THE BILE ACID RECEPTOR TGR5 MODULATES HIPPOCAMPAL NEURAL STEM CELL STATE AND AGEING

Ageing locks hippocampal neural stem cells (NSCs) into deeper quiescence and inflammation-driven senescence, which are also associated with impaired cognition. The bile-acid receptor TGR5, a member class I G-protein coupled receptors (GPCRs), is expressed in cultured hippocampal NSCs and in SOX2-positive cells of the adult sub granular zone, yet its role in NSC homeostasis is unknown. In this study we show that TGR5 selective agonist, TC-G 1005, expanded the NSC pool without forcing neuronal differentiation. Primary NSCs treatment with TC-G 1005 increased BrdU incorporation and PCNA in a concentration-dependent manner, and both responses were lost after TGR5 knockdown. TGR5 agonism in differentiating cultures increased nestin, left doublecortin (DCX) unchanged and suppressed MAP2 expression, preserving stemness rather than neuronal commitment. The agonist also released BMP4-imposed quiescence, lowering FOXO3a and restoring phospho-EGFR and ASCL1, and reopened autophagic flux, with less p62 and LC3-II, fewer LAMP2 puncta and more Beclin-1. Furthermore, activation of TGR5 suppressed IL-6 induced p53 and p16 expression, restored proliferation and contracted the inflammatory transcriptome by more than 90%, including Cdkn2a, Cdkn2b and Cdk6. In 18-month-old mice, brain-penetrant TC-G 1005 (5 mg/kg, subcutaneously, twice daily for 28 days) expanded SOX2-positive and proliferating NSCs, reduced p16, recovered ASCL1 and improved spatial memory, without changing locomotion or generating DCX-positive neurons. Dentate gyrus-restricted TGR5 knockdown abolished these cellular effects and the rescue of spatial and social discrimination. Hippocampal proteomic analysis revealed that TC-G 1005 treated aged mice occupied an intermediate, partially rejuvenated position between young and aged proteomes, with 86 proteins shared between ageing- and treatment-responsive sets, and mitochondrial and complement C1q modules shifted toward youthful levels. TGR5 activation therefore relieves both quiescence and senescence in the aged neurogenic niche without driving neuronal differentiation. Collectively, these results suggest that TGR5 could be targeted to preserve cognition in ageing by rejuvenating the hippocampal stem-cell niche.