title: Valproic acid-induced hepatotoxicity in Alpers syndrome is associated with mitochondrial permeability transition pore opening-dependent apoptotic sensitivity in an induced pluripotent stem cell model.
abstract: Valproic acid (VPA) is widely used to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy, but potentially causes idiosyncratic liver injury. Alpers-Huttenlocher syndrome (AHS), a neurometabolic disorder caused by mutations in mitochondrial DNA polymerase gamma (POLG), is associated with an increased risk of developing fatal VPA hepatotoxicity. However, the mechanistic link of this clinical mystery remains unknown. Here, fibroblasts from 2 AHS patients were reprogrammed to induced pluripotent stem cells (iPSCs) and then differentiated to hepatocyte-like cells (AHS iPSCs-Hep). Both AHS iPSCs-Hep are more sensitive to VPA-induced mitochondrial-dependent apoptosis than controls, showing more activated caspase-9 and cytochrome c release. Strikingly, levels of both soluble and oligomeric optic atrophy 1, which together keep cristae junctions tight, are reduced in AHS iPSCs-Hep. Furthermore, POLG mutation cells show reduced POLG expression, mitochondrial DNA (mtDNA) amount, mitochondrial adenosine triphosphate production, as well as abnormal mitochondrial ultrastructure after differentiation to hepatocyte-like cells. Superoxide flashes, spontaneous bursts of superoxide generation, caused by opening of the mitochondrial permeability transition pore (mPTP), occur more frequently in AHS iPSCs-Hep. Moreover, the mPTP inhibitor, cyclosporine A, rescues VPA-induced apoptotic sensitivity in AHS iPSCs-Hep. This result suggests that targeting mPTP opening could be an effective method to prevent hepatotoxicity by VPA in AHS patients. In addition, carnitine or N-acetylcysteine, which has been used in the treatment of VPA-induced hepatotoxicity, is able to rescue VPA-induced apoptotic sensitivity in AHS iPSCs-Hep.
  
  
  CONCLUSIONS
  AHS iPSCs-Hep are more sensitive to the VPA-induced mitochondrial-dependent apoptotic pathway, and this effect is mediated by mPTP opening. Toxicity models in genetic diseases using iPSCs enable the evaluation of drugs for therapeutic targets.
authors.affiliation: Key Laboratory of Regenerative Biology, Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China; University of Science and Technology of China, Hefei, Anhui, China.
authors.forename: Shengbiao
authors.initials: S
authors.lastname: Li
authors.forename: Jingyi
authors.initials: J
authors.lastname: Guo
authors.forename: Zhongfu
authors.initials: Z
authors.lastname: Ying
authors.forename: Shen
authors.initials: S
authors.lastname: Chen
authors.forename: Liang
authors.initials: L
authors.lastname: Yang
authors.forename: Keshi
authors.initials: K
authors.lastname: Chen
authors.forename: Qi
authors.initials: Q
authors.lastname: Long
authors.forename: Dajiang
authors.initials: D
authors.lastname: Qin
authors.forename: Duanqing
authors.initials: D
authors.lastname: Pei
authors.forename: Xingguo
authors.initials: X
authors.lastname: Liu
mesh_terms: D000927:Anticonvulsants / Q000009:adverse effects*; D017209:Apoptosis; D002478:Cells, Cultured; D056486:Chemical and Drug Induced Liver Injury / Q000209:etiology*; D002549:Diffuse Cerebral Sclerosis of Schilder / Q000150:complications*; D006801:Humans; D057026:Induced Pluripotent Stem Cells; D033681:Mitochondrial Membrane Transport Proteins / Q000502:physiology*; D000083162:Mitochondrial Permeability Transition Pore; D014635:Valproic Acid / Q000009:adverse effects*
chemical_list: D000927:Anticonvulsants; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D014635:Valproic Acid