Matthews, M. D.; Lunny, K.; Raju, L.; Tariq, S.; Naguib, N.; Wiesner, U. B.; Lewis, K. J.

Osteocytes detect mechanical forces within bone through signaling processes organized at the plasma membrane. Membrane cholesterol regulates membrane organization, dynamics, and mechanical properties, yet its role in osteocyte mechanotransduction in vivo remains unknown. Here, we developed an intravital multiphoton imaging approach to quantify membrane-associated uptake, retention, and clearance along-side load-induced Ca2+ signaling in osteocytes within the intact metatarsal. Using fluorescent nanoparticles and a membrane-labeling probe, we tracked these processes before and after pharmacological cholesterol depletion. Cholesterol depletion reduced osteocyte membrane uptake and retention and altered clearance in both sexes, while affecting load-induced Ca2+ signaling in a sex-dependent manner. In females, cholesterol depletion increased both the proportion of osteocytes responding to mechanical loading and the magnitude of their responses, whereas neither outcome changed in males. These findings identify plasma membrane cholesterol as a regulator of osteocyte membrane dynamics and mechanical responsiveness in vivo. More broadly, this work establishes an approach for directly examining how membrane composition and turnover regulate mechanotransduction in cells embedded within their native tissue environment.