Study Of The Expression Of NLRP3Inflammasome In Liver Fibrosis And Its Potential Mechanism

Liver fibrosis is a wound-healing response to chronic liver injury, whichif persistent leads to cirrhosis and liver failure. Liver injury induces necrosisand apoptosis of hepatocytes, activation of HSC the release of variouscytokine, and finally, the accumulation of ECM, which play a key role in theprocess of liver fibrosis. As liver fibrosis is reversible, looking for newbiomarkers and effective therapeutic target, may help to prevent and reverseliver fibrosis, avoiding serious consequences.Innate immunity is the first line of defense which is indispensable inforeign pathogen elimination and inducing effective immunity response. Theinnate immune system engages an array of pattern-recognition receptors(PRRs) to detect pathogen-associated molecular patterns (PAMPs). NOD-likereceptors(NLRs), members of the pattern recognition receptor family，canrecognize PAMPs as well as DAMPs. Based on different N-terminal domainstructure, the NLRs can be classified into four sub-groups: CIITA、NOD、NLRP and IPAF/NAIP, of which the NLRP sub-groups containing NLRP1～NLRP14. Activated NLRP forms a complex called inflammasome with theeffector molecule, pro-caspase-1as well as an adapter molecule ASC (CARDdomain containing protein). As an important part of innate immunity, theinflammasomes are capable of recognizing a diverse range of danger signalsand lead to inflammation by activation and secretion of many kinds ofinflammatory factors, thus playing a key role in body immunity andoccurrence of disease. The NLRP3inflammasome is currently the moststudied inflammasome and this inflammasome is activated by a wide varietyof cellular alarm signals. Once activated, caspase-1is cleaved, and then inducethe secretion of IL-1β and IL-18, contributes to inflammation. However, as theknowledge of the inflammasome has expanded, it was found that it can directly control collagen synthesis, leading to the increased deposition ofcollagens in the tissues such as the lung, liver, heart, and skin。In a study byWatanabe et al, they were able to demonstrate that the liver antagonistmonosodium urate upregulated TGF-β1and type I collagen, induced thereorganization of actin, and promoted cellular stellation， suggestinginflammasome may induce liver fibrosis by instigating activation of HSC, butthe mechanism is very not clear.Objective: To detect the expression of NLRP3inflammasome as well asdownstream protein factors in liver tissue of rats with liver fibrosis induced bycommon bile duct ligated(BDL) and exprore potential mechanism of NLRP3inflammasome involving in liver fibrosis.Methods：Adult male SD rats(36) were randomly divided into5groups：normal control(6), sham operated control (6) and BDL group，includingB1(8)，B2(8)，B3(8). Hepatic fibrosis was induced successfully by BDL.Livers in model group were harvested at fixed time points：1wk(B1)，2wk(B2)，3wk(B3) after operation．Livers in sham operation group were harvestedat3wk after operation． Histopathological changes were evaluated byhematoxylin and eosin Staining, sirus red and Masson’S trichromemethod． hydroxyproline content in liver tissue was measured，Alanineaminotransferase(ALT)，aspartate aminotransferase(AST)，bilirubin(BIL) inserum were evaluated. The expressions of NLRP3，ASC determined byWestern blot and immunohistochemistry．The activity of hydroxyproline wasanalyzed by using hydroxyproline kits, while the expressions of IL-1β andIL-18were detected by ELISA.Results：①HE, sirus red and Masson’S trichrome staining of liverconfirmed the successful establishment of liver fibrosis. The liver tissues ofBDL rats exhibited Marked proliferation of bile ducts and an extensivedeposition of collagen. Rats in BDL group developed hepatic injury asevidenced by significantly higher concentrations of AST, ALT and TBIL,meanwhile exhibited a remarkable higher expression of hydroxyproline;②The protein expressions of ASC by Western blot and the positive areas NLRP3, ASC by immunohistochemistry were increased during the process of liverfibrogenesis;③The activity of caspase-1enhanced with the process of liverfibrogenesis;④The expressions of IL-1β and IL-18increased during theprocess of liver fibrogenesis.Conclusions：The expression of NLRP3inflammasome increased in livertissue of rats with BDL-induced liver fibrosis，while its downstream factor，caspase-1was activated and the expression of IL-1β and IL-18elevated，suggesting NLRP3inflammasome may play a role in the process of liverfibrosis, one of the potential mechanism may be that its downstreamcytokines-IL-1βand IL-18are involved in liver fibrosis, the other explainationis caspase-1mediated hepatocyte apoptosis instigate liver fibrosis.