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Carolina B. Del Debbio, Sowmya Parameswaran, Iqbal Ahmad; Neurogenic Potential Of Mammalian Muller Stem Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2234.
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We have previously demonstrated that a subset of Muller cells in adult rat retina represent a latent stem cell population with neuorogenic potential (Das et al., 2006, Dev. Biol. 299:283) and recently observed that these cells can be activated through Notch and Wnt pathways towards their differentiation along rod photoreceptor lineage in vitro and in vivo (Del Debbio et al., 2010, PLoSOne 5:e12425). However, the neurogenic efficiency of Muller stem cells was low. To address this barrier to therapeutic regeneration we have began a systematic analysis of conditions and putative mechanisms that regulate Muller stem cells in vitro.
Enriched Muller cells were subjected to neurospheres culture assays in which Notch/Wnt/Shh/BMP/FGF pathways were perturbed alone or in combinations. Frequency, size, proliferation index, and Muller/neurogenic/retinal properties of neurospheres were examined. Expression of pluripotent genes was examined to determine de-differentiation. Finally, Muller stem cells were cultured in simulated environments of early and late histogenesis for analyzing their ability to generate early- and late-born retinal neurons.
Neurospheres were formed in all conditions studied. However, neurospheres generated in the condition of activated Notch and Wnt signaling were relatively larger in size compared to those generated in other conditions. The perturbation of Shh/BMP signaling had no noticeable effect on the frequency and size of neurospheres. Cells in neurospheres acquired the expression of neural progenitor and eye field genes. In contrast, expression of Muller cell markers, and cell cycle regulator, p27Kip1 decreased. Dedifferentiation was hinted by a low level expression of pluripotent genes, particularly cMyc and Lin28. Preliminary results suggest that BMP signaling inhibition facilitated neurogenic properties. The resulting neural progenitors differentiated along both early and late retinal cell lineages with consequent down regulation of REST, a transcriptional repressor of neuronal differentiation.
Neurogenic potential of Muller stem cells is regulated by both cell-intrinsic and cell-extrinsic factors.
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