Dynamic fluid flow stimulation on cortical bone and alterations of the gene expressions of osteogenic growth factors and transcription factors in a rat functional disuse model

Recently we have developed a dynamic hydraulic stimulation (DHS) as a loading modality to induce anabolic responses in bone. To further study the functional process of DHS regulated bone metabolism, the objective of this study was to evaluate the effects of DHS on cortical bone and its alterations on gene expressions of osteogenic growth factors and transcription factors as a function of time. Using a model system of 5-month-old hindlimb suspended (HLS) female Sprague-Dawley rats, DHS was applied to the right tibiae of the stimulated rats with a loading frequency of 2Hz with 30mmHg (p-p) dynamic pressure, 5days/week, for a total of 28days. Midshafts of the tibiae were analyzed using μCT and histology. Total RNA was analyzed using RT-PCR on selected osteogenic genes (RUNX2, β-catenin, osteopontin, VEGF, BMP2, IGF-1, and TGF-β) on 3-, 7-, 14- , and 21-day. Results showed increased Cort.Th and Ct.BV/TV as well as a time-dependent fashion of gradual changes in mRNA levels upon DHS. While DHS-driven fold changes of the mRNA levels remained low before Day-7, its fold changes started to elevate by Day-14 and then dropped by Day-21. This study further delineates the underlying molecular mechanism of DHS-derived mechanical signals, and its time-dependent optimization.