Activation of matrix metalloproteinases following anti-Aβ immunotherapy; implications for microhemorrhage occurrence

Amyloid-β (Aβ) immunotherapy induced microhemorrhages are associated with activated perivascular macrophages and peripheral monocyte recruitment in Alzheimer's disease mice

BACKGROUND

Amyloid-related imaging abnormalities (ARIA) have been identified as the most common and serious adverse events resulting from pathological changes in the cerebral vasculature during several recent anti-amyloid-β (Aβ) immunotherapy trials. However, the precise cellular and molecular mechanisms underlying how amyloid immunotherapy enhances cerebral amyloid angiopathy (CAA)-mediated alterations in vascular permeability and microhemorrhages are not currently understood. Interestingly, brain perivascular macrophages have been implicated in regulating CAA deposition and cerebrovascular function however, further investigations are required to understand how perivascular macrophages play a role in enhancing CAA-related vascular permeability and microhemorrhages associated with amyloid immunotherapy.

METHODS

In this study, we examined immune responses induced by amyloid-targeting antibodies and CAA-induced microhemorrhages using histology and gene expression analyses in Alzheimer's disease (AD) mouse models and primary culture systems.

RESULTS

In the present study, we demonstrate that anti-Aβ (3D6) immunotherapy leads to the formation of an antibody immune complex with vascular amyloid deposits and induces the activation of CD169+ perivascular macrophages. We show that macrophages activated by antibody mediated Fc receptor signaling have increased expression of inflammatory signaling and extracellular matrix remodeling genes such as Timp1 and MMP9 in vitro and confirm these key findings in vivo. Finally, we demonstrate enhanced vascular permeability of plasma proteins and recruitment of inflammatory monocytes around vascular amyloid deposits, which are associated with hemosiderin deposits from cerebral microhemorrhages, suggesting the multidimensional roles of activated perivascular macrophages in response to Aβ immunotherapy.

CONCLUSIONS

In summary, our study establishes a connection between Aβ antibodies engaged at CAA deposits, the activation of perivascular macrophages, and the upregulation of genes involved in vascular permeability. However, the implications of this phenomenon on the susceptibility to microhemorrhages remain to be fully elucidated. Further investigations are warranted to determine the precise role of CD169 + perivascular macrophages in enhancing CAA-mediated vascular permeability, extravasation of plasma proteins, and infiltration of immune cells associated with microhemorrhages.

Metal Complexes as Promising Matrix Metalloproteinases Regulators

Nowadays, cancers and dementia, such as Alzheimer's disease, are the most fatal causes of death. Many studies tried to understand the pathogenesis of those diseases clearly and develop a promising way to treat the diseases. Matrix metalloproteinases (MMPs) have been reported to be involved in the pathology of cancers and AD through tumor cell movement and amyloid degradation. Therefore, control of the levels and actions of MMPs, especially MMP-2 and MMP-9, is necessary to care for and/or cure cancer and AD. Various molecules have been examined for their potential application as regulators of MMPs expression and activity. Among the molecules, multiple metal complexes have shown advantages, including simple synthesis, less toxicity and specificity toward MMPs in cancer cells or in the brain. In this review, we summarize the recent studies and knowledge of metal complexes (e.g., Pt-, Ru-, Au-, Fe-, Cu-, Ni-, Zn-, and Sn-complexes) targeting MMPs and their potentials for treating and/or caring the most fatal human diseases, cancers and AD.

Disturbed Matrix Metalloproteinases Activity in Age-Related Macular Degeneration

Matrix metalloproteinases (MMPs) are a tightly regulated family of proteolytic enzymes that break down extracellular matrix (ECM) and basement membrane components. Because it is associated with development, morphogenesis, tissue remodeling, and repair, ECM remodeling is an important mechanism. MMPs are thought to act as a double-edged sword, as they contribute to maintaining photoreceptors/retinal pigment epithelium (RPE)/Bruch's membrane (BM)/choroid complex homeostasis and also contribute to the onset and progression of age-related macular degeneration (AMD). Polymorphisms and/or altered expression in MMPs and their tissue inhibitors (TIMPs) are associated with age-related macular degeneration (AMD). Here, we review the evidence for MMPs' role in the onset and progression of AMD via addressing their regulation and TIMPs' significant regulatory functions.

The Chemical Biology of NO that Regulates Oncogenic Signaling and Metabolism: NOS2 and Its Role in Inflammatory Disease

Nitric oxide (NO) and the enzyme that synthesizes it, nitric oxide synthase 2 (NOS2), have emerged as key players in inflammation and cancer. Expression of NOS2 in tumors has been correlated both with positive outcomes and with poor prognoses. The chemistry of NO is the major determinate to the biological outcome and the concentration of NO, which can range over five orders of magnitude, is critical in determining which pathways are activated. It is the activation of specific oncogenic and immunological mechanisms that shape the outcome. The kinetics of specific reactions determine the mechanisms of action. In this review, the relevant reactions of NO and related species are discussed with respect to these oncogenic and immunological signals.

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.

Alzheimer’s Disease: An Update and Insights Into Pathophysiology

Alzheimer’s disease (AD) is an irreversible brain disorder associated with slow, progressive loss of brain functions mostly in older people. The disease processes start years before the symptoms are manifested at which point most therapies may not be as effective. In the hippocampus, the key proteins involved in the JAK2/STAT3 signaling pathway, such as p-JAK2-Tyr1007 and p-STAT3-Tyr705 were found to be elevated in various models of AD. In addition to neurons, glial cells such as astrocytes also play a crucial role in the progression of AD. Without having a significant effect on tau and amyloid pathologies, the JAK2/STAT3 pathway in reactive astrocytes exhibits a behavioral impact in the experimental models of AD. Cholinergic atrophy in AD has been traced to a trophic failure in the NGF metabolic pathway, which is essential for the survival and maintenance of basal forebrain cholinergic neurons (BFCN). In AD, there is an alteration in the conversion of the proNGF to mature NGF (mNGF), in addition to an increase in degradation of the biologically active mNGF. Thus, the application of exogenous mNGF in experimental studies was shown to improve the recovery of atrophic BFCN. Furthermore, it is now coming to light that the FGF7/FGFR2/PI3K/Akt signaling pathway mediated by microRNA-107 is also involved in AD pathogenesis. Vascular dysfunction has long been associated with cognitive decline and increased risk of AD. Vascular risk factors are associated with higher tau and cerebral beta-amyloid (Aβ) burden, while synergistically acting with Aβ to induce cognitive decline. The apolipoprotein E4 polymorphism is not just one of the vascular risk factors, but also the most prevalent genetic risk factor of AD. More recently, the research focus on AD shifted toward metabolisms of various neurotransmitters, major and minor nutrients, thus giving rise to metabolomics, the most important “omics” tool for the diagnosis and prognosis of neurodegenerative diseases based on an individual’s metabolome. This review will therefore proffer a better understanding of novel signaling pathways associated with neural and glial mechanisms involved in AD, elaborate potential links between vascular dysfunction and AD, and recent developments in “omics”-based biomarkers in AD.

Molecular Pathobiology of the Cerebrovasculature in Aging and in Alzheimers Disease Cases With Cerebral Amyloid Angiopathy

Cerebrovascular dysfunction and cerebral amyloid angiopathy (CAA) are hallmark features of Alzheimer's disease (AD). Molecular damage to cerebrovessels in AD may result in alterations in vascular clearance mechanisms leading to amyloid deposition around blood vessels and diminished neurovascular-coupling. The sequelae of molecular events leading to these early pathogenic changes remains elusive. To address this, we conducted a comprehensive in-depth molecular characterization of the proteomic changes in enriched cerebrovessel fractions isolated from the inferior frontal gyrus of autopsy AD cases with low (85.5 ± 2.9 yrs) vs. high (81 ± 4.4 yrs) CAA score, aged-matched control (87.4 ± 1.5 yrs) and young healthy control (47 ± 3.3 yrs) cases. We employed a 10-plex tandem isobaric mass tag approach in combination with our ultra-high pressure liquid chromatography MS/MS (Q-Exactive) method. Enriched cerebrovascular fractions showed very high expression levels of proteins specific to endothelial cells, mural cells (pericytes and smooth muscle cells), and astrocytes. We observed 150 significantly regulated proteins in young vs. aged control cerebrovessels. The top pathways significantly modulated with aging included chemokine, reelin, HIF1α and synaptogenesis signaling pathways. There were 213 proteins significantly regulated in aged-matched control vs. high CAA cerebrovessels. The top three pathways significantly altered from this comparison were oxidative phosphorylation, Sirtuin signaling pathway and TCA cycle II. Comparison between low vs. high CAA cerebrovessels identified 84 significantly regulated proteins. Top three pathways significantly altered between low vs. high CAA cerebrovessels included TCA Cycle II, Oxidative phosphorylation and mitochondrial dysfunction. Notably, high CAA cases included more advanced AD pathology thus cerebrovascular effects may be driven by the severity of amyloid and Tangle pathology. These descriptive proteomic changes provide novel insights to explain the age-related and AD-related cerebrovascular changes contributing to AD pathogenesis. Particularly, disturbances in energy bioenergetics and mitochondrial biology rank among the top AD pathways altered in cerebrovessels. Targeting these failed mechanisms in endothelia and mural cells may provide novel disease modifying targets for developing therapeutic strategies against cerebrovascular deterioration and promoting cerebral perfusion in AD. Our future work will focus on interrogating and validating these novel targets and pathways and their functional significance.

Matrix Metalloproteinases as New Targets in Alzheimer's Disease: Opportunities and Challenges

Although matrix metalloproteinases (MMPs) are implicated in the regulation of numerous physiological processes, evidence of their pathological roles have also been obtained in the last decades, making MMPs attractive therapeutic targets for several diseases. Recent discoveries of their involvement in central nervous system (CNS) disorders, and in particular in Alzheimer's disease (AD), have paved the way to consider MMP modulators as promising therapeutic strategies. Over the past few decades, diverse approaches have been undertaken in the design of therapeutic agents targeting MMPs for various purposes, leading, more recently, to encouraging developments. In this article, we will present recent examples of inhibitors ranging from small molecules and peptidomimetics to biologics. We will also discuss the scientific knowledge that has led to the development of emerging tools and techniques to overcome the challenges of selective MMP inhibition.

The Important Interface Between Apolipoprotein E and Neuroinflammation in Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent form of neurodegenerative disease, currently affecting over 5 million Americans with projections expected to rise as the population ages. The hallmark pathologies of AD are Aβ plaques composed of aggregated beta-amyloid (Aβ), and tau tangles composed of hyperphosphorylated, aggregated tau. These pathologies are typically accompanied by an increase in neuroinflammation as an attempt to ameliorate the pathology. This idea has pushed the field toward focusing on mechanisms and the influence neuroinflammation has on disease progression. The vast majority of AD cases are sporadic and therefore, researchers investigate genetic risk factors that could lead to AD. Apolipoprotein E (ApoE) is the largest genetic risk factor for developing AD. ApoE has 3 isoforms-ApoE2, ApoE3, and ApoE4. ApoE4 constitutes an increased risk of AD, with one copy increasing the risk about 4-fold and two copies increasing the risk about 15-fold compared to those with the ApoE3 allele. ApoE4 has been shown to play a role in Aβ deposition, tau tangle formation, neuroinflammation and many subsequent pathways. However, while we know that ApoE4 plays a role in these pathways and virtually all aspects of AD, the exact mechanism of how ApoE4 impacts AD progression is murky at best and therefore the role ApoE4 plays in these pathways needs to be elucidated. This review aims to discuss the current literature regarding the pathways and mechanisms of ApoE4 in AD progression with a focus on its role in neuroinflammation.

A therapeutic approach towards microRNA29 family in vascular diabetic complications: A boon or curse?

Diabetes Mellitus (DM) is one of the major metabolic disorders and its severity leads to death. Enhancement in hyperglycaemic conditions of DM gives rise to endothelial impairment in small and large blood vessels contributing towards microvascular and macrovascular complications respectively. The pathogenesis of diabetic complications is associated with interruption of various signal transduction pathways due to epigenetic modifications such as aberrant histone modifications, DNA methylation and expression of miRNAs along with the long non-coding RNAs (lncRNAs). Amongst these epigenetic alterations, modulated expressions of miRNAs confer to apoptosis and endothelial dysfunction of organs that gives rise to vascular complications. In this review, we principally focussed on physiological role of miR29 family in DM and have discussed crosstalk between miR29 family and numerous genes involved in signal transduction pathways of Diabetic vascular complications. Incidences of diabetic retinopathy exploiting the role of miR29 in regulation of EMT process, differential expression patterns of miR29 and promising therapeutic role of miR29 have been discussed. We have summarised the therapeutic role of miR29 in podocyte impairment and how miR29 regulates the expressions of profibrotic, inflammatory and ECM encoding genes in renal fibrosis under diabetic conditions. We have also highlighted impact of miR29 expression patterns in cardiac angiopathy, cardiomyocyte's apoptosis and cardiac fibrosis. Additionally, we have also presented the contradictory actions of miR29 family in amelioration as well as in enhancement of diabetic complications.

A Novel Small Molecule Modulator of Amyloid Pathology

Because traditional approaches to drug development for Alzheimer's disease are becoming increasingly expensive and in many cases disappointingly unsuccessful, alternative approaches are required to shift the paradigm. Following leads from investigations of dihydropyridine calcium channel blockers, we observed unique properties from a class of functionalized naphthyridines and sought to develop these as novel therapeutics that minimize amyloid pathology without the adverse effects associated with current therapeutics. Our data show methyl 2,4-dimethyl-5-oxo-5,6-dihydrobenzo[c][2,7]naphthyridine-1-carboxylate (BNC-1) significantly decreases amyloid burden in a well-established mouse model of amyloid pathology through a unique mechanism mediated by Elk-1, a transcriptional repressor of presenilin-1. Additionally, BNC-1 treatment leads to increased levels of synaptophysin and synapsin, markers of synaptic integrity, but does not adversely impact presenilin-2 or processing of Notch-1, thus avoiding negative off target effects associated with pan-gamma secretase inhibition. Overall, our data show BNC-1 significantly decreases amyloid burden and improves markers of synaptic integrity in a well-established mouse model of amyloid deposition by promoting phosphorylation and activation of Elk-1, a transcriptional repressor of presenilin-1 but not presenilin-2. These data suggest BNC-1 might be a novel, disease-modifying therapeutic that will alter the pathogenesis of Alzheimer's disease.

Reduced Efficacy of Anti-Aβ Immunotherapy in a Mouse Model of Amyloid Deposition and Vascular Cognitive Impairment Comorbidity

Vascular cognitive impairment and dementia (VCID) is the second most common form of dementia behind Alzheimer's disease (AD). It is estimated that 40% of AD patients also have some form of VCID. One promising therapeutic for AD is anti-Aβ immunotherapy, which uses antibodies against Aβ to clear it from the brain. While successful in clearing Aβ and improving cognition in mice, anti-Aβ immunotherapy failed to reach primary cognitive outcomes in several different clinical trials. We hypothesized that one potential reason the anti-Aβ immunotherapy clinical trials were unsuccessful was due to this high percentage of VCID comorbidity in the AD population. We used our unique model of VCID-amyloid comorbidity to test this hypothesis. We placed 9-month-old wild-type and APP/PS1 mice on either a control diet or a diet that induces hyperhomocysteinemia (HHcy). After being placed on the diet for 3 months, the mice then received intraperotineal injections of either IgG2a control or 3D6 for another 3 months. While we found that treatment of our comorbidity model with 3D6 resulted in decreased total Aβ levels, there was no cognitive benefit of the anti-Aβ immunotherapy in our AD/VCID mice. Further, microhemorrhages were increased by 3D6 in the APP/PS1/control but further increased in an additive fashion when 3D6 was administered to the APP/PS1/HHcy mice. This suggests that the use of anti-Aβ immunotherapy in patients with both AD and VCID would be ineffective on cognitive outcomes.

SIGNIFICANCE STATEMENT

Despite significant mouse model data demonstrating both pathological and cognitive efficacy of anti-Aβ immunotherapy for the treatment of Alzheimer's disease, clinical trial outcomes have been underwhelming, failing to meet any primary endpoints. We show here that vascular cognitive impairment and dementia (VCID) comorbidity eliminates cognitive efficacy of anti-Aβ immunotherapy, despite amyloid clearance. Further, cerebrovascular adverse events of the anti-Aβ immunotherapy are significantly exacerbated by the VCID comorbidity. These data suggest that VCID comorbidity with Alzheimer's disease may mute the response to anti-Aβ immunotherapy.

Cerebral microhemorrhages: mechanisms, consequences, and prevention

The increasing prevalence of multifocal cerebral microhemorrhages (CMHs, also known as "cerebral microbleeds") is a significant, newly recognized problem in the aging population of the Western world. CMHs are associated with rupture of small intracerebral vessels and are thought to progressively impair neuronal function, potentially contributing to cognitive decline, geriatric psychiatric syndromes, and gait disorders. Clinical studies show that aging and hypertension significantly increase prevalence of CMHs. CMHs are also now recognized by the National Institutes of Health as a major factor in Alzheimer's disease pathology. Moreover, the presence of CMHs is an independent risk factor for subsequent larger intracerebral hemorrhages. In this article, we review the epidemiology, detection, risk factors, clinical significance, and pathogenesis of CMHs. The potential age-related cellular mechanisms underlying the development of CMHs are discussed, with a focus on the structural determinants of microvascular fragility, age-related alterations in cerebrovascular adaptation to hypertension, the role of oxidative stress and matrix metalloproteinase activation, and the deleterious effects of arterial stiffening, increased pulse pressure, and impaired myogenic autoregulatory protection on the brain microvasculature. Finally, we examine potential treatments for the prevention of CMHs based on the proposed model of aging- and hypertension-dependent activation of the reactive oxygen species-matrix metalloproteinases axis, and we discuss critical questions to be addressed by future studies.

Matrix Metalloproteinase in Blood-Brain Barrier Breakdown in Dementia

The neurovascular unit, which consists of astrocytic end-feet, neurons, pericytes, and endothelial cells, plays a key role in maintaining brain homeostasis by forming the blood-brain barrier and carefully controlling local cerebral blood flow. When the blood-brain barrier is disrupted, blood components can leak into the brain, damage the surrounding tissue and lead to cognitive impairment. This disruption in the blood-brain barrier and subsequent impairment in cognition are common after stroke and during cerebral amyloid angiopathy and Alzheimer's disease. Matrix metalloproteinases are proteases that degrade the extracellular matrix as well as tight junctions between endothelial cells and have been implicated in blood-brain barrier breakdown in neurodegenerative diseases. This review will focus on the roles of MMP2 and MMP9 in dementia, primarily post-stroke events that lead to dementia, cerebral amyloid angiopathy, and Alzheimer's disease.

MicroRNA-195a-3p inhibits angiogenesis by targeting Mmp2 in murine mesenchymal stem cells

MicroRNAs (miRNAs) modulate complex physiological and pathological processes, including the regulation of angiogenesis. Our previous study reported that bone marrow-derived mesenchymal stem cells (MSCs) are recruited into choroidal neovascularization lesions. miRNA-195 is highly expressed in MSCs, but its function remains unknown. In the present study, miR-195a-3p abundance was significantly decreased in hypoxia-treated murine MSCs; on the other hand, its overexpression reduced MSC proliferation and migration while increasing the activation of anti-angiogenic factor pigment epithelium-derived factor (PEDF). We further discovered that matrix metalloproteinase 2 (Mmp2) transcript is a target of miR-195a-3p, and that silencing Mmp2 phenocopied the reduced proliferation and migration of MSCs. The therapeutic potential of miR-195a-3p as an angiogenesis inhibitor was also demonstrated in a laser-induced choroidal neovascularization mouse model. These findings collectively indicate that miR-195a-3p is a negative modulator of angiogenesis, and could be used as an angiogenesis inhibitor. Mol. Reprod. Dev. 83: 413-423, 2016. © 2016 Wiley Periodicals, Inc.

Unfractionated bone marrow cells attenuate paraquat-induced glomerular injury and acute renal failure by modulating the inflammatory response

The aim of this study was to evaluate the efficacy of unfractionated bone marrow cells (BMCs) in attenuating acute kidney injury (AKI) induced by paraquat (PQ) in a mouse model. PQ (55 mg/kg BW) was intraperitoneally injected into C57BL/6 female mice to induce AKI, including renal function failure, glomerular damage and renal tubule injury. Glomerular podocytes were the first target damaged by PQ, which led to glomerular injury. Upon immunofluorescence staining, podocytes depletion was validated and accompanied by increased urinary podocin levels, measured on days 1 and 6. A total of 5.4 × 10(6) BMCs obtained from the same strain of male mice were injected into AKI mice through the tail vein at 3, 24, and 48 hours after PQ administration. As a result, renal function increased, tubular and glomerular injury were ameliorated, podocytes loss improved, and recipient mortality decreased. In addition, BMCs co-treatment decreased the extent of neutrophil infiltration and modulated the inflammatory response by shifting from pro-inflammatory Th1 to an anti-inflammatory Th2 profile, where IL-1β, TNF-α, IL-6 and IFN-γ levels declined and IL-10 and IL-4 levels increased. The present study provides a platform to investigate PQ-induced AKI and repeated BMCs injection represents an efficient therapeutic strategy.

Arginine deprivation and immune suppression in a mouse model of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is a critical unsolved question; and although recent studies have demonstrated a strong association between altered brain immune responses and disease progression, the mechanistic cause of neuronal dysfunction and death is unknown. We have previously described the unique CVN-AD mouse model of AD, in which immune-mediated nitric oxide is lowered to mimic human levels, resulting in a mouse model that demonstrates the cardinal features of AD, including amyloid deposition, hyperphosphorylated and aggregated tau, behavioral changes, and age-dependent hippocampal neuronal loss. Using this mouse model, we studied longitudinal changes in brain immunity in relation to neuronal loss and, contrary to the predominant view that AD pathology is driven by proinflammatory factors, we find that the pathology in CVN-AD mice is driven by local immune suppression. Areas of hippocampal neuronal death are associated with the presence of immunosuppressive CD11c(+) microglia and extracellular arginase, resulting in arginine catabolism and reduced levels of total brain arginine. Pharmacologic disruption of the arginine utilization pathway by an inhibitor of arginase and ornithine decarboxylase protected the mice from AD-like pathology and significantly decreased CD11c expression. Our findings strongly implicate local immune-mediated amino acid catabolism as a novel and potentially critical mechanism mediating the age-dependent and regional loss of neurons in humans with AD.

The impact of human and mouse differences in NOS2 gene expression on the brain's redox and immune environment

BACKGROUND

Mouse models are used in the study of human disease. Despite well-known homologies, the difference in immune response between mice and humans impacts the application of data derived from mice to human disease outcomes. Nitric oxide synthase-2 (NOS2) is a key gene that displays species-specific outcomes via altered regulation of the gene promoter and via post-transcriptional mechanisms in humans that are not found in mice. The resulting levels of NO produced by activation of human NOS2 are different from the levels of NO produced by mouse Nos2. Since both tissue redox environment and immune responsiveness are regulated by the level of NO and its interactions, we investigated the significance of mouse and human differences on brain oxidative stress and on immune activation in HuNOS2tg/mNos2-/- mice that express the entire human NOS2 gene and that lack a functional mNos2 compared to wild type (WT) mice that express normal mNos2.

METHODS/RESULTS

Similarly to human, brain tissue from HuNOS2tg/mNos2-/- mice showed the presence of a NOS2 gene 3'UTR binding site. We also identified miRNA-939, the binding partner for this site, in mouse brain lysates and further demonstrated reduced levels of nitric oxide (NO) typical of the human immune response on injection with lipopolysaccharide (LPS). HuNOS2tg/mNos2-/- brain samples were probed for characteristic differences in redox and immune gene profiles compared to WT mice using gene arrays. Selected genes were also compared against mNos2-/- brain lysates. Reconstitution of the human NOS2 gene significantly altered genes that encode multiple anti-oxidant proteins, oxidases, DNA repair, mitochondrial proteins and redox regulated immune proteins. Expression levels of typical pro-inflammatory, anti-inflammatory and chemokine genes were not significantly different with the exception of increased TNFα and Ccr1 mRNA expression in the HuNOS2tg/mNos2-/- mice compared to WT or mNos2-/- mice.

CONCLUSIONS

NO is a principle factor in establishing the tissue redox environment and changes in NO levels impact oxidative stress and immunity, both of which are primary characteristics of neurodegenerative diseases. The HuNOS2tg/mNos2-/- mice provide a potentially useful mechanism to address critical species- specific immune differences that can impact the study of human diseases.

Dietary methanol regulates human gene activity

Methanol (MeOH) is considered to be a poison in humans because of the alcohol dehydrogenase (ADH)-mediated conversion of MeOH to formaldehyde (FA), which is toxic. Our recent genome-wide analysis of the mouse brain demonstrated that an increase in endogenous MeOH after ADH inhibition led to a significant increase in the plasma MeOH concentration and a modification of mRNA synthesis. These findings suggest endogenous MeOH involvement in homeostasis regulation by controlling mRNA levels. Here, we demonstrate directly that study volunteers displayed increasing concentrations of MeOH and FA in their blood plasma when consuming citrus pectin, ethanol and red wine. A microarray analysis of white blood cells (WBC) from volunteers after pectin intake showed various responses for 30 significantly differentially regulated mRNAs, most of which were somehow involved in the pathogenesis of Alzheimer's disease (AD). There was also a decreased synthesis of hemoglobin mRNA, HBA and HBB, the presence of which in WBC RNA was not a result of red blood cells contamination because erythrocyte-specific marker genes were not significantly expressed. A qRT-PCR analysis of volunteer WBCs after pectin and red wine intake confirmed the complicated relationship between the plasma MeOH content and the mRNA accumulation of both genes that were previously identified, namely, GAPDH and SNX27, and genes revealed in this study, including MME, SORL1, DDIT4, HBA and HBB. We hypothesized that human plasma MeOH has an impact on the WBC mRNA levels of genes involved in cell signaling.

β-amyloid deposition is shifted to the vasculature and memory impairment is exacerbated when hyperhomocysteinemia is induced in APP/PS1 transgenic mice

Introduction

Vascular dementia is the second most common cause of dementia after Alzheimer’s disease (AD). In addition, it is estimated that almost half of all AD patients have significant cerebrovascular disease comorbid with their AD pathology. We hypothesized that cerebrovascular disease significantly impacts AD pathological progression.

Methods

We used a dietary model of cerebrovascular disease that relies on the induction of hyperhomocysteinemia (HHcy). HHcy is a significant clinical risk factor for stroke, cardiovascular disease and type 2 diabetes. In the present study, we induced HHcy in APP/PS1 transgenic mice.

Results

While total β-amyloid (Aβ) load is unchanged across groups, Congophilic amyloid deposition was decreased in the parenchyma and significantly increased in the vasculature as cerebral amyloid angiopathy (CAA; vascular amyloid deposition) in HHcy APP/PS1 mice. We also found that HHcy induced more microhemorrhages in the APP/PS1 mice than in the wild-type mice and that it switched the neuroinflammatory phenotype from an M2a biased state to an M1 biased state. Associated with these changes was an induction of the matrix metalloproteinase protein 2 (MMP2) and MMP9 systems. Interestingly, after 6 months of HHcy, the APP/PS1 mice were cognitively worse than wild-type HHcy mice or APP/PS1 mice, indicative of an additive effect of the cerebrovascular pathology and amyloid deposition.

Conclusions

These data show that cerebrovascular disease can significantly impact Aβ distribution in the brain, favoring vascular deposition. We predict that the presence of cerebrovascular disease with AD will have a significant impact on AD progression and the efficacy of therapeutics.

Aging mesenchymal stem cells fail to protect because of impaired migration and antiinflammatory response

RATIONALE

Aging is characterized by functional impairment and reduced capacity to respond appropriately to environmental stimuli and injury. With age, there is an increase in the incidence and severity of chronic and acute lung diseases. However, the relationship between age and the lung's reduced ability to repair is far from established and necessitates further research in the field.

OBJECTIVES

Little is currently known about age-related phenomena in mesenchymal stem cells (MSCs). On account of their ability to protect the endothelium and the alveolar epithelium through multiple paracrine mechanisms, we looked for adverse effects that aging might cause in MSC biology. Such age-related changes might partly account for the increased susceptibility of the aging lung to injury.

MEASUREMENTS AND MAIN RESULTS

We demonstrated that old mice have more inflammation in response to acute lung injury. To investigate the causes, we compared the global gene expression of aged and young bone marrow-derived MSCs (B-MSCs). Our results revealed that the expression levels of inflammatory response genes depended on the age of the B-MSCs. We demonstrated that the age-dependent decrease in expression of several cytokine and chemokine receptors is important for the migration and activation of B-MSCs. Finally, we showed by adoptive transfer of aged B-MSCs to young endotoxemic mice that aged cells lacked the antiinflammatory protective effect of their young counterparts.

CONCLUSIONS

Taken together, the decreased expression of cytokine and chemokine receptors in aged B-MSCs compromises their protective role by perturbing the potential of B-MSCs to become activated and mobilize to the site of injury.

Roles of NFκB-miR-29s-MMP-2 circuitry in experimental choroidal neovascularization

Background

Previous reports have indicated that matrix metallopeptidase-2 (MMP-2) regulates angiogenic processes, which are involved in choroidal neovascularization (CNV). However, the regulation of MMP-2 in CNV has not been well-characterized. To gain more information about the regulation of MMP-2 in CNV, we analyzed the circuitry associated with MMP-2 regulation in a CNV model and in cell cultures, focusing on NFκB and the microRNA-29 family (miR-29s).

Methods

The CNV model was established by subjecting C57BL/6 mice to fundus photocoagulation with a krypton red laser. In choroidal-retinal pigment epithelial (RPE) tissues of the model, immunohistochemistry was used to evaluate the angiogenesis and MMP-2 expression; reverse-transcription quantitative PCR (RT-qPCR) was used to determine the levels of miR-29s; and western blot was used to analyze the protein levels of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) inhibitor, IκBα, and its phosphorylated form, phospho-IκBα. At the cellular level, RT-qPCR was used to examine the levels of miR-29s following NFκB activation by tumor necrosis factor alpha (TNFα); and western blot and luciferase assay were used to determine the regulation of MMP-2 by miR-29s in a human RPE cell line (ARPE-19) and in an umbilical vein endothelial cell line (EA hy926).

Results

MMP-2 staining was increased in the choroidal neovascular membrane of laser-treated retina. Also, the NFκB pathway was induced in choroid-RPE tissue, as evidenced by a lower protein level of IκBα and a higher level of phospho-IκBα in the tissue homogenates than in those from non-treated eyes. During the period when the NFκB pathway was induced, reduced miR-29s were detected in the choroidal-RPE tissue of the laser-treated eyes. In cultured ARPE-19 cells, TNFα decreased miR-29a, b, and c, and the effects were rescued by NFκB decoy. In ARPE-19 and EA hy926, miR-29s mimics reduced the contents of secreted MMP-2 in the culture media. We also documented that miR-29s reduced MMP-2 3’-UTR-mediated luciferase transcription.

Conclusions

The results suggest that in CNV, NFκB activation inhibits miR-29s, which may contribute to angiogenesis by up-regulating the MMP-2 protein level in RPE cells. These observations may help in developing a strategy for resolving CNV by targeting miR-29s levels.

A coimmunization vaccine of Aβ42 ameliorates cognitive deficits without brain inflammation in an Alzheimer's disease model

INTRODUCTION

Vaccination against amyloid-β protein (Aβ42) induces high levels of antibody, making it a promising strategy for treating Alzheimer's disease (AD). One drawback in the past was that clinical trial approval was withheld because of speculation that the Aβ42 vaccine induces CD4(+) T cell infiltrations into the central nervous system. To reduce T-cell activation while concomitantly maintaining high anti-Aβ42 titers is a great challenge in immunology.

METHODS

We aimed to demonstrate that coimmunization with Aβ42 protein and expression plasmid can be beneficial in a mouse AD model and can prevent inflammation. We immunized the AD mice with the coimmunization vaccine and assessed behavior change and Aβ42 deposition. Furthermore, to determine the safety of the coimmunization vaccine, we used an induced Aβ42-EAE model to mimic the meningoencephalitis that happened in the AN-1792 vaccine clinical phase II trial and tested whether the coimmunization vaccine could ameliorate T-cell-mediated brain inflammation.

RESULTS

The coimmunization vaccination reduced Aβ plaques and significantly ameliorated cognitive deficit while inhibiting T-cell-mediated brain inflammation and infiltration. These studies demonstrate that the coimmunization strategy that we describe in this article can ameliorate AD pathology without notable adverse effects in mice.

CONCLUSIONS

A coimmunization strategy leading to the development of a safe immunotherapeutic/preventive protocol against AD in humans is warranted.

Imaging of cerebrovascular pathology in animal models of Alzheimer's disease

In Alzheimer's disease (AD), vascular pathology may interact with neurodegeneration and thus aggravate cognitive decline. As the relationship between these two processes is poorly understood, research has been increasingly focused on understanding the link between cerebrovascular alterations and AD. This has at last been spurred by the engineering of transgenic animals, which display pathological features of AD and develop cerebral amyloid angiopathy to various degrees. Transgenic models are versatile for investigating the role of amyloid deposition and vascular dysfunction, and for evaluating novel therapeutic concepts. In addition, research has benefited from the development of novel imaging techniques, which are capable of characterizing vascular pathology in vivo. They provide vascular structural read-outs and have the ability to assess the functional consequences of vascular dysfunction as well as to visualize and monitor the molecular processes underlying these pathological alterations. This article focusses on recent in vivo small animal imaging studies addressing vascular aspects related to AD. With the technical advances of imaging modalities such as magnetic resonance, nuclear and microscopic imaging, molecular, functional and structural information related to vascular pathology can now be visualized in vivo in small rodents. Imaging vascular and parenchymal amyloid-β (Aβ) deposition as well as Aβ transport pathways have been shown to be useful to characterize their dynamics and to elucidate their role in the development of cerebral amyloid angiopathy and AD. Structural and functional imaging read-outs have been employed to describe the deleterious affects of Aβ on vessel morphology, hemodynamics and vascular integrity. More recent imaging studies have also addressed how inflammatory processes partake in the pathogenesis of the disease. Moreover, imaging can be pivotal in the search for novel therapies targeting the vasculature.

Intracranial injection of Gammagard, a human IVIg, modulates the inflammatory response of the brain and lowers Aβ in APP/PS1 mice along a different time course than anti-Aβ antibodies

Gammagard IVIg is a therapeutic approach to treat Alzheimer's disease currently in phase 3 clinical trials. Despite the reported efficacy of the approach the mechanism of action is poorly understood. We have previously shown that intracranial injection of anti-Aβ antibodies into the frontal cortex and hippocampus reveals important information regarding the time course of events once the agent is in the brain. In the current study we compared IVIg, mouse-pooled IgG, and the anti-Aβ antibody 6E10 injected intracranially into the frontal cortex and hippocampus of 7-month-old APP/PS1 mice. We established a time course of events ranging from 1 to 21 d postinjection. IVIg and pooled mouse IgG both significantly reduced Aβ deposition to the same degree as the 6E10 anti-Aβ antibody; however, the clearance was much slower to occur, happening between the 3 and 7 d time points. In contrast, as we have previously shown, Aβ reductions were apparent with the 6E10 anti-Aβ group at the 1 d time point. Also, neuroinflammatory profiles were significantly altered by the antibody treatments. APP/PS1 transgenic mice at 7 months of age typically exhibit an M2a inflammatory phenotype. All antibody treatments stimulated an M2b response, yet anti-Aβ antibody was a more rapid change. Because the neuroinflammatory switch occurs before the detectable reductions in amyloid deposition, we hypothesize that the IVIg and pooled mouse IgG act as immune modulators and this immune modulation is responsible for the reductions in amyloid pathology.

Induction of hyperhomocysteinemia models vascular dementia by induction of cerebral microhemorrhages and neuroinflammation

Vascular dementia (VaD) is the second leading cause of dementia behind Alzheimer's disease (AD) and is a frequent comorbidity with AD, estimated to occur in as many as 40% of AD patients. The causes of VaD are varied and include chronic cerebral hypoperfusion, microhemorrhages, hemorrhagic infarcts, or ischemic infarcts. We have developed a model of VaD by inducing hyperhomocysteinemia (HHcy) in wild-type mice. By placing wild-type mice on a diet deficient in folate, B6, and B12 and supplemented with excess methionine, we induced a moderate HHcy (plasma level homocysteine 82.93 ± 3.561 μmol). After 11 weeks on the diet, the hyperhomocysteinemic mice showed a spatial memory deficit as assessed by the 2-day radial-arm water maze. Also, magnetic resonance imaging and subsequent histology revealed significant microhemorrhage occurrence. We found neuroinflammation induced in the hyperhomocysteinemic mice as determined by elevated interleukin (IL)-1β, tumor necrosis factor (TNF)α, and IL-6 in brain tissue. Finally, we found increased expression and increased activity of the matrix metalloproteinase 2 (MMP2) and MMP9 systems that are heavily implicated in the pathogenesis of cerebral hemorrhage. Overall, we have developed a dietary model of VaD that will be valuable for studying the pathophysiology of VaD and also for studying the comorbidity of VaD with other dementias and other neurodegenerative disorders.

A lipoprotein receptor cluster IV mutant preferentially binds amyloid-β and regulates its clearance from the mouse brain

Soluble low density lipoprotein receptor-related protein-1 (sLRP1) binds ~70% of amyloid β-peptide (Aβ) in human plasma. In Alzheimer disease (AD) and individuals with mild cognitive impairment converting to AD, plasma sLRP1 levels are reduced and sLRP1 is oxidized, which results in diminished Aβ peripheral binding and higher levels of free Aβ in plasma. Experimental studies have shown that free circulating Aβ re-enters the brain and that sLRP1 and/or its recombinant wild type cluster IV (WT-LRPIV) prevent Aβ from entering the brain. Treatment of Alzheimer APPsw(+/0) mice with WT-LRPIV has been shown to reduce brain Aβ pathology. In addition to Aβ, LRPIV binds multiple ligands. To enhance LRPIV binding for Aβ relative to other LRP1 ligands, we generated a library of LRPIV-derived fragments and full-length LRPIV variants with glycine replacing aspartic acid residues 3394, 3556, and 3674 in the calcium binding sites. Compared with WT-LRPIV, a lead LRPIV-D3674G mutant had 1.6- and 2.7-fold higher binding affinity for Aβ40 and Aβ42 in vitro, respectively, and a lower binding affinity for other LRP1 ligands (e.g. apolipoprotein E2, E3, and E4 (1.3-1.8-fold), tissue plasminogen activator (2.7-fold), matrix metalloproteinase-9 (4.1-fold), and Factor Xa (3.8-fold)). LRPIV-D3674G cleared mouse endogenous brain Aβ40 and Aβ42 25-27% better than WT-LRPIV. A 3-month subcutaneous treatment of APPsw(+/0) mice with LRPIV-D3674G (40 μg/kg/day) reduced Aβ40 and Αβ42 levels in the hippocampus, cortex, and cerebrospinal fluid by 60-80% and improved cerebral blood flow responses and hippocampal function at 9 months of age. Thus, LRPIV-D3674G is an efficient new Aβ clearance therapy.

Nitric oxide-mediated regulation of β-amyloid clearance via alterations of MMP-9/TIMP-1

Fibrillar amyloid plaques are largely composed of amyloid-beta (Aβ) peptides that are metabolized into products, including Aβ1-16, by proteases including matrix metalloproteinase 9 (MMP-9). The balance between production and degradation of Aβ proteins is critical to amyloid accumulation and resulting disease. Regulation of MMP-9 and its endogenous inhibitor tissue inhibitor of metalloproteinase (TIMP)-1 by nitric oxide (NO) has been shown. We hypothesize that nitric oxide synthase (NOS2) protects against Alzheimer's disease pathology by increasing amyloid clearance through NO regulation of MMP-9/TIMP-1 balance. We show NO-mediated increased MMP-9/TIMP-1 ratios enhanced the degradation of fibrillar Aβ in vitro, which was abolished when silenced for MMP-9 protein translation. The in vivo relationship between MMP-9, NO and Aβ degradation was examined by comparing an Alzheimer's disease mouse model that expresses NOS2 with a model lacking NOS2. To quantitate MMP-9 mediated changes, we generated an antibody recognizing the Aβ1-16 fragment, and used mass spectrometry multi-reaction monitoring assay for detection of immunoprecipitated Aβ1-16 peptides. Aβ1-16 levels decreased in brain lysates lacking NOS2 when compared with strains that express human amyloid precursor protein on the NOS2 background. TIMP-1 increased in the APPSwDI/NOS2(-/-) mice with decreased MMP activity and increased amyloid burden, thereby supporting roles for NO in the regulation of MMP/TIMP balance and plaque clearance.

Diverse inflammatory responses in transgenic mouse models of Alzheimer's disease and the effect of immunotherapy on these responses

While the presence of an inflammatory response in AD (Alzheimer's disease) is well known, the data on inflammation are conflicting, suggesting that inflammation either attenuates pathology, exacerbates it or has no effect. Our goal was to more fully characterize the inflammatory response in APP (amyloid precursor protein) transgenic mice with and without disease progression. In addition, we have examined how anti-Aβ (amyloid β-peptide) immunotherapy alters this inflammatory response. We have used quantitative RT–PCR (reverse transcription–PCR) and protein analysis to measure inflammatory responses ranging from pro-inflammatory to anti-inflammatory and repair factors in transgenic mice that develop amyloid deposits only (APPSw) and amyloid deposits with progression to tau pathology and neuron loss [APPSw/NOS2^−/− (nitric oxide synthase 2^−/−)]. We also examined tissues from previously published immunotherapy studies. These studies were a passive immunization study in APPSw mice and an active vaccination study in APPSw/NOS2^−/− mice. Both studies have already been shown to lower amyloid load and improve cognition. We have found that amyloid deposition is associated with high expression of alternative activation and acquired deactivation genes and low expression of pro-inflammatory genes, whereas disease progression is associated with a mixed phenotype including increased levels of some classical activation factors. Immunotherapy targeting amyloid deposition in both mouse models resulted in decreased alternative inflammatory markers and, in the case of passive immunization, a transient increase in pro-inflammatory markers. Our results suggest that an alternative immune response favours retention of amyloid deposits in the brain, and switching away from this state by immunotherapy permits removal of amyloid.