Identification of the Ghrelin and Cannabinoid CB2 Receptor Heteromer Functionality and Marked Upregulation in Striatal Neurons from Offspring of Mice under a High-Fat Diet

Abstract

Cannabinoids have been reported as orexigenic, i.e., as promoting food intake that, among others, is controlled by the so-called “hunger” hormone, ghrelin. The aim of this paper was to look for functional and/or molecular interactions between ghrelin GHSR1a and cannabinoid CB2 receptors at the central nervous system (CNS) level. In a heterologous system we identified CB2-GHSR1a receptor complexes with a particular heteromer print consisting of impairment of CB2 receptor/Gi-mediated signaling. The blockade was due to allosteric interactions within the heteromeric complex as it was reverted by antagonists of the GHSR1a receptor. Cannabinoids acting on the CB2 receptor did not affect cytosolic increases of calcium ions induced by ghrelin acting on the GHSR1a receptor. In situ proximity ligation imaging assays confirmed the expression of CB2-GHSR1a receptor complexes in both heterologous cells and primary striatal neurons. We tested heteromer expression in neurons from offspring of high-fat-diet mouse mothers as they have more risk to be obese. Interestingly, there was a marked upregulation of those complexes in striatal neurons from siblings of pregnant female mice under a high-fat diet.

Ghrelin and Cannabinoid Functional Interactions Mediated by Ghrelin/CB1 Receptor Heteromers That Are Upregulated in the Striatum From Offspring of Mice Under a High-Fat Diet

“…In this scenario, we aimed at defining possible interactions between cannabinoid receptors and the receptor for the so-called “hunger” hormone, ghrelin. In a recent article, we have shown the interaction of the cannabinoid CB 2 receptor (CB 2 R) with the GHS-R1a receptor in a heterologous expression system and in physiological cell models (Lillo et al, 2021 ). Therefore, the first aim of the present study was to address the possible interaction between the ghrelin receptor and the CB 1 R and to characterize the functional consequences of such interaction.…”

“…As previously highlighted, endocannabinoid tone may be important in controlling the inputs received by the reward circuits and that impact on food intake, especially as it relates to the hedonic part of eating (Coccurello and Maccarrone, 2018 ). Whereas cannabinoids acting on the CB 1 receptor affected calcium mobilization mediated by GHS-R1a-G q coupling, this is not the case for the CB 2 R-GHS-R1aHet (Lillo et al, 2021 ). As further discussed below, caution must be taken when trying to make general conclusions as the allosteric-cross interactions will occur in neurons expressing CB 1 R and GHS-R1a receptors and also CB 1 R-GHS-R1aHets; i.e., not all neurons express the two receptors, and a given neuron may express the CB 1 R-GHS-R1aHet plus other CB 1 R-containing heteromers (see, in http://www.gpcr-hetnet.com/, GPCRs that interact with the CB 1 R; accessed on October 22, 2021).…”

“…Cannabinoids acting on the CB 2 receptor do not alter the cytosolic Ca 2+ increases triggered by ghrelin. However, ghrelin receptor activation led to a blockade of CB 2 receptor-mediated Gi-dependent signaling (Lillo et al, 2021 ). The aim of this article was to investigate the potential molecular and/or functional interactions between CB 1 and GHS-R1a receptors.…”

Advances in the Development of Nonpeptide Small Molecules Targeting Ghrelin Receptor

“… 10 , 11 Moreover, GHS-R1a can form homodimers and heterodimers with a variety of GPCRs, including GHS-R1b, an inactive splicing variant of GHS-R1a, serotonin 5-HT2c receptor, dopamine D1 and D2 receptors, somatostatin SST5 receptor, orexin OX1 receptor, melanocortin MC3 receptor, and cannabinoid CB2 receptor. 10 , 12 − 14 …”

“…Although a minority of circulating ghrelin undergoes octanoylation, only the octanoylated AG is able to activate the growth hormone secretagogue receptor, a G protein-coupled receptor (GPCR) known as GHS-R1a consisting of 366 amino acid residues . This receptor couples to a Gαq/11 protein, promoting Ca 2+ mobilization from intracellular stores, through activation of the phospholipase C. It also signals through other G protein isoforms, including Gαi/o and Gα13 as well as β-arrestin scaffold proteins. − Additional complexity in GHS-R1a signaling derives from the fact that this receptor shows one of the highest constitutive signaling activities in the GPCR family, evoking signals at around 50% of the maximal ghrelin response. , Moreover, GHS-R1a can form homodimers and heterodimers with a variety of GPCRs, including GHS-R1b, an inactive splicing variant of GHS-R1a, serotonin 5-HT2c receptor, dopamine D1 and D2 receptors, somatostatin SST5 receptor, orexin OX1 receptor, melanocortin MC3 receptor, and cannabinoid CB2 receptor. ,− …”