Renal Processing of Albumin

描述(由申请人提供)：白蛋白排泄量增加是多种情况下肾脏损害的指标，包括高血压、糖尿病和衰老。正确认识蛋白尿的发病机制是解释其在不同情况下的意义以及设计合适的治疗方法的先决条件。目前关于小分子和大分子如何分离的一种观点认为，大分子的主要物理屏障是足细胞裂隙隔膜(SD)，肾小球基底膜(GBM)充当粗大的预过滤器。另一种观点将肾小球选择性归因于基底膜中存在不同大小的毛孔。2003年，我提出了凝胶渗透/扩散假说和计算机模拟假说，假设肾小球基底膜是肾脏大小选择性的主要来源，因为大分子可以渗透到基底膜(一种浓缩凝胶)中的空间有限。肾小球滤过率(GFR)清楚地控制着所有跨肾小球的水传输，但我和其他人的计算表明，决定特定目的的是扩散而不是过滤：(I)将通过使用透射电子显微镜直接确定纳米颗粒和不同尺寸的纳米颗粒标记的蛋白质是否达到凝胶渗透方程预测的GBM中的浓度，来检验渗透/扩散假说的主要假设。最初的实验将在体外用纯化的GBM进行；稍后的实验将在动物身上进行。为了测试扩散假设，我们将按照Ryan和Karnovsky(1976)使用的类似方案，评估当肾动脉被临时夹住时标记蛋白的肾脏分布。特殊目的(II)将检验当GFR显著降低时将出现蛋白尿的预测。我们的初步数据显示，在正常小鼠中，高剂量的血管紧张素转换酶和/或环氧合酶抑制剂会导致暂时的可逆性蛋白尿，低盐饮食会加剧这种情况。我们将进行实验，以确定导致这种蛋白尿的因素，以及是否可以通过减少GFR而在不损害基底膜、足细胞或小管的情况下实现这一目标。公共卫生相关性个人尿白蛋白的出现(蛋白尿)表明肾脏有问题。因此，了解肾脏中的哪些变化会导致蛋白尿，对于设计适当的治疗方法至关重要。我们最近提出了一个新的假说，挑战了目前关于蛋白尿原因的观点，并提议进行实验来验证这一假说。

DESCRIPTION (provided by applicant): Increased albumin excretion is an indicator of renal damage in a wide variety of conditions, including hypertension, diabetes and aging. Correctly understanding the pathogenesis of albuminuria is prerequisite for interpreting its significance in different conditions, and for designing appropriate therapies. One current view of how the separates small and large molecules assumes that the major physical barrier to macromolecules is the podocyte slit diaphragm (SD) with the glomerular basement membrane (GBM) acting as a coarse pre-filter. Another view ascribes glomerular selectivity to the presence in the GBM of pores of different sizes. In 2003, I proposed a gel permeation/diffusion hypothesis and computer simulation postulating that the GBM is the predominant source of the size selectivity of the kidney, because there is limited space in the GBM (a concentrated gel) into which macro-molecules can permeate. The glomerular filtration rate (GFR) clearly governs all trans-glomerular water transport, but calculations by me and others indicate that diffusion rather than filtration governs Specific Aim (i) will test the primary assumption of the permeation/diffusion hypothesis by directly determining with transmission electron microscopy whether nanoparticles and nanoparticle-tagged proteins of different sizes reach the concentrations in the GBM predicted by a well proven gel permeation equation. Initial experiments will be in vitro with purified GBM; later experiments will be in animals. To test the diffusion postulate we will evaluate the renal distribution of tagged proteins when the renal artery is temporarily clamped following a protocol comparable to that used by Ryan & Karnovsky (1976). Specific Aim (ii) will test the prediction that albuminuria will develop when GFR is substantially decreased. Our preliminary data show that in normal mice angiotensin converting enzyme and/or cyclooxygenase inhibitors in high dose cause temporary reversible albuminuria, exacerbated by a low salt diet. We will carry out experiments to determine the factors leading to this albuminuria, and whether it can be achieved by a decrease in GFR without damaging the GBM, podocytes or tubules. PUBLIC HEALTH RELEVANCE The occurrence of albumin in the urine of an individual (albuminuria) indicates that something is wrong with the kidney. Understanding what changes in the kidney lead to albuminuria is therefore essential for designing proper treatments. We have recently advanced a novel hypothesis that challenges current views on the causes of albuminuria, and are proposing experiments to test this hypothesis.