Mechanisms of Tubular Atrophy

美国有超过3000万人患有糖尿病;三分之一的人患有CKD，近一半的ESRD事件是 糖尿病肾病（DKD）。白蛋白尿和GFR降低反映肾小球功能障碍， DKD进展的风险。然而，肾小管萎缩作为DKD的预测因子优于肾小球病理学，其预测价值为上级 进展肾小管上皮细胞丢失的机制尚未确定。 非酯化脂肪酸（NEFA）与白蛋白结合或作为甘油三酯循环。两者都没有过滤，因为 他们的大小。低浓度的过滤NEFA被近端的顶端清道夫转运蛋白重吸收， 小管这一部分通常使用NEFA作为代谢底物，在基底外侧区被吸收。 膜的在DKD中，受损的肾小球允许大量白蛋白结合的NEFA滤过， 然后被顶端近曲小管转运蛋白重吸收，引起NEFA，长链酰基辅酶A， 和凋亡。心尖NEFA摄取主要由脂肪酸转运蛋白2（FATP 2）介导， 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FATP 2 而不是细胞毒性的。 我们发现，在DKD的遗传和诱导型小鼠模型中，整体FATP 2缺失可改善GFR， 肾小管萎缩和血糖，但机制尚不清楚。首先，FATP 2缺失不会 完全阻断AP近端小管NEFA摄取。第二，FATP 2缺失如何解释增强的 与DKD相关的NEFA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），其储存过量的NEFA以防止脂毒性。 周脂蛋白（Plin）蛋白促进LD组装和维持。Plin 5增强了LD与线粒体的对接， 从而增强自噬，减少ER应激和凋亡，并将代谢从-氧化转变为 脂质储存和葡萄糖利用。我们的数据显示，DKD患者近端小管Plin 5表达减弱， 随着FATP 2缺失而增加。Plin 5过表达受到抑制，Plin 5功能丧失加剧 脂肪细胞凋亡这些数据表明，FATP 2缺失的有益效果部分是由于增强了细胞内的细胞凋亡。 Plin 5的表达。我们还提出Plin 5介导了从-氧化到-氧化的代谢重编程。 糖酵解和减少的糖异生，这将介导FATP 2缺失的降血糖作用。 假设：在DKD相关的肾小球损伤中，组成性基底外侧NEFA转运，结合 顶端FATP 2调节的近端小管NEFA摄取导致脂毒性、肾小管萎缩和进行性肾小管损伤。 DKD。肾小管萎缩可以通过近端小管FATP 2缺失或Plin 5依赖性增强来避免。 脂滴扩张。该假设将追求以下具体目标：1。以确定 近端小管FATP 2是否介导脂毒性和DKD进展。2.要确定Plin 5在 近端小管代谢和DKD。3.确定FATP 2抑制在DKD中的治疗效用。

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.