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Integrin β1-enriched extracellular vesicles mediate monocyte adhesion and promote liver inflammation in murine NASH

Guo, Q., Furuta, K., Lucien, F. et al.

BACKGROUND AND AIMS:
Hepatic recruitment of monocyte-derived macrophages (MoMF) contributes to the inflammatory response in nonalcoholic steatohepatitis (NASH). However, how hepatocyte lipotoxicity promotes MoMF inflammation is unclear. Here we demonstrate that lipotoxic hepatocyte-derived extracellular vesicles (EVs) are enriched with active integrin β1 (ITGβ1), which promotes monocyte adhesion and liver inflammation in murine NASH.

METHODS:
Hepatocytes were treated with either vehicle or the toxic lipid mediator lysophosphatidylcholine (LPC); EVs were isolated from the conditioned media and subjected to proteomic analysis. C57BL/6J mice were fed a diet rich in fat, fructose, and cholesterol (FFC) to induce NASH. Mice were treated with anti-ITGβ1 neutralizing antibody (ITGβ1Ab) or control IgG isotype.

RESULTS:
Ingenuity Pathway Analysis of the lipotoxic hepatocyte-derived EV (LPC-EVs) proteome indicated that integrin signaling is an overrepresented canonical pathway. Immunogold electron microscopy and nanoscale flow cytometry confirmed enrichment of LPC-EVs with active ITGβ1. Furthermore, we showed that LPC treatment in hepatocytes activates ITGβ1 and mediates its endocytic trafficking and sorting into EVs. LPC-EVs-enhanced monocytes adhesion to liver sinusoidal endothelial cells (LSECs) was observed by shear stress adhesion assay, and was attenuated in the presence of ITGβ1Ab. FFC-fed, ITGβ1Ab-treated mice displayed reduced inflammation defined by decreased proinflammatory MoMF hepatic infiltration and activation as assessed by immunohistochemistry, mRNA expression, and flow cytometry. Likewise, mass cytometry by time-of-flight (CyTOF) on intrahepatic leukocytes (IHL) displayed reduced infiltrating proinflammatory monocytes. Furthermore, ITGβ1Ab treatment significantly ameliorated liver injury and fibrosis.

CONCLUSIONS:
Lipotoxic EVs mediate monocyte adhesion to LSECs mainly by an ITGβ1-dependent mechanism. ITGβ1Ab ameliorates diet-induced NASH in mice by reducing MoMF-driven inflammation, suggesting that blocking ITGβ1 is a potential anti-inflammatory therapeutic strategy in human NASH.

Citation

Guo, Q., Furuta, K., Lucien, F. et al. "Integrin β1-enriched extracellular vesicles mediate monocyte adhesion and promote liver inflammation in murine NASH" Journal of Hepatology (2019): doi: 10.1016/j.jhep.2019.07.019.