Stochastic kinetics of intracellular huntingtin aggregate formation

Neurodegeneration in Huntington disease is described by neuronal loss in which the probability of cell death remains constant with time1. However, the quantitative connection between the kinetics of cell death and the molecular mechanism initiating neurodegeneration remains unclear. One hypothesis is that nucleation of protein aggregates containing exon I fragments of the mutant huntingtin protein (mhttex1), which contains an expanded polyglutamine region in patients with the disease, is the explanation for the infrequent but steady occurrence of neuronal death, resulting in adult onset of the disease2. Recent in vitro evidence suggests that sufficiently long polyglutamine peptides undergo a unimolecular conformational change to form a nucleus that seeds aggregation3. Here we use this nucleation mechanism as the basis to derive a stochastic mathematical model describing the probability of aggregate formation in cells as a function of time and mhttex1 protein concentration, and validate the model experimentally. These findings suggest that therapeutic strategies for Huntington disease predicated on reducing the rate of mhttex1 aggregation need only make modest reductions in huntingtin expression level to substantially increase the delay time until aggregate formation.

[1]  F. Ferrone,et al.  Nonideality and the nucleation of sickle hemoglobin. , 2000, Biophysical journal.

[2]  Y. Chernoff,et al.  Huntingtin toxicity in yeast model depends on polyglutamine aggregation mediated by a prion-like protein Rnq1 , 2002, The Journal of cell biology.

[3]  D. Gillespie.  Exact Stochastic Simulation of Coupled Chemical Reactions , 1977 .

[4]  R. Kopito,et al.  Impairment of the ubiquitin-proteasome system by protein aggregation. , 2001, Science.

[5]  H. Paulson,et al.  RNA interference improves motor and neuropathological abnormalities in a Huntington's disease mouse model. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[6]  P. Lansbury,et al.  Molecular crowding accelerates fibrillization of alpha-synuclein: could an increase in the cytoplasmic protein concentration induce Parkinson's disease? , 2002, Biochemistry.

[7]  C A Ross,et al.  Interference by Huntingtin and Atrophin-1 with CBP-Mediated Transcription Leading to Cellular Toxicity , 2001, Science.

[8]  M. Hayden,et al.  Absence of behavioral abnormalities and neurodegeneration in vivo despite widespread neuronal huntingtin inclusions. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[9]  Ronald Wetzel,et al.  Huntington's disease age-of-onset linked to polyglutamine aggregation nucleation , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[10]  Mark R. Segal,et al.  Inclusion body formation reduces levels of mutant huntingtin and the risk of neuronal death , 2004, Nature.

[11]  Karen Marder,et al.  Venezuelan kindreds reveal that genetic and environmental factors modulate Huntington's disease age of onset. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[12]  A. Young,et al.  A potent small molecule inhibits polyglutamine aggregation in Huntington's disease neurons and suppresses neurodegeneration in vivo. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[13]  S. W. Davies,et al.  Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. , 1997, Science.

[14]  R. Myers,et al.  Juvenile onset Huntington's disease--clinical and research perspectives. , 2001, Mental retardation and developmental disabilities research reviews.

[15]  J. Hofrichter,et al.  Kinetics and mechanism of deoxyhemoglobin S gelation: a new approach to understanding sickle cell disease. , 1974, Proceedings of the National Academy of Sciences of the United States of America.

[16]  P. Lansbury,et al.  Seeding “one-dimensional crystallization” of amyloid: A pathogenic mechanism in Alzheimer's disease and scrapie? , 1993, Cell.

[17]  J. Caboche,et al.  Expanded huntingtin activates the C-JUN N TERMINAL KINASE/C-JUN pathway prior to aggregate formation in striatal neurons in culture , 2004, Neuroscience.

[18]  Hans Lehrach,et al.  Huntingtin-Encoded Polyglutamine Expansions Form Amyloid-like Protein Aggregates In Vitro and In Vivo , 1997, Cell.

[19]  M. Hayden,et al.  Homozygosity for CAG mutation in Huntington disease is associated with a more severe clinical course. , 2003, Brain : a journal of neurology.

[20]  S. Lindquist,et al.  Aggregation of huntingtin in yeast varies with the length of the polyglutamine expansion and the expression of chaperone proteins. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[21]  M. F. Perutz,et al.  Cause of neural death in neurodegenerative diseases attributable to expansion of glutamine repeats , 2001, Nature.

[22]  I. Módy,et al.  Pathological Cell-Cell Interactions Elicited by a Neuropathogenic Form of Mutant Huntingtin Contribute to Cortical Pathogenesis in HD Mice , 2005, Neuron.

[23]  Steven Finkbeiner,et al.  Automated microscope system for determining factors that predict neuronal fate. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[24]  H. J. Larson.  Introduction to Probability Theory and Statistical Inference , 1970 .

[25]  E. Cattaneo,et al.  Generation and characterization of embryonic striatal conditionally immortalized ST14A cells , 1998, Journal of neuroscience research.

[26]  George B. Benedek,et al.  Kinetic theory of fibrillogenesis of amyloid β-protein , 1997 .

[27]  F. Ferrone,et al.  Homogeneous nucleation in sickle hemoglobin: stochastic measurements with a parallel method. , 1997, Biophysical journal.

[28]  A. Szabó.  Fluctuations in the polymerization of sickle hemoglobin. A simple analytic model. , 1988, Journal of molecular biology.

[29]  James F. Gusella,et al.  Molecular genetics: Unmasking polyglutamine triggers in neurodegenerative disease , 2000, Nature Reviews Neuroscience.

[30]  A. Minton,et al.  Macromolecular Crowding Accelerates Amyloid Formation by Human Apolipoprotein C-II* , 2002, The Journal of Biological Chemistry.

[31]  A. Minton,et al.  The Influence of Macromolecular Crowding and Macromolecular Confinement on Biochemical Reactions in Physiological Media* , 2001, The Journal of Biological Chemistry.

[32]  Steven Finkbeiner,et al.  Huntingtin Acts in the Nucleus to Induce Apoptosis but Death Does Not Correlate with the Formation of Intranuclear Inclusions , 1998, Cell.

[33]  Eric Renshaw.  Modelling biological populations in space and time , 1990 .

[34]  David W. Colby,et al.  Potent inhibition of huntingtin aggregation and cytotoxicity by a disulfide bond-free single-domain intracellular antibody. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[35]  Ronald Wetzel,et al.  Polyglutamine aggregation nucleation: Thermodynamics of a highly unfavorable protein folding reaction , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[36]  D. F. Andrews,et al.  A one-hit model of cell death in inherited neuronal degenerations , 2000, Nature.

[37]  D. Housman,et al.  A bivalent Huntingtin binding peptide suppresses polyglutamine aggregation and pathogenesis in Drosophila , 2002, Nature Genetics.