Novel directions in the study of osteoporosis: focus on gut microbiota as a potential therapeutic target.

Osteoporosis is a significant social health problem, not only in terms of pain and disability but also in terms of mortality rate. In recent years, there is an increasing interest in studying the relationship between gut dysmicrobiosis, immune system and bone health, therefore the term "osteomicrobiology" has been recently coined. This review aims to summarize the current knowledge about the link between gut dysbiosis and osteoporosis, in order to define a potential preventive and therapeutic strategy. Gut microbiota (GM) plays a major role in maintaining body homeostasis, since it is involved in several physiological processes; in recent years, the gut microbiota has shown to modulate not only local processes but also systemic responses including bone metabolism. Several potential mechanisms may explain how gut microorganisms could affect bone metabolism, i.e. influencing the host metabolism, immune system and hormone secretion. The relationship between gut dysbiosis, immunological dysfunction and bone loss could be explained by mainly focusing on T cells. Moreover, it should be noted that the relationship between GM and the endocrine system could also explicate how the microbiome influences bone status. In this context, Insulin-Like Growth Factor-1 (IGF-1), vitamin D, serotonin and leptin might play a central role. GM could have a significant impact on bone metabolism, therefore future clinical studies are necessary to develop a new multidisciplinary approach for osteoporosis treatment and prevention.