Abstract
Objective In healthy livers, latent transforming growth factor-β (LTGF-β) is stored in the extracellular matrix and kept quiescent by extracellular matrix protein 1 (ECM1). Upon damage, ECM1 is downregulated in hepatocytes, facilitating LTGF-β activation and hepatic fibrosis. This study investigates the underlying molecular mechanisms by which ECM1 expression in the liver is controlled under patho-physiological conditions.
Design In silico promoter analysis was used to predict pathways that regulate Ecm1 transcription. Functional assays were performed in AML12 cells, mouse and human primary hepatocytes (MPHs, HPHs), and in liver tissue of mice and patients.
Results In healthy liver, EGF/Egfr signaling maintains Ecm1 expression through phosphorylation of Stat1 at S727, which promotes its binding to the Ecm1 gene promoter to enhance gene transcription. During liver inflammation, accumulated IFNγ interferes with EGF signaling by downregulating Egfr expression and by disrupting EGF/Egfr/Stat1-mediated Ecm1 promoter binding. Mechanistically, IFNγ induces Stat1 phosphorylation at position Y701, which is competing with the ability of p-Stat1 S727 to bind to the Ecm1 gene promoter. Additionally, IFNγ induces Nrf2 nuclear translocation and repressive binding to the Ecm1 gene promoter, thus further reducing Ecm1 expression. Importantly, patients suffering from liver cirrhosis who lack nuclear NRF2 expression consistently maintain higher levels of ECM1, inferring a better prognosis.
Conclusion ECM1 expression in healthy livers is controlled by EGF/EGFR/STAT1 signaling. Upon liver injury, ECM1 expression is repressed by accumulating IFNγ/NRF2, leading to increased LTGF-β activation and the onset of hepatic fibrosis.
Competing Interest Statement
The authors have declared no competing interest.
Abbreviations
- ADAMTS1
- A disintegrin and metalloproteinase with thrombospondin motifs 1
- BDL
- Bile duct ligation
- CCl4
- Carbon tetrachloride
- ChIP
- Chromatin immunoprecipitation
- CLD
- Chronic liver disease
- CYP1B1
- cytochrome P450 family 1 subfamily B member 1
- ECM1
- Extracellular matrix protein 1
- Ecm1-KO
- Ecm1 knockout
- EGF
- Epidermal growth factor
- EGFR
- Epidermal growth factor receptor
- GEO
- Gene Expression Omnibus
- H2O2
- Hydrogen peroxide
- HBV
- Hepatitis-B-virus
- HCC
- Hepatocellular carcinoma
- HPHs
- Human primary hepatocytes
- HSCs
- Hepatic stellate cells
- IFNγ
- Interferon gamma
- i.p.
- Intraperitoneal
- KEAP1
- Kelch-like ECH-associated protein 1
- LTGF-β
- Latent TGF-β
- MELD
- Model for End-Stage Liver Disease
- MMP
- Matrix metalloproteinase
- MPHs
- Mouse primary hepatocytes
- NAFLD
- Non-alcoholic fatty liver disease
- NASH
- Non-alcoholic steatohepatitis
- NQO1
- NAD(P)H:quinone oxidoreductase 1
- NRF2
- Nuclear factor erythroid 2-related factor 2
- OPZ
- Oltipraz
- qRT-PCR
- Quantitative real-time PCR
- ROS
- Reactive oxygen species
- siRNA
- Small interfering RNA
- S727
- Serine727
- TSP-1
- Thrombospondin 1
- TSS
- Transcription start site
- Y701
- Tyrosine701