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

BACKGROUND & AIMS: Hepatic recruitment of monocyte-derived macrophages (MoMFs) contributes to the inflammatory response in non-alcoholic steatohepatitis (NASH). However, how hepatocyte lipotoxicity promotes MoMF inflammation is unclear. Here we demonstrate that lipotoxic hepatocyte-derived extracellular vesicles (LPC-EVs) are enriched with active integrin β (ITGβ), 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-ITGβ neutralizing antibody (ITGβAb) or control IgG isotype.

RESULTS

Ingenuity® Pathway Analysis of the LPC-EV proteome indicated that ITG signaling is an overrepresented canonical pathway. Immunogold electron microscopy and nanoscale flow cytometry confirmed that LPC-EVs were enriched with activated ITGβ. Furthermore, we showed that LPC treatment in hepatocytes activates ITGβ and mediates its endocytic trafficking and sorting into EVs. LPC-EVs enhanced monocyte adhesion to liver sinusoidal cells, as observed by shear stress adhesion assay. This adhesion was attenuated in the presence of ITGβAb. FFC-fed, ITGβAb-treated mice displayed reduced inflammation, defined by decreased hepatic infiltration and activation of proinflammatory MoMFs, as assessed by immunohistochemistry, mRNA expression, and flow cytometry. Likewise, mass cytometry by time-of-flight on intrahepatic leukocytes showed that ITGβAb reduced levels of infiltrating proinflammatory monocytes. Furthermore, ITGβAb treatment significantly ameliorated liver injury and fibrosis.

CONCLUSIONS

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

LAY SUMMARY

Herein, we report that a cell adhesion molecule termed integrin β (ITGβ) plays a key role in the progression of non-alcoholic steatohepatitis (NASH). ITGβ is released from hepatocytes under lipotoxic stress as a cargo of extracellular vesicles, and mediates monocyte adhesion to liver sinusoidal endothelial cells, which is an essential step in hepatic inflammation. In a mouse model of NASH, blocking ITGβ reduces liver inflammation, injury and fibrosis. Hence, ITGβ inhibition may serve as a new therapeutic strategy for NASH.