Porphyromonas gingivalis lipopolysaccharide enhances the proliferation of human periodontal ligament cells via upregulation of cyclin D1, cyclin A and cyclin B1

Abstract

Human periodontal ligament cells (hPDLCs) play a notable role in periodontal tissue homeostasis and regeneration. However, the effect of Porphyromonas gingivalis lipopolysaccharide (Pg‑LPS) on the proliferation of hPDLCs remains unclear. The present study investigated the effects of Pg‑LPS on the proliferation profile of hPDLCs, and the involvement of cyclins and cyclin‑dependent kinases in the process. hPDLCs were treated with Pg‑LPS, and cell proliferation and cycle were detected using Cell Counting Kit‑8 assays and flow cytometry. The mRNA expression levels of the cyclins and cyclin‑dependent kinases (CDKs), including cyclins A, B1, D1 and D2 and CDK1, 2 and 4, were detected using reverse transcription‑quantitative PCR. The protein expression levels of cyclins A, B1 and D1 were analysed using western blotting. The proliferation of hPDLCs was significantly increased after treatment with Pg‑LPS at the concentrations of 0.001, 0.01, 0.1, 1 and 10 µg/ml for 24, 36 and 48 h compared with the cells cultured without LPS (P<0.01). The proliferation index of hPDLCs was significantly enhanced after treatment with Pg‑LPS (0.0001, 0.001, 0.01, 0.1, 1 and 10 µg/ml) for 24 h (P<0.01). However, the S‑phase fraction (SPF) only significantly increased after treatment with Pg‑LPS at 0.01 µg/ml for 24 h (P<0.05), while the G2/M‑phase fraction increased (P<0.01) and the G0/G1‑phase fraction decreased (P<0.01) compared with the controls. The proliferation index and SPF increased, peaked at 24 h and then decreased at 48 h in both Pg‑LPS‑stimulated and control groups. Notably, Pg‑LPS significantly upregulated the expression levels of cyclins D1, A and B1 after 24 h compared with those in the controls. Overall, the present study indicated that Pg‑LPS may enhance the proliferation of hPDLCs, potentially through upregulation of cyclins D1, A and B1.