Emerging roles of osteocytes in the regulation of bone and skeletal muscle mass.

Contrary to the popular perception that bone is merely a structural organ, decades of research has established its functional importance in whole-body metabolism. Osteocytes, which comprise >80% of all bone cells, were also initially thought to be terminally differentiated dormant cells lacking metabolic functions. New research, however, is increasingly providing evidence that osteocytes not only play a role in the structural integrity of bone but also have secretory functions that regulate other bone cells and other organs, including skeletal muscle, the structural-mechanical neighbor of the bone, via paracrine and endocrine pathways. However, interpretations of the publicly available preclinical and clinical data pertaining to the factors secreted by osteocytes and their functions in the musculoskeletal system largely fail to reach a consensus. This review aimed to objectively collate all information available in the public domain for efficient access by researchers in the field. We strongly believe that this review will assist researchers attempting the unbiased design of therapeutic strategies for musculoskeletal disorders.