Plasma membrane‐bound G protein–coupled bile acid receptor attenuates liver ischemia/reperfusion injury via the inhibition of toll‐like receptor 4 signaling in mice

Abstract

The plasma membrane-bound G protein-coupled bile acid receptor (TGR5) displays varied levels of expression in different tissues. TGR5-induced liver protection has been demonstrated during several liver diseases, except during ischemia/reperfusion injury (IRI). Male adult wild-type and TGR5 knockout (KO) mice were subjected to liver partial warm ischemia/reperfusion. Hepatic injury was evaluated based on serum alanine aminotransferase and serum aspartate aminotransferase. Liver histological injury and inflammatory cell infiltration were evaluated in tissue sections using liver immunohistochemical analysis. We used quantitative realtime polymerase chain reaction to analyze the liver expression of inflammatory cytokines. The toll-like receptor 4 (TLR4) signaling pathway and its related apoptotic molecules were investigated after reperfusion. Moreover, the effect of TGR5 on inflammation was determined with TGR5 1/1 or TGR5 2/2 primary bone marrow-derived macrophages in vitro. TGR5 significantly attenuated liver damage after IRI. As demonstrated by in vivo experiments, TGR5 significantly reduced the up-regulation of the TLR4-nuclear factor kappa B (NF-jB) pathway and inhibited caspase 8 activation after IRI. Later experiments showed that TGR5 KO significantly increased the expression of TLR4-NF-jB signaling molecules and promoted hepatocellular apoptosis. In addition, in vitro experiments showed that overexpression of 6alpha-ethyl-23(S)-methylcholic acid (INT-777)-activated TGR5 directly downregulated tumor necrosis factor a (TNF-a) and interleukin (IL) 6 expression but up-regulated IL10 expression in hypoxia/reoxygenation-induced primary TGR5 1/1 macrophages. Moreover, the expression of TLR4-NF-jB signaling molecules was significantly inhibited by the activation of TGR5. Importantly, these results were completely reversed in primary TGR5 2/2 macrophages. This work is the first to provide evidence for a TGR5-inhibited inflammatory response in IRI through suppression of the TLR4-NFjB pathway, which may be critical in reducing related inflammatory molecules and modulating innate inflammation. The plasma membrane-bound G protein-coupled bile acid receptor (TGR5) displays varied levels of expression in different tissues. (1)(2)(3) Growing evidence has shown that TGR5 can regulate bile acid homeostasis, increase energy expenditure in brown adipose tissue, and contribute to glucose metabolism. (4)(5)(6) In addition, another novel function of TGR5 is its potent anti-inflammatory effect. In hepatic tissue, TGR5 expression is detected in macrophages, including Kupffer cells. (2) An in vivo study has demonstrated that activation of TGR5 decreases lipopolysaccharide (LPS)-induced inflammation in the liver (7) and inflammation in atherosclerotic plaques. (8) InAbbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BMDM, bone marrow-derived macrophage; ELISA, enzyme-linked immunosorbent assay; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; GPCR, G protein-coupled receptor; HPRT, hypoxanthine-guanine phos...

Overexpression of TGR5 alleviates myocardial ischemia/reperfusion injury via AKT/GSK-3β mediated inflammation and mitochondrial pathway

“…Here, we studied the function and mechanism of TGR5 in H/R-induced injury in H9C2 and HCM cells. We found that the levels of TGR5 mRNA and protein were significantly increased and peaked after 6 h of reperfusion following Hypoxia for 4 h, which is similar to the studies of Yang et al [13] and Zhuang et al [14] who reported that the level of TGR5 improved in the early stages of reperfusion and peaked at 6 h after reperfusion in the liver and hepatocytes after I/R injury. Besides, our present results demonstrated that overexpressed TRG5 alleviates myocardial I/R-induced apoptosis rate and regulates the levels of apoptosis-related proteins.…”

“…In recent years, studies have shown that TGR5 plays a key role in myocardial adaptability, and activated TGR5 may be a potentially attractive treatment option in cardiac hypertrophy and heart failure [11,12]. At present, reports indicated that that TGR5 alleviates the liver I/R-related inflammation and protects hepatocytes from I/R-related apoptosis [13,14]. However, the role and function of TGR5 in myocardial I/R injury remained poorly understood.…”

TGR5, Not Only a Metabolic Regulator

“…In liver, TGR5 inhibits the expression of inflammatory mediators in response to NF-κB activation induced by LPS in wild-type (WT), but not TGR5 −/− mice (Wang et al, 2011). Yang et al (2016) reported that during ischemia/reperfusion injury TGR5 inhibited inflammatory response through suppression of the Toll-like receptor 4 (TLR4)-NF-κB pathway. TGR5 activation can also suppress LPS-induced production of cytokines in Kupffer cells and TGR5-overexpressed THP-1 cells (Kawamata et al, 2003; Keitel et al, 2008).…”

Characteristic MicroRNA Expression Induced by δ-Opioid Receptor Activation in the Rat Liver Under Prolonged Hypoxia

“…Indeed, hypoxia activates multiple hypoxia mediators and in turn accelerate or antagonize hepatic damage [1, 2]. A variety of pharmacological interventions have been proposed to alleviate hypoxic injury in the liver, however, there is no promising therapy for the prevention and treatment of hypoxic liver injury yet [3-6]. …”