Canbay, Ali

ABSTRACT Background and Aims Osteopontin (OPN) promotes the ductular reaction and is a major driver of chronic liver disease (CLD) progression. Although CLD is characterised by the accumulation of inflammatory cells including macrophages around the peri‐portal regions, the influence of OPN on recruitment is unclear. We investigated the role of OPN in cholangiocyte chemokine production and macrophage recruitment by combining in vivo, in vitro, and in silico approaches. Methods The effects of OPN on cholangiocyte chemokine production and macrophage migration were assessed in culture, alongside RNA‐sequencing to identify genes and pathways affected by OPN depletion. Murine liver injury models were used to assess liver chemokine expression and liver macrophage/monocyte recruitment. OPN and chemokine expression were analysed in liver tissue and plasma from biopsy‐proven metabolic dysfunction‐associated alcoholic steatohepatitis (MASH) patients. Results OPN‐knockdown in cholangiocytes reduced chemokine secretion. RNA‐sequencing showed OPN‐related effects clustered around immunity, chemotaxis and chemokine production. Macrophage exposure to cholangiocyte‐conditioned media showed OPN‐supported migration via chemokines chemokine (C‐C motif) ligand (CCL)2, CCL5 and chemokine (C‐X‐C motif) ligand (CXCL)1. These effects were related to NF‐κB signalling. Murine liver fibrosis was accompanied by upregulated liver OPN, CCL2, CCL5 and CXCL1 mRNA, and accumulation of liver cluster of differentiation (CD)11b/F4/80 + CC chemokine receptors (CCR2) high macrophages but treatment with OPN‐specific neutralising aptamers reduced fibrosis, chemokine mRNAs and accumulation of liver CD11b/F4/80 + CCR2 high /lymphocyte antigen 6 complex high inflammatory monocytes. In human MASH, liver OPN correlated with chemokines CCL2 and IL8 in association with portal injury and fibrosis. Plasma OPN, serum CCL2 and IL8 also increased with fibrosis stage. Conclusions OPN promotes cholangiocyte chemokine secretion and the accumulation of pro‐inflammatory monocytes. These data support neutralisation of OPN as an anti‐inflammatory and anti‐fibrotic strategy.

Hepatic steatosis predisposes the liver to cold ischemia-warm reperfusion (CI/WR) injury by unclear mechanisms. Because hepatic steatosis has recently been associated with a lysosomal pathway of apoptosis, our aim was to determine whether this cell-death pathway contributes to CI/WR injury of steatotic livers. Wild-type and cathepsin B-knockout ( Ctsb −/−) mice were fed the methionine/choline-deficient (MCD) diet for 2 wk to induce hepatic steatosis. Mouse livers were stored in the University of Wisconsin solution for 24 h at 4°C and reperfused for 1 h at 37°C in vitro. Immunofluorescence analysis of the lysosomal enzymes cathepsin B and D showed a punctated intracellular pattern consistent with lysosomal localization in wild-type mice fed a standard diet after CI/WR injury. In contrast, cathepsin B and D fluorescence became diffuse in livers from wild-type mice fed MCD diet after CI/WR, indicating that lysosomal permeabilization had occurred. Hepatocyte apoptosis was rare in both normal and steatotic livers in the absence of CI/WR injury but increased in wild-type mice fed an MCD diet and subjected to CI/WR injury. In contrast, hepatocyte apoptosis and liver damage were reduced in Ctsb −/− and cathepsin B inhibitor-treated mice fed the MCD diet following CI/WR injury. In conclusion, these findings support a prominent role for the lysosomal pathway of apoptosis in steatotic livers following CI/WR injury.