Reticulon-1介导的内质网应激在糖尿病肾病发病机制中的作用

Diabetes mellitus (DM) is a growing metabolic disease that continues to be a leading health problem worldwide. Although diabetic nephropathy (DN) is epidemic, the pathogenesis remains poorly defined. Recent studies have been verified that Endoplasmic Reticulum (ER) stress plays a critical role in the pathogenesis of kidney diseases. Disturbances like high glucose, oxidative stress can induce ER stress and Unfolded Protein Response (UPR) in kidney, by initiating intracellular signaling pathway. UPR at the early stage will ameliorate ER damage and ensure cell survival, but when ER stress is severe or prolonged, the cells will eventually cause apoptosis. However, the mechanism between ER stress and DN hasn’t yet been deeply studied. . In the previous study, we profiled gene expression in kidneys from a murine model of HIV-associated nephropathy (HIVAN) and identified an association between the expression of reticulon-1 (Rtn1), which encodes for an ER associated protein, and the severity of kidney disease. However, RTN1A has never been studied in the context of kidney disease before.We have found that RTN1A is increased in diseased kidneys of multiple animal models, such as HIVAN model and UUO model. We have determined the role of RTN1A in ER stress in kidney cells and proved it a key marker in the UPR signaling pathway. We also found that RTN1A mediates apoptosis in kidney cells. However, the relationship between RTN1A and diabetic nephropathy has never been studied. . Hereby in the present study, we like to determine high glucose effect on RTN1A expression in kidney tubular cells and podocyte.We try to find the role of RTN1A in high glucose induced ER stress as well as apoptosis of kidney cells. Next, we like to examine both ER stress markers and RTN1A expression in the kidney of db/db mice, a murine model of 2-DM. The effect of ER stress inhibitor, Tauroursodeoxycholic Acid (TUDCA) on RTN1A expression will be examined in db/db mice to find whether TUDCA can ameliorate RTN1A associated ER stress and apoptosis in db/db mice. Finally, we will perform immunostaining of RTN1A in kidney biopsies from patients with DN. The correlation between RTN1 staining and proteinuria or renal function will be quantified statistically.. In conclusion, RTN1 is a novel gene for kidney diseases. It is likely that increased expression of expression of RTN1 in kidney cells contributes to kidney injury and act as a key regulator mediating ER stress and apoptosis in DN. The study of RTN1 will shed a new light in the pathogenesis of ER stress in diabetic nephropathy.

内质网应激在糖尿病肾病（DN）进程中起着关键作用，但目前尚缺乏对其深入研究和全面认识。Reticulon1（RTN1）是最新被认识的内质网蛋白，我们前期的研究发现RTN1A在肾组织中表达，在肾脏疾病状态下表达显著增强，参与ER stress信号通路，促进细胞凋亡。RTN1与DN的关系知之甚少，本研究将首次关注。我们首先在体外观察RTN1A在高糖诱导的足细胞和肾小管上皮细胞ER stress中的作用及其与细胞凋亡的关系；其次通过ER stress抑制剂TUDCA对db/db小鼠的干预，观察RTN1A在2型DN小鼠肾脏ER stress中的作用；进一步采用组织学量化的方法，对DN患者肾组织中RTN1A的表达强度与蛋白尿和肾功能进行相关性分析。基于上述研究，确立RTN1A-ER stress-DN的关系。RTN1A的发现是ER stress理论一个新的突破口，将为DN发病机制的研究注入新的活力。

糖尿病肾病的发病机制至今尚不明确，内质网应激及其诱导的细胞凋亡参与糖尿病肾病的发生发展。Reticulon（RTN）是一组具有跨膜蛋白结构的内质网相关蛋白，参与内质网应激信号通路，诱导细胞凋亡，牛磺熊脱氧胆酸（Tauroursodeoxycholic acid，TUDCA）是一种内质网应激的有效抑制剂，改善内质网的折叠能力，处理突变蛋白在体内外调节内质网功能，在第一部分研究中，我们首先观察了RTN1A在足细胞和肾小管上皮细胞内质网应激中的作用，通过TUDCA对db/db小鼠的干预，探讨RTN1A在糖尿病肾病ER stress中的作用。在2型糖尿病小鼠（db/db小鼠）单侧肾切除（UNX）的加速型糖尿病肾病模型（db/db-UNX）小鼠模型中发现，TUDCA可以降低db/db-UNX小鼠血糖水平，改善蛋白尿与肾脏损伤，抑制RTN1A和内质网应激信号通路和肾小管细胞凋亡; 在足细胞研究方面，我们进一步发现给予TUDCA后能有效地减轻db/db-UNX小鼠蛋白尿，改善肾功能和肾组织学损伤，并可以抑制内质网应激信号通路和足细胞凋亡。体外细胞实验方面，使用永生化人足细胞株，在使用人血清白蛋白过量负荷诱导足细胞发生内质网应激前用TUDCA进行预处理，观察到足细胞的内质网应激和细胞凋亡情况有改善。在第二部分研究中，我们进一步研究了RTN1A与急性肾损伤的关系。在急性肾损伤患者肾脏穿刺肾组织检测发现，RTN1A的表达与急性肾损伤的严重程度、进展和预后密切相关。在急性肾损伤小鼠模型中，调控RTN1A表达水平可以有效影响肾脏损伤情况，抑制RTN1A可有效延缓急性肾损伤向慢性肾脏病进展。这些研究结果提示，RTN1A发挥肾脏保护作用与其参与内质网应激信号通路以及肾脏损伤有关。RTN1A有望成为内质网应激与糖尿病肾病相互作用关系作用的重要潜在靶点，为肾脏保护提供新的方向。