The X protein protects against mitochondrial and neuronal defects of OPA1-deficient neurons
Macarena S. Arrázola1, Venu Gurram1, Marion Szelechowski1, Djamaa Atamena1, Marlène Daloyau1, Daniel Gonzalez-Dunia2, Marie-Christine Miquel1 and Pascale Belenguer1
1Centre de Recherches sur la Cognition Animale (UMR5169), Centre de Biologie Intégrative (CBI), Université de Toulouse, CNRS-UPS, France; 2Centre de Physiopathologie de Toulouse Purpan, Inserm UMR1043, CNRS UMR5282, France
Mutations in the gene coding the mitochondrial fusion protein OPA1 lead to Dominant Optic Atrophy (DOA), a mitochondrial disease characterized by a reduction of visual acuity and blindness, to date without treatment. DOA mainly affects Retinal Ganglionic Cells (RGC), which axons form the optic nerve, although 20% of the patients also develop extra-ocular neuronal complications. Deficiency of OPA1 provokes mitochondrial fragmentation, alterations of mitochondrial distribution and function, leading to defects in neuronal arborization and synapse formation.
As mitochondria are dysfunctional in several neurodegenerative diseases, they appear as an attractive target for therapy. We recently showed that a viral protein called X protects neurons in vitro and in vivo against diverse neurodegenerative insults. The mitochondrial localization of X is mandatory for its protective properties. We thus sought to evaluate whether X could protect OPA1-deficient neurons against mitochondrial alterations and degeneration.
To test our hypothesis, we used an in vitro model of OPA1 haploinsufficiency due to expression of an siRNA against OPA1 in cortical neurons. Lentiviral transduction of the X protein and treatment with an X-derived cell-permeable peptide both restored mitochondrial morphology, dendritic length and normal level of synapses in OPA1-deficient neurons. Our results suggest that the X protein can indeed limit the adverse consequences of OPA1 deficiency in neurons in vitro. We are currently investigating if treatment with the X peptide can restore mitochondrial morphology defects in fibroblasts from DOA patients and RGC axonal deficiencies in retinal explants. Our in vitro results allow us to propose an in vivo gene therapy strategy to evaluate the effect of the X protein in a DOA mouse model, upon intravitreal injection of an AAV2/2-X vector and analysis of its impact in RGC and on optic nerve degeneration.
Funding: Chile CONICYT, AFM, UNADEV, Région Occitanie, ANR, B. Fouassier, CNRS-UPS