Ageing affects the proliferation and mineralization of rat dental pulp stem cells under inflammatory conditions

Aim: To comparatively evaluate changes in the proliferation and mineralization abilities of dental pulp stem cells (DPSCs) from juvenile and adult rats in a lipopolysaccharide (LPS)-induced inflammatory microenvironment to provide a theoretical basis for the age-related differences observed in DPSCs during repair of inflammatory injuries.

Methodology: DPSCs were isolated from juvenile (JDPSCs) and adult rats (ADPSCs), and senescence-associated β-galactosidase staining was used to compare senescence between JDPSCs and ADPSCs. Effects of LPS on JDPSCs and ADPSCs proliferation were investigated by cell counting kit-8 assays and flow cytometry. Alizarin red staining, quantitative reverse transcription polymerase chain reaction and Western blot assay were used to examine the effects of LPS on mineralization-related genes and proteins in JDPSCs and ADPSCs. Immunohistochemistry was used to compare interleukin-1β (IL-1β) and osteocalcin (OCN) expression in the pulpitis model. Unpaired Student's t-tests and one-way anova were used for statistical analysis.

Results: DPSCs were isolated from juvenile and adult rat dental pulp tissues. At low concentrations (0.1-1 μg mL^-1 ), LPS significantly promoted the proliferation of JDPSCs (P < 0.01) and ADPSCs (P < 0.01 or P < 0.05), with the effect being stronger in JDPSCs than in ADPSCs. In addition, mineralized nodules and the expression of mineralization-related genes (OCN, DSPP, ALP, BSP) increased significantly after stimulation with LPS (0.5 μg mL^-1 ) in JDPSCs and ADPSCs (P < 0.01 or P < 0.05), and JDPSCs displayed a more obvious increase than ADPSCs. Western blots revealed OCN and ALP expression levels in JDPSCs treated with LPS were significantly upregulated (P < 0.05); meanwhile, ALP expression in ADPSCs increased slightly but significantly (P < 0.05), and OCN expression was not affected. Finally, IL-1β expression was significantly higher (P < 0.05) and OCN expression was significantly lower (P < 0.05) in the inflamed dental pulp of adult rats than in juvenile rats.

Conclusions: A certain degree of inflammatory stimulation promoted the proliferation and mineralization of DPSCs; however, this effect declined with age. The DPSCs of adult donors in an inflammatory microenvironment have a weaker repair ability than that of juvenile donors, who are better candidates for tissues damage repair.