Investigating the Role of Insulin-like Growth Factor (IGF) Axis in the Osteogenic Differentiation of Osteoporotic Periodontal Stem Cells

Background: Utilising stem cells is a promising approach to treat chronic periodontitis. Limited data is available regarding the regenerative potential of osteoporotic periodontal ligament stem cells (OP-PDLSCs). The IGF axis including its binding proteins (IGFBPs) is involved in osteogenesis. IGFBP-4 is particularly inhibitory of IGF function in vitro. Hence, the aim of this project was to study the osteogenic differentiation capacity of OP-PDLSCs and assess the possible role of IGF axis, particularly IGFBP-4 and its protease (PAPP-A), in the process.

Methods: PDLSCs were characterised from healthy (H-PDLSCs) and osteoporotic donors (both n=3). To compare their osteogenic differentiation, cells were cultured in basal media (control) or osteogenic media (supplemented with 50µM L-ascorbic acid and 10µM dexamethasone). Differentiation was assessed at 2, 3 and 4 weeks using Alkaline Phosphatase (ALP) and Alizarin Red staining (ARS) assays. RT-qPCR was conducted to assess the expression of the osteogenic and IGF axis markers. ELISA was used to measure IGFBP-4 and PAPP-A proteins.

Results: The intensity of ALP staining under osteogenic conditions increased with time for H-PDLSCs but not in OP-PDLSCs (except at week 4). ARS quantification indicated increased mineral concentration under osteogenic conditions after 3 and 4 weeks in H-PDLSCs (average 0.041±0.033 mM) compared to OP-PDLSCs (average 0.011±0.004 mM). Lower gene expression of the osteogenic markers (ALPL, RUNX2, Osteocalcin and Col 1A1) was measured in OP-PDLSCs, particularly in osteogenic conditions. In OP-PDLSCs, the strongest trend for downregulation was observed for IGFBP1, under both culture conditions, whilst other molecules were more variable. IGFBP-4 protein showed slightly elevated levels in OP-PDLSCs while PAPP-A levels (IGFBP-4 protease) were below detection.

Conclusion: OP-PDLSCs showed lower osteogenic differentiation capacity and different pattern of IGF axis expression compared to healthy controls. Manipulating IGF axis may be a strategy to enhance periodontal regeneration in OP patients.