Mechanically induced Ca2+ oscillations in osteocytes release extracellular vesicles and enhance bone formation

• DOI: 10.1038/s41413-018-0007-x
• Publication Date: 2018-04-04T02:18:59Z
• Authors: Andrea E. Morrell; Genevieve N. Brown; Samuel T. Robinson; Rachel L. Sattler; Andrew D. Baik; Gehua Zhen; Xu Cao; Lynda F. Bonewald; Weiyang Jin; Lance C. Kam; X. Edward Guo
• Keywords: LAMP1; Osteocyte; Mechanotransduction; Extracellular vesicles; Sclerostin

Abstract The vast osteocytic network is believed to orchestrate bone metabolic activity in response mechanical stimuli through production of sclerostin, RANKL, and osteoprotegerin (OPG). However, the mechanisms osteocyte mechanotransduction remain poorly understood. We’ve previously shown that mechanosensitivity encoded unique intracellular calcium (Ca 2+ ) dynamics. Here, by simultaneously monitoring Ca actin dynamics single cells exposed fluid shear flow, we detected contractions immediately upon onset flow-induced transients, which were facilitated smooth muscle myosin further confirmed native osteocytes ex vivo. Actomyosin have been linked secretion extracellular vesicles (EVs), our studies demonstrate stimulation upregulates EV immunostaining for secretory vesicle marker Lysosomal-associated membrane protein 1 (LAMP1) quantifying release conditioned medium, both are blunted when signaling was inhibited neomycin. Axial tibia compression used induce anabolic formation responses mice, revealing upregulated LAMP1 expected downregulation sclerostin This load-related increase expression neomycin-injected mice compared vehicle. Micro-computed tomography revealed significant increases trabecular volume fraction cortical thickness after two weeks loading, neomycin treatment. In summary, found activates -dependent enhances EVs containing regulatory proteins. Further, blocking significantly attenuates adaptation loading vivo, suggesting a critical role -mediated adaptation.