NF-κB is the central transcriptional regulator of inflammatory and immune responses.39 Constitutive NF-κB activation has been implicated in the malignant progression of numerous human inflammatory
diseases, metabolic diseases, cancers, and diabetes.40 Inhibiting the aberrant activation of NF-κB signaling can slow down or stop these disease processes.41, 42 In this study, our analysis results of inflammatory gene expression revealed that TGR5 has anti-inflammatory properties in the mouse liver. Our data show that TGR5 activation prevents the phosphorylation of IκBα, nuclear translocation of p65, and NF-κB DNA-binding activity. Activation of NF-κB in Kupffer cells promotes liver cancer development through IL-6 and liver-inflammatory responses.43 Blockage of NF-κB by deletion of GSK3235025 IKKβ in Kupffer cells, in addition to hepatocytes, strongly inhibited diethylnitrosamine-induced HCC development.43 Thus, the suppression of NF-κB might be a therapeutical strategy for treating liver cancer, because the loss of NF-κB in Kupffer cells might suppress cancer. TGR5 is highly expressed in Kupffer cells of the liver.13, 14 In this study, we demonstrated that TGR5 activation is able to strongly suppress NF-κB-induced Mitomycin C supplier inflammation in vitro and in vivo, which suggests that TGR5 may be a
desirable therapeutic target for liver cancer treatment. It has been reported that TGR5 could be a potential target for the treatment of diabesity and associated metabolic disorders.10, 12, 44, 45 For example, Watanabe et al. reported that TGR5 activation by bile acids induces energy expenditure in muscle and brown adipose tissue.10 Thomas et al. found that TGR5 activation improves glucose tolerance and insulin sensitivity in fat-fed mice.12 These diseases, such as obesity, insulin resistance, and type 2 diabetes, are also closely associated with chronic inflammation, characterized by abnormal cytokine production, increased acute-phase reactants, and activation of a network of inflammatory signaling pathways.4,
46, 47 Inhibition of NF-κB-related inflammation is able to improve glucose metabolism in vivo.48, 49 Here, our data show that TGR5 is a negative modulator of NF-κB-mediated inflammation. Therefore, there is a potential link between anti-inflammation and Sclareol treatment of obesity and diabetes through TGR5. TGR5 may be an attractive therapeutic target for metabolic disorders through not only regulation of energy and glucose homeostasis, but also suppression of NF-κB signaling. In conclusion, our results reveal that TGR5 is a negative regulator of NF-κB-mediated hepatic inflammation, and indicate that TGR5 ligands have utility in anti-inflammation. These findings suggest that TGR5 is a potential target for anti-inflammatory drug design, and its agonist ligands offer possible therapies to prevent and treat inflammatory liver diseases. The authors thank Dr.