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

Human periodontal ligament cells (hPDLCs) play a notable role in periodontal tissue homeostasis and regeneration. However, the effect of lipopolysaccharide (-LPS) on the proliferation of hPDLCs remains unclear. The present study investigated the effects of -LPS on the proliferation profile of hPDLCs, and the involvement of cyclins and cyclin-dependent kinases in the process. hPDLCs were treated with -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 -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 -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 -LPS at 0.01 µg/ml for 24 h (P<0.05), while the G/M-phase fraction increased (P<0.01) and the G/G-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 -LPS-stimulated and control groups. Notably, -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 -LPS may enhance the proliferation of hPDLCs, potentially through upregulation of cyclins D1, A and B1.