Many recent studies have shown that CCN2 is expressed in normal bones during development, growth, and remodeling, and that treating osteoblast cultures with recombinant CCN2 enhances their proliferation and differentiation [69], Dasatinib [120] and [121]. Furthermore, the overexpression of CCN2 in ST-2 cells, a bone marrow-derived stromal cell line, increased alkaline phosphatase activity, osteocalcin and alkaline phosphatase mRNA levels, and mineralized nodule formation

[122]. Taken together, these studies have demonstrated that CCN2 is expressed in bone tissue and that its gene product exerts diverse modulatory functions on osteoblast differentiation and proliferation. The CCN2 gene is up-regulated in mechanically Epigenetics Compound Library in vivo challenged organ systems in response to various etiologies including hypertension, hemodynamic overload, metabolic injury and obstruction [123]. Mechanical regulation of the Cyr61/CCN1 and CTGF/CCN2 proteins has implications in mechanical stress-associated pathologies, with CCN2 gene expression induced in response to hydrostatic pressure [124], stretching [125], and shear stress [126] in various cell

types. Exposure of human mesangial cells to hydrostatic pressure for 48 h markedly increased CCN2 protein levels [125]. CCN2 mRNA expression decreased to 25% in 24 h after the load was removed in human lung fibroblasts [126], while it decreased to about 13% in vascular endothelial cells after fluid shear stress for 6 h [127]. Wong et al. [128] compared the effects of tensile strain and cyclic hydrostatic pressure on CCN2 expression in primary chondrocytes. Their data indicated that tensile strain induced CCN2 expression, whereas hydrostatic pressure had no effect; these findings were in contrast to the up-regulation

of CCN2 in mesangial cells exposed to hydrostatic pressure [125]. These reports suggest that mechanical stress may induce or inhibit CCN2 expression depending on the cell type. We performed a continuous application of mechanical stimulation in vivo using Bcl-w Waldo’s experimental tooth movement model in rats [129] and in mice [130] for mechanical-dependent bone remodeling. We found that CCN2 mRNA expression was markedly increased in osteocytes, especially on the pressured side of alveolar bone during bone resorption [130]. We showed that the proportion of CCN2 mRNA-expressing osteocytes significantly increased within 2 h after the initiation of tooth movement and reached a maximum at 12 h; thereafter, the proportion of CCN2-expressing osteocytes decreased from days 1 to 21 [130]. Our findings suggest that CCN2 produced during compressive strain might trigger bone resorption. Numerous studies concerning the function of CCN2 have been reported [66], [67], [68], [131], [132], [133] and [134] yet not in cultured primary osteocytes.