Anti‐apoptotic effects of allopregnanolone on P19 neurons

Abstract

Progesterone and its metabolites are potent allosteric modulators of GABA(A) receptor function, through a direct, non-genomic interaction with specific receptor subtypes. In addition, fluctuations in the concentration of progesterone, and allopregnanolone in particular, have been shown to modulate GABA(A) receptor gene expression and activity. In this study, mouse P19 cells were induced to differentiate into post-mitotic neurons which express specific neuronal markers, including GABA(A) and N-methyl-d-aspartate (NMDA) receptors. Apoptotic cell death, induced in the presence of NMDA, was efficiently prevented by allopregnanolone and dehydroepiandrosterone (DHEA) but not DHEA sulfate. Apoptosis was accompanied by cytochrome c release to the cytoplasm and Bax translocation to the mitochondria, while the levels of the anti-apoptotic proteins Bcl-2 and Bcl-xL remained unchanged. In the presence of the most potent neurosteroid, allopregnanolone, DNA fragmentation as well as cytochrome c and Bax translocation were prevented. On the other hand, short-term exposure (1-20 microm, 24 h) of P19-derived neurons to allopregnanolone and DHEA significantly increased the levels of alpha1 and beta2 mRNAs of GABA(A) receptor, while the levels of NR1 mRNA of NMDA receptor were not altered. These results suggest that neurosteroids, interfering with the mitochondrial apoptotic pathway, are able to act as survival factors in neuronal cells, while they contribute to GABA(A) receptor plasticity modulating the expression of its subunits.