Receptor Subtypes and Signal Transduction Mechanisms Contributing to the Estrogenic Attenuation of Cannabinoid-Induced Changes in Energy Homeostasis

Abstract

We examined the receptor subtypes and signal transduction mechanisms contributing to the estrogenic modulation of cannabinoid-induced changes in energy balance. Food intake and, in some cases, O₂ consumption, CO₂ production and the respiratory exchange ratio were evaluated in ovariectomized female guinea pigs treated s.c. with the cannabinoid receptor agonist WIN 55,212-2 or its cremephor/ethanol/0.9% saline vehicle, and either with estradiol benzoate (EB), the estrogen receptor (ER) α agonist PPT, the ERβ agonist DPN, the G_q-coupled membrane ER agonist STX, the GPR30 agonist G-1 or their respective vehicles. Patch-clamp recordings were performed in hypothalamic slices. EB, STX, PPT and G-1 decreased daily food intake. Of these, EB, STX and PPT blocked the WIN 55,212-2-induced increase in food intake within 1-4 h. The estrogenic diminution of cannabinoid-induced hyperphagia correlated with a rapid (within 15 min) attenuation of cannabinoid-mediated decreases in glutamatergic synaptic input onto arcuate neurons, which was completely blocked by inhibition of protein kinase C (PKC) and attenuated by inhibition of protein kinase A (PKA). STX, but not PPT, mimicked this rapid estrogenic effect. However, PPT abolished the cannabinoid-induced inhibition of glutamatergic neurotransmission in cells from animals treated 24 h prior. The estrogenic antagonism of this presynaptic inhibition was observed in anorexigenic proopiomelanocortin neurons. These data reveal that estrogens negatively modulate cannabinoid-induced changes in energy balance via G_q-coupled membrane ER- and ERα-mediated mechanisms involving activation of PKC and PKA. As such, they further our understanding of the pathways through which estrogens act to temper cannabinoid sensitivity in regulating energy homeostasis in females.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein–Coupled Estrogen Receptor and Its Pharmacologic Modulators

“…In Hec50 endometrial cancer cells (ER-negative/GPER-positive) several compounds initiated GPER-mediated PI3K and ERK1/2 activation, including E2, G-1, 4OHT, RAL, ICI, as well as PPT (with submaximal effects for PPT observed at 10 nM). This report provided the first evidence that PPT also functions as a GPER agonist at higher concentrations, demonstrating that although PPT remains selective for ERa over both ERb and GPER, care must be taken in the interpretation of results employing receptor-selective ligands, particularly with respect to the concentrations and doses of these compounds used in experimental systems (Washburn et al, 2013). Notably, the ERaselective antagonist (methyl-piperidino-pyrazole) (Sun et al, 2002;Harrington et al, 2003), which has not been as widely used as PPT, has not been evaluated for selectivity toward GPER.…”

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

“…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 previously shown that the EC 50 for E 2 in other ARC neurons is 7.5 nM, and the K i for estrogen receptor antagonist ICI 182,780 is 0.3 nM (21). We opted to use a 100 nM concentration of E 2 to promote more rapid pharmacokinetics in the slice (19,27,31).…”

“…Selective stimulation of NPY/AgRP neurons via optogenetics evokes intense feeding (3), and ablation of these neurons in adults causes starvation, evidently due to loss of inhibitory signaling to the brain stem (24,52,53). Similar and other approaches have revealed that POMC cells control the exact opposite actions in energy balance (3,13,32,39,50,54).These two populations of neurons are thought to regulate feeding through sensing blood-borne metabolic factors and then synaptically releasing their expressed peptides or derivatives into various brain regions such as the paraventricular nucleus and lateral hypothalamus (12).Estrogens, such as 17␤-estradiol (E 2 ), regulate energy balance in females and exert potent anorectic effects, at least partly through activating POMC neurons (34). E 2 increases the expression of POMC and its derived anorectic peptides (30,44), and deleting the estrogen receptor (ER)␣ from POMC cells results in hyperphagia and weight gain in females (54).…”