Effect of oscillating fluid flow stimulation on osteocyte mRNA expression

Structural adaptation of the bone tissue is mediated by loading-induced interstitial fluid flow within the bone microstructure. Within this framework, osteocytes fulfill the central mechanotransductive role in the bone remodeling process. While osteocytes have been demonstrated to be exquisitely sensitive to various forms of fluid flow stimulus in vitro, the effect of different oscillating fluid flow (OFF) parameters on osteocyte activity has yet to be systematically characterized. In this study, we investigate the effect of three OFF parameters on osteocyte activity in vitro and hypothesize that COX-2, RANKL, and OPG mRNA expression in osteocytes are sensitive to the OFF parameters: peak shear stress amplitude (0.5 Pa, 1 Pa, 2 Pa, and 5 Pa), oscillating frequency (0.5 Hz, 1 Hz, and 2 Hz), and total flow duration (1 h, 2 h, and 4 h). Our findings demonstrate that COX-2 mRNA levels are elevated in osteocytes subjected to higher peak shear stress amplitudes and longer flow durations, while RANKL/OPG mRNA levels decreased to a minimum threshold in response to higher peak shear stress amplitudes, faster oscillating frequencies, and longer flow durations. These findings suggest that dynamic fluid flow with higher peak shear stress amplitudes, faster oscillating frequencies, and longer loading durations provide the best conditions for promoting bone formation.