Bone is a biomechanical tissue shaped by forces from muscles and gravitation. Simultaneous bone and muscle decay and dysfunction (osteosarcopenia or sarco-
osteoporosis) is seen in ageing, numerous clinical situations including after
stroke or
paralysis, in neuromuscular dystrophies,
glucocorticoid excess, or in association with
vitamin D,
growth hormone/
insulin like growth factor or sex
steroid deficiency, as well as in spaceflight. Physical exercise may be beneficial in these situations, but further work is still needed to translate acceptable and effective biomechanical interventions like vibration
therapy from animal models to humans. Novel antiresorptive and anabolic
therapies are emerging for
osteoporosis as well as drugs for
sarcopenia,
cancer cachexia or muscle wasting disorders, including
antibodies against
myostatin or
activin receptor type IIA and IIB (e.g.
bimagrumab). Ideally, increasing muscle mass would increase muscle strength and restore bone loss from disuse. However, the classical view that muscle is unidirectionally dominant over bone via mechanical loading is overly simplistic. Indeed, recent studies indicate a role for neuronal regulation of not only muscle but also bone metabolism, bone signaling pathways like
receptor activator of nuclear factor kappa-B ligand (RANKL) implicated in muscle biology,
myokines affecting bone and possible bone-to-muscle communication. Moreover, pharmacological strategies inducing isolated myocyte
hypertrophy may not translate into increased muscle power because tendons, connective tissue, neurons and energy metabolism need to adapt as well. We aim here to critically review key musculoskeletal molecular pathways involved in mechanoregulation and their effect on the bone-muscle unit as a whole, as well as preclinical and emerging clinical evidence regarding the effects of
sarcopenia therapies on
osteoporosis and vice versa.