Perivascular Niche and Self-renewal of Dental Pulp Stem Cells

Abstract

Interactions with the microenvironment modulate the fate of stem cells in perivascular niches in tissues (e.g. bone) and organs (e.g. liver). However, the functional relevance of the molecular crosstalk between endothelial cells and stem cells within the perivascular niche in dental pulps is unclear. Here, we tested the hypothesis that endothelial cell-initiated signaling is necessary to maintain self-renewal of dental pulp stem cells. First, we show preferential localization of cells that express high levels of self-renewal stem cell markers (i.e. ALDH1 and Bmi-1) in physiological human dental pulps. Then, through an in vitro functional assay for self-renewal (i.e. secondary orosphere assay), we show that endothelial cell-derived factors promote self-renewal of dental pulp stem cells. Mechanistic studies demonstrated that endothelial cell-derived Interleukin (IL)-6 induces expression of Bmi-1 in dental pulp stem cells through the STAT3 signaling pathway. STAT3-silenced dental pulp stem cells (stably transduced with shRNA-STAT3) seeded in biodegradable scaffolds and transplanted into immunodeficient mice generated fewer perivascular niches comprised of endothelial cells and stem cells exhibiting features of self-renewal. In vitro capillary sprouting assays revealed that inhibition of IL-6 or STAT3 signaling decreases the vasculogenic potential of dental pulp stem cells, suggesting its importance in the establishment of the perivascular niche. Collectively, these data demonstrate that endothelial cell-derived factors mediate self-renewal of dental pulp stem cells through STAT3 signaling and induction of Bmi-1. Overall, these data suggest that a crosstalk between endothelial cells and stem cells within the perivascular niche is required for the maintenance of stem cell pools in dental pulp.