The intestinal microbiome and skeletal fitness: Connecting bugs and bones

- Changing the gut microbiome in mice alters bone mass.
- The gut microbiome influences multiple pathways known to regulate bone cells.
- Gut microbes may regulate bone cells via T cells, myeloid cells and cytokines.
- Other mechanisms include steroid hormones and microbial metabolites.
- Manipulation of the microbiome could be exploited to treat bone diseases.

Recent advances have dramatically increased our understanding of how organ systems interact. This has been especially true for immunology and bone biology, where the term “osteoimmunology” was coined to capture this relationship. The importance of the microbiome to the immune system has also emerged as a driver of health and disease. It makes sense therefore to ask the question: how does the intestinal microbiome influence bone biology and does dysbiosis promote bone disease? Surprisingly, few studies have analyzed this connection. A broader interpretation of this question reveals many mechanisms whereby the microbiome may affect bone cells. These include effects of the microbiome on immune cells, including myeloid progenitors and Th17 cells, as well as steroid hormones, fatty acids, serotonin and vitamin D. As mechanistic interactions of the microbiome and skeletal system are revealed within and without the immune system, novel strategies to optimize skeletal fitness may emerge.