Concanavalin A-induced autoimmune hepatitis model in mice: Mechanisms and future outlook

Abstract

The concanavalin A (Con A)-induced liver injury mouse model is a typical animal model focusing on T cell-dependent hepatic damage in the field of autoimmune hepatitis (AIH). However, the underlying mechanism of hepatic dysfunction due to cell activation or signaling pathways triggered by Con A has not been fully clarified. Therefore, the controversy on this model remains in the academic community. In this article, we first summarized the merit and demerit of this contentious model from the perspectives of cell dysfunction, microcirculation disturbance, involved signaling pathways, as well as the properties of Con A. Then, we summed up the scientific implications of the model in elucidating the pathogenesis of AIH, and the shortcomings of this model were also summarized to elucidate the pathogenesis and application prospect of this classical liver injury mouse model in the study of AIH.

Keywords: autoimmune hepatitis; concanavalin A; experimental animal models; inflammation; pathogenesis.

Figure 1

The multicellular participation mechanism participated in establishing the Con A-induced liver injury mouse model. Con A was capable of attaching to MHC class II, MR, and ICMA-1. Th0 cell differentiated into Th1, Th2, Th17, and Treg by the recognition of MHC class II-Con A complex via TCR, and Th1 and Th17 induced the hepatocyte necrosis and apoptosis by secreting TNF-α, IFN-γ, IL-17, and IL-22, while Th2 and Treg would induce tolerance toward Con A by secreting IL-10 or expressing CTLA. Th0 could also migrate to the inflamed tissue by adhering to CXCLs via CXCR3. The NKT directly induced the death of hepatocytes or SECs by expressing TNF-α and IFN-γ after combining with this lectin through TCR. The MRs, located on the surface of macrophages and neutrophils, contain multiple CTLD, and the N-acetylglucosamine of Con A can combinate to the MRs to induce the receptor-mediated endocytosis and phagocytosis to maintain the stability of the internal environment. At the same time, Con A also can lead to the activation of macrophages and neutrophils via MRs, to increase the release of superoxide anions and induce the synthesis of cytokines (including TNF-α, IFN-γ, IL-1β, MIP-2, and ROS). Con A promoted the expression of β 2-integrin on neutrophils, which was essential for neutrophil recruitment. The attachment of SECs to Con via MR, MHC class II, and ICAM-1 could give rise to their death, facilitating the adhesion of Con A to KCs. CTLs would activate by the Con A-mediated expression of TNF-α and IFN-γ and infiltrate to the necrotic area by recognizing MHC class I expressed on the surface of damaged hepatocytes, which is absent from the normal liver tissue. Both CTLs and NKTs contributed to the apoptosis of hepatic cells via the Fas/FasL pathway.

Figure 2

The signal transduction pathways targeting NF-κB are involved in building the Con A-induced AIH mouse model. Numerous inflammatory signals (such as IL-1β, IL-6, TNF-α, and some other pro-inflammatory cytokines) could give rise to the activation of IKKs and translocation of NF-κB dimers from the cytoplasm to the nucleus, through multiple signal transduction pathways, including “TLR signaling pathway”, “MAPK signaling pathway”, and “PI3K/Akt signaling pathway”. The nuclear translocation of NF-κB resulted in the synergistic expression of multiple inflammatory and innate immune genes eventually, involving IL-1β, IL-6, and TNF-α as well. Thus, IL-1β, IL-6, TNF-α, and NF-κB formed an amplifying feed-forward loop. (1) PI3K/Akt signaling pathway, (2) TLR-2 and 4 signaling pathway, (3) TNF-α signaling pathway, and (4) MAPK signaling pathway.

Figure 3

The microcirculation disturbance mechanism related to the foundation of Con A-induced AIH mouse model. Con A first caused a significant decrease in blood flow in the hepatic sinusoid after being administrated. Thereafter, abnormally activated T cells immediately produce a large amount of IFN-γ and TNF-α, and then the STAT1 signaling pathway is activated to promote the SECs and KCs to synergistically express tissue factor (TF). TF facilitated the fibrinogen agglutinating into fibrin clots as a type of starting factor of coagulation reaction. TNF-α triggered the production of plasminogen activator inhibitor type 1 to inhibit the anticoagulant pathway by suppressing the degradation of fibrin clots into fibrinogen degradation product. SECs and KCs could also express TF after adhering to Con A directly. All of them worked together to result in hypercoagulation and form numerous microthrombi, which would eventually contribute to the necrosis of hepatocytes. The anti-clotting agent, such as heparin, has significant protective effects on the hepatic injury induced by lectin through inhibiting the clotting activity.