介导VLDLR调节Wnt通路—非诺贝特治疗糖尿病视网膜病变的机制研究

Diabetic retinopathy (DR), leading to severe visual impairment, is the most feared complication by people with diabetes. So far, the strategies to treat DR are limited and not completely successful. Two independent clinical studies have reported that fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist, has robust therapeutic effects on microvascular complications of diabetes, including DR in type 2 diabetic patients. Further more，we found that topical application of fenofibrate eyedrop attenuated retinal vascular leakage, and ameliorated inflammation in the experimental diabetic models and prevented retinal neovascularization in the OIR and CNV models, which showed the therapeutic potential of fenofibrate eyedrop in preventing DR. However, the mechanism underlying its beneficial effect on DR has not been established. Some relative studies showed that Wnt signaling activation plays a pathogenic role in DR animal models, and that the very low-density lipoprotein receptor (VLDLR) is a key negative regulator of the Wnt signaling pathway. .Based on these findings, we hypothesize that fenofibrate directly prevents DR in diabetes, through inhibition of the Wnt pathway via up-regulation of VLDLR by PPARA activation. .We propose the following specific aims to test our hypothesis: (1) Define that fenofibrate is an inhibitor of the Wnt pathway in the retina. We will examine if fenofibrate inhibits Wnt signaling activation induced by hypoxia in retinal cells and in diabetic TOPGAL transgenic mice. (2) Determine if Wnt inhibition by fenofibrate is dependent on VLDLR up-regulation in the retina. We will observe that if fenofibrate lost the Wnt inhibitory activity and retinal protection effects in Vldlr-/- mice and in cultured retinal cells cell. (3) Determine if the up-regulation of VLDLR by fenofibrate is through PPARα activation in the retina. We will observe that if VLDLR expression depends on PPARα activation in cultured retinal cells, and if knock-down of PPARα abolishes fenofibrate’s VLDLR up-regulation function in retinal endothelial cells. .This project will for the first time establish the connection of PPARα with Wnt signaling. It will also reveal the target of the only effective oral drug for DR, which may also have the therapeutic potential of topical application. These mechanistic studies may also suggest potential use of fenofibrate or related drugs for other angiogenic diseases.

糖尿病视网膜病变（DR）是一种难治性、致盲性眼病，目前治疗方法有限。最近发表于The Lancet的文章，通过对9795名糖尿病患者的研究发现，口服非诺贝特可显著减缓DR进程；随后该药在澳大利亚获批用于治疗DR，但其机制不明。动物实验结果提示：非诺贝特滴眼液可改善动物的视网膜病变；Wnt信号通路过度激活，可使动物模型出现类似DR的病理改变；极低密度脂蛋白受体（VLDLR）是Wnt通路上游的负向调节因子。基于以上结果，本课题拟对DR动物模型玻璃体腔注射非诺贝特，以及体外的视网膜内皮细胞中，检测非诺贝特可否通过介导VLDLR抑制视网膜Wnt信号通路；当VLDLR缺失时，该抑制作用是否也随之消失。结果将揭示非诺贝特治疗DR的机制，是否符合我们提出的假设——“直接作用于视网膜，激活PPARα从而抑制Wnt信号通路，该抑制作用依赖于VLDLR的介导”，为DR的治疗提供新靶点和更为安全有效的给药方式。

糖尿病视网膜病变（DR）是一种难治性、致盲性眼病，目前治疗方法有限。研究发现口服非诺贝特可显著减缓DR进程，但其机制不明。动物实验结果提示：非诺贝特滴眼液可改善动物的视网膜病变；Wnt信号通路过度激活，可使动物模型出现类似DR的病理改变；极低密度脂蛋白受体（VLDLR）是Wnt通路上游的负向调节因子。因此，本课题在体外视网膜内皮细胞和DR动物模型中，发现检测非诺贝特通过介导VLDLR抑制视网膜内皮细胞Wnt信号通路；当VLDLR缺失时，该抑制作用是否也随之消失。该结果表明在视网膜内皮细胞中，非诺贝特通过激活PPARα从而抑制Wnt信号通路，该抑制作用依赖于VLDLR的介导，为DR的治疗提供新靶点。另外，有研究显示PPARα的激动剂非诺贝特可以抑制甲状腺相关眼病(Thyroid Associated Orbitopathy, TAO）患者原代成纤维细胞中的免疫调节因子，从而参与TAO的发病过程；Wnt信号通过参与了TAO的病理生理过程，在TAO患者和正常对照中，Wnt信号通路的某些关键因子有显著差异。但是非诺贝特调节TAO的原理并不明确。因此本课题也研究了非诺贝特调节TAO的过程是否通过Wnt信号通路实现。研究结果表明，在TAO成纤维细胞中，非诺贝特可以通过激活PPARα，抑制Wnt信号通路，降低炎症因子。