Blaine R. Roberts

Tau deficiency induces parkinsonism with dementia by impairing APP-mediated iron export

The microtubule-associated protein tau has risk alleles for both Alzheimers disease and Parkinsons disease and mutations that cause brain degenerative diseases termed tauopathies. Aggregated tau forms neurofibrillary tangles in these pathologies, but little is certain about the function of tau or its mode of involvement in pathogenesis. Neuronal iron accumulation has been observed pathologically in the cortex in Alzheimers disease, the substantia nigra (SN) in Parkinsons disease and various brain regions in the tauopathies. Here we report that tau-knockout mice develop age-dependent brain atrophy, iron accumulation and SN neuronal loss, with concomitant cognitive deficits and parkinsonism. These changes are prevented by oral treatment with a moderate iron chelator, clioquinol. Amyloid precursor protein (APP) ferroxidase activity couples with surface ferroportin to export iron, but its activity is inhibited in Alzheimers disease, thereby causing neuronal iron accumulation. In primary neuronal culture, we found loss of tau also causes iron retention, by decreasing surface trafficking of APP. Soluble tau levels fall in affected brain regions in Alzheimers disease and tauopathies, and we found a similar decrease of soluble tau in the SN in both Parkinsons disease and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. These data suggest that the loss of soluble tau could contribute to toxic neuronal iron accumulation in Alzheimers disease, Parkinsons disease and tauopathies, and that it can be rescued pharmacologically.

The role of metallobiology and amyloid‐β peptides in Alzheimer’s disease

J. Neurochem. (2012) 120 (Suppl. 1), 149–166.

The Caenorhabditis elegans Aβ1–42 Model of Alzheimer Disease Predominantly Expresses Aβ3–42

Transgenic expression of human amyloid β (Aβ) peptide in body wall muscle cells of Caenorhabditis elegans has been used to better understand aspects of Alzheimer disease (AD). In human aging and AD, Aβ undergoes post-translational changes including covalent modifications, truncations, and oligomerization. Amino truncated Aβ is increasingly recognized as potentially contributing to AD pathogenesis. Here we describe surface-enhanced laser desorption ionization-time of flight mass spectrometry mass spectrometry of Aβ peptide in established transgenic C. elegans lines. Surprisingly, the Aβ being expressed is not full-length 1–42 (amino acids) as expected but rather a 3–42 truncation product. In vitro analysis demonstrates that Aβ3–42 self-aggregates like Aβ1–42, but more rapidly, and forms fibrillar structures. Similarly, Aβ3–42 is also the more potent initiator of Aβ1–40 aggregation. Seeded aggregation via Aβ3–42 is further enhanced via co-incubation with the transition metal Cu(II). Although unexpected, the C. elegans model of Aβ expression can now be co-opted to study the proteotoxic effects and processing of Aβ3–42.

The hypoxia imaging agent CuII(atsm) is neuroprotective and improves motor and cognitive functions in multiple animal models of Parkinson’s disease

The PET imaging agent CuII(atsm) improves motor and cognitive function in Parkinson’s disease.

Utility of an improved model of amyloid-beta (Aβ1-42) toxicity in Caenorhabditis elegans for drug screening for Alzheimer’s disease

BackgroundThe definitive indicator of Alzheimer’s disease (AD) pathology is the profuse accumulation of amyloid-ß (Aß) within the brain. Various in vitro and cell-based models have been proposed for high throughput drug screening for potential therapeutic benefit in diseases of protein misfolding. Caenorhabditis elegans offers a convenient in vivo system for examination of Aß accumulation and toxicity in a complex multicellular organism. Ease of culturing and a short life cycle make this animal model well suited to rapid screening of candidate compounds.ResultsWe have generated a new transgenic strain of C. elegans that expresses full length Aß1-42. This strain differs from existing Aß models that predominantly express amino-truncated Aß3-42. The Aß1-42 is expressed in body wall muscle cells, where it oligomerizes, aggregates and results in severe, and fully penetrant, age progressive-paralysis. The in vivo accumulation of Aß1-42 also stains positive for amyloid dyes, consistent with in vivo fibril formation. The utility of this model for identification of potential protective compounds was examined using the investigational Alzheimer’s therapeutic PBT2, shown to be neuroprotective in mouse models of AD and significantly improve cognition in AD patients. We observed that treatment with PBT2 provided rapid and significant protection against the Aß-induced toxicity in C. elegans.ConclusionThis C. elegans model of full length Aß1-42 expression can now be adopted for use in screens to rapidly identify and assist in development of potential therapeutics and to study underlying toxic mechanism(s) of Aß.

THE Caernorhabditis elegans Abeta1-42 model of Alzheimer's disease predominantly expresses Abeta3-42

Transgenic expression of human amyloid β (Aβ) peptide in body wall muscle cells of Caenorhabditis elegans has been used to better understand aspects of Alzheimer disease (AD). In human aging and AD, Aβ undergoes post-translational changes including covalent modifications, truncations, and oligomerization. Amino truncated Aβ is increasingly recognized as potentially contributing to AD pathogenesis. Here we describe surface-enhanced laser desorption ionization-time of flight mass spectrometry mass spectrometry of Aβ peptide in established transgenic C. elegans lines. Surprisingly, the Aβ being expressed is not full-length 1–42 (amino acids) as expected but rather a 3–42 truncation product. In vitro analysis demonstrates that Aβ3–42 self-aggregates like Aβ1–42, but more rapidly, and forms fibrillar structures. Similarly, Aβ3–42 is also the more potent initiator of Aβ1–40 aggregation. Seeded aggregation via Aβ3–42 is further enhanced via co-incubation with the transition metal Cu(II). Although unexpected, the C. elegans model of Aβ expression can now be co-opted to study the proteotoxic effects and processing of Aβ3–42.

Copper Promotes the Trafficking of the Amyloid Precursor Protein

Accumulation of the amyloid β peptide in the cortical and hippocampal regions of the brain is a major pathological feature of Alzheimer disease. Amyloid β peptide is generated from the sequential protease cleavage of the amyloid precursor protein (APP). We reported previously that copper increases the level of APP at the cell surface. Here we report that copper, but not iron or zinc, promotes APP trafficking in cultured polarized epithelial cells and neuronal cells. In SH-SY5Y neuronal cells and primary cortical neurons, copper promoted a redistribution of APP from a perinuclear localization to a wider distribution, including neurites. Importantly, a change in APP localization was not attributed to an up-regulation of APP protein synthesis. Using live cell imaging and endocytosis assays, we found that copper promotes an increase in cell surface APP by increasing its exocytosis and reducing its endocytosis, respectively. This study identifies a novel mechanism by which copper regulates the localization and presumably the function of APP, which is of major significance for understanding the role of APP in copper homeostasis and the role of copper in Alzheimer disease.

Changes in plasma amyloid beta in a longitudinal study of aging and Alzheimer's disease

A practical biomarker is required to facilitate the preclinical diagnosis of Alzheimers disease (AD).

Oral Treatment with CuII(atsm) Increases Mutant SOD1 In Vivo but Protects Motor Neurons and Improves the Phenotype of a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

Mutations in the metallo-protein Cu/Zn-superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS) in humans and an expression level-dependent phenotype in transgenic rodents. We show that oral treatment with the therapeutic agent diacetyl-bis(4-methylthiosemicarbazonato)copperII [CuII(atsm)] increased the concentration of mutant SOD1 (SOD1G37R) in ALS model mice, but paradoxically improved locomotor function and survival of the mice. To determine why the mice with increased levels of mutant SOD1 had an improved phenotype, we analyzed tissues by mass spectrometry. These analyses revealed most SOD1 in the spinal cord tissue of the SOD1G37R mice was Cu deficient. Treating with CuII(atsm) decreased the pool of Cu-deficient SOD1 and increased the pool of fully metallated (holo) SOD1. Tracking isotopically enriched 65CuII(atsm) confirmed the increase in holo-SOD1 involved transfer of Cu from CuII(atsm) to SOD1, suggesting the improved locomotor function and survival of the CuII(atsm)-treated SOD1G37R mice involved, at least in part, the ability of the compound to improve the Cu content of the mutant SOD1. This was supported by improved survival of SOD1G37R mice that expressed the human gene for the Cu uptake protein CTR1. Improving the metal content of mutant SOD1 in vivo with CuII(atsm) did not decrease levels of misfolded SOD1. These outcomes indicate the metal content of SOD1 may be a greater determinant of the toxicity of the protein in mutant SOD1-associated forms of ALS than the mutations themselves. Improving the metal content of SOD1 therefore represents a valid therapeutic strategy for treating ALS caused by SOD1.

An iron–dopamine index predicts risk of parkinsonian neurodegeneration in the substantia nigra pars compacta

The co-localization of iron and dopamine raises the risk of a potentially toxic reaction. Disturbance of the balance in this unique chemical environment makes neurons in the substantia nigra pars compacta (SNc) particularly vulnerable to parkinsonian neurodegeneration in the aging brain. In Parkinsons disease, these neurons degenerate coincident with an elevation in brain iron levels, yet relatively little is known about specific regional iron distribution with respect to dopamine. To directly appraise the iron–dopamine redox couple, we applied immuno-assisted laser ablation-inductively coupled plasma-mass spectrometry imaging to co-localize iron with the dopamine-producing enzyme tyrosine hydroxylase at the coronal level of the substantia nigra. We found that in the healthy brain the SNc does not contain the greatest concentration of iron within the midbrain, while the dopamine-rich environment in this region reflects an increased oxidative load. The product of iron and dopamine was significantly greater in the SNc than the adjacent ventral tegmental area, which is less susceptible to neuron loss in Parkinsons disease. Accordingly, this ‘risk factor’ was elevated further following 6-hydroxydopamine (6-OHDA) lesioning. Considering mounting evidence that brain iron increases with age, this measurable iron–dopamine index provides direct experimental evidence of a relationship between these two redox-active chemicals in degenerating dopaminergic neurons.