IGF-I signaling prevents dehydroepiandrosterone (DHEA)-induced apoptosis in hypothalamic neurons.
Dehydroepiandrosterone (DHEA) is synthesized in the brain, but whether DHEA is involved in modulating neuronal cell survival is not yet fully understood. Herein we show that when deprived of trophic support, GT1-7 hypothalamic neurons undergo apoptosis following exposure to DHEA, as demonstrated both by morphological and biochemical criteria. This proapoptotic effect appeared to be specific to DHEA itself, and not through conversion of DHEA to other steroids such as androgen or estrogen. Importantly, we determined that IGF-I protects GT1-7 neurons from DHEA-induced cell death. DHEA-induced apoptosis was associated with increased activation of caspase 3 and decreased PARP, which were both attenuated with addition of IGF-I. Addition of DHEA prevented phosphorylation of both Akt and glycogen synthase kinase-3 beta (GSK-3beta), downstream effector molecules of the phosphatidylinositol 3-kinase (PI3K) pathway. Further IGF-I was able to sustain Akt activity and thus preventing GSK-3beta activation in the presence of DHEA. On the other hand, the MAP kinases, ERK, p38, and JNK, were not affected by DHEA. These findings suggest that in GT1-7 hypothalamic neurons, DHEA acts detrimentally to induce cell death and IGF-I is able to rescue the neurons by preserving the activity of Akt, and therefore maintaining the proapoptotic kinase GSK-3beta, in a phosphorylated catalytically inactive state.