IGFBP 5 enhances osteogenic differentiation potential of periodontal ligament stem cells and Wharton's jelly umbilical cord stem cells, via the JNK and MEK /Erk signalling pathways

Objectives Mesenchymal stem cell ( MSC )‐mediated tissue regeneration represents a promising strategy for repair of tissue defects, but its molecular mechanisms remain unclear, restricting the use of MSC s. Our previous study indicated that insulin‐like growth factor‐binding protein 5 ( IGFBP 5 ) exerted a valuable effect on osteogenic differentiation of MSC s, but its molecular mechanisms underlying directed differentiation remained unclear. In this study, we have investigated the molecular role of IGFBP 5 in regulating this osteogenic differentiation potential. Materials and methods Periodontal ligament stem cells ( PDLSC s) were isolated from periodontal ligament tissue. Wharton's jelly of umbilical cord stem cells ( WJCMSC s) was obtained commercially. Lentiviral IGFBP 5 sh RNA was used to silence IGFBP 5 . Retroviruses expressing wild‐type IGFBP 5 were used to overexpress IGFBP 5 in the WJCMSC s. Recombinant human IGFBP 5 protein (rh IGFBP 5) was used to treat PDLSC s for 24 h. Western blot analysis was used to detect the MAPK signalling pathway, and alkaline phosphatase ( ALP ) activity, Alizarin Red staining and quantitative calcium analysis were used to study osteogenic differentiation potentials. Results Overexpression of IGFBP 5 or rh IGFBP 5 increased expression levels of phosphorylated c‐Jun N‐terminal kinase (p‐ JNK ), phosphorylated mitogen‐activated protein kinase 1 and 2 (p‐ MEK 1/2) and phosphorylated extracellular regulated protein kinases (p‐Erk1/2) in both WJCMSC s and PDLSC s. Consistently, silenced IGFBP 5 was found to effectively inhibit expression of p‐ JNK , p‐Erk1/2 and p‐ MEK 1/2 in PDLSC s and WJCMSC s. Furthermore, inhibition of JNK by its inhibitor, SP 600125, or MEK /Erk signalling by its inhibitor, PD 98059, dramatically blocked IGFBP 5 ‐enhanced ALP activity and in vitro mineralization in both PDLSC s and WJCMSC s. Conclusions Our results demonstrated that IGFBP 5 promoted osteogenic differentiation potentials of PDLSC s and WJCMSC s via the JNK and MEK /Erk signalling pathways.