Pathogenesis of Diabetic Nephropathy

摘要 糖尿病肾病（DN）的特征在于代谢和细胞信号传导事件的紊乱， 增加ECM的合成。它们包括葡萄糖中间体和多元醇的流量增加， 在燃料传感分子中，例如，增加PKC活性，产生有害的AGEs， MAP/ERK激酶和Smad蛋白，促纤维化细胞因子和活性氧（ROS）的产生。 后者被认为是DN发病机制的核心。这些信号事件已经在 肾小球细胞和肾小管或间质细胞的信息有限。有趣的是， 更好地与肾功能参数紊乱相关;因此，有合理的需要定义 DN的生物学与“糖尿病性肾小管病变”有关。除了大量的信号事件，影响 肾小球的病理学，最近发现的葡萄糖醛酸-木酮糖（G-X）途径，显然与 糖尿病肾病特别是在肾小管室中起作用的糖尿病肾病很少受到关注。 G-X途径的事件由肌醇加氧酶（MIOX）启动，MIOX是一种具有增加的G-X途径活性的管状酶。 在DN中表达。在G-X事件期间，NADPH：NADP+和NAD+：NADH比率存在严重扰动， 因此，存在极大程度的“氧化还原失衡”和“NAD+缺乏”，导致相应的 不利的肾小管稳态（JEFFECT 2015，JBC 2016-1）。由于MIOX促进剂包括碳水化合物、氧化剂/ 抗氧化剂、渗透压和甾醇反应元件，MIOX的周期性刺激将在 高血糖症、糖尿病和化学氧化应激（JBC-2011、JBC 2016-2、JBC-2017）沿着持续 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年）。基于上述考虑，我们希望探讨 使用各种遗传修饰的MIOX小鼠模型的微管-微管的生物学。目的I是描述 使用高血糖小鼠模型，研究了调节MIOX表达的各种表观遗传机制， 高脂血症MIOX启动子的DNA甲基化/去甲基化，组蛋白甲基化/去甲基化和 将研究MIOX-TG和MIOX-KO小鼠中的乙酰化/脱乙酰化并将其与乙酰化程度相关 肾小管间质损伤目的II是阐明MIOX-TG加重肾小管间质损伤的机制 与野生型或基因敲除小鼠相比。肾功能紊乱，细胞氧化还原， 将研究线粒体动力学。拯救实验将包括用MIOX-/-杂交秋田 小鼠和评价的反映损伤改善的各种参数。目的III是描述机制 在高脂血症中增加MIOX-TG与WT & KO小鼠中的肾损伤。MIOX之后的事件- 表达，即，NAD+缺乏、谷胱甘肽耗竭和ROS生成增加， sirtuins的活性、p-AMPK、PGC-1α、线粒体动力学、ER应激和肾小管间质纤维化将是 评估。挽救实验将包括MIOX-/-与ob/ob和PPARαΔob/ob小鼠的杂交育种。

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.