Hepatitis C virus entry and neutralization

The processes of hepatitis C virus (HCV) entry and antibody-mediated neutralization are intimately linked. The high frequency of neutralizing antibodies (nAbs) that inhibit E2-CD81 interaction(s) suggests that this is a major target for the humoral immune response. The observation that HCV can transmit to naive cells by means of CD81-dependent and -independent routes in vitro awaits further investigation to assess the significance in vivo but may offer new strategies for HCV to escape nAbs. The identification of claudins in the entry process highlights the importance of cell polarity in defining routes of HCV entry and release, with recent experiments suggesting a polarized route of viral entry into cells in vitro. In this review, the authors summarize the current understanding of the mechanism(s) defining HCV entry and the role of nAbs in controlling HCV replication.     

Acquired deficit of forebrain glucocorticoid receptor produces depression-like changes in adrenal axis regulation and behavior

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is a hallmark of major depressive disorder. A number of studies have shown that this dysregulation is correlated with impaired forebrain glucocorticoid receptor (GR) function. To determine whether a primary, acquired deficit in forebrain GR signaling is an etiologic factor in the pathogenesis of depression, we generated a line of mice with time-dependent, forebrain-specific disruption of GR (FBGRKO). These mice develop a number of both physiological and behavioral abnormalities that mimic major depressive disorder in humans, including hyperactivity of the HPA axis, impaired negative feedback regulation of the HPA axis and, increased depression-like behavior. Importantly, a number of these abnormalities are normalized by chronic treatment with the tricyclic antidepressant, imipramine. Our findings suggest that imipramine's proposed activities on forebrain GR function are not essential for its antidepressant effects, and that alteration in GR expression may play a causative role in disease onset of major depressive disorder.     

Improved outcomes after aortic valve surgery for chronic aortic regurgitation with severe left ventricular dysfunction.

OBJECTIVES: Among patients undergoing aortic valve surgery for chronic aortic regurgitation (AR), we sought to: 1) compare survival among those with and without severe left ventricular dysfunction (LVD); 2) identify risk factors for death, including LVD and date of operation; and 3) estimate contemporary risk for cardiomyopathic patients. BACKGROUND: Patients with chronic AR and severe LVD have been considered high risk for aortic valve surgery, with limited prognosis. Transplantation is considered for some. METHODS: From 1972 to 1999, 724 patients underwent surgery for chronic AR; 88 (12%) had severe LVD. They were propensity matched to patients with nonsevere LVD to compare hospital mortality, interaction of operative date with severity of LVD, and late survival. Propensity score-adjusted multivariable analysis was performed for all 724 patients to identify risk factors for death. RESULTS: Survival was lower (p = 0.04) among patients with severe LVD than among matched patients with nonsevere LVD (30-day, 1-, 5-, and 25-year survival estimates were 91% vs. 96%, 81% vs. 92%, 68% vs. 81%, and 5% vs. 12%, respectively). However, survival of patients with severe LVD improved dramatically across the study time frame (p = 0.0004): hospital mortality decreased from 50% in 1975 to 0% after 1985, and time-related survival in patients with severe LVD operated on since 1985 became equivalent to that of matched patients with nonsevere LVD (p = 0.96). CONCLUSIONS: Neutralizing risk of severe LVD has improved early and late survival such that aortic valve surgery for chronic AR and cardiomyopathy is no longer a high-risk procedure for which transplantation is the best option.     

Activator of G protein signaling 3 null mice: I. Unexpected alterations in metabolic and cardiovascular function

Activator of G protein signaling (AGS)-3 plays functional roles in cell division, synaptic plasticity, addictive behavior, and neuronal development. As part of a broad effort to define the extent of functional diversity of AGS3-regulated-events in vivo, we generated AGS3 null mice. Surprisingly, AGS3 null adult mice exhibited unexpected alterations in cardiovascular and metabolic functions without any obvious changes in motor skills, basic behavioral traits, and brain morphology. AGS3 null mice exhibited a lean phenotype, reduced fat mass, and increased nocturnal energy expenditure. AGS3 null mice also exhibited altered blood pressure control mechanisms. These studies expand the functional repertoire for AGS3 and other G protein regulatory proteins providing unexpected mechanisms by which G protein systems may be targeted to influence obesity and cardiovascular function.     

How safe is primary knee replacement surgery? Perioperative complication rates in Northern Illinois, 1993–1999

Objective

To describe inpatient complications for primary total knee replacement (TKR) in a period of rapidly growing orthopedic surgery capacity, declining length of stay, and more frequent discharge to rehabilitation facilities.

Methods

Complication incidence according to published coding algorithms was estimated for 35,531 primary TKR admissions of northern Illinois residents to 65 Illinois hospitals. Complication odds were estimated as a function of patients' clinical and sociodemographic status, hospital volume, residency training, TKR length of stay, International Classification of Diseases, Ninth Revision (ICD‐9) coding intensity, and discharges to skilled nursing or rehabilitation facilities.

Results

Primary TKR admissions increased 36% between 1993 and 1999, length of stay declined 43%, average ICD‐9 code use increased 31%, and rehabilitation discharges increased 68%. Major complication rates declined 44% (12.4% to 6.9%; P < 0.0001) over this period, reflecting a 50% reduction in the adjusted odds of complication between 1993 and 1999. There was no association of procedure volume and outcome.

Conclusion

It is likely that the reduction in complications reflects true safety improvements as well as reduced length of stay.

     

CD4+ follicular regulatory T cells optimize the influenza virus–specific B cell response

CD4⁺ follicular regulatory T (Tfr) cells control B cell responses through the modulation of follicular helper T (Tfh) cells and germinal center development while suppressing autoreactivity; however, their role in the regulation of productive germinal center B cell responses and humoral memory is incompletely defined. We show that Tfr cells promote antigen-specific germinal center B cell responses upon influenza virus infection. Following viral challenge, we found that Tfr cells are necessary for robust generation of virus-specific, long-lived plasma cells, antibody production against both hemagglutinin (HA) and neuraminidase (NA), the two major influenza virus glycoproteins, and appropriate regulation of the BCR repertoire. To further investigate the functional relevance of Tfr cells during viral challenge, we used a sequential immunization model with repeated exposure of antigenically partially conserved strains of influenza viruses, revealing that Tfr cells promote recall antibody responses against the conserved HA stalk region. Thus, Tfr cells promote antigen-specific B cell responses and are essential for the development of long-term humoral memory.     

Sparing of the Dystrophin-Deficient Cranial Sartorius Muscle Is Associated with Classical and Novel Hypertrophy Pathways in GRMD Dogs

Both Duchenne and golden retriever muscular dystrophy (GRMD) are caused by dystrophin deficiency. The Duchenne muscular dystrophy sartorius muscle and orthologous GRMD cranial sartorius (CS) are relatively spared/hypertrophied. We completed hierarchical clustering studies to define molecular mechanisms contributing to this differential involvement and their role in the GRMD phenotype. GRMD dogs with larger CS muscles had more severe deficits, suggesting that selective hypertrophy could be detrimental. Serial biopsies from the hypertrophied CS and other atrophied muscles were studied in a subset of these dogs. Myostatin showed an age-dependent decrease and an inverse correlation with the degree of GRMD CS hypertrophy. Regulators of myostatin at the protein (AKT1) and miRNA (miR-539 and miR-208b targeting myostatin mRNA) levels were altered in GRMD CS, consistent with down-regulation of myostatin signaling, CS hypertrophy, and functional rescue of this muscle. mRNA and proteomic profiling was used to identify additional candidate genes associated with CS hypertrophy. The top-ranked network included α-dystroglycan and like-acetylglucosaminyltransferase. Proteomics demonstrated increases in myotrophin and spectrin that could promote hypertrophy and cytoskeletal stability, respectively. Our results suggest that multiple pathways, including decreased myostatin and up-regulated miRNAs, α-dystroglycan/like-acetylglucosaminyltransferase, spectrin, and myotrophin, contribute to hypertrophy and functional sparing of the CS. These data also underscore the muscle-specific responses to dystrophin deficiency and the potential deleterious effects of differential muscle involvement.Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin gene and occurs in approximately 1 in 3500 live male births.¹ DMD boys show signs of skeletal muscle weakness, evidenced by a delay in walking until approximately 18 months and loss of ambulation by the teenage years. Necrotic muscle ultimately fails to regenerate and is replaced with fibrous connective tissue and fat. Molecular and cellular mechanisms underlying gradual muscle deterioration are poorly understood.Animal models of DMD include the mdx mouse and golden retriever muscular dystrophy (GRMD) dog.^2,3 Despite sharing the same fundamental genetic and biochemical lesions, remarkable phenotypic variation occurs among dystrophin-deficient individuals and muscles. Mdx mice have a relatively mild phenotype,⁴ whereas affected dogs have clinical and pathological features consistent with those of DMD.⁵ Even among DMD patients, who all lack dystrophin except for rare revertant fibers, symptoms can vary markedly.⁶ Dogs with GRMD also demonstrate pronounced phenotypic variation, as some dogs lose the ability to walk within the first 6 months of life, whereas others remain ambulatory to 10 years of age or older.^7–9In GRMD neonatal dogs, flexor muscles such as the sartorius are generally more severely involved than extensors, potentially due to their role in crawling.^10,11 Early dystrophic histopathological changes seen in these diseased muscles include myofiber necrosis evidenced by hyaline fibers, mineralization, edema, and inflammation, with associated regeneration.¹⁰ Presumably, as dogs subsequently begin to walk, weight-bearing extensor muscles such as the vastus lateralis (VL) are more predisposed to injury and display these same acute dystrophic changes. With regard to individual muscle variation in DMD, extensors that undergo eccentric contraction (eg, quadriceps femoris) are particularly vulnerable to early weakness and wasting.¹² On the other hand, the extraocular muscles are largely spared.¹³In DMD patients, most muscles atrophy over time, but some, such as the gastrocnemius, undergo gross enlargement.¹⁴ On the basis of early histological studies of dystrophic muscle biopsies, this calf hypertrophy was initially attributed to deposition of fat and fibrotic tissue and was termed pseudohypertrophy.¹⁵ However, in a series of 350 neuromuscular patients, including 9 with Becker muscular dystrophy, quantitative ultrasound demonstrated that calf hypertrophy was most often due to an actual increase in contractile tissue.¹⁶ Mdx mice¹⁷ and dystrophin-deficient cats¹⁸ also have muscle hypertrophy in the absence of significant fat and connective tissue infiltration. The sartorius muscle is particularly intriguing in both DMD and GRMD. Humans have a single muscle, whereas dogs have cranial and caudal bellies. Serving principally as a hip flexor, the sartorius extends from the pelvis to the proximal tibia in people. Both heads of the canine sartorius also arise from the pelvis, but they insert at different sites (caudal, proximal tibia; cranial, distal femur). The cranial sartorius (CS) muscle of neonatal GRMD dogs sustains extensive necrosis¹⁹ and then regenerates, often undergoing dramatic true hypertrophy.^9,20 In DMD patients, the sartorius muscle is relatively spared and may hypertrophy late in the disease process.^21,22Studies showing variable phenotypes among dystrophin-deficient species, individuals, and muscles suggest that factors other than dystrophin deficiency, so-called secondary effects, are involved in the disease process.²³ Determining the molecular underpinnings of the variable clinical and histopathological response to dystrophin deficiency should provide insight into disease pathogenesis and an opportunity to identify potential targets for therapy. Phenotypic–molecular correlations are inherently limited in DMD patients due to unavoidable restrictions of muscle sampling. Animal studies are potentially more powerful because multiple muscles can be sampled at different ages, thus allowing clearer distinction of factors contributing to disease progression. We chose to use the GRMD model of DMD for this study because of the availability of archived biopsy samples of multiple muscles from affected dogs at two ages and corresponding systematic functional data that could be correlated with mRNA and protein expression findings.Hierarchical clustering of several phenotypic markers, including CS muscle size, tibiotarsal joint angle,⁷ and flexor and extensor torque,⁸ was first performed in a group of GRMD and normal dogs. Consistent with our prior studies,⁹ severely affected dogs tended to have larger CS muscles. To achieve a better understanding of the molecular signals that drive muscle hypertrophy, we extended a prior, largely pathological study of differential muscle involvement in the GRMD model.¹⁹ Proteins that are well known to influence muscle size [myostatin (MSTN)]^24,25 or potentially compensate for dystrophin deficiency [utrophin (UTRN)]²⁶ were assessed in a subset of the dogs evaluated by hierarchical clustering. MSTN showed an age-dependent decrease and an inverse correlation with the degree of CS hypertrophy. Regulators of MSTN at the protein (AKT1) and miRNA (miR-539 and miR-208b targeting myostatin mRNA) level were altered, consistent with down-regulation of MSTN signaling, CS hypertrophy, and functional rescue of this muscle. The growth factor myotrophin (MTPN) was increased in the CS. These studies were augmented by analysis of mRNA, miRNA, and proteomic profiles from several GRMD muscles at two different ages to elucidate additional hypertrophic pathways. Although UTRN was also uniformly increased in GRMD muscles, there was no association with CS size. Other membrane-associated proteins, including α-dystroglycan, like-acetylglucosaminyltransferase (LARGE), and β-spectrin, were increased in the GRMD CS, consistent with a role in membrane stabilization. These results indicate that several muscle proteins may act together to stabilize myofibers and promote muscle growth. Our findings also further substantiate that differential muscle involvement can exaggerate the GRMD phenotype. This suggests that care should be taken with treatments targeting specific pathways, such as MSTN, that could selectively exaggerate muscle hypertrophy.