Membrane estrogen receptors stimulate intracellular calcium release and progesterone synthesis in hypothalamic astrocytes.
In hypothalamic astrocytes obtained from adult female rats, estradiol rapidly increased free cytoplasmic calcium concentrations ([Ca(2+)](i)) that facilitate progesterone synthesis. The present study demonstrated that estradiol (1 nm) significantly and maximally stimulated progesterone synthesis within 5 min, supporting a rapid, nongenomic mechanism. The group I metabotropic glutamate receptor (mGluR1a) antagonist LY 367385 [(S)-(+)-a-amino-4-carboxy-2-methylbenzeneacetic acid] attenuated both the estradiol-induced [Ca(2+)](i) release and progesterone synthesis. To investigate membrane-associated estrogen receptors (mERs), agonists for ERα, ERβ, STX-activated protein, and GPR30 were compared. The selective ERα agonist propylpyrazole triole (PPT) and STX most closely mimicked the estradiol-induced [Ca(2+)](i) responses, where PPT was more potent but less efficacious than STX. Only high doses (100 nm) of selective ERβ agonist diarylpropionitrile (DPN) and GPR30 agonist G-1 induced estradiol-like [Ca(2+)](i) responses. With the exception of DPN (even at 100 nm), all agonists stimulated progesterone synthesis. The PPT- and STX-induced [Ca(2+)](i) release and progesterone synthesis were blocked by LY 367385. While the G-1-stimulated [Ca(2+)](i) release was blocked by LY 367385, progesterone synthesis was not. Since GPR30 was detected intracellularly but not in the membrane, we interpreted these results to suggest that G-1 could activate mGluR1a on the membrane and GPR30 on the smooth endoplasmic reticulum to release intracellular calcium. Although STX and G-1 maximally stimulated [Ca(2+)](i) release in astrocytes from estrogen receptor-α knock-out (ERKO) mice, estradiol in vivo did not stimulate progesterone synthesis in the ERKO mice. Together, these results indicate that mERα is mainly responsible for the rapid, membrane-initiated estradiol-signaling that leads to progesterone synthesis in hypothalamic astrocytes.
Kuo
John
J
Department of Neurobiology, Laboratory of Neuroendocrinology of the Brain Research Institute, Department of Obstetrics and Gynecology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
Hamid
Naheed
N
Bondar
Galyna
G
Prossnitz
Eric R
ER
Micevych
Paul
P
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D004958:Estradiol / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000819:agonists / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D005260:Female; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011374:Progesterone / Q000096:biosynthesis*; D051381:Rats; D020318:Rats, Long-Evans
D047628:Estrogen Receptor alpha; D011374:Progesterone; D004958:Estradiol; D002118:Calcium