17Beta-estradiol abrogates apoptosis in murine skeletal muscle cells through estrogen receptors: role of the phosphatidylinositol 3-kinase/Akt pathway.

Estrogens can regulate apoptosis in various cellular systems. The present study shows that 17beta-estradiol (E2), at physiological concentrations, abrogates DNA damage, poly (ADP-ribose) polymerase cleavage, and mitochondrial cytochrome c release induced by H2O2 or etoposide in mouse skeletal muscle C2C12 cells. This protective action, which involved PI3K/Akt activation and Bcl-2 associated death agonist (BAD) phosphorylation, was inhibited by antibodies against the estrogen receptor (ER) alpha or beta isoforms, or transfecting siRNA specific for each isoform. The inhibition of the antiapoptotic action of E2 at the mitochondrial level was more pronounced when ER-beta was immunoneutralized or suppressed by mRNA silencing, whereas transfection of C2C12 cells with either ER-alpha siRNA or ER-beta siRNA blocked the activation of Akt by E2, suggesting differential involvement of ER isoforms depending on the step of the apoptotic/survival pathway evaluated. These results indicate that E2 exerts antiapoptotic effects in skeletal muscle cells which are mediated by ER-beta and ER-alpha and involve the PI3K/Akt pathway.