The differences in neuroprotective efficacy of progesterone and medroxyprogesterone acetate correlate with their effects on brain-derived neurotrophic factor expression.
ABSTRACT Whereas hormone therapy is used for the treatment of menopausal symptoms, its efficacy in helping reduce the risk of other diseases such as Alzheimer's disease has been questioned in view of the results of recent clinical trials that appeared inconsistent with numerous basic research studies that supported the beneficial effects of hormones. One possible explanation of this discrepancy may lie in the choice of hormone used. For example, we and others found that progesterone is neuroprotective whereas medroxyprogesterone acetate (MPA), the synthetic progestin used in hormone therapy, is not. Because our data suggest that progesterone-induced protection is associated with the induction of brain-derived neurotrophic factor (BDNF) levels and, importantly, can be blocked by inhibiting the neurotrophin signaling, we determined whether progesterone and medroxyprogesterone acetate differed in their ability to regulate BDNF levels in the explants of the cerebral cortex. We found that progesterone elicited an increase in both BDNF mRNA and protein levels, whereas medroxyprogesterone acetate did not. Furthermore, using both a pharmacological inhibitor of the progesterone receptor (PR) and PR knockout mice, we determined that the effects of progesterone were mediated by the classical PR. Our results underscore the fact that not all progestins have equivalent effects on the brain and suggest that the selection of the appropriate progestin may influence the success of hormone therapy formulations used in treating the menopause and/or reducing the risk for diseases associated with the postmenopausal period.
- SourceAvailable from: Erich Jarvis[show abstract] [hide abstract]
ABSTRACT: The ventromedial hypothalamus (VMH) plays a central role in the regulation of the female reproductive behavior lordosis, a behavior dependent upon the sequential activation of receptors for the ovarian steroid hormones estradiol (E) and progesterone (P). These receptors function as transcription factors to alter the expression of target genes. To discover behaviorally relevant genes targeted by E and P in the VMH, we used the differential display PCR to identify messenger RNAs that are differentially expressed in the hypothalamus of ovariectomized (ovx) rats treated with E alone compared with ovariectomized rats treated with E and P. We show here that one interesting mRNA within the hypothalamus that is repressed by P after E priming encodes the protein 25-Dx, the rat homolog of the human membrane-associated P-binding protein Hpr6.6. Neurons in the brain containing the highest levels of 25-Dx are located in several nuclei of the basal forebrain, including the VMH. 25-Dx expression is also higher in the hypothalamus of female P receptor “knockout” mice than in their wild-type littermates. These findings suggest a mechanism in which the activation of nuclear P receptor represses expression of a membrane P receptor, 25-Dx, during lordosis facilitation.Proceedings of the National Academy of Sciences 12/2000; · 9.74 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Unopposed estrogens, both exogenous and endogenous, increase the risk of endometrial cancer although the magnitude of the association between estrogen replacement therapy and adenocarcinoma has been exaggerated by the epidemiologic case-control studies. Not all postmenopausal women need estrogen replacement therapy since some produce sufficient endogenous estrogens to remain asymptomatic and prevent atrophic vaginitis, osteoporosis and atherosclerosis. However, within this group may be those at risk for endometrial cancer, so they need to be identified and treated with cyclic progestogens. Sequential oral contraceptives did not protect young women from adenocarcinoma of the endometrium because of too little progestogen for too short a duration in view of the relatively high dosage of estrogen. However, combination birth control pills significantly decrease the risk for endometrial carcinoma. Endometrial hyperplasia is a precancerous lesion in some women and can be effectively reversed with 10-13 days of progestogen monthly in at least 98% of patients. The progestogen challenge test has been devised to identify postmenopausal women at greatest risk for adenocarcinoma. It should be administered to all postmenopausal women with an intact uterus. This includes asymptomatic women, patients receiving estrogen replacement therapy and women being evaluated for hormone therapy. If there is a positive response to the progestogen challenge, as manifested by withdrawal bleeding, then the progestogen should be continued for 13 days each month for as long as withdrawal bleeding results. If there is no response then the progestogen challenge test should be repeated at each annual examination. Universal use of the progestogen challenge test should prevent nearly all endometrial cancers.Clinics in obstetrics and gynaecology 01/1987; 13(4):695-723.
- [show abstract] [hide abstract]
ABSTRACT: Brain-derived neurotrophic factor (BDNF) promotes the function and survival of the major neuronal types affected in Alzheimer disease, such as hippocampal, cortical and basal forebrain cholinergic neurons. We and others have demonstrated a reduction in BDNF mRNA expression in Alzheimer's disease hippocampus and cortex, which may help to explain the selective vulnerability of these neurons. Several studies have also shown decreased BDNF protein in Alzheimer's disease. BDNF protein is synthesized as a precursor, proBDNF, which is cleaved to the mature 14-kDa form. We demonstrate here that BDNF exists as a mixture of proBDNF and mature BDNF in all regions tested of human brain. Using Western blotting, we observe a 40% reduction in proBDNF levels in Alzheimer's disease parietal cortex compared to controls. Thus, decreased BDNF protein measured by ELISA and immunohistochemistry likely represents a mixture of the two BDNF forms, and previously reported decreases in BDNF protein may be due, at least in part, to a significant reduction in proBDNF levels. Although the biological activity of proBDNF is unknown, reduced proBDNF may have functional consequences for the selective neuronal degeneration in Alzheimer's disease brain.Molecular Brain Research 04/2003; 111(1-2):148-54. · 2.00 Impact Factor