Interleukin‐18 signaling promotes activation of hepatic stellate cells in mouse liver fibrosis

Abstract

Background and Aims: Nucleotide‐binding oligomerization domain‐like receptor‐family pyrin domain‐containing 3 (NLRP3) inflammasome activation has been shown to result in liver fibrosis. Mechanisms and downstream signaling remain incompletely understood. Here, we studied the role of IL‐18 in hepatic stellate cells (HSCs), and its impact on liver fibrosis. Approach and Results: We observed significantly increased serum levels of IL‐18 (128.4 pg/ml vs. 74.9 pg/ml) and IL‐18 binding protein (BP; 46.50 ng/ml vs. 15.35 ng/ml) in patients with liver cirrhosis compared with healthy controls. Single cell RNA sequencing data showed that an immunoregulatory subset of murine HSCs highly expresses Il18 and Il18r1. Treatment of cultured primary murine HSC with recombinant mouse IL‐18 accelerated their transdifferentiation into myofibroblasts. In vivo, IL‐18 receptor‐deficient mice had reduced liver fibrosis in a model of fibrosis induced by HSC‐specific NLRP3 overactivation. Whole liver RNA sequencing analysis from a murine model of severe NASH‐induced fibrosis by feeding a choline‐deficient, L‐amino acid‐defined, high fat diet showed that genes related to IL‐18 and its downstream signaling were significantly upregulated, and Il18 −/− mice receiving this diet for 10 weeks showed protection from fibrotic changes with decreased number of alpha smooth muscle actin‐positive cells and collagen deposition. HSC activation triggered by NLRP3 inflammasome activation was abrogated when IL‐18 signaling was blocked by its naturally occurring antagonist IL‐18BP. Accordingly, we observed that the severe inflammatory phenotype associated with myeloid cell‐specific NLRP3 gain‐of‐function was rescued by IL‐18BP. Conclusions: Our study highlights the role of IL‐18 in the development of liver fibrosis by its direct effect on HSC activation identifying IL‐18 as a target to treat liver fibrosis.

Therapeutic modulation of the liver immune microenvironment

“…[62] NLRP3-induced liver fibrosis also involves IL-18, as IL-18-binding protein blocked hepatic inflammation and fibrosis in Nlrp3 gain-offunction mice, and IL-18 −/− mice exposed toward a dietary model of NASH had lower rates of hepatic fibrosis. [63] We demonstrated that inflammatory cytokines circulate in human chronic liver diseases, especially in case of liver cirrhosis, irrespective of etiology, supporting the notion that inflammation drives many features of chronic liver diseases. [64] Hepatic NLRP3 and caspase-1 expression are increased in patients with chronic hepatitis B infection [65] and in liver cirrhosis.…”

“…The NLRP3 inflammasome directly triggers upregulation of fibrotic markers at both mRNA and protein levels in activated HSCs, and importantly, Nlrp3 knock-in mice exhibited liver fibrosis with an increase in alpha-smooth muscle actin and collagen production independent of inflammatory infiltration 62 . NLRP3-induced liver fibrosis also involves IL-18, as IL-18-binding protein blocked hepatic inflammation and fibrosis in Nlrp3 gain-of-function mice, and IL-18 −/− mice exposed toward a dietary model of NASH had lower rates of hepatic fibrosis 63 . We demonstrated that inflammatory cytokines circulate in human chronic liver diseases, especially in case of liver cirrhosis, irrespective of etiology, supporting the notion that inflammation drives many features of chronic liver diseases 64 .…”

Enhanced Expression of ARK5 in Hepatic Stellate Cell and Hepatocyte Synergistically Promote Liver Fibrosis

“…Previous studies have shown that IL-6 activates HSCs by inducing the activation of the STAT3 pathway [ 42 ]. In addition, a recent study confirmed that IL-18 can directly promote the activation of hepatic stellate cells in mouse liver fibrosis [ 43 ]. Together with TGF-β1, they mediate the activation of HSCs through different mechanisms.…”

The discovery of NLRP3 and its function in cryopyrin‐associated periodic syndromes and innate immunity

“…The identification of IL‐1 independent mechanisms in the pathophysiology of murine CAPS directed our attention to other pro‐inflammatory cytokines, beginning with IL‐18, another inflammasome‐associated cytokine requiring caspase 1 for cleavage and activation. Mutant mice treated with an IL‐18 binding protein demonstrated significant improvement in rash, weight gain, survival, and liver pathology 141 . Similarly, mutant Nlrp3 mice on an IL‐18 or IL‐18R deficient background revealed a strong phenotypic rescue in pups with complete resolution of rash, and normal growth and survival through the first 2 months of life in the MWS model.…”