In vivo hepatic endoplasmic reticulum stress in patients with chronic hepatitis C

J Pathol. 2010 Jul;221(3):264-74. doi: 10.1002/path.2703.

Abstract

In hepatocytes, the accumulation of unfolded proteins in the endoplasmic reticulum (ER) causes ER stress and the unfolded protein response (UPR), mediated by the ER-resident stress sensors ATF-6, IRE1, and PERK. UPR-responsive genes are involved in the fate of ER-stressed cells. Cells carrying hepatitis C virus (HCV) subgenomic replicons exhibit in vitro ER stress and suggest that HCV inhibits the UPR. Since in vivo ER homeostasis is unknown in livers with chronic HCV infection, we investigated ER stress and the UPR in liver samples from untreated patients with chronic hepatitis C (CHC), in comparison with normal livers. Electron microscopy, western blotting, and real-time RT-PCR were used in liver biopsy specimens. Electron microscopy identified features showing ER stress in hepatocyte samples from patients with CHC; however, 'ER-stressed' hepatocytes were found in clusters (3-5 cells) that were scattered in the liver parenchyma. Western blot analysis confirmed the existence of hepatic ER stress by showing activation of the three ER stress sensors ATF-6, IRE1, and PERK in CHC. Real-time RT-PCR showed no significant induction of UPR-responsive genes in CHC. In contrast, genes involved in the control of diffuse processes such as liver proliferation, inflammation, and apoptosis were significantly induced in CHC. In conclusion, livers from patients with untreated CHC exhibit in vivo hepatocyte ER stress and activation of the three UPR sensors without apparent induction of UPR-responsive genes. This lack of gene induction may be explained by the inhibiting action of HCV per se (as suggested by in vitro studies) and/or by our finding of the localized nature of hepatocyte ER stress.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Activating Transcription Factor 6 / metabolism
  • Adult
  • Apoptosis / genetics
  • Cell Proliferation
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum / ultrastructure*
  • Endoribonucleases / metabolism
  • Female
  • Gene Expression Regulation / physiology
  • Hepatitis C, Chronic / metabolism
  • Hepatitis C, Chronic / pathology*
  • Hepatitis C, Chronic / physiopathology
  • Hepatocytes / metabolism
  • Hepatocytes / ultrastructure*
  • Humans
  • Liver Cirrhosis / pathology
  • Liver Cirrhosis / physiopathology
  • Liver Cirrhosis / virology
  • Male
  • Membrane Proteins / metabolism
  • Microscopy, Electron
  • Middle Aged
  • Protein-Serine-Threonine Kinases / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction / methods
  • Signal Transduction / physiology
  • Stress, Physiological / physiology
  • Unfolded Protein Response / genetics
  • Unfolded Protein Response / physiology
  • eIF-2 Kinase / metabolism

Substances

  • ATF6 protein, human
  • Activating Transcription Factor 6
  • Membrane Proteins
  • ERN2 protein, human
  • PERK kinase
  • Protein-Serine-Threonine Kinases
  • eIF-2 Kinase
  • Endoribonucleases