The bile acid receptor TGR5 is a modulator of bone marrow adipose tissue and the hematopoietic niche

The gut is an emerging regulator of bone marrow (BM) hematopoiesis, with several signaling molecules involved in this communication. Among them, bile acids (BAs) act as a relay between the microbiota and the rest of the body through the activation of specific receptors, including Takeda G protein-coupled receptor 5 (TGR5). TGR5 has potent regulatory effects in immune cells, but its role in the BM as a primary immune organ remains unknown. Here, we demonstrate that TGR5 is expressed in hematopoietic progenitors and BM stromal progenitors. TGR5 deficiency did not affect steady-state hematopoiesis but led to impaired short-term progenitor reconstitution and reduced regulated bone marrow adipose tissue (BMAT) in young male mice, but not in female mice. The reduction in BMAT was accompanied by an enrichment in BM adipocyte progenitors and was associated with enhanced hematopoietic recovery upon BM transplantation into Tgr5 ^−/− recipients. Moreover, its reduction was associated with lower myeloid-to-lymphoid progenitor ratios in obese and in aged Tgr5 ^−/− male mice, resembling more those of lean or young controls. Our results indicate that TGR5 is essential for maintaining a balanced BM microenvironment in a sex-dependent manner and open the possibility of modulating stromal hematopoietic support by acting on TGR5 signaling.