Biomedical subjects

Lih-Fen Lue

Publications and source records attributed to Lih-Fen Lue.

11 recordsLinked to original sources

PubMed2006

Secretory PLA2-IIA: a new inflammatory factor for Alzheimer's disease.

Secretory phospholipase A2-IIA (sPLA2-IIA) is an inflammatory protein known to play a role in the pathogenesis of many inflammatory diseases. Although this enzyme has also been implicated in the pathogenesis of neurodegenerative diseases, there has not been a direct demonstration of its expression in diseased human brain. In this study, we show that sPLA2-IIA mRNA is up-regulated in Alzheimer's disease (AD) brains as compared to non-demented elderly brains (ND). We also report a higher percentage of sPLA2-IIA-immunoreactive astrocytes present in AD hippocampus and inferior temporal gyrus (ITG). In ITG, the majority of sPLA2-IIA-positive astrocytes were associated with amyloid beta (Abeta)-containing plaques. Studies with human astrocytes in culture demonstrated the ability of oligomeric Abeta1-42 and interleukin-1beta (IL-1beta) to induce sPLA2-IIA mRNA expression, indicating that this gene is among those induced by inflammatory cytokines. Since exogenous sPLA2-IIA has been shown to cause neuronal injury, understanding the mechanism(s) and physiological consequences of sPLA2-IIA upregulation in AD brain may facilitate the development of novel therapeutic strategies to inhibit the inflammatory responses and to retard the progression of the disease.

Journal Article↗

PubMed2005

Gene expression changes by amyloid beta peptide-stimulated human postmortem brain microglia identify activation of multiple inflammatory processes.

A central feature of the inflammatory pathology in Alzheimer's disease is activated microglia clustered around aggregated amyloid beta (Abeta) peptide-containing plaques. In vitro-cultured microglia can be activated to an inflammatory state by aggregated Abeta with the induction of a range of different neurotoxic factors and provide a model system for studying microglia Abeta interactions. Gene expression responses of human postmortem brain-derived microglia to aggregated Abeta were measured using whole genome microarrays to address the hypothesis that Abeta interactions with human microglia primarily induce proinflammatory genes and not activation of genes involved in Abeta phagocytosis and removal. The results demonstrated that Abeta activation of microglia induced a large alteration in gene transcription including activation of many proinflammatory cytokines and chemokines, most notably, interleukin (IL)-1beta, IL-8, and matrix metalloproteinases (MMP), including MMP1, MMP3, MMP9, MMP10, and MMP12. All of these genes could amplify ongoing inflammation, resulting in further neuronal loss. Changes in expression of receptors associated with Abeta phagocytosis did not match the changes in proinflammatory gene expression. Time-course gene expression profiling, along with real-time polymerase chain reaction validation of expression changes, demonstrated an acute phase of gene induction for many proinflammatory genes but also chronic activation for many other potentially toxic products. These chronically activated genes included indoleamine 2,3-dioxygenase and kynureninase, which are involved in formation of the neurotoxin quinolinic acid, and S100A8, a potential proinflammatory chemokine. These studies show that activation of microglia by Abeta induces multiple genes that could be involved in inflammatory responses contributing to neurodegenerative processes.

Aged↗

PubMed2005

Perturbations in calcium-mediated signal transduction in microglia from Alzheimer's disease patients.

Calcium-sensitive fluorescence microscopy has been used to study Ca2+-dependent signal transduction pathways in microglia obtained from Alzheimer's disease (AD) patients and non-demented (ND) individuals. Data were obtained from nine AD cases and seven ND individuals and included basal levels of intracellular Ca2+ [Ca2+]i, peak amplitudes (Delta[Ca2+]i) and time courses of adenosine triphosphate (ATP) responses and amplitudes of an initial transient response and a subsequent second component of Ca2+ influx through store-operated channels (SOC) induced by platelet-activating factor (PAF). Overall, AD microglia were characterized by significantly higher (20%) basal Ca2+ [Ca2+]i relative to ND cells. The Delta[Ca2+]i of ATP and initial phase of PAF responses, which reflect rapid depletion of Ca2+ from endoplasmic reticulum stores, were reduced by respective values of 63% and 59% in AD cells relative to amplitudes recorded from ND microglia. Additionally, AD microglia showed diminished amplitudes (reduction of 61%) of SOC-mediated Ca2+ entry induced by PAF and prolonged time courses (increase of 60%) of ATP responses with respect to ND microglia. We have generally replicated these results with exposure of human fetal microglia to beta amyloid (5 microM Abeta1-42 applied for 24 hr). Overall, these data indicate significant abnormalities are present in Ca2+-mediated signal transduction in microglia isolated from AD patients.

Adenosine Triphosphate↗

PubMed2005

Electrophysiological properties of human hypothalamic hamartomas.

The hypothalamic hamartoma (HH) is a rare developmental malformation often characterized by gelastic seizures, which are usually refractory to medical therapy. The mechanisms of epileptogenesis operative in this subcortical lesion are unknown. In this study, we used standard patch-clamp electrophysiological techniques combined with histochemical approaches to study individual cells from human HH tissue immediately after surgical resection. More than 90% of dissociated HH cells were small (6-9 microm soma) and exhibited immunoreactivity to the neuronal marker NeuN, and to glutamic acid decarboxylase, but not to glial fibrillary acidic protein. Under current-clamp, whole-cell recordings in single dissociated cells or in intact HH slices demonstrated typical neuronal responses to depolarizing and hyperpolarizing current injection. In some cases, HH cells exhibited a "sag-like" membrane potential change during membrane hyperpolarization. Interestingly, most HH cells exhibited robust, spontaneous "pacemaker-like" action potential firing. Under voltage-clamp, dissociated HH cells exhibited functional tetrodotoxin (TTX)-sensitive Na(+) and tetraethylammonium-sensitive K(+) currents. Both GABA and glutamate evoked whole-cell currents, with GABA exhibiting a peak current amplitude 10-fold greater than glutamate. These findings suggest that human HH tissues, associated with gelastic seizures, contained predominantly small GABAergic inhibitory neurons that exhibited intrinsic "pacemaker-like" behavior.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2005

CD40 signaling regulates innate and adaptive activation of microglia in response to amyloid beta-peptide.

Although deposition of amyloid beta-peptide (Abeta) as Abeta plaques involves activation of microglia-mediated inflammatory responses, activated microglia ultimately fail to clear Abeta plaques in the brains of either Alzheimer's disease (AD) patients or AD mouse models. Mounting evidence suggests that chronic microglia-mediated immune response during Abeta deposition etiologically contributes to AD pathogenesis by promoting Abeta plaque formation. However, the mechanisms that govern microglia response in the context of cerebral Abeta/beta-amyloid pathology are not well understood. We show that ligation of CD40 by CD40L modulates Abeta-induced innate immune responses in microglia, including decreased microglia phagocytosis of exogenous Abeta(1-42) and increased production of pro-inflammatory cytokines. CD40 ligation in the presence of Abeta(1-42) leads to adaptive activation of microglia, as evidenced by increased co-localization of MHC class II with Abeta. To assess their antigen-presenting cell (APC) function, cultured microglia were pulsed with Abeta(1-42) in the presence of CD40L and co-cultured with CD4(+) T cells. Under these conditions, microglia stimulate T cell-derived IFN-gamma and IL-2 production, suggesting that CD40 signaling promotes the APC phenotype. These data provide a mechanistic explanation for our previous work showing decreased microgliosis associated with diminished cerebral Abeta/beta-amyloid pathology when blocking CD40 signaling in transgenic Alzheimer's mice.

Alzheimer Disease↗

PubMed2004

Insulin-degrading enzyme in brain microvessels: proteolysis of amyloid {beta} vasculotropic variants and reduced activity in cerebral amyloid angiopathy.

The accumulation of amyloid beta (Abeta) in the walls of small vessels in the cerebral cortex is associated with diseases characterized by dementia or stroke. These include Alzheimer's disease, Down syndrome, and sporadic and hereditary cerebral amyloid angiopathies (CAAs) related to mutations within the Abeta sequence. A higher tendency of Abeta to aggregate, a defective clearance to the systemic circulation, and insufficient proteolytic removal have been proposed as mechanisms that lead to Abeta accumulation in the brain. By using immunoprecipitation and mass spectrometry, we show that insulin-degrading enzyme (IDE) from isolated human brain microvessels was capable of degrading (125)I-insulin and cleaved Abeta-(1-40) wild type and the genetic variants Abeta A21G (Flemish), Abeta E22Q (Dutch), and Abeta E22K (Italian) at the predicted sites. In microvessels from Alzheimer's disease cases with CAA, IDE protein levels showed a 44% increase as determined by sandwich enzyme-linked immunosorbent assay and Western blot. However, the activity of IDE upon radiolabeled insulin was significantly reduced in CAA as compared with age-matched controls. These results support the notion that a defect in Abeta proteolysis by IDE contributes to the accumulation of this peptide in the cortical microvasculature. Moreover they raise the possibility that IDE inhibition or inactivation is a pathogenic mechanism that may open novel strategies for the treatment of cerebrovascular Abeta amyloidoses.

Adult↗

PubMed2004

RAGE potentiates Abeta-induced perturbation of neuronal function in transgenic mice.

Receptor for Advanced Glycation Endproducts (RAGE), a multiligand receptor in the immunoglobulin superfamily, functions as a signal-transducing cell surface acceptor for amyloid-beta peptide (Abeta). In view of increased neuronal expression of RAGE in Alzheimer's disease, a murine model was developed to assess the impact of RAGE in an Abeta-rich environment, employing transgenics (Tgs) with targeted neuronal overexpression of RAGE and mutant amyloid precursor protein (APP). Double Tgs (mutant APP (mAPP)/RAGE) displayed early abnormalities in spatial learning/memory, accompanied by altered activation of markers of synaptic plasticity and exaggerated neuropathologic findings, before such changes were found in mAPP mice. In contrast, Tg mice bearing a dominant-negative RAGE construct targeted to neurons crossed with mAPP animals displayed preservation of spatial learning/memory and diminished neuropathologic changes. These data indicate that RAGE is a cofactor for Abeta-induced neuronal perturbation in a model of Alzheimer's-type pathology, and suggest its potential as a therapeutic target to ameliorate cellular dysfunction.

Alzheimer Disease↗

PubMed2004

ABAD directly links Abeta to mitochondrial toxicity in Alzheimer's disease.

Mitochondrial dysfunction is a hallmark of beta-amyloid (Abeta)-induced neuronal toxicity in Alzheimer's disease (AD). Here, we demonstrate that Abeta-binding alcohol dehydrogenase (ABAD) is a direct molecular link from Abeta to mitochondrial toxicity. Abeta interacts with ABAD in the mitochondria of AD patients and transgenic mice. The crystal structure of Abeta-bound ABAD shows substantial deformation of the active site that prevents nicotinamide adenine dinucleotide (NAD) binding. An ABAD peptide specifically inhibits ABAD-Abeta interaction and suppresses Abeta-induced apoptosis and free-radical generation in neurons. Transgenic mice overexpressing ABAD in an Abeta-rich environment manifest exaggerated neuronal oxidative stress and impaired memory. These data suggest that the ABAD-Abeta interaction may be a therapeutic target in AD.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2004

CCAAT/enhancer binding protein delta (C/EBPdelta) expression and elevation in Alzheimer's disease.

The CCAAT-enhancer binding protein (C/EBP) family of transcription factors, particularly C/EBPdelta, is well known to regulate or co-regulate a wide range of inflammatory mediators and mechanisms in the periphery, including interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). These cytokines, in turn, can induce C/EBPdelta expression and translocation to the nucleus as an active transcription factor. Because IL-1, IL-6, and TNF-alpha are increased in pathologically vulnerable regions of the Alzheimer's disease (AD) brain, we sought to determine if C/EBPdelta might be expressed in AD cortex. Immunohistochemistry of AD tissue sections revealed profuse C/EBPdelta staining of astrocytes, particularly reactive astrocytes surrounding amyloid beta peptide deposits. Substantially less immunoreactivity was observed in comparable sections from nondemented elderly control (ND) patients. These qualitative findings were consistent with quantitative Western blot densitometry results showing significant increases in C/EBPdelta in AD compared to ND cortex samples. Additional in vitro studies were pursued in order to characterize functional activity of C/EBPdelta in human elderly astrocytes. Consistent with a functionally active transcription factor, C/EBPdelta immunoreactivity predominated in the nucleus of cultured AD and ND astrocytes, and exhibited increases and nuclear localization, as determined by Western blots and electrophoretic mobility shifts after exposure to C/EBPdelta-inducing cytokines.

Active Transport, Cell Nucleus↗

PubMed2002

Modeling Alzheimer's disease immune therapy mechanisms: interactions of human postmortem microglia with antibody-opsonized amyloid beta peptide.

The induction of an antibody response to amyloid beta (Abeta) peptide has become a strategy for the treatment of Alzheimer's disease (AD). This has proven effective in reducing the plaque burden in transgenic mice that develop Abeta plaques similar to human AD patients. The mechanism for enhanced clearance of Abeta is partly due to the interaction of immunoglobulin Fcgamma receptor-expressing microglia and specific antibody-opsonized Abeta deposits. This interaction can stimulate Fcgamma receptor-mediated phagocytosis, but also results in inflammatory activation of these cells. Consequently, interaction of microglia with antibody-antigen complexes could exacerbate the existing inflammation in the brains of AD patients. In this study, we used substrate-bound Abeta and cultured human microglia from AD and non-demented cases to model interaction of microglia and antibody-opsonized plaques in AD brains. Enhanced production of tumor necrosis factor-alpha, macrophage colony stimulating factor, interleukin-10, and superoxide ions was detected. We also demonstrated enhanced uptake of opsonized Abeta by microglia, which was reduced significantly in the presence of excess IgG, indicative of the involvement of Fcgamma receptor-mediated mechanisms. Human microglia were shown in this study to express mRNA for Fcgamma receptors I, IIa, IIb, and III. The expression of Fcgamma receptor II was augmented by proinflammatory stimulation. These results suggest that initial interactions of human microglia with antibody-opsonized amyloid could result in increased inflammation. The consequence of this on inflammatory pathology in AD brains needs to be considered before immunization is used as a strategy for treating AD.

Alzheimer Disease↗

PubMed2002

Increased expression of the urokinase plasminogen-activator receptor in amyloid beta peptide-treated human brain microglia and in AD brains.

The urokinase plasminogen-activator receptor (uPAR) is involved in many processes in inflammation including the migration of inflammatory-associated cells to sites of tissue damage. This receptor, also designated as CD87, is induced in response to a range of stimuli and is a marker of macrophage activation. Its role in inflammatory responses of microglia in Alzheimer's disease (AD) has not been previously investigated. In this study we demonstrate that uPAR mRNA and protein expression is induced following incubation of human post-mortem brain-derived microglia with fibrillar amyloid beta (Abeta) peptide. This response was stronger with Abeta peptide than with other tested pro-inflammatory agents. Induction of uPAR surface expression by microglia was inhibited by the antioxidant N-acetyl-cysteine, indicating that this gene may be induced as a result of oxidative stress-related mechanisms. The significance of these findings to AD was investigated. UPAR protein levels were significantly increased in human brain tissues from the hippocampus, superior frontal gyrus and inferior temporal gyrus of AD cases compared with similar tissues from non-demented cases. Increased uPAR expression was not demonstrated in AD cerebellum. Finally, increased uPAR immunoreactivity was demonstrated in activated microglia in AD brain samples using two different antibodies to uPAR. These results provide a connection between the induction of oxidative stress in AD and microglial activation, and establish a possible involvement of uPAR in AD pathogenesis.

Aged↗