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Keskin I, Forsgren E, Lange DJ, Weber M, Birve A, Synofzik M, Gilthorpe JD, Andersen PM, Marklund SL. Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients. PLoS One 2016; 11:e0150133. [PMID: 26919046 PMCID: PMC4769150 DOI: 10.1371/journal.pone.0150133] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 02/09/2016] [Indexed: 12/13/2022] Open
Abstract
Mutations in superoxide dismutase-1 (SOD1) are a common known cause of amyotrophic lateral sclerosis (ALS). The neurotoxicity of mutant SOD1s is most likely caused by misfolded molecular species, but disease pathogenesis is still not understood. Proposed mechanisms include impaired mitochondrial function, induction of endoplasmic reticulum stress, reduction in the activities of the proteasome and autophagy, and the formation of neurotoxic aggregates. Here we examined whether perturbations in these cellular pathways in turn influence levels of misfolded SOD1 species, potentially amplifying neurotoxicity. For the study we used fibroblasts, which express SOD1 at physiological levels under regulation of the native promoter. The cells were derived from ALS patients expressing 9 different SOD1 mutants of widely variable molecular characteristics, as well as from patients carrying the GGGGCC-repeat-expansion in C9orf72 and from non-disease controls. A specific ELISA was used to quantify soluble, misfolded SOD1, and aggregated SOD1 was analysed by western blotting. Misfolded SOD1 was detected in all lines. Levels were found to be much lower in non-disease control and the non-SOD1 C9orf72 ALS lines. This enabled us to validate patient fibroblasts for use in subsequent perturbation studies. Mitochondrial inhibition, endoplasmic reticulum stress or autophagy inhibition did not affect soluble misfolded SOD1 and in most cases, detergent-resistant SOD1 aggregates were not detected. However, proteasome inhibition led to uniformly large increases in misfolded SOD1 levels in all cell lines and an increase in SOD1 aggregation in some. Thus the ubiquitin-proteasome pathway is a principal determinant of misfolded SOD1 levels in cells derived both from patients and controls and a decline in activity with aging could be one of the factors behind the mid-to late-life onset of inherited ALS.
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Affiliation(s)
- Isil Keskin
- Department of Pharmacology and Clinical Neurosciences, Umeå University, Umeå, Sweden
| | - Elin Forsgren
- Department of Pharmacology and Clinical Neurosciences, Umeå University, Umeå, Sweden
| | - Dale J. Lange
- Department of Neurology, Hospital for Special Surgery and Weill Cornell Medical Center, New York, NY, United States of America
| | - Markus Weber
- Neuromusucular Diseases Unit/ALS Clinic, Kantonsspital St.Gallen, St. Gallen, Switzerland
| | - Anna Birve
- Department of Pharmacology and Clinical Neurosciences, Umeå University, Umeå, Sweden
| | - Matthis Synofzik
- Department of Neurodegenerative Diseases, Hertie Institute for Clinical Brain Research, Tübingen, Germany
- German Research Center for Neurodegenerative Diseases (DZNE), University of Tübingen, Tübingen, Germany
| | - Jonathan D. Gilthorpe
- Department of Pharmacology and Clinical Neurosciences, Umeå University, Umeå, Sweden
| | - Peter M. Andersen
- Department of Pharmacology and Clinical Neurosciences, Umeå University, Umeå, Sweden
| | - Stefan L. Marklund
- Department of Medical Biosciences, Clinical Chemistry, Umeå University, Umeå, Sweden
- * E-mail:
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Tokuda E, Brännström T, Andersen PM, Marklund SL. Low autophagy capacity implicated in motor system vulnerability to mutant superoxide dismutase. Acta Neuropathol Commun 2016; 4:6. [PMID: 26810478 PMCID: PMC4727314 DOI: 10.1186/s40478-016-0274-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Accepted: 01/09/2016] [Indexed: 11/10/2022] Open
Abstract
Introduction The motor system is selectively vulnerable to mutations in the ubiquitously expressed aggregation-prone enzyme superoxide dismutase-1 (SOD1). Results Autophagy clears aggregates, and factors involved in the process were analyzed in multiple areas of the CNS from human control subjects (n = 10) and amyotrophic lateral sclerosis (ALS) patients (n = 18) with or without SOD1 mutations. In control subjects, the key regulatory protein Beclin 1 and downstream factors were remarkably scarce in spinal motor areas. In ALS patients, there was evidence of moderate autophagy activation and also dysregulation. These changes were largest in SOD1 mutation carriers. To explore consequences of low autophagy capacity, effects of a heterozygous deletion of Beclin 1 were examined in ALS mouse models expressing mutant SOD1s. This caused earlier SOD1 aggregation, onset of symptoms, motor neuron loss, and a markedly shortened survival. In contrast, the levels of soluble misfolded SOD1 species were reduced. Conclusions The findings suggest that an inherent low autophagy capacity might cause the vulnerability of the motor system, and that SOD1 aggregation plays a crucial role in the pathogenesis. Electronic supplementary material The online version of this article (doi:10.1186/s40478-016-0274-y) contains supplementary material, which is available to authorized users.
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Broom HR, Vassall KA, Rumfeldt JAO, Doyle CM, Tong MS, Bonner JM, Meiering EM. Combined Isothermal Titration and Differential Scanning Calorimetry Define Three-State Thermodynamics of fALS-Associated Mutant Apo SOD1 Dimers and an Increased Population of Folded Monomer. Biochemistry 2016; 55:519-33. [PMID: 26710831 DOI: 10.1021/acs.biochem.5b01187] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Many proteins are naturally homooligomers, homodimers most frequently. The overall stability of oligomeric proteins may be described in terms of the stability of the constituent monomers and the stability of their association; together, these stabilities determine the populations of different monomer and associated species, which generally have different roles in the function or dysfunction of the protein. Here we show how a new combined calorimetry approach, using isothermal titration calorimetry to define monomer association energetics together with differential scanning calorimetry to measure total energetics of oligomer unfolding, can be used to analyze homodimeric unmetalated (apo) superoxide dismutase (SOD1) and determine the effects on the stability of structurally diverse mutations associated with amyotrophic lateral sclerosis (ALS). Despite being located throughout the protein, all mutations studied weaken the dimer interface, while concomitantly either decreasing or increasing the marginal stability of the monomer. Analysis of the populations of dimer, monomer, and unfolded monomer under physiological conditions of temperature, pH, and protein concentration shows that all mutations promote the formation of folded monomers. These findings may help rationalize the key roles proposed for monomer forms of SOD1 in neurotoxic aggregation in ALS, as well as roles for other forms of SOD1. Thus, the results obtained here provide a valuable approach for the quantitative analysis of homooligomeric protein stabilities, which can be used to elucidate the natural and aberrant roles of different forms of these proteins and to improve methods for predicting protein stabilities.
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Affiliation(s)
- Helen R Broom
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Kenrick A Vassall
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Jessica A O Rumfeldt
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Colleen M Doyle
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Ming Sze Tong
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Julia M Bonner
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Elizabeth M Meiering
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
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Roychaudhuri R, Zheng X, Lomakin A, Maiti P, Condron MM, Benedek GB, Bitan G, Bowers MT, Teplow DB. Role of Species-Specific Primary Structure Differences in Aβ42 Assembly and Neurotoxicity. ACS Chem Neurosci 2015; 6:1941-55. [PMID: 26421877 PMCID: PMC4844016 DOI: 10.1021/acschemneuro.5b00180] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
A variety of species express the amyloid β-protein (Aβ (the term "Aβ" refers both to Aβ40 and Aβ42, whereas "Aβ40" and "Aβ42" refer to each isoform specifically). Those species expressing Aβ with primary structure identical to that expressed in humans have been found to develop amyloid deposits and Alzheimer's disease-like neuropathology. In contrast, the Aβ sequence in mice and rats contains three amino acid substitutions, Arg5Gly, His13Arg, and Tyr10Phe, which apparently prevent the development of AD-like neuropathology. Interestingly, the brush-tailed rat, Octodon degus, expresses Aβ containing only one of these substitutions, His13Arg, and does develop AD-like pathology. We investigate here the biophysical and biological properties of Aβ peptides from humans, mice (Mus musculus), and rats (Octodon degus). We find that each peptide displays statistical coil → β-sheet secondary structure transitions, transitory formation of hydrophobic surfaces, oligomerization, formation of annuli, protofibrils, and fibrils, and an inverse correlation between rate of aggregation and aggregate size (faster aggregation produced smaller aggregates). The rank order of assembly rate was mouse > rat > Aβ42. The rank order of neurotoxicity of assemblies formed by each peptide immediately after preparation was Aβ42 > mouse ≈ rat. These data do not support long-standing hypotheses that the primary factor controlling development of AD-like neuropathology in rodents is Aβ sequence. Instead, the data support a hypothesis that assembly quaternary structure and organismal responses to toxic peptide assemblies mediate neuropathogenetic effects. The implication of this hypothesis is that a valid understanding of disease causation within a given system (organism, tissue, etc.) requires the coevaluation of both biophysical and cell biological properties of that system.
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Affiliation(s)
- Robin Roychaudhuri
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Xueyun Zheng
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106
| | - Aleksey Lomakin
- Department of Physics and Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Panchanan Maiti
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Margaret M. Condron
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - George B. Benedek
- Department of Physics and Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Gal Bitan
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Molecular Biology Institute and Brain Research Institute, University of California, Los Angeles, California 90095
| | - Michael T. Bowers
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106
| | - David B. Teplow
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Molecular Biology Institute and Brain Research Institute, University of California, Los Angeles, California 90095
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Abstract
Although protein folding and stability have been well explored under simplified conditions in vitro, it is yet unclear how these basic self-organization events are modulated by the crowded interior of live cells. To find out, we use here in-cell NMR to follow at atomic resolution the thermal unfolding of a β-barrel protein inside mammalian and bacterial cells. Challenging the view from in vitro crowding effects, we find that the cells destabilize the protein at 37 °C but with a conspicuous twist: While the melting temperature goes down the cold unfolding moves into the physiological regime, coupled to an augmented heat-capacity change. The effect seems induced by transient, sequence-specific, interactions with the cellular components, acting preferentially on the unfolded ensemble. This points to a model where the in vivo influence on protein behavior is case specific, determined by the individual protein's interplay with the functionally optimized "interaction landscape" of the cellular interior.
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Abstract
A longstanding challenge in studies of neurodegenerative disease has been that the pathologic protein aggregates in live tissue are not amenable to structural and kinetic analysis by conventional methods. The situation is put in focus by the current progress in demarcating protein aggregation in vitro, exposing new mechanistic details that are now calling for quantitative in vivo comparison. In this study, we bridge this gap by presenting a direct comparison of the aggregation kinetics of the ALS-associated protein superoxide dismutase 1 (SOD1) in vitro and in transgenic mice. The results based on tissue sampling by quantitative antibody assays show that the SOD1 fibrillation kinetics in vitro mirror with remarkable accuracy the spinal cord aggregate buildup and disease progression in transgenic mice. This similarity between in vitro and in vivo data suggests that, despite the complexity of live tissue, SOD1 aggregation follows robust and simplistic rules, providing new mechanistic insights into the ALS pathology and organism-level manifestation of protein aggregation phenomena in general.
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