Role of renal crystal deposition in the progression of polycystic kidney disease

常染色体显性多囊肾病（ADPKD）是一种常见病和遗传性疾病，发病率为1:500。该病进展缓慢，通常在40 - 60岁时发展为肾衰竭。由于未知的原因，即使在同一家庭中，患者之间的进展速度也不同，这表明环境因素可能影响疾病进展。最近的动物研究结果表明，除了基因突变外，肾囊肿的形成还需要肾脏损伤。但罕见形式的肾损伤似乎不太可能引发人类疾病的持续发展。Weimbs实验室最近的结果表明，一种更为普遍的亚临床肾损伤形式是肾囊肿形成的触发因素，它决定了ADPKD的进展速度：微晶体零星地沉积在肾小管腔中。他们发现，草酸钙（CaOx）晶体在肾小管中的沉积导致mTOR和Src/STAT3信号通路的快速激活，这两个信号通路在ADPKD中也被强烈激活。此外，CaOx晶体沉积会导致小管直径快速变宽，这可以被mTOR抑制所阻断。这些结果表明，小管扩张是一种有目的的、以前未被认识到的促进晶体排泄的保护机制。晶体清除后，小管直径在一周内恢复正常。然而，在缺乏PC1 （ADPKD中受影响的蛋白质）的小鼠中，CaOx挑战导致持续的小管扩张，“过度”导致囊性进展。这表明PC1是损伤后恢复正常小管直径所必需的。我们假设：(1)小管扩张是一种先天的肾脏保护机制，以对抗管状晶体；(2)该机制作为小管扩张的触发因素，导致ADPKD中囊肿的形成。如果正确的话，这些发现立即为治疗干预开辟了一条新的、高度可行的途径，因为针对复发性肾结石的成熟治疗方法（饮食改变、增加饮水量、柠檬酸盐）也应该能有效减缓ADPKD的进展。使用小鼠和大鼠CaOx肾结石模型，我们将研究晶体沉积对小管扩张和信号通路激活的响应，并测试柠檬酸盐治疗是否能预防这些影响（目的1）。使用药理学抑制剂和遗传小鼠模型，我们将确定小管扩张是否需要有效的晶体清除（目的2）。使用条件敲除小鼠对纤毛或PC1进行消融，我们将研究小管晶体沉积是否作为膀胱发生的触发因素（目的3）。利用PC1-KO小鼠模型和PKD大鼠模型，我们将确定晶体负荷是否调节PKD的疾病严重程度。

Autosomal-dominant polycystic kidney disease (ADPKD) is a common and inherited disease with a frequency of 1:500 in world’s population. The disease progresses slowly to renal failure, typically in the 4-6th decades of life. For unknown reasons the rate of progression varies from patient to patient even within the same family suggesting that environmental factors may influence disease progression. Recent results from animal studies suggest that renal insults are required – in addition to the gene mutation – for renal cysts to develop. But rare forms of renal injury seem unlikely to trigger the constant disease progression in humans.Recent results of the Weimbs Laboratory suggest that a much more prevalent form of subclinical renal insult is the trigger of renal cyst formation that determines the rate of progression in ADPKD: microcrystals that are sporadically lodged in renal tubule lumens. They show that deposition of calcium oxalate (CaOx) crystals in renal tubules lead to rapid activation of the mTOR and Src/STAT3 signaling pathways, which are both strongly activated in ADPKD, too. Additionally, CaOx crystal deposition leads to rapid tubule diameter widening that can be blocked by mTOR inhibition. These results indicate that tubule dilation is a purposeful, and previously unrecognized, protective mechanism that facilitates crystal excretion. After crystal clearance, tubule diameters normalize within a week. However, in mice lacking PC1 – the protein affected in ADPKD – CaOx challenge leads to persistent tubule dilation that “overshoots” to cystic progression. This suggests that PC1 is required for a return to normal tubule diameters after insults. We hypothesize (1) that tubule dilation is an innate renal protective mechanism against tubular crystals and (2) that this mechanism acts as a trigger for tubule dilation leading to cyst formation in ADPKD. If correct - these findings immediately open a new and highly feasible avenue for therapeutic intervention because well-established treatments for recurring nephrolithiasis (dietary changes, increased water intake, citrate) should also be effective in slowing the progression of ADPKD.Using mouse and rat models of CaOx nephrolithiasis we will investigate tubule dilation and signaling pathway activation in response to crystal deposition and test whether citrate treatment prevents these effects (Aim 1). Using pharmacological inhibitors and genetic mouse models we will determine if tubule dilation is required for effective crystal clearance (Aim 2). Using conditional knockout mice for the ablation of cilia or PC1, we will investigate if tubule crystal deposition acts as a trigger for cystogenesis (Aim 3). Using a mosaic PC1-KO mouse model and a rat model of PKD we will determine if crystal burden modulates disease severity in PKD.