title: Protein misfolding and the pathogenesis of ABCA4-associated retinal degenerations.
abstract: Mutations in the ABCA4 gene are a common cause of autosomal recessive retinal degeneration. All mouse models to date are based on knockouts of Abca4, even though the disease is often caused by missense mutations such as the complex allele L541P;A1038V (PV). We now show that the PV mutation causes severe human disease whereas the V mutation alone causes mild disease. Mutant ABCA4 proteins expressed heterologously in mammalian cells retained normal cellular localization. However, basal and all-trans-retinal-stimulated ATPase activities were reduced substantially for P and PV but only mildly for V. Electron microscopy revealed marked structural changes and misfolding for the P and PV mutants but few changes for the V mutant, consistent with the disease severity difference in patients. We generated Abca4(PV/PV) knock-in mice homozygous for the complex PV allele to investigate the effects of this misfolding mutation in vivo. Mutant ABCA4 RNA levels approximated WT ABCA4 RNA levels but, surprisingly, only trace amounts of mutant ABCA4 protein were noted in the retina. RNA sequencing of WT, Abca4(-/-) and Abca4(PV/PV) mice revealed mild gene expression alterations in the retina and RPE. Similar to Abca4(-/-) mice, Abca4(PV/PV) mice showed substantial A2E and lipofuscin accumulation in their RPE cells but no retinal degeneration up to 12 months of age. Thus, rapid degradation of this large misfolded mutant protein in mouse retina caused little detectable photoreceptor degeneration. These findings suggest likely differences in the unfolded protein response between murine and human photoreceptors and support development of therapies directed at increasing this capability in patients.
authors.affiliation: Department of Pharmacology and Cleveland Center for Membrane and Structural Biology and.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology and Cleveland Center for Membrane and Structural Biology and.
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Tsybovsky
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, 660 S. Euclid Avenue, Campus Box 8096, Saint Louis, MO 63110, USA.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Kolesnikov
authors.affiliation: Department of Ophthalmology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Rozanowska
authors.affiliation: Department of Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Swider
authors.affiliation: Department of Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Sharon B
authors.initials: SB
authors.lastname: Schwartz
authors.affiliation: Department of Ophthalmology, University of Iowa Carver College of Medicine, Iowa City, IA, USA Howard Hughes Medical Institute, Iowa City, IA, USA and.
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Stone
authors.affiliation: Polgenix, Inc., 11000 Cedar Ave, Suite 260, Cleveland, OH 44106, USA.
authors.forename: Grazyna
authors.initials: G
authors.lastname: Palczewska
authors.affiliation: Department of Ophthalmology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
authors.forename: Akiko
authors.initials: A
authors.lastname: Maeda
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, 660 S. Euclid Avenue, Campus Box 8096, Saint Louis, MO 63110, USA.
authors.forename: Vladimir J
authors.initials: VJ
authors.lastname: Kefalov
authors.affiliation: Department of Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Jacobson
authors.affiliation: Department of Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Artur V
authors.initials: AV
authors.lastname: Cideciyan
authors.affiliation: Department of Pharmacology and Cleveland Center for Membrane and Structural Biology and kxp65@case.edu.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000328:Adult; D017668:Age of Onset; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D018450:Disease Progression; D015870:Gene Expression; D056726:Genetic Association Studies; D057809:HEK293 Cells; D006801:Humans; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017354:Point Mutation; D017510:Protein Folding; D021381:Protein Transport; D012162:Retinal Degeneration / Q000201:enzymology / Q000235:genetics* / Q000473:pathology
chemical_list: C056475:ABCA4 protein, human; D018528:ATP-Binding Cassette Transporters