Polyamine metabolism in heart and kidney ischemic injury

描述(由申请人提供)：与缺血/再灌注损伤(IRI)相关的疾病，如心肌梗死和急性缺血性肾功能衰竭，是导致发病率和死亡率的主要原因。心脏和肾脏IRI的病理生理机制非常相似，毒性代谢产物(如H202)的产生增加，再灌注后细胞凋亡增加，细胞死亡，提示相同的途径(S)可能介导了IRI两个器官的细胞损伤和功能障碍。为探讨IRI的病理生理机制，采用抑制性消减杂交技术对正常大鼠肾脏和肾缺血30min(肾动脉结扎)再灌注12h的大鼠肾脏的RNA进行了检测。结果表明，IRI中参与多胺分解代谢的限速酶亚精胺/精胺N-1乙酰转移酶(SSAT)的表达增强。有趣的是，缺血30分钟(左前降支结扎)后再灌流6-12小时，在心肌损伤区诱发SSAT，正常心肌几乎检测不到SSAT的表达，再灌流6小时SSAT表达增加50倍。IRI时肾脏和心脏SSAT表达增强与腐胺浓度升高有关，腐胺是细胞凋亡的媒介，也是SSAT活性增强的一种现象。在培养细胞中条件性过表达SSAT会导致细胞生长减慢。 该提案中概述的研究将检验SSAT是细胞损伤的生物标记物的假设，其表达增加反映了心脏和肾脏与IRI相关的组织损伤的程度。我们进一步假设，SSA T在肾脏或心脏的表达增强，通过耗尽多胺、产生有毒代谢物(如H202、腐胺和各种醛)和诱导细胞凋亡而导致细胞损伤。为了验证这些假说，我们建议：1.研究SSAT和多胺途径在肾脏和心脏IRI中的表达和调控；2.确定SSAT过表达对肾和心脏IRI细胞存活和损伤易感性的作用；以及3.确定SSAT介导的细胞损伤在肾和心脏IRI中的机制。深入了解SSAT和其他参与多胺代谢的酶在IRI中的表达和调控，将有助于揭示IRI在心脏和肾脏的病理生理机制，并可能为早期发现、预防或治疗缺血性心脏病发作和急性缺血性肾功能衰竭提供新的诊断测试和治疗方案。

DESCRIPTION (provided by applicant): Conditions associated with ischemia/reperfusion injury (IRI) such as myocardial infarction and acute ischemic renal failure are among the major causes of morbidity and mortality. The pathophysiology of IRI is strikingly similar in heart and kidney, with enhanced production of toxic metabolites (i.e. H202), increased apoptosis, and cell death following reperfusion, raising the possibility that identical pathway(s) may mediate cell injury and dysfunction in both organs in IRI. In an attempt to identify the factors involved in the pathophysiology of IRI, suppression subtractive hybridization on RNA from normal rat kidneys and kidneys of animals subjected to 30 min of ischemia (renal artery ligation) followed by 12 hrs of reperfusion was performed. The results identified enhanced expression of Spermidine/Spermine N-1 acetyltransferase (SSAT), the rate limiting enzyme involved in the catabolism of polyamines, in IRI. Interestingly, thirty (30) min of ischemia (left anterior descending artery ligation) followed by 6-12 hrs of reperfusion resulted in the induction of SSAT in the injury zone in myocardium, with SSAT expression being almost undetectable in normal myocardium and increasing by >50-fold at 6 hrs of reperfusion. Enhanced SSAT expression in kidney and heart in IRI was associated with increased concentrations of putrescine, a mediator of apoptosis and a phenomenon indicative of increased activity of SSAT. Conditional overexpression of SSAT in cultured cells resulted in decreased cell growth. The studies outlined in this proposal will test the hypothesis that SSAT is a biomarker of cell injury and its increased expression reflects the extent of tissue damage associated with IRI in heart and kidney. We further hypothesize that enhanced expression of SSA T in kidney or heart leads to cell damage through depletion of polyamines, production of toxic metabolites (e.g. H202, putrescine and various aldehydes) and induction of apoptosis. To test these hypotheses, we propose to: 1. Examine the expression and regulation of SSAT and polyamine pathway in renal and heart IRI, 2. Ascertain the role of SSAT over expression on cell survival and susceptibility to injury in renal and cardiac IRI, and 3. Ascertain the mechanism of SSAT-mediated cell injury in renal and cardiac IRI. Insight into the expression and regulation of SSAT and other enzymes involved in polyamine metabolism in IRI will shed new lights into the pathophysiology of IRI in heart and kidney and may provide basis for novel diagnostic tests and therapeutic options targeted at early detection, prevention or treatment of ischemic heart attack and acute ischemic renal failure.