Human GPR17 missense variants identified in metabolic disease patients have distinct downstream signaling profiles

Jason M Conley,Hongmao Sun,Kristin L Ayers,Hu Zhu,Rong Chen,Min Shen,Matthew D Hall,Hongxia Ren

doi:10.1016/j.jbc.2021.100881

Abstract

GPR17 is a G-protein-coupled receptor (GPCR) implicated in the regulation of glucose metabolism and energy homeostasis. Such evidence is primarily drawn from mouse knockout studies and suggests GPR17 as a potential novel therapeutic target for the treatment of metabolic diseases. However, links between human GPR17 genetic variants, downstream cellular signaling, and metabolic diseases have yet to be reported. Here, we analyzed GPR17 coding sequences from control and disease cohorts consisting of individuals with adverse clinical metabolic deficits including severe insulin resistance, hypercholesterolemia, and obesity. We identified 18 nonsynonymous GPR17 variants, including eight variants that were exclusive to the disease cohort. We characterized the protein expression levels, membrane localization, and downstream signaling profiles of nine GPR17 variants (F43L, V96M, V103M, D105N, A131T, G136S, R248Q, R301H, and G354V). These nine GPR17 variants had similar protein expression and subcellular localization as wild-type GPR17; however, they showed diverse downstream signaling profiles. GPR17-G136S lost the capacity for agonist-mediated cAMP, Ca2+, and β-arrestin signaling. GPR17-V96M retained cAMP inhibition similar to GPR17-WT, but showed impaired Ca2+ and β-arrestin signaling. GPR17-D105N displayed impaired cAMP and Ca2+ signaling, but unaffected agonist-stimulated β-arrestin recruitment. The identification and functional profiling of naturally occurring human GPR17 variants from individuals with metabolic diseases revealed receptor variants with diverse signaling profiles, including differential signaling perturbations that resulted in GPCR signaling bias. Our findings provide a framework for structure–function relationship studies of GPR17 signaling and metabolic disease.

Highlights

Metabolic diseases including obesity, type 2 diabetes, and cardiovascular diseases are worldwide health challenges due to the increasing prevalence and negative effects on quality of life, premature mortality, and increased healthcare burden [1, 2]
The control cohorts consisted of 2432 individuals from the Avon Longitudinal Study of Parents and Children (ALSPAC; 740 samples) and The Department of Twin Research and Genetic Epidemiology Twin Registry at King’s College London (TWINS; 1692 samples)
The patients with obesity were from the Severe Childhood Onset Obesity Project (OB_SCOOP; 961 samples) and obese individuals from the Generation Scotland study (OB_GS; 411 samples)

Summary

Introduction

Type 2 diabetes, and cardiovascular diseases are worldwide health challenges due to the increasing prevalence and negative effects on quality of life, premature mortality, and increased healthcare burden [1, 2]. We sought to experimentally characterize the expression, localization, and functional signaling consequences of the naturally occurring human GPR17 genetic variants observed in the metabolic disease cohorts. No significant differences were observed in the basal or forskolin-stimulated cAMP levels in cells expressing hGPR17L variants as compared with hGPR17L-WT, suggesting similar levels of constitutive cAMP regulation (Fig. S3).

Results

Conclusion