Endocrine Abstracts

Objectives: Food intake is centrally regulated in hypothalamic nuclei where many G-protein-coupled receptors (GPCRs) are expressed which are known to be involved in weight regulation. Peripheral hormonal signals activate their corresponding receptors in the arcuate nucleus. Orexigenic signals activate POMC expression in one subset of neurons and inhibit AgRP and NPY expression in a second subset. Cleavage products of POMC, α- and β-MSH then stimulate melanocortin-4-receptors (MC4R) in the paraventricular nucleus of the hypothalamus to inhibit food intake or stimulate the melanocortin 3 receptor (MC3R) in the arcuate nucleus to activate a feedback loop. Other neuropeptides or neurotransmitters are involved in hypothalamic regulation of body weight, which also act through G-protein-coupled-receptors co-expressed with melanocortin receptors (MCR) in hypothalamic nuclei. The concept of homo and hetero-oligomerization of GPCRs today is well accepted. Recently we could show homo-oligomerization of MC4R. In a systematic approach we investigated the interaction of GPCRs that are expressed on the same neurons.

Methods: We used two different methods to investigate GPCR oligomerization: a sandwich-ELISA approach with differentially N- and C-terminal tagged receptors in COS-7 cells and the FRET-acceptor-photobleaching-technique which allows monitoring of GPCR interaction in living HEK-293 cells. Furthermore we investigated receptor co-localization on the cell surface by laser scanning microscopy.

Results: Here we report data on interaction of the MC3R and ghrelin receptor (GHSR) that are coexpressed on arcuate NPY/AgRP neurons. The usage of both methods results in a strong signal of MC3R/GHSR oligomerization.

Conclusion: We could demonstrate for the first time that GPCR from different subfamilies, that are expressed on the same neuron and are involved in weight regulation form receptor oligomeres. These findings may provide a mechanistic basis of a functional interaction between melanocortin and ghrelin receptors and thereby widen our understanding of hypothalamic signalling pathways involved in weight regulation.