BACKGROUND & AIMS Hepatocyte cellular dysfunction and death induced by lipids, and macrophage-associated inflammation are characteristics of nonalcoholic steatohepatitis (NASH). The fatty acid palmitate can activate death receptor 5 (DR5) on hepatocytes, leading to their death, but little is known about how this process contributes to macrophage-associated inflammation. We investigated whether lipid-induced DR5 signaling results in release of extracellular vesicles (EV) from hepatocytes, and whether these can induce an inflammatory macrophage phenotype. METHODS Primary mouse and human hepatocytes and Huh7 cells were incubated with palmitate, its metabolite lysophosphatidylcholine, or diluent (control). The released EV were isolated, characterized, quantified, and applied to macrophages. C57BL/6 mice were placed on chow or a diet high in fat, fructose, and cholesterol to induce NASH. Some mice were also given the ROCK1 inhibitor fasudil; 2 weeks later, serum EVs were isolated and characterized by immunoblot and nanoparticle-tracking analyses. Livers were collected and analyzed by histology, immunohistochemistry, and quantitative PCR. RESULTS Incubation of primary hepatocytes and Huh7 cells with palmitate or lysophosphatidylcholine increased their release of EV, compared with control cells. This release was reduced by inactivating mediators of the DR5 signaling pathway or ROCK1 inhibition. Hepatocyte-derived EV contained TRAIL and induced expression of interleukin-1, beta (Il1b) and Il6 mRNAs in mouse bone marrow-derived macrophages. Activation of macrophages required DR5 and RIP1. Administration of the ROCK1 inhibitor fasudil to mice with NASH reduced serum levels of EV; this reduction was associated with decreased liver injury, inflammation, and fibrosis. CONCLUSIONS Lipids, which stimulate DR5, induce release of hepatocyte EV, which activate an inflammatory phenotype in macrophages. Strategies to inhibit ROCK1-dependent release of EV by hepatocytes might be developed for treatment of patients with NASH.

Extracellular vesicles (EVs) are nanometer-sized, membrane-bound vesicles released by cells into the extracellular milieu. EVs are now recognized to play a critical role in cell-to-cell communication. EVs contain important cargo in the form of proteins, lipids and nucleic acids and serve as vectors for delivering this cargo from donor to acceptor or target cell. The EVs are released both under physiologic and pathologic conditions, including liver diseases, and exert a wide range of effects on target cells. This review provides an overview on EV biogenesis, secretion, cargo, and target cell interactions in the context of select liver diseases. Specifically, the diverse roles of EVs in nonalcoholic steatohepatitis, alcoholic liver disease, viral hepatitis, cholangiopathies and hepatobiliary malignancies are emphasized. Liver diseases often result in an increased release of EVs and/or in different cargo sorting into these EVs. Either of these alterations can drive disease pathogenesis. Given this fact, EVs represent a potential target for therapeutic intervention in liver disorders. Because altered EV composition may reflect the underlying disease condition, circulating EVs can be exploited for diagnostic and prognostic purposes as a liquid biopsy. Furthermore, ex vivo modified or synthesized EVs can be engineered as therapeutic nano-shuttles. Finally, we highlight areas that merit further investigation relevant to understanding how EVs regulate liver disease pathogenesis.

Background/Aims The mechanisms by which hepatocyte exposure to alcohol activates inflammatory cells such as macrophages in alcoholic liver disease (ALD) are unclear. The role of released nano-sized membrane vesicles, termed extracellular vesicles (EV), in cell-to-cell communication has become increasingly recognized. We tested the hypothesis that hepatocytes exposed to alcohol may increase EV release to elicit macrophage activation. Methods Primary hepatocytes or HepG2 hepatocyte cell lines overexpressing ethanol-metabolizing enzymes Alcohol dehydrogenase (HepG2ADH) or cytochrome P450 2E1 (HepG2Cyp2E1) were treated with ethanol and EV release was quantified with nanoparticle tracking analysis (NTA). EV mediated macrophage activation was monitored by analyzing inflammatory cytokines and macrophage associated mRNA expression, immunohistochemistry, biochemical serum ALT and triglycerides analysis in our in vitro macrophage activation and in vivo murine ethanol feeding studies. Results Ethanol significantly increased EV release by 3.3 fold from HepG2Cyp2E1 cells and was associated with activation of caspase-3. Blockade of caspase activation with pharmacological or genetic approaches abrogated alcohol induced EV release. EV stimulated macrophage activation and inflammatory cytokine induction. An unbiased microarray-based approach and antibody neutralization experiments demonstrated a critical role of CD40 ligand (CD40L) in EV mediated macrophage activation. In vivo, wild-type (WT) mice receiving a pan-caspase, Rho kinase inhibitor or with genetic deletion of CD40 (CD40−/−) or the caspase-activating TRAIL receptor (TR−/−), were protected from alcohol-induced injury and associated macrophage infiltration. Moreover, serum from patients with alcoholic hepatitis (AH) showed increased levels of CD40L enriched EV. Conclusion In conclusion, hepatocytes release CD40L containing EV in a caspase dependent manner in response to alcohol exposure which promotes macrophage activation, contributing to inflammation in ALD.

Exosomes are cell-derived extracellular vesicles thought to promote intercellular communication by delivering specific content to target cells. The aim of this study was to determine whether endothelial cell (EC)-derived exosomes could regulate the phenotype of hepatic stellate cells (HSCs). Initial microarray studies showed that fibroblast growth factor 2 induced a 2.4-fold increase in mRNA levels of sphingosine kinase 1 (SK1). Exosomes derived from an SK1-overexpressing EC line increased HSC migration 3.2-fold. Migration was not conferred by the dominant negative SK1 exosome. Incubation of HSCs with exosomes was also associated with an 8.3-fold increase in phosphorylation of AKT and 2.5-fold increase in migration. Exosomes were found to express the matrix protein and integrin ligand fibronectin (FN) by Western blot analysis and transmission electron microscopy. Blockade of the FN-integrin interaction with a CD29 neutralizing antibody or the RGD peptide attenuated exosome-induced HSC AKT phosphorylation and migration. Inhibition of endocytosis with transfection of dynamin siRNA, the dominant negative dynamin GTPase construct Dyn2K44A, or the pharmacological inhibitor Dynasore significantly attenuated exosome-induced AKT phosphorylation. SK1 levels were increased in serum exosomes derived from mice with experimental liver fibrosis, and SK1 mRNA levels were up-regulated 2.5-fold in human liver cirrhosis patient samples. Finally, S1PR2 inhibition protected mice from CCl 4 -induced liver fibrosis. Therefore, EC-derived SK1-containing exosomes regulate HSC signaling and migration through FNintegrin-dependent exosome adherence and dynamin-dependent exosome internalization. These findings advance our understanding of EC/HSC cross-talk and identify exosomes as a potential target to attenuate pathobiology signals.