Silke Vogelgesang

Deposition of Alzheimer's β-amyloid is inversely correlated with P-glycoprotein expression in the brains of elderly non-demented humans

Deposition of the beta-amyloid peptide (Abeta) in the brain occurs during normal ageing and is substantially accelerated in patients with Alzheimers disease. Since Abeta is continuously produced in the brain, it has been suggested that a clearance mechanism should exist to prevent its accumulation and subsequent aggregation. Until now, little attention has been paid to the possible role of P-glycoprotein (P-gp), a member of the ATP binding cassette superfamily of transporter proteins, in the pathogenesis of Alzheimers disease. A recent study demonstrated that Abeta40 and Abeta42 interact directly with P-gp. We therefore hypothesized that Abeta accumulation in the brain would correlate inversely with the degree of vascular P-gp expression. To study early pathogenetic factors that influence the deposition of Abeta, at routine autopsies, brain tissue samples were taken from 243 non-demented subjects who died between the ages of 50 and 91 years. Vascular P-gp expression and the number of Abeta40- and Abeta42-positive senile plaques were assessed immunohistochemically in the medial temporal lobe. In addition, the apolipoprotein E (apoE) genotypes, as well as multiple drug resistance gene 1 ( ) polymorphisms (exon 2, G-1A; exon 21, G2677T/A; exon 26, C3436T), were also determined for each case. P-gp expression was not correlated with genotypes, but we found a significant inverse correlation between P-gp expression and the deposition of both Abeta40 and Abeta42 in the medial temporal lobe. Our results provide the first evidence in human brain tissue that the accumulation of Abeta may be influenced by the expression of P-gp in blood vessels, and suggest that P-gp may influence the elimination of Abeta from brain.

MDR1-P-Glycoprotein (ABCB1) Mediates Transport of Alzheimer’s Amyloid-β Peptides—Implications for the Mechanisms of Aβ Clearance at the Blood–Brain Barrier

Amyloid‐β (Aβ) is the major component of the insoluble amyloid plaques that accumulate intracerebrally in patients with Alzheimer’s disease (AD). It has been suggested that MDR1‐P‐glycoprotein (ABCB1, P‐gp) plays a substantial role in the elimination of Aβ from the brain. In the present study, MDR1‐transfected LLC cells growing in a polarized cell layer were used to characterize the interaction of Aβ1‐40/1‐42 with P‐gp. In this system, P‐gp‐mediated transport can be followed by the efflux of the fluorescent dye rhodamine‐123, or of Aβ itself from the cells into the apical extracellular space. Aβ significantly decreased the apical efflux of rhodamine‐123, and the transcellular transport of Aβ1‐40 and Aβ1‐42 into the apical chamber could be demonstrated using both ELISA and fluorescence (FITC)‐labeled peptides. This transport was inhibited by a P‐gp modulator. Furthermore, ATP‐dependent, P‐gp‐mediated transport of the fluorescence‐labeled peptides could be demonstrated in isolated, inside‐out membrane vesicles. Our data support the concept that P‐gp is important for the clearance of Aβ from brain, and thus may represent a target protein for the prevention and/or treatment of neurodegenerative disorders such as AD.

The Role of P-glycoprotein in Cerebral Amyloid Angiopathy; Implications for the Early Pathogenesis of Alzheimer’s Disease

It has been shown in vitro that beta-amyloid (Abeta) is transported by P-glycoprotein (P-gp). Previously, we demonstrated that Abeta immunoreactivity is significantly elevated in brain tissue of individuals with low expression of P-gp in vascular endothelial cells. These findings led us to hypothesize that P-gp might be involved in the clearance of Abeta in normal aging and particularly in Alzheimers disease (AD). As we were interested in the early pathogenesis of Abeta deposition, we studied the correlation between cerebral amyloid angiopathy (CAA) and P-gp expression in brain tissue samples from 243 non-demented elderly cases (aged 50 to 91 years). We found that endothelial P-gp and vascular Abeta were never colocalized, i.e., vessels with high P-gp expression showed no Abeta deposition in their walls, and vice versa. Abeta deposition occurred first in arterioles where P-gp expression was primarily low, and disappeared completely with the accumulation of Abeta. At this early stage, P-gp was upregulated in capillaries, suggesting a compensatory mechanism to increase Abeta clearance from the brain. Capillaries were usually affected only at later stages of CAA, at which point P-gp was lost even in these vessels. We hypothesize that Abeta clearance may be altered in individuals with diminished P-gp expression due, e.g., to genetic or environmental effects (such as drug administration). The impairment of Abeta clearance could lead to the accumulation and earlier deposition of Abeta, both in the walls of blood vessels and in the brain parenchyma, thus elevating the risk of CAA and AD.

Expression and Localization of P-glycoprotein in Human Heart: Effects of Cardiomyopathy

ABC-type transport proteins, such as P-glycoprotein (P-gp), modify intracellular concentrations of many substrate compounds. They serve as functional barriers against entry of xenobiotics (e.g., in the gut or the blood-brain barrier) or contribute to drug excretion. Expression of transport proteins in the heart could be an important factor modifying cardiac concentrations of drugs known to be transported by P-gp (e.g., β-blockers, cardiac glycosides, doxorubicin). We therefore investigated the expression and localization of P-gp in human heart. Samples from 15 human hearts (left ventricle; five non-failing, five dilated cardiomyopathy, and five ischemic cardiomyopathy) were analyzed for expression of P-gp using real-time RT-PCR, immunohistochemistry, and in situ hybridization. Immunohistochemistry revealed expression of P-gp in endothelium of both arterioles and capillaries of all heart samples. Although P-gp mRNA was detected in all samples, its expression level was significantly reduced in patients with dilated cardiomyopathy. We describe variable expression of P-gp in human heart and its localization in the endothelial wall. Thus, intracardiac concentrations of various compounds may be modified, depending on the individual P-gp level.

The ATP-binding cassette transporter ABCG2 (BCRP), a marker for side population stem cells, is expressed in human heart

Efforts to improve severely impaired myocardial function include transplantation of autologous hematopoietic side population (SP) stem cells. The transmembrane ABC-type (ATP binding cassette) half-transporter ABCG2 (BCRP) serves as a marker protein for SP cell selection. We have recently shown that other ABC transport proteins such as ABCB1 and ABCC5 are differentially expressed in normal and diseased human heart. Here we investigated localization and individual ABCG2 expression in 15 ventricular (including 10 cardiomyopathic) and 51 auricular heart tissue samples using immunohistochemistry, confocal laser scanning fluorescence microscopy, and real-time RT-PCR. Individual genotypes were assigned using PCR–restriction fragment length polymorphism (RFLP) analysis and subsequently correlated to ABCG2 mRNA levels. ABCG2 was localized in endothelial cells of capillaries and arterioles of all samples. Ventricular samples from cardiomyopathic hearts exhibited significantly increased levels of ABCG2 mRNA (ABCG2/18S rRNA: 1.08 ± 0.30 × 10−7; p = 0.028 (dilative cardiomyopathy) and 1.16 ± 0.46 × 10−7; p = 0.009 (ischemic cardiomyopathy) compared with 0.44 ± 0.26 × 10−7 in nonfailing hearts). The individual haplotypes were not associated with altered mRNA expression. ABCG2 is variably expressed in endothelial cells of human heart, where it may function as a protective barrier against cardiotoxic drugs such as anthracyclines or mitoxantrone. ABCG2 expression is induced in dilative and ischemic cardiomyopathies.

Apolipoprotein E4 promotes the early deposition of Aβ42 and then Aβ40 in the elderly

Abstract The apolipoprotein Eɛ4 allele (ApoEɛ4) is associated with a selective increase in deposition of the 40-amino acid form of the β-amyloid peptide (Aβ40) in end-stage Alzheimer’s disease. To determine how apoE genotype affects the early events in β-amyloid pathogenesis, we analyzed the medial temporal lobes of 244 elderly persons who were not clinically demented using antibodies selective for the C termini of Aβ40 and Aβ42. We found that: (1) the number of both Aβ42- and Aβ40-positive senile plaques increase with age; (2) Aβ42 appears at younger ages, and in more amyloid deposits, than does Aβ40 in all ApoE groups; (3) when compared at similar ages, older persons with ApoEɛ4 are more likely to have Aβ42- and Aβ40-immunoreactive deposits than are persons without ApoEɛ4; (4) Aβ40-containing plaques arise at least a decade later than do Aβ42 plaques, and are seldom found in the medial temporal lobe of older persons lacking ApoEɛ4; and (5) in the absence of overt Alzheimer’s disease, cerebral amyloid angiopathy is rare in the elderly, but in our sample was significantly augmented in ApoEɛ4 homozygotes. We conclude that ApoEɛ4 hastens the onset of Aβ42 deposition in the senescent brain, which in turn fosters the earlier evolution of fibrillar, Aβ40-positive plaques, thereby increasing the risk of Alzheimer’s disease.

Digital necroses and vascular thrombosis in severe spinal muscular atrophy

Infantile spinal muscular atrophy (SMA) caused by homozygous SMN1 gene deletions/mutations is characterized by neuronal loss and axonopathy of motor neurons. We report two unrelated patients with severe SMA type I who had only one SMN2 copy and developed ulcerations and necroses of the fingers and toes. Sural nerve biopsy was normal in patient 1, whose affected skin displayed necroses and thrombotic occlusions of small vessels. Corresponding to a mouse model and other patients with similar findings, we believe that severe survival motor neuron (SMN) deficiency may present as vasculopathy. Muscle Nerve 42: 144–147, 2010

Good interobserver and intraobserver agreement in the evaluation of the new ILAE classification of focal cortical dysplasias

Purpose:  An International League Against Epilepsy (ILAE) consensus classification system for focal cortical dysplasias (FCDs) has been published in 2011 specifying clinicopathologic FCD variants. The aim of the present work was to microscopically assess interobserver agreement and intraobserver reproducibility for FCD categories among an international group of neuropathologists with different levels of experience and access to epilepsy surgery tissue.

Beta-Amyloid Downregulates MDR1-P-Glycoprotein (Abcb1) Expression at the Blood-Brain Barrier in Mice

Neurovascular dysfunction is an important component of Alzheimers disease, leading to reduced clearance across the blood-brain barrier and accumulation of neurotoxic β-amyloid (Aβ) peptides in the brain. It has been shown that the ABC transport protein P-glycoprotein (P-gp, ABCB1) is involved in the export of Aβ from the brain into the blood. To determine whether Aβ influences the expression of key Aβ transporters, we studied the effects of 1-day subcutaneous Aβ1-40 and Aβ1-42 administration via Alzet mini-osmotic pumps on P-gp, BCRP, LRP1, and RAGE expression in the brain of 90-day-old male FVB mice. Our results demonstrate significantly reduced P-gp, LRP1, and RAGE mRNA expression in mice treated with Aβ1-42 compared to controls, while BCRP expression was not affected. The expression of the four proteins was unchanged in mice treated with Aβ1-40 or reverse-sequence peptides. These findings indicate that, in addition to the age-related decrease of P-gp expression, Aβ1-42 itself downregulates the expression of P-gp and other Aβ-transporters, which could exacerbate the intracerebral accumulation of Aβ and thereby accelerate neurodegeneration in Alzheimers disease and cerebral β-amyloid angiopathy.

Association of ABCB1 genetic variants 3435C>T and 2677G>T to ABCB1 mRNA and protein expression in brain tissue from refractory epilepsy patients

Purpose: There is evidence from studies in rodents that P‐glycoprotein (P‐gp) overexpression is implicated in the causation of refractory epilepsy. Genetic variants in the human ABCB1 (MDR1) gene were shown to affect the expression levels of the transporter in various tissues and to be associated with refractory epilepsy. However, the effect of the genetic variants on the P‐gp level in epileptogenic brain tissue is poorly investigated. In the present study, we examined the impact of putatively functional polymorphisms 3435C>T and 2677G>T in the ABCB1 gene on the ABCB1 mRNA expression and P‐gp content in human brain tissue from epileptogenic foci of the patients with refractory epilepsy.