Unacylated ghrelin promotes skeletal muscle regeneration following hindlimb ischemia via SOD-2-mediated miR-221/222 expression.

Background: Surgical treatment of peripheral artery disease, even if successful, does not prevent reoccurrence. Under these conditions, increased oxidative stress is a crucial determinant of tissue damage. Given its reported antioxidant effects, we investigated the potential of unacylated-ghrelin (UnAG) to reduce ischemia-induced tissue damage in a mouse model of peripheral artery disease.
Methods and Results: We show that UnAG but not acylated ghrelin (AG) induces skeletal muscle regeneration in response to ischemia via canonical p38/mitogen-actived protein kinase signaling UnAG protected against reactive oxygen species-induced cell injuries by inducing the expression of superoxide dismutase-2 (SOD-2) in satellite cells. This led to a reduced number of infiltrating CD68(+) cells and was followed by induction of the myogenic process and a reduction in functional impairment. Moreover, we found that miR-221/222, previously linked to muscle regeneration processes, was up-regulated and negatively correlated with p57(Kip2) expression in UnAG-treated mice. UnAG, unlike AG, promoted cell-cycle entry in satellite cells of mice lacking the genes for ghrelin and its receptor (GHSR1a). UnAG-induced p38/mitogen-actived protein kinase phosphorylation, leading to activation of the myogenic process, was prevented in SOD-2-depleted SCs. By siRNA technology, we also demonstrated that SOD-2 is the antioxidant enzyme involved in the control of miR-221/222-driven posttranscriptional p57(Kip2) regulation. Loss-of-function experiments targeting miR-221/222 and local pre-miR-221/222 injection in vivo confirmed a role for miR-221/222 in driving skeletal muscle regeneration after ischemia.
Conclusions: These results indicate that UnAG-induced skeletal muscle regeneration after ischemia depends on SOD-2-induced miR-221/222 expression and highlight its clinical potential for the treatment of reactive oxygen species-mediated skeletal muscle damage.