Intracellular Ca2+ signaling mediates IGF-1-induced osteogenic differentiation in bone marrow mesenchymal stem cells

Abstract

Insulin-like growth factor 1 (IGF-1), a multifunctional peptide that involves in cell proliferation and differentiation, can induce strong osteogenic differentiation in bone marrow mesenchymal stem cells (BMMSCs). However, it remains unknown whether intracellular Ca²⁺ signal contributes to the IGF-1-induced osteogenic differentiation of BMMSCs. In this study, we attempted to investigate the effect of IGF-1 on the gene expression of intracellular Ca²⁺-handling proteins and figure out whether the intracellular Ca²⁺ signal affects IGF-1-induced osteogenic differentiation. We found that IGF-1 treatment significantly increased cell proliferation and induced cell morphological changes with an increase of cell surface area. Quantitative PCR and Western blot analysis showed that osteoblast marker proteins, including alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2) and osteocalcin (OCN) were significantly upregulated by IGF-1 treatment, indicating IGF-1 induced osteogenic differentiation in BMMSCs. Interestingly, the expression levels of the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) 3 and inositol-1,4,5-triphosphate receptor (IP₃R) 2 were dramatically elevated during the IGF-1-induced osteogenic differentiation. Consistently, IGF-1-treated cells exhibited greater Ca²⁺ response to ATP. Importantly, blocking SERCA by thapsigargin markedly impaired IGF-1-induced osteogenic differentiation, indicating that intracellular Ca²⁺ mediated IGF-1-induced osteogenic differentiation in BMMSCs, probably via Akt signal pathway, which may provide new insight for the treatment of osteoporosis.

Keywords: BMMSCs; IGF-1; Intracellular Ca(2+) signal; Osteogenic differentiation; SERCA.