A reduction in Drp1-mediated fission compromises mitochondrial health in autosomal recessive spastic ataxia of Charlevoix Saguenay.
The neurodegenerative disease autosomal recessive spastic ataxia of Charlevoix Saguenay (ARSACS) is caused by loss of function of sacsin, a modular protein that is required for normal mitochondrial network organization. To further understand cellular consequences of loss of sacsin, we performed microarray analyses in sacsin knockdown cells and ARSACS patient fibroblasts. This identified altered transcript levels for oxidative phosphorylation and oxidative stress genes. These changes in mitochondrial gene networks were validated by quantitative reverse transcription PCR. Functional impairment of oxidative phosphorylation was then demonstrated by comparison of mitochondria bioenergetics through extracellular flux analyses. Moreover, staining with the mitochondrial-specific fluorescent probe MitoSox suggested increased levels of superoxide in patient cells with reduced levels of sacsin.Key to maintaining mitochondrial health is mitochondrial fission, which facilitates the dynamic exchange of mitochondrial components and separates damaged parts of the mitochondrial network for selective elimination by mitophagy. Fission is dependent on dynamin-related protein 1 (Drp1), which is recruited to prospective sites of division where it mediates scission. In sacsin knockdown cells and ARSACS fibroblasts, we observed a decreased incidence of mitochondrial associated Drp1 foci. This phenotype persists even when fission is induced by drug treatment. Mitochondrial-associated Drp1 foci are also smaller in sacsin knockdown cells and ARSACS fibroblasts. These data suggest a model for ARSACS where neurons with reduced levels of sacsin are compromised in their ability to recruit or retain Drp1 at the mitochondrial membrane leading to a decline in mitochondrial health, potentially through impaired mitochondrial quality control.
William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary University of London, London EC1M 6BQ, United Kingdom j.p.chapple@qmul.ac.uk.
Teisha Y
TY
Bradshaw
William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary University of London, London EC1M 6BQ, United Kingdom.
Lisa E L
LE
Romano
William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary University of London, London EC1M 6BQ, United Kingdom.
Emma J
EJ
Duncan
William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary University of London, London EC1M 6BQ, United Kingdom.
Suran
S
Nethisinghe
Department of Molecular Neuroscience, UCL Institute of Neurology, London WC1N 3BG, United Kingdom.
Rosella
R
Abeti
Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London E1 2AT, United Kingdom.
Gregory J
GJ
Michael
Department of Molecular Neuroscience, UCL Institute of Neurology, London WC1N 3BG, United Kingdom.
Paola
P
Giunti
Department of Clinical Genetics, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
Sascha
S
Vermeer
William Harvey Research Institute, Barts and the London School of Medicine, Queen Mary University of London, London EC1M 6BQ, United Kingdom j.p.chapple@qmul.ac.uk.
J Paul
JP
Chapple
D045744:Cell Line, Tumor; D034281:Dynamins; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008297:Male; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D063154:Mitochondrial Dynamics; D051336:Mitochondrial Membranes / Q000378:metabolism* / Q000473:pathology; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009128:Muscle Spasticity / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D020754:Spinocerebellar Ataxias / Q000151:congenital* / Q000235:genetics / Q000378:metabolism / Q000473:pathology
D006360:Heat-Shock Proteins; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; C404403:SACS protein, human; D020558:GTP Phosphohydrolases; C110768:DNM1L protein, human; D034281:Dynamins