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Departments of Neurology, and Anatomy and Neurobiology, University of Maryland, School of Medicine, Baltimore, Maryland 21201
Address all correspondence and requests for reprints to: Carol Lee Koski, M.D., N4W46, Neurology, UMMS, 22 South Greene Street, Baltimore, Maryland 21201. E-mail: ckoski{at}umaryland.edu.
Mechanisms underlying the divergent effects of ovarian hormones on neuron death induced by TNF
were investigated in differentiated PC12 cells (dPC12). dPC12 cells were exposed to 17ß-estradiol (E, 1.0 nM), progesterone (P, 100 nM), or a combination of both hormones for 0–72 h before treatment with TNF (0–150 ng) to induce cell death. Cells undergoing apoptosis were identified by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay and fluorescence-activated cell sorting after 18 h. Cell death induced by TNF was decreased 89% after E treatment and increased 2-fold after P treatment compared with cells treated with TNF alone. Treatment with E for 24 h before TNF exposure was required for maximum neuroprotection, whereas P-enhanced death was maximal after a 30-min P treatment. TNF induced a 3-fold increased activity of c-JUN-N-terminal kinase (JNK) 1 in d PC12 cells within 20 min that could be increased 5- to 8-fold by P together with TNF. A peptide inhibitor of JNK1 abrogated P enhancement of TNF-mediated dPC12 death but had only a minimal effect on cell death by TNF alone. Inhibition of caspase-8 activation reduced death induced by TNF alone but was much less effective for P+TNF. P alone did not activate caspase-8. E increased estrogen receptor (ER) and Bcl-xL expression and all but abolished TNF receptor 1 (TNFR1) expression. P decreased ER and Bcl-xL expression and doubled TNFR1 expression. These data suggest that P regulates apoptosis or survival through augmentation of JNK signaling and altered TNFR1 expression, whereas E mainly affects the expression of BCL-xL, TNFR1, and ER.
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