Abstract
BackgroundRetinal degeneration is a leading cause of blindness in the world; its etiology is complex and involves genetic defects and stress-associated aging. In addition to gene therapies for known genetically defective retinal degeneration, cellular therapies have been widely explored for restoring vision in both preclinical animal models and clinical trials. Stem cells of distinct tissue sources and their derived lineages have been tested for treating retinal degeneration; most of them were reported to be effective to some extent in restoring/improving deteriorated vision. Whether this visual improvement is due to a functional integration of grafted cells to substitute for lost retinal neurons in recipients or due to their neuroprotective and neurotrophic effects to retain recipient functional neurons, or both, is still under debate.MethodsWe compared the results of subretinal transplantation of various somatic cell types, such as stem cells and differentiated cells, into RhoP23H/+ mice, a retinal degeneration model for human retinitis pigmentosa (RP) by evaluating their optokinetic response (OKR) and retinal histology. We identified some paracrine factors in the media that cultured cells secreted by western blotting (WB) and functionally evaluated the vascular endothelial growth factor Vegfa for its potential neurotrophic and neuroprotective effects on the neuroretina of model animals by intravitreal injection of VEGF antibody.ResultsWe found that live cells, regardless of whether they were stem cells or differentiated cell types, had a positive effect on improving degenerating retinas after subretinal transplantation; the efficacy depended on their survival duration in the host tissue. A few paracrine factors were identified in cell culture media; Vegfa was the most relevant neurotrophic and neuroprotective factor identified by our experiments to extend neuron survival duration in vivo.ConclusionsCellular therapy-produced benefits for remediating retinal degeneration are mostly, if not completely, due to a paracrine effect of implanted cells on the remaining host retinal neurons.
Highlights
Retinal degeneration is a leading cause of blindness in the world; its etiology is complex and involves genetic defects and stress-associated aging
It is speculated that PSCderived target cells restore vision mainly by cell substitution, whereas adult stem cells would rescue vision essentially by paracrine effects because no cell substitution was observed in the grafted eyes [1, 2, 6, 13]
As reported with other bone marrow-derived stromal cells (BMSCs) [24], sphere-derived stem cell (SDSC) could differentiate into neuron-like cells after being cultured in a neural differentiation medium for 3 weeks
Summary
Retinal degeneration is a leading cause of blindness in the world; its etiology is complex and involves genetic defects and stress-associated aging. Age-related macular degeneration (AMD), retinitis pigmentosa (RP), diabetic retinopathy (DR), and glaucomainduced degeneration of retinal ganglion neurons are the major retinal disorders and leading causes for blindness worldwide Their etiologies are distinct and complex and involve genetic defects and stress-associated aging [1, 2]. Stem cell-based therapies are basically targeting the replacement of lost and diseased retinal neurons and retinal pigment epithelium (RPE) cells and have demonstrated their potential in restoring the deteriorated vision in both model animals and clinical trials [2, 6, 7] Whether this visual restoration is due to a functional integration of the grafted cells to substitute for lost retinal neurons in recipients or due to their neuroprotective and neurotrophic effects to retain recipient functional neurons, or both, is still under debate. It is speculated that PSCderived target cells restore vision mainly by cell substitution, whereas adult stem cells would rescue vision essentially by paracrine effects because no cell substitution was observed in the grafted eyes [1, 2, 6, 13]
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