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FR-06

PINK1-dependent mitophagy is associated with increased turnover of

mitochondria containing m.8344A>G mutation in cultured cells of patients

with MERRF syndrome

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Y u -Ting Wu, Hui-Yi Tay, Jung-Tse Yang, Hsiao-Hui Liao, Yau-Huei Wei* ,1,2

1 Center for Mitochondrial Medicine and Free Radical Research, Changhua Christian
Hospital, Changhua City, Taiwan 500
2 Institute of Clinical Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
112
* E-mail: yhweibabi@gmail.com

Abstract
Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome is one of the major
mitochondrial diseases, caused by a maternally inherited m.8344A>G mutation. The
pathogenesis has not yet been fully elucidated and no effective treatments are available for this
mitochondrial disease. Mitophagy is a specialized form of autophagy that selectively removes
damaged mitochondria or mitochondrial components to maintain cellular homeostasis.
Imbalanced mitophagy can lead to the accumulation of defective mitochondria and exacerbate
the pathology of the disease. However, the role of mitophagy in the pathophysiology of MERRF
syndrome remains controversial. In this study, we showed that mitochondrial respiration was
impaired and intracellular levels of reactive oxygen species (ROS) were increased in skin
fibroblasts of MERRF patients harboring the m.8344A>G mutation. We then used carbonyl
cyanide-chlorophenyl hydrazine (CCCP), a mitochondrial uncoupler, to induce autophagy in
skin fibroblasts from patients with MERRF syndrome and normal subjects. The results showed
that CCCP induced enhanced activation of PINK1-mediated mitophagy led to an increased
turnover of damaged mitochondria in the MERRF skin fibroblasts. Moreover, we found that N-
acetylcysteine (NAC) prevented PINK1 accumulation and ubiquitin phosphorylation in
mitochondria and thereby impeded the removal of dysfunctional mitochondria in MERRF skin
fibroblasts. The inhibitory effect of NAC on the PINK1-mediated mitophagy was confirmed in
the neurons differentiated from induced pluripotent stem cells (iPSCs) of MERRF patients.
These neurons retained the m.8344A>G mutation and exhibited mitochondrial dysfunction and
ROS overproduction. Our findings indicate that oxidative stress contributes to increased
susceptibility of cultured cells of MERRF patients to mitophagy induction. The results of this
study provide insight into the possibility that restoring a proper mitophagy may be a potential
strategy for effective treatment of patients with MERRF syndrome.

Keywords: iPSC-derived neuron; MERRF syndrome; mtDNA mutation; Mitophagy; PINK1