Dominant optic atrophy is a rare inherited optic nerve degeneration caused by mutations in the mitochondrial fusion gene OPA1. Recently, the clinical spectrum of dominant optic atrophy has been ...extended to frequent syndromic forms, exhibiting various degrees of neurological and muscle impairments frequently found in mitochondrial diseases. Although characterized by a specific loss of retinal ganglion cells, the pathophysiology of dominant optic atrophy is still poorly understood. We generated an Opa1 mouse model carrying the recurrent Opa1delTTAG
mutation, which is found in 30% of all patients with dominant optic atrophy. We show that this mouse displays a multi-systemic poly-degenerative phenotype, with a presentation associating signs of visual failure, deafness, encephalomyopathy, peripheral neuropathy, ataxia and cardiomyopathy. Moreover, we found premature age-related axonal and myelin degenerations, increased autophagy and mitophagy and mitochondrial supercomplex instability preceding degeneration and cell death. Thus, these results support the concept that Opa1 protects against neuronal degeneration and opens new perspectives for the exploration and the treatment of mitochondrial diseases.
In most eucaryote cells, release of apoptotic proteins from mitochondria involves fission of the mitochondrial network and drastic remodelling of the cristae structures. The intramitochondrial ...dynamin OPA1, as a potential central actor of these processes, exists as eight isoforms resulting from the alternate splicing combinations of exons (Ex) 4, 4b and 5b, which functions remain undetermined. Here, we show that Ex4 that is conserved throughout evolution confers functions to OPA1 involved in the maintenance of the DeltaPsi(m) and in the fusion of the mitochondrial network. Conversely, Ex4b and Ex5b, which are vertebrate specific, define a function involved in cytochrome c release, an apoptotic process also restricted to vertebrates. The drastic changes of OPA1 variant abundance in different organs suggest that nuclear splicing can control mitochondrial dynamic fate and susceptibility to apoptosis and pathologies.
Ligation of CD47 by its natural ligand thrombospondin (TSP), or cross-linking by CD47 antibodies, triggers caspase-independent cell death in normal and leukemic cells. This kind of cell death is ...characterised by the cytoplasmic events of apoptosis including externalisation of phosphatidylserines and mitochondria swelling. We report herein selective mitochondrial changes in CD47–dependent cell death of T cells. After T cell stimulation via CD47, a rapid mitochondrial transmembrane potential (ΔΨ
m) disruption is accompanied by the production of reactive oxygen species (ROS) and phosphatidylserine exposure. Surprisingly, mitochondrial dysfunction does not induce cytochrome
c or AIF release. Moreover, the dying cells do not exhibit caspase-3 activation and display intact nuclei without any large-scale, or oligonucleosomal DNA fragmentation. We conclude that ΔΨ
m loss and ROS production are an early step in CD47–dependent killing and neither cytochrome
c, nor AIF are implicated in this new cell death pathway.
Aconitase 2 (ACO2) encodes the mitochondrial aconitase (ACO2), an enzyme catalyzing interconversion of citrate into isocitrate in the Krebs cycle. ACO2 mutations have been initially associated with ...infantile cerebellar-retinal degeneration combining optic atrophy, retinal degeneration, severe encephalopathy, epilepsy, and cerebellar ataxia 1-3 ; subsequently, ACO2 mutations have also been associated with milder presentations including isolated optic atrophy 2 or cerebellar ataxia without optic atrophy. 4 We report here a patient presenting with a novel ACO2 phenotype associating optic atrophy with spastic paraplegia. Methods Mini-exome sequencing by exon capture (TruSight One Sequencing Panel kit-Montpellier NGS platform) was performed in a patient with familial syndromic optic atrophy. Written informed consent was obtained. Aconitase enzymatic activity was measured as previously described. 5 Case report A now 56-year-old white lady issued from a nonconsanguineous union presented because of severe optic atrophy and spastic paraplegia. Her symptoms had been slowly progressive since infancy and associated with delayed motor (walking at about 3 years) and mental development. An ophthalmologist (C.H.) first examined her at the age of 38 years because of her visual problems. She came to the neurologic clinic at the age of 49 years because of aggravation of the spastic paraplegia, requiring a walking aid. She currently presents with mild cognitive involvement allowing a relatively autonomous life with a sheltered social work. Her sister (not directly examined) has a similar but more severe clinical presentation with visual problems, spasticity, and mental retardation. Cerebral MRI showed mild vermian cerebellar atrophy and nonspecific T2 and fluid-attenuated inversion recovery hyperintensities in cerebellar dentate nuclei and supratentorial white matter (figure, AD). Neurologic examination revealed severe visual impairment, mild upper limb ataxia, diffuse hyperreflexia, and severe spastic paraplegia with bilateral extensor plantar reflex. Ophthalmological evaluation confirmed the presence of bilateral optic atrophy without retinal involvement, globally stable since first examination at the age of 38 years. Visual acuity was severely reduced (right eye: counts the fingers at 30 cm; left eye: counts the fingers at 1 m). The patient did not present any signs of peripheral neuropathy, and the EMG was normal. Mini-exome analysis identified compound heterozygous mutations in the ACO2 gene (c.2135C>T p.(Pro712Leu) 4 ; c.940+5G>C) in the patient and her
Autosomal dominant optic atrophy type 1 (DOA) is the most common form of hereditary optic atrophy in human. We have previously identified the OPA1 gene and shown that it was mutated in patients with ...DOA. OPA1 is a novel member of the dynamin GTPase family that play a role in the distribution of the mitochondrial network. The Bst (belly spot and tail) mutant mice show atrophy of the optic nerves and previous mapping data raise the possibility that Bst and OPA1 are orthologs. In order to analyse the Bst mouse as a model for DOA, we therefore characterized mouse Opa1 and evaluated it as a candidate for the Bst mutant mouse.
Comparison of mouse and human OPA1 sequences revealed 88% and 97% identity at the nucleotide and amino acid levels, respectively. Presence of alternatively spliced mRNAs as seen in human was conserved in the mouse. Screening of the whole mRNA coding sequence and of the 31 exons of Opa1 did not reveal any mutation in Bst. Using a radiation hybrid panel (T31), we mapped Opa1 to chromosome 16 between genetic markers D16Mit3 and D16Mit124, which is 10 cM centromeric to the Bst locus.
On the basis of these results we conclude that Opa1 and Bst are distinct genes and that the Bst mouse is not the mouse model for DOA.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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