Heme and heme degradation products as effectors of hepatic perfusion and excretion failure

越来越多的人认识到细胞外“游离”血红素促进脓毒症相关器官衰竭的发展。反之亦然，组织游离血红素的缓冲或降解已显示介导“疾病耐受性”，即细菌的存在不传播器官功能障碍的状态。发展的战略，以诱导疾病的耐受性是必要的，因为传统的战略，以控制进展，从单纯感染脓毒症与器官衰竭是有限的，在光的负担越来越重的抗菌药物resistance.The预后意义的发展肝排泄衰竭的细菌性脓毒症是以前证明了我们的小组。在FOR 1738的第一个资助期内，我们证实了血红素作为一种强血管收缩剂和细胞毒性因子的意外作用，可被白蛋白中和。同样，深刻的保护血液动力学和细胞毒性作用的血红素可以实现事先诱导血红素加氧酶基因的表达。胆红素氧化终产物Z-BOX A和B作为血红素降解的高级代谢产物未能影响血管张力，但可表征为Rev-erba的部分激动剂，Rev-erba是组织发育和昼夜节律的转录调节因子。这两个盒子的肝细胞骨架的组织，一个重要的因素控制小管膜组织与肝排泄failure.In本基金期间，我们的目标是进一步表征血红素和血红素降解产物（HHDPs）的作用，脓毒症引起的排泄性肝衰竭的发病机制。具体而言，我们将通过他莫昔芬诱导的非特异性或细胞类型特异性敲低其在肝细胞，枯否细胞和血管内皮细胞中的基因表达来表征血红素加氧酶1（HO 1）的细胞类型特异性适应性作用，从而研究HHDP在不同隔室中的作用。将对条件性和细胞类型特异性敲低小鼠品系进行血红素灌注的血流动力学反应评估以及在有或没有预先诱导HO 1的情况下对它们在健康和疾病中的应激耐受性进行系统研究。这些模型系统将使我们能够研究血红素作为收缩剂和一氧化碳（CO）作为血红素降解后产生的扩张剂的相互作用和限制HO 1介导的保护的因素，如形成盒A和B。将专门检测胆红素的这些高级代谢物在炎症刺激后干扰小管膜组织方面的作用。这些研究将表征血红素及其降解产物Z-BOX A和B对第一个资助期内观察到的肝细胞形态和功能的非预期功能。

Extracellular "free" heme is increasingly recognized to promote the development of sepsisassociated organ failure. Vice versa, buffering or degradation of tissue free heme has been shown to mediate "disease tolerance", a state in which presence of bacteria does not propagate organ dysfunction. The development of strategies to induce disease tolerance is necessary because conventional strategies to control progression from uncomplicated infection to sepsis with organ failure are limited in the light of an increasing burden of antimicrobial resistances.The prognostic significance of development of hepatic excretory failure in bacterial sepsis was previously demonstrated by our group. In the first funding period of FOR 1738, we confirmed an unexpected role of heme as a strong vasoconstrictor and cytotoxic factor which could beneutralized by albumin. Similarly, profound protection against hemodynamic and cytotoxic actions of heme could be achieved by prior induction of heme oxygenase gene expression. Bilirubin oxidation end products Z-BOX A and B as higher-order metabolites of heme degradation failed to affect vascular tone but could be characterized as partial agonists of Rev-erba, a transcriptional regulator of tissue development and circadian rhythm. Both BOXes acted on the organization of the hepatocellular cytoskeleton, an important factor controlling the canalicular membrane organization associated with hepatic excretory failure.In this funding period we aim to further characterize the role of heme and heme degradation products (HHDPs) in the pathogenesis of sepsis-induced excretory liver failure. Specifically, we will characterize the cell type-specific adaptive role of heme oxygenase 1 (HO1) by tamoxifeninduced unspecific or cell type-specific knock-down of its gene expression in hepatocytes, Kupffer cells and vascular endothelium, and, thus, investigating the role of HHDPs in distinct compartments. Conditional and cell type-specific knock-down mouse strains will be subjected to both, assessment of hemodynamic response to heme perfusion as well as to systematic studies of their stress tolerance in health and disease with or without prior induction of HO1. These model systems will enable us to study the interaction of heme as a constrictor and carbon monoxide (CO) as a dilator generated upon heme degradation and factors that limit HO1-mediated protection, such as formation of BOXes A and B. These higher-order metabolites of bilirubin will be tested specifically regarding their role in disturbing the canalicular membrane organization upon inflammatory stimuli. These studies will characterize the unexpected functions of heme as well as its degradation products Z-BOX A and B on hepatic cell morphology and function observed in the first funding period.