A Functional Role of GAS6/TAM in Nonalcoholic Steatohepatitis Progression Implicates AXL as Therapeutic Target

Cell Mol Gastroenterol Hepatol. 2020;9(3):349-368. doi: 10.1016/j.jcmgh.2019.10.010. Epub 2019 Nov 2.

Abstract

Background and aims: GAS6 signaling, through the TAM receptor tyrosine kinases AXL and MERTK, participates in chronic liver pathologies. Here, we addressed GAS6/TAM involvement in Non-Alcoholic SteatoHepatitis (NASH) development.

Methods: GAS6/TAM signaling was analyzed in cultured primary hepatocytes, hepatic stellate cells (HSC) and Kupffer cells (KCs). Axl-/-, Mertk-/- and wild-type C57BL/6 mice were fed with Chow, High Fat Choline-Deficient Methionine-Restricted (HFD) or methionine-choline-deficient (MCD) diet. HSC activation, liver inflammation and cytokine/chemokine production were measured by qPCR, mRNA Array analysis, western blotting and ELISA. GAS6, soluble AXL (sAXL) and MERTK (sMERTK) levels were analyzed in control individuals, steatotic and NASH patients.

Results: In primary mouse cultures, GAS6 or MERTK activation protected primary hepatocytes against lipid toxicity via AKT/STAT-3 signaling, while bemcentinib (small molecule AXL inhibitor BGB324) blocked AXL-induced fibrogenesis in primary HSCs and cytokine production in LPS-treated KCs. Accordingly; bemcentinib diminished liver inflammation and fibrosis in MCD- and HFD-fed mice. Upregulation of AXL and ADAM10/ADAM17 metalloproteinases increased sAXL in HFD-fed mice. Transcriptome profiling revealed major reduction in fibrotic- and inflammatory-related genes in HFD-fed mice after bemcentinib administration. HFD-fed Mertk-/- mice exhibited enhanced NASH, while Axl-/- mice were partially protected. In human serum, sAXL levels augmented even at initial stages, whereas GAS6 and sMERTK increased only in cirrhotic NASH patients. In agreement, sAXL increased in HFD-fed mice before fibrosis establishment, while bemcentinib prevented liver fibrosis/inflammation in early NASH.

Conclusion: AXL signaling, increased in NASH patients, promotes fibrosis in HSCs and inflammation in KCs, while GAS6 protects cultured hepatocytes against lipotoxicity via MERTK. Bemcentinib, by blocking AXL signaling and increasing GAS6 levels, reduces experimental NASH, revealing AXL as an effective therapeutic target for clinical practice.

Keywords: Bemcentinib (BGB324); GAS6/TAM Signaling; Hepatic Stellate Cells; Liver Fibrosis; Liver Inflammation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Animals
  • Axl Receptor Tyrosine Kinase
  • Benzocycloheptenes / pharmacology*
  • Benzocycloheptenes / therapeutic use
  • Biomarkers / blood
  • Biomarkers / metabolism
  • Biopsy
  • Cells, Cultured
  • Disease Models, Animal
  • Disease Progression
  • Female
  • Hepatic Stellate Cells / drug effects
  • Hepatic Stellate Cells / pathology
  • Hepatocytes / drug effects
  • Hepatocytes / pathology
  • Humans
  • Intercellular Signaling Peptides and Proteins / genetics
  • Intercellular Signaling Peptides and Proteins / metabolism
  • Kupffer Cells / drug effects
  • Kupffer Cells / immunology
  • Liver / cytology
  • Liver / drug effects
  • Liver / pathology*
  • Liver Cirrhosis / immunology
  • Liver Cirrhosis / pathology
  • Liver Cirrhosis / prevention & control*
  • Male
  • Mice
  • Mice, Knockout
  • Middle Aged
  • Non-alcoholic Fatty Liver Disease / blood
  • Non-alcoholic Fatty Liver Disease / drug therapy*
  • Non-alcoholic Fatty Liver Disease / immunology
  • Non-alcoholic Fatty Liver Disease / pathology
  • Primary Cell Culture
  • Proto-Oncogene Proteins / antagonists & inhibitors*
  • Proto-Oncogene Proteins / blood
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • Receptor Protein-Tyrosine Kinases / antagonists & inhibitors*
  • Receptor Protein-Tyrosine Kinases / blood
  • Receptor Protein-Tyrosine Kinases / genetics
  • Receptor Protein-Tyrosine Kinases / metabolism
  • STAT3 Transcription Factor / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / genetics
  • Triazoles / pharmacology*
  • Triazoles / therapeutic use
  • c-Mer Tyrosine Kinase / genetics
  • c-Mer Tyrosine Kinase / metabolism

Substances

  • Benzocycloheptenes
  • Biomarkers
  • Intercellular Signaling Peptides and Proteins
  • Proto-Oncogene Proteins
  • STAT3 Transcription Factor
  • Stat3 protein, mouse
  • Triazoles
  • growth arrest-specific protein 6
  • bemcentinib
  • Mertk protein, mouse
  • Receptor Protein-Tyrosine Kinases
  • c-Mer Tyrosine Kinase
  • Proto-Oncogene Proteins c-akt
  • Axl Receptor Tyrosine Kinase