Coupling Hippocampal Neurogenesisto Brain pH throughProneurogenic Small Molecules That Regulate Proton Sensing G Protein-CoupledReceptors

摘要

Acidosis, a critical aspect of central nervous system (CNS) pathophysiology and a metabolic corollary of the hypoxic stem cell niche, could be an expedient trigger for hippocampal neurogenesis and brain repair. We recently tracked the function of our isoxazole stem cell-modulator small molecules (Isx) through a chemical biology-target discovery strategy to GPR68, a proton (pH) sensing G protein-coupled receptor with no known function in brain. Isx and GPR68 coregulated neuronal target genes such as Bex1 (brain-enriched X-linked protein-1) in hippocampal neural progenitors (HCN cells), which further amplified GPR68 signaling by producing metabolic acid in response to Isx. To evaluate this proneurogenic small molecule/proton signaling circuit in vivo, we explored GPR68 and BEX1 expression in brain and probed brain function with Isx. We localized proton-sensing GPR68 to radial processes of hippocampal type 1 neural stem cells (NSCs) and, conversely, localized BEX1 to neurons. At the transcriptome level, Isx demonstrated unrivaled proneurogenic activity in primary hippocampal NSC cultures. In vivo, Isx pharmacologicallytargeted type 1 NSCs, promoting neurogenesis in young mice, depletingthe progenitor pool without adversely affecting hippocampal learningand memory function. After traumatic brain injury, cerebral corticalastrocytes abundantly expressed GPR68, suggesting an additional rolefor proton-GPCR signaling in reactive astrogliosis. Thus, probinga novel proneurogenic synthetic small molecule’s mechanism-of-action,candidate target, and pharmacological activity, we identified a newGPR68 regulatory pathway for integrating neural stem and astroglialcell functions with brain pH.