Abstract
The neuroactive steroids dehydroepiandrosterone (DHEA), its sulfate ester DHEA sulfate (DHEAS), and allopregnanolone (Allo), produced by the CNS and the adrenals, appear to exert a protective effect in hippocampal and cortical neuron ischemia- and excitotoxicity-induced injury. We hypothesized that they may also play a protective role on the adrenal medulla, an important part of the sympathetic nervous system, and the tissue adjacent to their primary site of production. DHEA, DHEAS, and Allo protected rat chromaffin cells and the rat pheochromocytoma PC12 cell line, an established model for the study of adrenomedullary cell apoptosis and survival, against serum deprivation-induced apoptosis. Their effects were time- and dose-dependent, with EC50 1.8, 1.1, and 1.5 nM, respectively. The antiapoptotic effect of DHEA DHEAS and Allo was compared to that of a long list of structurally related compounds and was found to be structure-specific, confined mainly to conformation 3beta-OH-Delta5 for androstenes and 3alpha-OH for pregnanes. Indeed, 3-keto, Delta4, or C7 hydroxylated androstenes and 3beta pregnanes were ineffective. The prosurvival effect of DHEA(S) and Allo was N-methyl-D-aspartate-, GABAA-, sigma1-, or estrogen receptor-independent. It involved the antiapoptotic Bcl-2 proteins, their role being sine qua non for their action because Bcl-2 antisense oligonucleotides reversed their effects. Finally, DHEA(S) and Allo activated cAMP response element-binding protein and NF-kappaB, upstream effectors of antiapoptotic Bcl-2 protein expression. They also activated the antiapoptotic kinase PKCalpha/beta, a posttranslational activator of Bcl-2 protein. Our findings suggest that decline of DHEA(S) and Allo during aging or stress may leave the adrenal medulla unprotected against proapoptotic challenges.