Mechanisms of Tubular Atrophy

在美国，超过3000万人患有糖尿病；三分之一的人患有CKD，几乎一半的ESRD事件是 由于糖尿病肾病(DKD)。蛋白尿和肾小球滤过率降低反映肾小球功能障碍 DKD进展的风险。然而，作为DKD的预测指标，肾小管萎缩优于肾小球病理。 进步。肾小管上皮细胞丢失的机制尚未建立。 非酯化脂肪酸(NEFA)与白蛋白或甘油三酯结合循环。由于以下原因，两者均未过滤 他们的体型。低浓度过滤的NEFA被心尖清道夫转运蛋白在近端重新吸收 小管。这一段通常使用NEFA作为代谢底物，通过基底外侧吸收 薄膜。在DKD中，受损的肾小球允许白蛋白结合的NEFA大量过滤，这是 然后被心尖近端小管转运蛋白重吸收，导致NEFA，长链酰基-COAs， 和细胞凋亡。心尖部NEFA的摄取主要由脂肪酸运输蛋白-2(FATP2)介导，而在 在体外模拟DKD的NEFA浓度具有细胞毒性。基底外侧NEFA摄取不依赖于FATP2 而且没有细胞毒性。 我们发现，在遗传性和诱导性DKD小鼠模型中，FATP2的全局缺失可以改善GFR， 肾小管萎缩和血糖升高，但其机制尚不清楚。首先，删除FATP2不会 完全阻断AP近端小管NEFA摄取。第二，FATP2的缺失如何解释增强的 与DKD相关的NEFA的合成和降解减少，尚未得到协调。 在DKD中，近端小管积累脂滴(LD)，储存多余的NEFA以防止脂毒性。 Perilipin(Plin)蛋白有助于LD的组装和维护。Plin5增加了LD与线粒体的对接， 从而增强自噬，减少内质网应激和细胞凋亡，并将代谢从氧化转变为 脂肪储存和葡萄糖利用。我们的数据显示近端小管Plin5在DKD中的表达减弱， 且随FATP2缺失而增加。Plin5过表达受到抑制，Plin5功能丧失加剧 脂细胞凋亡。这些数据表明，FATP2缺失的有益效果部分是由于增强了 Plin5的表达。我们还认为，Plin5介导代谢重编程从氧化到 糖酵解和糖异生减少，这将介导FATP2缺失的降糖作用。 假设：在DKD相关的肾小球损伤中，结构性的基底外侧NEFA转运，与 心尖FATP2调节的近端小管NEFA摄取导致脂毒性、肾小管萎缩和进行性 DKD。近曲小管FATP2缺失或增强的Plin5依赖可避免肾小管萎缩 脂滴扩张。这一假说的具体目的如下：1.确定 近端小管FATP2是否介导脂毒性和DKD进展。2.确定Plin5在 近曲小管代谢与DKD3.探讨FATP2抑制剂对DKD的治疗作用。

Over 30M people in the U.S. suffer from diabetes; one-third have CKD and almost half of incident ESRD is due to diabetic kidney disease (DKD). Albuminuria and decreased GFR reflect glomerular dysfunction, and are risks for DKD progression. However, tubular atrophy is superior to glomerular pathology as a predictor of DKD progression. The mechanisms for loss of tubular epithelial cells have not been established. Non-esterified fatty acids (NEFA) circulate bound to albumin, or as triglycerides. Neither is filtered due to their size. Low concentrations of filtered NEFA are reabsorbed by apical scavenger transporters in the proximal tubule. This segment normally uses NEFA as metabolic substrates that are taken up across the basolateral membrane. In DKD, injured glomeruli permit filtration of albumin-bound NEFA in large quantities, which are then reabsorbed by apical proximal tubule transporters, causing accumulation of NEFA, long-chain acyl-CoAs, and apoptosis. Apical NEFA uptake is mediated primarily by fatty acid transport protein-2 (FATP2), and at NEFA concentrations that mimic DKD in vitro, is cytotoxic. Basolateral NEFA uptake is FATP2-independent and not cytotoxic. We showed that global FATP2 deletion in genetic and inducible mouse models of DKD improves GFR, tubular atrophy and plasma glucose, but the mechanisms are not understood. First, FATP2 deletion does not completely block AP proximal tubule NEFA uptake. Second, how FATP2 deletion account for the enhanced synthesis and decreased degradation of NEFA associated with DKD, has not been reconciled. In DKD proximal tubules accumulate lipid droplets (LD), which store excess NEFA to prevent lipotoxicity. Perilipin (Plin) proteins facilitate LD assembly and maintenance. Plin5 augments LD docking with mitochondria, thereby enhancing autophagy, reducing ER stress and apoptosis, and shifts metabolism from -oxidation to lipid storage and glucose utilization. Our data show that proximal tubule Plin5 expression is blunted in DKD, and increased with FATP2 deletion. Plin5 overexpression inhibited, and Plin5 loss of function exacerbated lipoapoptosis. These data suggest that the beneficial effect of FATP2 deletion is partly due to enhanced expression of Plin5. We also propose that Plin5 mediates metabolic reprogramming from -oxidation to glycolysis and decreased gluconeogenesis, which would mediate the hypoglycemic effects of FATP2 deletion. Hypothesis: In DKD-associated glomerular injury, constitutive basolateral NEFA transport, combined with apical FATP2-regulated proximal tubule NEFA uptake leads to lipotoxicity, tubular atrophy and progressive DKD. Tubular atrophy can be circumvented by proximal tubule FATP2 deletion or enhanced Plin5-dependent lipid droplet expansion. The hypothesis will be pursued with the following specific aims: 1. To determine whether proximal tubule FATP2 mediates lipotoxicity and DKD progression. 2. To determine the role of Plin5 in proximal tubule metabolism and DKD. 3. To determine the therapeutic utility of FATP2 inhibition in DKD.