Methods: DPSC and MSC were isolated from rat incisors and femurs, respectively. Stem cells at passage 2-4 were then tested in in vitro and in vivo adult rat retinal ganglion cell (RGC) injury models. Following co-culture with axotomized RGC, neuronal survival and neuritogenesis was analysed using βIII-tubulin immunostaining. For the in vivo studies, DPSC and MSC were transplanted into the vitreous body of the eye following surgically-induced optic nerve crush injury that axotomises RGC. Optical coherence tomography (OCT) was used to monitor RGC survival over time. RGC axonal regeneration was quantified 21 days post-lesion using immunohistochemical methods.
Results: When co-cultured with injured RGC, DPSC significantly enhanced cell survival and neurite outgrowth compared with RGC cultured alone or RGC co-cultured with bone marrow-derived MSC. The neuroprotective and pro-regenerative effects of the DPSC were abolished by Trk receptor blockers, suggesting involvement of paracrine neurotrophins produced by the DPSC. Consistent with these findings, enzyme-immunoassays indicated the secretion of significantly higher titres of the neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and NT-3 by DPSC than that produced by bone marrow MSC. Finally, in vivo intravitreal DPSC transplantation after optic nerve crush injury resulted in significant protection of RGC from apoptosis and regeneration of their axons, as analysed by Brn3a and growth-associated protein-43 immunostaining.
Conclusion: This study highlights the potential of DPSC as a cellular paracrine therapy for treating damaged neurons by providing a supportive neuroprotective/axogenic trophic environment.