The Role of Wheat-Gluten in Polycystic Kidney Disease

常染色体显性多囊肾病（ADPKD）是由PKD1或PKD2基因突变引起的。即使在具有相同PKD基因突变的家庭中，疾病的严重程度也是高度可变的。这种变化部分归因于环境因素。其中，高蛋白饮食是公认的ADPKD进展加速因素之一。蛋白质组成也是影响囊肿生长速度的关键因素。例如，在啮齿类动物PKD模型中，与酪蛋白（动物蛋白）相比，大豆蛋白可以减缓肾脏囊肿。我们的临床前数据显示，与酪蛋白饮食相比，麦麸（WG）饮食减少了pkd1敲除小鼠肾巨噬细胞的数量（MФ）、Ccl2的表达（但不包括Csf1或Ccl5），并减缓了囊肿的生长速度。因此，基于动物的蛋白质负荷可能通过增强促囊生成的Ccl2途径具有促囊生成的作用。先前的研究表明，Pkd1的缺失增加了肾小管中的Ccl2，促进MФ的募集，促进肾囊肿的生长，而这些作用在Ccl2-Pkd1双敲除小鼠中减弱。我们发现动物蛋白负荷会损害pkd1敲除小鼠的肾脏线粒体功能。当这些小鼠饲喂富含酪蛋白的前3种氨基酸的WG日粮时，与饲喂等热量WG日粮的小鼠相比，肾脏MФ和囊肿的生长数量增加。这表明酪蛋白饮食中的特定AAs促进了囊肿的生长。此外，用赖氨酸（酪蛋白中AA含量比WG高）而不是天冬氨酸（酪蛋白中AA含量第二高）或谷氨酸（酪蛋白中谷氨酸含量最高）处理小鼠肾细胞，抑制了线粒体功能标记物，损害了葡萄糖代谢，增加了糖异生标记物磷酸烯醇丙酮酸（Pepck1），增加了Pkd1小鼠肾细胞的小管损伤。与给予生理盐水的小鼠相比，Pkd1敲除小鼠口服赖氨酸（1周）增加了肾囊肿的生长和Pepck1的水平。这些数据与肾脏通过线粒体在AA代谢中发挥的主要作用相一致，线粒体是一种被PKD突变功能受损的细胞器。我们的首要假设是，动物蛋白饮食中丰富的特定AA(s)会加剧线粒体功能障碍，增加趋化因子表达，MФ募集，并加速膀胱形成。Aim1将验证高酪蛋白饮食损害线粒体功能，激活趋化因子Ccl2表达，增加肾脏MФ积累，促进囊肿生长的假设；而在pkd1敲除小鼠中，Ccl2的缺失则有相反的效果。目的2将验证一种假设，即与植物性饮食相比，动物性蛋白质饮食中富含的特异性赖氨酸（AA）会导致线粒体功能障碍、免疫反应增强和囊肿生长加速。这项拨款提案的临床意义在于，PKD患者可以从植物性蛋白饮食中受益，最近植物性肉类的发展使得饮食蛋白质的改变成为一种可行的干预措施，对需要长期治疗的ADPKD患者是安全的，可以立即产生影响。

Autosomal dominant polycystic kidney disease (ADPKD), is caused by mutations in PKD1 or PKD2 genes. Disease severity is highly variable, even among families with the same PKD gene mutation. This variability has been attributed, in part, to environmental factors. Among them, a high protein diet is one of the most recognized ADPKD progression-accelerating factor. Protein composition is also a key element that can affect the rate of cyst growth. For example, soy protein compared to casein (animal-based protein) diet slows kidney cyst in rodent PKD models. Our preclinical data shows that wheat gluten (WG) diet compared to casein protein diet decreased the number of kidney macrophages (MФ), expression of Ccl2 (but not Csf1 or Ccl5) and slowed the rate of cyst growth in Pkd1-knockout mice. Therefore, animal-based protein load may have cystogenesis-promoting effects through augmentation of the cystogenesis-promoting Ccl2 pathway. Previous studies show that loss of Pkd1 increases Ccl2 in the renal tubules facilitating the recruitment of MФ, promoting kidney cyst growth and that these effects were attenuated in Ccl2-Pkd1 double knockout mice. We found that animal protein load impairs kidney mitochondrial function in Pkd1-knockout mice. When these mice were fed a WG diet enriched with top 3 amino acids abundant in casein compared to WG diet, there was increased number of kidney MФ and cyst growth compared to counterparts fed an isocaloric WG diet. This suggest that specific AAs in the casein diet promotes cyst growth. Furthermore, treatment with lysine (most abundant AA in casein compared to WG diet), but not aspartate (second abundant in casein) or glutamate (most abundant in WG), suppressed markers of mitochondrial function, impaired glucose metabolism, increased gluconeogenesis marker phosphoenolpyruvate (Pepck1) and increased tubular injury in Pkd1 mouse kidney cells. Oral lysine supplementation (1wk) in Pkd1 knockout mouse increased kidney cyst growth and levels of Pepck1 compared to counterparts given a saline. These data are well aligned with a major role kidneys play in AA metabolism through the mitochondria, an organelle that is functionally impaired by PKD mutations. Our overarching hypothesis is that specific AA(s) abundant in an animal protein-based diet exacerbate mitochondrial dysfunction, increase chemokine expression, MФ recruitment, and accelerate cystogenesis. Aim1 will test the hypothesis that high casein-protein diet impairs mitochondrial function, activates chemokine Ccl2 expression, increases kidney MФ accumulation, and promotes cyst growth; and deletion of Ccl2 in Pkd1-knockout mice have opposite effects. Aim2 will test the hypothesis that specific AA (lysine) abundant in an animal-based protein diet compared to a plant-based diet, leads to mitochondrial dysfunction, increased immune response and accelerated cyst growth. The clinical significance of this grant proposal is that patients with PKD could benefit from a plant-based protein diet and recent plant-based meat development has made dietary protein modification a feasible intervention that is safe and can have immediate impact for patients with ADPKD that require long-term treatment.