Faculty Bibliography

Aims Acetylcholinesterase (AChE) exists as different splicing variants with particular regional, cellular, and subcellular locations that may reflect differential physiological roles. So we aimed to study the expression of AChE variants in Alzheimer's disease (AD) brain. Method We have analyzed protein levels of AChE variants in postmortem cerebral cortex from AD patients by Western blot using specific anti-AChE antibodies. Levels of AChE transcripts were also analysed by qRT-PCR. Further, we investigated expression levels of the anchoring AChE subunit proline-rich membrane anchor (PRiMA-1), limiting factor for correct localization of cholinergic AChE at plasma membrane. In addition we analysed expression levels of AChE variants in cell cultures after PRiMA overexpression. Changes in AChE promoter were also evaluated by Luciferase assays. Results We found similar protein and mRNA levels of the major cholinergic "tailed"-variant (AChE-T) and the anchorage subunit PRiMA-1 in cortex from AD patients and non-demented controls. Interestingly, we observed an increment in protein and transcript levels of the non-cholinergic "readthrought" AChE (AChE-R) subunits in cortex of AD patients compared to controls. Moreover an increase in N-extended variants of AChE, which were assigned to N-AChE-R variants, was detected in AD cortex. We further observed that PRiMA 1 could regulate the expression of AChE-T variants without effect in AChE-R forms. Conclusion Our findings reveal previously unknown expression patterns of AChE variants in AD cortex likely reflecting specific roles and/or differential regulation for each variant in AD, which may have strong implications for the re-evaluation of AChE inhibitors as therapeutic agents in dementia

Aims Biochemical and proteomic analysis of brain deposits and biological fluids reveal a high degree of Abeta heterogeneity that goes far beyond the classical Abeta40/Abeta42 dichotomy, displaying numerous post-translational modifications and multiple truncations at both N- and C-terminal ends of the molecule likely reflecting local action of resident enzymes. In spite of innumerable studies focusing in Abeta, the relevance of N- and C-terminal truncated species in the mechanism of AD pathogenesis remains largely understudied. Method Abeta species in brain tissue extracts were identified via immunoprecipitation/mass spectrometry. Synthetic homologues of intact and truncated peptides were compared in their solubility properties, self-oligomerization propensity, and brain clearance characteristics. Novel antibodies recognizing specific N- and C-terminal truncations were employed to immunolabel amyloid deposits in AD brains and transgenic models. Intracerebral injections of monomeric and oligomeric radiolabeled homologues were used to assess their brain clearance characteristics. Results N- and C-terminal truncated fragments in brain homogenates exhibit differential fractionation characteristics and topographic localization. Water-soluble brain extracts were enriched in C-terminal fragments -resembling the CSF Abeta peptidome- whereas N-terminal truncations required formic acid for solubilization. Synthetic homologues confirmed the differences in solubility and revealed contrasting oligomerization/ fibrillization characteristics. Notably, oligomerization largely increased brain retention, a characteristic mostly evident in fragments truncated at Phe4, topographically abundant in the plaque cores. Conclusion Abeta degradation at the C-terminal-end generates fragments likely associated to catabolic/clearance mechanisms while truncations at the N-terminus favor oligomerization and brain retention, with the potential to exacerbate the process of amyloidogenesis

In Alzheimer's disease, soluble tau accumulates and deposits as neurofibrillary tangles (NFTs). However, a precise toxic mechanism of tau is not well understood. We hypothesized that overexpression of wild-type tau downregulates brain-derived neurotrophic factor (BDNF), a neurotrophic peptide essential for learning and memory. Two transgenic mouse models of human tau expression and human tau (hTau40)-transfected human neuroblastoma (SH-SY5Y) cells were used to examine the effect of excess or pathologically modified wild-type human tau on BDNF expression. Both transgenic mouse models, with or without NFTs, as well as hTau40-SH-SY5Y cells significantly downregulated BDNF messenger RNA compared with controls. Similarly, transgenic mice overexpressing amyloid-beta (Abeta) significantly downregulated BDNF expression. However, when crossed with tau knockout mice, the resulting animals exhibited BDNF levels that were not statistically different from wild-type mice. These results demonstrate that excess or pathologically modified wild-type human tau downregulates BDNF and that neither a mutation in tau nor the presence of NFTs is required for toxicity. Moreover, our findings suggest that tau at least partially mediates Abeta-induced BDNF downregulation. Therefore, Alzheimer's disease treatments targeting Abeta alone may not be effective without considering the impact of tau pathology on neurotrophic pathways.

Defective autophagy contributes to Alzheimer disease (AD) pathogenesis although evidence is conflicting on whether multiple stages are impaired. Here, for the first time, we have comprehensively evaluated the entire autophagic process specifically in CA1 pyramidal neurons of hippocampus from early and late-stage AD subjects and nondemented controls. CA1 neurons aspirated by laser capture microdissection were analyzed using a custom-designed microarray comprising 578 neuropathology- and neuroscience-associated genes. Striking upregulation of autophagy-related genes, exceeding that of other gene ontology groups, reflected increases in autophagosome formation and lysosomal biogenesis beginning at early AD stages. Upregulated autophagosome formation was further indicated by elevated gene and protein expression levels for autophagosome components and increased LC3-positive puncta. Increased lysosomal biogenesis was evidenced by activation of MiTF/TFE family transcriptional regulators, particularly TFE3 (transcription factor binding to IGHM enhancer 3) and by elevated expression of their target genes and encoded proteins. Notably, TFEB (transcription factor EB) activation was associated more strongly with glia than neurons. These findings establish that autophagic sequestration is both competent and upregulated in AD. Autophagosome-lysosome fusion is not evidently altered. Despite this early disease response, however, autophagy flux is progressively impeded due to deficient substrate clearance, as reflected by autolysosomal accumulation of LC3-II and SQSTM1/p62 and expansion of autolysosomal size and total area. We propose that sustained induction of autophagy in the face of progressively declining lysosomal clearance of substrates explains the uncommonly robust autophagic pathology and neuritic dystrophy implicated in AD pathogenesis.

Individuals with Down syndrome (DS) exhibit intellectual disability and develop Alzheimer's disease-like neuropathology during the third decade of life. The Ts65Dn mouse model of DS exhibits key features of both disorders, including impairments in learning, attention and memory, as well as atrophy of basal forebrain cholinergic neurons (BFCNs). The present study evaluated attentional function in relation to BFCN morphology in young (3 months) and middle-aged (12 months) Ts65Dn mice and disomic (2N) controls. Ts65Dn mice exhibited attentional dysfunction at both ages, with greater impairment in older trisomics. Density of BFCNs was significantly lower for Ts65Dn mice independent of age, which may contribute to attentional dysfunction since BFCN density was positively associated with performance on an attention task. BFCN volume decreased with age in 2N but not Ts65Dn mice. Paradoxically, BFCN volume was greater in older trisomic mice, suggestive of a compensatory response. In sum, attentional dysfunction occurred in both young and middle-aged Ts65Dn mice, which may in part reflect reduced density and/or phenotypic alterations in BFCNs.

Autophagy and endocytosis deliver unneeded cellular materials to lysosomes for degradation. Beyond processing cellular waste, lysosomes release metabolites and ions that serve signaling and nutrient sensing roles, linking the functions of the lysosome to various pathways for intracellular metabolism and nutrient homeostasis. Each of these lysosomal behaviors is influenced by the intraluminal pH of the lysosome, which is maintained in the low acidic range by a proton pump, the vacuolar ATPase (v-ATPase). New reports implicate altered v-ATPase activity and lysosomal pH dysregulation in cellular aging, longevity, and adult-onset neurodegenerative diseases, including forms of Parkinson Disease and Alzheimer Disease. Genetic defects of subunits composing the v-ATPase or v-ATPase-related proteins occur in an increasingly recognized group of familial neurodegenerative diseases. Here, we review the expanding roles of the v-ATPase complex as a platform regulating lysosomal proteolysis and cellular homeostasis. We discuss the unique vulnerability of neurons to persistent low level lysosomal dysfunction and review recent clinical and experimental studies that link dysfunction of the v-ATPase complex to neurodegenerative diseases across the age spectrum.

Under normal conditions, the function of catalytically active proteases is regulated, in part, by their endogenous inhibitors, and any change in the synthesis and/or function of a protease or its endogenous inhibitors may result in inappropriate protease activity. Altered proteolysis as a result of an imbalance between active proteases and their endogenous inhibitors can occur during normal aging, and such changes have also been associated with multiple neuronal diseases, including Amyotrophic Lateral Sclerosis (ALS), rare heritable neurodegenerative disorders, ischemia, some forms of epilepsy, and Alzheimer's disease (AD). One of the most extensively studied endogenous inhibitor is the cysteine-protease inhibitor cystatin C (CysC). Changes in the expression and secretion of CysC in the brain have been described in various neurological disorders and in animal models of neurodegeneration, underscoring a role for CysC in these conditions. In the brain, multiple in vitro and in vivo findings have demonstrated that CysC plays protective roles via pathways that depend upon the inhibition of endosomal-lysosomal pathway cysteine proteases, such as cathepsin B (Cat B), via the induction of cellular autophagy, via the induction of cell proliferation, or via the inhibition of amyloid-beta (Abeta) aggregation. We review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced by CysC under various conditions. Beyond highlighting the essential role that balanced proteolytic activity plays in supporting normal brain aging, these findings suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.

Glucocorticoid resistance is a risk factor for Alzheimer's disease (AD). Molecular and cellular mechanisms of glucocorticoid resistance in the brain have remained unknown and are potential therapeutic targets. Phosphorylation of glucocorticoid receptors (GR) by brain-derived neurotrophic factor (BDNF) signaling integrates both pathways for remodeling synaptic structure and plasticity. The goal of this study is to test the role of the BDNF-dependent pathway on glucocorticoid signaling in a mouse model of glucocorticoid resistance. We report that deletion of GR phosphorylation at BDNF-responding sites and downstream signaling via the MAPK-phosphatase DUSP1 triggers tau phosphorylation and dendritic spine atrophy in mouse cortex. In human cortex, DUSP1 protein expression correlates with tau phosphorylation, synaptic defects and cognitive decline in subjects diagnosed with AD. These findings provide evidence for a causal role of BDNF-dependent GR signaling in tau neuropathology and indicate that DUSP1 is a potential target for therapeutic interventions.

Although the two pathological hallmarks of Alzheimer's disease (AD), senile plaques composed of amyloid-beta (Abeta) peptides and neurofibrillary tangles (NFTs) consisting of hyperphosphorylated tau, have been studied extensively in postmortem AD and relevant animal and cellular models, the pathogenesis of AD remains unknown, particularly in the early stages of the disease where therapies presumably would be most effective. We and others have demonstrated that Abeta plaques and NFTs are present in varying degrees before the onset and throughout the progression of dementia. In this regard, aged people with no cognitive impairment (NCI), mild cognitive impairment (MCI, a presumed prodromal AD transitional state), and AD all present at autopsy with varying levels of pathological hallmarks. Cognitive decline, a requisite for the clinical diagnosis of dementia associated with AD, generally correlates better with NFTs than Abeta plaques. However, correlations are even higher between cognitive decline and synaptic loss. In this review, we illustrate relevant clinical pathological research in preclinical AD and throughout the progression of dementia in several areas including Abeta and tau pathobiology, single population expression profiling of vulnerable hippocampal and basal forebrain neurons, neuron plasticity, neuroimaging, cerebrospinal fluid (CSF) biomarker studies and their correlation with antemortem cognitive endpoints. In each of these areas, we provide evidence for the importance of studying the pathological hallmarks of AD not in isolation, but rather in conjunction with other molecular, cellular, and imaging markers to provide a more systematic and comprehensive assessment of the multiple changes that occur during the transition from NCI to MCI to frank AD.