Bone Abstracts

Background: Fibrodysplasia Ossificans Progressiva (FOP) is a progressive disease characterized by periods of heterotopic ossification, often in ligaments. The underlying mechanism is far from clear, partially due to limited access to patient-derived cell models. Periodontal ligament fibroblasts (PLF) from extracted teeth can potentially be used to study deviant bone remodelling processes in vitro since these cells are derived from actual ligaments. They further provide a tool to study the hitherto unknown role of ACVR1 mutation, the BMP- receptor that is mutated in FOP patients, in osteoclastogenesis. Several studies suggest a role for TGF-β in FOP osteogenesis. Moreover, TGF-β is a candidate protein for periodontal ligament-induced osteoclast formation.

Objective: To assess the role of FOP PLF in osteogenesis and osteoclastogenesis and the involvement of TGF-β herewith.

Methods: FOP and control PLF (n=6 of each) were used in osteogenesis and osteoclastogenesis assays in the absence or presence of TGF-β receptor inhibitor GW788388. Alkaline phosphatase (ALP) activity and alizarin red staining was measured to asses osteoblast differentiation. TRACP staining and multinuclearity in PLF-PBMC co-cultures on cortical bone slices was used as a measure of osteoclast formation. In these cocultures TGF-β expression and RANKL/OPG ratio was measured by QPCR.

Results: Although FOP-PLF displayed a slightly higher ALP activity at 7 days, mineralization was similar at 21 days. GW788388 did not influence mineral deposition in both groups. However, in the osteoclastogenesis cultures, FOP-PLF displayed a two-fold higher osteoclastogenesis on cortical bone slices. Osteoclast formation was inhibited by TGF-β receptor inhibitor GW788388, both in control and FOP cultures. Interestingly, GW788388 inhibited TGF-β expression and had a pronounced effect on the RANKL/OPG ratio in osteoclastogenesis cultures.

Conclusion: Our study emanates an important role for TGF-β in periodontal ligament fibroblasts associated osteoclastogenesis.