Role of proteolytic suPAR fragment in insulin dependent diabetes and kidney disease

慢性肾脏病（CKD）的全球流行正在以惊人的速度发展。CKD影响美国估计有3700万人（占成年人口的15%;超过七分之一的成年人），并且这个数字在过去二十年中增加了一倍多。与肾脏有关的疾病正在迅速摆脱目前的治疗选择和资源。CKD的三种常见病因是糖尿病、高血压和肾小球肾炎。我们和其他人认为可溶性尿激酶激活受体（suPAR）是CKD发病和进展的重要危险因素之一，无论其病因如何。除了其作为生物标志物的作用，我们和其他人已经表明，suPAR是一种致病/瘢痕形成因子，其通过激活足细胞上的整合素suPAR β 3而成为足细胞损伤的基础。足细胞是终末分化的细胞，对维持肾滤器的特异性至关重要。我们的初步数据表明，血浆中suPAR的蛋白水解片段，D2 D3片段的存在通过激活足细胞上的整合素β 2 β 3诱导肾小球损伤。此外，非常出乎意料的是，我们的初步研究表明，D2 D3片段也损伤胰腺的胰岛细胞。总之，这些见解提出了一个假设，即循环D2 D3片段同时导致肾脏和胰腺两个器官的损伤。我们在三个具体目标中检验了这一假设。在具体目标1中，我们通过检查D2 D3-Tg小鼠的器官功能来定义D2 D3诱导肾脏和胰腺损伤的生理机制，这些小鼠接受肾毒性血清或阿霉素的常规和高脂饮食。此外，我们将D2 D3-Tg小鼠与非肥胖糖尿病（NOD）小鼠杂交以检查胰腺损伤后的协同作用。抗suPAR抗体和靶向调节性GTP酶（发动蛋白、Cdc 42、Rac 1）的小分子（其作用将在目标2和3中阐明）将作为潜在治疗剂进行测试。由于D2 D3-Tg小鼠表现出双器官损伤，因此还将研究靶向不同细胞类型中不同途径的联合治疗。在具体目标2中，我们研究了在存在和不存在脂毒性刺激或高葡萄糖水平的情况下，D2 D3片段对肌动蛋白细胞骨架、调节性GTP酶、线粒体功能和终末分化和原代足细胞中基因表达的影响。我们专注于D2 D3对肌动蛋白细胞骨架和线粒体功能之间的反馈回路的影响，以及足细胞生理学变化对其进行的修改。在具体目标3中，我们研究了D2 D3对葡萄糖摄取、细胞内Ca 2+动力学、细胞骨架动力学和胰岛细胞、离体小鼠胰岛和组织切片中基因表达的影响。这项研究描述了双器官损伤的分子机制和生理相关性，是开发CKD和胰岛素依赖型糖尿病新机制特异性治疗方法的关键一步。

The global epidemic of chronic kidney disease (CKD) is progressing at an alarming rate. CKD affects an estimated 37 million people in the U.S. (15% of the adult population; more than 1 in 7 adults), and this number has more than doubled in the last two decades. Kidney-related diseases are rapidly eluding present treatment options and resources. The three common causes of CKD are diabetes mellitus, hypertension, and glomerulonephritis. We and others have implicated soluble urokinase activating receptor (suPAR) as one of the significant risk factors for both, the onset as well as the progression of CKD, regardless of its etiologies. In addition to its role as a biomarker, we and others have suggested that suPAR is a pathogenic/scarring factor that underlies podocyte injury by activating v3 integrin on podocytes. Podocytes are terminally differentiated cells essential for maintaining the specificity of the kidney filter. Our preliminary data suggest that the presence of the proteolytic fragment of suPAR, D2D3 fragment, in the plasma induces glomerular injury by activating v3 integrin on podocytes. In addition, and highly unexpectedly, our preliminary studies suggest that the D2D3 fragment also injures -cells of the pancreas. Together, these insights suggest a hypothesis that circulating D2D3 fragment simultaneously causes injury to two organs, the kidney and pancreas. We test this hypothesis in 3 Specific Aims. In Specific Aim 1, we define the physiological mechanisms by which D2D3 induces kidney and pancreas injuries by examining organ functions in D2D3-Tg mice on regular- and high-fat- diet challenged by nephrotoxic serum or Adriamycin. In addition, we will cross D2D3-Tg mice with Non-Obese Diabetic (NOD) mice to examine synergy upon pancreas injury. Anti-suPAR antibodies and small molecules that target regulatory GTPases (dynamin, Cdc42, Rac1), whose roles will be elucidated in Aims 2 and 3, will be tested as potential therapeutics. As D2D3-Tg mice exhibit dual organ injury, combination treatments targeting diverse pathways in distinct cell types will also be investigated. In Specific Aim 2, we examine the effects of the D2D3 fragment on the actin cytoskeleton, regulatory GTPases, mitochondrial function, and gene expression in terminally differentiated and primary podocytes in the presence and absence of lipotoxic stimuli or high glucose levels. We focus on the effects of D2D3 on a feedback loop between the actin cytoskeleton and mitochondrial function, and its modifications by changes in podocyte physiology. In Specific Aim 3, we examine the effects of D2D3 on glucose uptake, intracellular Ca2+ dynamics, cytoskeleton dynamics, and gene expression in -cells, isolated mouse islets, and tissue slices. The proposed study, delineating molecular mechanisms and the physiological relevance of dual organ injury, is a critical step in developing novel mechanism-specific therapeutics for CKD and insulin-dependent diabetes mellitus.