Stenkamp D L, Adler R
Johns Hopkins University School of Medicine, Baltimore, MD 21287-9257.
Exp Eye Res. 1994 Jun;58(6):675-87. doi: 10.1006/exer.1994.1065.
Biological functions of retinoids in the vertebrate retina include the role of 11-cis retinaldehyde as visual pigment chromophore, and possible effects of retinoic acid in histogenesis and cell survival. Qualitative and quantitative regulation of retinoid availability for these complex processes could involve several cell types, including retinal pigment epithelium, Müller glia and retinal photoreceptors and non-photoreceptor neurons; their relative contributions, however, have not been fully elucidated. Using purified cultures, we have carried out a study of cell-type-specific metabolism and storage of retinoids in chick embryo retinal photoreceptors and other neuronal cells, as compared to those of retinal glia. Retinal glia were found to synthesize both retinoic acid and retinyl esters, and to hydrolyse the latter; they also displayed retinol dehydrogenase activities. Cultured neurons and photoreceptors also synthesized and hydrolysed retinyl esters; their capacity for retinaldehyde synthesis from a retinol or retinyl ester substrate suggested the presence of retinol dehydrogenase activity. Retinoic acid was not synthesized in differentiated neuronal cultures, although some synthesis was detectable at early culture stages when the cells were still morphologically undifferentiated. These findings indicate that cell-type-specific metabolic activities are expressed during retinal cell differentiation in vitro, and that embryonic retinal photoreceptors and nonphotoreceptor neurons are active participants in the metabolism and storage of retinoids.
类视黄醇在脊椎动物视网膜中的生物学功能包括11-顺式视黄醛作为视觉色素发色团的作用，以及视黄酸在组织发生和细胞存活中的可能作用。对于这些复杂过程，类视黄醇可用性的定性和定量调节可能涉及多种细胞类型，包括视网膜色素上皮、米勒胶质细胞、视网膜光感受器和非光感受器神经元；然而，它们的相对作用尚未完全阐明。与视网膜神经胶质细胞相比，我们利用纯化培养物对鸡胚视网膜光感受器和其他神经元细胞中类视黄醇的细胞类型特异性代谢和储存进行了研究。发现视网膜神经胶质细胞既能合成视黄酸和视黄酯，又能水解视黄酯；它们还表现出视黄醇脱氢酶活性。培养的神经元和光感受器也能合成和水解视黄酯；它们从视黄醇或视黄酯底物合成视黄醛的能力表明存在视黄醇脱氢酶活性。在分化的神经元培养物中未合成视黄酸，尽管在细胞形态仍未分化的早期培养阶段可检测到一些合成。这些发现表明，细胞类型特异性代谢活动在体外视网膜细胞分化过程中得以表达，并且胚胎视网膜光感受器和非光感受器神经元是类视黄醇代谢和储存的积极参与者。
