MAI Zhi-hui, PENG Zhu-li, ZHANG Jing-lan, CHEN Lin, LIANG Huan-you, CAI Bin, AI Hong

Abstract:
Background  Mechanical stress plays an important role in the maintenance of bone homeostasis. Current hypotheses suggest that interstitial fluid flow is an important component of the system by which tissue level strains are amplified in bone. This study aimed to test the hypothesis that the short-term and appropriate fluid shear stress (FSS) is expected to promote the terminal differentiation of pre-osteoblasts and detect the expression profile of microRNAs in the FSS-induced osteogenic differentiation in MC3T3-E1 cells.
Methods  MC3T3-E1 cells were subjected to 1 hour of FSS at 12 dyn/cm2 using a parallel plate flow system. After FSS treatment, cytoskeleton immunohistochemical staining and microRNAs (miRNAs) were detected immediately. Osteogenic gene expression and immunohistochemical staining for collagen type I were tested at the 24th hour after treatment, alkaline phosphatase (ALP) activity assay was performed at 24th, 48th, and 72th hours after FSS treatment, and Alizarin Red Staining was checked at day 12.
Results  One hour of FSS at 12 dyn/cm2 induced actin stress fiber formation and rearrangement, up-regulated osteogenic gene expression, increased ALP activity, promoted synthesis and secretion of type I collagen, enhanced nodule formation, and promoted terminal differentiation in MC3T3-E1 cells. During osteogenic differentiation, expression levels of miR-20a, -21, -19b, -34a, -34c, -140, and -200b in FSS-induced cells were significantly down-regulated.
Conclusion  The short-term and appropriate FSS is sufficient to promote terminal differentiation of pre-osteoblasts and a group of miRNAs may be invovled in FSS-induced pre-osteoblast differentiation.