Cerebral microvascular amyloid beta protein deposition induces vascular degeneration and neuroinflammation in transgenic mice expressing human vasculotropic mutant amyloid beta precursor protein

Genetic animal models of cerebral vasculopathies

Cerebral amyloid angiopathy (CAA) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) are genetic cerebrovasculopathies associated with neurodegeneration and vascular cognitive impairment. Linked to autosomal dominant mutations in diverse genes that encode cell-surface receptors (i.e., amyloid precursor protein in CAA and NOTCH3 in CADASIL), both diseases are associated with accumulation of abnormal material around cerebral vessels, such as amyloid in CAA or granular osmiophilic material in CADASIL. Both CAA and CADASIL share clinical features of white matter degeneration and infarcts, and vascular dementia in the human adult; microbleeds occur in both CADASIL and CAA, but large intracerebral hemorrhages are more characteristic for the latter. While the mechanisms are poorly understood, wall thickening, luminal narrowing, and eventual loss of vascular smooth muscle cells are overlapping pathologies involving leptomeningeal, and pial or penetrating small arteries and arterioles in CAA and CADASIL. Dysregulation of cerebral blood flow and eventual hypoperfusion are believed to be the key pathophysiological steps in neurodegeneration and cognitive impairment. Although animal models expressing CAA or CADASIL mutations have partially reproduced the human pathology, there has been marked heterogeneity in the phenotypic spectrum, possibly due to genetic background differences among mouse models, and obvious species differences between mouse and man. Here, we provide an overview of animal models of CAA and CADASIL and the insight on molecular and physiological mechanisms of disease gained from these models.

Review: sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) may result from focal to widespread amyloid-β protein (Aβ) deposition within leptomeningeal and intracortical cerebral blood vessels. In addition, pericapillary Aβ refers to Aβ depositions in the glia limitans and adjacent neuropil, whereas in capillary CAA Aβ depositions are present in the capillary wall. CAA may cause lobar intracerebral haemorrhages and microbleeds. Hypoperfusion and reduced vascular autoregulation due to CAA might cause infarcts and white matter lesions. CAA thus causes vascular lesions that potentially lead to (vascular) dementia and may further contribute to dementia by impeding the clearance of solutes out of the brain and transport of nutrients across the blood brain barrier. Severe CAA is an independent risk factor for cognitive decline. The clinical diagnosis of CAA is based on the assessment of associated cerebrovascular lesions. In addition, perivascular spaces in the white matter and reduced concentrations of both Aβ(40) and Aβ(42) in cerebrospinal fluid may prove to be suggestive for CAA. Transgenic mouse models that overexpress human Aβ precursor protein show parenchymal Aβ and CAA, thus corroborating the current concept of CAA pathogenesis: neuronal Aβ enters the perivascular drainage pathway and may accumulate in vessel walls due to increased amounts and/or decreased clearance of Aβ, respectively. We suggest that pericapillary Aβ represents early impairment of the perivascular drainage pathway while capillary CAA is associated with decreased transendothelial clearance of Aβ. CAA plays an important role in the multimorbid condition of the ageing brain but its contribution to neurodegeneration remains to be elucidated.

Perivascular drainage of solutes is impaired in the ageing mouse brain and in the presence of cerebral amyloid angiopathy

The deposition of amyloid-β (Aβ) peptides in the walls of leptomeningeal and cortical blood vessels as cerebral amyloid angiopathy (CAA) is present in normal ageing and the majority of Alzheimer's disease (AD) brains. The failure of clearance mechanisms to eliminate Aβ from the brain contributes to the development of sporadic CAA and AD. Here, we investigated the effects of CAA and ageing on the pattern of perivascular drainage of solutes in the brains of naïve mice and in the Tg2576 mouse model of AD. We report that drainage of small molecular weight dextran along cerebrovascular basement membranes is impaired in the hippocampal capillaries and arteries of 22-month-old wild-type mice compared to 3- and 7-month-old animals, which was associated with age-dependent changes in capillary density. Age-related alterations in the levels of laminin, fibronectin and perlecan in vascular basement membranes were also noted in wild-type mice. Furthermore, dextran was observed in the walls of veins of Tg2576 mice in the presence of CAA, suggesting that deposition of Aβ in vessel walls disrupts the normal route of elimination of solutes from the brain parenchyma. These data support the hypothesis that perivascular solute drainage from the brain is altered both in the ageing brain and as a consequence of CAA. These findings have implications for the success of therapeutic strategies for the treatment of AD that rely upon the health of the ageing cerebral vasculature.

Alzheimer's dementia begins as a disease of small blood vessels, damaged by oxidative-induced inflammation and dysregulated amyloid metabolism: implications for early detection and therapy

There is a widely shared view among Alzheimer's disease (AD) investigators that the amyloid hypothesis best describes the pathogenic cascade that leads, ultimately, to neuronal degeneration and irreversible dementia. The most persuasive evidence comes from studies of damaged brains of patients in the late stages of AD and from animal studies that attempt to mimic the hereditary forms of early-onset dementia. Despite this impressive body of knowledge, we still lack the means to either arrest or prevent this horrible contagion. This essay attempts to describe what we know, and do not know, about the earliest stages of the disease, focusing on the possibility that the initial pathological changes involve oxidative-induced inflammatory damage to small blood vessels. The resulting ischemia activates amyloid-processing enzymes and other proinflammatory factors that eventually compromise neuronal functions, leading, over time, to the complex lesions that characterize advanced disease. The idea that blood vessel damage is primary has a long history and many prior advocates. The novel addition offered here is the speculation that low-abundance, gain-of-function somatic mutations of the amyloid precursor protein may be part of the triggering mechanism.

Enhanced capillary amyloid angiopathy-associated pathology in Tg-SwDI mice with deleted nitric oxide synthase 2

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy Type 1 is characterized by amyloid β protein deposition along cerebral capillaries and is accompanied by perivascular neuroinflammation and accumulation of phospho-tau protein. Tg-SwDI mice recapitulate capillary amyloid deposition and associated neuroinflammation but lack accumulation of perivascular phospho-tau protein.

METHODS

Tg-SwDI mice were bred onto a nitric oxide synthase 2 gene knockout background and aged for 1 year. Brains were harvested and analyzed using immunohistochemical and quantitative stereological methods to determine the extent of capillary amyloid deposition, perivascular activated microglia, and cell-specific accumulation of phospho-tau protein. Similar methods were also used to compare Tg-SwDI/NOS2(-/-) and human cerebral amyloid angiopathy Type 1 brain tissues.

RESULTS

The absence of nitric oxide synthase 2 gene had no effect on the regional pattern or frequency of capillary cerebral amyloid angiopathy or the numbers of perivascular activated microglia in Tg-SwDI mice. On the other hand, Tg-SwDI/NOS2(-/-) mice accumulated phospho-tau protein in perivascular neurons and activated microglia. Tg-SwDI/NOS2(-/-) mice exhibited a very similar distribution of capillary amyloid, activated microglia, and perivascular phospho-tau protein as seen in human cerebral amyloid angiopathy Type 1.

CONCLUSIONS

These findings indicate that Tg-SwDI/NOS2(-/-) mice more fully recapitulate the pathological changes observed with capillary amyloid in human cerebral amyloid angiopathy Type 1.

Preclinical and clinical research on inflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is one of the most lethal stroke subtypes. Despite the high morbidity and mortality associated with ICH, its pathophysiology has not been investigated as well as that of ischemic stroke. Available evidence from preclinical and clinical studies suggests that inflammatory mechanisms are involved in the progression of ICH-induced secondary brain injury. For example, in preclinical ICH models, microglial activation has been shown to occur within 1h, much earlier than neutrophil infiltration. Recent advances in our understanding of neuroinflammatory pathways have revealed several new molecular targets, and related therapeutic strategies have been tested in preclinical ICH models. This review summarizes recent progress made in preclinical models of ICH, surveys preclinical and clinical studies of inflammatory cells (leukocytes, macrophages, microglia, and astrocytes) and inflammatory mediators (matrix metalloproteinases, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron), and highlights the emerging areas of therapeutic promise.

Role of vascular risk factors and vascular dysfunction in Alzheimer's disease

Recent findings indicate that vascular risk factors and neurovascular dysfunction play integral roles in the pathogenesis of Alzheimer's disease. In addition to aging, the most common risk factors for Alzheimer's disease are apolipoprotein e4 allele, hypertension, hypotension, diabetes, and hypercholesterolemia. All of these can be characterized by vascular pathology attributed to conditions such as cerebral amyloid angiopathy and subsequent blood-brain barrier dysfunction. Many epidemiological, clinical, and pharmacotherapeutic studies have assessed the associations between such risk factors and Alzheimer's disease and have found positive associations between hypertension, hypotension, and diabetes mellitus. However, there are still many conflicting results from these population-based studies, and they should be interpreted carefully. Recognition of these factors and the mechanisms by which they contribute to Alzheimer's disease will be beneficial in the current treatment regimens for Alzheimer's disease and in the development of future therapies. Here we discuss vascular factors with respect to Alzheimer's disease and dementia and review the factors that give rise to vascular dysfunction and contribute to Alzheimer's disease.

ABCG2 is upregulated in Alzheimer's brain with cerebral amyloid angiopathy and may act as a gatekeeper at the blood-brain barrier for Abeta(1-40) peptides

Alzheimer's disease (AD) is characterized by accumulation and deposition of Abeta peptides in the brain. Abeta deposition in cerebrovessels occurs in many AD patients and results in cerebral amyloid angiopathy (AD/CAA). Since Abeta can be transported across blood-brain barrier (BBB), aberrant Abeta trafficking across BBB may contribute to Abeta accumulation in the brain and CAA development. Expression analyses of 273 BBB-related genes performed in this study showed that the drug transporter, ABCG2, was significantly upregulated in the brains of AD/CAA compared with age-matched controls. Increased ABCG2 expression was confirmed by Q-PCR, Western blot, and immunohistochemistry. Abcg2 was also increased in mouse AD models, Tg-SwDI and 3XTg. Abeta alone or in combination with hypoxia/ischemia failed to stimulate ABCG2 expression in BBB endothelial cells; however, conditioned media from Abeta-activated microglia strongly induced ABCG2 expression. ABCG2 protein in AD/CAA brains interacted and coimmunoprecipitated with Abeta. Overexpression of hABCG2 reduced drug uptake in cells; however, interaction of Abeta(1-40) with ABCG2 impaired ABCG2-mediated drug efflux. The role of Abcg2 in Abeta transport at the BBB was investigated in Abcg2-null and wild-type mice after intravenous injection of Cy5.5-labeled Abeta(1-40) or scrambled Abeta(40-1). Optical imaging analyses of live animals and their brains showed that Abcg2-null mice accumulated significantly more Abeta in their brains than wild-type mice. The finding was confirmed by immunohistochemistry. These results suggest that ABCG2 may act as a gatekeeper at the BBB to prevent blood Abeta from entering into brain. ABCG2 upregulation may serve as a biomarker of CAA vascular pathology in AD patients.

Hereditary and sporadic forms of abeta-cerebrovascular amyloidosis and relevant transgenic mouse models

Cerebral amyloid angiopathy (CAA) refers to the specific deposition of amyloid fibrils in the leptomeningeal and cerebral blood vessel walls, often causing secondary vascular degenerative changes. Although many kinds of peptides are known to be deposited as vascular amyloid, amyloid-beta (Abeta)-CAA is the most common type associated with normal aging, sporadic CAA, Alzheimer's disease (AD) and Down's syndrome. Moreover, Abeta-CAA is also associated with rare hereditary cerebrovascular amyloidosis due to mutations within the Abeta domain of the amyloid precursor protein (APP) such as Dutch and Flemish APP mutations. Genetics and clinicopathological studies on these familial diseases as well as sporadic conditions have already shown that CAA not only causes haemorrhagic and ischemic strokes, but also leads to progressive dementia. Transgenic mouse models based on familial AD mutations have also successfully reproduced many of the features found in human disease, providing us with important insights into the pathogenesis of CAA. Importantly, such studies have pointed out that specific vastopic Abeta variants or an unaltered Abeta42/Abeta40 ratio favor vascular Abeta deposition over parenchymal plaques, but higher than critical levels of Abeta40 are also observed to be anti-amyloidogenic. These data would be important in the development of therapies targeting amyloid in vessels.

Selective targeting of perivascular macrophages for clearance of beta-amyloid in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA), the deposition of beta-amyloid (Abeta) peptides in leptomeningeal and cortical blood vessels, affects the majority of patients with Alzheimer's disease (AD). Evidence suggests that vascular amyloid deposits may result from impaired clearance of neuronal Abeta along perivascular spaces. We investigated the role of perivascular macrophages in regulating CAA severity in the TgCRND8 mouse model of AD. Depletion of perivascular macrophages significantly increased the number of thioflavin S-positive cortical blood vessels. ELISA confirmed that this increase was underscored by elevations in total vascular Abeta(42) levels. Conversely, stimulation of perivascular macrophage turnover reduced cerebral CAA load, an effect that was not mediated through clearance by microglia or astrocytes. These results highlight a function for the physiological role of perivascular macrophages in the regulation of CAA and suggest that selective targeting of perivascular macrophage activation might constitute a therapeutic strategy to clear vascular amyloid.

Human apolipoprotein E4 targeted replacement mice show increased prevalence of intracerebral hemorrhage associated with vascular amyloid deposition

Previous studies show that APOE *4 carriers are at increased risk for ischemic stroke and intracerebral hemorrhage (ICH). The APOE *4 gene is also linked to increased incidence of cerebral amyloid angiopathy. It has been suggested that apolipoprotein E4 expression leads to increased vascular amyloid deposition, which may explain the increased incidence of ICH in APOE *4 carriers. Here we show a significant increase in ICH in apoE4 targeted replacement mice compared with apoE3 mice. In all, 89% of the vessels in the apoE4 mice that showed evidence for hemorrhage contained fibrillar amyloid beta based on thioflavine-S staining. Aged apoE4 mice contained predominantly vascular amyloid deposits in the frontal cortex and hippocampus, but also showed evidence for parenchymal amyloid deposits. Most of the parenchymal amyloid appeared diffuse in nature; however, a small fraction was thioflavine-S positive, indicating presence of fibrillar amyloid. Electron microscopy further revealed evidence for fibrillar deposits in the vessel walls of apoE4 mice, but not apoE3 mice. The apoE4 targeted replacement mice do not harbor any mutation in the amyloid precursor protein gene and, therefore, are similar to the majority of humans susceptible to cerebral amyloid angiopathy and ICH, where the APOE genetic polymorphism is the only known genetic risk factor.

Impaired visual evoked flow velocity response in cerebral amyloid angiopathy

OBJECTIVE

Animal models of cerebral amyloid angiopathy (CAA) exhibit abnormal vascular reactivity. We determined whether vascular reactivity, measured by transcranial Doppler ultrasound (TCD), is reduced in humans with CAA.

METHODS

Cases were recruited from an established prospective study of CAA. Healthy controls were recruited from a study of normal aging. Evoked mean flow velocity increase in the posterior cerebral artery (PCA) was measured while subjects viewed a flashing alternating checkerboard stimulus. In a separate but partially overlapping cohort we measured the mean flow velocity increase in the middle cerebral artery (MCA) while subjects inhaled carbon dioxide.

RESULTS

The visual evoked mean flow velocity increase was 8.0 +/- 6.1% in CAA (n = 11) compared to 17.4 +/- 5.7% in controls (n = 9, p = 0.002). The PCA pulsatility index, a marker of distal vascular resistance, was higher in CAA (CAA 1.35 +/- 0.35, control 1.04 +/- 0.14, p = 0.03). Among CAA subjects, lower visual evoked mean flow velocity increase was associated with a higher number of hemorrhages seen on MRI (r = -0.87, p = 0.0005) and higher MRI white matter hyperintensity volume (r = -0.67, p = 0.02). The MCA response to carbon dioxide did not differ between CAA and control in 20 subjects (9 CAA, 11 control, p = 0.54).

CONCLUSIONS

Cerebral amyloid angiopathy (CAA) was associated with decreased vascular reactivity in response to visual stimulation, possibly reflecting the occipital predilection of the disease. The association of posterior cerebral artery (PCA) evoked flow velocity response with elevated PCA pulsatility index and MRI markers of small vessel disease suggests that abnormal PCA evoked flow velocity in CAA is caused by pathology of the distal resistance vessels.

The effects of NOS2 gene deletion on mice expressing mutated human AbetaPP

Nitric oxide synthase 2 (NOS2) and its gene product, inducible NOS (iNOS) play an important role in neuroinflammation by generating nitric oxide (NO), a critical signaling and redox factor in the brain. Although NO is associated with tissue damage, it can also promote cell survival. We hypothesize that during long-term exposure to amyloid-beta (Abeta) in Alzheimer's disease (AD), NO levels fall in the brain to a threshold at which the protective effects of NO cannot be sustained, promoting Abeta mediated damage. Two new mouse models of AD have been developed that utilize this concept of NO's action. These mice express human amyloid-beta protein precursor (AbetaPP) mutations that generate Abeta peptides on a mouse NOS2 knockout background. The APP/NOS2(-/-) bigenic mice progress from Abeta production and amyloid deposition to hyperphosphorylated normal mouse tau at AD-associated epitopes, aggregation and redistribution of tau to somatodendritic regions of neurons and significant neuronal loss including loss of interneurons. This AD-like pathology is accompanied by robust behavioral changes. As APP/NOS2(-/-) bigenic mice more fully model the human AD disease pathology, they may serve as a tool to better understand disease progression in AD and the role of NO in altering chronic neurological disease processes.

S14G-Humanin ameliorates Abeta25-35-induced behavioral deficits by reducing neuroinflammatory responses and apoptosis in mice

Cerebral amyloid-beta protein (Abeta) deposition and associated neuroinflammation and apoptosis are increasingly recognized as an important component leading to cognitive impairment in Alzheimer's disease (AD). Humanin (HN) and its derivative, S14G-HN (HNG), are best known for their ability to suppress neuronal death induced by AD-related insults in vitro. Furthermore, limited in vivo studies show that HNG can ameliorate memory impairment induced by intracerebroventricular injection of anti-cholinergic drugs or Abeta25-35. However, the mechanism underlying the in vivo effect remains unclear. In this study, we sought to determine the effects of HNG on neuroinflammatory responses and apoptosis associated with behavioral deficits induced by Abeta25-35 in vivo. Our results indicate that intracerebroventricular injection of aggregated Abeta25-35 induced impairment of learning and memory, markedly elevated numbers of reactive astrocytes, activated microglia, and apoptotic cells, as well as remarkable increased levels of IL-6 and TNFalpha. Moreover, intraperitoneal HNG treatment ameliorated behavioral deficits, and reduced neuroinflammatory responses and apoptotic cells in the brain. Cumulatively, these finding demonstrate for the first time that HNG may have the potential for attenuating Abeta-induced cognitive deficits by reducing inflammatory responses and apoptosis in vivo, which may add to the novel evidence for anti-inflammatory and antiapoptosis properties of HNG in AD treatment.

Alpha7 nicotinic acetylcholine receptor expression by vascular smooth muscle cells facilitates the deposition of Abeta peptides and promotes cerebrovascular amyloid angiopathy

Deposition of beta-amyloid (Abeta) peptides in the walls of brain blood vessels, cerebral amyloid angiopathy (CAA), is common in patients with Alzheimer's disease (AD). Previous studies have demonstrated Abeta peptide deposition among vascular smooth muscle cells (VSMCs), but the source of the Abeta and basis for its selective deposition in VSMCs are unknown. In the present study, we examined the deposition patterns of Abeta peptides, Abeta40 and Abeta42, within the cerebrovasculature of AD and control patients using single- and double-label immunohistochemistry. Abeta40 and Abeta42 were abundant in VSMCs, especially in leptomeningeal arteries and their initial cortical branches; in later-stage AD brains this pattern extended into the microvasculature. Abeta peptide deposition was linked to loss of VSMC viability. Perivascular leak clouds of Abeta-positive material were associated primarily with arterioles. By contrast, control brains possessed far fewer Abeta42- and Abeta40-immunopositive blood vessels, with perivascular leak clouds of Abeta-immunopositive material rarely observed. We also demonstrate that VSMCs in brain blood vessels express the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), which has high binding affinity for Abeta peptides, especially Abeta42. These results suggest that the blood and blood-brain barrier permeability provide a major source of the Abeta peptides that gradually deposit in brain VSMCs, and the presence and abundance of the alpha7nAChR on VSMCs may facilitate the selective accumulation of Abeta peptides in these cells.

Tg-SwDI transgenic mice exhibit novel alterations in AbetaPP processing, Abeta degradation, and resilient amyloid angiopathy

Alzheimer's disease (AD) is characterized by the accumulation of extracellular insoluble amyloid, primarily derived from polymerized amyloid-beta (Abeta) peptides. We characterized the chemical composition of the Abeta peptides deposited in the brain parenchyma and cerebrovascular walls of triple transgenic Tg-SwDI mice that produce a rapid and profuse Abeta accumulation. The processing of the N- and C-terminal regions of mutant AbetaPP differs substantially from humans because the brain parenchyma accumulates numerous, diffuse, nonfibrillar plaques, whereas the thalamic microvessels harbor overwhelming amounts of compact, fibrillar, thioflavine-S- and apolipoprotein E-positive amyloid deposits. The abundant accretion of vascular amyloid, despite low AbetaPP transgene expression levels, suggests that inefficient Abeta proteolysis because of conformational changes and dimerization may be key pathogenic factors in this animal model. The disruption of amyloid plaque cores by immunotherapy is accompanied by increased perivascular deposition in both humans and transgenic mice. This analogous susceptibility and response to the disruption of amyloid deposits suggests that Tg-SwDI mice provide an excellent model in which to study the functional aftermath of immunotherapeutic interventions. These mice might also reveal new avenues to promote amyloidogenic AbetaPP processing and fundamental insights into the faulty degradation and clearance of Abeta in AD, pivotal issues in understanding AD pathophysiology and the assessment of new therapeutic agents.

Human apolipoprotein E redistributes fibrillar amyloid deposition in Tg-SwDI mice

Human apolipoprotein (ApoE) genotype influences the development of Alzheimer's disease and cerebral amyloid angiopathy (CAA). Specific mutations within the amyloid-beta protein (Abeta) peptide have been identified that cause familial forms of CAA. However, the effect of APOE genotype on accumulation of CAA mutant Abeta in brain is not well understood. In the present study, we determined how human ApoE3 or ApoE4 influence cerebral Abeta accumulation in transgenic mice (Tg-SwDI) that accumulate human Dutch/Iowa (E22Q/D23N) CAA mutant Abeta in brain, primarily in the form of fibrillar cerebral microvascular amyloid. Using Tg-SwDI mice bred onto a human APOE3/3 or human APOE4/4 background, we found that both human ApoE3 and ApoE4 proteins led to a strong reduction in the amount of cerebral microvascular amyloid with an unexpected concomitant appearance of extensive fibrillar parenchymal plaque amyloid. There was strong colocalization of all ApoE proteins with fibrillar amyloid deposits in the mice. In Tg-SwDI/hAPOE3/3 and Tg-SwDI/hAPOE4/4 mice, there was no change in the levels of total Abeta(40) and Abeta(42) or in the amounts of soluble and insoluble Abeta in brain compared with Tg-SwDI mice on the endogenous mouse APOE background. The shift from primarily cerebral microvascular amyloid to parenchymal plaque amyloid in Tg-SwDI/hAPOE3/3 and Tg-SwDI/hAPOE4/4 mice resulted in a parallel shift in the association of activated microglia. These findings indicate that human ApoE has a strong influence on the spatial development of human Dutch/Iowa CAA mutant amyloid accumulation in mouse brain and that microglial activation is in response to the spatial accumulation of fibrillar amyloid.

Cerebral amyloid angiopathy and parenchymal amyloid deposition in transgenic mice expressing the Danish mutant form of human BRI2

Familial Danish dementia (FDD) is an autosomal dominant neurodegenerative disease clinically characterized by the presence of cataracts, hearing impairment, cerebellar ataxia and dementia. Neuropathologically, FDD is characterized by the presence of widespread cerebral amyloid angiopathy (CAA), parenchymal amyloid deposition and neurofibrillary tangles. FDD is caused by a 10‐nucleotide duplication‐insertion in the BRI₂ gene that generates a larger‐than‐normal precursor protein, of which the Danish amyloid subunit (ADan) comprises the last 34 amino acids. Here, we describe a transgenic mouse model for FDD (Tg‐FDD) in which the mouse Prnp (prion protein) promoter drives the expression of the Danish mutant form of human BRI₂ . The main neuropathological findings in Tg‐FDD mice are the presence of widespread CAA and parenchymal deposition of ADan. In addition, we observe the presence of amyloid‐associated gliosis, an inflammatory response and deposition of oligomeric ADan. As the animals aged, they showed abnormal grooming behavior, an arched back, and walked with a wide‐based gait and shorter steps. This mouse model may give insights on the pathogenesis of FDD and will prove useful for the development of therapeutics. Moreover, the study of Tg‐FDD mice may offer new insights into the role of amyloid in neurodegeneration in other disorders, including Alzheimer disease.

Cerebral amyloid angiopathy: pathogenetic mechanisms and link to dense amyloid plaques

Cerebral amyloid angiopathy (CAA) of the amyloid-beta (Abeta) type is the most common form of sporadic CAA and is now also accepted as an early and integral part of Alzheimer's disease (AD) pathogenesis. Cerebral amyloid angiopathy is a risk factor for haemorrhagic stroke and is believed to independently contribute to dementia. Rare forms of hereditary cerebral amyloidosis caused by mutations within the Abeta domain of amyloid precursor protein (APP) have been identified, where mutant Abeta preferably deposits in vessels because of a decreased fibrillogenic potential and/or increased vasotopicity. A review of factors involved in CAA caused by wild-type Abeta suggests that increased Abeta levels in brain without an increased Abeta42/Abeta40 ratio is one of the most important prerequisites for vascular amyloidosis. This is exemplified by CAA observed in APP duplication and Down's syndrome patients, neprilysin polymorphism patients and knockout mice and Swedish APP (KM670/671NL) mice. Select presenilin mutations also lead to a prominent CAA, and importantly, presenilin mutations are shown to have varied effects on the production of Abeta40, the predominant amyloid found in CAA. Conversely, APP mutations such as Austrian APP (T714I) drastically decrease Abeta40 production and are deficient in CAA. Apolipoprotein E-epsilon4 is also shown to be a risk factor for CAA, and this might be because of its specific role in the aggregation of Abeta40. Recent data also suggest that dense-core senile plaques in humans and dense plaques in transgenic mice, composed predominantly of Abeta40, associate with vessels. This review highlights some of these aspects of genetics and biochemistry of CAA and pathological descriptions linked to a prominent CAA and/or dense plaques in humans and relevant mouse models and discusses how this knowledge has led to a better understanding of the processes involved in vascular amyloidosis, and in causing dementia, and thus has important therapeutic implications.

Progression of amyloid pathology to Alzheimer's disease pathology in an amyloid precursor protein transgenic mouse model by removal of nitric oxide synthase 2

Alzheimer's disease (AD) is characterized by three primary pathologies in the brain: amyloid plaques, neurofibrillary tangles, and neuron loss. Mouse models have been useful for studying components of AD but are limited in their ability to fully recapitulate all pathologies. We crossed the APPSwDI transgenic mouse, which develops amyloid beta (Abeta)-protein deposits only, with a nitric oxide synthase 2 (NOS2) knock-out mouse, which develops no AD-like pathology. APPSwDI/NOS2(-/-) mice displayed impaired spatial memory compared with the APPSwDI mice, yet they have unaltered levels of Abeta. APPSwDI mice do not show tau pathology, whereas APPSwDI/NOS2(-/-) mice displayed extensive tau pathology associated with regions of dense microvascular amyloid deposition. Also, APPSwDI mice do not have any neuron loss, whereas the APPSwDI/NOS2(-/-) mice have significant neuron loss in the hippocampus and subiculum. Neuropeptide Y neurons have been shown to be particularly vulnerable in AD. These neurons appear to be particularly vulnerable in the APPSwDI/NOS2(-/-) mice as we observe a dramatic reduction in the number of NPY neurons in the hippocampus and subiculum. These data show that removal of NOS2 from an APP transgenic mouse results in development of a much greater spectrum of AD-like pathology and behavioral impairments.

Experimental investigation of antibody-mediated clearance mechanisms of amyloid-beta in CNS of Tg-SwDI transgenic mice

Novel amyloid precursor protein transgenic mice, which contain the Swedish as well as the vasculotropic Dutch and Iowa mutations (Tg-SwDI), were used to investigate the mechanisms of antibody-mediated clearance of amyloid-beta (Abeta) from the brain. Export of the Abeta-DI peptide across the blood-brain barrier is severely reduced because of the vasculotropic mutations. Therefore, antibody-mediated clearance of Abeta-DI is dependent on antibodies entering the brain. In this report, we immunized Tg-SwDI mice with various peptide antigens, including Abeta40-DI, Abeta42, and an Abeta epitope vaccine. Immunization of Tg-SwDI mice with substantial cortical diffuse and vascular fibrillar deposits failed to promote clearance of parenchymal or vascular amyloid deposits. We then immunized young Tg-SwDI mice before the accumulation of Abeta and saw no evidence that anti-Abeta antibodies could diminish deposition of parenchymal or vascular amyloid deposits. However, injection of anti-Abeta antibodies, affinity-purified from immunized Tg-SwDI mice, into the hippocampus induced a rapid clearance of diffuse Abeta deposits but not vascular amyloid deposits. These results further support the "peripheral sink hypothesis" as a legitimate mechanism of antibody-mediated clearance of Abeta when the blood-brain barrier remains intact. Thus, approaches that deliver immunotherapy to the brain may be more effective at clearing Abeta than immunization strategies in which the majority of the antibodies are in the periphery.

Human postmortem brain-derived cerebrovascular smooth muscle cells express all genes of the classical complement pathway: a potential mechanism for vascular damage in cerebral amyloid angiopathy and Alzheimer's disease

Deposition of amyloid around blood vessels, known as cerebral amyloid angiopathy (CAA), is a major pathological feature found in the majority of Alzheimer's disease (AD) cases, and activated complement fragments have been detected on CAA deposits in AD brains. In this study, we demonstrate for the first time that human cerebrovascular smooth muscle cells (HCSMC) isolated from cortical vessels derived from postmortem brains can express mRNAs for complement genes C1qB, C1r, C1s, C2, C3, C4, C5, C6, C7, C8 and C9, the components of the classical complement pathway. Secretion of the corresponding complement proteins for these genes was also demonstrated, except for C1q and C5. Of particular significance was the observation that treatment of HCSMC with aggregated amyloid beta (Abeta) 1-42 increased expression of complement C3 mRNA and increased release of C3 protein. Abeta treatment of HCSMC also increased expression of C6 mRNA. Interferon-gamma induced expression and release of complement C1r, C1s, C2 and C4. As HCSMC are closely associated with Abeta deposits in vessels in the brain, their production of complement proteins could amplify the proinflammatory effects of amyloid in the perivascular environment, further compromising brain vascular integrity.

Soluble aggregates of the amyloid-beta protein activate endothelial monolayers for adhesion and subsequent transmigration of monocyte cells

Increasing evidence suggests that the deposition of amyloid plaques, composed primarily of the amyloid-beta protein (Abeta), within the cerebrovasculature is a frequent occurrence in Alzheimer's disease and may play a significant role in disease progression. Accordingly, the pathogenic mechanisms by which Abeta can alter vascular function may have therapeutic implications. Despite observations that Abeta elicits a number of physiological responses in endothelial cells, ranging from alteration of protein expression to cell death, the Abeta species accountable for these responses remains unexplored. In the current study, we show that isolated soluble Abeta aggregation intermediates activate human brain microvascular endothelial cells for both adhesion and subsequent transmigration of monocyte cells in the absence of endothelial cell death and monolayer disruption. In contrast, unaggregated Abeta monomer and mature Abeta fibril fail to induce any change in endothelial adhesion or transmigration. Correlations between average Abeta aggregate size and observed increases in adhesion illustrate that smaller soluble aggregates are more potent activators of endothelium. These results support previous studies demonstrating heightened neuronal activity of soluble Abeta aggregates, including Abeta-derived diffusible ligands, oligomers, and protofibrils, and further show that soluble aggregates also selectively exhibit activity in a vascular cell model.

BACE1 and mutated presenilin-1 differently modulate Abeta40 and Abeta42 levels and cerebral amyloidosis in APPDutch transgenic mice

APPDutch transgenic (tg) mice develop cerebral amyloid angiopathy (CAA) that consists mainly of AbetaDutch40, with virtually no parenchymal amyloid plaques. To modulate cerebral amyloidosis, we crossbred APPDutch mice with either BACE1 tg mice to increase total AbetaDutch, or with G384A-mutated PS1 tg mice to elevate the ratio of AbetaDutch42 to AbetaDutch40. We analyzed all mice at 22 months of age. Compared to APPDutch mice, double-tg APPDutch/BACE1 mice revealed increased CAA mainly due to extensive vascular amyloid accumulation in the thalamus. In addition, they developed parenchymal amyloid in cortex and subiculum. In contrast, APPDutch/G384A-PS1 mice showed extensive, predominantly parenchymal amyloid throughout the entire brain, interestingly, even in the thalamus. The amyloid, composed largely of AbetaDutch42, was different compared to that in APPDutch/BACE1 mice which was composed mainly of AbetaDutch40. In summary, these mouse models reveal a broad variety and region-specificity of parenchymal versus vascular cerebral amyloid. This is partially explained by the absolute amount of neuronally produced AbetaDutch42 and AbetaDutch40 and ratio between the two. We conclude that the absolute levels of Abeta in combination with the ratio of Abeta42 to Abeta40 play a key role in determining the cerebral compartment and brain region in which Abeta is deposited.

Induction of complement proteins in a mouse model for cerebral microvascular A beta deposition

The deposition of amyloid β-protein (Aβ) in cerebral vasculature, known as cerebral amyloid angiopathy (CAA), is a common pathological feature of Alzheimer's disease and related disorders. In familial forms of CAA single mutations in the Aβ peptide have been linked to the increase of vascular Aβ deposits accompanied by a strong localized activation of glial cells and elevated expression of neuroinflammatory mediators including complement proteins. We have developed human amyloid-β precursor protein transgenic mice harboring two CAA Aβ mutations (Dutch E693Q and Iowa D694N) that mimic the prevalent cerebral microvascular Aβ deposition observed in those patients, and the Swedish mutations (K670N/M671L) to increase Aβ production. In these Tg-SwDI mice, we have reported predominant fibrillar Aβ along microvessels in the thalamic region and diffuse plaques in cortical region. Concurrently, activated microglia and reactive astrocytes have been detected primarily in association with fibrillar cerebral microvascular Aβ in this model. Here we show that three native complement components in classical and alternative complement pathways, C1q, C3, and C4, are elevated in Tg-SwDI mice in regions rich in fibrillar microvascular Aβ. Immunohistochemical staining of all three proteins was increased in thalamus, hippocampus, and subiculum, but not frontal cortex. Western blot analysis showed significant increases of all three proteins in the thalamic region (with hippocampus) as well as the cortical region, except C3 that was below detection level in cortex. Also, in the thalamic region (with hippocampus), C1q and C3 mRNAs were significantly up-regulated. These complement proteins appeared to be expressed largely by activated microglial cells associated with the fibrillar microvascular Aβ deposits. Our findings demonstrate that Tg-SwDI mice exhibit elevated complement protein expression in response to fibrillar vascular Aβ deposition that is observed in patients with familial CAA.

Quantitative measurement of postural sway in mouse models of human neurodegenerative disease

Detection of motor dysfunction in genetic mouse models of neurodegenerative disease requires reproducible, standardized and sensitive behavioral assays. We have utilized a center of pressure (CoP) assay in mice to quantify postural sway produced by genetic mutations that affect motor control centers of the brain. As a positive control for postural instability, wild type mice were injected with harmaline, a tremorigenic agent, and the average areas of the 95% confidence ellipse, which measures 95% of the CoP trajectory values recorded in a single trial, were measured. Ellipse area significantly increased in mice treated with increasing doses of harmaline and returned to control values after recovery. We also examined postural sway in mice expressing mutations that mimic frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) (T-279, P301L or P301L-nitric oxide synthase 2 (NOS2)(-/-) mice) and that demonstrate motor symptoms. These mice were then compared with a mouse model of Alzheimer's disease (APPSwDI mice) that demonstrates cognitive, but not motor deficits. T-279 and P301L-NOS2(-/-) mice demonstrated a significant increase in CoP ellipse area compared with appropriate wild type control mice or to mice expressing the P301L mutation alone. In contrast, postural instability was significantly reduced in APPSwDI mice that have cognitive deficits but do not have associated motor deficits. The CoP assay provides a simple, sensitive and quantitative tool to detect motor deficits resulting from postural abnormalities in mice and may be useful in understanding the underlying mechanisms of disease.

Minocycline reduces microglial activation and improves behavioral deficits in a transgenic model of cerebral microvascular amyloid

Cerebral microvascular amyloid beta protein (Abeta) deposition and associated neuroinflammation is increasingly recognized as an important component leading to cognitive impairment in Alzheimer's disease and related cerebral amyloid angiopathy disorders. Transgenic mice expressing the vasculotropic Dutch/Iowa (E693Q/D694N) mutant human Abeta precursor protein in brain (Tg-SwDI) accumulate abundant cerebral microvascular fibrillar amyloid deposits and exhibit robust neuroinflammation. In the present study, we investigated the effect of the anti-inflammatory drug minocycline on Abeta accumulation, neuroinflammation, and behavioral deficits in Tg-SwDI mice. Twelve-month-old mice were treated with saline or minocycline by intraperitoneal injection every other day for a total of 4 weeks. During the final week of treatment, the mice were tested for impaired learning and memory. Brains were then harvested for biochemical and immunohistochemical analysis. Minocycline treatment did not alter the cerebral deposition of Abeta or the restriction of fibrillar amyloid to the cerebral microvasculature. Similarly, minocycline-treated Tg-SwDI mice exhibited no change in the levels of total Abeta, the ratios of Abeta40 and Abeta42, or the amounts of soluble, insoluble, or oligomeric Abeta compared with the saline-treated control Tg-SwDI mice. In contrast, the numbers of activated microglia and levels of interleukin-6 were significantly reduced in minocycline-treated Tg-SwDI mice compared with saline-treated Tg-SwDI mice. In addition, there was a significant improvement in behavioral performance of the minocycline-treated Tg-SwDI mice. These finding suggest that anti-inflammatory treatment targeted for cerebral microvascular amyloid-induced microglial activation can improve cognitive deficits without altering the accumulation and distribution of Abeta.

Ccr2 deficiency impairs microglial accumulation and accelerates progression of Alzheimer-like disease

Microglia are the principal immune cells of the brain. In Alzheimer disease, these brain mononuclear phagocytes are recruited from the blood and accumulate in senile plaques. However, the role of microglia in Alzheimer disease has not been resolved. Microglia may be neuroprotective by phagocytosing amyloid-beta (Abeta), but their activation and the secretion of neurotoxins may also cause neurodegeneration. Ccr2 is a chemokine receptor expressed on microglia, which mediates the accumulation of mononuclear phagocytes at sites of inflammation. Here we show that Ccr2 deficiency accelerates early disease progression and markedly impairs microglial accumulation in a transgenic mouse model of Alzheimer disease (Tg2576). Alzheimer disease mice deficient in Ccr2 accumulated Abeta earlier and died prematurely, in a manner that correlated with Ccr2 gene dosage, indicating that absence of early microglial accumulation leads to decreased Abeta clearance and increased mortality. Thus, Ccr2-dependent microglial accumulation plays a protective role in the early stages of Alzheimer disease by promoting Abeta clearance.

Early-onset subicular microvascular amyloid and neuroinflammation correlate with behavioral deficits in vasculotropic mutant amyloid beta-protein precursor transgenic mice

Cerebral microvascular amyloid beta protein (Abeta) deposition and associated neuroinflammation are increasingly recognized as an important component leading to cognitive impairment in Alzheimer's disease and related cerebral amyloid angiopathy (CAA) disorders. Transgenic mice expressing the vasculotropic Dutch/Iowa (E693Q/D694N) mutant human Abeta precursor protein in brain (Tg-SwDI) accumulate abundant cerebral microvascular fibrillar amyloid deposits exhibiting robust neuroinflammation. In the present study, we sought to determine if the unique amyloid pathology of Tg-SwDI mice was associated with deficits in behavioral performance. Behavioral performance tests that assessed a variety of psychological functions, including overall activity, motor ability, balance and strength, anxiety, impulsivity, and learning were conducted on homozygous Tg-SwDI mice and similarly aged wild-type C57Bl/6 mice. Our results indicate that Tg-SwDI mice were impaired in the performance of the Barnes maze learning and memory task at 3, 9, and 12 months of age. While more widespread cerebral microvascular Abeta pathology was evident in older animals, the evaluation of the Abeta pathology in the 3 months old transgenic animals revealed specific accumulation of microvascular amyloid and markedly elevated numbers of reactive astrocytes and activated microglia restricted to the subiculum. These findings indicate that early-onset accumulation of subicular microvascular amyloid and accompanying neuroinflammation correlates with impaired performance in the learning and memory task in Tg-SwDI mice.

Disturbed cross talk between insulin-like growth factor I and AMP-activated protein kinase as a possible cause of vascular dysfunction in the amyloid precursor protein/presenilin 2 mouse model of Alzheimer's disease

Cerebrovascular dysfunction appears to be involved in Alzheimer's disease (AD). In double mutant amyloid precursor protein/presenilin 2 (APP/PS2) mice, a transgenic model of AD, vessel homeostasis is disturbed. These mice have elevated levels of vascular endothelial growth factor (VEGF) and increased brain endothelial cell division but abnormally low brain vessel density. Examination of the potential involvement of insulin-like growth factor I (IGF-I) in these alterations revealed that treatment with IGF-I, a potent vessel growth promoter in the brain that ameliorates cognitive dysfunction in APP/PS2 mice, counteracted vascular dysfunction as follows: VEGF levels and endothelial cell proliferation were reduced, whereas vascular density was normalized. Notably, abnormally elevated brain IGF-I receptor levels in APP/PS2 mice were also normalized by IGF-I treatment. Analysis of possible processes involved in these alterations indicated that AMP-activated protein kinase (AMPK), a cell energy sensor that intervenes in angiogenic signaling and interacts with IGF-I, was also abnormally activated in APP/PS2 brains. Examination of the consequences of AMPK activation on cultured brain endothelial cells revealed increased VEGF levels together with enhanced endothelial cell proliferation and metabolism. Although these effects were also independently elicited by IGF-I, when both IGF-I and AMPK pathways were simultaneously activated on brain endothelial cells, VEGF production and endothelial cell proliferation ceased while cells remained metabolically activated (glucose use, peroxide production, and mitochondrial activity were elevated) and became more resistant to oxidative stress. Therefore, high IGF-I receptor and phosphoAMPK levels in APP/PS2 brains may reflect imbalanced IGF-I and AMPK angiogenic cross talk that could underlie vascular dysfunction in this model of AD.

Metallothionein-I and -III expression in animal models of Alzheimer disease

Previous studies have described altered expression of metallothioneins (MTs) in neurodegenerative diseases like multiple sclerosis (MS), Down syndrome, and Alzheimer's disease (AD). In order to gain insight into the possible role of MTs in neurodegenerative processes and especially in human diseases, the use of animal models is a valuable tool. Several transgenic mouse models of AD amyloid deposits are currently available. These models express human beta-amyloid precursor protein (AbetaPP) carrying different mutations that subsequently result in a varied pattern of beta-amyloid (Abeta) deposition within the brain. We have evaluated the expression of MT-I and MT-III mRNA by in situ hybridization in three different transgenic mice models of AD: Tg2576 (carrying AbetaPP harboring the Swedish K670N/M671L mutations), TgCRND8 (Swedish and the Indiana V717F mutations), and Tg-SwDI (Swedish and Dutch/Iowa E693Q/D694N mutations). MT-I mRNA levels were induced in all transgenic lines studied, although the pattern of induction differed between the models. In the Tg2576 mice MT-I was weakly upregulated in cells surrounding Congo Red-positive plaques in the cortex and hippocampus. A more potent induction of MT-I was observed in the cortex and hippocampus of the TgCRND8 mice, likely reflecting their higher amyloid plaques content. MT-I upregulation was also more significant in Tg-SwDI mice, especially in the subiculum and hippocampus CA1 area. Immunofluorescence stainings demonstrate that astrocytes and microglia/macrophages surrounding the plaques express MT-I&II. In general, MT-I regulation follows a similar but less potent response than glial fibrillary acidic protein (GFAP) expression. In contrast to MT-I, MT-III mRNA expression was not significantly altered in any of the models examined suggesting that the various MT isoforms may have different roles in these experimental systems, and perhaps also in human AD.

Expression profiles for macrophage alternative activation genes in AD and in mouse models of AD

Background

Microglia are associated with neuritic plaques in Alzheimer disease (AD) and serve as a primary component of the innate immune response in the brain. Neuritic plaques are fibrous deposits composed of the amyloid beta-peptide fragments (Abeta) of the amyloid precursor protein (APP). Numerous studies have shown that the immune cells in the vicinity of amyloid deposits in AD express mRNA and proteins for pro-inflammatory cytokines, leading to the hypothesis that microglia demonstrate classical (Th-1) immune activation in AD. Nonetheless, the complex role of microglial activation has yet to be fully explored since recent studies show that peripheral macrophages enter an "alternative" activation state.

Methods

To study alternative activation of microglia, we used quantitative RT-PCR to identify genes associated with alternative activation in microglia, including arginase I (AGI), mannose receptor (MRC1), found in inflammatory zone 1 (FIZZ1), and chitinase 3-like 3 (YM1).

Results

Our findings confirmed that treatment of microglia with anti-inflammatory cytokines such as IL-4 and IL-13 induces a gene profile typical of alternative activation similar to that previously observed in peripheral macrophages. We then used this gene expression profile to examine two mouse models of AD, the APPsw (Tg-2576) and Tg-SwDI, models for amyloid deposition and for cerebral amyloid angiopathy (CAA) respectively. AGI, MRC1 and YM1 mRNA levels were significantly increased in the Tg-2576 mouse brains compared to age-matched controls while TNFα and NOS2 mRNA levels, genes commonly associated with classical activation, increased or did not change, respectively. Only TNFα mRNA increased in the Tg-SwDI mouse brain. Alternative activation genes were also identified in brain samples from individuals with AD and were compared to age-matched control individuals. In AD brain, mRNAs for TNFα, AGI, MRC1 and the chitinase-3 like 1 and 2 genes (CHI3L1; CHI3L2) were significantly increased while NOS2 and IL-1β mRNAs were unchanged.

Conclusion

Immune cells within the brain display gene profiles that suggest heterogeneous, functional phenotypes that range from a pro-inflammatory, classical activation state to an alternative activation state involved in repair and extracellular matrix remodeling. Our data suggest that innate immune cells in AD may exhibit a hybrid activation state that includes characteristics of classical and alternative activation.

Mean age-of-onset of familial alzheimer disease caused by presenilin mutations correlates with both increased Abeta42 and decreased Abeta40

The varied ways in which mutations in presenilins (PSEN1 and PSEN2) affect amyloid b precursor protein (APP) processing in causing early-onset familial Alzheimer disease (FAD) are complex and not yet properly understood. Nonetheless, one useful diagnostic marker is an increased ratio of Ab42 to Ab40 (Ab42/Ab40) in patients' brain and biological fluids as well as in transgenic mice and cells. We studied Ab and APP processing for a set of nine clinical PSEN mutations on a novel and highly reproducible enzyme-linked immunosorbent assay (ELISA)-based in vitro method and also sought correlation with brain Ab analyzed by image densitometry and mass spectrometry. All mutations significantly increased Ab42/Ab40 in vitro by significantly decreasing Ab40 with accumulation of APP C-terminal fragments, a sign of decreased PSEN activity. A significant increase in absolute levels of Ab42 was observed for only half of the mutations tested. We also showed that age-of-onset of PSEN1-linked FAD correlated inversely with Ab42/Ab40 (r = -0.89; P = 0.001) and absolute levels of Ab42 (r = -0.83; P = 0.006), but directly with Ab40 levels (r = 0.69; P = 0.035). These changes also partly correlated with brain Ab42 and Ab40 levels. Together, our data suggested that Ab40 might be protective by perhaps sequestering the more toxic Ab42 and facilitating its clearance. Also, the in vitro method we describe here is a valid tool for assaying the pathogenic potential of clinical PSEN mutations in a molecular diagnostic setting.

Effects of anoxia and hypoxia on amyloid precursor protein processing in cerebral microvascular smooth muscle cells

Cerebral amyloid angiopathy (CAA) is characterized by the degeneration of cerebral microvascular smooth muscle cells (MV-SMC) and the replacement of normal vessel wall components by beta-amyloid (Abeta) protein. Little is known regarding the mechanisms of SMC degeneration in CAA. The effects of anoxia on the metabolism of the amyloid precursor protein (APP) were studied to investigate the MV-SMC response to anoxic stress and its possible role in the pathogenesis of CAA. MV-SMC exposed to chronic anoxia (24-48 hours) showed a decrease in expression of the 2 putative alpha-secretase enzymes, mature TACE (TNFalpha-converting enzyme) and ADAM10 (a disintegrin and metalloprotease). A concomitant decrease in the alpha-secretase cleavage products sAPPalpha and C83 was observed. Investigation of mRNA expression showed an increase in TACE and a sharp decrease in ADAM10 at 24 hours. Exposing MV-SMC to hypoxia (1% O2) revealed a different pattern of expression with no significant change in TACE protein, but an increase in TACE mRNA occurring at a later time point (48 hours). There was no change in ADAM10 mRNA expression, but a reduction in mature ADAM10 with a parallel increase in immature ADAM10 protein. These results demonstrate a requirement for oxygen in the regulation of the alpha-secretase pathway during APP metabolism.

Dexamethasone diminishes the pro-inflammatory and cytotoxic effects of amyloid beta-protein in cerebrovascular smooth muscle cells

BACKGROUND

Cerebrovascular deposition of fibrillar amyloid beta-protein (Abeta), a condition known as cerebral amyloid angiopathy (CAA), is a prominent pathological feature of Alzheimer's disease (AD) and related disorders. Accumulation of cerebral vascular fibrillar Abeta is implicated in promoting local neuroinflammation, causes marked degeneration of smooth muscle cells, and can lead to loss of vessel wall integrity with hemorrhage. However, the relationship between cerebral vascular fibrillar Abeta-induced inflammatory responses and localized cytotoxicity in the vessel wall remains unclear.Steroidal-based anti-inflammatory agents, such as dexamethasone, have been reported to reduce neuroinflammation and hemorrhage associated with CAA. Nevertheless, the basis for the beneficial effects of steroidal anti-inflammatory drug treatment with respect to local inflammation and hemorrhage in CAA is unknown. The cultured human cerebrovascular smooth muscle (HCSM) cell system is a useful in vitro model to study the pathogenic effects of Abeta in CAA. To examine the possibility that dexamethasone may influence CAA-induced cellular pathology, we investigated the effect of this anti-inflammatory agent on inflammatory and cytotoxic responses to Abeta by HCSM cells.

METHODS

Primary cultures of HCSM cells were treated with or without pathogenic Abeta in the presence or absence of the steroidal anti-inflammatory agent dexamethasone or the non-steroidal anti-inflammatory drugs indomethacin or ibuprofen. Cell viability was measured using a fluorescent live cell/dead cell assay. Quantitative immunoblotting was performed to determine the amount of cell surface Abeta and amyloid beta-protein precursor (AbetaPP) accumulation and loss of vascular smooth cell alpha actin. To assess the extent of inflammation secreted interleukin-6 (IL-6) levels were measured by ELISA and active matrix metalloproteinase-2 (MMP-2) levels were evaluated by gelatin zymography.

RESULTS

Pathogenic Abeta-induced HCSM cell death was markedly reduced by dexamethasone but was unaffected by ibuprofen or indomethacin. Dexamethasone had no effect on the initial pathogenic effects of Abeta including HCSM cell surface binding, cell surface fibril-like assembly, and accumulation of cell surface AbetaPP. However, later stage pathological consequences of Abeta treatment associated with inflammation and cell degeneration including increased levels of IL-6, activation of MMP-2, and loss of HCSM alpha actin were significantly diminished by dexamethasone but not by indomethacin or ibuprofen.

CONCLUSION

Our results suggest that although dexamethasone has no appreciable consequence on HCSM cell surface fibrillar Abeta accumulation it effectively reduces the subsequent pathologic responses including elevated levels of IL-6, MMP-2 activation, and depletion of HCSM alpha actin. Dexamethasone, unlike indomethacin or ibuprofen, may diminish these pathological processes that likely contribute to inflammation and loss of vessel wall integrity leading to hemorrhage in CAA.

Mechanism of cerebral beta-amyloid angiopathy: murine and cellular models

Cerebral amyloid angiopathy of the beta-amyloid type (Abeta-CAA) is a risk factor for hemorrhagic stroke and independently is believed to contribute to dementia. Naturally occurring animal models of Abeta-CAA are scarce and not well suited for the laboratory. To this end, a variety of transgenic mouse models have been developed that, similar to cerebral Abeta-amyloidosis in humans, develop either Abeta-CAA only or both Abeta-CAA and parenchymal amyloid, or primarily parenchymal amyloid with only scarce Abeta-CAA. The lessons learned from these mouse models are: i) Abeta-CAA alone is sufficient to induce cerebral hemorrhage and associate pathologies including neuroinflammation, ii) the origin of vascular amyloid is mainly neuronal, iii) Abeta-CAA results largely from impaired Abeta clearance, iv) a high ratio Abeta40:42 favors vascular over parenchymal amyloidosis, and v) genetic risk factors such as ApoE modulate Abeta-CAA and CAA-induced hemorrhages. Therapeutic strategies to inhibit Abeta-CAA are poor at the present time. Once Abeta-CAA is present current Abeta immunotherapy strategies have failed to clear vascular amyloid and even run the risk of serious side effects. Despite this progress in deciphering the pathomechanism of Abeta-CAA, with these first generation mouse models of Abeta-CAA, refining these models is needed and will help to understand the emerging importance of Abeta-CAA for dementia and to develop biomarkers and therapeutic strategies.

Neuroprotective properties of the innate immune system and bone marrow stem cells in Alzheimer's disease

The role of innate immunity and microglia in the brain is currently a matter of great debate and controversy. While several studies have provided evidence that they contribute to neurodegeneration in various animal models of brain diseases and traumas, others have shown that their inhibition may in contrast be associated with more damages or less repair. We have recently reported the existence of two different types of microglia, the resident and the newly differentiated microglia that derive from the bone marrow stem cells. Of great interest is the fact that blood-derived microglial cells are associated with amyloid plaques and these cells are able to prevent the formation or eliminate the presence of amyloid deposits in mice that develop the major hallmark of Alzheimer's disease (AD). These newly recruited cells are specifically attracted to the beta-amyloid 40/42 isoforms in vivo and they participate in the elimination of these proteins by phagocytosis. This review presents the mechanisms involved in the control of the innate immune response by microglia and the beneficial properties of such a response in brain diseases, such as AD.