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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.

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Free fatty acids (FFA) induce hepatocyte lipoapoptosis by a c-Jun N-terminal kinase (JNK)-dependent mechanism. However, the cellular processes by which JNK engages the core apoptotic machinery during lipotoxicity, especially activation of BH3-only proteins, remain incompletely understood. Thus, our aim was to determine whether JNK mediates induction of BH3-only proteins during hepatocyte lipoapoptosis. The saturated FFA palmitate, but not the monounsaturated FFA oleate, induces an increase in PUMA mRNA and protein levels. Palmitate induction of PUMA was JNK1-dependent in primary murine hepatocytes. Palmitate-mediated PUMA expression was inhibited by a dominant negative c-Jun, and direct binding of a phosphorylated c-Jun containing the activator protein 1 complex to the PUMA promoter was identified by electrophoretic mobility shift assay and a chromatin immunoprecipitation assay. Short hairpin RNA-targeted knockdown of PUMA attenuated Bax activation, caspase 3/7 activity, and cell death. Similarly, the genetic deficiency of Puma rendered murine hepatocytes resistant to lipoapoptosis. PUMA expression was also increased in liver biopsy specimens from patients with non-alcoholic steatohepatitis as compared with patients with simple steatosis or controls. Collectively, the data implicate JNK1-dependent PUMA expression as a mechanism contributing to hepatocyte lipoapoptosis.