Accumulation of protein aggregates and ubiquitin (Ub) into cytoplasmic inclusion bodies (IB) is the single most definitive diagnostic neuropathological marker of neurodegenerative disease. Despite this universal diagnostic significance, the cell biological mechanisms underlying IB formation and, indeed, whether formation of these structures reflects a pathogenic or protective process, remains an unresolved mystery. The long-term objective of this research project is to elucidate the molecular mechanisms that underlie IB formation and Ub deposition and to develop an integrated understanding of how mammalian cells respond to the chronic expression of pathogenic, aggregation-prone proteins. The research supported by this project during the previous funding period exploited single-cell analysis of a cellular model of Huntington's disease (HD) to show that, although mature IB contain both aggregated huntingtin (htt) and Ub, the two proteins are recruited to IB with vastly different kinetics. These observations, together with emerging data from genetic models of neurodegenerative disease, suggest a model in which chronic expression of a folding-defective aggregation-prone protein like htt, burdens the cell's proteostasis capacity (ie, the cell's ability to maintain the correct dynamic equilibrium between protein folding and degradation) leading to a progressive diversion of normal proteins from productive folding to the ubiquitin proteasome system, ultimately overwhelming the cell's capacity to degrade proteins. The research in this proposal aims to rigorously testand refine this emerging model using state-of-the-art proteomic and bioimaging technologies. These studies will provide a comprehensive understanding of the dynamic interaction between protein aggregation and proteostasis and will illuminate one of the longest-standing controversies in neurodegenerative disease biology.

Public Health Relevance

The aging of the US population portends an epidemic of neurodegenerative disorders. Emerging research suggests that these diseases are closely associated with the capacity of brain cells to resist the stress of protein synthesis, folding and degradation. The proposed research will exploit state-of-the-art methodology to understand how cells deal with these stressors using a powerful genetic model of neurodegeneration, and will provide important insights into the development of new therapeutic targets and biomarkers.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-MDCN-C (03))
Program Officer
Sutherland, Margaret L
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Stanford University
Schools of Arts and Sciences
United States
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Pearce, Margaret M P; Kopito, Ron R (2018) Prion-Like Characteristics of Polyglutamine-Containing Proteins. Cold Spring Harb Perspect Med 8:
Bersuker, Kirill; Brandeis, Michael; Kopito, Ron R (2016) Protein misfolding specifies recruitment to cytoplasmic inclusion bodies. J Cell Biol 213:229-41
Pearce, Margaret M P; Spartz, Ellen J; Hong, Weizhe et al. (2015) Prion-like transmission of neuronal huntingtin aggregates to phagocytic glia in the Drosophila brain. Nat Commun 6:6768
Bersuker, Kirill; Hipp, Mark S; Calamini, Barbara et al. (2013) Heat shock response activation exacerbates inclusion body formation in a cellular model of Huntington disease. J Biol Chem 288:23633-8
Streets, Aaron M; Sourigues, Yannick; Kopito, Ron R et al. (2013) Simultaneous measurement of amyloid fibril formation by dynamic light scattering and fluorescence reveals complex aggregation kinetics. PLoS One 8:e54541
Trevino, R Sean; Lauckner, Jane E; Sourigues, Yannick et al. (2012) Fibrillar structure and charge determine the interaction of polyglutamine protein aggregates with the cell surface. J Biol Chem 287:29722-8
Hipp, Mark S; Patel, Chetan N; Bersuker, Kirill et al. (2012) Indirect inhibition of 26S proteasome activity in a cellular model of Huntington's disease. J Cell Biol 196:573-87
Hipp, Mark S; Bersuker, Kirill; Kopito, Ron R (2012) Live-cell imaging of ubiquitin-proteasome system function. Methods Mol Biol 832:463-72
Ryu, Kwon-Yul; Park, Hyejin; Rossi, Derrick J et al. (2012) Perturbation of the hematopoietic system during embryonic liver development due to disruption of polyubiquitin gene Ubc in mice. PLoS One 7:e32956
Riley, Brigit E; Kaiser, Stephen E; Kopito, Ron R (2011) Autophagy inhibition engages Nrf2-p62 Ub-associated signaling. Autophagy 7:338-40

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