Quaternary dynamics and plasticity underlie small heat shock protein chaperone function

Small Heat Shock Proteins (sHSPs) are a diverse family of molecular chaperones that prevent protein aggregation by binding clients destabilized during cellular stress. Here we probe the architecture and dynamics of complexes formed between an oligomeric sHSP and client by employing unique mass spectrometry strategies. We observe over 300 different stoichiometries of interaction, demonstrating that an ensemble of structures underlies the protection these chaperones confer to unfolding clients. This astonishing heterogeneity not only makes the system quite distinct in behavior to ATP-dependent chaperones, but also renders it intractable by conventional structural biology approaches. We find that thermally regulated quaternary dynamics of the sHSP establish and maintain the plasticity of the system. This extends the paradigm that intrinsic dynamics are crucial to protein function to include equilibrium fluctuations in quaternary structure, and suggests they are integral to the sHSPs’ role in the cellular protein homeostasis network.     

The Evolution of Transcranial Laser Therapy for Acute Ischemic Stroke, Including a Pooled Analysis of NEST-1 and NEST-2

Intravenous tissue plasminogen activator is the only proven therapy for acute ischemic stroke. Not enough patients are eligible for treatment and additional new therapies are needed. Recently, laser technology has been applied to acute ischemic stroke. This noninvasive technique uses near-infrared wavelengths applied to the scalp within 24 h of symptom onset. The mechanism is incompletely understood but may involve increased mitochondrial adenosine triphosphate production. Animal models demonstrated safety and efficacy warranting randomized controlled trials in humans. NEST-1 (phase 2) and NEST-2 (phase 3) confirmed the safety of transcranial laser therapy, although efficacy was not found in NEST-2. Pooled analysis of NEST-1 and NEST-2 revealed a significantly improved success rate in patients treated with laser therapy. Further phase 3 testing is planned and may create a new paradigm for the treatment of acute ischemic stroke.     

From the Cover: Loss of phosphatidylinositol 4-kinase 2α activity causes late onset degeneration of spinal cord axons

Phosphoinositide (PI) lipids are intracellular membrane signaling intermediates and effectors produced by localized PI kinase and phosphatase activities. Although many signaling roles of PI kinases have been identified in cultured cell lines, transgenic animal studies have produced unexpected insight into the in vivo functions of specific PI 3- and 5-kinases, but no mammalian PI 4-kinase (PI4K) knockout has previously been reported. Prior studies using cultured cells implicated the PI4K2α isozyme in diverse functions, including receptor signaling, ion channel regulation, endosomal trafficking, and regulated secretion. We now show that despite these important functions, mice lacking PI4K2α kinase activity initially appear normal. However, adult Pi4k2a^GT/GT animals develop a progressive neurological disease characterized by tremor, limb weakness, urinary incontinence, and premature mortality. Histological analysis of aged Pi4k2a^GT/GT animals revealed lipofuscin-like deposition and gliosis in the cerebellum, and loss of Purkinje cells. Peripheral nerves are essentially normal, but massive axonal degeneration was found in the spinal cord in both ascending and descending tracts. These results reveal a previously undescribed role for aberrant PI signaling in neurological disease that resembles autosomal recessive hereditary spastic paraplegia.     

Silent somatotroph pituitary adenomas: an update

Silent growth hormone adenomas (SGHA) are a rare entity of non-functioning pituitary neuroendocrine tumors. Diagnosis is invariably made post-operatively of a tumor immunopositive for GH (and Pit-1 in selected cases) but without clinical acromegaly. Mainly young females are affected, and tumors are often uncovered by investigation for headaches or oligoamenorrhea. Integration of clinical, pathological and biochemical data is required for proper diagnosis. Beside normal IGF-1 levels, a third of SGHAs displays elevated GH levels and some will eventually progress to acromegaly. Almost two-thirds will be mixed GH-prolactin tumors and sparsely-granulated monohormonal GH tumors seems the more aggressive subtype. Recurrence and need for radiation is higher than other non-functioning tumors so close follow-up is warranted.     

Lipid-altering therapy and atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia with significant morbidity and public health cost. Because of limitations of efficacy and safety of conventional antiarrhythmic agents, alternative therapies for AF are needed. The potential antiarrhythmic properties of lipid-altering therapy, including the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors and fish oils, are increasingly recognized, particularly in light of their potential anti-inflammatory properties. This review examines the known effects of lipid-altering therapy on atrial arrhythmias in both experimental and clinical settings. Inflammatory states, such as post-cardiac surgery and AF of recent onset, show promise as targets. In contrast, lipid-lowering therapy is less likely to affect longstanding persistent AF. Current recommendations for the use of lipid-altering therapy for prevention and treatment of AF are summarized.     

Detection of exercise-induced ischemia by changes in B-type natriuretic peptides

OBJECTIVES: The purpose of this study was to examine the effect of exercise-induced ischemia on levels of B-type natriuretic peptide (BNP) and its inactive N-terminal fragment (NT-pro-BNP)and to determine whether measurement of these peptides can improve the diagnostic accuracy of exercise testing. BACKGROUND: The ability of exercise testing to detect coronary artery disease (CAD) is limited by modest sensitivity and specificity. B-type natriuretic peptides (NT-pro-BNP and BNP) are released by ventricular myocytes in response to wall stress. We hypothesized that exercise-induced ischemia results in increased wall stress and triggers release of NT-pro-BNP and BNP. METHODS: A total of 74 patients with known CAD, normal left ventricular function, and normal resting levels of NT-pro-BNP and BNP who were referred for exercise testing with radionuclide imaging, and 21 healthy volunteers, were enrolled. Blood was drawn before and after maximal exercise and analyzed for NT-pro-BNP and BNP. RESULTS: Of the patients with CAD, 40 had ischemia on perfusion images and 34 did not. Median post-exercise increases in NT-pro-BNP and BNP (DeltaNT-pro-BNP and DeltaBNP) were approximately four-fold higher in the ischemic group than in the nonischemic group (DeltaNT-pro-BNP 14.5 vs. 4 pg/ml, p < 0.0001; DeltaBNP 36.5 vs. 7.5 pg/ml, p < 0.0001). In volunteers, median DeltaNT-pro-BNP was almost identical to that of the nonischemic patient group. At equal specificity to the electrocardiogram (ECG) (58.8%), the sensitivities of DeltaNT-pro-BNP and DeltaBNP for detecting ischemia were 90% and 80%, respectively; in contrast, the sensitivity of the exercise ECG was 37.5%. CONCLUSIONS: Measurement of exercise-induced increases in BNPs more than doubles the sensitivity of the exercise test for detecting ischemia with no loss of specificity.     

Stem cell niches as clinical targets: the future of anti-ischemic therapy?

This article provides context for the research presented by Napoli et al., reported in this journal. Treatment strategies that target stem cell niches are promising avenues for stimulating inducible angiogenesis in many vascular diseases, such as diabetes mellitus and atherosclerosis. Here we discuss the study carried out by Napoli and colleagues--an analysis of the effects of parathyroid hormone on the vascular stem cell niche in peripheral ischemia. Napoli et al. demonstrate that parathyroid hormone administered in combination with granulocyte colony-stimulating factor induces angiogenesis in a hindlimb ischemia mouse model. This treatment seems to mobilize and localize endothelial cell progenitors specifically to ischemic vascular cell beds. We explore the mechanisms through which the multiple cells within the vascular niche respond to ischemia. The interaction between parathyroid hormone and granulocyte colony-stimulating factor in humans is also discussed. Further assessment is needed to elucidate the factors involved in migration and differentiation of endothelial cell progenitors in ischemia-damaged tissues.     

Galpha(12/13) mediates alpha(1)-adrenergic receptor-induced cardiac hypertrophy

In neonatal cardiomyocytes, activation of the G(q)-coupled alpha(1)-adrenergic receptor (alpha(1)AR) induces hypertrophy by activating mitogen-activated protein kinases, including c-Jun NH(2)-terminal kinase (JNK). Here, we show that JNK activation is essential for alpha(1)AR-induced hypertrophy, in that alpha(1)AR-induced hypertrophic responses, such as reorganization of the actin cytoskeleton and increased protein synthesis, could be blocked by expressing the JNK-binding domain of JNK-interacting protein-1, a specific inhibitor of JNK. We also identified the classes and subunits of G proteins that mediate alpha(1)AR-induced JNK activation and hypertrophic responses by generating several recombinant adenoviruses that express polypeptides capable of inhibiting the function of specific G-protein subunits. alpha(1)AR-induced JNK activation was inhibited by the expression of carboxyl terminal regions of Galpha(q), Galpha(12), and Galpha(13). JNK activation was also inhibited by the Galpha(q/11)- or Galpha(12/13)-specific regulator of G-protein signaling (RGS) domains and by C3 toxin but was not affected by treatment with pertussis toxin or by expression of the carboxyl terminal region of G protein-coupled receptor kinase 2, a polypeptide that sequesters Gbetagamma. alpha(1)AR-induced hypertrophic responses were inhibited by Galpha(q/11)- and Galpha(12/13)-specific RGS domains, C3 toxin, and the carboxyl terminal region of G protein-coupled receptor kinase 2 but not by pertussis toxin. Activation of Rho was inhibited by carboxyl terminal regions of Galpha(12) and Galpha(13) but not by Galpha(q). Our findings suggest that alpha(1)AR-induced hypertrophic responses are mediated in part by a Galpha(12/13)-Rho-JNK pathway, in part by a G(q/11)-JNK pathway that is Rho independent, and in part by a Gbetagamma pathway that is JNK independent.