Age-Related Insulin-Like Growth Factor Binding Protein-4 Overexpression Inhibits Osteogenic Differentiation of Rat Mesenchymal Stem Cells.

BACKGROUND/AIMS Insulin-like growth factor binding proteins (IGFBP) play important roles in bone metabolism. IGFBP4 is involved in senescent-associated phenomena in mesenchymal stem cells (MSCs). The goal of the present study was to determine whether age-related IGFBP4 overexpression is associated with the impaired osteogenic differentiation potential of aged bone marrow derived MSCs. METHODS MSCs were isolated from Sprague-Dawley rats aged 3-26 months. The bone morphogenetic protein (BMP)-2-induced osteogenic differentiation of rat MSCs was assessed by analyzing the expression levels of osteoblast marker genes [runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), and osteocalcin (OC)], ALP activity and calcification. RESULTS Our study showed that IGFBP4 mRNA and protein expression increased with age in parallel with impaired osteogenic differentiation of MSCs cultured in BMP2-containing osteogenic medium, as evidenced by the downregulation of osteoblast marker genes, and decreased ALP activity and calcium deposits. IGFBP4 overexpression impaired BMP2-induced osteogenic differentiation potential of young MSCs, whereas IGFBP4 knockdown restored the osteogenic potency of aged MSCs. Moreover, IGFBP4 knockdown stimulated the activation of Erk and Smad by increasing phosphorylation. CONCLUSION Collectively, our results demonstrate that IGFBP4 overexpression plays a role in the impairment of MSC differentiation potential via the Erk and Smad pathways, suggesting potential targets to improve MSC function for cell therapy applications.