Mechanical force inhibits osteoclastogenic potential of human periodontal ligament fibroblasts through OPG production and ERK‐mediated signaling

Abstract

Periodontal ligament and gingival fibroblasts play important roles in bone remodeling. Periodontal ligament fibroblasts stimulate bone remodeling while gingival fibroblasts protect abnormal bone resorption. However, few studies had examined the differences in stimulation of osteoclast formation between the two fibroblast populations. The precise effect of mechanical forces on osteoclastogenesis of these populations is also unknown. This study revealed that more osteoclast-like cells were induced in the co-cultures of bone marrow cells with periodontal ligament than gingival fibroblasts, and this was considerably increased when anti-osteoprotegerin (OPG) antibody was added to the co-cultures. mRNA levels of receptor activator of nuclear factor-kappaB ligand (RANKL) were increased in both populations when they were cultured with dexamethasone and vitamin D(3). Centrifugal forces inhibited osteoclastogenesis of both populations, and this was likely related to the force-induced OPG up-regulation. Inhibition of extracellular signal-regulated kinase (ERK) signaling by a pharmacological inhibitor (10 microM PD98059) or by siERK transfection suppressed the force-induced OPG up-regulation along with the augmentation of osteoclast-like cells that were decreased by the force. These results suggest that periodontal ligament fibroblasts are naturally better at osteoclast induction than gingival fibroblasts, and that centrifugal force inhibited osteoclastogenesis of the periodontal fibroblasts through OPG production and ERK activation.

Human periodontal ligament fibroblasts stimulate osteoclastogenesis in response to compression force through TNF-α-mediated activation of CD4+ T cells

“…The results of the current study indicate that various fibroblastic cells naturally produce OPG, thereby supporting the inhibitory roles of fibroblasts on osteoclastogenesis. There are also significant findings showing that mechanical force induces the production of both OPG and RANKL by PLF, while OPG is predominant over RANKL [Yamamoto et al, 2006;Nakajima et al, 2008;Kook et al, 2009]. Importantly, however, the results from GCF analysis showed that the levels of RANKL are naturally higher than those of OPG in this cell type.…”

Centrifugal Force Induces Human Ligamentum Flavum Fibroblasts Inflammation Through Activation of JNK and p38 Pathways

“…Numerous studies have, however, pointed out that various types of cells, including endothelial cells, smooth muscle cells, osteoblasts, chondrocytes, and fibroblasts, appear to share common signaling pathways; nevertheless, the eventual response of a given cell type to mechanical load depends on mechanical loading conditions and the types of signaling molecules and transcription factors that are expressed [14]. In this study, ligamentum flavum fibroblasts were exposed to mechanical force by applying a well-established in vitro compression model of centrifugation of cultured cells [9,10]. The result demonstrated that viability of ligamentum flavum fibroblasts decreased in proportion to the centrifugal stress loaded, whereas no significant cellular death was noted.…”

“…Cells were centrifuged at 500 and 1000 rpm/min for 10, 30, 60, and 90 min by horizontal microplate rotor (Eppendorf 5810R Centrifuge, Hamburg, Germany) under ambient conditions (temperaturecontrolled, but ambient room air) as previously described [9,10]. The paired -control of each tested condition was adjusted for each paired period ambient condition (temperature-controlled, but ambient room air) for 10, 30, 60, and 90 min.…”

“…To gain further insight into the mechanisms of mechanotransduction in ligamentum flavum, we have studied the role of MAPK pathways in response to mechanical compression of ligamentum flavum fibroblasts. In this study, mechanical stress was applied by subjecting the cells in monolayer to different magnitudes of centrifugal forces [9,10]. The goal of this study was to test the hypothesis that human ligamentum flavum fibroblasts can detect and respond to mechanical stress and to investigate the molecular and biochemical mechanisms by which mechanical stress induces inflammatory responses.…”

Effects of HSP70 on the compression force-induced TNF-α and RANKL expression in human periodontal ligament cells

“…Transcription factors of the NF-jB family are key players in the initiation of the inflammatory response, and NF-jB regulates inflammatory cytokines, including TNF-a and RANKL [29]. Many investigators have reported that signaling molecules, such as Rho kinase [30,31], focal adhesion kinase (FAK) [30], NF-jB [32,33], c-fos [34], mitogen-activated protein kinase (MAPK) [extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK) and p38 MAPK] [35][36][37][38][39], and nitric oxide [40] are increased in PDL cells after mechanical stimulation. Furthermore, Copland and Post [41] found that stretch-induced HSP70 expression was mediated via NF-jB in fetal lung epithelial cells.…”