DNase II activated by the mitochondrial apoptotic pathway regulates RIP1-dependent non-apoptotic hepatocyte death via the TLR9/IFN-β signaling pathway

Cell Death Differ. 2019 Mar;26(3):470-486. doi: 10.1038/s41418-018-0131-6. Epub 2018 May 31.

Abstract

Cell death, including apoptotic and non-apoptotic cell death, is frequently observed in liver disease. Upon activation of the mitochondrial apoptotic pathway, mitochondria release not only apoptogenic cytochrome c but also mitochondrial DNA (mtDNA) into the cytosol. The impact of DNase II, a lysosomal acid DNase that degrades mtDNA, on hepatocyte death remains unclear. Administration of ABT-737, a Bcl-xL inhibitor, upregulated DNase II activity in murine hepatocyte cell line BNL CL.2 cells and induced apoptosis. In cells treated with DNase II siRNA, ABT-737 led to accumulation of mtDNA in the cytosol and increased expression of interferon (IFN)-β and induction of propidium iodide (PI)-positive cells, in addition to apoptosis. Induced PI-positive cells were suppressed by RIP1 inhibitor, Necrostatin-1, but not by pan-caspase inhibitor, ZVAD-FMK, suggesting non-apoptotic cell death. Both the increase in IFN-β and the induction of non-apoptotic cell death were abolished by administering a TLR9 antagonist, ODN2088, or by the removal of mtDNA from cells with ethidium bromide. Hepatocyte-specific Mcl-1 knockout mice developed hepatocyte apoptosis accompanied by upregulated DNase II activity in their livers. Further knockout of DNase II induced IFN-β expression and RIP1-dependent non-apoptotic hepatocyte death, both of which were suppressed by the administration of ODN2088. Mice fed a high-fat diet (HFD), an obesity-associated fatty liver model, showed increased expression of IFN-β with suppression of DNase II activity in their livers and developed not only hepatocyte apoptosis but also non-apoptotic hepatocyte death. Hepatocyte-specific knockout of DNase II exacerbated HFD-induced non-apoptotic hepatocyte death and liver fibrosis. In conclusion, without DNase II, apoptotic stimulation on hepatocytes induces TLR9-dependent IFN-β production and RIP1-dependent non-apoptotic cell death originating from mtDNA. In fatty livers, DNase II activity is suppressed in contrast to simple inactivation of Bcl-xL or Mcl-1, and both apoptotic and non-apoptotic hepatocyte death can develop, leading to the progression of liver fibrosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / physiology
  • Biphenyl Compounds / pharmacology
  • Cell Death / physiology
  • Endodeoxyribonucleases / metabolism*
  • Enzyme Activation
  • GTPase-Activating Proteins / metabolism*
  • Hepatocytes / cytology
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism*
  • Hepatocytes / pathology
  • Interferon-beta / metabolism*
  • Liver Cirrhosis / metabolism
  • Liver Cirrhosis / pathology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mitochondria / metabolism*
  • Nitrophenols / pharmacology
  • Oligodeoxyribonucleotides / pharmacology
  • Piperazines / pharmacology
  • Signal Transduction
  • Sulfonamides / pharmacology
  • Toll-Like Receptor 9 / metabolism*
  • Up-Regulation / drug effects

Substances

  • ABT-737
  • Biphenyl Compounds
  • GTPase-Activating Proteins
  • Nitrophenols
  • Oligodeoxyribonucleotides
  • Piperazines
  • Ralbp1 protein, mouse
  • Sulfonamides
  • Tlr9 protein, mouse
  • Toll-Like Receptor 9
  • iCpG-ODN
  • Interferon-beta
  • Endodeoxyribonucleases
  • deoxyribonuclease II