Abstract
Purpose: :
We have demonstrated that the Muller cells in the mammalian retina are latent stem cells, capable of differentiating into early (ganglion cells) and late (rod photoreceptors) born retinal neurons in vitro and in vivo (Das et al., 2006, Dev. Biol. 299:283), raising the prospect of Muller cell-based regenerative repair of diseased retina. We have begun an evaluation of the regenerative capacity of Muller stem cells in animal models of photoreceptor degeneration (MNU-treated rats, rd mice, S334ter rats) in vivo. To study the regenerative process in controlled conditions the study was carried out in retinal explant culture as well.
Methods: :
To study regeneration in chemically induced degeneration model animals were injected intraperitoneally with N-methyl-N-nitrosourea (MNU, 75mg/body weigh) to damage photoreceptors. MNU-treated animals or genetic model of photoreceptor degeneration received intraocular injection of Wnt3A, Jagged1 and Shh with BrdU to activate Muller stem cells. Morphological and immunohistochemical analysis of the retina was carried out at 4-7 days to examine the efficiency of the activation of Muller stem cells and at 8-14 days to detect Muller stem cells differentiation into rods. Similar treatment was simulated in explant culture of retina obtained from rd mice.
Results: :
In both in vivo and retinal explants, the activation of Wnt, Notch and Shh pathways lead to an increase in the number of BrdU+ cells expressing different Muller cell markers, compared to controls. Not all Muller cells incorporated BrdU, confirming our previous observations that only a subset of Muller cells possesses stem cell properties. The proliferating Muller cells were localized in the inner retina at the end of the 4th day following the treatment. At the 8th day we observed some BrdU+ Muller cells in the outer retina and a subset of them were positive for immunoreactivities corresponding to rods.
Conclusions: :
Our results confirm the stem cell properties and regenerative capacity of Muller cells in different animal models. The effect of Notch, Wnt and Shh signaling on the efficiency of Muller cell mediated retinal regeneration will be presented.
Keywords: Muller cells • regeneration • signal transduction