OPA1 gene therapy prevents retinal ganglion cell loss in a Dominant Optic Atrophy mouse model.

Dominant optic atrophy (DOA) is a rare progressive and irreversible blinding disease which is one of the most frequent forms of hereditary optic neuropathy. DOA is mainly caused by dominant mutation in the OPA1 gene encoding a large mitochondrial GTPase with crucial roles in membrane dynamics and cell survival. Hereditary optic neuropathies are commonly characterized by the degeneration of retinal ganglion cells, leading to the optic nerve atrophy and the progressive loss of visual acuity. Up to now, despite increasing advances in the understanding of the pathological mechanisms, DOA remains intractable. Here, we tested the efficiency of gene therapy on a genetically-modified mouse model reproducing DOA vision loss. We performed intravitreal injections of an Adeno-Associated Virus carrying the human OPA1 cDNA under the control of the cytomegalovirus promotor. Our results provide the first evidence that gene therapy is efficient on a mouse model of DOA as the wild-type OPA1 expression is able to alleviate the OPA1-induced retinal ganglion cell degeneration, the hallmark of the disease. These results displayed encouraging effects of gene therapy for Dominant Optic Atrophy, fostering future investigations aiming at clinical trials in patients.

Increased steroidogenesis promotes early-onset and severe vision loss in females with OPA1 dominant optic atrophy.

OPA1 mutations are responsible for autosomal dominant optic atrophy (ADOA), a progressive blinding disease characterized by retinal ganglion cell (RGC) degeneration and large phenotypic variations, the underlying mechanisms of which are poorly understood. OPA1 encodes a mitochondrial protein with essential biological functions, its main roles residing in the control of mitochondrial membrane dynamics as a pro-fusion protein and prevention of apoptosis. Considering recent findings showing the importance of the mitochondrial fusion process and the involvement of OPA1 in controlling steroidogenesis, we tested the hypothesis of deregulated steroid production in retina due to a disease-causing OPA1 mutation and its contribution to the visual phenotypic variations. Using the mouse model carrying the human recurrent OPA1 mutation, we disclosed that Opa1 haploinsufficiency leads to very high circulating levels of steroid precursor pregnenolone in females, causing an early-onset vision loss, abolished by ovariectomy. In addition, steroid production in retina is also increased which, in conjunction with high circulating levels, impairs estrogen receptor expression and mitochondrial respiratory complex IV activity, promoting RGC apoptosis in females. We further demonstrate the involvement of Muller glial cells as increased pregnenolone production in female cells is noxious and compromises their role in supporting RGC survival. In parallel, we analyzed ophthalmological data of a multicentre OPA1 patient cohort and found that women undergo more severe visual loss at adolescence and greater progressive thinning of the retinal nerve fibres than males. Thus, we disclosed a gender-dependent effect on ADOA severity, involving for the first time steroids and Müller glial cells, responsible for RGC degeneration.