Augmented delayed infarct expansion and reactive astrocytosis after permanent focal ischemia in apolipoprotein E4 knock-in mice

Targeting apolipoprotein E and N-terminal amyloid β-protein precursor interaction improves cognition and reduces amyloid pathology in Alzheimer's mice

Apolipoprotein E (apoE) interaction with amyloid β-protein precursor (APP) has garnered attention as the therapeutic target for Alzheimer's disease (AD). Having discovered the apoE antagonist (6KApoEp) that blocks apoE binding to N-terminal APP, we tested the therapeutic potential of 6KApoEp on AD-relevant phenotypes in amyloid β-protein precursor/presenilin 1 (APP/PS1) mice that express each human apoE isoform of apoE2, apoE3, or apoE4 (designated APP/PS1/E2, APP/PS1/E3, or APP/PS1/E4 mice). At 12 months of age, we intraperitoneally administered 6KApoEp (250 μg/kg) or vehicle once daily for 3 months. At 15 months of age, blockage of apoE and N-terminal APP interaction by 6KApoEp treatment improved cognitive impairment in most tests of learning and memory, including novel object recognition and maze tasks in APP/PS1/E2, APP/PS1/E3, and APP/PS1/E4 mice versus each vehicle-treated mouse line and did not alter behavior in nontransgenic littermates. Moreover, 6KApoEp therapy ameliorated brain parenchymal and cerebral vascular β-amyloid deposits and decreased abundance of amyloid β-protein (Aβ) in APP/PS1/E2, APP/PS1/E3, and APP/PS1/E4 mice versus each vehicle-treated mouse group. Notably, the highest effect in Aβ-lowering by 6KApoEp treatment was observed in APP/PS1/E4 mice versus APP/PS1/E2 or APP/PS1/E3 mice. These effects occured through shifting toward lessened amyloidogenic APP processing due to decreasing APP abundance at the plasma membrane, reducing APP transcription, and inhibiting p44/42 mitogen-activated protein kinase phosphorylation. Our findings provide the preclinical evidence that 6KApoEp therapy aimed at targeting apoE and N-terminal APP interaction is a promising strategy and may be suitable for patients with AD carrying the apoE4 isoform.

Ferulic acid ameliorates cerebral infarction by activating Akt/mTOR/4E‑BP1/Bcl‑2 anti‑apoptotic signaling in the penumbral cortex following permanent cerebral ischemia in rats

The aim of the present study was to determine the effects of ferulic acid (FerA) administered immediately following the onset of permanent middle cerebral artery occlusion (MCAo) and then 7 days of ischemia, and also to explore the involvement of protein kinase B (Akt)‑induced signaling in the penumbral cortex. Immediately following the onset of MCAo, FerA was intravenously administered to rats at a dose of 60 mg/kg (FerA‑60 mg), 80 mg/kg (FerA‑80 mg), or 100 mg/kg (FerA‑100 mg). FerA‑80 mg and FerA‑100 mg effectively ameliorated cerebral infarction and neurological deficits 7 days following permanent cerebral ischemia. FerA‑80 mg and FerA‑100 mg significantly upregulated the expression of phospho‑Akt (p‑Akt), phospho‑mammalian target of rapamycin (p‑mTOR), and eukaryotic initiation factor 4E (eIF4E)‑binding protein 1 (4E‑BP1), and the phospho‑4E‑BP1 (p‑4E‑BP1)/4E‑BP1 and mitochondrial Bcl‑2/Bax ratios, and markedly downregulated the levels of cytochrome c‑, cleaved caspase‑3‑, and terminal deoxynucleotidyl transferase‑mediated dUTP‑biotin nick‑end labeling‑immunoreactive cells in the penumbral cortex at 7 days post‑ischemia. LY294002, a selective inhibitor of phosphoinositide 3‑kinase/Akt signaling, was administered 30 min prior to ischemia, which abrogated the upregulating effects of FerA‑100 mg on the expression of p‑Akt, p‑mTOR, 4E‑BP1, p‑4E‑BP1 and eIF4E, the mitochondrial Bcl‑2/Bax ratio and the ameliorating effect of FerA‑100 mg on cerebral infarction. FerA administered at doses of 80 and 100 mg/kg exerted beneficial effects against cerebral ischemia by activating Akt‑induced signaling. The effects of FerA at doses of 80 and 100 mg/kg on mitochondrial B‑cell lymphoma-2 (Bcl‑2)‑associated X protein‑related apoptosis were attributed to the activation of Akt/mTOR/4E‑BP1/Bcl‑2 anti‑apoptotic signaling, and eventually contributed to suppression of the cytochrome c/caspase‑3 activation pathway in the penumbral cortex 7 days following permanent cerebral ischemia.

Western-type diet modulates inflammatory responses and impairs functional outcome following permanent middle cerebral artery occlusion in aged mice expressing the human apolipoprotein E4 allele

Background

Numerous clinical trials in stroke have failed, most probably partially due to preclinical studies using young, healthy male rodents with little relevance to the heterogenic conditions of human stroke. Co-morbid conditions such as atherosclerosis and infections coupled with advanced age are known to contribute to increased risk of cerebrovascular diseases. Clinical and preclinical studies have shown that the E4 allele of human apolipoprotein (ApoE4) is linked to poorer outcome in various conditions of brain injury and neurodegeneration, including cerebral ischemia. Since ApoE is a known regulator of lipid homeostasis, we studied the impact of a high-cholesterol diet in aged mice in the context of relevant human ApoE isoforms on the outcome of focal brain ischemia.

Methods

Aged mice expressing human E3 and E4 isoforms of ApoE in C57BL/6J background and C57BL/6J mice fed on either a high-fat diet or a normal diet underwent permanent middle cerebral artery occlusion. The impact of a high-cholesterol diet was assessed by measuring the serum cholesterol level and the infarction volume was determined by magnetic resonance imaging. Sensorimotor deficits were assessed using an adhesive removal test and the findings were correlated with inflammatory markers.

Results

We show that expression of human ApoE4 renders aged mice fed with a western-type diet more susceptible to sensorimotor deficits upon stroke. These deficits are not associated with atherosclerosis but are accompanied with altered astroglial activation, neurogenesis, cyclooxygenase-2 immunoreactivity and increased plasma IL-6.

Conclusions

Our results support the hypothesis that ApoE alleles modify the inflammatory responses in the brain and the periphery, thus contributing to altered functional outcome following stroke.

Tetrandrine ameliorates cognitive impairment via inhibiting astrocyte-derived S100B activation in a rat model of chronic cerebral hypoperfusion

OBJECTIVES

To investigate the effects of tetrandrine (Tet) on cognitive impairment induced by chronic cerebral hypoperfusion and its potential anti-inflammatory mechanism by modulating the expression of S100B, interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS).

METHODS

Chronic cerebral hypoperfusion was induced by ligation of the bilateral common carotid arteries for 8 weeks. Rats were treated with Tet (10 mg/kg or 30 mg/kg) intraperitoneally every 3 days for 4 weeks. Cognitive function of rats was evaluated by the Morris water maze. Hematoxylin eosin (H & E) and Nissl staining were used to observe neuronal damage in the hippocampal CA1 region. Immunofluorescence, quantitative real-time polymerase chain reaction (QT-PCR), and western blot were performed to measure S100B, IL-1 beta, TNF-alpha, and iNOS levels in the CA1 region of chronic cerebral hypoperfusion rats.

RESULTS

The Tet-treated group significantly decreased the escape latency of chronic cerebral hypoperfusion rats in finding the hidden platform (P <0.05). Compared with the 2-VO (two-vessel occlusion) group, more neurons with regular morphology and/or Nissl bodies in the hippocampus were observed in the Tet-treated group, suggesting attenuated neuronal damage and degeneration. Additionally, S100B, IL-1 beta, TNF-alpha, and iNOS levels were significantly (P <0.05) decreased in the CA1 region of the chronic cerebral hypoperfusion affected rats treated with Tet.

CONCLUSION

Our results found that Tet could improve cognitive impairment in the chronic cerebral hypoperfusion rats. Tetrandrine may be a novel and promising candidate for future treatment and/or prevention of chronic cerebral hypoperfusion via inhibiting S100B activation and decreasing the expression of IL-1 beta, TNF-alpha, and iNOS in the hippocampal CA1 region.

Targeting S100B in Cerebral Ischemia and in Alzheimer's Disease

S100B is an EF-hand calcium-binding protein that exerts both intracellular and extracellular effects on a variety of cellular processes. The protein is predominantly expressed in the central nervous system by astrocytes, both physiologically and during the course of neurological disease. In the healthy adult brain and during development, constitutive S100B expression acts as a trophic factor to drive neurite extension and to referee neuroplasticity. Yet, when induced during central nervous system disease, the protein can take on maladaptive roles and thereby exacerbate brain pathology. Based on genetic and pharmacological lines of evidence, we consider such deleterious roles of S100B in two common brain pathologies: ischemic stroke and Alzheimer's disease (AD). In rodent models of ischemic brain damage, S100B is induced early on during the subacute phase, where it exacerbates gliosis and delayed infarct expansion and thereby worsens functional recovery. In mouse models of AD, S100B drives brain inflammation and gliosis that accelerate cerebral amyloidosis. Pharmacological inhibition of S100B synthesis mitigates hallmark pathologies of both brain diseases, opening the door for translational approaches to treat these devastating neurological disorders.

Overexpression of human S100B exacerbates cerebral amyloidosis and gliosis in the Tg2576 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common progressive dementia and is pathologically characterized by brain deposition of amyloid-beta (Abeta) peptide as senile plaques. Inflammatory and immune response pathways are chronically activated in AD patient brains at low levels, and likely play a role in disease progression. Like microglia, activated astrocytes produce numerous acute-phase reactants and proinflammatory molecules in the AD brain. One such molecule, S100B, is highly expressed by reactive astrocytes in close vicinity of beta-amyloid deposits. We have previously shown that augmented and prolonged activation of astrocytes has a detrimental impact on neuronal survival. Furthermore, we have implicated astrocyte-derived S100B as a candidate molecule responsible for this deleterious effect. To evaluate a putative relationship between S100B and AD pathogenesis, we crossed transgenic mice overexpressing human S100B (TghuS100B mice) with the Tg2576 mouse model of AD, and examined AD-like pathology. Brain parenchymal and cerebral vascular beta-amyloid deposits and Abeta levels were increased in bigenic Tg2576-huS100B mice. These effects were associated with increased cleavage of the beta-C-terminal fragment of amyloid precursor protein (APP), elevation of the N-terminal APP cleavage product (soluble APPbeta), and activation of beta-site APP cleaving enzyme 1. In addition, double transgenic mice showed augmented reactive astrocytosis and microgliosis, high levels of S100 expression, and increased levels of proinflammatory cytokines as early as 7-9 months of age. These results provide evidence that (over)-expression of S100B acts to accelerate AD-like pathology, and suggest that inhibiting astrocytic activation by blocking S100B biosynthesis may be a promising therapeutic strategy to delay AD progression..

Overexpression of human S100B exacerbates brain damage and periinfarct gliosis after permanent focal ischemia

BACKGROUND AND PURPOSE

We have previously demonstrated that augmented and prolonged activation of astrocytes detrimentally influences both the subacute and chronic phases of cerebral ischemia. Furthermore, we have suggested that the astrocyte-derived protein S100B may be important in these pathogenic events. However, the causal relationship between S100B and exacerbation of brain damage in vivo remains to be elucidated.

METHODS

Using transgenic mice overexpressing human S100B (Tg huS100B mice), we examined whether S100B plays a cardinal role in aggravation of brain damage after permanent middle cerebral artery occlusion (pMCAO).

RESULTS

Tg huS100B mice had significantly larger infarct volumes and worse neurological deficits at any time point examined after pMCAO as compared with CD-1 background strain-matched control mice. Infarct volumes in Tg huS100B mice were significantly increased from 1 to 3 and 5 days after pMCAO (delayed infarct expansion), whereas those in control mice were not significantly altered. S100, glial fibrillary acidic protein, and Iba1 burdens in the periinfarct area were significantly increased through to 7 days after pMCAO in Tg huS100B mice, whereas those in control mice reached a plateau at 3 days after pMCAO.

CONCLUSIONS

These results provide genetic evidence that overexpression of human S100B acts to exacerbate brain damage and periinfarct reactive gliosis (astrocytosis and microgliosis) during the subacute phase of pMCAO.

Apolipoprotein E and neurological disease: therapeutic potential and pharmacogenomic interactions

The apolipoprotein E (apoE) polymorphism is emerging as a uniquely important genetic modifier that affects functional outcome from both acute and chronic neurological injuries. Recent attention has focused on common denominator mechanisms by which apoE might affect brain injury and/or brain repair responses in clinically diverse diseases. Although endogenous apoE likely serves several adaptive functions in the injured CNS, there is growing evidence that its effect on modifying brain inflammatory responses and providing protection from excitotoxic injury may be central to its protective properties. A more complete understanding of the role that apoE plays in the injured brain has led to novel therapeutic strategies for both acute and chronic neurological disease.

Induction of platelet derived-endothelial cell growth factor in the brain after ischemia

OBJECTIVES

Platelet derived-endothelial cell growth factor (PD-ECGF) is a highly potent angiogenic factor. Although angiogenesis plays an active role in pathophysiology of stroke, the expression pattern of this molecule in ischemic brain has not been investigated. In the present study, therefore, we investigated the change of PD-ECGF expression in the brain after ischemia.

METHODS

Using male Wistar rats, the right middle cerebral artery was occluded by a nylon thread for 90 minutes. The animals were decapitated 3 hours, 1, 4 and 10 days after the reperfusion, and frozen sections were prepared. We then performed immunohistochemistry for PD-ECGF and identified the cell phenotype which strongly expressed it by fluorescent double staining.

RESULTS

In the sham-operated brain, only small numbers of cells slightly expressed PD-ECGF. The number of positively stained cells increased at the peri-ischemic area from hour 3 of reperfusion. Not only small-sized cells but also large-sized cells became stained. The number of stained cells further increased, and peaked at day 4 for large-sized cells and at day 10 as to small-sized cells. Fluorescent double staining revealed that both large-sized and small-sized cells were neurons, indicating that neurons are the main source of PD-ECGF production in the ischemic brain.

DISCUSSION

PD-ECGF has a strong angiogenic property without vascular permeability increasing effect. This molecule may have a therapeutic potential for ischemic stroke treatment.

MRI monitoring of focal cerebral ischemia in peroxisome proliferator-activated receptor (PPAR)-deficient mice

Peroxisome proliferator-activated receptors (PPARs) are a potential target for neuroprotection in focal ischemic stroke. These nuclear receptors have major effects in lipid metabolism, but they are also involved in inflammatory processes. Three PPAR isotypes have been identified: alpha, beta (or delta) and gamma. The development of PPAR transgenic mice offers a promising tool for prospective therapeutic studies. This study used MRI to assess the role of PPARalpha and PPARbeta in the development of stroke. Permanent middle cerebral artery occlusion induced focal ischemia in wild-type, PPARalpha-null mice and PPARbeta-null mice. T(2)-weighted MRI was performed with a 7 T MRI scan on day 0, 1, 3, 7 and 14 to monitor lesion growth in the various genotypes. General Linear Model statistical analysis found a significant difference in lesion volume between wild-type and PPAR-null mice for both alpha and beta isotypes. These data validate high-resolution MRI for monitoring cerebral ischemic lesions, and confirm the neuroprotective role of PPARalpha and PPARbeta in the brain.

A review of genetic causes of ischemic and hemorrhagic stroke

Genetic predisposition to stroke has been proven in animal models and in humans. Unraveling the genetic factors that play a role in common stroke is very difficult, as the causation of stroke is multifactorial (a combination of environmental and genetic risk factors) and the genetic part is very complex (polygenic, multiple genes play a role). Many common risk factors for stroke like diabetes and arterial hypertension are partly inherited, so many genetic loci contribute more or less to the stroke phenotype. Recent knowledge is increased for monogenic forms of stroke, such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy and the amyloid angiopathies. These disorders can serve as models to study environmental or genetic factors that contribute also to the common forms of stroke. Animal model of stroke can also provide valuable information on genetic factors involved in stroke predisposition. In this review, the focus lies on monogenic forms of stroke that can serve as models to study the more common phenotypes.

Arundic Acid Ameliorates Cerebral Amyloidosis and Gliosis in Alzheimer Transgenic Mice

Like microglia, reactive astrocytes produce a myriad of neurotoxic substances in various brain pathologies, such as Alzheimer's disease (AD), trauma, and cerebral ischemia. Among the numerous products of reactive astrocytes, attention has recently been directed toward the possible detrimental role of S100B, because the protein has been shown to be highly expressed along with the progression of brain damage and to exert neurotoxic effects at high concentrations. The present study aimed to examine the possible role of astrocyte-derived S100B in the progression of cerebral amyloidosis and gliosis in transgenic mice overproducing mutant amyloid precursor protein (Tg APP(sw) mice, line 2576). For this purpose, arundic acid (Ono Pharmaceutical Co., Ltd., Mishima, Osaka, Japan), which is known to negatively regulate astrocyte synthesis of S100B, was orally administered to Tg APP(sw) mice for 6 months from 12 months of age, and the effects of the agent on the above parameters were examined. Here, we report that beta-amyloid deposits along with amyloid-beta peptide/S100B levels, as well as beta-amyloid plaque-associated reactive gliosis (astrocytosis and microgliosis), were significantly ameliorated in arundic acid-treated Tg APP(sw) mice relative to vehicle-treated Tg APP(sw) mice at 19 months of age. Based on the above results, arundic acid is considered to deserve further exploration as a promising therapeutic agent for AD.

APOE-epsilon4 predisposes to cognitive dysfunction following uncomplicated carotid endarterectomy

BACKGROUND

Between 9% and 23% of patients undergoing otherwise uncomplicated carotid endarterectomy (CEA) develop subtle cognitive decline 1 month postoperatively. The APOE-epsilon4 allele has been associated with worse outcome following stroke.

OBJECTIVE

To investigate the ability of APOE-epsilon4 to predict post-CEA neurocognitive dysfunction.

METHODS

Seventy-five patients with CEA undergoing elective CEA were prospectively recruited in this nested cohort study and demographic variables were recorded. Patients were evaluated before and 1 month after surgery with a standard battery of five neuropsychological tests. APOE genotyping was performed by restriction fragment length polymorphism analysis in all patients. Neuropsychological deficits were identified by comparing changes (before to 1 month post-operation) in individual performance on the test battery. Logistic regression was performed for APOE-epsilon4 and previously identified risk factors.

RESULTS

Twelve of 75 (16%) CEA patients possessed the APOE-epsilon4 allele. Eight of 75 (11%) patients experienced neurocognitive dysfunction on postoperative day 30. One month post-CEA, APOE-epsilon4-positive patients were more likely to be cognitively injured (42%) than APOE-epsilon4-negative patients (5%) (p = 0.002). In multivariate analysis, the presence of the APOE-epsilon4 allele increased the risk of neurocognitive dysfunction at 1 month 62-fold (62.28, 3.15 to 1229, p = 0.007). Diabetes (51.42, 1.94 to 1363, p = 0.02), and obesity (24.43, 1.41 to 422.9, p = 0.03) also predisposed to injury.

CONCLUSION

The APOE-epsilon4 allele is a robust independent predictor of neurocognitive decline 1 month following CEA.

Modulation of astrocytic activation by arundic acid (ONO-2506) mitigates detrimental effects of the apolipoprotein E4 isoform after permanent focal ischemia in apolipoprotein E knock-in mice

Using homozygous human apolipoprotein E2 (apoE2) (2/2)-, apoE3 (3/3)-, or apoE4 (4/4)-knock-in (KI) mice, we have shown that delayed infarct expansion and reactive astrocytosis after permanent middle cerebral artery occlusion (pMCAO) were markedly exacerbated in 4/4-KI mice as compared with 2/2- or 3/3-KI mice. Here, we probed the putative causal relationship between enhanced astrocytic activation and exacerbation of brain damage in 4/4-KI mice using arundic acid (ONO-2506, Ono Pharmaceutical Co. Ltd), which is known to oppose astrocytic activation through its inhibitory action on S100B synthesis. In all of the KI mice, administration of arundic acid (10 mg/kg day, intraperitoneal, started immediately after pMCAO) induced significant amelioration of brain damage at 5 days after pMCAO in terms of infarct volumes (results expressed as the mean infarct volume (mm(3)) +/-1s.d. in 2/2-, 3/3-, or 4/4-KI mice in the vehicle groups: 16 +/- 2, 15 +/- 2, or 22 +/- 2; in the arundic acid groups: 11 +/- 2 (P < 0.001), 11 +/- 2 (P < 0.001), or 12 +/- 2 (P < 0.001), as compared with the vehicle groups), neurologic deficits, and S100/glial fibrillary acidic protein burden in the peri-infarct area. The beneficial effects of arundic acid were most pronounced in 4/4-KI mice, wherein delayed infarct expansion together with deterioration of neurologic deficits was almost completely mitigated. The above results support the notion that the apoE4 isoform exacerbates brain damage during the subacute phase of pMCAO through augmentation of astrocytic activation. Thus, pharmacological modulation of astrocytic activation may confer a novel therapeutic strategy for ischemic brain damage, particularly in APOE epsilon4 carriers.