RESUMEN
The role of myosin light chain II (MLCII) in cellular differentiation of rat mandibular condylar chondrocytes (MCCs) induced by cyclical uniaxial compressive stress (CUCS) remains unclear. In the current study, a fourpoint bending system was used to apply CUCS to primary cultured MCCs from rats. It was identified that CUCS stimulated features of cellular differentiation including morphological alterations, cytoskeleton rearrangement and overproduction of proteoglycans. Furthermore, CUCS promoted runtrelated transcription factor2 (RUNX2) expression at mRNA (P<0.01) and protein levels (P<0.05) and elevated alkaline phosphatase (ALP) activity (P<0.01), which are both markers of osteogenic differentiation. Under conditions of stress, western blotting indicated that the ratio of phosphorylated MLCII to total MLCII was increased significantly (P<0.05). Silencing MLCII by RNA interference reduced ALP activity (P<0.01), and eliminated RUNX2 mRNA expression (P<0.01). Addition of the MLC kinase inhibitor, ML7, reduced the CUCSassociated upregulation of RUNX2 expression (P<0.01) and ALP activity (P<0.01). The data indicated that CUCS promoted cellular differentiation of rat primary MCCs, and this was suggested to be via the phosphorylation of MLCII.