(P19-055-25) SCFA-GPR43 Axis Mediates Gut Microbiota Promotion of Juvenile Bone Growth

Objectives: Emerging evidence suggests an important role of gut microbiome in bone homeostasis. However, the mechanism underlying its impact on juvenile skeletal growth is not well understood. G protein coupled 43 (GPR43), primarily activated short-chain fatty acids (SCFA) produced through microbial fermentation of dietary fibers, plays a crucial role in mediating host-microbiome interaction. In this study, we test the hypothesis that gut microbiome promotes bone growth in juvenile mice through the SCFA-GPR43 axis.

Methods: Wild-type (WT) and Gpr43^-/- juvenile mice (3.5-week-old) or young adult (5.5-week-old) mice were treated with vancomycin in drinking water for 2 weeks. In another cohort, WT juvenile mice were first treated with 2-week vancomycin in drinking water, followed by 3-week supplementation of SCFA in the vancomycin containing water. Fecal microbiome sequencing, LC-MS of fecal SCFA, femur μCT, bone marrow qPCR, histology of growth plate thickness and cell proliferation were analyzed.

Results: Vancomycin treatment significantly decreased fecal microbial abundance, diversities and SCFA production in both WT and Gpr43^-/- mice. No fundamental difference in the fecal microbiome was found between WT and Gpr43^-/- mice. Microbiota depletion by vancomycin significantly reduced femur longitudinal growth in WT juvenile mice. In contrast, skeletal growth in young adult WT mice was not sensitive to vancomycin treatment. Gut microbiota effects are likely mediated by SCFA, as 3 weeks of propionate supplementation to vancomycin treated mice stimulated bone growth and increased the expression of bone marrow osteoblastogenesis gene Runx2 and Wnt10b. The negative effect of microbiota depletion by vancomycin on skeletal growth was abrogated in Gpr43^-/- mice. Growth plate thickness and chondrocyte proliferation assessed by expression of Ki67 was significantly reduced by vancomycin in WT juvenile mice but not in Gpr43^-/- mice.

Conclusions: In conclusion, juvenile age is a critical window during which gut microbiome has a significant impact on skeletal growth in mice. This effect appears to be mediated by SCFA and their receptor GPR43.

Funding Sources: This work was supported by grants from the Peabody Foundation, the BWH Department of Orthopaedic Surgery and the NIH T32.