👤 N Wettschureck

Understudied orphan GPCRs lack identified natural ligands, yet understanding their function is critical for therapeutic development. GPRC5B is a brain-enriched, retinoic acid (RA)-induced orphan GPCR. While RA is used to treat severe acne, chronic exposure is associated with depression, likely due to its inhibition of adult hippocampal neurogenesis. Here, we tested whether GPRC5B plays a role in the molecular and cellular mechanisms underlying RA-induced depressive-like behaviors in mice by suppressing adult hippocampal neurogenesis. We found that Gprc5b knockout (KO) mice were resilient to RA-induced behavioral effects and that RA increased GPRC5B expression in the hippocampal neurogenic subgranular zone. This correlated with RA-mediated inhibition of adult hippocampal neurogenesis, an effect absent in Gprc5b KO mice, which also exhibited a larger pool of proliferative neuronal stem cells. Collectively, these findings suggest that GPRC5B mediates RA-induced anti-neurogenic effects and depressive-like behaviors. Show less

In vitro studies have implicated orphan receptor GPRC5B in β cell survival, proliferation, and insulin secretion, but its relevance for glucose homeostasis in vivo is largely unknown. Using tamoxifen-inducible, β cell-specific GPRC5B-KO mice (Ins-G5b-KOs), we show here that loss of GPRC5B does not affect β cell function in the lean state but results in strongly reduced insulin secretion and disturbed glucose tolerance in mice subjected to high-fat diet for 16 weeks. Flow cytometry and single-cell expression analyses in islets from obese mice show a reduced β cell abundance and a less mature β cell phenotype in Ins-G5b-KOs. Expression of β cell-specific transcription factor MafA is reduced both on the RNA and protein level, as are transcripts of MafA target genes. Mechanistically, we show that phosphorylation of cAMP response element-binding protein (CREB), a major regulator of MafA expression, is reduced in islets of obese Ins-G5b-KOs, and we show that this phenotype precedes the downregulation of MafA and MafA target genes. Taken together, GPRC5B helps to maintain mature β cell function in obesity through cAMP/CREB-dependent regulation of MafA expression. Show less

Macrophages express numerous G protein-coupled receptors (GPCRs) that regulate adhesion, migration, and activation, but the function of orphan receptor GPRC5B in macrophages is unknown. Both resident peritoneal and bone marrow-derived macrophages from myeloid-specific GPRC5B-deficient mice show increased migration and phagocytosis, resulting in improved bacterial clearance in a peritonitis model. In other models such as myocardial infarction, increased myeloid cell recruitment has adverse effects. Mechanistically, we found that GPRC5B physically interacts with GPCRs of the prostanoid receptor family, resulting in enhanced signaling through the prostaglandin E receptor 2 (EP2). In GPRC5B-deficient macrophages, EP2-mediated anti-inflammatory effects are diminished, resulting in hyperactivity. Using in silico modelling and docking, we identify residues potentially mediating GPRC5B/EP2 dimerization and show that their mutation results in loss of GPRC5B-mediated facilitation of EP2 signaling. Finally, we demonstrate that decoy peptides mimicking the interacting sequence are able to reduce GPRC5B-mediated facilitation of EP2-induced cAMP signaling in macrophages. Show less

G protein-coupled receptors are important regulators of contractility and differentiation in vascular smooth muscle cells (SMCs), but the specific function of SMC-expressed orphan G protein-coupled receptor class C group 5 member B (GPRC5B) is unclear. We studied the role of GPRC5B in the regulation of contractility and dedifferentiation in human and murine SMCs in vitro and in iSM- Mesenteric arteries from SMC-specific Taken together, our data show that GPRC5B regulates vascular SMC tone and differentiation by negatively regulating IP signaling. Show less

G-protein-coupled receptor (GPCR) expression is extensively studied in bulk cDNA, but heterogeneity and functional patterning of GPCR expression in individual vascular cells is poorly understood. Here, we perform a microfluidic-based single-cell GPCR expression analysis in primary smooth muscle cells (SMC) and endothelial cells (EC). GPCR expression is highly heterogeneous in all cell types, which is confirmed in reporter mice, on the protein level and in human cells. Inflammatory activation in murine models of sepsis or atherosclerosis results in characteristic changes in the GPCR repertoire, and we identify functionally relevant subgroups of cells that are characterized by specific GPCR patterns. We further show that dedifferentiating SMC upregulate GPCRs such as Gpr39, Gprc5b, Gprc5c or Gpr124, and that selective targeting of Gprc5b modulates their differentiation state. Taken together, single-cell profiling identifies receptors expressed on pathologically relevant subpopulations and provides a basis for the development of new therapeutic strategies in vascular diseases. Show less