A study of regulatory effects of TLR4 and NF-κB on primary biliary cholangitis

To investigate the regulatory effects of the Toll-like receptor 4 (TLR4) and the nuclear factor kappa-light-chain-enhancer of the activated B cells (NF-κB) on primary biliary cholangitis (PBC) and to analyze the possible mechanisms.

A total of 24 C57BL/6 mice were randomly divided into M group (n=12, intraperitoneally injected with polyinosinic acid-polycytidine acid (PolyI:C) for 12 consecutive weeks, 2 times/week) and C group (n=12, intraperitoneally injected with the same volume of normal saline). After 12 weeks, the mice were sacrificed to collect liver tissues. Then, an enzyme-linked immunosorbent assay (ELISA) kit was used to detect the content of interleukin-6 (IL-6), IL-10, and tumor necrosis factor-alpha (TNF-α) in liver tissues. Hematoxylin-eosin (HE) staining assay was performed to observe the pathological changes of liver tissues, and measure the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in peripheral blood of mice. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) staining was applied to determine cell apoptosis in liver tissues. The relative messenger ribonucleic acid (mRNA) expression levels of TLR4 and NF-κB in liver tissues were detected by quantitative Polymerase Chain Reaction (qPCR). Western blotting was adopted to measure the protein expressions of TLR4, NF-κB, myeloid differentiation factor 88 (MyD88), B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax), and Caspase-3.

Compared with that in C group, the content of IL-6 and TNF-α in liver tissues in M group was significantly increased (p<0.01), but the level of IL-10 was statistically downregulated (p<0.01). According to HE staining, liver damage of mice in M group was evidently severer than that in C group, and the levels of ALT and AST in M group were significantly higher than those in C group (p<0.01). The amount of TUNEL-positive cells in liver tissues in M group was significantly greater than that in C group (p<0.01). The levels of TLR4 and NF-κB mRNA in liver tissues from M group were significantly elevated in comparison with the C group (p<0.01). Compared with those in C group, the expressions of TLR4, NF-κB, MyD88, and Caspase-3 proteins in M group showed statistical increases in liver tissues (p<0.01), whereas that of Bcl-2/Bax was significantly declined (p<0.01).

PBC activates the TLR4/MyD88/NF-κB signaling pathway, induces the release of inflammatory factors and produces a large number of apoptotic proteins, which results in liver damage and cell apoptosis in mice.