PAX9 Is Involved in Periodontal Ligament Stem Cell-like Differentiation of Human-Induced Pluripotent Stem Cells by Regulating Extracellular Matrix

Periodontal ligament stem cells (PDLSCs) play central roles in periodontal ligament (PDL) tissue homeostasis, repair, and regeneration. Previously, we established a protocol to differentiate human-induced pluripotent stem cell-derived neural crest-like cells (iNCs) into PDLSC-like cells (iPDLSCs) using human PDL cell-derived extracellular matrix (ECM). However, it remained unclear what factors principally regulate the differentiation of iNCs into iPDLSCs. In this study, we aimed to identify the transcription factor regulating production of human PDL cell-derived ECM, which is responsible for the generation of iPDLSCs. We cultured iNCs on ECMs of two human PDL cell lines (HPDLC-3S and HPDLC-3U) and of human dermal fibroblasts (HDF). iNCs cultured on HPDLC-3U demonstrated higher iPDLSC-associated gene expression and mesenchymal differentiation capacity than cells cultured on HDF or HPDLC-3S. The transcription factor PAX9 was highly expressed in HPDLC-3U compared with HDF and HPDLC-3S. iNCs cultured on siPAX9-transfected HPDLC-3U displayed downregulation of iPDLSC-associated marker expression and adipocytic differentiation capacity relative to controls. Our findings suggest that PAX9 is one of the transcription factors regulating ECM production in human PDL cells, which is responsible for the differentiation of iNCs into iPDLSCs.