecology of a Middle Paleolithic Neandertal individual. Based on the extremely low δ⁶⁶Zn value observed in the Neandertal’s tooth enamel, our results support the interpretation of Neandertals as carnivores as already suggested by δ¹⁵N isotope values of specimens from other regions. Further work could help identify if such isotopic peculiarities (lowest δ⁶⁶Zn and highest δ¹⁵N of the food web) are due to a metabolic and/or dietary specificity of the Neandertals.

Over the last 30 years, analyses of nitrogen isotopes in collagen (δ¹⁵N_collagen) have provided direct evidence for Neandertal diets across Europe and Asia. These studies all indicate a carnivorous (1–12), or at least a meat-heavy, diet for European Neandertals. However, one peculiarity of Neandertal δ¹⁵N_collagen remains the subject of an ongoing debate. From the one Siberian and eight western European sites, where both Neandertal and associated fauna have been analyzed, nitrogen isotope ratios in Neandertal collagen are systematically higher than that of other carnivores (3, 6–8, 10, 11, 13, 14). An explanation for such elevated values could be the consumption of herbivores, such as mammoths, which themselves exhibit elevated δ¹⁵N values due to the consumption of plants growing on arid soils (1, 2, 7). While mammoth remains are usually scarce at Neandertal fossil localities, they were nonetheless occasionally consumed, as suggested by remains with cut marks and other human butchery signatures (15). The absence of mammoth remains at Middle Paleolithic sites could be a result of 1) Neandertals chose to leave large bone elements at the kill site and transport other edible carcass products, mainly meat, back to the habitation site (15), or 2) mammoths were not frequently consumed, and the δ¹⁵N peculiarity consequently reflects the consumption of other resources enriched in ¹⁵N.Alongside this δ¹⁵N peculiarity, one major obstacle to our knowledge of Neandertals’ subsistence patterns is that the preservation of organic matter limits the application of collagen-bound nitrogen isotope analysis to fossil specimens. Collagen degrades over time at a varying speed depending on climatic and environmental conditions (16). The oldest hominin specimen in which bone protein is preserved is that of Scladina (Belgium), which dates to 90,000 cal BP (calibrated years before the present) (17), but most studied specimens are younger than 50,000 cal BP (1–3, 6–8, 10–13, 18). Furthermore, these specimens are only from sites in northwestern and central Europe and Siberia, where climatic conditions favored collagen preservation. As a result, the variability of Neandertals’ diet over time and between regions may not accurately be reflected by the currently available isotope data. In Iberia, where the latest surviving Neandertals have been discovered (19, 20), collagen was successfully extracted for only one site (21). Therefore, our knowledge of Iberian Neandertal diets mostly relies on zooarcheological and dental calculus data, which show some inconsistencies (21–25). For instance, similar to other western European sites, zooarcheological studies emphasize the consumption of terrestrial mammals and birds (21). In contrast, analysis of dental calculus for microremains and ancient DNA metagenomic analysis (26–28) highlight the frequent consumption of plants and mushrooms. Indeed, Weyrich et al. (26) even suggest that Neandertals at El Sidrón (Fig. 1) rarely consumed meat but often ate mushrooms, which would also result in elevated δ¹⁵N values (29). The consumption of marine foods is also attested for coastal Neandertals, but its frequency cannot be truly assessed in the absence of isotope studies (21, 23–25, 30). Finally, cannibalism has been documented at two Iberian sites (El Sidrón and Zafarraya) (22, 31) (Fig. 1), though such practices appear limited and most likely occurred only during periods of nutritional stress (32). Therefore, it is challenging to confirm the homogeneity of Neandertals’ diets across time and space, calling into question a direct link between their subsistence strategy and disappearance.Open in a separate windowFig. 1.(A) Location of the Gabasa site as well as other Neandertal sites mentioned in the text. (B) Detailed map of the Gabasa region. San Estaban de Litera and Benabarre are nearby modern cities.This study aims to investigate if the Zn isotope proxy could help elucidate the dietary behaviors of Neandertals and the source of their δ¹⁵N peculiarity, specifically by studying a Late Pleistocene Iberian food web where the presence of mammoth has not been documented (33). The development of Zn isotope analysis (⁶⁶Zn/⁶⁴Zn, expressed as δ⁶⁶Zn) has proven that trophic level information can be retrieved from mammalian tooth enamel (δ⁶⁶Zn_enamel) (34, 35), including fossil samples from Pleistocene food webs where organic matter is typically not preserved (36, 37). Previous studies have demonstrated that δ⁶⁶Zn_enamel decreases by ca. 0.30 to 0.60 ‰ with each step in archeological and modern food webs (34–38) and that δ⁶⁶Zn values associated with breastfeeding are higher than postweaning-associated values (39). While the main source of variation of δ⁶⁶Zn_enamel values is diet, local geology can also likely influence the isotope ratio of a given animal (36, 39). To date, three modern assemblages from Koobi Fora (Kenya), Kruger Park, and the western Cape (South Africa) (40), a few animals from a historical site (Rennes, France) (41), and three Late Pleistocene sites (Tam Hay Marklot, Nam Lot, and Tam Pa Ling, Laos) (36, 37) are the only terrestrial food webs for which Zn isotope data in teeth and/or bones have been published (SI Appendix, Fig. S14). In the modern Koobi Fora savannah food web, δ⁶⁶Zn_enamel differences have been observed between browsers and grazers (35), but this pattern was not seen in any of the three Pleistocene Asian forest food webs (36, 37). Among modern and historical human populations, historically documented diets relying on plants are associated with higher δ⁶⁶Zn values than those that include a substantial quantity of animal products (41–44). Zinc isotopes of ancient hominins have been analyzed only in one Pleistocene Homo sapiens individual (37) from Southeast Asia, but not yet in any Neandertal specimen.This current study contributes significantly to our understanding of Iberian Neandertal diets by providing information on their trophic ecology for a region where traditional nitrogen isotope analyses are unfeasible due to the poor preservation of organic matter. We use the Zn isotopic tool as well as other mobility, ecological, and dietary proxies applied on tooth enamel from hominin and animal remains from the cave site Cueva de los Moros 1 (Gabasa, Pyrenees, Spain; Fig. 1). The site, excavated in the 1980s, is very well documented [for stratigraphic context, see Montes and Utrilla (45) and SI Appendix, Section S1]. All remains come from layers e, f, and g of a single stratigraphic layer directly above layer h dated to 143 ± 43 ka. Numerous carnivore remains were recovered along with Neandertal remains (layers e and f), allowing for comparison of the different meat-eating taxa. Coexisting herbivores from three different types of environmental contexts are homogeneously represented in layers e, f, and g: mountains (Iberian ibex [Capra pyrenaica], chamois [Rupicapra rupicapra]), forest (cervids including red deer [Cervus elaphus]), and open environments (horses [Equus ferus], European wild asses [Equus hydruntinus]).     

Symmetric activation and modulation of the human calcium-sensing receptor

The human extracellular calcium-sensing (CaS) receptor controls plasma Ca²⁺ levels and contributes to nutrient-dependent maintenance and metabolism of diverse organs. Allosteric modulation of the CaS receptor corrects disorders of calcium homeostasis. Here, we report the cryogenic-electron microscopy reconstructions of a near–full-length CaS receptor in the absence and presence of allosteric modulators. Activation of the homodimeric CaS receptor requires a break in the transmembrane 6 (TM6) helix of each subunit, which facilitates the formation of a TM6-mediated homodimer interface and expansion of homodimer interactions. This transformation in TM6 occurs without a positive allosteric modulator. Two modulators with opposite functional roles bind to overlapping sites within the transmembrane domain through common interactions, acting to stabilize distinct rotamer conformations of key residues on the TM6 helix. The positive modulator reinforces TM6 distortion and maximizes subunit contact to enhance receptor activity, while the negative modulator strengthens an intact TM6 to dampen receptor function. In both active and inactive states, the receptor displays symmetrical transmembrane conformations that are consistent with its homodimeric assembly.

Critical to the maintenance of Ca²⁺ homeostasis, the extracellular calcium-sensing (CaS) receptor was the first G protein–coupled receptor (GPCR) discovered to sense ions (1–3). The CaS receptor detects fluctuations in plasma Ca²⁺ at the parathyroid. In response to increases in Ca²⁺, it transmits signals to inhibit the release of parathyroid hormone, in turn preventing further rises in Ca²⁺ concentration (2, 3). In the cortical thick ascending limb of the renal nephron, the CaS receptor is also activated by surges in plasma Ca²⁺ and responds by inhibiting Ca²⁺ reabsorption. The excess urinary calcium excretion arising from CaS receptor activation lowers the plasma Ca²⁺ level. The CaS receptor is implicated in various pathologies associated with hypercalcemia and hypocalcemia (4). It has also been linked to the progression of diseases such as breast and colon cancer, in which the receptor modulates tumor growth (3, 5–7).The CaS receptor senses a diverse array of extracellular stimuli. During normal function, it activates multiple intracellular signaling pathways involving G_q/11, G_i/o, or G_12/13; in tumor cells, it is coupled to G_s (2, 3, 8, 9). In addition to the principal agonist Ca²⁺, the receptor is directly activated by aromatic l-amino acids (10, 11). Other CaS agonists include various divalent and trivalent cations (12), referred to as type I calcimimetics for mimicking the action of Ca²⁺ (13).The activity of the CaS receptor is also subject to allosteric modulation. Positive allosteric modulators (PAMs) are classified as type II calcimimetics for increasing the receptor sensitivity for Ca²⁺ (12–16). The prototypical PAM molecules share a phenylalkylamine structure, including cinacalcet and NPS R-568 (abbreviated as R-568). Cinacalcet was the first drug described to target a GPCR allosterically, and it is used clinically to treat hyperparathyroidism in patients with chronic kidney diseases (15). Negative allosteric modulators (NAMs) of the CaS receptor are referred to as calcilytics for suppressing the receptor response to Ca²⁺ (12–16). Synthetic calcilytics such as NPS-2143 and ronacaleret are also structurally related to phenylalkylamines. Recently, inorganic phosphate has been identified as an inhibitor of the receptor (11, 17).The CaS receptor rests within the class C family of GPCRs and functions as an obligate homodimer. Like other class C GPCRs, each CaS subunit contains a large extracellular domain (ECD) involved in orthosteric ligand binding, a seven-helix transmembrane (TM) domain responsible for G protein coupling, followed by an extended cytoplasmic tail (18–23). The conformations of the CaS ECDs in both the inactive and active states have been determined by X-ray crystallography (11, 24). The ECD structures also revealed how the receptor recognizes various extracellular ligands, including Ca²⁺, the amino acid l-Trp, and inorganic phosphate. Although the role of amino acids is still under debate (25), recent structural studies of full-length CaS receptor further confirmed that Ca²⁺ and amino acids cooperate to activate the receptor (26–28).The TM domain of the CaS receptor harbors the binding sites for PAM and NAM molecules according to previous mutagenesis studies (29–32). Recently reported modulator-bound CaS receptor structures revealed asymmetric TM configurations that are stabilized by PAM molecules binding in different poses within the separate subunits of the homodimer (33). We have determined PAM- and NAM-bound, as well as PAM-free, structures of a near–full-length CaS receptor using cryogenic-electron microscopy (cryo-EM) that display symmetric TM dimers and modulator poses, instead. This finding presents the possibility of receptor activation without requiring asymmetric conformational transition. Our structures also illustrate how distortion of TM6 provides the driving force for receptor activation. Furthermore, the presence of a PAM or NAM stabilizes distinct TM6 helix conformations to promote specific dimer arrangements and differentially modulate receptor function.