Induction of clusterin/apoJ expression by histone deacetylase inhibitors in neural cells

A green-inspired method to prepare non-split high-density lipoprotein (HDL) carrier with anti-dysfunctional activities superior to reconstituted HDL

Numerous studies have demonstrated that dysfunctional high-density lipoprotein (HDL), especially oxidized HDL (OxHDL), could generate multifaceted in vivo proatherogenic effects that run counter to the antiatherogenic activities of HDL. It thereby reminded us that the in vitro reconstituted HDL (rHDL) might encountered with oxidation-induced dysfunction. Accordingly, a green-inspired method was employed to recycle non-split HDL from human plasma fraction IV. Then it was compared with rHDL formulated by an ethanol-injection method in terms of physicochemical properties and anti-dysfunctional activities. Results exhibited that rHDL oxidation extent exceeded that of non-split HDL evidenced by higher malondialdehy content, weaker inhibition on low-density lipoprotein (LDL) oxidation and more superoxide anion. The reserved paraoxonase-1 activity on non-split HDL could partially explain for above experimental results. In the targeted transport mechanism experiment, upon SR-BI receptor inhibition and/or CD36 receptor blockage, the almost unchanged non-split HDL uptake in lipid-laden macrophage indicated its negligible oxidation modification profile with regard to rHDL again. Furthermore, compared to rHDL, better macrophage biofunctions were observed for non-split HDL as illustrated by accelerated cholesterol efflux, inhibited oxidized LDL uptake and lessened cellular lipid accumulation. Along with decreased ROS secretion, obviously weakened oxidative stress damage was also detected under treatment with non-split HDL. More importantly, foam cells with non-split HDL-intervention inspired an enhanced inflammation repression and apoptosis inhibition effect. Collectively, the anti-dysfunctional activities of non-split HDL make it suitable as a potential nanocarrier platform for cardiovascular drug payload and delivery.

Involvement of Lipids in Alzheimer's Disease Pathology and Potential Therapies

Lipids constitute the bulk of the dry mass of the brain and have been associated with healthy function as well as the most common pathological conditions of the brain. Demographic factors, genetics, and lifestyles are the major factors that influence lipid metabolism and are also the key components of lipid disruption in Alzheimer's disease (AD). Additionally, the most common genetic risk factor of AD, APOE ϵ4 genotype, is involved in lipid transport and metabolism. We propose that lipids are at the center of Alzheimer's disease pathology based on their involvement in the blood-brain barrier function, amyloid precursor protein (APP) processing, myelination, membrane remodeling, receptor signaling, inflammation, oxidation, and energy balance. Under healthy conditions, lipid homeostasis bestows a balanced cellular environment that enables the proper functioning of brain cells. However, under pathological conditions, dyshomeostasis of brain lipid composition can result in disturbed BBB, abnormal processing of APP, dysfunction in endocytosis/exocytosis/autophagocytosis, altered myelination, disturbed signaling, unbalanced energy metabolism, and enhanced inflammation. These lipid disturbances may contribute to abnormalities in brain function that are the hallmark of AD. The wide variance of lipid disturbances associated with brain function suggest that AD pathology may present as a complex interaction between several metabolic pathways that are augmented by risk factors such as age, genetics, and lifestyles. Herewith, we examine factors that influence brain lipid composition, review the association of lipids with all known facets of AD pathology, and offer pointers for potential therapies that target lipid pathways.

Transcriptome level analysis in Rett syndrome using human samples from different tissues

The mechanisms of neuro-genetic disorders have been mostly investigated in the brain, however, for some pathologies, transcriptomic analysis in multiple tissues represent an opportunity and a challenge to understand the consequences of the genetic mutation. This is the case for Rett Syndrome (RTT): a neurodevelopmental disorder predominantly affecting females that is characterised by a loss of purposeful movements and language accompanied by gait abnormalities and hand stereotypies. Although the genetic aetiology is largely associated to Methyl CpG binding protein 2 (MECP2) mutations, linking the pathophysiology of RTT and its clinical symptoms to direct molecular mechanisms has been difficult.One approach used to study the consequences of MECP2 dysfunction in patients, is to perform transcriptomic analysis in tissues derived from RTT patients or Induced Pluripotent Stem cells. The growing affordability and efficiency of this approach has led to a far greater understanding of the complexities of RTT syndrome but is also raised questions about previously held convictions such as the regulatory role of MECP2, the effects of different molecular mechanisms in different tissues and role of X Chromosome Inactivation in RTT.In this review we consider the results of a number of different transcriptomic analyses in different patients-derived preparations to unveil specific trends in differential gene expression across the studies. Although the analyses present limitations- such as the limited sample size- overlaps exist across these studies, and they report dysregulations in three main categories: dendritic connectivity and synapse maturation, mitochondrial dysfunction, and glial cell activity.These observations have a direct application to the disorder and give insights on the altered mechanisms in RTT, with implications on potential diagnostic criteria and treatments.

Recent studies on cellular and molecular mechanisms in Alzheimer’s disease: focus on epigenetic factors and histone deacetylase

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders mainly affecting elderly people. It is characterized by progressive loss of memory and cognitive function. More than 95% of AD cases are related to sporadic or late-onset AD (LOAD). The etiology of LOAD is still unclear. It has been reported that environmental factors and epigenetic alterations play a significant role in AD pathogenesis. Furthermore, recently, genome-wide association studies (GWAS) identified 10 novel risk genes:ABCA7,APOE,BIN1,CD2AP,CD33,CLU,CR1,MS4A6A,MS4A4E, andPICALM, which play an important role for LOAD. In this review, the therapeutic approaches of AD by epigenetic modifications have been discussed. Nowadays, HDAC inhibitors have clinically proven its activity for epigenetic modifications. Furthermore, we try to establish the relationship between HDAC inhibitors and above mentioned LOAD risk genes. Finally, we are hoping that this review may open new area of research for AD treatment.

Epigenetics in Alzheimer's Disease: Perspective of DNA Methylation

Research over the years has shown that causes of Alzheimer's disease are not well understood, but over the past years, the involvement of epigenetic mechanisms in the developing memory formation either under pathological or physiological conditions has become clear. The term epigenetics represents the heredity of changes in phenotype that are independent of altered DNA sequences. Different studies validated that cytosine methylation of genomic DNA decreases with age in different tissues of mammals, and therefore, the role of epigenetic factors in developing neurological disorders in aging has been under focus. In this review, we summarized and reviewed the involvement of different epigenetic mechanisms especially the DNA methylation in Alzheimer's disease (AD), late-onset Alzheimer's disease (LOAD), familial Alzheimer's disease (FAD), and autosomal dominant Alzheimer's disease (ADAD). Down to the minutest of details, we tried to discuss the methylation patterns like mitochondrial DNA methylation and ribosomal DNA (rDNA) methylation. Additionally, we mentioned some therapeutic approaches related to epigenetics, which could provide a potential cure for AD. Moreover, we reviewed some recent studies that validate DNA methylation as a potential biomarker and its role in AD. We hope that this review will provide new insights into the understanding of AD pathogenesis from the epigenetic perspective especially from the perspective of DNA methylation.

Integrated late onset Alzheimer's disease (LOAD) susceptibility genes: Cholesterol metabolism and trafficking perspectives

Late onset Alzheimer's disease (LOAD) is the most common type of dementia and is characterized by decreased amyloid-β (Aβ) clearance from the brain. Cholesterol regulates the production and clearance of Aβ. Genome-wide association study (GWAS) suggests that at least 20 genes are associated with LOAD. The genes APOE, CLU, SORL1, PICALM, and BIN1 have a relatively high LOAD susceptibility. Additional experimental and bioinformatic approaches to integrate data from genetics, epigenetics, and molecular networks may further increase our understanding of LOAD in relation to cholesterol metabolism and trafficking.

The epigenetics of aging and neurodegeneration

Epigenetics is a quickly growing field encompassing mechanisms regulating gene expression that do not involve changes in the genotype. Epigenetics is of increasing relevance to neuroscience, with epigenetic mechanisms being implicated in brain development and neuronal differentiation, as well as in more dynamic processes related to cognition. Epigenetic regulation covers multiple levels of gene expression; from direct modifications of the DNA and histone tails, regulating the level of transcription, to interactions with messenger RNAs, regulating the level of translation. Importantly, epigenetic dysregulation currently garners much attention as a pivotal player in aging and age-related neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, where it may mediate interactions between genetic and environmental risk factors, or directly interact with disease-specific pathological factors. We review current knowledge about the major epigenetic mechanisms, including DNA methylation and DNA demethylation, chromatin remodeling and non-coding RNAs, as well as the involvement of these mechanisms in normal aging and in the pathophysiology of the most common neurodegenerative diseases. Additionally, we examine the current state of epigenetics-based therapeutic strategies for these diseases, which either aim to restore the epigenetic homeostasis or skew it to a favorable direction to counter disease pathology. Finally, methodological challenges of epigenetic investigations and future perspectives are discussed.

Plasma and platelet clusterin ratio is altered in Alzheimer's disease patients with distinct neuropsychiatric symptoms: findings from a pilot study

BACKGROUND

Clusterin protein in plasma has been found to differentiate between people with and without cognitive changes. However, these findings are not conclusive, despite the clusterin gene variations repeatedly being linked to increased risk for dementia, in particular Alzheimer's disease (AD).

METHOD

We analysed the level of clusterin in platelet and plasma in 25 subjects with a clinical diagnosis of AD and 26 subjects with no cognitive impairment.

RESULTS

In the current study, we report that the levels of both plasma and platelet clusterin are similar between AD and cognitively intact individuals. Clusterin plasma and platelet levels, as well as the plasma/platelet clusterin ratio, were not affected by age, gender, cognitive impairment and/or overt behavioural symptomatology, including presence of hallucinations and delusions, as well as depression. However, the plasma/platelet clusterin ratio was positively associated in with the Neuropsychiatric Inventory measures of agitation, apathy, irritability and motor aberrant behaviour in AD subjects.

CONCLUSION

Previous inconsistencies in reported blood clusterin levels may be a result of underlying non-cognitive symptoms in people with AD. Our findings need now to be replicated in larger group of dementia subjects.

Epigenetic regulation of cholesterol homeostasis

Although best known as a risk factor for cardiovascular disease, cholesterol is a vital component of all mammalian cells. In addition to key structural roles, cholesterol is a vital biochemical precursor for numerous biologically important compounds including oxysterols and bile acids, as well as acting as an activator of critical morphogenic systems (e.g., the Hedgehog system). A variety of sophisticated regulatory mechanisms interact to coordinate the overall level of cholesterol in cells, tissues and the entire organism. Accumulating evidence indicates that in additional to the more “traditional” regulatory schemes, cholesterol homeostasis is also under the control of epigenetic mechanisms such as histone acetylation and DNA methylation. The available evidence supporting a role for these mechanisms in the control of cholesterol synthesis, elimination, transport and storage are the focus of this review.

Epigenetic mechanisms in Alzheimer's disease: implications for pathogenesis and therapy

The vast majority of Alzheimer's disease (AD) are late-onset forms (LOAD) likely due to the interplay of environmental influences and individual genetic susceptibility. Epigenetic mechanisms, including DNA methylation, histone modifications and non-coding RNAs, constitute dynamic intracellular processes for translating environmental stimuli into modifications in gene expression. Over the past decade it has become increasingly clear that epigenetic mechanisms play a pivotal role in aging the pathogenesis of AD. Here, we provide a review of the major mechanisms for epigenetic modification and how they are reportedly altered in aging and AD. Moreover, we also consider how aberrant epigenetic modifications may lead to AD pathogenesis, and we review the therapeutic potential of epigenetic treatments for AD.

HDAC6 as a target for neurodegenerative diseases: what makes it different from the other HDACs?

Histone deacetylase (HDAC) inhibitors have been demonstrated to be beneficial in animal models of neurodegenerative diseases. Such results were mainly associated with the epigenetic modulation caused by HDACs, especially those from class I, via chromatin deacetylation. However, other mechanisms may contribute to the neuroprotective effect of HDAC inhibitors, since each HDAC may present distinct specific functions within the neurodegenerative cascades. Such an example is HDAC6 for which the role in neurodegeneration has been partially elucidated so far. The strategy to be adopted in promising therapeutics targeting HDAC6 is still controversial. Specific inhibitors exert neuroprotection by increasing the acetylation levels of α-tubulin with subsequent improvement of the axonal transport, which is usually impaired in neurodegenerative disorders. On the other hand, an induction of HDAC6 would theoretically contribute to the degradation of protein aggregates which characterize various neurodegenerative disorders, including Alzheimer’s, Parkinson’s and Hutington’s diseases. This review describes the specific role of HDAC6 compared to the other HDACs in the context of neurodegeneration, by collecting in silico, in vitro and in vivo results regarding the inhibition and/or knockdown of HDAC6 and other HDACs. Moreover, structure, function, subcellular localization, as well as the level of HDAC6 expression within brain regions are reviewed and compared to the other HDAC isoforms. In various neurodegenerative diseases, the mechanisms underlying HDAC6 interaction with other proteins seem to be a promising approach in understanding the modulation of HDAC6 activity.

Clusterin in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a ubiquitous multifunctional glycoprotein. Following its identification in 1983, clusterin was found to be clearly increased in Alzheimer's disease (AD). Later research demonstrated that clusterin could bind amyloid-beta (Abeta) peptides and prevent fibril formation, a hallmark of AD pathology. In addition to preventing excessive inflammation, intracellular clusterin was found to reduce apoptosis and oxidative stress. Although early studies were inconclusive, two recent large-scale genome-wide association studies (GWAS) independently identified variants within the clusterin gene as risk factors for developing AD. This review focuses on the characteristics of clusterin and possible mechanisms of its relationship to AD.

The role of clusterin in Alzheimer's disease: pathways, pathogenesis, and therapy

Genetic variation in clusterin gene, also known as apolipoprotein J, has been associated with Alzheimer's disease (AD) through replicated genome-wide studies, and plasma clusterin levels are associated with brain atrophy, baseline prevalence and severity, and rapid clinical progression in patients with AD, highlighting the importance of clusterin in AD pathogenesis. Emerging data suggest that clusterin contributes to AD through various pathways, including amyloid-β aggregation and clearance, lipid metabolism, neuroinflammation, and neuronal cell cycle control and apoptosis. Moreover, epigenetic regulation of the clusterin expression also seems to play an important role in the pathogenesis of AD. Emerging knowledge of the contribution of clusterin to the pathogenesis of AD presents new opportunities for AD therapy.

Downstream targets of methyl CpG binding protein 2 and their abnormal expression in the frontal cortex of the human Rett syndrome brain

Background

The Rett Syndrome (RTT) brain displays regional histopathology and volumetric reduction, with frontal cortex showing such abnormalities, whereas the occipital cortex is relatively less affected.

Results

Using microarrays and quantitative PCR, the mRNA expression profiles of these two neuroanatomical regions were compared in postmortem brain tissue from RTT patients and normal controls. A subset of genes was differentially expressed in the frontal cortex of RTT brains, some of which are known to be associated with neurological disorders (clusterin and cytochrome c oxidase subunit 1) or are involved in synaptic vesicle cycling (dynamin 1). RNAi-mediated knockdown of MeCP2 in vitro, followed by further expression analysis demonstrated that the same direction of abnormal expression was recapitulated with MeCP2 knockdown, which for cytochrome c oxidase subunit 1 was associated with a functional respiratory chain defect. Chromatin immunoprecipitation (ChIP) analysis showed that MeCP2 associated with the promoter regions of some of these genes suggesting that loss of MeCP2 function may be responsible for their overexpression.

Conclusions

This study has shed more light on the subset of aberrantly expressed genes that result from MECP2 mutations. The mitochondrion has long been implicated in the pathogenesis of RTT, however it has not been at the forefront of RTT research interest since the discovery of MECP2 mutations. The functional consequence of the underexpression of cytochrome c oxidase subunit 1 indicates that this is an area that should be revisited.

Regulation of CLU gene expression by oncogenes and epigenetic factors implications for tumorigenesis

In no other field has the function of clusterin (CLU) been more controversial than in cancer genetics. After more than 20 years of research, there is still uncertainty with regard to the role of CLU in human cancers. Some investigators believe CLU to be an oncogene, others-an inhibitor of tumorigenesis. However, owing to the recent efforts of several laboratories, the role of CLU in important cellular processes like proliferation, apoptosis, differentiation, and transformation is beginning to emerge. The "enigmatic" CLU is becoming less so. In this chapter, we will review the work of research teams interested in understanding how CLU is regulated by oncogenic signaling. We will discuss how and under what circumstances oncogenes and epigenetic factors modify CLU expression, with important consequences for mammalian tumorigenesis.

Genetic inactivation of ApoJ/clusterin: effects on prostate tumourigenesis and metastatic spread

ApoJ/Clusterin (CLU) is a heterodimeric protein localized in the nucleus, cytoplasm or secretory organelles and involved in cell survival and neoplastic transformation. Its function in human cancer is still highly controversial. In this study, we examined the prostate of mice in which CLU has been genetically inactivated. Surprisingly, we observed transformation of the prostate epithelium in the majority of CLU knockout mice. Either PIN (prostate intraepithelial neoplasia) or differentiated carcinoma was observed in 100 and 87% of mice with homozygous or heterozygous deletion of CLU, respectively. Crossing CLU knockout with TRAMP (prostate cancer prone) mice results in a strong enhancement of metastatic spread. Finally, CLU depletion causes tumourigenesis in female TRAMP mice, which are normally cancer free. Mechanistically, deletion of CLU induces activation of nuclear factor-kB, a potentially oncogenic transcription factor important for the proliferation and survival of prostate cells.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Clusterin, a haploinsufficient tumor suppressor gene in neuroblastomas

BACKGROUND

Clusterin expression in various types of human cancers may be higher or lower than in normal tissue, and clusterin may promote or inhibit apoptosis, cell motility, and inflammation. We investigated the role of clusterin in tumor development in mouse models of neuroblastoma.

METHODS

We assessed expression of microRNAs in the miR-17-92 cluster by real-time reverse transcription-polymerase chain reaction in MYCN-transfected SH-SY5Y and SH-EP cells and inhibited expression by transfection with microRNA antisense oligonucleotides. Tumor development was studied in mice (n = 66) that were heterozygous or homozygous for the MYCN transgene and/or for the clusterin gene; these mice were from a cross between MYCN-transgenic mice, which develop neuroblastoma, and clusterin-knockout mice. Tumor growth and metastasis were studied in immunodeficient mice that were injected with human neuroblastoma cells that had enhanced (by clusterin transfection, four mice per group) or reduced (by clusterin short hairpin RNA [shRNA] transfection, eight mice per group) clusterin expression. All statistical tests were two-sided.

RESULTS

Clusterin expression increased when expression of MYCN-induced miR-17-92 microRNA cluster in SH-SY5Y neuroblastoma cells was inhibited by transfection with antisense oligonucleotides compared with scrambled oligonucleotides. Statistically significantly more neuroblastoma-bearing MYCN-transgenic mice were found in groups with zero or one clusterin allele than in those with two clusterin alleles (eg, 12 tumor-bearing mice in the zero-allele group vs three in the two-allele group, n = 22 mice per group; relative risk for neuroblastoma development = 4.85, 95% confidence interval [CI] = 1.69 to 14.00; P = .005). Five weeks after injection, fewer clusterin-overexpressing LA-N-5 human neuroblastoma cells than control cells were found in mouse liver or bone marrow, but statistically significantly more clusterin shRNA-transfected HTLA230 cells (3.27%, with decreased clusterin expression) than control-transfected cells (1.53%) were found in the bone marrow (difference = 1.74%, 95% CI = 0.24% to 3.24%, P = .026).

CONCLUSIONS

We report, to our knowledge, the first genetic evidence that clusterin is a tumor and metastasis suppressor gene.

Hepatitis delta virus epigenetically enhances clusterin expression via histone acetylation in human hepatocellular carcinoma cells

Both isoforms of the hepatitis delta antigen (HDAg) of hepatitis delta virus (HDV) are highly associated with virus proliferation and may act as co-activators of cellular gene expression. Human hepatocellular carcinoma (HCC) cell line Huh7, which stably expresses HDAgs, was differentially screened and the results showed that clusterin gene expression was enhanced. The mechanisms for HDAg-mediated clusterin gene upregulation were investigated. Expression of HDAgs was associated with enhanced histone H3 acetylation within the clusterin promoter in a chromatin immunoprecipitation assay. Transient transfection of HDAg-expressing plasmids into Huh7 cells also enhanced clusterin expression and histone acetylation. Furthermore, HDV replication was associated with histone hyperacetylation and clusterin induction. The effect of increased clusterin expression was determined by a chemosensitivity assay with adriamycin treatment. These data indicated that HDV-induced clusterin protein increases cell survival potential. Thus, it is possible that epigenetic regulation by HDV contributes to a pathological outcome of hepatitis D/hepatitis B viral hepatitis and HCC.

Induction of GRP78 by valproic acid is dependent upon histone deacetylase inhibition

Valproic (2-propylpentanoic) acid is a commonly used drug in the treatment of bipolar disorder and epilepsy. The molecular mechanism that underlies its clinical efficacy remains controversial and is complicated by the broad range of intracellular effects of valproic acid, including its ability to inhibit histone deacetylase (HDAC) and induce protein chaperone expression. Here we show that an established HDAC inhibitor, trichostatin A, promotes ER chaperone expression in HEK293 cells. Furthermore, we use chemical derivatives of valproic acid to show that the ability to promote GRP78 levels directly correlates with the induction of histone H4 hyperacetylation. These results suggest that exposure to valproic acid enhances chaperone expression by a mechanism that involves histone hyperacetylation.

Epigenetic regulation of clusterin/apolipoprotein J expression in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is the leading cause of blindness worldwide. AMD is characterized by the deposition of drusen aggregates under the retinal pigment epithelium (RPE). Clusterin/apo J, a multifunctional secreted chaperone, is one of the major proteins accumulating in drusen deposits. The regulation of clusterin expression is not well characterized but the promoter of clusterin contains a CpG-rich methylation domain. Since aging affects both DNA methylation and histone acetylation status, the epigenetic regulation might have an important role in clusterin/apo J expression. Our purpose was to elucidate whether the induction of DNA hypomethylation with 5-aza-2'-deoxycytidine (AZA) and histone hyperacetylation with trichostatin A (TSA) could affect the clusterin transcription, protein levels, and secretion in retinal pigment epithelial cells. We observed that both TSA and AZA treatments induced a prominent increase in the expression levels of clusterin mRNA and protein in ARPE-19 cells, as well as in the secretion of clusterin protein. Furthermore, valproic acid, an antiepileptic drug and a recently identified inhibitor of histone deacetylases (HDAC), induced a significant increase in clusterin protein expression and secretion in retinal pigment epithelial cells. HDAC inhibitors are characterized as inhibitors of angiogenesis, and clusterin as a complement inhibitor. Our results indicate that epigenetic factors regulate the clusterin expression of RPE cells and thus might affect the pathogenesis of AMD via the inhibition of angiogenesis and inflammation.

Amyloid-β 1–42 induced endocytosis and clusterin/apoJ protein accumulation in cultured human astrocytes

Recent studies indicate that astrocytes may be the primary target of secreted amyloid-beta 1-42 peptides, with the neurotoxicity representing a secondary response to astrocytic stress. Our purpose was to clarify the astrocytic stress response induced by amyloid-beta peptides in human and rat astrocytes. Human amyloid-beta 1-42 peptides and fibrils induced the appearance of cytoplasmic vacuoles in normal human astrocytes (NHA) and CCFsttg1 astrocytoma cells. Vacuoles appeared 9-12h after the amyloid-beta exposure and remained present for several days. Rat primary neonatal astrocytes showed similar but less prominent vacuolar response. Human amyloid-beta peptides 1-16, 1-28, 10-20, 17-21 and 25-35 did not cause vacuole formation. Electron microscopic observations revealed large endocytic vacuoles containing fibrillar amyloid material. Stress marker analysis did not show any increase in protein levels of HSP70, HSP90, GRP78 and GRP94. However, the protein level of clusterin/apoJ, a secreted chaperone, was strongly increased both in NHA and CCFsttg1 astrocytes. Endocytic response associated with the accumulation of clusterin/apoJ protein suggests that clusterin/apoJ has a role in the clearance of amyloid-beta peptides.

5-Aza-2'-deoxycytidine and depsipeptide synergistically induce expression of BIK (BCL2-interacting killer)

DNA methylation and histone acetylation are main epigenetic events regulating gene expression, serving as anticancer drug targets. A combination of the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine with the histone deacetylase inhibitor depsipeptide synergistically induces apoptosis. To characterize genes involved in this process, we measured expression of 376 apoptosis-related genes with microarrays after treatment with the two inhibitors alone or in combination. The pro-apoptotic BIK (Bcl2-interacting killer) was the only gene synergistically upregulated in all four cancer cell lines tested (A549, PC-3, TK-10, and UO-31). BIK induction was confirmed by RT-PCR and Western blots. Histone acetylation of the BIK promoter region increased with depsipeptide treatment but was not further affected by 5-aza-2'-deoxycytidine. In summary, synergistic upregulation of pro-apoptotic BIK-previously shown to suppress tumor growth-appears to play a critical role in anticancer effects of 5-aza-2'-deoxycytidine plus depsipeptide.