TLR5 silencing reduced hyperammonaemia-induced liver injury by inhibiting oxidative stress and inflammation responses via inactivating NF-κB and MAPK signals
Introduction
Liver injury, induced by multiple factors such as viral hepatitis, alcoholism, drugs and metabolic diseases, can result in serious liver diseases such as liver fibrosis, acute liver failure and liver encephalopathy [[1], [2], [3]]. Hyperammonaemia (HA), characterized by increased serum ammonia levels, is a common clinical feature in patients with liver disease [4]. Also, earlier findings revealed that acute liver failure patients with persistent HA had lower survival rates and poor prognosis [5]. Moreover, It is a scientific consensus that HA functions as a central player in the pathogenesis of hepatic encephalopathy (HE) (a common complication of liver cirrhosis) and liver cirrhosis [6]. For instance, some documents disclosed that arterial blood ammonia concentration was higher in patients with cirrhosis with HE relative to the same patients after recovery from HE; both values were higher than in patients with cirrhosis with on history of HE [7]. Blood ammonia concentration was higher in patients with liver cirrhosis with respect to healthy controls [8]. Also, HA is related with the increasing severity of liver cirrhosis and HE [9,10]. Moreover, some studies showed that the reduction of blood ammonia level could relieve HE and the increase of blood or brain ammonia level could reproduce the clinical, pathological, and biochemical changes of HE and exacerbate HE development [[11], [12], [13]]. Additionally, ammonium chloride could induce HA, liver injury, and oxidative stress in rats [[14], [15], [16]]. Hence, in the present study, ammonium chloride-induced rat HA models were used to further explore the aetiology of liver injury.
Pattern-recognition receptors (PRRs) including toll-like receptors (TLRs), RIG-I-like receptors, NOD-like receptors, and C-type lectin receptors play central roles in pathogen recognition and initiate innate immune responses [17]. Toll-like receptor 5 (TLR5), a member of toll-like receptor (TLR) family, is known to be a critical mediator in flagellated bacterial pathogens-induced innate immune responses [18]. Recently, the fundamental roles of TLR5 in immune homeostasis beyond recognizing flagellin are gradually appreciated [19]. For example, a study pointed out that TLR5 could function as an antimetastatic and hepatoprotective reagent [20]. Also, previous studies demonstrated that TLR5 activation by flagellin could induce liver injury and TLR5 knockdown alleviated carbon tetrachloride (CCl4)-induced liver injury in mice [21,22] and our previous study showed that TLR5 was abnormally expressed, hinting the vital roles of TLR5 in HA-induced liver injury.
In the present study, we aimed to further delve into the function and molecular basis of TLR5 in HA-induced rat liver injury models.
Section snippets
Liver injury models
Male Sprague-Dawley (SD) wide type (WT) rats (n = 12, 6 weeks old, 200 g ± 25 g weight) and TLR5−/− rats (n = 12, 6 weeks old, 200 g ± 25 g weight) were purchased from BIORAY LABORATORIES Inc. (Shanghai, China). All experiment procedures were performed with the approval of Animal Ethics Committee of the First Affiliated Hospital of Zhengzhou University and the institutional guidelines for the care and use of laboratory animals. WT rats were randomly divided into WT-Control and WT-HA group with
TLR5 was highly expressed in liver tissues of HA rats
To explore the role of TLR5 in liver injury, rat models of HA-induced liver injury were established by constantly intragastrical administration with ammonium chloride into rats. Firstly, we validated that the physiological status of rats under the treatment of saline or ammonium chloride were satisfactory without ammonia toxicity. Then, serum ammonia concentrations were measured at the indicated time points (1, 2, 3, 4 weeks) after ammonium chloride treatment. Results showed that medium level
Discussion
Liver injury is an enormous threat for human health and life, and is responsible for substantial economic and social expenditure worldwide [[1], [2], [3]]. Earlier studies revealed that HA (induced by ammonium salts) could enhance oxidative stress and trigger liver dysfunction and failure [[26], [27], [28]]. Moreover, the reduction of blood ammonia levels at an early time point notably relieved liver injury in HA rats with acute liver failure [29]. Additionally, delayed diagnosis or treatment
Conclusion
In summary, our study revealed that TLR5 silencing reduced HA-induced liver injury by inhibiting oxidative stress and inflammation responses via inactivating NF-κB and MAPK signaling pathways, demonstrating the central roles of TLR5 in HA-induced liver injury and providing a potential target for alleviating liver injury.
Acknowledgements
Not applicable.
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These authors contributed to this work equally.