Estrogen regulates Bcl-w and Bim expression:: Role in protection against β-amyloid peptide-induced neuronal death

Estrogen is neuroprotective against a variety of insults, including beta-amyloid peptide (A beta); however, the underlying mechanism(s) is not fully understood. Here, we report that 17 beta-estradiol (E2) selectively regulates neuronal expression of the Bcl-2 family (bcl-2, bcl-x, bcl-w, bax, bak, bad, bik, bnip3, bid, and bim). In primary cerebrocortical neuron cultures under basal conditions, we observe that E2 upregulates expression of antiapoptotic Bcl-w and downregulates expression of proapoptotic Bim in an estrogen receptor (ER)-dependent manner. In the presence of toxic levels of A beta, we observe that E2 attenuates indices of neuronal apoptosis: c-Jun N-terminal kinase (JNK)-dependent downregulation of Bcl-w and upregulation of Bim, mitochondrial release of cytochrome c and Smac, and cell death. These neuroprotective effects of E2 against A beta-induced apoptosis are mimicked by the JNK inhibitor SP600125 (anthra[1,9-cd] pyrazol-6(2H)-one). In addition, E2 attenuates A beta-induced JNK phosphorylation in an ER-dependent manner, but does not affect basal levels of JNK phosphorylation. These results suggest that E2 may reduce A beta-induced neuronal apoptosis at least in part by two complementary pathways: (1)ER-dependent, JNK-independent upregulation of Bcl-w and downregulation of Bim under basal conditions, and (2) ER-dependent inhibition of A beta-induced JNK activation and subsequent JNK-dependent downregulation of Bcl-w and upregulation of Bim, resulting in mitochondrial release of cytochrome c and Smac and eventual cell death. These data provide new understanding into the mechanisms contributing to estrogen neuroprotection, a neural function with potential therapeutic relevance to Alzheimer's disease.