Abstract
Abstract: :
Purpose: RPE cells and neuroretinal cells are derived from the same sheet of neuroepithelium during development. Under certain conditions, RPE cells can be induced to differentiate into retinal neuronal cells. We have previously reported transdifferentiation of the human RPE cell line (ARPE–19) by fenretinide, a synthetic retinoid (Chen et al., 2003). The differentiated cells had neuronal cell morphology and increased expression of neuronal markers, such as N–CAM, calretinin and neurofilaments. The purpose of this study was to determine whether the differentiated cells acquire neuronal cell function and the possible mechanism involved in fenretinide–induced neuronal differentiation. Methods: ARPE–19 cells were transformed into neuronal phenotype cells by treating with 1µM fenretinide as previously described (Chen et al., 2003). Total RNA was extracted from control and treated cells for RT–PCR analysis in order to determine the involvement of the retinoic acid receptor pathway in ARPE–19 cell neuronal differentiation. Immunohistochemical analysis using antibodies against retinoid receptors (RAR–α, RAR–ß or RXR–ß) were applied to both control and treated cells. The neuronal function of differentiated cells was tested using a voltage probe (oxonol, DiBaC4(5)) to detect membrane potential changes induced by the neurotransmitters GABA and glutamate. Results: Fenretinide treatment changed RAR and RXR mRNA and protein expression in ARPE–19 cells. RT–PCR analysis showed that RAR–γ and RXR–ß mRNA are up–regulated after 3 hours of fenretinide treatment. Immunocytochemical analysis revealed that RXR–ß receptor protein in ARPE–19 cells was increased after 5 days of fenretinide treatment. Voltage probe recordings showed that some fenretinide–treated ARPE–19 cells had cell membrane responses different from that of the control cells. We observed that 4 out of 25 plates of treated cells showed either a delayed GABA response, or a delayed glutamate response. These responses were not seen in the control cells. Conclusions: The regulation of RAR and RXR receptors by fenretinide suggests that fenretinde–induced neuronal differentiation of ARPE–19 cells is mediated by RAR and RXR receptor pathways. The presence of GABA and glutamate responses on some of the treated cells revealed by physiological recordings suggests that the fenretinide–induced differentiated cells may possess a neuron–like function. Ref: Chen et al., J. Neurochemistry, 2003, 84, 972–981.
Keywords: electrophysiology: non–clinical • retinoids/retinoid binding proteins • retinal pigment epithelium