Archaeal Unfoldase Counteracts Protein Misfolding Retinopathy in Mice

Deregulation of cellular proteostasis due to the failure of the ubiquitin proteasome system to dispose of misfolded aggregation-prone proteins is a hallmark of various neurodegenerative diseases in humans. Microorganisms have evolved to survive massive protein misfolding and aggregation triggered by heat shock using their protein-unfolding ATPases (unfoldases) from the Hsp100 family. Because the Hsp100 chaperones are absent in homoeothermic mammals, we hypothesized that the vulnerability of mammalian neurons to misfolded proteins could be mitigated by expressing a xenogeneic unfoldase. To test this idea, we expressed proteasome-activating nucleotidase (PAN), a protein-unfolding ATPase from thermophilic Archaea, which is homologous to the 19S eukaryotic proteasome and similar to the Hsp100 family chaperones in rod photoreceptors of mice. We found that PAN had no obvious effect in healthy rods; however, it effectively counteracted protein-misfolding retinopathy in G₁ knock-out mice. We conclude that archaeal PAN can rescue a protein-misfolding neurodegenerative disease, likely by recognizing misfolded mammalian proteins.

SIGNIFICANCE STATEMENT This study demonstrates successful therapeutic application of an archaeal molecular chaperone in an animal model of neurodegenerative disease. Introducing the archaeal protein-unfolding ATPase proteasome-activating nucleotidase (PAN) into the retinal photoreceptors of mice protected these neurons from the cytotoxic effect of misfolded proteins. We propose that xenogeneic protein-unfolding chaperones could be equally effective against other types of neurodegenerative diseases of protein-misfolding etiology.

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