Apoptosis repressor with caspase recruitment domain is dramatically reduced in cardiac, skeletal, and vascular smooth muscle during hypertension

Apoptosis repressor with caspase recruitment domain (ARC) is a unique anti-apoptotic protein with a distinct tissue distribution. In addition, unlike most anti-apoptotic proteins which act on one pathway, ARC can inhibit apoptosis mediated by both the death-receptor and mitochondrial signaling pathways. In this study, we confirm previous reports showing high levels of ARC protein in rat heart and skeletal muscle, but demonstrate for the first time that ARC is also expressed in rat aorta. Immunoblot analysis on endothelium-denuded aorta as well as immunohistochemical analysis on intact aorta demonstrated that ARC was highly expressed in smooth muscle. Immunoblot analysis also found that ARC protein was severely downregulated in skeletal muscle (−82%; P < 0.001), heart (−80%; P < 0.001), and aorta (−71%; P < 0.001) of spontaneously hypertensive rats (SHR) compared to normotensive Wistar-Kyoto (WKY) rats. Decreased ARC levels were also confirmed in tissues of hypertensive animals by immunohistochemical analysis. Collectively, this data suggests that ARC protein is expressed in vascular smooth muscle and is significantly reduced in several target tissues during hypertension.     

GNE is involved in the early development of skeletal and cardiac muscle

UDP-N-acetylglucosamine 2 epimerase/N-acetylmannosamime kinase (GNE) is a bifunctional enzyme which catalyzes the two key sequential steps in the biosynthetic pathway of sialic acid, the most abundant terminal monosaccharide on glycoconjugates of eukaryotic cells. GNE knock out (GNE KO) mice are embryonically lethal at day E8.5. Although the role of GNE in the sialic pathway has been well established as well as the importance of sialylation in many diverse biological pathways, less is known about the involvement of GNE in muscle development. To address this issue we have studied the role of GNE during in vitro embryogenesis by comparing the developmental profile in culture of embryonic stem cells (ES) from wild type and from GNE KO E3.5 mice embryos, during 45 days. Neuronal cells appeared rarely in GNE KO ES cultures and did not reach an advanced differentiated stage. Although primary cardiac cells appeared at the same time in both normal and GNE KO ES cultures, GNE KO cardiac cells degraded very soon and their beating capacity decayed rapidly. Furthermore very rare skeletal muscle committed cells were detected in the GNE KO ES cultures at any stage of differentiation, as assessed by analysis of the expression of either Pax7, MyoD and MyHC markers. Beyond the supporting evidence that GNE plays an important role in neuronal cell and brain development, these results show that GNE is strongly involved in cardiac tissue and skeletal muscle early survival and organization. These findings could open new avenues in the understanding of muscle function mechanisms in health and in disease.     

MicroRNAs in skeletal and cardiac muscle development

MicroRNAs (miRNAs) are a recently discovered class of small non-coding RNAs, which are approximately 22 nucleotides in length. miRNAs negatively regulate gene expression by translational repression and target mRNA degradation. It has become clear that miRNAs are involved in many biological processes, including development, differentiation, proliferation, and apoptosis. Interestingly, many miRNAs are expressed in a tissue-specific manner and several miRNAs are specifically expressed in cardiac and skeletal muscles. In this review, we focus on those miRNAs that have been shown to be involved in muscle development. Compelling evidences have demonstrated that muscle miRNAs play an important role in the regulation of muscle proliferation and differentiation processes. However, it appears that miRNAs are not essential for early myogenesis and muscle specification. Importantly, dysregulation of miRNAs has been linked to muscle-related diseases, such as cardiac hypertrophy. A mutation resulting in a gain-of-function miRNA target site in the myostatin gene leads to down regulation of the targeted protein in Texel sheep. miRNAs therefore are a new class of regulators of muscle biology and they might become novel therapeutic targets in muscle-related human diseases.     

The subcellular distribution of dystrophin in mouse skeletal, cardiac, and smooth muscle

We use a highly specific and sensitive antibody to further characterize the distribution of dystrophin in skeletal, cardiac, and smooth muscle. No evidence for localization other than at the cell surface is apparent in skeletal muscle and no 427-kD dystrophin labeling was detected in sciatic nerve. An elevated concentration of dystrophin appears at the myotendinous junction and the neuromuscular junction, labeling in the latter being more intense specifically in the troughs of the synaptic folds. In cardiac muscle the distribution of dystrophin is limited to the surface plasma membrane but is notably absent from the membrane that overlays adherens junctions of the intercalated disks. In smooth muscle, the plasma membrane labeling is considerably less abundant than in cardiac or skeletal muscle and is found in areas of membrane underlain by membranous vesicles. As in cardiac muscle, smooth muscle dystrophin seems to be excluded from membrane above densities that mark adherens junctions. Dystrophin appears as a doublet on Western blots of skeletal and cardiac muscle, and as a single band of lower abundance in smooth muscle that corresponds most closely in molecular weight to the upper band of the striated muscle doublet. The lower band of the doublet in striated muscle appears to lack a portion of the carboxyl terminus and may represent a dystrophin isoform. Isoform differences and the presence of dystrophin on different specialized membrane surfaces imply multiple functional roles for the dystrophin protein.