Insulin-Like Growth Factor-Binding Protein 5 Promotes the Cell Proliferation and Osteogenic Potential of Dental Pulp Stem Cells Dependent on Its Nuclear Localisation Sequence.

Objectives: Dental pulp stem cells (DPSCs) have been extensively used for tissue regeneration owing to their notable capabilities. Insulin-like growth factor-binding protein 5 (IGFBP5) regulates osteogenic differentiation of mesenchymal stem cells (MSCs); however, the underlying regulatory mechanisms require further investigation.

Materials and methods: Carboxyfluorescein succinimidyl ester, an alkaline phosphatase (ALP) activity assay and Alizarin Red staining were used to reveal the role of IGFBP5 in DPSCs. Protein expression levels were determined using western blotting. Immunofluorescence was used to observe cell sub-localisation. Subcutaneous transplantation in nude mice was used to observe the osteogenesis of DPSCs in vivo.

Results: IGFBP5 enhanced the proliferation and osteogenic differentiation of DPSCs. Deletion of the nuclear localisation sequence (NLS) of IGFBP5 prevented its nuclear import and abolished all its promoting effects on DPSCs; ivermectin stimulation attenuated the enhancement of ALP activity by IGBFP5. Bone-like tissue formation promoted by IGFBP5 in vivo vanishes when the NLS is deleted. Inhibition of IGFBP5 nuclear import attenuated the IGFBP5-induced phosphorylation of JNK (p-JNK) and phosphorylated ERK (p-ERK) in DPSCs.

Conclusion: Our findings suggest that cell proliferation and osteogenic differentiation effects exerted by IGFBP5 on DPSCs are closely associated with their entry into the nucleus, thereby providing a novel potential target for tissue regeneration.