Herbert J, Cavallaro T, Martone R
Department of Neurology, Columbia University, College of Physicians and Surgeons, New York City, NY.
Invest Ophthalmol Vis Sci. 1991 Feb;32(2):302-9.
Although a constant supply of retinol is a critical requirement for the visual cycle, the molecular mechanisms underlying retinol delivery, uptake, storage, and transport in the eye are not well understood. Previously the synthesis of serum retinol-binding protein (RBP) in the mammalian eye was reported. Now the distribution of RBP and RBP mRNA in the rat eye has been studied by immunohistochemical and in situ hybridization techniques has been studied. The RBP mRNA was present only in the cytoplasm of retinal pigment epithelial (RPE) cells, terminating abruptly at the pars plana. On the other hand, RBP immunoreactivity was more widespread. The most intense immunostaining was present in retinal ganglion cells, the corneal endothelium, and under certain conditions of tissue fixation, the corneal epithelium. Consistent but less intense immunoreactivity was detected in the photoreceptors, Müller cells, inner plexiform layer, ciliary epithelium and stroma, iris epithelium, retinal pigment epithelium, lacrimal glandular epithelium, and periorbital soft tissues. These findings suggest that RBP synthesized by the RPE may be secreted to various ocular locations. However, at present, uptake from plasma cannot be excluded as another possible source of ocular RBP. In the plasma, holo-RBP (the retinol-RBP complex) is transported in complex with another plasma protein, transthyretin (TTR). This substance is also synthesized by the RPE and its distribution in the eye is similar to that described for RBP. Taken together, these findings support the proposal that ocular RBP and TTR may function cooperatively in the intraocular translocation of retinol.
尽管持续供应视黄醇对视循环至关重要，但视黄醇在眼内的递送、摄取、储存和运输的分子机制尚未完全明了。此前曾报道哺乳动物眼中血清视黄醇结合蛋白（RBP）的合成。现在，已通过免疫组织化学和原位杂交技术研究了RBP及其mRNA在大鼠眼中的分布。RBP mRNA仅存在于视网膜色素上皮（RPE）细胞的细胞质中，在锯齿缘处突然终止。另一方面，RBP免疫反应性分布更为广泛。最强的免疫染色出现在视网膜神经节细胞、角膜内皮，以及在特定组织固定条件下的角膜上皮中。在光感受器、穆勒细胞、内网层、睫状体上皮和基质、虹膜上皮、视网膜色素上皮、泪腺上皮和眶周软组织中检测到一致但较弱的免疫反应性。这些发现表明，由RPE合成的RBP可能分泌到眼内的各个部位。然而，目前不能排除从血浆摄取是眼内RBP的另一个可能来源。在血浆中，全RBP（视黄醇-RBP复合物）与另一种血浆蛋白甲状腺素转运蛋白（TTR）结合运输。这种物质也由RPE合成，其在眼中的分布与RBP相似。综上所述，这些发现支持了眼内RBP和TTR可能在视黄醇的眼内转运中协同发挥作用的观点。
