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Celine Brooks, Aaron Snoberger, Marychairman Belcastro, Oleg Kisselev, David Smith, Maxim Sokolov; Archaeal Protein-Unfolding ATPase Counteracts Protein-Misfolding Retinopathy in Mice. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4980.
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Neurotoxicity of misfolded (non-native) proteins may contribute to the development of congenital late-onset retinopathies, including retinitis pigmentosa. We hypothesized that a protein-unfolding ATPase that evolved in a unicellular organism could counteract retinal degeneration caused by protein-misfolding. To test this idea, we introduced Proteasome-Activating Nucleotidase (PAN), an Archaeal homolog to the 19S ATPase subunit of the eukaryotic 26S proteasome, into Gγ1-/- mice, a model for protein-misfolding retinopathy.
PAN containing an epitope tag was expressed in mice from a transgene (Tg:PAN) driven by a rod-specific promoter. PAN was detected by Western blotting and immunofluorescence microscopy. The specific activity of PAN was determined by the GFP unfolding assay in pull-downs from retinal extracts. The long-term physiological effect of PAN was evaluated in wild-type and Gγ1-/- backgrounds, by analyzing retinal morphology and light responses, using light microscopy and electroretinography (ERG), respectively.
Heterozygous Tg:PAN+/- mice of wild type background retained normal retinal morphology and function for at least 1 year of life. PAN was localized in all rod cellular compartments, except for the outer segment. No aging-associated decline of PAN expression was observed. The PAN complex captured from retinal extracts displayed GFP-unfolding activity at body temperature. When expressed in Gγ1-/- mice, PAN completely preserved visual responses and averted the death of retinal photoreceptors, otherwise completed by the age of 7 months.
As evident from the absence of an adverse phenotype in wild-type mice, PAN does not appear to have a detrimental effect on native proteins in mouse rods. The protective effect of PAN in Gγ1-/- mice indicates that PAN could purge misfolded proteins that cause retinal degeneration. Our data provide the proof of principle for the therapeutic application of PAN, a xenogeneic protein-unfolding ATPase against neurodegeneration in mammals.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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