Reprogramming progeny cells of embryonic RPE to produce photoreceptors: development of advanced photoreceptor traits under the induction of neuroD

¹ Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
² Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States; Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong, China
³ Ophthalmology, University of Alabama at Birmingham, DB104, CEFH, Birmingham, Alabama, 35294-0009, United States

^* To whom correspondence should be addressed. E-mail: szwang{at}uab.edu.

	Abstract

Purpose. To address issues critical to the prospect of producing functional photoreceptors by reprogramming the differentiation of RPE progeny cells, this study examines whether reprogrammed cells can develop highly specialized ultrastructural and physiological traits that characterize retinal photoreceptors. Methods. Cultured chick RPE cells were reprogrammed to differentiate along the photoreceptor pathway by ectopic expression of neuroD. Cellular ultrastructure was examined with electron microscopy. Cellular physiology was studied by monitoring cellular, free calcium (Ca++) levels in dark-adapted cells in response to light and in light-bleached cells in response to 9-cis-retinal. Results. Reprogrammed cells were found to localize red opsin protein appropriately to the apex. These cells developed inner segments rich in mitochondria, and while in culture some formed rudimentary outer segments, analogous to those of developing photoreceptors in the retina. In response to light, reprogrammed cells reduced their Ca++ levels, as observed with developing retinal photoreceptors in culture. Further, upon exposure to 9-cis -retinal, light-bleached, reprogrammed cells increased their Ca++ levels, reminiscent of the visual cycle recovery. Conclusions. These results indicate the potential of reprogrammed cells to develop advanced ultrastructural and physiological traits of photoreceptors and point to reprogramming progeny cells of embryonic RPE as a possible alternative in producing developing photoreceptors.

Key Words: photoreceptor, regeneration, retinal pigment epithelium, Ca++ imaging, light response, 9-cis-retinal