Poster Presentation The 42nd Lorne Conference on Protein Structure and Function 2017

Mechanisms of inclusion assembly in Huntington's disease (#248)

Mikhail Trubetskov 1 , Yasmin Mohamed Ramdzan 1 , Angelique Ormsby 1 , Estella Newcombe 1 , Xiaojing Sui 1 , Mark Tobin 2 , Marie Bongiovanni 3 , Sally Gras 4 , Grant Dewson 5 , Jason Miller 6 , Steven Finkbeiner 7 , Nagaraj Moily 1 , Jonathan Niclis 8 , Clare Parish 8 , Anthony Purcell 9 , Michael Baker 1 , Jackie Wilce 9 , Saboora Waris 9 , Diana Stojanovski 1 , Till Böcking 10 , Ching-Seng Ang 11 , Gavin Reid 1 12 , Danny Hatters 1
  1. University of Melbourne, Melbourne, VIC, Australia
  2. , Australian Synchrotron, 800 Blackburn Road, Clayton, , VIC 3168, Australia
  3. Department of Chemistry, University of Cambridge, Cambridge, UK
  4. Department of Chemical and Molecular Engineering, University of Melbourne, Melbourne, VIC, Australia
  5. Walter and Eliza Hall Institute, Melbourne, VIC, Australia
  6. Kellogg Eye Center, University of Michigan , 1000 Wall Street, Ann Arbor, MI 48105 , USA
  7. Gladstone Institute of Neurological Disease, 1650 Owens Street, San Francisco, CA 94158-2261, USA
  8. The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, VIC 3010, Australia
  9. Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, Australia
  10. School of Medical Sciences, The University of New South Wales, Sydney, NSW 2052, Australia
  11. Bio21 Mass Spectrometry and Proteomics Facility, The University of Melbourne, Parkville, VIC, 3010, Australia
  12. School of Chemistry, The University of Melbourne, Parkville, VIC, 3010, Australia

Two popular models for how mutant Huntingtin exon 1 (Httex1) aggregation into inclusions relates to pathogenesis involve seemingly contradictory mechanisms. In one model, inclusions are adaptive by sequestering the proteotoxicity of soluble Httex1. In the other, inclusions compromise cellular activity from proteome co-aggregation. Via a biosensor of Httex1 conformation in mammalian cell models, we discovered a mechanism that explains this contradiction. Newly-formed inclusions are comprised 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 both soluble Httex1 and inclusions are toxic, yet inclusions impair programmed cell death arising from stalled cellular functioning. Hence cells live longer in a metabolically quiescent state and ultimately die by necrosis.