👤 Timur A Yorgan

Bone is a dynamic tissue that is constantly remodeled throughout adult life. Recently, it has been shown that bone turnover decreases shortly after food consumption. This process has been linked to the fermentation of non-digestible food ingredients such as inulin by gut microbes, which results in the production of the short-chain fatty acids (SCFAs) acetate, propionate and butyrate. SCFAs exert various metabolic functions, which in part can be explained by activation of G protein-coupled receptors (Gpr) 41 and 43. However, the potential relevance of a SCFA-Gpr41/43 signaling axis for bone metabolism has not been established. The aim of our study is to investigate the role of Gpr41/43 in bone metabolism and osteogenic differentiation of mesenchymal stem cells. For this purpose, we analyzed the skeletal phenotype of wild type controls (WT) and Gpr41/43 double knockout (Gpr41/43 dKO) mice fed either a chow or an inulin-enriched diet. In addition, we isolated bone marrow derived mesenchymal stem cells from WT and Gpr41/43 dKO mice and differentiated them into osteoblasts in the absence or presence of acetate. MicroCT scanning of femoral bones of Gpr41/43 dKO mice revealed a significant increase of trabecular bone volume and trabecular compared to WT controls. Treatment of WT bone marrow-derived osteoblasts with acetate resulted in decreased mineralization and substantial downregulation of bone formation markers such as Show less

Skeletal pathologies are frequently observed in lysosomal storage disorders, yet the relevance of specific lysosomal enzymes in bone remodeling cell types is poorly defined. Two lysosomal enzymes, ie, cathepsin K (Ctsk) and Acp5 (also known as tartrate-resistant acid phosphatase), have long been known as molecular marker proteins of differentiated osteoclasts. However, whereas the cysteine protease Ctsk is directly involved in the degradation of bone matrix proteins, the molecular function of Acp5 in osteoclasts is still unknown. Here we show that Acp5, in concert with Acp2 (lysosomal acid phosphatase), is required for dephosphorylation of the lysosomal mannose 6-phosphate targeting signal to promote the activity of specific lysosomal enzymes. Using an unbiased approach we identified the glycosaminoglycan-degrading enzyme arylsulfatase B (Arsb), mutated in mucopolysaccharidosis type VI (MPS-VI), as an osteoclast marker, whose activity depends on dephosphorylation by Acp2 and Acp5. Similar to Acp2/Acp5 Show less