Huntingtin Inclusions Trigger Cellular Quiescence, Deactivate Apoptosis, and Lead to Delayed Necrosis
Yasmin M. Ramdzan,
Mikhail M. Trubetskov,
Angelique R. Ormsby,
Estella A. Newcombe,
Xiaojing Sui,
Mark J. Tobin,
Marie N. Bongiovanni,
Sally L. Gras,
Grant Dewson,
Jason M.L. Miller,
Steven Finkbeiner,
Nagaraj S. Moily,
Jonathan Niclis,
Clare L. Parish,
Anthony W. Purcell,
Michael J. Baker,
Jacqueline A. Wilce,
Saboora Waris,
Diana Stojanovski,
Till Böcking,
Ching-Seng Ang,
David B. Ascher,
Gavin E. Reid,
Danny M. Hatters
Affiliations
Yasmin M. Ramdzan
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Mikhail M. Trubetskov
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Angelique R. Ormsby
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Estella A. Newcombe
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Xiaojing Sui
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Mark J. Tobin
Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia
Marie N. Bongiovanni
Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK
Sally L. Gras
Department of Chemical and Biomolecular Engineering and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Grant Dewson
Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Parkville, Melbourne, VIC 3010, Australia
Jason M.L. Miller
University of Michigan Kellogg Eye Center, 1000 Wall Street, Ann Arbor, MI 48105, USA
Steven Finkbeiner
Gladstone Institute of Neurological Disease, 1650 Owens Street, San Francisco, CA 94158-2261, USA
Nagaraj S. Moily
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Jonathan Niclis
The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, VIC 3010, Australia
Clare L. Parish
The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, VIC 3010, Australia
Anthony W. Purcell
Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia
Michael J. Baker
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Jacqueline A. Wilce
Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia
Saboora Waris
Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia
Diana Stojanovski
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Till Böcking
School of Medical Sciences, The University of New South Wales, Sydney, NSW 2052, Australia
Ching-Seng Ang
Bio21 Mass Spectrometry and Proteomics Facility, The University of Melbourne, Melbourne, VIC 3010, Australia
David B. Ascher
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
Gavin E. Reid
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia; School of Chemistry, The University of Melbourne, Melbourne, VIC 3010, Australia
Danny M. Hatters
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia; Corresponding author
Summary: Competing models exist in the literature for the relationship between mutant Huntingtin exon 1 (Httex1) inclusion formation and toxicity. In one, inclusions are adaptive by sequestering the proteotoxicity of soluble Httex1. In the other, inclusions compromise cellular activity as a result of proteome co-aggregation. Using a biosensor of Httex1 conformation in mammalian cell models, we discovered a mechanism that reconciles these competing models. Newly formed inclusions were composed of disordered Httex1 and ribonucleoproteins. As inclusions matured, Httex1 reconfigured into amyloid, and other glutamine-rich and prion domain-containing proteins were recruited. Soluble Httex1 caused a hyperpolarized mitochondrial membrane potential, increased reactive oxygen species, and promoted apoptosis. Inclusion formation triggered a collapsed mitochondrial potential, cellular quiescence, and deactivated apoptosis. We propose a revised model where sequestration of soluble Httex1 inclusions can remove the trigger for apoptosis but also co-aggregate other proteins, which curtails cellular metabolism and leads to a slow death by necrosis. : Httex1 aggregation into inclusions has paradoxically been reported as either toxic or beneficial in Huntington’s disease. Ramdzan et al. define a dual mechanism of toxicity that explains this paradox. Soluble Httex1 triggers a fast death by apoptosis, whereas Httex1 inclusions invoke quiescence and redirect death to a slower necrotic pathway. Keywords: Huntington’s disease, flow cytometry, ribosome quality control, stress granule, RNA granule, P bodies, translation
