Investigating the Role of Insulin-like Growth Factor (IGF) Axis in Stem Cell Based Periodontal Bone Regeneration in Osteoporotic Conditions

Abstract

Osteoporosis and periodontal disease share common risk factors and are both prevalent in the elderly population. The use of stem cells has given hope to in various disciplines including periodontal regeneration. This project aims to characterise periodontal ligament stem cells isolated from postmenopausal osteoporotic patients (OP-PDLSCs) and study their osteogenic differentiation along with exploring the potential role of Insulin-like Growth Factor (IGF) axis, which is known to be highly linked to osteogenesis, in this process. OP- PDLSCs (n=3) were studied in comparison to healthy PDLSCs (H-PDLSCs) (n=4). Characterisation for clonogenicity, proliferation rate and surface marker expression was carried out using colony forming unit-fibroblasts, population doubling time and flow cytometry assays respectively. Osteogenic differentiation was assessed using alkaline phosphatase (ALP), and alizarin red (ARS) staining and mineralisation nodules quantification assay. RT-qPCR was used to investigate the gene expression of osteogenic and bone remodelling markers, estrogen receptors (ERs) and IGF axis. ELISA was utilised to study the protein expression of IGF binding protein 4 (IGFBP-4) and its protease (PAPP-A). Compared to controls, clonogenic and proliferative capacities were lower in the osteoporotic group. Flow cytometry indicated a similar cell surface markers expression for all markers assessed (CD73+, CD90+, CD105+, CD14- , CD19-, CD45-) except for CD34- and HLADR-, where the expression was slightly higher in the osteoporotic group. ALP and ARS showed lower osteogenic differentiation and mineralisation in OP-PDLSCs. Gene expression showed comparable to lower relative expression levels for RUNX2, ALPL, ColI⍺ 1, POSTN, OCN, RANKL, ERs and higher levels for OPG in OP-PDLSCs. Gene expression showed overall lower expression in OP-PDLSCs samples for all IGF axis members except for IGF-1 (inconsistent), IGFBP-2, IGFBP-4 and PAPP-A (higher). Protein levels for IGFBP-4 and PAPP-A were higher in OP-PDLSCs. In conclusion, OP- PDLSCs showed similar phenotypic characteristics to H-PDLSCs with a trend of lower osteogenic differentiation and mineralisation capacities. Further investigations on IGFBP-4 are needed as it could be a target to enhance osteogenic regenerative capacity in postmenopausal OP-PDLSCs.