Faculty Bibliography

There are growing genetic, transcriptomic and proteomic data pointing to the complexity of Alzheimer's disease (AD) pathogenesis. Unbiased "omics" approaches are essential for the future development of effective AD research, which will need to be combined and personalized, given that multiple distinct pathways can drive AD pathology. It is essential to gain a better understanding of the AD pathogenesis subtype variety and to develop several distinct therapeutic approaches tailored to address this diversity, as well as the common presence of mixed pathologies. These nonmutually exclusive therapeutic approaches include the targeting of multiple toxic oligomeric species concurrently, targeting the apolipoprotein E/amyloid β interaction and the modulation of innate immunity, as well as more "out of the box" ideas such as targeting infectious agents that may play a role in AD.

INTRODUCTION/BACKGROUND:Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by protein aggregates of amyloid β (Aβ) and tau. These proteins have normal physiological functions, but in AD they undergo a conformational change and aggregate as toxic oligomeric and fibrillar species with a high β-sheet content. Areas covered: Active and passive immunotherapeutic approaches are among the most attractive methods for targeting misfolded Aβ and tau. Promising preclinical testing of various immunotherapeutic approaches have yet to translate to cognitive benefits in human clinical trials. Knowledge gained from these past failures has led to the development of second generation Aβ active immunotherapies, anti-Aβ monoclonal antibodies targeting a wide array of Aβ conformations, and to a number of immunotherapies targeting pathological tau. This review covers the more recent advances in vaccine development for AD from 2016 to present. Expert commentary: Due to the complex pathophysiology of AD, greatest clinical efficacy will most likely be achieved by concurrently targeting the most toxic forms of both Aβ and tau.

BACKGROUND:Oligomeric forms of amyloid-β (Aβ) and tau are increasing being recognized as key toxins in the pathogenesis of Alzheimer's disease (AD). METHODS:We developed a novel monoclonal antibody (mAb), GW-23B7, that recognizes β-sheet secondary structure on pathological oligomers of neurodegenerative diseases. RESULTS:The pentameric immunoglobulin M kappa chain (IgMκp) we developed specifically distinguishes intra- and extracellular pathology in human AD brains. Purified GW-23B7 showed a dissociation constant in the nanomolar range for oligomeric Aβ and did not bind monomeric Aβ. In enzyme-linked immunosorbent assays, it recognized oligomeric forms of both Aβ and hyperphosphorylated tau. Aged triple-transgenic AD mice with both Aβ and tau pathology infused intraperitoneally for 2 months showed IgMκp in the soluble brain homogenate, peaking at 24 h postinoculation. Treated mice exhibited significant cognitive rescue on radial arm maze testing compared with vehicle control-infused mice. Immunohistochemically, treatment resulted in a significant decrease of extracellular pathology. Biochemically, treatment resulted in significant reductions of oligomeric forms of Aβ and tau. CONCLUSIONS:These results suggest that GW-23B7, an anti-β-sheet conformational mAb humanized for clinical trials, may be an effective therapeutic agent for human AD.

Here, we describe a new method that allows localized proteomics of amyloid plaques and neurofibrillary tangles (NFTs), which are the two pathological hallmarks of Alzheimer's disease (AD). Amyloid plaques and NFTs are visualized using immunohistochemistry and microdissected from archived, formalin-fixed paraffin-embedded (FFPE) human tissue samples using laser-capture microdissection. The majority of human tissue specimens are FFPE; hence the use of this type of tissue is a particular advantage of this technique. Microdissected tissue samples are solubilized with formic acid and deparaffinized, reduced, alkylated, proteolytically digested, and desalted. The resulting protein content of plaques and NFTs is determined using label-free quantitative LC-MS. This results in the unbiased and simultaneous quantification of ~900 proteins in plaques and ~500 proteins in NFTs. This approach permits downstream pathway and network analysis, hence providing a comprehensive overview of pathological protein accumulation found in neuropathological features in AD.

There is growing genetic and proteomic data highlighting the complexity of Alzheimer's disease (AD) pathogenesis. Greater use of unbiased "omics" approaches is being increasingly recognized as essential for the future development of effective AD research, that need to better reflect the multiple distinct pathway abnormalities that can drive AD 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. We highlight our recent efforts to increase use of human tissue to gain a better understanding of the AD pathogenesis subtype variety and to develop several distinct therapeutic approaches tailored to address this diversity. These therapeutic approaches include the blocking of the Aβ/apoE interaction, stimulation of innate immunity, and the simultaneous blocking of Aβ/tau oligomer toxicity. We believe that future successful therapeutic approaches will need to be combined to better reflect the complexity of the abnormal pathways triggered in AD pathogenesis.

Rapidly progressive Alzheimer's disease (rpAD) is a particularly aggressive form of Alzheimer's disease, with a median survival time of 7-10 months after diagnosis. Why these patients have such a rapid progression of Alzheimer's disease is currently unknown. To further understand pathological differences between rpAD and typical sporadic Alzheimer's disease (sAD) we used localized proteomics to analyze the protein differences in amyloid plaques in rpAD and sAD. Label-free quantitative LC-MS/MS was performed on amyloid plaques microdissected from rpAD and sAD patients (n = 22 for each patient group) and protein expression differences were quantified. On average, 913 +/- 30 (mean +/- SEM) proteins were quantified in plaques from each patient and 279 of these proteins were consistently found in plaques from every patient. We found significant differences in protein composition between rpAD and sAD plaques. We found that rpAD plaques contained significantly higher levels of neuronal proteins (p = 0.0017) and significantly lower levels of astrocytic proteins (p = 1.08 x 10-6). Unexpectedly, cumulative protein differences in rpAD plaques did not suggest accelerated typical sAD. Plaques from patients with rpAD were particularly abundant in synaptic proteins, especially those involved in synaptic vesicle release, highlighting the potential importance of synaptic dysfunction in the accelerated development of plaque pathology in rpAD. Combined, our data provide new direct evidence that amyloid plaques do not all have the same protein composition and that the proteomic differences in plaques could provide important insight into the factors that contribute to plaque development. The cumulative protein differences in rpAD plaques suggest rpAD may be a novel subtype of Alzheimer's disease.

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.