The Function And Mechanism Of Tollip In Hepatic Ischemia Reperfusion Injury

Hepatic ischemia reperfusion injury?IRI?is a major complication of hypovolemic shock,liver resection and transplantation,and lacks effective therapeutic treatments in clinic.Hepatic IRI is a dynamic process involving two stages of ischemic injury and inflammatory-mediated reperfusion injury.During the liver ischemia stage,hypoxia leads to low oxidative phosphorylation function of mitochondria,rapid depletion of adenosine triphosphate?ATP?,large accumulation of acidic substances,Ca²⁺overload,etc.,which lead to initial damage of liver parenchymal cells.During reperfusion,the re-input of blood leads to a large amount of reactive oxygen species?ROS?production,Kupffer cells activation,increased inflammation-related factors,increased expression of cell adhesion factors.And all these factors in turn promote the activation of neutrophils and their infiltration into damaged hepatocytes and lead to the apoptosis and necrosis of hepatocytes further.Numerous studies have shown that inflammatory responses and cell death during reperfusion are the main causes of tissue destruction caused by IR in the liver.Therefore,seeking factors that are highly sensitive to the process of hepatic IRI and closely regulating these pathological features is an urgent need for developing therapeutic applications for hepatic IR injury.Toll-interacting protein?Tollip?is a protein that interacts with the cytoplasmic part of interleukin-1 receptor accessory protein?IL-1RAcP?and has complex regulatory functions in the inflammatory pathway.In the Toll-like signaling pathway,Tollip acts as a negative regulator and inhibits the occurrence of the Toll signaling pathway.However,in liver tissues,the absence of Tollip could attenuate the expression of inflammatory factors by blocking the production of ROS.On the other hand,Tollip promots cellular inflammation and apoptosis by regulating the PI3K-Akt and nuclear factor kappa B?NF-?B?signaling pathway in the models of myocardial infarction and stroke.Tollip plays an important role in regulating cell inflammation and apoptosis,but the function of Tollip in hepatic IRI has not been reported.This study used a variety of omics methods to systematically analyze the prominent contributors and potential therapeutic targets of hepatic IRI.Based on an unbiased proteomics analysis,we found that Tollip protein expression was closely correlated with hepatic IRI process.Using Tollip knockout?Tollip-KO?mice in vivo and Tollip knockdown hepatocytes in vitro,we confirmed that hepatocyte Tollip plays an important role in the pathogenesis of IRI.Through phenotypic evaluation combined with RNA-seq data analysis,we found that Tollip deficiency in hepatocytes significantly reduced IR-induced liver injury by inhibiting cell death and inflammatory responses.Mechanistically,Tollip interacts with apoptosis signal-regulating kinase 1?ASK1?and promotes the recruitment of tumor necrosis factor receptor associated factor 6?TRAF6?to ASK1,thereby enhancing N-terminal dimerization of ASK1 and activating ASK1-c-jun N-terminal kinase?JNK?/p38 cascades.The Tollip MF motif and TRAF6 ubiquitinating activity are required for Tollip-regulated ASK1-mitogen-activated protein kinases?MAPK?axis activation.Our studies confirmed that Tollip plays an important role in hepatic IRI and Tollip deficiency alleviates this process through inhibiting ASK1-JNK/p38 axis activation.Targeting Tollip or its interaction with ASK1 might represent highly promising approaches for treating liver damage.