Irene López-González

Glial and neuronal tau pathology in tauopathies: characterization of disease-specific phenotypes and tau pathology progression.

Tauopathies are degenerative diseases characterized by the accumulation of phosphorylated tau in neurons and glial cells. With some exceptions, tau deposits in neurons are mainly manifested as pretangles and tangles unrelated to the tauopathy. It is thought that abnormal tau deposition in neurons occurs following specific steps, but little is known about the progression of tau pathology in glial cells in tauopathies. We compared tau pathology in different astrocyte phenotypes and oligodendroglial inclusions with that in neurons in a large series of tauopathies, including progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, Pick disease, frontotemporal lobar degenerations (FTLD) associated with mutations in the tau gene, globular glial tauopathy (GGT), and tauopathy in the elderly. Our findings indicate that disease-specific astroglial phenotypes depend on i) the primary amino acid sequence of tau (mutated tau, 3Rtau, and 4Rtau); ii) phospho-specific sites of tau phosphorylation, tau conformation, tau truncation, and ubiquitination in that order (which parallel tau modifications related to pretangle and tangle stages in neurons); and iii) modifications of the astroglial cytoskeleton. In contrast to astrocytes, coiled bodies in oligodendrocytes have similar characteristics whatever the tauopathy, except glial globular inclusions in GGT, and coiled bodies and globular oligodendroglial inclusions in FTLD-tau/K317M. These observations indicate that tau pathology in glial cells largely parallels, but is not identical to, that in neurons in many tauopathies.

Amyloid Generation and Dysfunctional Immunoproteasome Activation with Disease Progression in Animal Model of Familial Alzheimer's Disease

Double‐transgenic amyloid precursor protein/presenilin 1 (APP/PS1) mice express a chimeric mouse/human APP bearing the Swedish mutation (Mo/HuAPP695swe) and a mutant human PS1‐dE9 both causative of familial Alzheimers disease (FAD). Transgenic mice show impaired memory and learning performance from the age of 6 months onwards. Double‐transgenic APP/PS1 mice express altered APP and PS1 mRNAs and proteins, reduced β‐secretase 1 (BACE1) mRNA and normal BACE1 protein, all of which suggest a particular mechanism of amyloidogenesis when compared with sporadic AD. The first β‐amyloid plaques in APP/PS1 mice appear at 3 months, and they increase in number and distribution with disease progression in parallel with increased levels of brain soluble β‐amyloid 1–42 and 1–40, but also with reduced 1–42/1–40 ratio with age. Amyloid deposition in plaques is accompanied by altered mitochondria and increased oxidative damage, post‐translational modifications and accumulation of altered proteins at the dystrophic neurites surrounding plaques. Degradation pathways are also modified with disease progression including activation of the immunoproteasome together with variable alterations of the different protease activities of the ubiquitin‐proteasome system. Present observations show modifications in the production of β‐amyloid and activation and malfunction of the subcellular degradation pathways that have general implications in the pathogenesis of AD and more particularly in specificities of FAD amyloidogenesis.

Neuroinflammatory signals in alzheimer disease and APP/PS1 transgenic mice: Correlations with plaques, tangles, and oligomeric species

Abstract To understand neuroinflammation-related gene regulation during normal aging and in sporadic Alzheimer disease (sAD), we performed functional genomics analysis and analyzed messenger RNA (mRNA) expression by quantitative reverse transcription–polymerase chain reaction of 22 genes involved in neuroinflammation-like responses in the cerebral cortex of wild-type and APP/PS1 transgenic mice. For direct comparisons, mRNA expression of 18 of the same genes was then analyzed in the entorhinal cortex, orbitofrontal cortex, and frontal cortex area 8 of middle-aged human subjects lacking Alzheimer disease–related pathology and in older subjects with sAD pathology covering Stages I–II/0(A), III–IV/A–B, and V–VI/C of Braak and Braak classification. Modifications of cytokine and immune mediator mRNA expression were found with normal aging in wild-type mice and in middle-aged individuals and patients with early stages of sAD-related pathology; these were accompanied by increased protein expression of certain mediators in ramified microglia. In APP/PS1 mice, inflammatory changes coincided with &bgr;-amyloid (A&bgr;) deposition; increased levels of soluble oligomers paralleled the modified mRNA expression of cytokines and mediators in wild-type mice. In patients with sAD, regulation was stage- and region-dependent and not merely acceleration and exacerbation of mRNA regulation with aging. Gene regulation at first stages of AD was not related to hyperphosphorylated tau deposition in neurofibrillary tangles, A&bgr; plaque burden, concentration of A&bgr;1–40 (A&bgr;40) and A&bgr;1–42 (A&bgr;42), or fibrillar A&bgr; linked to membranes but rather to increased levels of soluble oligomers. Thus, species differences and region- and stage-dependent inflammatory responses in sAD, particularly at the initial stages, indicate the need to identify new anti-inflammatory compounds with specific molecular therapeutic targets.

Subtype and Regional-Specific Neuroinflammation in Sporadic Creutzfeldt–Jakob Disease

The present study identifies deregulated cytokines and mediators of the immune response in the frontal cortex and cerebellum of sporadic Creutzfeldt–Jakob disease (sCJD) MM1 and VV2 subtypes compared to age-matched controls. Deregulated genes include pro- and anti-inflammatory cytokines, toll-like receptors, colony stimulating factors, cathepsins, members of the complement system, and members of the integrin and CTL/CTLD family with particular regional and sCJD subtype patterns. Analysis of cytokines and mediators at protein level shows expression of selected molecules and receptors in neurons, in astrocytes, and/or in microglia, thus suggesting interactions between neurons and glial cells, mainly microglia, in the neuroinflammatory response in sCJD. Similar inflammatory responses have been shown in the tg340 sCJD MM1 mice, revealing a progressive deregulation of inflammatory mediators with disease progression. Yet, inflammatory molecules involved are subjected to species differences in humans and mice. Moreover, inflammatory-related cell signaling pathways NFκB/IKK and JAK/STAT are activated in sCJD and sCJD MM1 mice. Together, the present observations show a self-sustained complex inflammatory and inflammatory-related responses occurring already at early clinical stages in animal model and dramatically progressing at advanced stages of sCJD. Considering this scenario, measures tailored to modulate (activate or inhibit) specific molecules could be therapeutic options in CJD.

PrP mRNA and protein expression in brain and PrPc in CSF in Creutzfeldt-Jakob disease MM1 and VV2

Creutzfeldt-Jakob disease (CJD) is a heterogenic neurodegenerative disorder associated with abnormal post-translational processing of cellular prion protein (PrPc). CJD displays distinctive clinical and pathological features which correlate with the genotype at the codon 129 (methionine or valine: M or V respectively) in the prion protein gene and with size of the protease-resistant core of the abnormal prion protein PrPsc (type 1: 20/21 kDa and type 2: 19 kDa). MM1 and VV2 are the most common sporadic CJD (sCJD) subtypes. PrP mRNA expression levels in the frontal cortex and cerebellum are reduced in sCJD in a form subtype-dependent. Total PrP protein levels and PrPsc levels in the frontal cortex and cerebellum accumulate differentially in sCJD MM1 and sCJD VV2 with no relation between PrPsc deposition and spongiform degeneration and neuron loss, but with microgliosis, and IL6 and TNF-α response. In the CSF, reduced PrPc, the only form present in this compartment, occurs in sCJD MM1 and VV2. PrP mRNA expression is also reduced in the frontal cortex in advanced stages of Alzheimer disease, Lewy body disease, progressive supranuclear palsy, and frontotemporal lobe degeneration, but PrPc levels in brain varies from one disease to another. Reduced PrPc levels in CSF correlate with PrP mRNA expression in brain, which in turn reflects severity of degeneration in sCJD.

Novel Levetiracetam Derivatives That Are Effective against the Alzheimer-like Phenotype in Mice: Synthesis, in Vitro, ex Vivo, and in Vivo Efficacy Studies.

We have synthesized a series of heptamethylene-linked levetiracetam-huprine and levetiracetam-(6-chloro)tacrine hybrids to hit amyloid, tau, and cholinergic pathologies as well as β-amyloid (Aβ)-induced epileptiform activity, some of the mechanisms that eventually lead to cognitive deficits in Alzheimers disease patients. These hybrids are potent inhibitors of human acetylcholinesterase and butyrylcholinesterase in vitro and moderately potent Aβ42 and tau antiaggregating agents in a simple E. coli model of amyloid aggregation. Ex vivo determination of the brain acetylcholinesterase inhibitory activity of these compounds after intraperitoneal injection to C57BL6J mice has demonstrated their ability to enter the brain. The levetiracetam-huprine hybrid 10 significantly reduced the incidence of epileptic seizures, cortical amyloid burden, and neuroinflammation in APP/PS1 mice after a 4-week treatment with a 5 mg/kg dose. Moreover, the hybrid 10 rescued transgenic mice from cognitive deficits, thereby emerging as an interesting disease-modifying anti-Alzheimer drug candidate.

Neuroinflammatory Gene Regulation, Mitochondrial Function, Oxidative Stress, and Brain Lipid Modifications With Disease Progression in Tau P301S Transgenic Mice as a Model of Frontotemporal Lobar Degeneration-Tau.

Abstract Tau P301S transgenic mice (PS19 line) are used as a model of frontotemporal lobar degeneration (FTLD)-tau. Behavioral alterations in these mice begin at approximately 4 months of age. We analyzed molecular changes related to disease progression in these mice. Hyperphosphorylated 4Rtau increased in neurons from 1 month of age in entorhinal and piriform cortices to the neocortex and other regions. A small percentage of neurons developed an abnormal tau conformation, tau truncation, and ubiquitination only at 9/10 months of age. Astrocytosis, microgliosis, and increased inflammatory cytokine and immune mediator expression also occurred at this late stage; hippocampi were the most markedly affected. Altered mitochondrial function, increased reactive oxygen species production, and limited protein oxidative damage were observed in advanced disease. Tau oligomers were only present in P301S mice, they were found in somatosensory cortex and hippocampi at the age of 3 months, and they increased across time in the somatosensory cortex and were higher and sustained in hippocampi. Age-related modifications in lipid composition occurred in both P301S and wild-type mice with regional and phenotypic differences; however, changes of total lipids did not seem to have pathogenic implications. Apoptosis only occurred in restricted regions in late disease. The complex tau pathology, mitochondrial alterations, oxidative stress damage, glial reactions, neuroinflammation, and cell death in P301S mice likely parallel those in FTLD-tau. Thus, therapies should focus first on abnormal tau rather than secondary events that appear late in the course of FTLD-tau.

Characterization of Thorn-Shaped Astrocytes in White Matter of Temporal Lobe in Alzheimer's Disease Brains

Thorn‐shaped astrocytes (TsA) are mainly localized in the periventricular white matter of the temporal lobe in a subgroup of aged individuals usually in the context of Alzheimers disease (AD). Immunohistochemistry of TsA shows 4Rtau deposition, tau phosphorylation at different sites recognized with phosphospecific anti‐tau antibodies Thr181, Ser202, Ser214, Thr231, Ser396, Ser422, and clones AT8 and PHF‐1, and conformational changes revealed with Alz50 and MC‐1 antibodies; TsA are also immunostained with antibodies to active tau kinases MAPK/ERK‐P, SAPK/JNK‐P, p38‐P and GSK‐3β. These findings are common to neurofibrillary tangles in AD. However, TsA are not stained with 3Rtau antibodies, and they are seldom stained or not at all with phosphospecific tauSer262 and with Tau‐C3 antibody, which recognizes the latter tau truncation at aspartic acid 421. Previous studies have shown that tau phosphorylation at Ser262 reduces tau binding to microtubules and increases caspase‐3 activity, whereas tau truncation at aspartic acid 421 is associated with tau ubiquitination, and toxic effects of tau. In this line, ubiquitin is not accumulated in TsA, and in situ end‐labeling of nuclear DNA fragmentation shows absence of degeneration in TsA. These observations support the concept that tau lesions in neurons differ from those seen in TsA in AD.

Cerebellar Amyloid-β Plaques: Disturbed Cortical Circuitry in AβPP/PS1 Transgenic Mice as a Model of Familial Alzheimer's Disease

Cerebellar amyloid-β (Aβ) deposition in the form of neuritic plaques and Purkinje cell loss are common in certain pedigrees of familial Alzheimers disease (FAD) mainly linked to PS1 mutations. AβPP/PS1 transgenic mice, here used as a model of FAD, show a few Aβ plaques in the molecular layer of the cerebellum at 6 months, and which increase in number with age. Motor impairment is apparent in transgenic mice aged 12 months. Combined methods have shown degenerated parallel fibers as the main component of dystrophic neurites of Aβ plaques, loss of synaptic contacts between parallel fibers and dendritic spines of Purkinje cells, and degeneration of granule cells starting at 12 months and increasing in mice 18/20 months old. In addition, abnormal mitochondria and focal loss of Purkinje and basket cells, together with occasional axonal torpedoes and increased collaterals of Purkinje cells in mice aged 18/20 months, is suggested to be a concomitant defect presumably related to soluble extracellular or intracellular Aβ. These observations demonstrate serious deterioration of the neuronal circuitry in the cerebellum of AβPP/PS1 transgenic mice, and they provide support for the interpretation of similar alterations occurring in certain pedigrees with FAD.

DNA methylation profiles of selected pro-inflammatory cytokines in Alzheimer disease

By means of functional genomics analysis, we recently described the mRNA expression profiles of various genes involved in the neuroinflammatory response in the brains of subjects with late-onset Alzheimer Disease (LOAD). Some of these genes, namely interleukin (IL)-1&bgr; and IL-6, showed distinct expression profiles with peak expression during the first stages of the disease and control-like levels at later stages. IL-1&bgr; and IL-6 genes are modulated by DNA methylation in different chronic and degenerative diseases; it is also well known that LOAD may have an epigenetic basis. Indeed, we and others have previously reported gene-specific DNA methylation alterations in LOAD and in related animal models. Based on these data, we studied the DNA methylation profiles, at single cytosine resolution, of IL-1&bgr; and IL-6 5’-flanking region by bisulphite modification in the cortex of healthy controls and LOAD patients at 2 different disease stages: Braak I-II/A and Braak V-VI/C. Our analysis provides evidence that neuroinflammation in LOAD is associated with (and possibly mediated by) epigenetic modifications.