Vision defects associated with loss of C-Vps function

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ABSTRACT Leukodystrophies (LD) and genetic Leukoencephalopathies (gLE) are genetic disorders affecting the white matter (myelin) in the central nervous system. LDs and gLEs progressively affect the motor and sensory systems, including the visual systems. Parents of affected children first note visual problems as a gradual loss in the ability of their child/children to track visual cues. Vision slowly worsens over subsequent years, likely due to the loss of myelin in the optic nerve and brain, termed cortical blindness. An MRI is typically diagnostic for myelination defects, but a clear diagnosis of disease-specific LDs and gLEs remains a challenge, and the majority of LDs and gLEs have an unknown genetic origin. We recently identified a mutation in VPS11 as a causative allele in the gLE phenotypes observed in five individuals from three unrelated Ashkenazi Jewish (AJ) families. Our analysis indicates a carrier rate of 1:250 AJ individuals. VPS11 functions in a complex of four C- VPS proteins, which are conserved from yeast to humans, and control critical cellular processes in the endolysosomal and autophagy pathways. These processes are only beginning to be investigated at the molecular level, mainly in yeast. Indeed, prior to our recent report, there were no known human mutations of any of the C-VPS proteins. However, we previously characterized a zebrafish vps11 mutant and have recently discovered that it shares many of the phenotypes of the human mutant, including defects in endolysosomal and autophagy pathways, myelination defects in the CNS, loss of retinal and CNS neurons, and motor defects. This proposal aims to take advantage of the zebrafish model to characterize the pathology underlying the vision loss associated with loss of C-Vps function. Aim 1 will further characterize the vision and motor defects associated with loss of Vps11 function in our zebrafish model and characterize the gLE phenotypes associated with loss of other C-Vps proteins. Aim 2 will analyze the intercellular consequences of the specific VPS11 mutation that underlies the gLE phenotypes and screen for compounds that will rescue the autophagy flux defects associated with this disease. Aim 3 utilizes a mammalian cell culture model to co-culture oligodendrocytes and neurons to test the role of VPS11 in myelin formation, which is the first investigation of VPS11 function in oligodendrocytes in any species. By combining mammalian in vitro techniques with the power of the zebrafish mutant model, the successful completion of these aims will significantly advance our long-term goal of elucidating the mechanism that underlies VPS11-mediated vision loss.