In studies in vitro, Uaesoontrachoon et al. (2008) reported that OPN released by myoblasts served as a link between the inflammatory response PTC124 in vitro and myogenesis during the early phase of muscle regeneration and repair. Our findings corroborate the close relationship in timing between the second phase of OPN upregulation and the significant increase in myogenin expression initiated at 18 h, with peaks at 3 days and 7 days post-venom. Our results showed that

B. lanceolatus venom promoted connective tissue disorganization in the acute stage of envenoming followed by patches of intense collagen deposition 3–7 days post-venom. Fibrotic processes may represent a barrier for tissue revascularization and limit the access of important molecules or cells involved in tissue regeneration. The finding that the small diameter of regenerated fibers at 21 days post-venom was significantly lower than in time-matched controls suggests that fibrosis may have impaired complete regeneration. It is worth

mentioning that OPN has been pointed out as a pro-fibrotic promoter in hepatic and renal diseases ( Lorena et al., 2006 and Irita et al., 2008). In cardiac muscle dysfunction ( Singh et al., 2010) and skeletal and cardiac muscles of mdx mice ( Vetrone et al., 2009) the upregulation of OPN has been correlated with enhanced collagen synthesis and accumulation, whereas deletion of the OPN gene reduced fibrosis and improved regeneration. Our findings selleck chemicals llc also showed two other interesting data: the expression of myogenin in the cytoplasm of myoblasts and myotubes instead of its usual expression in the nucleus, and the population of CD68 + macrophages significantly elevated in the proliferative stage of myoblasts (3 days post-venom), and in the acute inflammatory phase (3–6 h post-venom). Nuclear myogenin is needed for regulation of the transcription of specific myogenic promoters whereas its retention in the cytoplasm may Urease regulate the biological activity of proteins and prevent differentiation;

the transfer of myogenin into the nucleus occurs when proliferative signals cease and the protein level increases significantly (Ferri et al., 2009). On the other hand, macrophages can release products that inhibit the transition of myogenic cells from proliferative to differentiating stages (Merly et al., 1999). Whether this significant presence of phagocytic M1 macrophages on day 3 post-venom has a role in the atypical retention of myogenin in the cytoplasm and in delayed muscle repair is unknown. This is an interesting possibility since it was only from day 14 post-venom onwards that myogenin labeling was no longer observed in the cytoplasm and that CD68 macrophage numbers were as low as in control muscle.