Loss of the retinal glycocalyx in diabetes

糖尿病患者视网膜糖萼的丧失

基本信息

批准号：
9756387
负责人：
NORMAN R HARRIS
金额：
$ 36.25万
依托单位：
LOUISIANA STATE UNIV HSC SHREVEPORT
依托单位国家：
美国
项目类别：
财政年份：
2016
资助国家：
美国
起止时间：
2016-08-01 至 2021-07-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/9756387
关键词：
Address Adhesions Adult Attenuated Back Binding Blindness Blood Circulation Blood Vessels Blood capillaries CD31 Antigens Cell Adhesion Cell surface Cessation of life Cleaved cell Clinical Development Diabetes Mellitus Diabetic Retinopathy Disease Docking Dropout Emigrations Endothelial Cells Endothelium Enzymes Experimental Models Extracellular Domain Glycocalyx Glycoproteins Glycosaminoglycans Glypican Health Hemorrhage Heparan Sulfate Proteoglycan Heparitin Sulfate Hypoxia Individual Lead Leukocyte Adhesion Molecules Leukocytes Matrix Metalloproteinases Mechanics Mediating Microaneurysm Microcirculation Microvascular Dysfunction Modeling Nitric Oxide Pathology Permeability Plasma Production Proteoglycan Retina Retinal Role Sampling Signal Transduction Site Surface Testing Thick Thrombosis Tissues Tube Vision angiogenesis cotton wool spots cytokine diabetic heparanase neovascularization prevent receptor retina blood vessel structure shear stress syndecan

项目摘要

Diabetic retinopathy, the leading cause of blindness in adults, is recognized as a microvascular complication of the disease, with retinal microvessels characterized by microaneurysms, leukocyte-endothelial cell adhesion, hemorrhages, increased permeability, capillary occlusion, neovascularization, etc. We propose that an underlying contributor to the retinal pathology is the loss of the endothelial surface layer (glycocalyx). The glycocalyx is a dense layer of molecules including proteoglycans (e.g., syndecan-1) and glycosaminoglycans (GAGs, e.g., heparan sulfate). The glycocalyx facilitates the interactions between plasma molecules and their endothelial receptors, inhibits thrombosis, shields against leukocyte-endothelial cell adhesion, transduces shear force, and acts as a permeability barrier. Inasmuch as heparan sulfate can be cleaved by heparanase, and syndecan-1 has multiple sites on its extracellular domain susceptible to cleavage by matrix metalloproteinases (MMPs), we hypothesize a role for these enzymes in the loss of the glycocalyx in diabetes. With a combined attack on both syndecan-1 and heparan sulfate, the functions of the glycocalyx could be substantially lost, which has been shown in many models to enhance leukocyte-endothelial cell adhesion. Such adhesion is thought to promote the occlusion of capillaries in the diabetic retina, leading to the subsequent development of “acellular” capillaries that are no longer perfused, creating ischemic zones. Ultimately, the resulting hypoxia promotes uncontrolled angiogenesis that interferes with clear vision. When a leukocyte adheres to the endothelial surface, it can eventually be coerced back into the bloodstream by shear forces, or alternatively, cross the endothelium (emigrate) into the surrounding tissue in a mechanism mediated by platelet endothelial cell adhesion molecule-1 (PECAM-1). However, loss of PECAM-1 prevents leukocyte emigration, and adherent leukocytes can be trapped within capillaries causing continued occlusion and eventual capillary death. We and others have noted a loss of PECAM-1 from the diabetic retinal microcirculation, with this loss possibly caused by mechanisms such as MMP-mediated cleavage, cytokine- mediated decrease in production, and/or proteasomal degradation. The following specific aims address the overall hypothesis that diabetes induces the loss of key endothelial surface molecules that results in leukocyte adhesion, capillary occlusion, and eventual development of acellular capillaries: (1) Investigate the hypothesis that the loss of heparan sulfate from the diabetic retinal microcirculation is mediated directly by heparanase and indirectly by MMP-facilitated cleavage of syndecan-1, (2) Determine the mechanism(s) responsible for the loss of PECAM-1 from the diabetic retinal microcirculation, by testing for decreased expression, increased proteasomal degradation, and cleavage from the endothelial cell surface, and (3) Investigate the hypothesis that capillary occlusion by leukocytes and the development of acellular capillaries can be attenuated by protection of the endothelial surface layer.

糖尿病视网膜病变是成人失明的主要原因，被认为是一种微血管并发症。该疾病以视网膜微血管的微动脉瘤、白细胞-内皮细胞粘附为特征，出血、通透性增加、毛细血管闭塞、新生血管形成等。我们建议视网膜病理的根本原因是内皮表面层（糖萼）的丧失。糖萼是一层致密的分子，包括蛋白聚糖（例如 Syndecan-1）和糖胺聚糖（GAG，例如硫酸乙酰肝素）糖萼促进血浆分子与其分子之间的相互作用。内皮受体，抑制血栓形成，防止白细胞-内皮细胞粘附，转导剪切力，并充当渗透屏障，因为硫酸乙酰肝素可以被乙酰肝素酶裂解， syndecan-1 的胞外结构域上有多个位点，容易被基质切割金属蛋白酶（MMP），我们研究了这些酶在糖尿病糖萼丢失中的作用。通过对 syndecan-1 和硫酸乙酰肝素的联合攻击，糖萼的功能可能是大量丢失，在许多模型中已显示其可增强白细胞-内皮细胞的粘附。这种粘附被认为会促进糖尿病视网膜毛细血管的闭塞，从而导致随后“无细胞”毛细血管发育，不再灌注，形成缺血区。最终，由此产生的缺氧会促进不受控制的血管生成，从而干扰清晰的视力。白细胞粘附在内皮表面，最终可以通过剪切力迫使其返回血流力，或者以介导的机制穿过内皮（迁移）到周围组织中血小板内皮细胞粘附分子-1 (PECAM-1) 然而，PECAM-1 的缺失会阻止白细胞的产生。迁移，粘附的白细胞可能被困在毛细血管内，导致持续的闭塞和我们和其他人注意到糖尿病视网膜中 PECAM-1 的丢失。微循环障碍，这种损失可能是由 MMP 介导的裂解、细胞因子- 介导的产量减少和/或蛋白酶体降解以下具体目标涉及以下问题。总体假设是糖尿病会导致关键内皮表面分子的丢失，从而导致白细胞粘附、毛细血管闭塞和无细胞毛细血管的最终发育：(1) 研究假设糖尿病视网膜微循环中硫酸乙酰肝素的损失是由乙酰肝素酶直接介导的并间接通过 MMP 促进 syndecan-1 裂解，(2) 确定负责该作用的机制通过测试表达减少，糖尿病视网膜微循环中 PECAM-1 的缺失，增加蛋白酶体降解和内皮细胞表面裂解，以及 (3) 研究假设白细胞的毛细血管闭塞和无细胞毛细血管的发育可以通过保护内皮表层。