Muscle catabolic mechanisms:from disuse atrophy to cachexia.

The phatophysiology of muscle atrophy is a complex multifactor process, which occurs in response to environmental solicitations, injury, various disease states, disuse and normal aging. Persistent low-grade or acute activation of inflammatory/oxidative cascade, acute stress, altered energy intake, or reduced mechanical action, contribute to muscle decline, as well as to the progression of chronic and acute associated disease. Elevated concentrations of pro-inflammatory markers have also devastating effects on the vasculature and are implicated in the pathogenesis of atherosclerosis, which at peripheral level contributes to muscle suffering. A more understanding of the molecular relationships underpinning muscle atrophy, inflammation and cardiovascular risk in different human clinical models should be helpful to design new therapies to the recovery of muscle. Thus, we investigated the effect of some effectors of inflammatory/oxidative responses on muscle atrophy, inflammation and cardiovascular dysfunction, in chronic, acute or healthy conditions. We explored: a) the interaction between energy restriction and muscle unloading in the regulation of lean body mass, protein kinetics or inflammatory response in healthy subjects; b) the links among inflammation, organ failure, cardiovascular risk and cytokine genotypes, in models of chronic muscle atrophy; c) the cross-interaction connecting translational machinery, proteolysis and apoptotic response with skeletal muscle atrophy induced by acute stress. We highlighted a link between inflammatory process, cardiovascular risk and muscle unloading, likely involving leptin hormone and the long pentraxin PTX3; the latter may represent a novel key of reading of some bed-rest effect on vasculature or inflammatory system. Cytokine genotypes (interpheron-gamma), and the extent of renal functions on cytokine clearence, may account of intraindividual variability and vulnerability to the process. Finally, we gained knowledge about a novel catabolic mechanism, involving the eukariotic elongation factor EEF1A1 and the stress response protein p66(ShcA) in acute muscle atrophy. We suggest that, a more controlled energy intake combined with various exercise regimes might protect from the effects of unloading and may be a reasonable approach to maintain muscle mass in health but also in disease conditions.