Pim-3促进自噬对脓毒血症所致肾小管上皮细胞损伤的保护作用

Sepsis-induced acute kidney injury (AKI) is the most common form of AKI observed in patients in Intensive Care Units(ICUs). Compared with septic patients without AKI,it remains high mortality and worse outcome partly due to our poor outstanding of its pathophysiological mechanisms. Our preliminary observation found that autophagy, as an important survial mechanism, activated in tubular epithelial cells(TECs) when severe sepsis occurred in vivo(cecal ligation and puncture rat model,CLP) and in vitro(LPS stimulation), whereas declined autophagy by 3-MA, an autophagic inhibitor,increased apoptotic TECs, indicating the protective role of autophagy in the pathogenesis of sepsis-induced AKI.Pim-3,a member of serine/threonine kinase family,has been reported to prevent apoptosis and promote cell survival in cancer, inflammatory disorders and ischemic diseases. However,whether its antiapoptotic effect is regulated by autophagy remains unknown.Besides, Pim-3 shares several important substrates with rapamycin, an well-known mTOR inhibtor,indicating Pim-3 play a role in autophagy which is possibly dependent of mTOR. In our study, we in the first time observed the activation of Pim-3 in septic TECs both in vivo and in vitro, and Pim inhibitor SGI-1776 downregulated expression of autophagic proteins such as LCII and Beclin1,which ultimately lead to increased tubular apoptosis. Based on this, we hypothesize that (1) autophagy is a protective response in sepsis-induced AKI to limit cellular death.(2)Pim-3,a vital cell-signaling pathway that occurs in response to cellular injury or stress,protects against sepsis-induced tubular epithelial injury via promoting autophgy dependent of mTOR. To test our hypothesis, we build the classcical sepsis model in vivo(CLP model) and in vitro(LPS model). (1)we first investigate the impact of autophagy on renal outcome when severe sepsis occurs by induction of autophagy (rapamycin, an mTOR inhibtor) and inhibtion of autophagy (3-MA),using HE, PAS and Masson dye to evaulate the pathology of renal injury,serum Scr,BUN, Cystatin C to test renal function, Kim-1,NGAL to evaluate AKI;TUNEL or Annexin V/PI double staining to test tubular epithelial apoptosis;electron microscopy, immunofluorecnce and Western-blot of Beclin1, LC3 I/II to detect authophagy. (2) To investigate the role of Pim-3 on autopahgy in sepsis, we up-regulate expression of Pim-3 by viral transfection and down-regulate Pim-3 by SiRNA in vitro. （3）To determine the possible mechanmism, by which mTOR-dependent pathway is involved in Pim-3 medidated autophagy, we examine phosphorylated mTOR and related substrates,for example,4EBP-1 and p70 S6K from mRNA and protein level. Our reseach will elucidate new mechanism of TECs injury during sepsis and provide new evidence in targeting sepsis-induced AKI.

脓毒血症是ICU患者发生急性肾损伤（AKI）的最常见原因。脓毒血症并发AKI死亡率极高，但机制仍不清楚。我们前期的工作发现，脓毒血症动物模型及脂多糖LPS刺激均可触发肾小管上皮细胞（TEC）自噬，且先于细胞凋亡；抗凋亡蛋白丝/苏氨酸激酶家族蛋白Pim-3表达增加，且其抑制剂可减少TEC自噬，促进凋亡，提示pim-3可能通过增强自噬，抑制脓毒血症所致的TEC损伤。本项目拟进一步深入研究：①建立脓毒血症动物和细胞模型，采用雷帕霉素和3-MA分别增强和抑制自噬，获得增强自噬减轻AKI的直接证据。②上调或下调TEC中pim-3水平，观察LPS介导TEC自噬和凋亡的关系，明确pim-3在LPS介导TEC损伤中的保护作用。 ③探讨pim-3调控自噬mTOR依赖途径的可能机制。本课题将从新的角度阐明脓毒血症TEC损伤的机制，及pim-3通过增强自噬减轻AKI的信号通路，为脓毒血症AKI的防治提供新靶点。

脓毒血症是ICU患者发生急性肾损伤（AKI）的最常见原因。脓毒血症并发AKI死亡率极高，机制仍不清楚,但目前认为其机制与缺血再灌注及肾毒性药物所致AKI机制不同。自噬可能在脓毒血症肾小管上皮细胞损伤中发挥重要作用，但相关研究非常少。线粒体保护蛋白humanin在肾脏中的研究未见报道。.本研究探讨humanin促进自噬保护脓毒血症AKI时肾小管上皮细胞及其机制。通过脂多糖LPS诱导脓毒血症AKI小鼠模型及体外刺激人肾小管上皮细胞（HK-2）模型，发现：（1）LPS可诱导脓毒血症肾功能损伤（血肌酐增高），但肾组织病理并未见明确肾小管上皮细胞损伤，提示存在亚细胞器损伤；（2）LPS可诱导肾小管上皮细胞发生自噬，且自噬先于细胞凋亡凋亡；3-MA抑制剂可减少TEC自噬，促进凋亡，自噬诱导剂雷帕霉素可增强自噬，减少凋亡；提示自噬在脓毒血症肾脏损伤中发挥保护作用；（3）LPS诱导的AKI可能与肾小管上皮细胞线粒体功能障碍相关（线粒体膜电位下降），同时线粒体自噬相关蛋白PINK1,Parkin激活,可观察到线粒体自噬现象,提示线粒体自噬参与了AKI的发生；（4）Humanin，一种线粒体外膜蛋白，在脓毒血症AKI模型中明显改善肾功能，且在此过程中，自噬相关蛋白发生改变；体外模型中，humanin改善线粒体功能,PINK1/parkin表达改变,提示humanin的保护作用可能与自噬/线粒体蛋白相关,其机制有待进一步探讨。因此，本研究揭示了脓毒血症时肾小管上皮细胞自噬与凋亡的关系，并发现线粒体保护蛋白humanin在脓毒血症时的肾脏保护作用。