Pathogenesis of Diabetic Nephropathy

摘要 糖尿病肾病(DN)的特征是代谢紊乱和细胞信号事件导致 增加细胞外基质的合成。它们包括葡萄糖中间体和多元醇的流量增大、像差 在燃料传感分子中，例如AMPK；以及PKC活性增加，产生有害的AGEs，表达 MAP/ERK激酶和Smad蛋白，促纤维化细胞因子和产生活性氧(ROS)。 后者被认为是糖尿病肾病发病机制的核心。这些信号事件已在 肾小球细胞和肾小管或间质细胞的信息有限。有趣的是，肾小管间质改变 与肾功能参数紊乱有更好的相关性；因此，有必要合理地定义 糖尿病肾病的生物学与“糖尿病小管病变”有关。除了影响 肾小球的病理，一种最近发现的葡萄糖醛酸-木糖(G-X)途径，显然与 糖尿病肾病是一种专门在肾小管腔内操作的疾病，很少受到关注。 G-X途径的事件是由肌醇加氧酶(MIOX)启动的，MIOX是一种管状酶，具有 以dN表示的表达式。在G-X事件期间，NADPH：NADP+和NAD+：NADH比率发生严重扰动， 因此，严重的“氧化还原失衡”和“NAD+缺乏症”导致了 不利的肾小管稳态(JASN 2015，JBC 2016-1)。由于MIOX启动子包括碳水化合物、氧化剂/ 抗氧化剂、渗透压和类固醇反应元件MIOX的循环刺激将在下列情况下进行 高血糖、血脂和化学氧化应激(JBC-2011、JBC 2016-2、JASN-2017) MIOX的上调和ROS的产生。它的调节也受到表观遗传修饰的调节。 (AJP 2017)。考虑到上述考虑，我们希望探讨以下机制 不同转基因MIOX小鼠模型的肾小管间质生物学研究。我的目的是描绘出 不同的表观遗传机制，调节MIOX的表达，使用高血糖和 高脂血症。MIOX启动子DNA甲基化/去甲基化，组蛋白甲基化/去甲基化 将研究MIOX-TG和MIOX-KO小鼠的乙酰化/去乙基化，并与 肾小管间质损伤。目的II阐明MIOX-TG加重肾小管间质损伤的机制 比较WT或-KO小鼠在高血糖和AGEs超负荷时的变化。肾功能紊乱，细胞氧化还原， 将对线粒体动力学进行研究。救援实验将包括与MIOX-/-杂交秋田 评价小鼠及反映损伤改善程度的各项参数。目标三是描述机制 这增加了MIOX-TG与WT&KO小鼠在高脂血症中的肾脏损伤。MIOX之后发生的事件- 表达，即NAD+缺乏，谷胱甘肽耗竭和ROS的增强生成，扰动在 Sirtuins活性、p-AMPK、PGC-1α、线粒体动力学、内质网应激和肾小管间质纤维化 评估过了。救援实验将包括将MIOX-/-与ob/ob和pparαΔob/ob小鼠杂交。

ABSTRACT Diabetic nephropathy (DN) is characterized by disturbances in metabolic & cellular signaling events leading to increased synthesis of ECM. They include accentuated flux of glucose intermediaries & polyols, aberrations in fuel sensing molecules, e.g., AMPK; and increased PKC activity, generation of nocuous AGEs, expression of MAP/ERK kinases and Smad proteins, profibrogenic cytokines & production of reactive oxygen species (ROS). The latter are regarded as central to the pathogenesis of DN. These signaling events have been studied in glomerular cells and information for tubular or interstitial cells is limited. Interestingly, tubulointerstitial changes correlate better with derangement in renal functional parameters; thus there is a legitimate need to define the biology of DN with respect to “diabetic tubulopathy”. In addition to a multitude of signaling events that affect the pathology of the glomerulus, a recently discovered glucuronate-xylulose (G-X) pathway, apparently relevant to diabetic nephropathy that is operative specifically in the tubular compartment, has received very little attention. Events of G-X pathway are initiated by myo-inositol oxygenase (MIOX), a tubular enzyme that has an increased expression in DN. During G-X events there are severe perturbations in NADPH:NADP+ & NAD+:NADH ratios, as a result there is a tremendous degree of "redox imbalance" and "NAD+ deficiency" leading to consequential adverse tubular homeostasis (JASN 2015, JBC 2016-1). Since MIOX promoter includes carbohydrate, oxidant/ antioxidant, osmotic and sterol response elements a cyclic stimulation of MIOX would be anticipated following hyperglycemia, lipidemia and chemical oxidant stress (JBC-2011, JBC 2016-2, JASN-2017) along with sustained up-regulation of MIOX and generation of ROS. Its regulation is also modulated by epigenetic modifications (AJP 2017). Keeping in perspective the above considerations we wish to explore the mechanisms involved in the biology of tubulo-interstitium using various genetically modified MIOX mice models. AIM I is to delineate various epigenetic mechanisms that modulate MIOX expression, using mice models of hyperglycemia and hyperlipidemia. DNA methylation/demethylation of MIOX promoter, histone methylation/demethylation and acetylation/decetylation in MIOX-TG and MIOX-KO mice will be investigated and correlated with the extent of tubulointerstitial injury. AIM II is to delineate mechanisms that accentuate tubulointerstitial injury in MIOX-TG vs WT or -KO mice during hyperglycemia and AGEs' overload. Perturbations in renal functions, cellular redox, mitochondrial dynamics will be investigated. Rescue experiments will include cross-breeding Akita with MIOX-/- mice and various parameters reflecting amelioration of injury appraised. AIM III is to delineate mechanisms that augment renal injury in MIOX-TG vs WT & KO mice in hyperlipidemia. The events following MIOX over- expression, i.e., NAD+ deficiency, glutathione depletion and augmented generation of ROS, perturbations in sirtuins' activity, p-AMPK, PGC-1α, mitochondrial dynamics, ER stress and tubulo-interstitial fibrosis will be assessed. Rescue experiments will include cross-breeding of MIOX-/- with ob/ob and PPARαΔob/ob mice.