Muscle proteolysis

Insulin stimulates peripheral tissue protein synthesis by stimulating amino acid uptake and protein synthesis at the level of translation and by inhibiting protein degradation. At low insulin levels, muscle proteolysis occurs. As the levels increase, proteolysis decreases and protein synthesis is favored. Exercise decreases proteolysis and increases protein synthesis, whereas disuse results in muscle wasting and depressed protein synthesis. Exercise increases sensitivity to insulin, whereas disuse makes the tissue insulin-resistant. Obesity, pregnancy, and glucocorticoids also increase insulin resistance. 

Microglia Osteoclast activation Decreased proteoglycan synthesis Fibroblast proliferation Muscle proteolysis Endothelial cell activation... 

The weight loss often noted in septic patients is primarily cansed by a loss of appetite resulting from the effect of certain cytokines on the mednllary appetite center. Other causes include increased energy expenditure from fever and enhanced muscle proteolysis. 

Recall that in prolonged starvation muscle proteolysis is induced to provide substrates for gluconeoge-nesis by the liver. This does not, however, alter the use of fatty acids by the muscle for its own energy needs under these conditions. 

LouardRJ, Barrett EJ, GelfandRA. (1995) Overnight branched-chain amino acid infusion causes sustained suppression of muscle proteolysis. Metabolism 44, 424-A29. 

Du, J., Wang, X., Miereles, C. etal.. Activation of caspase-3 is an initial step triggering accelerated muscle proteolysis in catabolic conditions, J Clin Invest, 113, 115, 2004. 

The results suggest that suppression of muscle proteolysis after the changing dietary lysine levels may be attributed to down-regulation of caspase 3 and atrogin-1 mRNAs expression. Since corticosterone induces expression of atrogin-1 mRNA (Sacheck et al., 2004), change of the concentrations of the... 

Proteolysis of muscle during starvation supplies amino acids for gluconeogenesis. 

Kitazawa T, Kobayashi S, Horiuti K, Somlyo AV, Somlyo AP 1989 Receptor coupled, permeabilized smooth muscle role of the phosphatidylinositol cascade, G proteins and modulation of the contractile response to Ca2+. J Biol Chem 264 5339-5342 Lopez-Lopez JR, Shacklock PS, Balke CW, Wier WG 1995 Local calcium transients triggered by single L-type calcium channel currents in cardiac cells. Science 268 1042-1045 Marks AR, Fleischer S, Tempst P 1990 Surface topography analysis of the ryanodine receptor/ junctional channel complex based on proteolysis sensitivity mapping. J Biol Chem 265 13143-13149... 

In view of the close association of peptide with acid-insoluble mammalian-muscle glycogen that had been subjected to proteolysis, the possibil-... 

Figure 2. A proposed model demonstrating several different prominent calcium-related pathways whose activity may be altered in dystrophic muscle. Increased activity of mechanosensitive channels (MS) and store-activated channels (SOC), which are likely derived from the same gene product (TRPC), and the calcium leak channel, which could represent a proteolyzed TRPC SOC channel. Decreased mechanical coupling between L-type VGCC and ryanodine receptors may increase basal calcium release from calcium stores (not shown). Further, increased IP, and IP, receptor levels may also enhance basal and stimulated calcium-induced calcium release (CICR) from calcium stores. Calcium store depletion can increase translocation of SOCs from intracellular vesicles to the sarcolemma. Finally, the relationship between increased membrane fragility and tearing is less certain, but calcium influx through sarcolemmal tears could lead to calcium-dependent proteolysis and increased activity of calcium leak channels, as well as proteolysis of other targets, and increased release of calcium from intracellular stores through CICR. This model is not meant to be comprehensive, and other calcium-related molecules are discussed in the text...

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