Protein kinase-A-dependent osteoprotegerin production on interleukin-1 stimulation in human gingival fibroblasts is distinct from periodontal ligament fibroblasts

Abstract

SummaryPeriodontitis, a chronic inflammatory disease, is characterized by increased expression of interleukin (IL)-1 and other inflammatory mediators resulting in extensive osteoclast formation and bone loss. Expression of receptor activator of nuclear factor kappa B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), by osteoblasts is important to regulate osteoclast differentiation. The aim of the present study was to investigate the regulatory effects of IL-1 on RANKL and OPG production by mesenchymal fibroblasts in periodontal tissue. Human gingival fibroblasts (HGF) and periodontal ligament fibroblasts (PDL) were stimulated with IL-1α α α α with or without protein synthesis inhibitor cycloheximide (CHX), protein kinase A (PKA) inhibitors, protein kinase C (PKC) inhibitors and prostaglandin E 2 (PGE 2 ) inhibitor. In some experiments, the cultured cells were directly stimulated with either PKA or PKC activators. In HGF, IL-1α α α α -stimulated OPG mRNA expression was high and could be reduced by CHX. PKA inhibitor completely abrogated IL-1α α α α -induced OPG mRNA expression and OPG production. Endogenous PGE 2 further enhanced IL-1α α α α -induced OPG production in HGF. In PDL, RANKL mRNA expression was greatly augmented by IL-1α α α α . IL-1α α α α induced OPG mRNA expression and protein production. PKC inhibitor partially reduced IL-1α α α α -induced OPG production and PKC activator enhanced OPG production in PDL. The IL-1α α α α -stimulated OPG mRNA expression in HGF was greater than PDL. These results provide new evidence for the possible osteoclastogenesis-inhibitory function of HGF through PKA activity pathway. PDL utilized PKC for OPG production. Thus, we emphasize that HGF and PDL have different characteristics of host defence mechanism against inflammatory process.

Internal prostaglandin synthesis augments osteoprotegerin production in human gingival fibroblasts stimulated by lipopolysaccharide

“…The total formation of intracellular cAMP was greater in cells expressing the EP2 receptor than in those expressing the EP4 receptor [34]. We have reported previously that IL-1b-induced OPG production in HGF was different from that in PDL and osteoblasts, and that the activation of the PKA pathway is crucial for OPG production in HGF [35]. In this study, EP1 and EP2 agonists stimulated OPG production in HGF, but the EP4 agonist did not.…”

“…It remains to be determined whether OPG produced by HGF is sufficient to suppress RANKL expression in osteoblasts, T lymphocytes and PDL that are activated by IL-1, IL-6, PGE2 and LPS in periodontitis tissue. The amount of OPG produced by HGF was higher than that produced by periodontal ligament fibroblasts [35]; HGF are better at inhibiting osteoclast differentiation than periodontal ligament fibroblasts [43]. HGF constitute 65% of the cellular population of gingival tissue [44]; this suggests that the total amount of OPG produced by HGF might be effective to suppress RANKL in gingival tissue.…”

Statins Regulate IL-1β - Induced RANKL and OPG Production by Human Gingival Fibroblasts

“…As discussed in Chapter I, human gingival fibroblasts and periodontal ligament fibroblasts can produce RANKL and OPG. Therefore in addition to osteoblasts, it is now believed that fibroblasts are involved in the regulation of alveolar bone metabolism (47)(48)(49)(50)52). It is unknown however whether statins have an effect on OPG and RANKL production by human gingival fibroblasts.…”

“…Gingival fibroblasts, periodontal ligament fibroblasts, and osteoblasts are the three types of fibroblastic cells of mesenchymal origin in human periodontal tissue (47). Gingival fibroblasts make up 65% of the cell population in gingiva, and appear to be active participants in soft and hard tissue remodeling (51).…”

“…RANKL and OPG are produced by many cells in the body including HGF and PDL cells (47,48). Some studies report an increase in OPG production by HGF when stimulated by lipopolysaccharide (LPS) from Aggregatibacter actinomycetemcomitans (A.a.) and Porphyromonas gingivalis (P.g.…”