ROLE OF RETINAL PIGMENT EPITHELIUM IN RETINAL DISORDERS

视网膜色素上皮（RPE）是存在于视网膜和脉络膜之间的单层细胞片，对于视网膜的正常功能至关重要。 视网膜的许多炎性、感染性和遗传性疾病与RPE的变性和/或功能障碍有关。 我们建立了人视网膜色素上皮细胞培养系统，并将其作为研究视网膜色素上皮在视网膜疾病病理生理学中的各种作用的模型。由于TGF-β与视网膜增生性疾病、炎症性疾病和感染性疾病有关，因此我们将注意力集中在TGF-β上。TGF-β在玻璃体、视网膜和RPE中的高表达与视网膜纤维化和脉络膜新生血管形成密切相关。 此外，临床研究表明TGF-β在治疗黄斑裂孔中的潜在用途。我们以前曾报道过炎症细胞因子对TGF-β表达的调节。 IL-1和TNF-α促进TGF-β 1和TGF-β 2的分泌。 IFN-g可促进RPE细胞TGF-β_1的表达，抑制TGF-β_2的分泌。IFN-g对TGF-β 1和TGF-β 2的对比作用表明TGF-β 1和TGF-β 2在视网膜炎性疾病中的不同作用。脉络膜新生血管（CNV）是老年性黄斑变性（ARMD）的主要病变之一，ARMD是老年人视力损害的主要原因。由于血管内皮生长因子（VEGF）与CNV相关，我们检测了VEGF在RPE中的表达。在测试的各种细胞因子中，发现TGF-β是VEGF的有效诱导剂。 VEGF的分泌在1 ng/ml浓度时达到最大值，并分别被mRNA转录和翻译抑制剂放线菌素D和环己脲完全抑制。 RT-PCR分析表明RPE中存在121、165和189个氨基酸的VEGF异构体，其被TGF-β上调。 放线菌素D显著抑制TGF-β诱导的VEGFmRNA表达，提示TGF-β在转录水平的作用。通过使用特异性信号转导抑制剂，我们发现TGF-β通过MAPK和smad 2和smad 4途径转录激活VEGF。TGF-β对VEGF表达的调节强烈提示TGF-β在ARMD的CNV中起重要作用。

Retinal pigment epithelium (RPE), a single layer of sheet of cells present between the retina and choroid, is vital for the normal functioning of the retina. Many of the inflammatory, infectious and hereditary diseases of the retina are associated with the degeneration and /or dysfunction of RPE. We have developed human RPE cell culture system and used as a model to investigate the various roles of RPE in the pathophysiology of retinal disorders. We have focussed our attention on transforming growth factor-beta (TGF-b), since TGF-b is involved in retinal disorders of proliferative, inflammatory and infectious etiology. Elevated expression of TGF-b in vitreous, retina and RPE has been closely correlated with the retinal fibrosis and choroidal neovascularization. Furthermore, clinical studies indicated potential use of TGF-b for the treatment of macular holes. We have previously reported the regulation of TGF-b expression by inflammatory cytokines. IL-1 and TNF-a enhanced the secretion of both TGF-b1 and TGF-b2. Enhancement of TGF-b1 and inhibition of TGF-b2 expression and secretion by IFN-g was observed in RPE cells. The contrasting effects of IFN-g on TGF-b1 and TGF-b2 suggest differential roles of TGF-b1 and TGF-b2 in the inflammatory diseases of the retina. Choroidal neovascularization (CNV) is one of the major events in the age related macular degeneration (ARMD), a leading cause of visual impairment in the aged population. Since vascular endothelial growth factor (VEGF) is associated with CNV, we have examined the expression of VEGF in RPE. Of various cytokines tested, TGF-b was found to be the potent inducer of VEGF. The Secretion of VEGF was maximal at 1ng/ml concentration and is completely abolished by actinomycin-D and cyclohexamide, inhibitors of transcription and translation of mRNA respectively. RT-PCR analyses indicated the presence of 121,165 and 189 aa isoforms of VEGF in RPE, which are upregulated by TGF-b. Actinomycin-D significantly inhibited TGF-b induced VEGF mRNA expression suggesting the action of TGF-b at transcriptional level. By using specific inhibitors of signal transduction, we found that TGF-b transcriptionally activate VEGF through MAPK and smad2 and smad4 pathway. Regulation of the expression of VEGF by TGF-b strongly suggests an important role for TGF-b in CNV in ARMD.