A novel deletion in the GTPase domain of OPA1 causes defects in mitochondrial morphology and distribution, but not in function.
Autosomal dominant optic atrophy (ADOA), the commonest cause of inherited optic atrophy, is caused by mutations in the ubiquitously expressed gene optic atrophy 1 (OPA1), involved in fusion and biogenesis of the inner membrane of mitochondria. Bioenergetic failure, mitochondrial network abnormalities and increased apoptosis have all been proposed as possible causal factors. However, their relative contribution to pathogenesis as well as the prominent susceptibility of the retinal ganglion cell (RGC) in this disease remains uncertain. Here we identify a novel deletion of OPA1 gene in the GTPase domain in three patients affected by ADOA. Muscle biopsy of the patients showed neurogenic atrophy and abnormal morphology and distribution of mitochondria. Confocal microscopy revealed increased mitochondrial fragmentation in fibroblasts as well as in myotubes, where mitochondria were also unevenly distributed, with clustered organelles alternating with areas where mitochondria were sparse. These abnormalities were not associated with altered bioenergetics or increased susceptibility to pro-apoptotic stimuli. Therefore, changes in mitochondrial shape and distribution can be independent of other reported effects of OPA1 mutations, and therefore may be the primary cause of the disease. The arrangement of mitochondria in RGCs, which degenerate in ADOA, may be exquisitely sensitive to disturbance, and this may lead to bioenergetic crisis and/or induction of apoptosis. Our results highlight the importance of mitochondrial dynamics in the disease per se, and point to the loss of the fine positioning of mitochondria in the axons of RGCs as a possible explanation for their predominant degeneration in ADOA.
Spinazzi
Marco
M
Neurosciences Department, University of Padova, Italy. marco.spinazzi@unipd.it
Cazzola
Silvia
S
Bortolozzi
Mario
M
Baracca
Alessandra
A
Loro
Emanuele
E
Casarin
Alberto
A
Solaini
Giancarlo
G
Sgarbi
Gianluca
G
Casalena
Gabriella
G
Cenacchi
Giovanna
G
Malena
Adriana
A
Frezza
Christian
C
Carrara
Franco
F
Angelini
Corrado
C
Scorrano
Luca
L
Salviati
Leonardo
L
Vergani
Lodovica
L
D000293:Adolescent; D000328:Adult; D017209:Apoptosis; D002478:Cells, Cultured; D002648:Child; D004734:Energy Metabolism; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D018482:Muscle, Skeletal / Q000002:abnormalities / Q000201:enzymology; D029241:Optic Atrophy, Autosomal Dominant / Q000235:genetics* / Q000503:physiopathology; D010375:Pedigree; D017382:Reactive Oxygen Species / Q000378:metabolism; D012160:Retina / Q000473:pathology; D017384:Sequence Deletion; D055815:Young Adult
D017382:Reactive Oxygen Species; D020558:GTP Phosphohydrolases; C415198:OPA1 protein, human