Silver nanoparticles promote osteogenic differentiation of human periodontal ligament fibroblasts by regulating the RhoA-TAZ axis

Silver nanoparticles (AgNps) are well established antibacterial agents, which have been reported to promote osteogenesis of stem cells. Ras homolog gene family member A (RhoA) and Tafazzin (TAZ) have been recently shown to be involved in osteogenic differentiation. The present study aimed to evaluate the effects of AgNps on osteogenic differentiation of human periodontal ligament fibroblasts (HPDLFs), and investigate the underlying mechanisms of AgNps activity. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was employed to determine the safe concentration of AgNps in HPDLFs. Using an alkaline phosphatase assay, Alizarin red S staining and detection of the expression of alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), osterix (OSX), and collagen-I, we found that AgNps, at a concentration range of 25-100 mu M, promoted osteogenic differentiation of HPDLFs in a dose-dependent manner. We also found that 100 mu M AgNps up-regulated the active RhoA expression level. The results of ALP activity and expression of osteogenic markers showed that the effects of AgNps on osteogenic differentiation were abrogated by a RhoA pathway inhibitor, C3 reagent. Additionally, silencing of TAZ attenuated the AgNps-induced osteogenic differentiation of HPDLFs, as shown by decreased ALP activity and down-regulation of osteogenic markers. Interestingly, TAZ knockdown had a very small effect on the activity of RhoA, whereas C3 suppressed the expression of TAZ, indicating that TAZ was a downstream effector of RhoA. In conclusion, the present work demonstrated that AgNps promoted osteogenic differentiation of HPDLFs by activating the RhoA-TAZ axis.