Rapid Signaling of Estrogen in Hypothalamic Neurons Involves a Novel G-Protein-Coupled Estrogen Receptor that Activates Protein Kinase C

Abstract

Classically, 17beta-estradiol (E2) is thought to control homeostatic functions such as reproduction, stress responses, feeding, sleep cycles, temperature regulation, and motivated behaviors through transcriptional events. Although it is increasingly evident that E2 can also rapidly activate kinase pathways to have multiple downstream actions in CNS neurons, the receptor(s) and the signal transduction pathways involved have not been identified. We discovered that E2 can alter mu-opioid and GABA neurotransmission rapidly through nontranscriptional events in hypothalamic GABA, proopiomelanocortin (POMC), and dopamine neurons. Therefore, we examined the effects of E2 in these neurons using whole-cell recording techniques in ovariectomized female guinea pigs. E2 reduced rapidly the potency of the GABAB receptor agonist baclofen to activate G-protein-coupled, inwardly rectifying K+ channels in hypothalamic neurons. These effects were mimicked by the membrane impermeant E2-BSA and selective estrogen receptor modulators, including a new diphenylacrylamide compound, STX, that does not bind to intracellular estrogen receptors alpha or beta, suggesting that E2 acts through a unique membrane receptor. We characterized the coupling of this estrogen receptor to a Galpha(q)-mediated activation of phospholipase C, leading to the upregulation of protein kinase Cdelta and protein kinase A activity in these neurons. Moreover, using single-cell reverse transcription-PCR, we identified the critical transcripts, PKCdelta and its downstream target adenylyl cyclase VII, for rapid, novel signaling of E2 in GABA, POMC, and dopamine neurons. Therefore, this unique Gq-coupled estrogen receptor may be involved in rapid signaling in hypothalamic neurons that are critical for normal homeostatic functions.

Modulation of hypothalamic neuronal activity through a novel G-protein-coupled estrogen membrane receptor

“…Interestingly, ER-X also has a distinct pharmacology in that 17α-estradiol is as equipotent as E 2 in activating the MAP kinase pathway [15,30]. However, we did not see any effects of 17α-estradiol on the GABA B response [17] or the μ-opioid response [21]. Similarly, Gu and Moss found that 17α-estradiol did not mimic the actions of E 2 in the hippocampus to potentiate the glutamate (kainate)-mediated currents in CA1 pyramidal neurons [35].…”

“…Notably, AC VII has a potential binding site for PKCδ that is not present in the sequences of the other adenylyl cyclases, which would allow PKCδ to directly phosphorylate AC VII [43]. In our study, we have shown that hypothalamic POMC neurons express AC VII transcripts [17]. Moreover, internal perfusion of BIS completely blocked the inhibition of the baclofen response by E 2 but did not attenuate the inhibition of the baclofen response by forskolin applied via bath perfusion, suggesting that PKC activation is upstream of PKA activation.…”

“…In recent experiments, we used the whole-cell recording method to measure the rapid effects of E 2 on the activation of the GIRK conductance by the GABA B receptor agonist baclofen (Figure 1a) [17]. The pharmacokinetics of this rapid estrogen response further supported the involvement of a novel transmembrane estrogen receptor.…”

“…The "rapid" and "nongenomic" events are also believed to be mediated via ERα and ERβ [14,15]; however, growing evidence suggests the involvement of plasma membrane receptors, especially G protein-coupled receptors (GPCRs). Potential candidates for novel membrane ERs include ER-X and the G-proteincoupled receptors, Gαq-mER and GPR30 [16][17][18][19][20].…”

“…In hypothalamic arcuate neurons including POMC neurons, we have identified a putative membrane-associated estrogen receptor (mER) that is Gαq-coupled to a phospholipase Cprotein kinase C-protein kinase A (PLC-PKC-PKA) pathway [17,21]. The activation of this pathway by E 2 can rapidly dis-inhibit female arcuate neurons through desensitizing μ-opioid and GABA B receptors.…”