Claudia Mistl

Neuropathology in Mice Expressing Human α-Synuclein

The presynaptic protein α-synuclein is a prime suspect for contributing to Lewy pathology and clinical aspects of diseases, including Parkinsons disease, dementia with Lewy bodies, and a Lewy body variant of Alzheimers disease. α-Synuclein accumulates in Lewy bodies and Lewy neurites, and two missense mutations (A53T and A30P) in the α-synuclein gene are genetically linked to rare familial forms of Parkinsons disease. Under control of mouse Thy1 regulatory sequences, expression of A53T mutant human α-synuclein in the nervous system of transgenic mice generated animals with neuronal α-synucleinopathy, features strikingly similar to those observed in human brains with Lewy pathology, neuronal degeneration, and motor defects, despite a lack of transgene expression in dopaminergic neurons of the substantia nigra pars compacta. Neurons in brainstem and motor neurons appeared particularly vulnerable. Motor neuron pathology included axonal damage and denervation of neuromuscular junctions in several muscles examined, suggesting that α-synuclein interfered with a universal mechanism of synapse maintenance. Thy1 transgene expression of wild-type human α-synuclein resulted in similar pathological changes, thus supporting a central role for mutant and wild-type α-synuclein in familial and idiotypic forms of diseases with neuronal α-synucleinopathy and Lewy pathology. These mouse models provide a means to address fundamental aspects of α-synucleinopathy and test therapeutic strategies.

Axonopathy and amyotrophy in mice transgenic for human four-repeat tau protein

Abstract Coding region and intronic mutations in the tau gene cause frontotemporal dementia and parkinsonism linked to chromosome 17. Some of these mutations lead to an overproduction of tau isoforms with four microtubule-binding repeats. Here we have expressed the longest four-repeat human brain tau isoform in transgenic mice under the control of the murine Thy1 promoter. Transgenic mice aged 3 weeks to 25 months overexpressed human tau protein in nerve cells of brain and spinal cord. Numerous abnormal, tau-immunoreactive nerve cell bodies and dendrites were seen. In addition, large numbers of pathologically enlarged axons containing neurofilament- and tau-immunoreactive spheroids were present, especially in spinal cord. Signs of Wallerian degeneration and neurogenic muscle atrophy were observed. When motor function was tested, transgenic mice showed signs of muscle weakness. Taken together, these findings demonstrate that overexpression of human four-repeat tau leads to a central and peripheral axonopathy that results in nerve cell dysfunction and amyotrophy.

Distinct role of protein phosphatase 2A subunit Cα in the regulation of E-cadherin and β-catenin during development

Abstract Protein phosphatase 2A (PP2A) plays central roles in development, cell growth and transformation. Inactivation of the gene encoding the PP2A catalytic subunit C α by gene targeting generates a lethal embryonic phenotype. No mesoderm is formed in C α −/− embryos. Here, we found that during normal early embryonic development C α was predominantly present at the plasma membrane whereas the highly homologous isoform C β was localized to the cytoplasm and nuclei, suggesting the inability of C β to compensate for vital functions of C α in C α −/− embryos. In addition, PP2A was found in a complex containing the PP2A substrates E-cadherin and β -catenin. In C α −/− embryos, E-cadherin and β -catenin were redistributed from the plasma membrane to the cytosol. Cytosolic concentrations of β -catenin were low. Our results suggest that C α is required for stabilization of E-cadherin/ β -catenin complexes at the plasma membrane.

Argyrophilic grains of Braak: occurrence in dendrites of neurons containing hyperphosphorylated tau protein.

M. Tolnay, C. Mistl, S. Ipsen and A. Probst (1998) Neuropathology and Applied Neurobiology24,53–59

Mouse models of α-synucleinopathy and Lewy pathology

The discovery of two missense mutations (A53T and A30P) in the gene encoding the presynaptic protein alpha-synuclein (alphaSN) that are genetically linked to rare familial forms of Parkinsons disease and its accumulation in Lewy bodies and Lewy neurites has triggered several attempts to generate transgenic mice overexpressing human alphaSN. Analogous to a successful strategy for the production of transgenic animal models for Alzheimers disease we generated mice expressing wildtype and the A53T mutant of human alphaSN in the nervous system under control of mouse Thy1 regulatory sequences. These animals develop neuronal alpha-synucleinopathy, striking features of Lewy pathology, neuronal degeneration and motor defects. Neurons in brainstem and motor neurons appeared particularly vulnerable. Motor neuron pathology included axonal damage and denervation of neuromuscular junctions, suggesting that alphaSN may interfere with a universal mechanism of synapse maintenance. Thy1-transgene expression of wildtype human alphaSN resulted in comparable pathological changes thus supporting a central role for mutant and wildtype alphaSN in familial and idiopathic forms of diseases with neuronal alpha-synucleinopathy and Lewy pathology. The mouse models provide means to address fundamental aspects of alpha-synucleinopathy and to test therapeutic strategies.

The Bartonella henselae VirB/Bep system interferes with vascular endothelial growth factor (VEGF) signalling in human vascular endothelial cells

The vasculotropic pathogen Bartonella henselae (Bh) intimately interacts with human endothelial cells (ECs) and subverts multiple cellular functions. Here we report that Bh specifically interferes with vascular endothelial growth factor (VEGF) signalling in ECs. Bh infection abrogated VEGF‐induced proliferation and wound closure of EC monolayers as well as the capillary‐like sprouting of EC spheroids. On the molecular level, Bh infection did not alter VEGF receptor 2 (VEGFR2) expression or cell surface localization, but impeded VEGF‐stimulated phosphorylation of VEGFR2 at tyrosine1175. Consistently, we observed that Bh infection diminished downstream events of the tyrosine1175‐dependent VEGFR2‐signalling pathway leading to EC proliferation, i.e. phospholipase‐Cγ activation, cytosolic calcium fluxes and mitogen‐activated protein kinase ERK1/2 phosphorylation. Pervanadate treatment neutralized the inhibitory activity of Bh on VEGF signalling, suggesting that Bh infection may activate a phosphatase that alleviates VEGFR2 phosphorylation. Inhibition of VEGFR2 signalling by Bh infection was strictly dependent on a functional VirB type IV secretion system and thereby translocated Bep effector proteins. The data presented in this study underscore the role of the VirB/Bep system as important factor controlling EC proliferation in response to Bh infection; not only as previously reported by counter‐acting an intrinsic bacterial mitogenic stimulus, but also by restricting the exogenous angiogenic stimulation by Bh‐induced VEGF.

Evolutionary Dynamics of Pathoadaptation Revealed by Three Independent Acquisitions of the VirB/D4 Type IV Secretion System in Bartonella

The α-proteobacterial genus Bartonella comprises a group of ubiquitous mammalian pathogens that are studied as a model for the evolution of bacterial pathogenesis. Vast abundance of two particular phylogenetic lineages of Bartonella had been linked to enhanced host adaptability enabled by lineage-specific acquisition of a VirB/D4 type IV secretion system (T4SS) and parallel evolution of complex effector repertoires. However, the limited availability of genome sequences from one of those lineages as well as other, remote branches of Bartonella has so far hampered comprehensive understanding of how the VirB/D4 T4SS and its effectors called Beps have shaped Bartonella evolution. Here, we report the discovery of a third repertoire of Beps associated with the VirB/D4 T4SS of B. ancashensis, a novel human pathogen that lacks any signs of host adaptability and is only distantly related to the two species-rich lineages encoding a VirB/D4 T4SS. Furthermore, sequencing of ten new Bartonella isolates from under-sampled lineages enabled combined in silico analyses and wet lab experiments that suggest several parallel layers of functional diversification during evolution of the three Bep repertoires from a single ancestral effector. Our analyses show that the Beps of B. ancashensis share many features with the two other repertoires, but may represent a more ancestral state that has not yet unleashed the adaptive potential of such an effector set. We anticipate that the effectors of B. ancashensis will enable future studies to dissect the evolutionary history of Bartonella effectors and help unraveling the evolutionary forces underlying bacterial host adaptation.

Perisomatic Granules of Hippocampal CA1 Neurons in Alzheimer’s Disease, Pre-Alzheimer Stage and Pick’s Disease: An Overlooked Pathological Entity

There is overall consensus that neuronal loss occurs selectively in vulnerable areas of the brain in Alzheimer’s disease (AD) compared to age-matched normal specimens. Significant and disease specific loss of hippocampal neurons is known to occur in CA1 neuronal subsets which appear to be more severely affected than other hippocampal subregions’. However, the cause of cell death in the hippocampus remains unknown. One possibility is that, in some neurons at least, the accumulation of tau protein in an aggregated fibrillar form (the neurofibrillary tangle-NFT) results in the demise of the cell, although the way tau filaments interfere with neuronal function is largely unknown. Other proposed mechanisms leading to cell death are oxidative stress or excitatory amino acid (EAA) receptor-mediated exitotoxicity2.