Establishment of an in vitro system to screen for substances to improve osteogenesis imperfecta osteoblasts’ functions

Abstract

Background: Osteogenesis imperfecta (OI) is a heritable bone disorder caused mainly by dominant mutations in genes encoding collagen-related proteins which are COL1A1 and COL1A2. Genotype-phenotype correlation has some discrepancies which lead to the difficult prediction of the clinical outcome of OI patients. We identified a child with dentinogenesis imperfecta (DI) and OI who was homozygous for c.1009G>A (p.G337S) mutation in COL1A2. Her parents were heterozygous for the mutation and had only DI. This family provides the opportunity to explore the biochemical changes which are different between the homozygous with DI and OI and the heterozygous with DI only. Methods: We established patients-specific induced pluripotent stem cells (iPSCs) from the trio to use as an in vitro system to screen for biochemical substances. They were used to study the expression of the osteogenic marker genes (COL1A1, COL1A2, SPP1, OCN, ALP) and their products along the time course of osteoblast differentiation. Results: We successfully generated patient-specific iPSCs from the trio. They all showed the characteristic features of iPSCs. We then differentiated them to mesenchymal stem cells (MSCs) and osteoblasts. Their osteoblasts showed various defective expression of the osteogenic markers and calcium mineralization. Interestingly, osteopontin was absent in iPSCs-derived osteoblasts of patients with OI, while it was significantly lower in those with DI-only compared to an unaffected control. In addition, osteocalcin was significantly lower in those with OI compared to DI-only and an unaffected control. Conclusion: Levels of osteopontin and osteocalcin in iPSCs-derived MSC of patients with OI were significantly low during osteoblasts differentiation. These cells could be used to screen for substances which can increase osteopontin and osteocalcin.