Published online Jun 28, 2019. doi: 10.3748/wjg.v25.i24.3044
Peer-review started: March 20, 2019
First decision: April 4, 2019
Revised: April 27, 2019
Accepted: June 1, 2019
Article in press: June 1, 2019
Published online: June 28, 2019
The formation of liver fibrosis is mainly caused by the activation of hepatic stellate cells (HSCs) and the imbalance of extracellular matrix (ECM) production and degradation. The treatment of liver fibrosis mainly includes removing the cause, inhibiting the activation of HSCs, and inhibiting inflammation. NOD-like receptor (NLR) family, caspase activation and recruitment domain (CARD) domain containing 5/NOD27/CLR16.1 (NLRC5) is a highly conserved member of the NLR family and is involved in inflammation and immune responses by regulating various signaling pathways such as nuclear factor-κB (NF-κB) signaling. It has been found that NLRC5 plays an important role in liver fibrosis, but its specific effect and possible mechanism remain to be fully elucidated.
To investigate the role of NLRC5 in the activation and reversion of HSCs induced with transforming growth factor-β (TGF-β) and MDI, and to explore its relationship with liver fibrosis.
A total of 24 male C57BL/6 mice were randomly divided into three groups, including normal, fibrosis, and recovery groups. Twenty-four hours after a liver fibrosis and spontaneous reversion model was established, the mice were sacrificed and pathological examination of liver tissue was performed to observe the degree of liver fibrosis in each group. LX-2 cells were cultured in vitro and treated with TGF-β1 and MDI. Real-time quantitative PCR (qPCR) and Western blot were used to analyze the expression levels of NLRC5, α-smooth muscle actin (α-SMA), and collagen type I alpha1 (Col1a1) in each group. The activity of NF-κB in each group of cells transfected with NLRC5-siRNA was detected.
Compared with the normal mice, the expression level of NLRC5 increased significantly (P < 0.01) in the fibrosis group, but decreased significantly in the recovery group (P < 0.01). In in vitro experiments, the content of NLRC5 was enhanced after TGF-β1 stimulation and decreased to a lower level when treated with MDI (P < 0.01). The expression of α-SMA and Col1a1 proteins and mRNAs in TGF-β1-mediated cells was suppressed by transfection with NLRC5-siRNA (P < 0.01). Western blot analysis showed that the expression of NF-κB p65 protein and phosphorylated IκBα (p-IκBα) was increased in the liver of mice in the fibrosis group but decreased in the recovery group (P < 0.01), and the protein level of nuclear p65 and p-IκBα was significantly increased after treatment with NLRC5-siRNA (P < 0.01).
NLRC5 may play a key role in the development and reversal of hepatic fibrosis through the NF-κB signaling pathway, and it is expected to be one of the clinical therapeutic targets.
Core tip: Liver fibrosis is a pathological tissue repair process characterized by excessive deposition of extracellular matrix in the liver, accompanied by inflammation, and eventually progresses to cirrhosis. Several recent reports have shown that effective treatment can reverse liver fibrosis, which is associated with inactivation of hepatic stellate cells (HSCs) and multiple signaling pathways. NOD-like receptor (NLR) family, caspase activation and recruitment domain (CARD) domain containing 5/NOD27/CLR16.1 (NLRC5) is the largest member of the NLR family and is highly expressed in immune tissues or organs such as the spleen, lung, thymus, and liver, mediating inflammation inhibition and antiviral response. This study aimed to investigate the role of NLRC5 in activating and devitalization of HSCs and its mechanism. The results demonstrate that NLRC5 may be involved in the development and reversal of liver fibrosis by negative regulation of nuclear factor-κB.