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Dale Schenk

Publications and source records attributed to Dale Schenk.

At least 19 recordsLinked to original sources
PubMed2006

Increased T cell recruitment to the CNS after amyloid beta 1-42 immunization in Alzheimer's mice overproducing transforming growth factor-beta 1.

Immunotherapy targeting the amyloid beta (Abeta) peptide is a novel therapy under investigation for the treatment of Alzheimer's disease (AD). A clinical trial using Abeta(1-42) (AN1792) as the immunogen was halted as a result of development of meningoencephalitis in a small number of patients. The cytokine TGF-beta1 is a key modulator of immune responses that is increased in the brain in AD. We show here that local overexpression of TGF-beta1 in the brain increases both meningeal and parenchymal T lymphocyte number. Furthermore, TGF-beta1 overexpression in a mouse model for AD [amyloid precursor protein (APP) mice] leads to development of additional T cell infiltrates when mice were immunized at a young but not old age with AN1792. Notably, only mice overproducing both Abeta (APP mice) and TGF-beta1 experienced a rise in T lymphocyte number after immunization. One-third of infiltrating T cells were CD4 positive. We did not observe significant differences in B lymphocyte numbers in any of the genotypes or treatment groups. These results demonstrate that TGF-beta1 overproduction in the brain can promote T cell infiltration, in particular after Abeta(1-42) immunization. Likewise, levels of TGF-beta1 or other immune factors in brains of AD patients may influence the response to Abeta(1-42) immunization.

Alzheimer Disease↗
PubMed2006

Phosphorylation of Ser-129 is the dominant pathological modification of alpha-synuclein in familial and sporadic Lewy body disease.

A comprehensive, unbiased inventory of synuclein forms present in Lewy bodies from patients with dementia with Lewy bodies was carried out using two-dimensional immunoblot analysis, novel sandwich enzyme-linked immunosorbent assays with modification-specific synuclein antibodies, and mass spectroscopy. The predominant modification of alpha-synuclein in Lewy bodies is a single phosphorylation at Ser-129. In addition, there is a set of characteristic modifications that are present to a lesser extent, including ubiquitination at Lys residues 12, 21, and 23 and specific truncations at Asp-115, Asp-119, Asn-122, Tyr-133, and Asp-135. No other modifications are detectable by tandem mass spectrometry mapping, except for a ubiquitous N-terminal acetylation. Small amounts of Ser-129 phosphorylated and Asp-119-truncated alpha-synuclein are present in the soluble fraction of both normal and disease brains, suggesting that these Lewy body-associated forms are produced during normal metabolism of alpha-synuclein. In contrast, ubiquitination is only detected in Lewy bodies and is primarily present on phosphorylated synuclein; it therefore likely occurs after phosphorylated synuclein has deposited into Lewy bodies. This invariant pattern of specific phosphorylation, truncation, and ubiquitination is also present in the detergent-insoluble fraction of brain from patients with familial Parkinson's disease (synuclein A53T mutation) as well as multiple system atrophy, suggesting a common pathogenic pathway for both genetic and sporadic Lewy body diseases. These observations are most consistent with a model in which preferential accumulation of normally produced Ser-129 phosphorylated alpha-synuclein is the key event responsible for the formation of Lewy bodies in various Lewy body diseases.

Amino Acid Sequence↗
PubMed2006

Abeta species removal after abeta42 immunization.

Neuropathologic examination of 3 patients with Alzheimer disease in the Elan Pharmaceuticals trial using antibodies specific for different Abeta species showed in one case, 4 months after the immunization, evidence of a stage of active plaque clearance with "moth-eaten" plaques and abundant Abeta phagocytosis by microglia. At 1 to 2 years after immunization, 2 cases showed extensive areas cleared of plaques (69% and 86% of the temporal cortex was plaque-free). Cortex cleared of plaques in all 3 cases had a characteristic constellation of features, including a very low plaque burden, sparse residual dense plaque cores, and phagocytosed Abeta within microglia. There was resolution of tau-containing dystrophic neurites, although other features of tau pathology (tangles and neuropil threads) remained and cerebral amyloid angiopathy persisted. Although most antibodies generated by Abeta42 immunization in humans bind the intact N-terminus, immunohistochemistry with specific antibodies showed clearance of all major species of Abeta (Abeta40, Abeta42, and N-terminus truncated Abeta). Abeta immunotherapy can clear all Abeta species from the cortex. However, if it is to be used for treatment of established Alzheimer disease, then the residual tau pathology and cerebral amyloid angiopathy require further study.

Alzheimer Disease↗
PubMed2006

Mice as models: transgenic approaches and Alzheimer's disease.

Progress in understanding and treating Alzheimer's disease (AD) has been tremendously bolstered by the era of transgenic models of AD. The identification of disease-causing mutations in proteins such as amyloid-beta precursor protein (betaAPP) and presenilin1 (PS1), together with the discovery of other high risk factors (e.g., Apolipoprotein E4), as well as pathogenic mutations in the tau protein has led to the creation of several transgenic mice, including those expressing bi- and tri-genic constructs. Each model has unique pathologies that provide insights into disease mechanisms and interactive features of neuropathologic cascades. More importantly, therapeutic hypotheses are now testable in a manner unheard of less than 15 years ago. The wealth of new approaches currently in clinical and preclinical evaluations can be directly attributed to the impact of these animals on our ability to model relevant aspects of the disease. As a result, we may see containment or even the elimination of AD in the near future as a direct consequence of these advances.

Alzheimer Disease↗
PubMed2005

Altered APP processing in PDAPP (Val717 --> Phe) transgenic mice yields extended-length Abeta peptides.

Central to the pathology of Alzheimer's disease (AD) is the profuse accumulation of amyloid-beta (Abeta) peptides in the brain of affected individuals, and several amyloid precursor protein (APP) transgenic (Tg) mice models have been created to mimic Abeta deposition. Among these, the PDAPP Tg mice carrying the familial AD APP 717 Val --> Phe mutation have been widely used to test potential AD therapeutic interventions including active and passive anti-Abeta immunizations. The structure and biochemistry of the PDAPP Tg mice Abeta-related peptides were investigated using acid and detergent lysis of brain tissue, ultracentrifugation, FPLC, HPLC, enzymatic and chemical cleavage of peptides, Western blot, immunoprecipitation, and MALDI-TOF and SELDI-TOF mass spectrometry. Our experiments reveal that PDAPP mice produce a variety of C-terminally elongated Abeta peptides in addition to Abeta n-40 and Abeta n-42, as well as N-terminally truncated peptides, suggesting anomalous proteolysis of both APP and Abeta. Important alterations in the overall APP degradation also occur in this model, resulting in a striking comparative lack of CT83 and CT99 fragments, which may be inherent to the strain of mice, a generalized gamma-secretase failure, or the ultimate manifestation of the overwhelming amount of expressed human transgene; these alterations are not observed in other strains of APP Tg mice or in sporadic AD. Understanding at the molecular level the nature of these important animal models will permit a better understanding of therapeutic interventions directed to prevent, delay, or reverse the ravages of sporadic AD.

Amino Acid Sequence↗
PubMed2005

Beta-amyloid immunotherapy prevents synaptic degeneration in a mouse model of Alzheimer's disease.

Alzheimer's disease neuropathology is characterized by key features that include the deposition of the amyloid beta peptide (Abeta) into plaques, the formation of neurofibrillary tangles, and the loss of neurons and synapses in specific brain regions. The loss of synapses, and particularly the associated presynaptic vesicle protein synaptophysin in the hippocampus and association cortices, has been widely reported to be one of the most robust correlates of Alzheimer's disease-associated cognitive decline. The beta-amyloid hypothesis supports the idea that Abeta is the cause of these pathologies. However, the hypothesis is still controversial, in part because the direct role of Abeta in synaptic degeneration awaits confirmation. In this study, we show that Abeta reduction by active or passive Abeta immunization protects against the progressive loss of synaptophysin in the hippocampal molecular layer and frontal neocortex of a transgenic mouse model of Alzheimer's disease. These results, substantiated by quantitative electron microscopic analysis of synaptic densities, strongly support a direct causative role of Abeta in the synaptic degeneration seen in Alzheimer's disease and strengthen the potential of Abeta immunotherapy as a treatment approach for this disease.

Age Factors↗
PubMed2005

Effects of alpha-synuclein immunization in a mouse model of Parkinson's disease.

Abnormal folding of alpha-synuclein (alpha-syn) is thought to lead to neurodegeneration and the characteristic symptoms of Lewy body disease (LBD). Since previous studies suggest that immunization might be a potential therapy for Alzheimer's disease, we hypothesized that immunization with human (h)alpha-syn might have therapeutic effects in LBD. For this purpose, halpha-syn transgenic (tg) mice were vaccinated with halpha-syn. In mice that produced high relative affinity antibodies, there was decreased accumulation of aggregated halpha-syn in neuronal cell bodies and synapses that was associated with reduced neurodegeneration. Furthermore, antibodies produced by immunized mice recognized abnormal halpha-syn associated with the neuronal membrane and promoted the degradation of halpha-syn aggregates, probably via lysosomal pathways. Similar effects were observed with an exogenously applied FITC-tagged halpha-syn antibody. These results suggest that vaccination is effective in reducing neuronal accumulation of halpha-syn aggregates and that further development of this approach might have a potential role in the treatment of LBD.

Animals↗
PubMed2005

Amyloid-beta neurotoxicity is mediated by FISH adapter protein and ADAM12 metalloprotease activity.

Based on a variety of genetic, biochemical, and neuropathological evidence, amyloid-beta peptide (Abeta) has been suggested to be causal in Alzheimer's disease (AD). Abeta has been shown to mediate neurodegenerative and inflammatory changes associated with amyloid plaques, as well as exert direct neurotoxicity through oligomeric forms of Abeta. The mechanism of Abeta toxicity, however, remains largely unknown. In this work, we show that an early event after exposure of postmitotic neurons to Abeta is tyrosine phosphorylation of FISH adapter protein. FISH binds to and potentially regulates certain ADAM family members. We present evidence that FISH and ADAM12 mediate the neurotoxic effect of Abeta. Expression of an ADAM12 protease-deficient mutant (ADAM12DeltaMP) blocks Abeta-induced neuronal death, and expression of an N-terminal fragment of FISH reduces Abeta toxicity. The C-terminal fragment of FISH containing the ADAMs binding region is found to be sufficient for induction of neuronal death, which is prevented by coexpression of the ADAM12DeltaMP. Abeta treatment, as well as expression of the C-terminal toxic FISH fragment, induces accumulation of ADAM12 N-terminal cleavage product in conditioned medium, demonstrating activation of the ADAM metalloprotease/sheddase activity. ADAM12 protein is reduced in AD brains, pointing to a possible increase in ADAM12 proteolytic activity. These data suggest that Abeta toxicity is mediated by FISH and ADAM12 and may provide insights into therapeutic strategies for AD treatment.

ADAM Proteins↗
PubMed2005

Abeta42 immunization in Alzheimer's disease generates Abeta N-terminal antibodies.

Serum samples from Alzheimer's disease (AD) patients immunized with Abeta42 (AN1792) were analyzed to determine the induced antibody properties including precise amyloid-beta peptide (Abeta) epitopes and amyloid plaque-binding characteristics. The predominant response in these patients is independent of whether or not meningoencephalitis developed and is against the free amino terminus of Abeta. The immunostaining of amyloid plaques in brain tissue by patient sera is adsorbable by a linear Abeta1-8 peptide, demonstrating that the antibodies are directed predominantly to this epitope and not dependent on Abeta conformations or aggregates specific to plaques. Furthermore, the antibodies are not capable of binding amyloid precursor protein and would be predicted to be competent in facilitating clearance of amyloid plaques in AD brains.

Alzheimer Disease↗
PubMed2004

Identification of loci determining susceptibility to the lethal effects of amyloid precursor protein transgene overexpression.

Phenotypes produced by expression of human amyloid precursor protein (APP) transgenes vary depending on the genetic background of the mouse. FVB/N mice overexpressing human APP695 develop a central nervous system disorder and die prematurely, precluding development of Abeta peptide amyloid plaques. 129S6 mice are resistant to the lethal effects of APP overexpression, allowing sufficient levels of Abeta expression for the development of amyloid plaques and age-dependent memory deficits. To identify the genes that determine susceptibility or resistance to APP we analyzed crosses involving FVB/NCr and 129S6.Tg2576 mice that overexpress 'Swedish' mutant (K670N, M671L) APP695. APP transgene-positive FVB129S6F1 (F1) mice are resistant to the lethal effects of APP overexpression, so FVBxF1 backcross and F2 intercross offspring were produced. Analysis of age of death as a quantitative trait revealed significant linkage to loci on proximal chromosome 14 and on chromosome 9; 129S6 alleles protect against the lethal effects of APP. Within the chromosome 14 interval are segments homologous to regions on human chromosome 10 that have been linked to late onset Alzheimer's disease or to levels of Abeta peptide in plasma. However, analysis of plasma Abeta peptide concentrations at 6 weeks in backcross offspring produced no significant linkage. Similarly, elevation of human Abeta peptide concentrations by expression of mutant presenilin transgenes did not increase the proportion of mice dying prematurely, suggesting that early death reflects effects of APP or fragments other than Abeta.

Alzheimer Disease↗
PubMed2004

Selective vulnerability of dentate granule cells prior to amyloid deposition in PDAPP mice: digital morphometric analyses.

Increasing evidence from mouse models of Alzheimer's disease shows that overexpression of a mutant form of the amyloid precursor protein (APP) and its product, beta-amyloid peptide, initiate pathological changes before amyloid deposition. To evaluate the cytological basis for one of these early changes, namely reduced volume of the dentate gyrus (DG), we have used high-throughput diOlistic cell loading and 3D neuronal reconstruction to investigate potential dendritic pathology of granule cells (GCs) in 90-day-old PDAPP mice. Labeled GCs from fixed hippocampal slices were selected randomly and imaged digitally by using confocal laser-scanning microscopy. The dendritic complexity of GCs was quantified according to subordinate morphological parameters, including soma position within the granule cell layer (superficial versus deep) and topographic location within the DG (dorsal versus ventral blade) along the anterior-posterior hippocampal axis. Initial analysis, which included all sampled GC types, revealed a 12% reduction of total dendritic length in PDAPP mice compared with littermate controls. Further analysis, performed with refined subgroups, found that superficially located GCs in the dorsal blade were profoundly altered, exhibiting a 23% loss in total dendritic length, whereas neurons in the ventral blade were unaffected. Superficial GCs were particularly vulnerable (a 32% reduction) in the posterior region of the DG. Furthermore, the dendritic reductions of this select group were uniformly localized within middle-to-outer portions of the dentate molecular layer. We conclude that substantial dendritic pathology is evident in 90-day-old PDAPP mice for a spatially defined subset of GCs well before amyloid accumulation occurs.

Amyloid beta-Protein Precursor↗
PubMed2004

Current progress in beta-amyloid immunotherapy.

As neuroscientists, we are taught that the brain is immune privileged and thus unlikely to be affected by the peripheral immune system. Accordingly, initial results demonstrating the effectiveness of beta-amyloid (Abeta) immunotherapy in mouse models of Alzheimer's disease (AD) were viewed with considerable surprise and some skepticism. Many groups have since demonstrated efficacy with Abeta immunotherapy in models of AD, using Abeta-based immunogens and anti-Abeta antibodies. Clinical trials involving Abeta immunotherapy for AD are in progress and are providing a wealth of information around the amyloid hypothesis of AD. Abeta immunotherapy is also raising new opportunities and questions about the general role of the immune system in neurodegenerative diseases.

Alzheimer Disease↗
PubMed2004

Morphological characterization of Thioflavin-S-positive amyloid plaques in transgenic Alzheimer mice and effect of passive Abeta immunotherapy on their clearance.

Transgenic mice mimicking certain features of Alzheimer's disease (AD)-pathology, namely amyloid plaques and neurofibrillary tangles, have been developed in an effort to better understand the mechanism leading to the formation of these characteristic cerebral lesions. More recently, these animal models have been widely used to investigate emergent therapies aimed at the reduction of the cerebral amyloid load. Several studies have shown that immunotherapy targeting the amyloid peptide (Abeta) is efficacious at clearing the amyloid plaques or preventing their formation, and at reducing the memory/behavior impairment observed in these animals. In AD, different types of plaques likely have different pathogenic significance, and further characterization of plaque pathology in the PDAPP transgenic mice would enhance the evaluation of potential therapeutics. In the present study, a morphological classification of amyloid plaques present in the brains of PDAPP mice was established by using Thioflavin-S staining. Neuritic dystrophy associated with amyloid plaques was also investigated. Finally, the efficacy of passive immunization with anti-Abeta antibodies on the clearance of Thio-S positive amyloid plaques was studied. Our results show that distinct morphological types of plaques are differentially cleared depending upon the isotype of the antibody.

Alzheimer Disease↗
PubMed2003

Amyloid deposition in the hippocampus and entorhinal cortex: quantitative analysis of a transgenic mouse model.

Various transgenic mouse models of Alzheimer's disease (AD) have been developed that overexpress mutant forms of amyloid precursor protein in an effort to elucidate more fully the potential role of beta-amyloid (A beta) in the etiopathogenesis of the disease. The present study represents the first complete 3D reconstruction of A beta in the hippocampus and entorhinal cortex of PDAPP transgenic mice. A beta deposits were detected by immunostaining and thioflavin fluorescence, and quantified by using high-throughput digital image acquisition and analysis. Quantitative analysis of amyloid load in hippocampal subfields showed a dramatic increase between 12 and 15 months of age, with little or no earlier detectable deposition. Three-dimensional reconstruction in the oldest brains visualized previously unrecognized sheets of A beta coursing through the hippocampus and cerebral cortex. In contrast with previous hypotheses, compact plaques form before significant deposition of diffuse A beta, suggesting that different mechanisms are involved in the deposition of diffuse amyloid and the aggregation into plaques. The dentate gyrus was the hippocampal subfield with the greatest amyloid burden. Sublaminar distribution of A beta in the dentate gyrus correlated most closely with the termination of afferent projections from the lateral entorhinal cortex, mirroring the selective vulnerability of this circuit in human AD. This detailed temporal and spatial analysis of A beta and compact amyloid deposition suggests that specific corticocortical circuits express selective, but late, vulnerability to the pathognomonic markers of amyloid deposition, and can provide a basis for detecting prior vulnerability factors.

Alzheimer Disease↗
PubMed2003

Epitope and isotype specificities of antibodies to beta -amyloid peptide for protection against Alzheimer's disease-like neuropathology.

Transgenic PDAPP mice, which express a disease-linked isoform of the human amyloid precursor protein, exhibit CNS pathology that is similar to Alzheimer's disease. In an age-dependent fashion, the mice develop plaques containing beta-amyloid peptide (Abeta) and exhibit neuronal dystrophy and synaptic loss. It has been shown in previous studies that pathology can be prevented and even reversed by immunization of the mice with the Abeta peptide. Similar protection could be achieved by passive administration of some but not all monoclonal antibodies against Abeta. In the current studies we sought to define the optimal antibody response for reducing neuropathology. Immune sera with reactivity against different Abeta epitopes and monoclonal antibodies with different isotypes were examined for efficacy both ex vivo and in vivo. The studies showed that: (i) of the purified or elicited antibodies tested, only antibodies against the N-terminal regions of Abeta were able to invoke plaque clearance; (ii) plaque binding correlated with a clearance response and neuronal protection, whereas the ability of antibodies to capture soluble Abeta was not necessarily correlated with efficacy; (iii) the isotype of the antibody dramatically influenced the degree of plaque clearance and neuronal protection; (iv) high affinity of the antibody for Fc receptors on microglial cells seemed more important than high affinity for Abeta itself; and (v) complement activation was not required for plaque clearance. These results indicate that antibody Fc-mediated plaque clearance is a highly efficient and effective process for protection against neuropathology in an animal model of Alzheimer's disease.

Alzheimer Disease↗
PubMed2002

Non-Fc-mediated mechanisms are involved in clearance of amyloid-beta in vivo by immunotherapy.

Transgenic (Tg) mouse models overexpressing amyloid precursor protein (APP) develop senile plaques similar to those found in Alzheimer's disease in an age-dependent manner. Recent reports demonstrated that immunotherapy is effective at preventing or removing amyloid-beta deposits in the mouse models. To characterize the mechanisms involved in clearance, we used antibodies of either IgG1 (10d5) or IgG2b (3d6) applied directly to the brains of 18-month-old Tg2576 or 20-month-old PDAPP mice. Both 10d5 and 3d6 led to clearance of 50% of diffuse amyloid deposits in both animal models within 3 d. Fc receptor-mediated clearance has been shown to be important in an ex vivo assay showing antibody-mediated clearance of plaques by microglia. We now show, using in vivo multiphoton microscopy, that FITC-labeled F(ab')2 fragments of 3d6 (which lack the Fc region of the antibody) also led to clearance of 45% of the deposits within 3 d, similar to the results obtained with full-length 3d6 antibody. This result suggests that direct disruption of plaques, in addition to Fc-dependent phagocytosis, is involved in the antibody-mediated clearance of amyloid-beta deposits in vivo. Dense-core deposits that were not cleared were reduced in size by approximately 30% with full-length antibodies and F(ab')2 fragments 3 d after a topical treatment. Together, these results indicate that clearance of amyloid deposits in vivo may involve, in addition to Fc-dependent clearance, a non-Fc-mediated disruption of plaque structure.

Administration, Topical↗