Genes Associated with Membrane-Initiated Signaling of Estrogen and Energy Homeostasis

Abstract

During the reproductive cycle, fluctuations in circulating estrogens affect multiple homeostatic systems controlled by hypothalamic neurons. Two of these neuronal populations are arcuate proopiomelanocortin and neuropeptide Y neurons, which control energy homeostasis and feeding. Estradiol modulates these neurons either through the classical estrogen receptors (ERs) to control gene transcription or through a G protein-coupled receptor (mER) activating multiple signaling pathways. To differentiate between these two divergent ER-mediated mechanisms and their effects on homeostasis, female guinea pigs were ovariectomized and treated systemically with vehicle, estradiol benzoate (EB) or STX, a selective mER agonist, for 4 wk, starting 7 d after ovariectomy. Individual body weights were measured after each injection day for 28 d, at which time the animals were euthanized, and the arcuate nucleus was microdissected. As predicted, the body weight gain was significantly lower for EB-treated females after d 5 and for STX-treated females after d 12 compared with vehicle-treated females. Total arcuate RNA was extracted from all groups, but only the vehicle and STX-treated samples were prepared for gene microarray analysis using a custom guinea pig gene microarray. In the arcuate nucleus, 241 identified genes were significantly regulated by STX, several of which were confirmed by quantitative real-time PCR and compared with EB-treated groups. The lower weight gain of EB-treated and STX-treated females suggests that estradiol controls energy homeostasis through both ERalpha and mER-mediated mechanisms. Genes regulated by STX indicate that not only does it control neuronal excitability but also alters gene transcription via signal transduction cascades initiated from mER activation.

The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in NPY/AgRP neurons: role in mediating the anorexigenic effects of 17β-estradiol

“…7). Although STX did not affect body weight over this short period of administration, our previous work showed that longer-term treatment significantly reduces post-ovariectomy weight gain in females (32,37). These findings are consistent with the in vitro effects of STX on NPY/AgRP and POMC neurons (21,31,32).…”

“…In previous studies, the Gq-mER ligand STX showed a clear anorectic effect in female guinea pigs (37,50). Since our in vitro experiments suggested that STX would also be anorectic in males, we wanted to compare food intake in both sexes.…”

“…Wortmannin (PI3K inhibitor, Sigma), LY-294002 (PI3K inhibitor; EMD Millipore, Billerica, MA), and TGX-221 [P13K p110␤ subunit inhibitor; 7-methyl-2-morpholino- Feeding experiments. We chose to use guinea pigs for the feeding experiments on the basis of our previous publications that the diphenylacrylamide compound STX decreases food intake and weight gain following ovariectomy in females (32,37,50) and the fact that STX is bioavailable (F ϭ 22%) and centrally active in the female guinea pig (35). For the feeding studies, a Comprehensive Lab Animal Monitoring Systems (CLAMS; Columbus Instruments, Columbus, OH) recorded daily food intake in adult gonadectomized male (n ϭ 10) and female guinea pigs (n ϭ 12) as previously described (35).…”

“…We have designed a Gq-mER-selective ligand, STX, that potently increases the membrane excitability in POMC cells through attenuating GABA B -GIRK coupling via a PLC-PKC-PKA signaling pathway (31) In addition, STX attenuates the presynaptic, CB1 receptor-mediated decrease in glutamate release, further enhancing the excitability of these neurons (50). STX predictably mimics the anorexigenic effects of E 2 to reduce food intake and weight gain following ovariectomy (32,37).…”

Genetic rescue of nonclassical ERα signaling normalizes energy balance in obese Erα-null mutant mice

“…Our observations suggest that any such effects may be species or paradigm specific, or, more likely, that they are mediated by signaling pathways activated via ERα-independent mechanisms. As an example, a putative membrane estrogen receptor -a Gq-coupled, membrane-initiated pathway -has been implicated in the anorectic effects of E 2 in hypoestrogenic female guinea pigs (36)(37)(38).…”