IL-33 guides osteogenesis and increases proliferation and pluripotency marker expression in dental stem cells

Soluble IL-33 (interleukin (IL)-1-like cytokine) acts as endogenous alarm signal (alarmin). Since alarmins, besides activating immune system, act to restore tissue homeostasis, we investigated whether IL-33 exerts beneficial effects on oral stem cell pull.

Clonogenicity, proliferation, differentiation and senescence of stem cells derived from human periodontal ligament (PDLSCs) and dental pulp (DPSCs) were determined after in vitro exposure to IL-33. Cellular changes were detected by flow cytometry, Western blot, immunocytochemistry and semiquantitative RT-PCR.

IL-33 stimulated proliferation, clonogenicity and expression of pluripotency markers, OCT-4, SOX-2 and NANOG, but it inhibited ALP activity and mineralization in both PDLSCs and DPSCs. Higher Ki67 expression and reduced β-galactosidase activity in IL-33-treated cells were demonstrated, whereas these trends were more conspicuous in osteogenic medium. However, after 7-day IL-33 pretreatment, differentiation capacity of IL-33-pretreated cells was retained, and increased ALP activity was observed in both cell types. Results showed that IL-33 regulates NF-κB and β-catenin signalling, indicating the association of these molecules with changes observed in IL-33-treated PDLSCs and DPSCs, particularly their proliferation, pluripotency-associated marker expression and osteogenesis.

IL-33 treatment impairs osteogenesis of PDLSCs and DPSCs, while increases their clonogenicity, proliferation and pluripotency marker expression. After exposure to IL-33, osteogenic capacity of cells stayed intact. NF-κB and β-catenin are implicated in the effects achieved by IL-33 in PDLSCs and DPSCs.