Directing adult human periodontal ligament-derived stem cells to retinal fate.

PURPOSE: To investigate the retinal fate competence of human postnatal periodontal ligament (PDL)-derived stem cells (PDLSC) through a directed differentiation mimicking mammalian retinogenesis.
METHODS: Human teeth were collected from healthy subjects younger than 35 years old. Primary PDLSC were isolated by collagenase digestion and cultivated. PDLSC at passage 3 were cultured in the induction media containing Noggin (antagonist of bone morphogenic protein) and Dkk-1 (antagonist of Wnt/β-catenin signaling). Gene expression of neural crest cells, retinal progenitors, and retinal neurons, including photoreceptors, was revealed by RNA analyses, immunofluorescence, and flow cytometry. The neuronal-like property of differentiated cells in response to excitatory glutamate was examined by fluo-4-acetoxymethyl calcium imaging assay.
RESULTS: Primary human PDLSC stably expressed marker genes for neural crest (Notch1, BMP2, Slug, Snail, nestin, and Tuj1), mesenchymal stem cell (CD44, CD90, and vimentin), and embryonic stem cell (c-Myc, Klf4, Nanog, and SSEA4). Under low attachment culture, PDLSC generated neurospheres expressing nestin, p75/NGFR, Pax6, and Tuj1 (markers of neural progenitors). When neurospheres were plated on Matrigel-coated surface, they exhibited rosette-like outgrowth. They expressed eye field transcription factors (Pax6, Rx, Lhx, Otx2). By flow cytometry, 94% of cells were Pax6(nuclear)Rx(+), indicative of retinal progenitors. At prolonged induction, they expressed photoreceptor markers (Nrl, rhodopsin and its kinase) and showed significant responsiveness to excitatory glutamate.
CONCLUSIONS: Primary human PDLSC could be directed to retinal progenitors with competence for photoreceptor differentiation. Human neural crest-derived PDL is readily accessible and can be an ample autologous source of undifferentiated cells for retinal cell regeneration.