Molecular Mechanism of THM1-Medicated Renal Cystogenesis

囊性肾病（CKD）被认为起源于潜在的纤毛缺陷，尽管分子机制尚不清楚。我们发现了一种新的纤毛蛋白THM1（四肽重复含有刺猬调节因子1，也称为TTC21B或IFT139），它负调控刺猬（Hh）信号。近年来，THM1已被证明是纤毛病患者中致病性最高的等位基因，包括Meckel-Gruber综合征（MKS）、Bardet-Bledl综合征（BBS）、肾病（NPHP）、Joubert综合征（JS）和Jeune's窒息性胸病（JATD）。这些纤毛病的一个主要临床特征是慢性肾病，事实上，在胚胎发生晚期Thml基因缺失会导致成年小鼠的慢性肾病。虽然Hh信号尚未在CKD中得到广泛研究，但我们对THM1的分析使我们研究了Hh活性增强在肾囊形成中的可能作用。为了支持这一假设，CKD胚胎培养模型中的囊肿形成可以通过基因缺失Gli2 （Hh信号的主要转录激活因子）和小分子Hh抑制剂来阻止。本提案的目的是确定Hh活性增强是否会导致肾囊肿。在第一个目标中，将通过对Thm1条件敲除小鼠中Hh信号的时空定量评估来阐明分泌旁分泌Hh信号在CKD中的作用。在第二个目标中，这个空间分析将通过检查消融Thm1对肾小管上皮细胞和肾间质细胞的影响来扩展。在第三个目标中，将通过在Thm1条件敲除小鼠中基因和药理学上下调Hh通路来探索肾囊发生中Hh信号增加的因果关系。在空间背景下检测基因表达可能为更好地了解CKD的发病机制提供一种工具。此外，这些实验将确定Hh信号在肾囊发生中的因果作用，并可能为设计CKD的预防策略提供重要意义。

Cysfic kidney disease (CKD) is proposed to originate from an underlying ciliary defect, though molecular mechanisms remain unclear. We have identified a novel ciliary protein, THM1 (Tetratricopeptide Repeat Containing Hedgehog Modulator 1, also termed TTC21B or IFT139), which negatively regulates Hedgehog (Hh) signaling. Recently, THM1 has been shown to contribute the most pathogenic alleles among ciliary genes to patients with ciliopathies, including Meckel-Gruber Syndrome (MKS), Bardet-Bledl Syndrome (BBS), nephronophthisis (NPHP), Joubert's Syndrome (JS) and Jeune's Asphyxiating Thoracic Disorder (JATD). A major clinical feature of these ciliopathies is CKD, and indeed, genetic deletion of Thml during late embryogenesis results in CKD in the adult mouse. While Hh signaling has not been studied extensively in CKD, our analyses of THM1 have led us to investigate a possible role for enhanced Hh activity in renal cystogenesis. In support of this hypothesis, cyst formation in an embryonic culture model of CKD was prevented by genetic deletion of Gli2, the main transcriptional activator of Hh signaling, and by treatment with small molecule Hh inhibitors. The goal of this proposal is to determine whether enhanced Hh activity leads to renal cysts. In the first aim, the effect of paracrine Hh signaling in CKD will be elucidated by conducting a spatial and temporal quantitative assessment of Hh signaling in the Thm1 conditional knock-out mouse. In the second aim, this spatial analysis will be extended by examining the effects of ablating Thm1 in renal tubular epithelial cells versus in renal stromal cells. In the third aim, causality of increased Hh signaling in renal cystogenesis will be explored by down regulating the Hh pathway genetically and pharmacologically in Thm1 conditional knock-out mice. Examining gene expression in a spatial context may provide a tool with which to gain better understanding of the pathogenesis of CKD. Furthermore, these experiments will establish a causal role for Hh signaling in renal cystogenesis and may offer important implications for the design of preventive strategies against CKD.