ECE2008 Oral Communications Diabetes and obesity (9 abstracts)
Food intake is centrally regulated in hypothalamic nuclei. Peripheral hormonal signals activate their corresponding receptors in the arcuate nucleus (arc) and modulate the expression of pro-opiomelanocortin (POMC) and neuropetide Y (NPY)/agouti-related-protein (AgRP). Cleavage products of POMC stimulate melanocortin-4-receptors (MC4R) in the paraventricular nucleus (PVN) to inhibit food intake or stimulate MC3Rs in the arc to activate a feedback loop. Further more other neuropeptides or neurotransmitters are involved in hypothalamic regulation of body weight, which also act through GPCR coexpressed with melanocortin receptors in hypothalamic nuclei. The concept of homodimerization of GPCRs today is well Recently we could show homodimerization of MC4R.
In a systematic approach, we investigated the interaction of GPCRs that are expressed on the same neurons. We report the interaction of the MC3R and GHSR that are coexpressed on arcuate NPY/AgRP neurons. Mutations in both receptors were shown to influence body weight. We used two different methods to investigate GPCR oligodimerization: a sandwich-ELISA approach with differentially N- and C-terminally tagged receptors and the FRET acceptor photobleaching technique which allows monitoring of GPCR interaction in living cells. Both methods displayed a strong signal of MC3R/GHSR oligomerization. We could demonstrate a co-localization of the heterologously expressed receptors on the cell surface of living cells by confocal laser scanning microscopy. Functional analysis revealed that co-transfection of GHSR and MC3R increases the maximal secondary messenger answer after melanocortin stimulation in COS-7 cells compared to MC3R transfected alone. Additionally co-internalization of the dimer could be shown.
In conclusion, we demonstrate that GPCR from different subfamilies that are expressed on the same neuron and are involved in weight regulation are able to form receptor oligomers. These findings may provide a mechanistic basis of a functional interaction between melanocortin and ghrelin receptors and thereby widen our understanding of hypothalamic signaling pathways involved in weight regulation.