The expression of alpha-dystrobrevin and dystrophin during skeletal muscle regeneration

Epigenetic modifications in muscle regeneration and progression of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a multisystemic disorder that affects 1:5000 boys. The severity of the phenotype varies dependent on the mutation site in the DMD gene and the resultant dystrophin expression profile. In skeletal muscle, dystrophin loss is associated with the disintegration of myofibers and their ineffective regeneration due to defective expansion and differentiation of the muscle stem cell pool. Some of these phenotypic alterations stem from the dystrophin absence-mediated serine-threonine protein kinase 2 (MARK2) misplacement/downregulation in activated muscle stem (satellite) cells and neuronal nitric oxide synthase loss in cells committed to myogenesis. Here, we trace changes in DNA methylation, histone modifications, and expression of regulatory noncoding RNAs during muscle regeneration, from the stage of satellite cells to myofibers. Furthermore, we describe the abrogation of these epigenetic regulatory processes due to changes in signal transduction in DMD and point to therapeutic treatments increasing the regenerative potential of diseased muscles based on this acquired knowledge.

Integrated analysis identified an intestinal-like and a diffuse-like gene sets that predict gastric cancer outcome

The two major histological types of gastric cancer, intestinal and diffuse subtypes, have distinct epidemiological and pathophysiological features and were also suggested to be of diverse clinical outcomes. Although the gene expression spectrum of gastric cancer subtypes has been reported by previous studies, its linkage with gastric cancer clinical features and outcomes remains elusive. We investigated large-sample online gastric cancer datasets for seeking genes correlated with the clinical diversities between gastric cancer intestinal and diffuse subtypes. Genes differently expressed between the two subtypes were assessed by multiple statistical analysis and were testified on cellular level by quantitative RT-PCR. Related genes were combined to generate a risk signature, and their mutual linkages were also explored. Among genes overexpressed in intestinal subtype, ATPIF1, PRDX2, PRKAR2A, and SMC1A were correlated with positive prognosis. Among genes overexpressed in diffuse subtype, DTNA, GPR161, IDS, RHOQ, and TSHZ2 were correlated with negative prognosis. These nine genes were all novel independent prognostic factors. When used in combination as signatures, these two gene sets displayed strong efficacy for prediction of the prognosis and clinical variables in gastric and colorectal cancer. Hence, these two genes sets were respectively defined as the favorable intestinal-like and adverse diffuse-like gene sets. We identified nine novel genes correlated with the clinical diversity between the intestinal and diffuse subtypes of gastric cancer. The malignant changes from the intestinal to diffuse subtype might be due to the reduction of the four intestinal-like genes, as well as the elevation of the five diffuse-like genes.

Beta-synemin expression in cardiotoxin-injected rat skeletal muscle

Background

β-synemin was originally identified in humans as an α-dystrobrevin-binding protein through a yeast two-hybrid screen using an amino acid sequence derived from exons 1 through 16 of α-dystrobrevin, a region common to both α-dystrobrevin-1 and -2. α-Dystrobrevin-1 and -2 are both expressed in muscle and co-localization experiments have determined which isoform preferentially functions with β-synemin in vivo. The aim of our study is to show whether each α-dystrobrevin isoform has the same affinity for β-synemin or whether one of the isoforms preferentially functions with β-synemin in muscle.

Methods

The two α-dystrobrevin isoforms (-1 and -2) and β-synemin were localized in regenerating rat tibialis anterior muscle using immunoprecipitation, immunohistochemical and immunoblot analyses. Immunoprecipitation and co-localization studies for α-dystrobrevin and β-synemin were performed in regenerating muscle following cardiotoxin injection. Protein expression was then compared to that of developing rat muscle using immunoblot analysis.

Results

With an anti-α-dystrobrevin antibody, β-synemin co-immunoprecipitated with α-dystrobrevin whereas with an anti-β-synemin antibody, α-dystrobrevin-1 (rather than the -2 isoform) preferentially co-immunoprecipitated with β-synemin. Immunohistochemical experiments show that β-synemin and α-dystrobrevin co-localize in rat skeletal muscle. In regenerating muscle, β-synemin is first expressed at the sarcolemma and in the cytoplasm at day 5 following cardiotoxin injection. Similarly, β-synemin and α-dystrobrevin-1 are detected by immunoblot analysis as weak bands by day 7. In contrast, immunoblot analysis shows that α-dystrobrevin-2 is expressed as early as 1 day post-injection in regenerating muscle. These results are similar to that of developing muscle. For example, in embryonic rats, immunoblot analysis shows that β-synemin and α-dystrobevin-1 are weakly expressed in developing lower limb muscle at 5 days post-birth, while α-dystrobrevin-2 is detectable before birth in 20-day post-fertilization embryos.

Conclusion

Our results clearly show that β-synemin expression correlates with that of α-dystrobrevin-1, suggesting that β-synemin preferentially functions with α-dystrobrevin-1 in vivo and that these proteins are likely to function coordinately to play a vital role in developing and regenerating muscle.

Transcriptomic and proteomic responses of human renal HEK293 cells to uranium toxicity

The industrial use of uranium, in particular depleted uranium, has pin-pointed the need to review its chemical impact on human health. Global methodologies, applied to the field of toxicology, have demonstrated their applicability to investigation of fine molecular mechanisms. This report illustrate the power of toxicogenomics to evaluate the involvement of certain genes or proteins in response to uranium. We particularly show that 25% of modulated genes concern signal transduction and trafficking, that the calcium pathway is heavily disturbed and that nephroblastomas-related genes are involved (WIT-1, STMN1, and STMN2). A set of 18 genes was deregulated whatever the concentration of toxicant, which could constitute a signature of uranium exposure. Moreover, a group of downregulated genes, with corresponding disappearing proteins (HSP90, 14-3-3 protein, HMGB1) in two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), are good candidates for use as biomarkers of uranium effects. These results reveal a cross-checking between transcriptomic and proteomic technologies. Moreover, our temporal gene expression profiles suggest the existence of a concentration threshold between adaptive response and severe cell deregulation. Our results confirm the involvement of genes already described and also provide new highlights on cellular response to uranium.

Clathrin isoform CHC22, a component of neuromuscular and myotendinous junctions, binds sorting nexin 5 and has increased expression during myogenesis and muscle regeneration

The muscle isoform of clathrin heavy chain, CHC22, has 85% sequence identity to the ubiquitously expressed CHC17, yet its expression pattern and function appear to be distinct from those of well-characterized clathrin-coated vesicles. In mature muscle CHC22 is preferentially concentrated at neuromuscular and myotendinous junctions, suggesting a role at sarcolemmal contacts with extracellular matrix. During myoblast differentiation, CHC22 expression is increased, initially localized with desmin and nestin and then preferentially segregated to the poles of fused myoblasts. CHC22 expression is also increased in regenerating muscle fibers with the same time course as embryonic myosin, indicating a role in muscle repair. CHC22 binds to sorting nexin 5 through a coiled-coil domain present in both partners, which is absent in CHC17 and coincides with the region on CHC17 that binds the regulatory light-chain subunit. These differential binding data suggest a mechanism for the distinct functions of CHC22 relative to CHC17 in membrane traffic during muscle development, repair, and at neuromuscular and myotendinous junctions.