Modulazione dell’attività autofagica nella preservazione della fibra muscolare scheletrica

Autophagy is a physiological mechanism, responsible for cell homeostasis, aimed to remove damaged organelles and unfolded proteins avoiding their accumulation in the cytoplasm. Autophagic flux impairment seems to be involved in several diseases, including muscular dystrophies and myopathies (Park et al., 2009; Sandri et al., 2013), cancer (Lu et al., 2013), diabetes (Kang et al., 2016), Parkinson’s, Alzheimer’s, Huntington’s disease (Cheung et al., 2011) as well as Lysosomal Storage Disorders (Settembre et al., 2008). According to few papers in literature, chemotherapeutic drug treatments are able to trigger autophagy (Fanzani et al., 2011). Previous works, conducted by our group, demonstrated that C2C12 myotubes treated with etoposide (eto), a chemotherapeutic drug known to induce cell death and oxidative stress, undergo an abnormal autophagic activation, as well as nuclear disorganization and cytoplasmic shrinkage (Salucci et al., 2013). Amino acid supplementation, stimulated by glutamine, has been described as protective from the degradative effect of proinflammatory cytokines (TNF-α) implicated in many degenerative processes (Bonetto et al., 2011). Moreover, dietary glutamine intake represents a conditioning therapy before chemotherapy, to counteract drug side effects (Yoshida et al., 2001; Mora et al., 2002; Gaurav et al., 2012; Pesarini et al., 2014). Starvation is a common used strategy to conduct studies on autophagy, since nutrient deprivation is an effective stimuli for autophagic induction (Desgeorges et al., 2014). Aim: The aim of this work was to find a strategy, based on diet modulation, to prevent antineoplastic treatment induced damage. An in vitro model of skeletal muscle has been exposed to etoposide, to mimic chemotherapeutic induced damage. Glutamine supplementation and nutrient deprivation have been chosen as pre-treatment to counteract autophagic flux impairment and myotube atrophy. Methods: Differentiated C2C12 cells have been exposed to eto after a previous treatment with glutamine or starvation. Cytofluorimetric, morphological and morpho-functional analyses revealed that eto treatment induces damage to the lysosomal compartment, causing the accumulation of autophagic vacuoles, and a reduction of myotube area. Interestingly, both pre-treatments were able to rescue myotubes from damage. Glutamine supply, in particular, seemed to be a good strategy to preserve cell size and prevent the autophagic impairment, partially restoring the normal lysosomal activity. Starvation, secondly, was able to activate a survival autophagy, avoiding autophagosome and damaged organelle accumulation induced by etoposide. Conclusions and future purposes: These findings suggest that a diet modulation could prevent the eto-induced abnormal autophagic activation and hamper the atrophic pathway activation in differentiated C2C12 cells. Further molecular studies are already ongoing to validate these data. Once achieved comprehensive results in vitro, it could be interesting to go towards an in vivo approach, to investigate if a diet modulation could prevent muscle atrophy in tumor-bearing rats undergoing chemotherapy.