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Brain. 2015 Oct;138(Pt 10):2834-46. doi: 10.1093/brain/awv182. Epub 2015 Jun 29.

Signal transducer and activator of transcription 2 deficiency is a novel disorder of mitochondrial fission.

Author information

1
1 Mitochondrial Research Group, Genetics and Genomic Medicine, UCL Institute of Child Health, Guilford Street, London, UK shamima.rahman@ucl.ac.uk.
2
2 Molecular Immunology Unit, Great Ormond Street Hospital, London, UK.
3
3 Histopathology Unit, Great Ormond Street Hospital, London, UK.
4
4 Department of Biochemistry and Molecular Biology, Monash University, Melbourne 3800, Australia.
5
5 Primary Immunodeficiency Group, Institute of Cellular Medicine, Newcastle University, UK.
6
3 Histopathology Unit, Great Ormond Street Hospital, London, UK 6 Developmental Neurosciences, UCL Institute of Child Health, London, UK.
7
1 Mitochondrial Research Group, Genetics and Genomic Medicine, UCL Institute of Child Health, Guilford Street, London, UK.
8
7 Department of Clinical Neurosciences, UCL Institute of Neurology, Rowland Hill Street, London, UK.
9
8 UCL Genetics Institute, London, UK.
10
9 Neurometabolic Unit, National Hospital for Neurology and Neurosurgery, London, UK.
11
10 Cell and Developmental Biology, University College London, UK.
12
1 Mitochondrial Research Group, Genetics and Genomic Medicine, UCL Institute of Child Health, Guilford Street, London, UK 1 Mitochondrial Research Group, Genetics and Genomic Medicine, UCL Institute of Child Health, Guilford Street, London, UK.

Abstract

Defects of mitochondrial dynamics are emerging causes of neurological disease. In two children presenting with severe neurological deterioration following viral infection we identified a novel homozygous STAT2 mutation, c.1836 C>A (p.Cys612Ter), using whole exome sequencing. In muscle and fibroblasts from these patients, and a third unrelated STAT2-deficient patient, we observed extremely elongated mitochondria. Western blot analysis revealed absence of the STAT2 protein and that the mitochondrial fission protein DRP1 (encoded by DNM1L) is inactive, as shown by its phosphorylation state. All three patients harboured decreased levels of DRP1 phosphorylated at serine residue 616 (P-DRP1(S616)), a post-translational modification known to activate DRP1, and increased levels of DRP1 phosphorylated at serine 637 (P-DRP1(S637)), associated with the inactive state of the DRP1 GTPase. Knockdown of STAT2 in SHSY5Y cells recapitulated the fission defect, with elongated mitochondria and decreased P-DRP1(S616) levels. Furthermore the mitochondrial fission defect in patient fibroblasts was rescued following lentiviral transduction with wild-type STAT2 in all three patients, with normalization of mitochondrial length and increased P-DRP1(S616) levels. Taken together, these findings implicate STAT2 as a novel regulator of DRP1 phosphorylation at serine 616, and thus of mitochondrial fission, and suggest that there are interactions between immunity and mitochondria. This is the first study to link the innate immune system to mitochondrial dynamics and morphology. We hypothesize that variability in JAK-STAT signalling may contribute to the phenotypic heterogeneity of mitochondrial disease, and may explain why some patients with underlying mitochondrial disease decompensate after seemingly trivial viral infections. Modulating JAK-STAT activity may represent a novel therapeutic avenue for mitochondrial diseases, which remain largely untreatable. This may also be relevant for more common neurodegenerative diseases, including Alzheimer's, Huntington's and Parkinson's diseases, in which abnormalities of mitochondrial morphology have been implicated in disease pathogenesis.

KEYWORDS:

JAK-STAT signalling; STAT2; dynamin-related protein 1 (DRP1); mitochondrial disease; mitochondrial fission; mitochondrial fusion

PMID:
26122121
PMCID:
PMC5808733
DOI:
10.1093/brain/awv182
[Indexed for MEDLINE]
Free PMC Article

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