Raats C J, Van Den Born J, Berden J H
Division of Nephrology, University Hospital St. Radboud, Nijmegen, The Netherlands.
Kidney Int. 2000 Feb;57(2):385-400. doi: 10.1046/j.1523-1755.2000.00858.x.
Heparan sulfate (HS) is the anionic polysaccharide side chain of HS proteoglycans (HSPGs) present in basement membranes, in extracellular matrix, and on cell surfaces. Recently, agrin was identified as a major HSPG present in the glomerular basement membrane (GBM). An increased permeability of the GBM for proteins after digestion of HS by heparitinase or after antibody binding to HS demonstrated the importance of HS for the permselective properties of the GBM. With recently developed antibodies directed against the GBM HSPG (agrin) core protein and the HS side chain, we demonstrated a decrease in HS staining in the GBM in different human proteinuric glomerulopathies, such as systemic lupus erythematosus (SLE), minimal change disease, membranous glomerulonephritis, and diabetic nephropathy, whereas the staining of the agrin core protein remained unaltered. This suggested changes in the HS side chains of HSPG in proteinuric glomerular diseases. To gain more insight into the mechanisms responsible for this observation, we studied GBM HS(PG) expression in experimental models of proteinuria. Similar HS changes were found in murine lupus nephritis, adriamycin nephropathy, and active Heymann nephritis. In these models, an inverse correlation was found between HS staining in the GBM and proteinuria. From these investigations, four new and different mechanisms have emerged. First, in lupus nephritis, HS was found to be masked by nucleosomes complexed to antinuclear autoantibodies. This masking was due to the binding of cationic moieties on the N-terminal parts of the core histones to anionic determinants in HS. Second, in adriamycin nephropathy, glomerular HS was depolymerized by reactive oxygen species (ROS), mainly hydroxyl radicals, which could be prevented by scavengers both in vitro (exposure of HS to ROS) and in vivo. Third, in vivo renal perfusion of purified elastase led to a decrease of HS in the GBM caused by proteolytic cleavage of the agrin core protein near the attachment sites of HS by the HS-bound enzyme. Fourth, in streptozotocin-induced diabetic nephropathy and during culture of glomerular cells under high glucose conditions, evidence was obtained that hyperglycemia led to a down-regulation of HS synthesis, accompanied by a reduction in the degree of HS sulfation.
硫酸乙酰肝素（HS）是存在于基底膜、细胞外基质和细胞表面的HS蛋白聚糖（HSPG）的阴离子多糖侧链。最近，聚集蛋白被鉴定为肾小球基底膜（GBM）中存在的一种主要HSPG。用肝素酶消化HS后或抗体与HS结合后，GBM对蛋白质的通透性增加，这表明HS对GBM的选择通透性特性很重要。利用最近开发的针对GBM HSPG（聚集蛋白）核心蛋白和HS侧链的抗体，我们发现在不同的人类蛋白尿性肾小球病，如系统性红斑狼疮（SLE）、微小病变病、膜性肾小球肾炎和糖尿病肾病中，GBM中HS染色减少，而聚集蛋白核心蛋白的染色保持不变。这表明蛋白尿性肾小球疾病中HSPG的HS侧链发生了变化。为了更深入了解导致这一观察结果的机制，我们在蛋白尿的实验模型中研究了GBM HS（PG）的表达。在小鼠狼疮性肾炎、阿霉素肾病和活动性海曼肾炎中发现了类似的HS变化。在这些模型中，GBM中的HS染色与蛋白尿之间存在负相关。从这些研究中，出现了四种新的不同机制。第一，在狼疮性肾炎中，发现HS被与抗核自身抗体复合的核小体掩盖。这种掩盖是由于核心组蛋白N端部分的阳离子部分与HS中的阴离子决定簇结合。第二，在阿霉素肾病中，肾小球HS被活性氧（ROS），主要是羟基自由基解聚，这在体外（HS暴露于ROS）和体内都可以被清除剂阻止。第三，体内灌注纯化的弹性蛋白酶导致GBM中HS减少，这是由于HS结合酶在HS附着位点附近对聚集蛋白核心蛋白进行蛋白水解切割所致。第四，在链脲佐菌素诱导的糖尿病肾病以及高糖条件下肾小球细胞培养过程中，有证据表明高血糖导致HS合成下调，同时HS硫酸化程度降低。
