Endogenous retinal neural stem cell reprogramming for neuronal regeneration

In humans, optic nerve injuries and associated neurodegenerative diseases are often followed by perma- nent vision loss. Consequently, an important challenge is to develop safe and effective methods to replace retinal neurons and thereby restore neuronal functions and vision. Identifying cellular and molecular mechanisms allowing to replace damaged neurons is a major goal for basic and translational research in regenerative medicine. Contrary to mammals, the zebrafish has the capacity to fully regenerate entire parts of the nervous system, including retina. This regenerative process depends on endogenous retinal neural stem cells, the Miiller glial cells. Following injury, zebrafish Miiller cells go back into cell cycle to proliferate and generate new neurons, while mammalian Mtiller cells undergo reactive gliosis. Recently, transcription factors and microRNAs have been identified to control the formation of new neurons derived from ze- brafish and mammalian Mtiller cells, indicating that cellular reprogramming can be an efficient strategy to regenerate human retinal neurons. Here we discuss recent insights into the use of endogenous neural stem cell reprogramming for neuronal regeneration, differences between zebrafish and mammalian Mtiller cells, and the need to pursue the identification and characterization of new molecular factors with an instructive and potent function in order to develop theurapeutic strategies for eye diseases.

Ephrin-A2 and-A3 are negative regulators of the regenerative potential of Müller cells

Background In a previous study, we demonstrated that ephrin-A2 and -A3 negatively regulate the growth of neural progenitor cells in the central nervous system. Adult mice deficient in ephrin-A2 and -A3 （A2＋A3＋） displayed active ongoing neurogenesis throughout the brain, and mice deficient in ephrin-A3 alone showed increased proliferation of ciliary epithelium derived retinal stem cells. This study aimed to detect that the increase in proliferation and neurogenic potential of MOiler cells is influenced by the absence of ephrin-A2 and -A3. Methods We assessed the retinal and MOiler cell expression of ephrin-As and their receptor and neural progenitor cell markers by immunostaining and real-time PCR. We cultured purified primary MOiler cells derived from wild-type and A2＋A3＋ mice in a defined culture medium that enables trans-differentiation of Mu11er cells into retinal neurons. To evaluate proliferating MOiler cells in vivo, we injected 5＇-ethylnyl-2-deoxiuridine （EdU） intraperitoneally to adult mice. Results Expression of ephrin-A2/A3 and their receptor EphA4 were detected in the retinas of adult mice, with EphA4 expression particularly enriched in MOiler cells. MOiler cells of A2＋A3＋ mice exhibited significantly elevated expression of retinal progenitor cell markers, Pax6 and Chx10, when compared with those from wild-type mice. Moreover, a higher percentage of Mu11er cells of A2＋A3＋ mice trans-differentiated and became recoverin＋ and β-Ⅲ-tublin＋ in the culture than those from wild type mice. Strikingly, an increased number of EdU＋ retinal cells was detected in the retinas of adult A2＋A3＋ mice as compared with wild-type mice. Conclusions Ephrin-A2 and -A3 are negative regulators of the proliferative and neurogenic potentials of Mu11er cells. Manipulating ephrin-A signaling may thus represent a novel strategy for stimulating neuroregeneration from endogenous progenitors to participate in retinal repair in case of disease or damage.