Regulated expression of pH sensing G protein-coupled receptor-68 identified through chemical biology defines a new drug target for ischemic heart disease

摘要

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 (µM) 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 (nM) target-based drug lead discovery.