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Tutor: Scicchitano, Bianca Maria
Adamo, Sergio
Keywords: Vasopressin
Muscular atrophy
Issue Date: 14-Feb-2014
Abstract: This study aims to evaluate the effects of the stimulation of the AVP-dependent pathways on muscular atrophy. Arg-vasopressin (AVP) has been demonstrated to have a potent effect as myogenic promoting factor both in vitro and in vivo. In skeletal muscle AVP signaling is mediated by the V1a receptor, whose stimulation results in the activation of PLC and PLD, increased cytosolic calcium concentration and stimulation of CaMK (Ca2+/calmodulin-dependent protein kinase) and calcineurin pathways, leading to the formation of multifactor complexes on the promoter of muscle specific genes, thus activating their transcription. In this study we induced muscular atrophy by local over-expression of TNF and we evaluated the effects of the stimulation of AVP signaling pathways in this condition by over-expressing V1a receptor. TNF is a pro-inflammatory cytokine and it is known to inhibit myogenic differentiation both in vitro and in vivo, and we have previously demonstrated that the negative effects of TNF in vitro is counteracted by AVP treatment. Moreover it has been demonstrated that TNF plays a key role in the activation of the inflammatory pathways mediated by NF-kB and in the stimulation of protein catabolism. For these reasons, we evaluated, in TNF-expressing muscle, the effects of V1aR over-expression in the regeneration process, in the inflammatory status and in protein degradation. Morphological and morphometric analysis demonstrated that the local over-expression of V1aR in the atrophic muscle enhances the cross-sectional area of the regenerating fibers. Since we noted the presence of infiltrating mono-nucleated cells in muscles over-expressing TNF, we investigated the nature of the infiltrate: it is positive for esterase activity, demonstrating the presence of macrophages. Esterase activity is reduced in muscles over-expressing both TNF and V1aR. We further demonstrated that the up-regulation of NF-kB expression by TNF is reduced by the contemporary over-expression of V1aR. We noted a prevalence of chemokines and cytokines specific of the pro-inflammatory phenotype of macrophages (M1) in the presence of TNF, but an increased levels of antigens and anti-inflammatory cytokines specific for M2 macrophage phenotype in muscle over-expressing both TNF and V1aR. In regards to the regenerative process, the expression levels of early regeneration markers, such as Pax7 and desmin, are up-regulated by TNF, whereas late differentiation markers, such as myogenin and MHC, are down-regulated. The simultaneous over-expression of V1aR up-regulates the expression of both early and late differentiation markers. These data demonstrate that the stimulation of AVP-dependent pathways enhances skeletal muscle regeneration. We also analyzed PI3K/Akt pathway because TNF is known to induce protein degradation. V1 over-expression maintains the phosphorylation levels of Akt and FoxO, at least inhibiting atrogin-1 transcription activated by TNF, thus counteracting protein degradation. According to these results we are extending our studies to the effects of AVP signaling in muscular dystrophies. Very preliminary data suggest a positive role of AVP even in dystrophic muscles in mdx and Scgβ-null mice, though technical issues have yet to be solved.
Research interests: Tissues engineering, Molecular and Cellular biology, Image Cytometry
Personal skills keywords: Histology, Animal care and usage, molecular biology, image cytometry

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