Faculty Bibliography

Studies in vivo and in vitro have suggested that the mechanism underlying Alzheimer's disease (AD) neuropathogenesis is initiated by an interaction between the cellular prion protein (PrPC) and amyloid-beta oligomers (Abetao). This PrPC-Abetao complex activates Fyn kinase which, in turn, hyperphosphorylates tau (P-Tau) resulting in synaptic dysfunction, neuronal loss and cognitive deficits. AD transgenic mice lacking PrPC accumulate Abeta, but show normal survival and no loss of spatial learning and memory suggesting that PrPC functions downstream of Abetao production but upstream of intracellular toxicity within neurons. Since AD and traumatic brain injury (TBI)-linked chronic traumatic encephalopathy are tauopathies, we examined whether similar mechanistic pathways are responsible for both AD and TBI pathophysiologies. Using transgenic mice expressing different levels of PrPC, our studies investigated the influence and necessity of PrPC on biomarker (total-tau [T-Tau], P-Tau, GFAP) levels in brain and blood as measured biochemically following severe TBI in the form of severe closed head injury (sCHI). We found that following sCHI, increasing levels of T-Tau and P-Tau in the brain were associated with the PrPC expression levels. A similar relationship between PrPC expression and P-Tau levels following sCHI were found in blood in the absence of significant T-Tau changes. This effect was not seen with GFAP which increased within 24 h following sCHI and progressively decreased by the 7 day time point regardless of the PrPC expression levels. Changes in the levels of all biomarkers were independent of gender. We further enhanced and expanded the quantitation of brain biomarkers with correlative studies using immunohisochemistry. We also demonstrate that a TBI-induced calpain hyperactivation is not required for the generation of P-Tau. A relationship was demonstrated between the presence/absence of PrPC, the levels of P-Tau and cognitive dysfunction. Our studies suggest that PrPC is important in mediating TBI related pathology.

Experimental models of Alzheimer's disease (AD) are critical to gaining a better understanding of pathogenesis and to assess the potential of novel therapeutic approaches. The most commonly used experimental animal models are transgenic mice that overexpress human genes associated with familial AD (FAD) that result in the formation of amyloid plaques. However, AD is defined by the presence and interplay of both amyloid plaques and neurofibrillary tangle pathology. The track record of success in AD clinical trials thus far has been very poor. In part, this high failure rate has been related to the premature translation of highly successful results in animal models that mirror only limited aspects of AD pathology to humans. A greater understanding of the strengths and weakness of each of the various models and the use of more than one model to evaluate potential therapies would help enhance the success of therapy translation from preclinical studies to patients. In this review, we summarize the pathological features and limitations of the major experimental models of AD, including transgenic mice, transgenic rats, various physiological models of sporadic AD and in vitro human cell culture models.

Alzheimer's disease (AD) is the most common form of dementia worldwide. It is characterized by an imbalance between the production and clearance of amyloid beta (Abeta) and tau proteins. In AD these normal proteins accumulate, leading to aggregation and a conformational change forming oligomeric and fibrillary species with a high beta-sheet content. Active and passive immunotherapeutic approaches result in dramatic reduction of Abeta pathology in AD animal models. However, there is much more limited evidence in human studies of significant clinical benefits from these strategies and it is becoming apparent that they may only be effective very early in AD. Vaccination targeting only tau pathology has shown benefits in some mouse studies but human studies are limited. Greater therapeutic efficacy for the next generation of vaccine approaches will likely benefit from specifically targeting the most toxic species of Abeta and tau, ideally simultaneously.

PURPOSE: There is considerable variability in the extent and nature of the glial response to injury and neurodegeneration. Transplantation of fetal cortical tissue onto the brain of neonatal host rats or mice results in region-specific changes dependent on where the fetal tissue is placed. These changes include chronic astrocytic and microglial gliosis, oxidative stress, and altered metabolism of a number of proteins associated with the pathogenesis of Alzheimer's disease. Such changes are only observed in heterotopic (cortex-to-midbrain) grafts and are not observed in homotopic cortex-to-cortex grafts. We investigated two possible triggers for the region-specific gliosis observed in our transplant model hypothesizing that either i) poor vascularization and lack of blood brain barrier integrity or ii) an inflammatory response initiated by the transplantation process, contributed to establishing chronic pathological changes. METHODS: We analyzed the time course of neovascularization, blood brain barrier permeability and inflammation using a combination of immunohistochemistry, enzyme-linked immunosorbant assay and Evan's blue dye extravasation techniques. RESULTS: Blood brain barrier permeability and altered neovascularization occurred prior to the onset of gliosis in heterotopic grafts. CONCLUSION: These data suggest that ischemic conditions and blood brain barrier damage can be a primary mechanism that initiates chronic gliosis and associated inflammatory changes in central nervous system tissue.

Aggregation of amyloid beta-peptide (Abeta) is implicated in the pathology of Alzheimer's disease (AD), with the soluble, Abeta oligomeric species thought to be the critical pathological species. Identification and characterization of intermediate species formed during the aggregation process is crucial to the understanding of the mechanisms by which oligomeric species mediate neuronal toxicity and following disease progression. Probing these species proved to be extremely challenging, as evident by the lack of reliable sensors, due to their heterogeneous and transient nature. We describe here an oligomer-specific fluorescent chemical probe, BoDipy-Oligomer (BD-Oligo), developed through the use of the diversity-oriented fluorescent library approach (DOFLA) and high-content, imaging-based screening. This probe enables dynamic oligomer monitoring during fibrillogenesis in vitro and shows in vivo Abeta oligomers staining possibility in the AD mice model.

The vast majority of human tissue specimens are formalin-fixed, paraffin embedded (FFPE) archival samples, making this type of tissue a potential gold mine for medical research. It is now accepted that proteomics can be done using FFPE tissue and can generate similar results as snap-frozen tissue. However, the current methodology requires a large amount of starting protein, limiting the questions that can be answered in these types of proteomics studies and making cell-type specific proteomics studies difficult. Cell-type specific proteomics has the potential to greatly enhance understanding of cell functioning in both normal and disease states. Therefore, here we describe a new method that allows localized proteomics on individual cell populations isolated from FFPE tissue sections using laser capture microdissection. To demonstrate this technique we microdissected neurons from archived tissue blocks of the temporal cortex from patients with Alzheimer's disease. Using this method we identified over 400 proteins in microdissected neurons; on average 78% that were neuronal and 50% that were associated with Alzheimer's disease. Therefore, this technique is able to provide accurate and meaningful data and has great potential for any future study that wishes to perform localized proteomics using very small amounts of archived FFPE tissue.

Background: It has been increasingly recognized that the pathogenesis of many neurodegenerative diseases is related to the accumulation of diverse proteins in aggregated/oligomeric forms. The pathological conformers can spread to different areas of the brain via a "prion-like" conversion mechanism mediated by the mobile b-sheet oligomeric structure of each particular peptide or protein. Previously we have characterized conformational monoclonal antibodies that react to both oligomers of Abeta and tau in AD, as well as to prion disease proteins. We have nowdetermined their binding specificity and capacity to be extended to synthetic oligomers of alpha-synuclein and to pathological intracellular structures present in Lewy body containing neurons of Parkinson's disease (PD) subjects. Methods: Recombinant alpha-synuclein was produced and characterized in monomeric, oligomeric and fibrillar forms by electron microscopy and circular dichroism. Histological specimens of formalin fixed brains from human AD and PD confirmed cases were used for reaction with three anti-conformational mAbs IgM previously described. The mAbs that reacted to oligomeric Abeta and tau and showed high affinity, specific binding by surface plasmon resonance, and/or were shown to reverse AD pathology after infusion in old 3xTg AD animal models were used for immunohistochemical detection on human PD brain specimens and detection of different alpha-synuclein conformers. Results: By SDS-PAGE the mAbs IgM showed specificity for oligomeric forms of polymerized alpha-synuclein but not to the monomeric forms. The mAbs showed specific intraneuronal reactivity around the Lewy bodies in human brains from confirmed cases of PD. Conclusions: Conformational monoclonal antibodies that are well characterized to react against pathological conformers in AD human brains and that can produce amelioration of existing AD pathology in AD animal models can also recognize oligomeric forms of alpha-synuclein and intraneuronal structures associated with Lewy bodies. Monoclonal antibodies that are specific for pathology associated conformations are good candidates to be used as immunotherapeutical agents alone or in combination with other approaches in many neurodegenerative diseases including Parkinson's disease