Hepatocytes release ceramide-enriched pro-inflammatory extracellular vesicles in an IRE1 α -dependent manner

Eiji Kakazu, Amy S. Mauer, Meng Yin, Harmeet M Malhi

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Nonalcoholic steatohepatitis (NASH) is a lipotoxic disease wherein activation of endoplasmic reticulum (ER) stress response and macrophage-mediated hepatic inflammation are key pathogenic features. However, the lipid mediators linking these two observations remain elusive. We postulated that ER stress-regulated release of pro-inflammatory extracellular vesicles (EVs) from lipotoxic hepatocytes may be this link. EVs were isolated from cell culture supernatants of hepatocytes treated with palmitate (PA) to induce lipotoxic ER stress, characterized by immunofluorescence, Western blotting, electron microscopy, and nanoparticle tracking analysis. Sphingolipids were measured by tandem mass spectrometry. EVs were employed in macrophage chemotaxis assays. PA induced significant EV release. Because PA activates ER stress, we used KO hepatocytes to demonstrate that PA-induced EV release was mediated by inositol requiring enzyme 1 α (IRE1α )/X-box binding protein-1. PAinduced EVs were enriched in C16:0 ceramide in an IRE1 α -dependent manner, and activated macrophage chemotaxis via formation of sphingosine-1-phosphate (S1P) from C16:0 ceramide. This chemotaxis was blocked by sphingosine kinase inhibitors and S1P receptor inhibitors. Lastly, elevated circulating EVs in experimental and human NASH demonstrated increased C16:0 ceramide. PA induces C16:0 ceramide-enriched EV release in an IRE1α-dependent manner. The ceramide metabolite, S1P, activates macrophage chemotaxis, a potential mechanism for the recruitment of macrophages to the liver under lipotoxic conditions.

Original languageEnglish (US)
Pages (from-to)233-245
Number of pages13
JournalJournal of Lipid Research
Volume57
Issue number2
DOIs
StatePublished - Feb 1 2016

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Macrophages
Palmitates
Ceramides
Inositol
Hepatocytes
Endoplasmic Reticulum Stress
Chemotaxis
Enzymes
Lysosphingolipid Receptors
Sphingolipids
Metabolites
Cell culture
Liver
Electron microscopy
Mass spectrometry
Assays
Carrier Proteins
Chemical activation
Extracellular Vesicles
Nanoparticles

Keywords

  • Endoplasmic reticulum stress
  • Exosome
  • Inositol requiring enzyme 1 α
  • Lipoinflammation
  • Microvesicle
  • Nonalcoholic steatohepatitis

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Endocrinology

Cite this

Hepatocytes release ceramide-enriched pro-inflammatory extracellular vesicles in an IRE1 α -dependent manner. / Kakazu, Eiji; Mauer, Amy S.; Yin, Meng; Malhi, Harmeet M.

In: Journal of Lipid Research, Vol. 57, No. 2, 01.02.2016, p. 233-245.

Research output: Contribution to journalArticle

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