Testosterone-Down-Regulated Akt Pathway During Cardiac Ischemia/Reperfusion: A Mechanism Involving BAD, Bcl-2 and FOXO3a

Abstract

Lower levels of myocardial Akt activity in males are associated with a higher incidence of heart failure and worsened cardiac function after ischemia/reperfusion (I/R). While Akt activation by estrogen provides cardioprotection in females, no information exists regarding the effect of testosterone on the myocardial Akt pathway following I/R. We hypothesized that following I/R: (1) endogenous testosterone will decrease myocardial Akt activation in male hearts; (2) endogenous testosterone will mediate downstream signals of Akt, including Bad, Bcl-2, and FOXO3a; (3) administration of exogenous testosterone will recapitulate negative effects on the Akt pathway in castrated male hearts. Rat hearts from age-matched adult males, females, castrated males, males with androgen receptor blocker-flutamide, castrated males with chronic 5α-dihydrotestosterone (DHT) implantation, or acute testosterone infusion (ATI) (n = 9/group) were subjected to I/R (Langendorff). Castration or flutamide treatment significantly up-regulated myocardial Akt activation, increased downstream apoptosis-regulatory molecules p-Bad, Bcl-2, p-FOXO3a, but reduced Fas-L, consistent with decreased myocardial injury in male hearts following I/R. ATI administration, but not chronic DHT, reversed these effects on Akt signaling associated with further exacerbated cardiac dysfunction in castrated males. Notably, lower levels of MnSOD were observed in male hearts, and castration or flutamide treatment restored myocardial MnSOD expression to the levels of females in male hearts after I/R. Our study represents the initial evidence of testosterone-induced down-regulation of the Akt pathway in male hearts following I/R, thereby mediating cardiac injury through decreased p-Bad, reduced ratio of Bcl-2/Bax in the cytoplasm, and increased FOXO3a in the nucleus.