Frederic Hoerndli

Transgenic animal models of Alzheimer's disease and related disorders: histopathology, behavior and therapy

Alzheimers disease (AD) is a devastating neurodegenerative disease that affects more than 15 million people worldwide. Within the next generation, these numbers will more than double. To assist in the elucidation of pathogenic mechanisms of AD and related disorders, such as frontotemporal dementia (FTDP-17), genetically modified mice, flies, fish and worms were developed, which reproduce aspects of the human histopathology, such as β-amyloid-containing plaques and tau-containing neurofibrillary tangles (NFT). In mice, the tau pathology caused selective behavioral impairment, depending on the distribution of the tau aggregates in the brain. β-Amyloid induced an increase in the numbers of NFT, whereas the opposite was not observed in mice. In β-amyloid-producing transgenic mice, memory impairment was associated with increased levels of β-amyloid. Active and passive β-amyloid-directed immunization caused the removal of β-amyloid plaques and restored memory functions. These findings have since been translated to human therapy. This review aims to discuss the suitability and limitations of the various animal models and their contribution to an understanding of the pathophysiology of AD and related disorders.

β-Amyloid Induces Paired Helical Filament-like Tau Filaments in Tissue Culture

Paired helical filaments (PHF) are the principal pathologic components of neurofibrillary tangles in Alzheimers disease (AD). To reproduce the formation of PHF in tissue culture, we stably expressed human tau with and without pathogenic mutations in human SH-SY5Y cells and exposed them for 5 days to aggregated synthetic β-amyloid peptide (Aβ42). This caused a decreased solubility of tau along with the generation of PHF-like tau-containing filaments. These were 20 nm wide and had periodicities of 130-140 nm in the presence of P301L mutant tau or 150-160 nm in the presence of wild-type tau. Mutagenesis of the phosphoepitope serine 422 of tau prevented both the Aβ42-mediated decrease in solubility and the generation of PHF-like filaments, suggesting a role of serine 422 or its phosphorylation in tau filament formation. Together, our data underscore a role of Aβ42 in the formation of PHF-like filaments. Our culture system will be useful to map phosphoepitopes of tau involved in PHF formation and to identify and characterize modifiers of the tau pathology. Further adaptation of the system may allow the screening and validation of compounds designed to prevent PHF formation.

Functional Genomics meets neurodegenerative disorders. Part II: application and data integration.

The transcriptomic and proteomic techniques presented in part I (Functional Genomics meets neurodegenerative disorders. Part I: transcriptomic and proteomic technology) of this back-to-back review have been applied to a range of neurodegenerative disorders, including Huntingtons disease (HD), Prion diseases (PrD), Creutzfeldt-Jakob disease, amyotrophic lateral sclerosis (ALS), Alzheimers disease (AD), frontotemporal dementia (FTD) and Parkinsons disease (PD). Samples have been derived either from human brain and cerebrospinal fluid, tissue culture cells or brains and spinal cord of experimental animal models. With the availability of huge data sets it will firstly be a major challenge to extract meaningful information and secondly, not to obtain contradicting results when data are collected in parallel from the same source of biological specimen using different techniques. Reliability of the data highly depends on proper normalization and validation both of which are discussed together with an outlook on developments that can be anticipated in the future and are expected to fuel the field. The new insight undoubtedly will lead to a redefinition and subdivision of disease entities based on biochemical criteria rather than the clinical presentation. This will have important implications for treatment strategies.

A Conserved Function of C. elegans CASY-1 Calsyntenin in Associative Learning

Background Whole-genome association studies in humans have enabled the unbiased discovery of new genes associated with human memory performance. However, such studies do not allow for a functional or causal testing of newly identified candidate genes. Since polymorphisms in Calsyntenin 2 (CLSTN2) showed a significant association with episodic memory performance in humans, we tested the C. elegans CLSTN2 ortholog CASY-1 for possible functions in the associative behavior of C. elegans. Methodology/Principal Findings Using three different associative learning paradigms and functional rescue experiments, we show that CASY-1 plays an important role during associative learning in C. elegans. Furthermore, neuronal expression of human CLSTN2 in C. elegans rescues the learning defects of casy-1 mutants. Finally, genetic interaction studies and neuron-specific expression experiments suggest that CASY-1 may regulate AMPA-like GLR-1 glutamate receptor signaling. Conclusion/Significance Our experiments demonstrate a remarkable conservation of the molecular function of Calsyntenins between nematodes and humans and point at a role of C. elegans casy-1 in regulating a glutamate receptor signaling pathway.

Aβ treatment and P301L tau expression in an Alzheimer's disease tissue culture model act synergistically to promote aberrant cell cycle re-entry

Microarrays enable the observation of gene expression in experimental models of Alzheimers disease (AD), with implications for the human pathology. Histopathologically, AD is characterized by Aβ‐containing plaques and tau‐containing neurofibrillary tangles. Here, we used a human SH‐SY5Y neuroblastoma cell system to assess the role of P301L mutant human tau expression, and treatment with or without Aβ on gene regulation. We found that Aβ and P301L tau expression independently affect the regulation of genes controlling cell proliferation and synaptic elements. Moreover, Aβ and P301L tau act synergistically on cell cycle and DNA damage genes, yet influence specific genes within these categories. By using neuronally differentiated P301L tau cells, we can show that Aβ treatment induces an early upregulation of cell cycle control and synaptic genes. At the protein level, by using Kinetworks™ multi‐immunoblotting and BrdU labelling, we found that although P301L tau and Aβ both affected levels of cell cycle proteins, their effects were distinct, in particular concerning DNA damage proteins. Moreover, DNA synthesis was observed only when SH‐SY5Y cells overexpressed human wild‐type or P301L tau and were incubated with Aβ. Thus, our study shows that Aβ treatment and human tau overexpression in an AD cell culture model act synergistically to promote aberrant cell cycle re‐entry, supporting the mitosis failure hypothesis in AD.

Functional Genomics Dissects Pathomechanisms in Tauopathies: Mitosis Failure and Unfolded Protein Response

Background: Alzheimer’s disease (AD) is characterized by β-amyloid (Aβ) peptide-containing plaques and tau-containing neurofibrillary tangles. By intracerebral injection of Aβ42, both pathologies have been combined in P301L tau mutant mice. Furthermore, in cell culture, Aβ42 induces tau aggregation. While both Aβ42 and mutant tau cause neuronal dysfunction, their modes of action are only vaguely understood. Methods: To determine which processes are disrupted by Aβ42 and/or P301L mutant tau, we used transcriptomic and proteomic techniques followed by functional validation and analysis of human AD tissue. Results: Our transcriptomic study in the SH-SY5Y cell culture system revealed that Aβ42 and P301L tau expression independently affect genes controlling the cell cycle and cell proliferation. Proteomics applied to Aβ42-treated P301L tau-expressing SH-SY5Y cells and the amygdala of Aβ42-injected P301L transgenic mice revealed that a significant fraction of proteins altered in both systems belonged to the same functional categories, i.e. stress response and metabolism. Among the proteins identified was valosin-containing protein (VCP), a component of the quality control system during endoplasmic reticulum stress. Mutations in VCP have recently been linked to frontotemporal dementia. Conclusion: Our data support the mitosis failure hypothesis that claims that aberrant cell cycle reentry of postmitotic neurons induces apoptosis. Furthermore, our data underline a role of Aβ42 in the stress response associated with protein folding.