Abstract
Purpose: :
Induced pluripotent stem (iPS) cells differentiate into cell types of all three embryonic lineages and therefore represent a renewable source for sustaining ex-vivo cell therapy to treat intractable degenerative diseases. Previously, we had shown that mouse fibroblast iPS cells, reprogrammed by forced expression of exogenous transcription factors, have the potential to generate both early and late born retinal cells (Parameswaran et al., 2010, Stem Cells, 28: 695-703). Here, we demonstrate the potential of iPS cells, derived from adult limbal progenitors (=limbal iPS cells) by non-cell autonomous reprogramming, to generate RGCs.
Methods: :
Rat limbal progenitors were reprogrammed into iPS cells as previously described (Balasubramanian et al., 2009, Stem cells, 27:3053-3062) and subjected to standard neural induction protocol for embryonic stem (ES) cells. Following neural induction, cells were cultured in the presence of Noggin and FGF2 to enrich retinal progenitors. Limbal iPS cell-derived retinal progenitors were cultured in the presence of rat E14 retinal cell conditioned medium (E14CM), BDNF, and GDNF to generate RGCs. RGCs were identified by their ability to express RGC-specific regulators and markers, and their target specificity.
Results: :
Limbal iPS cell-derived progenitors, besides expressing pan neural progenitor markers such as Nestin and Musashi, expressed eye field genes such as Pax6, Rx, Lhx2, and Six3. When cultured in E14CM these cells acquired elaborate neuronal morphology and expressed Ath5, the basic helix loop helix (bHLH) transcription factor critical for the specification of RGCs and Brn3b, the homeodomain transcription factor necessary for their maturation. In addition, neuronal cells expressing RGC markers extended processes to superior colliculus and not inferior colliculus explants, demonstrating their target specificity. Results of their in vivo RGC differentiation following transplantation in the experimental model of glaucoma will be presented.
Conclusions: :
Limbal iPS cells can serve as a renewable source of RGCs for formulating cell or small molecule-based approaches to treat glaucomatous retinal degeneration.
Keywords: retina • ganglion cells • superior colliculus/optic tectum