Odontogenic Potential of α7 Integrin Positive Human Skeletal Muscle Stem Cells

Abstract

Recently, the development of new dental tissue regeneration therapies, which enable regrowth of enamel, dentin and the tooth itself, have enabled new clinical treatments. Interestingly, it is suggested that dental pulp precursor cells and/or dental pulp stem cells are related to activation and regeneration of dentin. Therefore, there exists the possibility of effective therapies involving stem cell injection instead of the usual dental caries treatment and pulp capping methods. We previously reported the potential of isolated α7 integrin positive (α7⁺) cells, isolated from pure populations of myoblasts in human muscle, to undergo myogenesis and convert to other mesenchymal differentiation programs such as osteoblasts and adipocytes. In the present study, we examined the potential of α7⁺ myoblasts to differentiate into the odontogenic pathway and regenerate dentin. α7⁺ myoblasts were harvested from both human adult and fetal muscle by fluorescence activated cell sorting (FACS). To assess the potential of the α7⁺ myoblasts to differentiate into the odontogenic lineage, aggregates of 10³ cells per 10μl cells were treated with the hanging drop for 2 days. Cell aggregates were then pooled and cultured in suspension with 10^-7mol/l retinoic acid (RA) for 3 days. Cells were plated on gelatin-coated dishes and cultured with bone morphogenetic protein-4 (BMP-4) for 7 days. Odontogenic differentiation was assessed by expression of the odontoblast phenotype markers dentin sialophosphoprotein (DSPP) and dentin sialoprotein (DSP). We also examined modulation of integrin expression and adhesion/motility functions with the extracellular matrix proteins laminin-1, laminin-2 and collagen type I following differentiation into the odontogenic lineage. Following RA and BMP-4 treatment, α7⁺ myoblasts failed to fuse and transdifferentiated along an odontogenic pathway expressing DSPP, DSP and ALP activity. RA and BMP-4 treatment induced α1 integrin and αVβ3 integrin expression, and enhanced adhesion and migration on collagen type I substrates. These observations show that α7⁺ myoblasts are pluripotent stem cells capable of differentiation along odontogenic lineages. Following differentiation to odontoblasts, there is a coordinated switch in the integrin expression profile that potentiates adhesion and motility on extracellular matrix molecules. Our results suggest that α⁺ multipotent muscle stem cells may provide a means to enhance new tissue regeneration therapies of cell injection in dentistry. This study was approved by the UCSF Committee on Human Research and Aichi Gakuin University Ethics Committee.