Androgen Receptor-Independent Mechanisms for Dihydrotestosterone (DHT)-induced Protection in the C6 Glioma Model of Astrocytes

Testosterone and dihydrotestosterone (DHT) exert protection through the activation of the intracellular androgen receptor (AR). However, studies suggest DHT may also exert protective effects by way of alternate mechanisms, including through prior conversion to 3beta-diol, a metabolite that can bind and activate estrogen receptors. Using the AR-deficient C6 glioma, a model of astrocytes, we found DHT was protective against iodoacetic acid (IAA) toxicity. The protective effects of DHT, as assessed by the Calcein-AM viability assay (which is a surrogate measure of cell number), were blocked by the co-application of the non-selective estrogen receptor antagonist, ICI-182,780. Using a complementary viability assay, the MTT assay, which is a surrogate for mitochondrial respiration/activity, we reproduced DHT protection and extended our results to find that 3beta-diol was also protective against IAA-induced reduction in mitochondrial activity. Interestingly, while the effects of 3beta-diol, the presumptive mediator of the effects of DHT, were blocked by ICI 182,780, they were not blocked by the estrogen receptor isoform-selective antagonists MPP (against ERa) and PHTPP (against ERb). Collectively, these data support our hypothesis that DHT is protective against cytotoxicity in a cell line devoid of the classical/intracellular androgen receptor, and that the metabolite of DHT, 3beta-diol, may be an important mediator of DHT’s effects in the central nervous system. Our results also suggest that the capacity to convert DHT to 3beta-diol may be relevant to the protective influence of androgens and estrogens in the postmenopausal women, a time when estrogen and progesterone levels decline significantly, but androgen levels persist.