By a systematic approach we investigated the interaction of a selective number of GPCRs that are expressed in the arcuate nucleus and known to play an essential role in hypothalamic weight regulation. Based on the results of a sandwich ELISA and fluorescence resonance energy transfer (FRET) approach we report the interaction of the melanocortin three receptor (MC3R) and the growth hormone secretagogue receptor (GHSR) which are coexpressed on arcuate NPY/AgRP neurons. Furthermore, we demonstrated a co-localization of the heterologously expressed receptors on the cell surface of living cells by confocal laser scanning microscopy. Heterodimerization of unrelated receptors is well acepted today and examples implicate profound functional consequences. It is known that MC3R couple to the Gαs whereas GHSR couple to the Gαq signaling pathway. However, here we observed that co-expression of MC3R and GHSR profoundly increase cAMP-accumulation after melanocortin challenge, that is higher compared to MC3R activation alone. In-depth characterization of the new signalling properties of the MC3R/GHSR heterodimer revealed the activation of Gαi in the presents of both endogene agonists.
In summary, our results indicate a cross talk between the signaling pathways of the two hypothalamic receptors and adds to the understanding of the complexity of weight regulation. Maybe these findings provide an explanation for snacking between meals and the dicision to eat a second slice of the cake because cAMP rising in the NPY/AgRP neurons supported the expression of the neuropeptide Y.