Regulated Expression of pH Sensing G Protein-Coupled Receptor-68 Identified through Chemical Biology Defines a New Drug Target for Ischemic Heart Disease

• Published in: ACS chemical biology Vol. 7; no. 6; pp. 1077 - 1083
• Main Authors: Russell, Jamie L, Goetsch, Sean C, Aguilar, Hector R, Coe, Helen, Luo, Xiang, Liu, Ning, van Rooij, Eva, Frantz, Doug E, Schneider, Jay W
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.06.2012
• Subjects: Animals; Calcium - metabolism; Cell Line; Cells, Cultured; Isoxazoles - chemistry; Isoxazoles - pharmacology; Mice; Myocardial Infarction - drug therapy; Myocardial Infarction - genetics; Myocardial Infarction - metabolism; Myocardial Infarction - pathology; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - metabolism; Myocytes, Cardiac - pathology; Pericardium - cytology; Pericardium - drug effects; Pericardium - metabolism; Pericardium - pathology; Receptors, G-Protein-Coupled - genetics; Receptors, Notch - metabolism; Transcriptional Activation - drug effects
• ISSN: 1554-8929; 1554-8937
• DOI: 10.1021/cb300001m

Chemical biology promises discovery of new and unexpected mechanistic pathways, protein functions and disease targets. Here, we probed the mechanism-of-action and protein targets of 3,5-disubstituted isoxazoles (Isx), cardiomyogenic small molecules that target Notch-activated epicardium-derived cells (NECs) in vivo and promote functional recovery after myocardial infarction (MI). Mechanistic studies in NECs led to an Isx-activated Gq protein-coupled receptor (GqPCR) hypothesis tested in a cell-based functional target screen for GPCRs regulated by Isx. This screen identified one agonist hit, the extracellular proton/pH-sensing GPCR GPR68, confirmed through genetic gain- and loss-of-function. Overlooked until now, GPR68 expression and localization were highly regulated in early post-natal and adult post-infarct mouse heart, where GPR68-expressing cells accumulated subepicardially. Remarkably, GPR68-expressing cardiomyocytes established a proton-sensing cellular “buffer zone” surrounding the MI. Isx pharmacologically regulated gene expression (mRNAs and miRs) in this GPR68-enriched border zone, driving cardiomyogenic and pro-survival transcriptional programs in vivo. In conclusion, we tracked a (micromolar) bioactive small molecule’s mechanism-of-action to a candidate target protein, GPR68, and validated this target as a previously unrecognized regulator of myocardial cellular responses to tissue acidosis, setting the stage for future (nanomolar) target-based drug lead discovery.