The Biology of Genetic Variants in Human Kidney Disease

描述(由申请人提供)：我们已经在肾炎样肾功能衰竭(O‘Toole，et.艾尔2010)。受影响的患者肾脏大小正常，有罕见的小囊肿，肾脏组织学以间质纤维化和肾小管萎缩为主，类似于肾单位病(NPHP)，这是儿童终末期肾脏疾病最常见的遗传原因(Hildebrandt，et)。艾尔2009年)。我们已经清楚地表明XPNPEP3定位于线粒体，而不是初级纤毛/中心体/基底复合体(O‘Toole等人。2010)与其他NPHP基因产品的典型情况一样。XPNPEP3的酵母同源基因YER078c定位于线粒体，但不定位于胞浆(Naamati等人)。艾尔2009)，是一种氨基肽酶，通常从其蛋白质靶标的氨基末端移除单一残基(Vogtle等人。2009年)。这种翻译后处理稳定了这些靶点，并通过阻止进入以N-端规则为特征的线粒体蛋白质降解途径来增加它们的半衰期(Voglte，et。艾尔2009年，巴赫迈尔等人。艾尔1986)。我们认为，线粒体蛋白降解增加，如XPNPEP3功能丧失可能发生的那样，可以激活TOR，因为我们发现YER078c缺失酿酒酵母中TOR活性增加，这可以通过线粒体靶向的人XPNPEP3的表达来纠正。检查XpnPep3/-小鼠，mTOR在2个月龄时激活，随后在4个月龄时发生肾小管损伤，并出现明显的细胞质空泡化。这些结果表明，线粒体蛋白XPNPEP3通过一种新的线粒体mTOR激活机制导致肾单位病样肾病。我们认为mTOR激活可能将XPNPEP3与其他NPHP基因联系在一起，其中mTOR激活在其发病机制中起重要作用，但其激活机制尚不清楚。我们的总体假设是，XPNPEP3功能的丧失会增加线粒体蛋白质降解成多肽片段，这些片段被运输到细胞质中，在那里它们上调TOR活性。正是通过这种线粒体途径激活mTOR，导致患者出现肾间质纤维化、肾小管萎缩和囊变的表型。我们将使用酵母和小鼠XpnPep3缺失的遗传模型来验证这一假说，以检查其在肾脏疾病进展中的作用，并研究导致mTOR激活和缺陷蛋白降解的机制。

DESCRIPTION (provided by applicant): We have identified recessive XPNPEP3 mutations in families with nephronophthisis-like renal failure (O'Toole, et. al. 2010). Affected individuals have normal kidney size with rare, small cysts and renal histology dominated by interstitial fibrosis and tubular atrophy similar to that seen in nephronophthisis (NPHP), the most common genetic cause of end-stage renal disease in the pediatric population (Hildebrandt, et. al. 2009). We have clearly shown that XPNPEP3 localizes to the mitochondria, rather than the primary cilia/centrosome/basal body complex (O'Toole, et al. 2010) as typical for other NPHP gene products. The yeast ortholog of XPNPEP3, YER078c, localizes to the mitochondria, but not to the cytosol (Naamati, et. al. 2009) and is an aminopeptidase that generally removes a single residue from the amino-terminus of its protein targets (Vogtle, et al. 2009). This post-translational processing stabilizes these targets and increases their half-life by blocking entry into a mitochondrial protein degradation pathway characterized by the N-end rule (Voglte, et. al. 2009, Bachmair, et. al. 1986). We believe that increased mitochondrial protein degradation, as may occur with loss of XPNPEP3 function, can activate TOR, as we found increased TOR activity in YER078c deletion strains of S. cerevisiae which is corrected by the expression of mitochondrially targeted human XPNPEP3. Examining Xpnpep3-/- mice, mTOR activation occurred by 2 months of age followed by the development of tubular damage with pronounced cytoplasmic vacuolization by 4 months of age. These results suggest that the mitochondrial protein XPNPEP3 causes a nephronophthsis-like kidney disease through a novel mitochondrial mechanism of mTOR activation. We believe that mTOR activation may link XPNPEP3 to other NPHP genes, where mTOR activation is known to be important in their pathogenesis, but the mechanisms underlying its activation are poorly understood. Our overall hypothesis is that loss of XPNPEP3 function increases the degradation of mitochondrial proteins to peptide fragments, which are transported into the cytosol where they upregulate TOR activity. It is the activation of mTOR through this mitochondrial pathway that leads to the renal phenotype of interstitial fibrosis, tubular atrophy and cyst formation observed in affected individuals. We will test this hypothesis using yeast and murine genetic models of Xpnpep3 deletion to examine its role in the progression of kidney disease and study the mechanisms leading to mTOR activation and defective protein degradation.