ROLE OF HUMAN SIALIDASES IN THE DIFFERENTIATION OF NORMAL AND PHATOLOGICAL SKELETAL MUSCLE TISSUE

So far the physiological function of sialidases in skeletal muscle differentiation is not well known (Sato et al., 1995;), however the down regulation of the sialidase Neu2 isoform in C2C12 myoblasts induces cell differentiation (Fanzani et al., 2003), by seerum starvation, suggesting an important role of the sialidase enzyme in the myogenic process but it's still unanswered the question if these proteins are also differently exxpressed during muscle regeration. Since previous approach using retroviral vector failed to transduce efficiently sialidases in human myocytes, we produce more suittable lentiviral vectors able to transduce the different human isoforms of sialidases Neu2 and Neu3 in human myocytes, and we also down regulate the expression of the 2 enzymes by RNA interference (siRNA). The results of these two technical appproaches showed the key roles of the sialidase proteins in muscle regeneration. Innappropriate overexpression of sialidase 48 h after the onset of differentiation results in downregulation of myogenin as well as myosin heavy chain expression and in a halt of the differentiation cascade. While Neu2 upregulation per se is sufficient to trigger myoblast differentiation also in hmnan myoblast, Neu3 downregulation is able to abolish cell fusion, resulting in mono-nucleated cells expressing myosin heavy chain. This study indicates that lysosomal sialidases are potent regulators of myogenesis. The research project will be developed in order to analyze the role of sialidases in physiological and pathological condition of skeletal muscle differentiaation.