Investigation of GPCR activation by healthy and insulin-resistant adipocytes

Abstract

In obesity, chronic caloric excess results in maladaptive secretion of adipokine hormones from over-expanded adipose tissues. These secretions are critical in the development of insulin-resistance and type II diabetes. Many adipokines are endogenous ligands to G protein-coupled receptors (GPCR). Thus, it is possible that these disease-modulating hormones are connected to GPCRs with currently unidentified endogenous ligands, orphan GPCRs. The aim of this study was to identify if orphan GPCRs are adipokine sensing receptors and can detect the difference between healthy and insulin-resistant adipocytes. This was achieved through the screening of healthy and insulin-resistant adipocyte-conditioned media against 71 orphan GPCRs. Receptor activation was quantified using the PRESTO-Tango β-arrestin recruitment assay. Adipocyte-conditioned media significantly altered the activation of 19 receptor candidates. Further, insulin-resistant adipocyte conditioned media significantly altered the activation of GPR17, GPR45 and GPR54 relative to healthy adipocyte-conditioned media. This led to a recommendation of 12 receptor candidates for further investigation. The activation of these twelve receptors was summarized into three categories: 1) receptors significantly activated by both adipocyte-conditioned media 2) receptors with significantly decreased activation by both adipocyte-conditioned media and 3) receptors that were differentially activated between the two adipocyte-conditioned media. These findings demonstrate the diverse connections between adipocytes and the receptor candidates. Further investigation into the 12 receptor candidates will lead to greater knowledge about the function of these elusive receptors. This will aid in identifying endogenous ligands for these receptor candidates, and in the application of these findings to the development of therapeutic treatments for type II diabetes.