A TLR2/S100A9/CXCL-2 signaling network is necessary for neutrophil recruitment in acute and chronic liver injury in the mouse

Abstract

Background and aims Neutrophils are important immune effectors required for sterile and non-sterile inflammatory responses. However, neutrophils are associated with pathology in drug-induced liver injury, acute alcoholic liver disease and ischemia-reperfusion injury. An understanding of the complex mechanisms that control neutrophil recruitment to the injured liver is desirable for developing strategies aimed at limiting neutrophil-mediated cellular damage. Methods Wt, tlr2−/−, tlr4−/− and s100a9−/− mice were administered CCl4 either acutely (8, 24, 48 or 72 hrs) or chronically (8 weeks) and livers investigated by histological (IHC for neutrophils, fibrogenesis, proliferation and chemotactic proteins) or molecular approaches (qRT-PCR for neutrophil chemoattractant chemokines and cytokines as well as pro-fibrogenic genes). Results Mice lacking TLR2 or S100A9 failed to recruit neutrophils to the injured liver and had a defective hepatic induction of the neutrophil chemokine CXCL-2. Hierarchy between TLR2 and S100A9 proved to be complex. While induction of S100A9 was dependent on TLR2 in isolated neutrophils, there was a more complicated two-way signalling cross-talk between TLR2 and S100A9 in whole liver. However, wound-healing and regenerative responses of the liver were unaffected in these genetic backgrounds as well as in wild type mice in which neutrophils were depleted by infusion of Ly-6G antibody. Conclusion We have identified TLR2 and S100A8/S100A9 as key regulators of hepatic CXCL-2 expression and neutrophil recruitment. This novel TLR2-S100A9-CXCL-2 pathway may be of use in development of new strategies for selectively manipulating neutrophils in liver disease without impairing normal wound healing and regenerative responses.

Neutrophils alleviate fibrosis in the CCl4‐induced mouse chronic liver injury model

“…Neutrophils reportedly have a minimal impact on wound repair and regeneration,22 which contradicts our findings. However, the experimental setting of Moles et al differed from ours in that they used S100A9 KO mice in which inflammatory cytokines were reduced and neutrophil levels in the liver remained 50%‐60% of the normal level 22.…”

“…However, the experimental setting of Moles et al differed from ours in that they used S100A9 KO mice in which inflammatory cytokines were reduced and neutrophil levels in the liver remained 50%‐60% of the normal level 22. In our system, neutrophil levels were reduced to 14% in the peripheral blood and 30% in the liver by Ly6G antibody.…”

Hepatocyte-specific Bid depletion reduces tumor development by suppressing inflammation-related compensatory proliferation

“…39 Carbon tetrachloride model: CCL4 injections were performed as previously described. 40 Eight-week-old Bid Δhep and Bid flo/flo mice were injected intraperitoneally with a single prediluted (1 : 3 in olive oil) dose (1 μl/g) of CCL4.…”

Roles for Chemokines in Liver Disease

“…22 The accumulation of neutrophils, which is endorsed via CXCL8 in humans 120 and via CXCL1 and CXCL2 in mice, 121 appears functionally less relevant for hepatic fibrosis. 122 Another functionally important chemokine pathway in liver fibrosis is CCL5 (RANTES); the receptors are CCR1 and CCR5. CCL5 and the related CCR5 ligands CCL3 and CCL4 are up-regulated in livers of patients with fibrosis.…”