Sonia Franciosi

Minocycline inhibits neuronal death and glial activation induced by β-amyloid peptide in rat hippocampus

Minocycline, a second‐generation tetracycline compound, has been examined as a neuroprotectant in β‐amyloid (Aβ)‐injected rat hippocampus. At 7 days post‐injection, Aβ1‐42 caused a significant loss of granule cell layer neurons (28% reduction) compared to control uninjected hippocampus. Hippocampal injection of Aβ peptide also led to marked gliosis with numbers of microglia (increased by 26‐fold) and immunoreactivity of astrocytes (increased by 11‐fold) relative to control, as determined from immunohistochemical analysis. Intraperitoneal administration of minocycline significantly reduced neuronal loss induced by Aβ1‐42 (by 80%) and also diminished numbers of microglia (by 69%) and astrocytes (by 36%) relative to peptide alone. Peptide injection increased expression of cyclooxygenase‐2 (COX‐2) in most (about 70%) of granule cells, a subset (about 20%) of microglia, but not in astrocytes; in the presence of minocycline, COX‐2 immunostaining was abolished in microglia. The results from this study suggest that minocycline may have efficacy in the treatment of AD.

Specific Loss of Brain ABCA1 Increases Brain Cholesterol Uptake and Influences Neuronal Structure and Function

The expression of the cholesterol transporter ATP-binding cassette transporter A1 (ABCA1) in the brain and its role in the lipidation of apolipoproteins indicate that ABCA1 may play a critical role in brain cholesterol metabolism. To investigate the role of ABCA1 in brain cholesterol homeostasis and trafficking, we characterized mice that specifically lacked ABCA1 in the CNS, generated using the Cre/loxP recombination system. These mice showed reduced plasma high-density lipoprotein (HDL) cholesterol levels associated with decreased brain cholesterol content and enhanced brain uptake of esterified cholesterol from plasma HDL. Increased levels of HDL receptor SR-BI in brain capillaries and apolipoprotein A-I in brain and CSF of mutant mice were evident. Cholesterol homeostasis changes were mirrored by disturbances in motor activity and sensorimotor function. Changes in synaptic ultrastructure including reduced synapse and synaptic vesicle numbers were observed. These data show that ABCA1 is a key regulator of brain cholesterol metabolism and that disturbances in cholesterol transport in the CNS are associated with structural and functional deficits in neurons. Moreover, our findings also demonstrate that specific changes in brain cholesterol metabolism can lead to alterations in cholesterol uptake from plasma to brain.

Marked differences in neurochemistry and aggregates despite similar behavioural and neuropathological features of Huntington disease in the full-length BACHD and YAC128 mice

The development of animal models of Huntington disease (HD) has enabled studies that help define the molecular aberrations underlying the disease. The BACHD and YAC128 transgenic mouse models of HD harbor a full-length mutant huntingtin (mHTT) and recapitulate many of the behavioural and neuropathological features of the human condition. Here, we demonstrate that while BACHD and YAC128 animals exhibit similar deficits in motor learning and coordination, depressive-like symptoms, striatal volume loss and forebrain weight loss, they show obvious differences in key features characteristic of HD. While YAC128 mice exhibit significant and widespread accumulation of mHTT striatal aggregates, these mHTT aggregates are absent in BACHD mice. Furthermore, the levels of several striatally enriched mRNA for genes, such as DARPP-32, enkephalin, dopamine receptors D1 and D2 and cannabinoid receptor 1, are significantly decreased in YAC128 but not BACHD mice. These findings may reflect sequence differences in the human mHTT transgenes harboured by the BACHD and YAC128 mice, including both single nucleotide polymorphisms as well as differences in the nature of CAA interruptions of the CAG tract. Our findings highlight a similar profile of HD-like behavioural and neuropathological deficits and illuminate differences that inform the use of distinct endpoints in trials of therapeutic agents in the YAC128 and BACHD mice.

Altered palmitoylation and neuropathological deficits in mice lacking HIP14

Huntingtin interacting protein 14 (HIP14, ZDHHC17) is a huntingtin (HTT) interacting protein with palmitoyl transferase activity. In order to interrogate the function of Hip14, we generated mice with disruption in their Hip14 gene. Hip14-/- mice displayed behavioral, biochemical and neuropathological defects that are reminiscent of Huntington disease (HD). Palmitoylation of other HIP14 substrates, but not Htt, was reduced in the Hip14-/- mice. Hip14 is dysfunctional in the presence of mutant htt in the YAC128 mouse model of HD, suggesting that altered palmitoylation mediated by HIP14 may contribute to HD.

IL-8 enhancement of amyloid-beta (Aβ1-42)-induced expression and production of pro-inflammatory cytokines and COX-2 in cultured human microglia

The effects of the chemokine IL-8 on amyloid beta peptide (Abeta(1-42))-induced responses in cultured human microglia were investigated using RT-PCR, ELISA and immunocytochemistry. Abeta(1-42) (5 microM) applied for 8 h induced the expression and increased the production of the pro-inflammatory cytokines IL-6, IL-1beta, TNF-alpha, the inducible enzyme COX-2 and chemokine IL-8. Microglial treatment with IL-8 added (at 100 ng/mL) with Abeta(1-42) led to enhancement in both expression and production of all of these pro-inflammatory factors compared with peptide alone. Stimulation with IL-8 itself was effective in increasing microglial expression of pro-inflammatory cytokines, IL-8 and COX-2, however, had no effect on protein levels of all these factors. The expression of the anti-inflammatory cytokines IL-10 and TGFbeta(1) remained unchanged from basal levels with stimulation using either Abeta(1-42), IL-8 or the peptide together with IL-8. The actions of IL-8 to potentiate Abeta(1-42)-induced inflammatory mediators may have particular relevance to Alzheimer disease brain which exhibits elevated levels of the chemokine.

Age-dependent neurovascular abnormalities and altered microglial morphology in the YAC128 mouse model of Huntington disease.

Central nervous system (CNS) inflammatory processes including microglial activation have been implicated in the pathogenesis of neurodegenerative diseases such as Huntington Disease (HD). We report age-dependent changes in striatal microglial morphology and vasculature in the YAC128 mouse model of HD. Decreases in microglial ramification along with a decrease in vessel diameter and increased vessel density and length suggest the presence of microgliosis and proangiogenic activity in YAC128 mice. Our hypothesis for this study was that the changes in microglial morphology and perturbations in vasculature may be involved in the pathogenesis of HD and that peripheral challenge with the bacterial endotoxin, lipopolysaccharide (LPS), will exacerbate these microglial and vascular changes as well as the HD phenotype in YAC128 mice at 12 months. Chronic peripheral LPS (1mg/kg) potentiated microglial activation indicated by an increase in microglial cell body size and retraction of processes. This potentiation in microglial activation with chronic peripheral LPS challenge was paralleled with vascular remodeling including dilatation, increased vessel wall thickness, increased BBB permeability and fibrinogen deposition in YAC128 striatum. Although peripheral LPS caused an increase in microglial activation and degenerative changes in cerebrovasculature, the phenotypic hallmarks of HD in YAC128 mice such as motor coordination deficits and decreased striatal volume were not exacerbated by chronic peripheral LPS exposure. This study identifies age-dependent increases in microglial activation and angiogenesis in YAC128 at 12 months. Peripheral inflammation induced by chronic LPS causes similar changes but does not influence the HD phenotype in YAC128 mice.

Broad-Spectrum Effects of 4-Aminopyridine to Modulate Amyloid β1–42-Induced Cell Signaling and Functional Responses in Human Microglia

We investigated the modulating actions of the nonselective K+ channel blocker 4-aminopyridine (4-AP) on amyloid β (Aβ1–42)-induced human microglial signaling pathways and functional processes. Whole-cell patch-clamp studies showed acute application of Aβ1–42 (5 μm) to human microglia led to rapid expression of a 4-AP-sensitive, non-inactivating outwardly rectifying K+ current (IK). Intracellular application of the nonhydrolyzable analog of GTP, GTPγS, induced an outward K+ current with similar properties to the Aβ1–42-induced IK including sensitivity to 4-AP (IC50 = 5 mm). Reverse transcriptase-PCR showed a rapid expression of a delayed rectifier Kv3.1 channel in Aβ1–42-treated microglia. Aβ1–42 peptide also caused a slow, progressive increase in levels of [Ca2+]i (intracellular calcium) that was partially blocked by 4-AP. Chronic exposure of human microglia to Aβ1–42 led to enhanced p38 mitogen-activated protein kinase and nuclear factor κB expression with factors inhibited by 4-AP. Aβ1–42 also induced the expression and production of the pro-inflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-α, the chemokine IL-8, and the enzyme cyclooxygenase-2; 4-AP was effective in reducing all of these pro-inflammatory mediators. Additionally, toxicity of supernatant from Aβ1–42-treated microglia on cultured rat hippocampal neurons was reduced if 4-AP was included with peptide. In vivo, injection of Aβ1–42 into rat hippocampus induced neuronal damage and increased microglial activation. Daily administration of 1 mg/kg 4-AP was found to suppress microglial activation and exhibited neuroprotection. The overall results suggest that 4-AP modulation of an Aβ1–42-induced IK (candidate channel Kv3.1) and intracellular signaling pathways in human microglia could serve as a therapeutic strategy for neuroprotection in Alzheimers disease pathology.

Rescue from excitotoxicity and axonal degeneration accompanied by age-dependent behavioral and neuroanatomical alterations in caspase-6-deficient mice

Apoptosis, or programmed cell death, is a cellular pathway involved in normal cell turnover, developmental tissue remodeling, embryonic development, cellular homeostasis maintenance and chemical-induced cell death. Caspases are a family of intracellular proteases that play a key role in apoptosis. Aberrant activation of caspases has been implicated in human diseases. In particular, numerous findings implicate Caspase-6 (Casp6) in neurodegenerative diseases, including Alzheimer disease (AD) and Huntington disease (HD), highlighting the need for a deeper understanding of Casp6 biology and its role in brain development. The use of targeted caspase-deficient mice has been instrumental for studying the involvement of caspases in apoptosis. The goal of this study was to perform an in-depth neuroanatomical and behavioral characterization of constitutive Casp6-deficient (Casp6-/-) mice in order to understand the physiological function of Casp6 in brain development, structure and function. We demonstrate that Casp6-/- neurons are protected against excitotoxicity, nerve growth factor deprivation and myelin-induced axonal degeneration. Furthermore, Casp6-deficient mice show an age-dependent increase in cortical and striatal volume. In addition, these mice show a hypoactive phenotype and display learning deficits. The age-dependent behavioral and region-specific neuroanatomical changes observed in the Casp6-/- mice suggest that Casp6 deficiency has a more pronounced effect in brain regions that are involved in neurodegenerative diseases, such as the striatum in HD and the cortex in AD.

A fully humanized transgenic mouse model of Huntington disease

Silencing the mutant huntingtin gene (muHTT) is a direct and simple therapeutic strategy for the treatment of Huntington disease (HD) in principle. However, targeting the HD mutation presents challenges because it is an expansion of a common genetic element (a CAG tract) that is found throughout the genome. Moreover, the HTT protein is important for neuronal health throughout life, and silencing strategies that also reduce the wild-type HTT allele may not be well tolerated during the long-term treatment of HD. Several HTT silencing strategies are in development that target genetic sites in HTT that are outside of the CAG expansion, including HD mutation-linked single-nucleotide polymorphisms and the HTT promoter. Preclinical testing of these genetic therapies has required the development of a new mouse model of HD that carries these human-specific genetic targets. To generate a fully humanized mouse model of HD, we have cross-bred BACHD and YAC18 on the Hdh(-/-) background. The resulting line, Hu97/18, is the first murine model of HD that fully genetically recapitulates human HD having two human HTT genes, no mouse Hdh genes and heterozygosity of the HD mutation. We find that Hu97/18 mice display many of the behavioral changes associated with HD including motor, psychiatric and cognitive deficits, as well as canonical neuropathological abnormalities. This mouse line will be useful for gaining additional insights into the disease mechanisms of HD as well as for testing genetic therapies targeting human HTT.

Natural history of disease in the YAC128 mouse reveals a discrete signature of pathology in Huntington disease

Models of Huntington disease (HD) recapitulate some neuropathological features of the disease. However, a global natural history of neuroanatomy in a mouse expressing full-length huntingtin has not been conducted. We investigated neuropathological changes in the YAC128 murine model of HD using magnetic resonance imaging (MRI). Structures affected in human HD are reduced in the YAC128 mice both in absolute terms and in terms of percentage of brain volume. Structures resistant to degeneration in HD, including the cerebellum and hippocampus, are spared in the YAC128 mice. Segmentation of major white matter structures confirms specific, progressive, loss of white matter in HD. In parallel with their specific volume loss, the YAC128 mice also show progressive increases in total ventricular volume, similarly to human HD patients. Cortical atrophy in the YAC128 mice is layer specific, which is the observed pattern of cortical loss in human HD patients. Finally, we have used a classification tree analysis to maximize separation of genotypes using all 62 structure volumes in an objective manner. This analysis demonstrates that sub-cortical gray matter structures (striatum, globus pallidus, thalamus) and cerebral white matter structures (corpus callosum, anterior commisure, fimbria) are the most discriminatory. The high resolution of the current study enables robust measurement of subtle early pathological changes. The use of mice furthermore enables us to address questions difficult to address in humans, including the sequential changes of HD from baseline and the relation between MRI and stereological measures.