Modulation of apolipoprotein D and apolipoprotein E expression in rat hippocampus after entorhinal cortex lesion

Association of TMEM106B with Cortical APOE Gene Expression in Neurodegenerative Conditions

The e4 allele of the apolipoprotein E gene is the strongest genetic risk factor for sporadic Alzheimer's disease. Nevertheless, how APOE is regulated is still elusive. In a trans-eQTL analysis, we found a genome-wide significant association between transmembrane protein 106B (TMEM106B) genetic variants and cortical APOE mRNA levels in human brains. The goal of this study is to determine whether TMEM106B is mis-regulated in Alzheimer's disease or in other neurodegenerative conditions. Available genomic, transcriptomic and proteomic data from human brains were downloaded from the Mayo Clinic Brain Bank and the Religious Orders Study and Memory and Aging Project. An in-house mouse model of the hippocampal deafferentation/reinnervation was achieved via a stereotaxic lesioning surgery to the entorhinal cortex, and mRNA levels were measured using RNAseq technology. In human temporal cortices, the mean TMEM106B expression was significantly higher in Alzheimer's disease compared to cognitively unimpaired individuals. In the mouse model, hippocampal Tmem106b reached maximum levels during the early phase of reinnervation. These results suggest an active response to tissue damage that is consistent with compensatory synaptic and terminal remodeling.

Apolipoprotein D in Oxidative Stress and Inflammation

Apolipoprotein D (ApoD) is lipocalin able to bind hydrophobic ligands. The APOD gene is upregulated in a number of pathologies, including Alzheimer's disease, Parkinson's disease, cancer, and hypothyroidism. Upregulation of ApoD is linked to decreased oxidative stress and inflammation in several models, including humans, mice, Drosophila melanogaster and plants. Studies suggest that the mechanism through which ApoD modulates oxidative stress and regulate inflammation is via its capacity to bind arachidonic acid (ARA). This polyunsaturated omega-6 fatty acid can be metabolised to generate large variety of pro-inflammatory mediators. ApoD serves as a sequester, blocking and/or altering arachidonic metabolism. In recent studies of diet-induced obesity, ApoD has been shown to modulate lipid mediators derived from ARA, but also from eicosapentaenoic acid and docosahexaenoic acid in an anti-inflammatory way. High levels of ApoD have also been linked to better metabolic health and inflammatory state in the round ligament of morbidly obese women. Since ApoD expression is upregulated in numerous diseases, it might serve as a therapeutic agent against pathologies aggravated by OS and inflammation such as many obesity comorbidities. This review will present the most recent findings underlying the central role of ApoD in the modulation of both OS and inflammation.

The Lipocalin Apolipoprotein D Functional Portrait: A Systematic Review

Apolipoprotein D is a chordate gene early originated in the Lipocalin protein family. Among other features, regulation of its expression in a wide variety of disease conditions in humans, as apparently unrelated as neurodegeneration or breast cancer, have called for attention on this gene. Also, its presence in different tissues, from blood to brain, and different subcellular locations, from HDL lipoparticles to the interior of lysosomes or the surface of extracellular vesicles, poses an interesting challenge in deciphering its physiological function: Is ApoD a moonlighting protein, serving different roles in different cellular compartments, tissues, or organisms? Or does it have a unique biochemical mechanism of action that accounts for such apparently diverse roles in different physiological situations? To answer these questions, we have performed a systematic review of all primary publications where ApoD properties have been investigated in chordates. We conclude that ApoD ligand binding in the Lipocalin pocket, combined with an antioxidant activity performed at the rim of the pocket are properties sufficient to explain ApoD association with different lipid-based structures, where its physiological function is better described as lipid-management than by long-range lipid-transport. Controlling the redox state of these lipid structures in particular subcellular locations or extracellular structures, ApoD is able to modulate an enormous array of apparently diverse processes in the organism, both in health and disease. The new picture emerging from these data should help to put the physiological role of ApoD in new contexts and to inspire well-focused future research.

Apolipoprotein B is a novel marker for early tau pathology in Alzheimer's disease

INTRODUCTION

We examine the role of brain apolipoprotein B (apoB) as a putative marker of early tau pathology and cognitive decline.

METHODS

Cerebrospinal fluid (CSF) samples from cognitively normal and Alzheimer's disease (AD) participants were collected to measure protein levels of apoB and AD biomarkers amyloid beta (Aβ), t-tau and p-tau, as well as synaptic markers GAP43, SYNAPTOTAGMIN-1, synaptosome associated protein 25 (SNAP-25), and NEUROGRANIN. CSF apoB levels were contrasted with positron emission tomography (PET) scan measures of Aβ (18F-NAV4694) and Tau (flortaucipir) along with cognitive assessment alterations over 6 to 8 years.

RESULTS

CSF apoB levels were elevated in AD participants and correlated with t-tau, p-tau, and the four synaptic markers in pre-symptomatic individuals. In the latter, CSF apoB levels correlated with PET flortaucipir-binding in entorhinal, parahippocampal, and fusiform regions. Baseline CSF apoB levels were associated with longitudinal visuospatial cognitive decline.

DISCUSSION

CSF apoB markedly associates with early tau dysregulation in asymptomatic subjects and identifies at-risk individuals predisposed to develop visuospatial cognitive decline over time.

Persistence of Lipoproteins and Cholesterol Alterations after Sepsis: Implication for Atherosclerosis Progression

(1) Background: Sepsis is one of the most common critical care illnesses with increasing survivorship. The quality of life in sepsis survivors is adversely affected by several co-morbidities, including increased incidence of dementia, stroke, cardiac disease and at least temporary deterioration in cognitive dysfunction. One of the potential explanations for their progression is the persistence of lipid profile abnormalities induced during acute sepsis into recovery, resulting in acceleration of atherosclerosis. (2) Methods: This is a targeted review of the abnormalities in the long-term lipid profile abnormalities after sepsis; (3) Results: There is a well-established body of evidence demonstrating acute alteration in lipid profile (HDL-c ↓↓, LDL-C -c ↓↓). In contrast, a limited number of studies demonstrated depression of HDL-c levels with a concomitant increase in LDL-C -c in the wake of sepsis. VLDL-C -c and Lp(a) remained unaltered in few studies as well. Apolipoprotein A1 was altered in survivors suggesting abnormalities in lipoprotein metabolism concomitant to overall lipoprotein abnormalities. However, most of the studies were limited to a four-month follow-up and patient groups were relatively small. Only one study looked at the atherosclerosis progression in sepsis survivors using clinical correlates, demonstrating an acceleration of plaque formation in the aorta, and a large metanalysis suggested an increase in the risk of stroke or acute coronary event between 3% to 9% in sepsis survivors. (4) Conclusions: The limited evidence suggests an emergence and persistence of the proatherogenic lipid profile in sepsis survivors that potentially contributes, along with other factors, to the clinical sequel of atherosclerosis.

Apolipoprotein D

ApoD is a 25 to 30 kDa glycosylated protein, member of the lipocalin superfamily. As a transporter of several small hydrophobic molecules, its known biological functions are mostly associated to lipid metabolism and neuroprotection. ApoD is a multi-ligand, multi-function protein that is involved lipid trafficking, food intake, inflammation, antioxidative response and development and in different types of cancers. An important aspect of ApoD's role in lipid metabolism appears to involve the transport of arachidonic acid, and the modulation of eicosanoid production and delivery in metabolic tissues. ApoD expression in metabolic tissues has been associated positively and negatively with insulin sensitivity and glucose homeostasis in a tissue dependent manner. ApoD levels rise considerably in association with aging and neuropathologies such as Alzheimer's disease, stroke, meningoencephalitis, moto-neuron disease, multiple sclerosis, schizophrenia and Parkinson's disease. ApoD is also modulated in several animal models of nervous system injury/pathology.

Studies of ApoD-/- and ApoD-/-ApoE-/- mice uncover the APOD significance for retinal metabolism, function, and status of chorioretinal blood vessels

Apolipoprotein D (APOD) is an atypical apolipoprotein with unknown significance for retinal structure and function. Conversely, apolipoprotein E (APOE) is a typical apolipoprotein with established roles in retinal cholesterol transport. Herein, we immunolocalized APOD to the photoreceptor inner segments and conducted ophthalmic characterizations of ApoD^-/- and ApoD^-/-ApoE^-/- mice. ApoD^-/- mice had normal levels of retinal sterols but changes in the chorioretinal blood vessels and impaired retinal function. The whole-body glucose disposal was impaired in this genotype but the retinal glucose metabolism was unchanged. ApoD^-/-ApoE^-/- mice had altered sterol profile in the retina but apparently normal chorioretinal vasculature and function. The whole-body glucose disposal and retinal glucose utilization were enhanced in this genotype. OB-Rb, both leptin and APOD receptor, was found to be expressed in the photoreceptor inner segments and was at increased abundance in the ApoD^-/- and ApoD^-/-ApoE^-/- retinas. Retinal levels of Glut4 and Cd36, the glucose transporter and scavenger receptor, respectively, were increased as well, thus linking APOD to retinal glucose and fatty acid metabolism and suggesting the APOD-OB-Rb-GLUT4/CD36 axis. In vivo isotopic labeling, transmission electron microscopy, and retinal proteomics provided additional insights into the mechanism underlying the retinal phenotypes of ApoD^-/- and ApoD^-/-ApoE^-/- mice. Collectively, our data suggest that the APOD roles in the retina are context specific and could determine retinal glucose fluxes into different pathways. APOD and APOE do not play redundant, complementary or opposing roles in the retina, rather their interplay is more complex and reflects retinal responses elicited by lack of these apolipoproteins.

Relationship between Apolipoprotein Superfamily and Parkinson's Disease

Objective:

Parkinson's disease (PD) is featured with motor disorder and nonmotor manifestations including psychological symptoms, autonomic nervous system dysfunction, and paresthesia, which results in great inconvenience to the patients’ life. The apolipoprotein (Apo) superfamily, as a group of potentially modifiable biomarkers in clinical practice, is of increasing significance in the diagnosis, evaluation, and prognosis of PD. The present review summarized the current understanding and emerging findings of the relationship between Apo superfamily and PD.

Data Sources:

All literatures were identified by systematically searching PubMed, Embase, and Cochrane electronic databases with terms “Parkinson disease,” “apolipoprotein,” and their synonyms until May 2017.

Study Selection:

We have thoroughly examined titles and abstracts of all the literatures that met our search strategy and the full text if the research is identified or not so definite. Reference lists of retrieved articles were also scrutinized for additional relevant studies.

Results:

The levels of plasma ApoA1 are inversely correlated with the risk of PD and the lower levels of ApoA1 trend toward association with poorer motor performance. Higher ApoD expression in neurons represents more puissant protection against PD, which is critical in delaying the neurodegeneration process of PD. It is suggested that APOE alleles are related to development and progression of cognitive decline and age of PD onset, but conclusions are not completely identical, which may be attributed to different ApoE isoforms. APOJ gene expressions are upregulated in PD patients and it is possible that high ApoJ level is an indicator of PD dementia and correlates with specific phenotypic variations in PD.

Conclusions:

The Apo superfamily has been proved to be closely involved in the initiation, progression, and prognosis of PD. Apos and their genes are of great value in predicting the susceptibility of PD and hopeful to become the target of medical intervention to prevent the onset of PD or slow down the progress. Therefore, further large-scale studies are warranted to elucidate the precise mechanisms of Apos in PD.

The Glia-Neuron Lactate Shuttle and Elevated ROS Promote Lipid Synthesis in Neurons and Lipid Droplet Accumulation in Glia via APOE/D

Elevated reactive oxygen species (ROS) induce the formation of lipids in neurons that are transferred to glia, where they form lipid droplets (LDs). We show that glial and neuronal monocarboxylate transporters (MCTs), fatty acid transport proteins (FATPs), and apolipoproteins are critical for glial LD formation. MCTs enable glia to secrete and neurons to absorb lactate, which is converted to pyruvate and acetyl-CoA in neurons. Lactate metabolites provide a substrate for synthesis of fatty acids, which are processed and transferred to glia by FATP and apolipoproteins. In the presence of high ROS, inhibiting lactate transfer or lowering FATP or apolipoprotein levels decreases glial LD accumulation in flies and in primary mouse glial-neuronal cultures. We show that human APOE can substitute for a fly glial apolipoprotein and that APOE4, an Alzheimer's disease susceptibility allele, is impaired in lipid transport and promotes neurodegeneration, providing insights into disease mechanisms.

Apolipoprotein D deficiency is associated to high bone turnover, low bone mass and impaired osteoblastic function in aged female mice

BACKGROUND

Apolipoprotein D (ApoD) is a member of the lipocalin family known to transport small hydrophobic ligands. A major site of ApoD expression in mice is the central nervous system where evidence suggests that it plays a protective role. Gene expression of ApoD was reported in bone-forming osteoblasts but its impact on bone metabolism remains undocumented.

METHODS

We compared basic bone parameters of ApoD(-/-) (null) and transgenic (tg) mice to wild-type (wt) littermates through microCT and histochemistry, as well as ApoD expression and secretion in osteoblasts under various culture conditions through real-time PCR and immunoblotting.

RESULTS

ApoD-null females displayed progressive bone loss with aging, resulting in a 50% reduction in trabecular bone volume and a 23% reduction in cortical bone volume by 9months of age. Only cortical bone volume was significantly reduced in ApoD-null males by an average of 24%. Histochemistry indicated significantly higher osteoblast surface and number of osteoclasts in femora from ApoD-null females. ApoD gene expression was confirmed in primary cultures of bone marrow mesenchymal cells (MSC), with higher expression levels in MSC from females compared to males. ApoD-null MSC exhibited impaired proliferation and differentiation potentials. Moreover, exogenous ApoD partially rescued the osteogenic potential of null MSC, which were shown to readily uptake the protein from media. ApoD expression was upregulated under low proliferation conditions, by contact inhibition and osteoblastic differentiation in MC3T3-E1 osteoblast-like cells.

CONCLUSION

Our results indicate that ApoD influences bone metabolism in mice in a gender-specific manner, potentially through an auto-/paracrine pathway.

Apolipoprotein D Overexpression Protects Against Kainate-Induced Neurotoxicity in Mice

Excitotoxicity due to the excessive activation of glutamatergic receptors leads to neuronal dysfunction and death. Excitotoxicity has been implicated in the pathogenesis of a myriad of neurodegenerative diseases with distinct etiologies such as Alzheimer's and Parkinson's. Numerous studies link apolipoprotein D (apoD), a secreted glycoprotein highly expressed in the central nervous system (CNS), to maintain and protect neurons in various mouse models of acute stress and neurodegeneration. Here, we used a mouse model overexpressing human apoD in neurons (H-apoD Tg) to test the neuroprotective effects of apoD in the kainic acid (KA)-lesioned hippocampus. Our results show that apoD overexpression in H-apoD Tg mice induces an increased resistance to KA-induced seizures, significantly attenuates inflammatory responses and confers protection against KA-induced cell apoptosis in the hippocampus. The apoD-mediated protection against KA-induced toxicity is imputable in part to increased plasma membrane Ca2+ ATPase type 2 expression (1.7-fold), decreased N-methyl-D-aspartate receptor (NMDAR) subunit NR2B levels (30 %) and lipid metabolism alterations. Indeed, we demonstrate that apoD can attenuate intracellular cholesterol content in primary hippocampal neurons and in brain of H-apoD Tg mice. In addition, apoD can be internalised by neurons and this internalisation is accentuated in ageing and injury conditions. Our results provide additional mechanistic information on the apoD-mediated neuroprotection in neurodegenerative conditions.

Cerebral Apolipoprotein-D Is Hypoglycosylated Compared to Peripheral Tissues and Is Variably Expressed in Mouse and Human Brain Regions

Recent studies have shown that cerebral apoD levels increase with age and in Alzheimer’s disease (AD). In addition, loss of cerebral apoD in the mouse increases sensitivity to lipid peroxidation and accelerates AD pathology. Very little data are available, however, regarding the expression of apoD protein levels in different brain regions. This is important as both brain lipid peroxidation and neurodegeneration occur in a region-specific manner. Here we addressed this using western blotting of seven different regions (olfactory bulb, hippocampus, frontal cortex, striatum, cerebellum, thalamus and brain stem) of the mouse brain. Our data indicate that compared to most brain regions, the hippocampus is deficient in apoD. In comparison to other major organs and tissues (liver, spleen, kidney, adrenal gland, heart and skeletal muscle), brain apoD was approximately 10-fold higher (corrected for total protein levels). Our analysis also revealed that brain apoD was present at a lower apparent molecular weight than tissue and plasma apoD. Utilising peptide N-glycosidase-F and neuraminidase to remove N-glycans and sialic acids, respectively, we found that N-glycan composition (but not sialylation alone) were responsible for this reduction in molecular weight. We extended the studies to an analysis of human brain regions (hippocampus, frontal cortex, temporal cortex and cerebellum) where we found that the hippocampus had the lowest levels of apoD. We also confirmed that human brain apoD was present at a lower molecular weight than in plasma. In conclusion, we demonstrate apoD protein levels are variable across different brain regions, that apoD levels are much higher in the brain compared to other tissues and organs, and that cerebral apoD has a lower molecular weight than peripheral apoD; a phenomenon that is due to the N-glycan content of the protein.

Apolipoprotein D subcellular distribution pattern in neuronal cells during oxidative stress

Apolipoprotein D (Apo D) is a secreted glycoprotein, member of the lipocalin superfamily, with a related beneficial role in metabolism and lipid transport due to the presence of a binding pocket that allows its interaction with several lipids. Nowadays, it has been clearly demonstrated that Apo D expression is induced and its subcellular location undergoes modifications in stressful and pathological conditions that characterize aging processes and neurodegenerative diseases. The aim of the present work was to study in detail the effect of H2O2 on the subcellular location of Apo D, in the hippocampal cell line HT22, by structural, ultrastructural, immunocytochemical, and molecular techniques in order to characterize the Apo D distribution pattern in neurons during oxidative stress. Our results indicate that Apo D is located in the cytoplasm under physiological conditions but treatment with H2O2 induces apoptosis and causes a displacement of Apo D location to the nucleus, coinciding with DNA fragmentation. In addition, we demonstrated that Apo D tends to accumulate around the nuclear envelope in neurons and glial cells of different brain areas in some neurodegenerative diseases and during human aging, but never inside the nucleus. These data suggest that the presence of Apo D in the nucleus, which some authors related with a specific transport, is a consequence of structural and functional alterations during oxidative stress and not the result of a specific role in the regulation of nuclear processes.

Apolipoprotein D modulates amyloid pathology in APP/PS1 Alzheimer's disease mice

Apolipoprotein D (apoD) is expressed in the brain and levels are increased in affected brain regions in Alzheimer's disease (AD). The role that apoD may play in regulating AD pathology has not been addressed. Here, we crossed both apoD-null mice and Thy-1 human apoD transgenic mice with APP-PS1 amyloidogenic AD mice. Loss of apoD resulted in a nearly 2-fold increase in hippocampal amyloid plaque load, as assessed by immunohistochemical staining. Conversely, transgenic expression of neuronal apoD reduced hippocampal plaque load by approximately 35%. This latter finding was associated with a 60% decrease in amyloid β 1-40 peptide levels, and a 34% decrease in insoluble amyloid β 1-42 peptide. Assessment of β-site amyloid precursor protein cleaving enzyme-1 (BACE1) levels and proteolytic products of amyloid precursor protein and neuregulin-1 point toward a possible association of altered BACE1 activity in association with altered apoD levels. In conclusion, the current studies provide clear evidence that apoD regulates amyloid plaque pathology in a mouse model of AD.

Potential neurochemical links between cholesterol and suicidal behavior

The role of cholesterol in psychiatric diseases has aroused the interest of the medical community, particularly in association with violent and suicidal behavior. Herein, we discuss some aspects of brain cholesterol metabolism, exploring possible mechanisms underlying the findings and reviewing the available literature on the possible neurochemical link between suicide and low or reduced levels of serum cholesterol. Most of the current hypotheses suggest a decreased serotonergic activity due to a decrease in cholesterol in the lipid rafts of synaptic membranes. Some aspects and limitations of this assumption are emphasized. In addition to serotonin hypofunction, other mechanisms have been proposed to explain increased impulsivity in suicidal individuals, including steroid modulation and brain-derived neurotrophic factor decrease, which could also be related to changes in lipid rafts. Other putative markers of suicidal behavior (e.g. protein S100B) are discussed in connection with cholesterol metabolism in the brain tissue.

Binding and repressive activities of apolipoprotein E3 and E4 isoforms on the human ApoD promoter

Apolipoprotein D (ApoD) gene expression is increased in several neurological disorders such as Alzheimer’s disease (AD) and multiple sclerosis. We previously showed that transgenic mice that overexpress human ApoD show a better resistance against paraquat or OC43 coronavirus-induced neurodegeneration. Here, we identified several nuclear factors from the cortex of control and OC43-infected mice which bind a fragment of the proximal ApoD promoter in vitro. Of interest, we detected apolipoprotein E (ApoE). Human ApoE consists of three isoforms (E2, E3, and E4) with the E4 and E2 alleles representing a greater and a lower risk for developping AD, respectively. Our results show that ApoE is located in the nucleus and on the ApoD promoter in human hepatic and glioblastoma cells lines. Furthermore, overexpression of ApoE3 and ApoE4 isoforms but not ApoE2 significantly inhibited the ApoD promoter activity in U87 cells (E3/E3 genotype) cultured under normal or different stress conditions while ApoE knock-down by siRNA had a converse effect. Consistent with these results, we also demonstrated by ChIP assay that E3 and E4 isoforms, but not E2, bind the ApoD promoter. Moreover, using the Allen Brain Atlas in situ hybridization database, we observed an inverse correlation between ApoD and ApoE mRNA expression during development and in several regions of the mouse brain, notably in the cortex, hippocampus, plexus choroid, and cerebellum. This negative correlation was also observed for cortex layers IV–VI based on a new Transcriptomic Atlas of the Mouse Neocortical Layers. These findings reveal a new function for ApoE by regulating ApoD gene expression.

Lipid metabolism and glial lipoproteins in the central nervous system

Lipoproteins in the central nervous system (CNS) are not incorporated from the blood but are formed mainly by glial cells within the CNS. In addition, cholesterol in the CNS is synthesized endogenously because the blood-brain barrier segregates the CNS from the peripheral circulation. Apolipoprotein (apo) E is a major apo in the CNS. In normal condition, apo E is secreted from glia, mainly from astrocytes, and forms cholesterol-rich lipoproteins by ATP-binding cassette transporters. Subsequently, apo E-containing glial lipoproteins supply cholesterol and other components to neurons via a receptor-mediated process. Recent findings demonstrated that receptors of the low density lipoprotein (LDL) receptor family not only internalize lipoproteins into the cells but also, like signaling receptors, transduce signals upon binding the ligands. In this review, the regulation of lipid homeostasis will be discussed as well as roles of lipoproteins and functions of receptors of LDL receptor family in the CNS. Furthermore, the relation between lipid metabolism and Alzheimer's disease (AD) is discussed.

Cholesterol metabolism in neurons and astrocytes

Cells in the mammalian body must accurately maintain their content of cholesterol, which is an essential membrane component and precursor for vital signalling molecules. Outside the brain, cholesterol homeostasis is guaranteed by a lipoprotein shuttle between the liver, intestine and other organs via the blood circulation. Cells inside the brain are cut off from this circuit by the blood-brain barrier and must regulate their cholesterol content in a different manner. Here, we review how this is accomplished by neurons and astrocytes, two cell types of the central nervous system, whose cooperation is essential for normal brain development and function. The key observation is a remarkable cell-specific distribution of proteins that mediate different steps of cholesterol metabolism. This form of metabolic compartmentalization identifies astrocytes as net producers of cholesterol and neurons as consumers with unique means to prevent cholesterol overload. The idea that cholesterol turnover in neurons depends on close cooperation with astrocytes raises new questions that need to be addressed by new experimental approaches to monitor and manipulate cholesterol homeostasis in a cell-specific manner. We conclude that an understanding of cholesterol metabolism in the brain and its role in disease requires a close look at individual cell types.

Apolipoprotein D mediates autocrine protection of astrocytes and controls their reactivity level, contributing to the functional maintenance of paraquat-challenged dopaminergic systems

The study of glial derived factors induced by injury and degeneration is important to understand the nervous system response to deteriorating conditions. We focus on Apolipoprotein D (ApoD), a Lipocalin expressed by glia and strongly induced upon aging, injury or neurodegeneration. Here we study ApoD function in the brain of wild type and ApoD-KO mice by combining in vivo experiments with astrocyte cultures. Locomotor performance, dopamine concentration, and gene expression levels in the substantia nigra were assayed in mice treated with paraquat (PQ). The regulation of ApoD transcription, a molecular screening of oxidative stress (OS)-related genes, cell viability and oxidation status, and the effects of adding human ApoD were tested in astrocyte cultures. We demonstrate that (1) ApoD is required for an adequate locomotor performance, modifies the gene expression profile of PQ-challenged nigrostriatal system, and contributes to its functional maintenance; (2) ApoD expression in astrocytes is controlled by the OS-responsive JNK pathway; (3) ApoD contributes to an autocrine protecting mechanism in astrocytes, avoiding peroxidated lipids accumulation and altering the PQ transcriptional response of genes involved in ROS managing and the inflammatory response to OS; (4) Addition of human ApoD to ApoD-KO astrocytes promotes survival through a mechanism accompanied by protein internalization and modulation of astroglial reactivity. Our data support that ApoD contributes to the endurance of astrocytes and decreases their reactivity level in vitro and in vivo. ApoD function as a maintenance factor for astrocytes would suffice to explain the observed protection by ApoD of OS-vulnerable dopaminergic circuits in vivo.

Apolipoproteins in the brain: implications for neurological and psychiatric disorders

The brain is the most lipid-rich organ in the body and, owing to the impermeable nature of the blood-brain barrier, lipid and lipoprotein metabolism within this organ is distinct from the rest of the body. Apolipoproteins play a well-established role in the transport and metabolism of lipids within the CNS; however, evidence is emerging that they also fulfill a number of functions that extend beyond lipid transport and are critical for healthy brain function. The importance of apolipoproteins in brain physiology is highlighted by genetic studies, where apolipoprotein gene polymorphisms have been identified as risk factors for several neurological diseases. Furthermore, the expression of brain apolipoproteins is significantly altered in several brain disorders. The purpose of this article is to provide an up-to-date assessment of the major apolipoproteins found in the brain (ApoE, ApoJ, ApoD and ApoA-I), covering their proposed roles and the factors influencing their level of expression. Particular emphasis is placed on associations with neurological and psychiatric disorders.

Apolipoprotein D synthesis progressively increases in frontal cortex during human lifespan

Apolipoprotein D (apo D) is a lipocalin present in the nervous system that may be related to processes of reinnervation, regeneration and neuronal cell protection. On the other hand, apo D expression has been correlated, in some brain regions, with normal ageing and neurodegenerative diseases. To elucidate the regional and cellular expression of apo Din normal human brain during ageing, we performed a detailed and extensive study in samples of post-mortem human cerebral cortices. To achieve this study, slot-blot techniques, for protein and mRNA,as well as immunohistochemistry and hybridohistochemistry methods, were used. A positive correlation for apo D expression with ageing was found;furthermore, mRNA levels, as well as the protein ones, were higher in the white than in the grey matter. Immunohistochemistry and non-isotopic in situ hybridization showed that apo D is synthesised in both neurons and glial cells. Apo D expression is notorious in oligodendrocytes, but with ageing, the number of neurons that synthesise apo D is increased.Our results indicate that apo D could play a fundamental role in central nervous system ageing and in the reduction of products derived from lipid peroxidation. The increment in the expression of apo D with ageing can be included in a global mechanism of cellular protection to prevent the deleterious effects caused by ageing.

Prenatal exposure to environmental tobacco smoke alters gene expression in the developing murine hippocampus

BACKGROUND

Little is known about the effects of passive smoke exposures on the developing brain.

OBJECTIVE

The purpose of the current study was to identify changes in gene expression in the murine hippocampus as a consequence of in utero exposure to sidestream cigarette smoke (an experimental equivalent of environmental tobacco smoke (ETS)) at exposure levels that do not result in fetal growth inhibition.

METHODS

A whole body smoke inhalation exposure system was utilized to deliver ETS to pregnant C57BL/6J mice for 6 h/day from gestational days 6-17 (gd 6-17) [for microarray] or gd 6-18.5 [for fetal phenotyping].

RESULTS

There were no significant effects of ETS exposure on fetal phenotype. However, 61 "expressed" genes in the gd 18.5 fetal hippocampus were differentially regulated (up- or down-regulated by 1.5-fold or greater) by maternal exposure to ETS. Of these 61 genes, 25 genes were upregulated while 36 genes were down-regulated. A systems biology approach, including computational methodologies, identified cellular response pathways, and biological themes, underlying altered fetal programming of the embryonic hippocampus by in utero cigarette smoke exposure.

CONCLUSIONS

Results from the present study suggest that even in the absence of effects on fetal growth, prenatal smoke exposure can alter gene expression during the "early" period of hippocampal growth and may result in abnormal hippocampal morphology, connectivity, and function.

Modulation of Apolipoprotein D levels in human pregnancy and association with gestational weight gain

BACKGROUND

Apolipoprotein D (ApoD) is a lipocalin involved in several processes including lipid transport, but its modulation during human pregnancy was never examined.

METHODS

We investigated the changes in the levels of ApoD in the plasma of pregnant women at the two first trimesters of gestation and at delivery as well as in the placenta and in venous cord blood. These changes were studied in 151 women classified into 9 groups in relation to their prepregnancy body mass index (BMI) and gestational weight gain (GWG).

RESULTS

Plasma ApoD levels decrease significantly during normal uncomplicated pregnancy. ApoD is further decreased in women with excessive GWG and their newborns. In these women, the ApoD concentration was tightly associated with the lipid parameters. However, the similar ApoD levels in low cholesterol (LC) and high cholesterol (HC) women suggest that the plasma ApoD variation is not cholesterol dependant. A tight regulation of both placental ApoD transcription and protein content is most probably at the basis of the low circulating ApoD concentrations in women with excessive GWG. After delivery, the plasma ApoD concentrations depended on whether the mother was breast-feeding or not, lactation favoring a faster return to baseline values.

CONCLUSION

It is speculated that the decrease in plasma ApoD concentration during pregnancy is an adaptive response aimed at maintaining fetal lipid homeostasis. The exact mechanism of this adaptation is not known.

Expression of somatostatin and somatostatin receptor subtypes in Apolipoprotein D (ApoD) knockout mouse brain: An immunohistochemical analysis

Apolipoprotein D (ApoD) is widely distributed in central and peripheral nervous system. ApoD expression has been shown to increase in several neurodegenerative and neuropsychiatric disorders, as well as during regeneration in the nervous system. Like ApoD, in the central nervous system somatostatin (SST) is widely present and functions as neurotransmitter and neuromodulator. The biological effects of SST are mediated via binding to five high-affinity G-protein coupled receptors termed SSTR1-5. Mice lacking ApoD exhibit reduced SST labeling in cortex and hippocampus and increased expression in striatum and amygdala without any noticeable changes in substantia nigra. Changes in SSTRs expressions have been described in several neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. In the present study, using SSTR1-5 receptor-specific antibodies, we mapped their distribution in wild type (wt) and ApoD knockout (ApoD(-/-)) mouse brain. SSTR1-5 expression was observed both as membrane and cytoplasmic protein and display regions and receptor specific differences between wt and ApoD(-/-) mice brains. In cortex and hippocampus, SSTR subtypes like immunoreactivity are decreased in ApoD(-/-) mice brain. Unlike cortex and hippocampus, in the striatum of ApoD(-/-) mice, projection neurons showed increased SSTR immunoreactivity, as compared to wt. Higher SSTR subtypes immunoreactivity is seen in substantia nigra pars compacta (SNpc) whereas lower in substantia nigra pars reticulata (SNpr) of ApoD(-/-) mice brains as compared to wt. Whereas, amygdala displayed SSTR subtypes changes in different nuclei of ApoD(-/-) mice in comparison to wt mice brain. Taken together, our results describe receptor and region specific changes in SST and SSTR subtypes expression in ApoD(-/-) mice brain, which may be linked to specific neurological disorders.

Apolipoproteins D and E3 exert neurotrophic and synaptogenic effects in dorsal root ganglion cell cultures

Co-cultures of 3T3-L1 adipocytes with neurons from the rat dorsal root ganglia (DRG) showed enhanced neuritogenesis and synaptogenesis. Microarray analysis for upregulated genes in adipocyte/DRG co-cultures currently points to apolipoproteins D and E (ApoD, ApoE) as influential proteins. We therefore tested adipocyte-secreted cholesterol and the carrier proteins ApoD and ApoE3. Cholesterol, ApoD, and ApoE3 each increased neurite outgrowth and upregulated the expression of presynaptic synaptophysin and synaptotagmin, as well as the postsynaptic density protein 95. The neurotrophic effects of ApoD and ApoE3 were associated with an increased expression of the low-density lipoprotein receptor and apolipoprotein E receptor 2. Simultaneous treatment with receptor-associated protein, an apolipoprotein receptor antagonist, inhibited the neurotrophic function of both apolipoproteins. The application of ApoD, ApoE3, and cholesterol to DRG cell cultures corresponded with increased expression of the chemokine stromal cell-derived factor 1 and its receptor CXC chemokine receptor 4 (CXCR4). Surprisingly, the inhibition of CXCR4 by the antagonistic drug AMD3100 decreased the apolipoprotein/cholesterol dependent neurotrophic effects. We thus assume that apolipoprotein-induced neuritogenesis in DRG cells interferes with CXCR4 signaling, and that adipocyte-derived apolipoproteins might be helpful in nerve repair.

Human apolipoprotein D overexpression in transgenic mice induces insulin resistance and alters lipid metabolism

Apolipoprotein D (apoD), a widely expressed lipocalin, has the capacity to transport small hydrophobic molecules. Although it has been proposed that apoD may have multiple tissue-specific, physiological ligands and functions, these have yet to be identified. To gain insight in some of its functions, we generated transgenic mice overexpressing human apoD (H-apoD) under the control of neuron-specific promoters. In Thy-1/apoD and NSE/apoD mice, expression of H-apoD was strong in the nervous system although weakly detected in peripheral organs such as the liver and blood cells. These mice displayed not entirely anticipated metabolic defects. Although they are not obese and have normal lipid concentration in circulation, Thy-1/apoD and NSE/apoD mice are glucose intolerant, insulin resistant, and develop hepatic steatosis. The steatosis and its associated insulin resistance are correlated with impairments in hepatic lipogenesis. However, they are not strongly related with inflammation. This impaired insulin response is not caused by a decrease in circulating leptin or a modulation of adiponectin and resistin levels. These results suggest that variations in the levels and/or sites of apoD expression influence the lipid and glucose metabolism, consolidating apoD as a target for insulin-resistance-related disorders.

Apolipoprotein D modulates F2-isoprostane and 7-ketocholesterol formation and has a neuroprotective effect on organotypic hippocampal cultures after kainate-induced excitotoxic injury

Apolipoprotein D (apoD), a member of the lipocalin family of transporter proteins binds a number of small lipophilic molecules including arachidonic acid and cholesterol. Recent studies showed a protective function of mammalian apoD as well as its insect and plant homologs against oxidative stress. In this study we investigated the effect of direct addition of exogenous human apoD protein purified from breast cystic fluid to rat hippocampal slice cultures after excitotoxic injury induced by the glutamate analog kainate. ApoD at a concentration of 10 microg/ml partially prevented loss of MAP2 immunostaining and LDH release from injured hippocampal neurons after kainate injury. ApoD also attenuated the increase in oxidative products of arachidonic acid and cholesterol, F(2)-isoprostanes and 7-ketocholesterol, respectively, after kainate treatment. In view of the molecular structure of apoD which consists of an eight stranded beta barrel that forms a binding pocket for a number of small hydrophobic molecules, we propose that apoD promotes its neuroprotective effects by binding to arachidonic acid and cholesterol thus preventing their oxidation to neurotoxic products such as 4-hydroxynonenal (4-HNE) and 7-ketocholesterol.

Neuroprotective effect of apolipoprotein D against human coronavirus OC43-induced encephalitis in mice

Apolipoprotein D (apoD) is a lipocalin upregulated in the nervous system after injury or pathologies such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. We previously demonstrated that apoD protects against neuropathology by controlling the level of peroxidated lipids. Here, we further investigated the biological function of apoD in a mouse model of acute encephalitis. Our results show that apoD transcript and protein are upregulated during acute encephalitis induced by the human coronavirus OC43 (HCoV-OC43) infection. The apoD upregulation coincides with glial activation, and its expression returns to normal levels when the virus is cleared, concomitantly to a resolved glial reactivity. In addition, the overexpression of human apoD in the neurons of Thy-1/ApoD transgenic mice results in a threefold increase of the number of mice surviving to HCoV-OC43 infection. This increased survival rate is correlated with an upregulated glial activation associated with a limited innate immune response (cytokines, chemokines) and T-cell infiltration into infected brains. Moreover, the protection seems to be associated with a restricted phospholipase A2 activity. These data reveal a role for apoD in the regulation of inflammation and suggest that it protects from HCoV-OC43-induced encephalitis, most likely through the phospholipase A2 signaling pathways.

Association between polymorphisms in the apolipoprotein D gene and sporadic Alzheimer's disease

Apolipoprotein D (apoD) is a lipoprotein-associated glycoprotein that is increased in the hippocampus and cerebrospinal fluid of patients with Alzheimer's disease (AD), which implies that apoD might be involved in the pathogenesis of AD. We used polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing techniques to screen all exons (1-5) and the flanking exon-intron boundaries of the apoD gene (APOD). Thirty subjects [15 sporadic AD (SAD) patients and 15 controls] were randomly selected and tested for APOD variations by direct sequencing. Two APOD polymorphisms (rs5952T/C and rs1568566C/T) were detected. We further investigated APOD polymorphisms in 256 SAD patients and 294 healthy subjects from a North Chinese population to investigate whether they affect the risk of SAD. Logistic analysis revealed that both rs5952 C and rs1568566 T alleles increase the risk of SAD [rs5952, adjusted odds ratio (OR) 1.817, 95% confidence interval (CI) 1.237-2.669, P = 0.002; rs1568566, adjusted OR 1.563, 95% CI 1.060-2.306, P = 0.024). The rs5952T-rs1568566C haplotype showed lower risk of SAD (OR 0.421, 95% CI 0.305-0.583, P = 0.000). Case-control analysis revealed that the rs5952T-rs1568566C haplotype could serve as a novel defendant factor against SAD. APOD polymorphisms might play an important role in modifying SAD risk in some way.

Heat shock proteins and amateur chaperones in amyloid-Beta accumulation and clearance in Alzheimer's disease

The pathologic lesions of Alzheimer’s disease (AD) are characterized by accumulation of protein aggregates consisting of intracellular or extracellular misfolded proteins. The amyloid-β (Aβ) protein accumulates extracellularly in senile plaques and cerebral amyloid angiopathy, whereas the hyperphosphorylated tau protein accumulates intracellularly as neurofibrillary tangles. “Professional chaperones”, such as the heat shock protein family, have a function in the prevention of protein misfolding and subsequent aggregation. “Amateur” chaperones, such as apolipoproteins and heparan sulfate proteoglycans, bind amyloidogenic proteins and may affect their aggregation process. Professional and amateur chaperones not only colocalize with the pathological lesions of AD, but may also be involved in conformational changes of Aβ, and in the clearance of Aβ from the brain via phagocytosis or active transport across the blood–brain barrier. Thus, both professional and amateur chaperones may be involved in the aggregation, accumulation, persistence, and clearance of Aβ and tau and in other Aβ-associated reactions such as inflammation associated with AD lesions, and may, therefore, serve as potential targets for therapeutic intervention.

Transcriptional pathways associated with skeletal muscle disuse atrophy in humans

Disuse atrophy is a common clinical phenomenon that significantly impacts muscle function and activities of daily living. The purpose of this study was to implement genome-wide expression profiling to identify transcriptional pathways associated with muscle remodeling in a clinical model of disuse. Skeletal muscle biopsies were acquired from the medial gastrocnemius in patients with an ankle fracture and from healthy volunteers subjected to 4-11 days of cast immobilization. We identified 277 misregulated transcripts in immobilized muscles of patients, of which the majority were downregulated. The most broadly affected pathways were involved in energy metabolism, mitochondrial function, and cell cycle regulation. We also found decreased expression in genes encoding proteolytic proteins, calpain-3 and calpastatin, and members of the myostatin and IGF-I pathway. Only 26 genes showed increased expression in immobilized muscles, including apolipoprotein (APOD) and leptin receptor (LEPR). Upregulation of APOD (5.0-fold, P < 0.001) and LEPR (5.7-fold, P < 0.05) was confirmed by quantitative RT-PCR and immunohistochemistry. In addition, atrogin-1/MAFbx was found to be 2.4-fold upregulated (P < 0.005) by quantitative RT-PCR. Interestingly, 96% of the transcripts differentially regulated in immobilized limbs also showed the same trend of change in the contralateral legs of patients but not the contralateral legs of healthy volunteers. Information obtained in this study complements findings in animal models of disuse and provides important feedback for future clinical studies targeting the restoration of muscle function following limb disuse in humans.

Modulation of apolipoprotein D expression and translocation under specific stress conditions

Apolipoprotein D is a lipocalin, primarily associated with high density lipoproteins in human plasma. Its expression is induced in several pathological and stressful conditions including growth arrest suggesting that it could act as a nonspecific stress protein. A survey of cellular stresses shows those causing an extended growth arrest, as hydrogen peroxide and UV light increase apoD expression. Alternatively, lipopolysaccharide (LPS), a pro-inflammatory agonist showed a time- and dose-dependent effect on apoD expression that correlates with an increase in proliferation. At the promoter level, NF-kB, AP-1 and APRE-3 proved to be the elements implicated in the LPS response. Colocalization of apoDh-GFP fusion constructs with DNA and Golgi markers, immunocytochemistry of the endogenous protein and cell fractionation showed that both serum starvation and LPS treatment caused a displacement of apoD localization. In normal conditions, apoD is mainly perinuclear but it accumulates in cytoplasm and nucleus under these stress conditions. Since nuclear apoD appears derived from the secreted protein, it may act as an extracellular ligand transporter as well as a transcriptional regulator depending on its location. This role of apoD inside the cell is not only dependent of endogenous apoD but may also be provided by exogenous apoD entering the cell.

Gene expression pathways induced by axotomy and decentralization of rat superior cervical ganglion neurons

To identify genes potentially involved in remodelling synaptic connections, we induced the temporary detachment of pre- and post-synaptic elements by axotomy or denervation of rat superior cervical ganglion neurons. cDNA microarray analysis followed by stringent selection criteria allowed the identification of a panel of genes whose expression was modulated by axotomy at various time points after injury. Among these genes, 11 were validated by real-time reverse transcriptase-polymerase chain reaction on independently prepared samples after superior cervical ganglion neuron axotomy (1, 3 and 6 days) and compared with the effect of decentralization (8 h, 1 and 3 days). These genes code for extracellular matrix/space [apolipoprotein D (apoD), decorin, collagen alpha1 type I, collagen alpha1 type III] and intermediate filament (vimentin) proteins, for modulators of neurite outgrowth (thrombin receptor, plasminogen activator inhibitor-1, bone morphogenetic protein 4, annexin II and S-100-related protein, clone 42C) and for a nerve cell transcription factor (brain finger protein). Eight of these 11 genes showed significant and persistent modulations after both types of injury. Finally, protein levels of apoD were shown to increase in superior cervical ganglion after axotomy. Our results identify hitherto unrecorded genes responsive to axotomy and decentralization of superior cervical ganglion neurons, and probably involved in synapse formation, remodelling and elimination.

Association of plasma apolipoproteins D with RBC membrane arachidonic acid levels in schizophrenia

Apolipoprotein D (apoD) is a member of the lipocalin superfamily of transporter proteins that bind small hydrophobic molecules, including arachidonic acid (AA). The ability of apoD to bind AA implicates it in pathways associated with membrane phospholipid signal transduction and metabolism. Recent findings of an increased expression of apoD in the mouse brain after clozapine treatment suggested a role for apoD in the pharmacological action of clozapine. Moreover, clozapine has been shown to increase membrane AA levels in RBC phospholipids from schizophrenic patients. ApoD levels have also been shown to be elevated in the CNS of subjects with chronic schizophrenia, a disorder associated with AA dysfunction. In this study, we examined whether plasma apoD levels are related to red blood cell membrane AA contents in the first-episode neuroleptic-naive schizophrenic (FENNS) patients. Plasma apoD levels as measured by enzyme-linked immunosorbent assay (ELISA) were not significantly different (F = 0.51, df = 2,86, p = 0.60) among healthy controls (n = 36), FENNS patients (n = 33) and patients with other psychiatric disorders (n = 19). However, plasma apoD levels were significantly correlated with RBC-AA (p = 0.0022) and docosapentaenoic acid (p = 0.0008) in FENNS patients. There are several known mechanisms that can lead to the type of membrane fatty acid defects that have been identified in schizophrenia. Whether plasma apoD alone is a major determinant of reduced RBC membrane AA levels in FENNS patients remains to be determined, although these preliminary data appear not to support this premise. Taken together with other in vitro studies, however, the present data support the view that an increased expression of apoD such as induced by atypical neuroleptic drug, may facilitate incorporation of AA into membrane phospholipids by its selective binding to AA.

Regulated transcripts in the hippocampus following transections of the entorhinal afferents

Based on the data from a cDNA microarray experiment which was carried out to screen the differential expressed genes in the rat hippocampus 10 days after removal of the entorhinal afferents, we confirmed the increase of expression of eight transcripts encoding protein osteonectin, thymosin-beta4, gelsolin, MHC I, MHC II, beta2-microglobulin, and interferon-gamma receptor using Northern blot. In situ hybridization revealed that the up-regulation of all these 8 transcripts localized specifically in the denervated target areas, the hippocampal stratum lacunosum-moleculare, and the dentate outer molecular layer. The results suggest that these molecules may have roles in the plasticity events in the hippocampus after entorhinal deafferentation.

Immunohistochemical study of distribution of apolipoproteins E and D in human cerebral beta amyloid deposits

Several molecules are known to be closely associated with amyloid deposits in human brain. Among these, apolipoproteins such as apolipoproteins E (apo E) and J (apo J) have been found in two neuropathological hallmarks of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA): senile plaques (SPs) and cerebrovascular amyloid. These apolipoproteins may be implicated in amyloid fibrillogenesis. Apo D is a multiligand-multifunctional glycoprotein present in SPs, as we previously reported. The aim of this work is to study the link between immunolocalization of apo E and apo D in AD and CAA brains. Both apolipoproteins were found in all types of SPs, but apo E was observed more often than apo D in mature plaques. Whereas apo E is always located overlapping the amyloid core, apo D seems to situate preferably around and near the amyloid. Immunohistochemistry revealed that these apolipoproteins behave differently in cerebral vessels. Apo E labeling in vessels appears mainly linked to amyloid deposits, whereas apo D shows a distribution almost opposite to that of apo E. This could be an indication of the different roles that each apolipoprotein plays in the pathogenesis of amyloid deposition.

Apolipoprotein D modulates arachidonic acid signaling in cultured cells: implications for psychiatric disorders

Deficiencies in arachidonic acid (AA) parameters have been reported in schizophrenic patients. AA is a primary binding ligand for apolipoprotein D (apoD), which is increased in response to antipsychotic drug treatment and elevated in subjects with schizophrenia and bipolar disorder. In this study, we investigated whether apoD might modulate AA signaling/mobilization in cultured embryonic kidney (HEK) 293T cells. Immunofluorescent labeling revealed both cytosolic and membrane-bound expression of apoD protein in apoD-transfected cells. In cells expressing apoD, phorbal 12-myristate 13-acetate-induced AA release was inhibited compared to controls and membrane levels of AA were elevated, as indicated by the amount of AA maximally incorporated into membrane phospholipids. In addition, exogenous apoD added directly to the incubation media prevented cellular uptake of free [3H]AA. These results suggest that apoD acts to stabilize membrane-associated AA by preventing release and sequestering free AA in the cell. These actions of apoD may be beneficial to psychiatric patients.

Apolipoprotein D expression in human brain reactive astrocytes

Astrocytosis is a hallmark of damage that frequently occurs during aging in human brain. Astrocytes proliferate in elderly subjects, becoming hypertrophic and highly immunoreactive for glial fibrillary acidic protein (GFAP). These cells are one type that actively responds in the repair and reorganization of damage to the neural parenchyma and are a source of several peptides and growth factors. One of these biomolecules is apolipoprotein D (apo D), a member of the lipocalin family implicated in the transport of small hydrophobic molecules. Although the role of apo D is unknown, increments in brain apo D expression have been observed in association with aging and with some types of neuropathology. We have found an overexpression of apo D mRNA in reactive astrocytes by in situ hybridization in combination with immunohistochemistry for apo D in normal aged human brains. The number of double-labeled cells varied according to the cerebral area and the gliosis grade. The possible significance of this increased synthesis of apo D in reactive astrocytes is discussed in relation to the role of apo D in aging and in glial function.

Hippocampal apolipoprotein D level depends on Braak stage and APOE genotype

Apolipoprotein (APO, gene; apo, protein) D, a member of the lipocalin family, has been implicated in several, pathological conditions but neither its physiologic function(s) nor ligand(s) has been clearly identified so far. Presuming a role in nerve de- and regeneration, several groups investigated apoD alterations in Alzheimer's disease (AD). Reported data, however, were not unanimous. We determined apoD protein levels in the hippocampus in a large, carefully matched autopsy case sample. ApoD levels were compared with the severity of neuropathological changes as determined by the Braak classification and with APOE genotype, a major risk factor for developing AD. ApoD was found to be related to the severity of AD-related neurofibrillary (NF) changes and not to old age alone. No correlation was found to amyloid deposits. Brain samples with widespread NF changes showed significantly higher apoD than cases with low Braak stages. This increase, however, was restricted to the APOE epsilon3/3 group, whereas the APOE epsilon4 group did not show significant variations in hippocampal apoD.

Prenatal exposure of rats to Ginkgo biloba extract (EGb 761) increases neuronal survival/growth and alters gene expression in the developing fetal hippocampus

Hippocampal neuron survival/growth and gene expression have been examined after prenatal (in utero) exposure of rats to EGb 761, a leaf extract of Ginkgo biloba. Oral administration of EGb 761 (100 or 300 mg/kg/day) to pregnant dams for 5 days increased the number of hippocampal neurons (maintained in culture) of their fetuses, indicating a neurotrophic effect of the extract. Using large-scale oligonucleotide microarrays containing over 8000 combined rat genes and expressed sequence tag clusters, it was shown that treatment of pregnant dams with EGb 761 (25, 50 or 100 mg/kg/day for 5 days) altered the expression of 187 genes in the hippocampi of male fetuses and 160 genes in those of female fetuses. Using gene-cluster analysis, these genes were grouped into 18 distinct clusters for males and 17 distinct clusters for females. Among these clusters, 35 genes shared a common expression pattern in male and female hippocampal development. Of these genes, the changes observed in insulin growth factor II, insulin growth factor binding protein 2, testosterone repressed prostate message-2, glutathione-dependent dehydroascorbate reductase, lipoprotein lipase, guanylate cyclase and DNA binding protein Brn-2 were confirmed by real-time quantitative polymerase chain reaction. These findings, which have provided the first genetic profile of the effects of EGb 761 on the developing rat hippocampus, increase our understanding of the molecular and genetic programs that are activated by the extract. These effects of EGb 761 may underlie its neuroprotective properties.

Antipsychotic drugs differentially modulate apolipoprotein D in rat brain

Apolipoprotein-D (apoD), a member of the lipocalin family of proteins, binds to arachidonic acid and cholesterol among other hydrophobic molecules. Recently, elevated apoD levels have been reported in the post-mortem brains, as well as plasma, of schizophrenic patients and in rodent brains after chronic treatment with clozapine (CLOZ). These findings and the evidence for altered membrane lipid metabolism in schizophrenia suggest that apoD may have a role in the pathophysiology of illness, and also in the differential clinical outcome following treatment with typical and atypical antipsychotic drugs. Here, we compared the effects of these antipsychotics on the expression of apoD in rat brain. Chronic treatment with typical antipsychotic, haloperidol (HAL) reduced apoD expression in hippocampus, piriform cortex and caudate-putamen (p = 0.027-0.002), whereas atypical antipsychotics, risperidone (RISP) and olanzapine (OLZ) increased (p = 0.051 to < 0.001 and p = 0.048 to < 0.001, respectively) apoD expression. In hippocampus, HAL-induced changes were present in CA1, CA3 and dentate gyrus, however, apoD levels in motor cortex were unchanged. There were also very dramatic effects of HAL on the neuronal morphology, particularly, cellular shrinkage and disorganization with the loss of neuropil. Post-treatment, either with RISP or OLZ, was very effective in restoring the HAL-induced reduction of apoD, as well as cellular morphology. Similarly, pre-treatments were also effective, but slightly less than post-treatment, in preventing HAL-induced reduction of apoD. The increased expression of apoD by atypical antipsychotics may reflect a novel molecular mechanism underlying their favorable effects compared with HAL on cognition, negative symptoms and extra-pyramidal symptoms in schizophrenia.

Transcriptional profile of the human peripheral nervous system by serial analysis of gene expression

The peripheral nerve contains both nonmyelinating and myelinating Schwann cells. The interactions between axons, surrounding myelin, and Schwann cells are thought to be important for the correct functioning of the nervous system. To get insight into the genes involved in human myelination and maintenance of the myelin sheath and nerve, we performed a serial analysis of gene expression of human sciatic nerve and cultured Schwann cells. In the sciatic nerve library, we found high expression of genes encoding proteins related to lipid metabolism, the complement system, and the cell cycle, while cultured Schwann cells showed mainly high expression of genes encoding extracellular matrix proteins. The results of our study will assist in the identification of genes involved in maintenance of myelin and peripheral nerve and of genes involved in inherited peripheral neuropathies.

Genotype-related differences of hippocampal apolipoprotein E levels only in early stages of neuropathological changes in Alzheimer's disease

Inheritance of the epsilon4 allele of apolipoprotein E (APOE, gene; apoE, protein) represents the most common genetic risk factor for developing Alzheimer's disease (AD), but the role of apoE in AD pathogenesis is yet to be clarified. A number of studies investigating apoE expression and protein levels in AD brain in correlation to its genetic polymorphism has yielded controversial results. We designed our approach based on neuropathological characteristics of AD to investigate apoE levels in relation to the APOE genotype and AD-related neurofibrillary changes, and amyloid deposits. We determined hippocampal apoE levels by reducing sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting in 70 Braak-staged and APOE-genotyped autopsy brains. In our stage-, age- and gender-matched case sample, we found a significant increase of hippocampal apoE in the APOE epsilon3 homozygotes with beginning AD-related pathology (Braak stages I and II) compared with brain samples free of neurofibrillary changes and amyloid deposits. In the APOE epsilon4 allele carriers no such increase was found. In both genotype groups, severely affected brain samples with widespread neurofibrillary changes (Braak stages V and VI) and amyloid deposits (Braak stage C) showed low apoE levels comparable to those found in unaffected brain samples (Braak stage 0). Our data suggests that the isoform-specific impact of apoE on the development of AD may be of crucial importance only in the early stages of the disease. These stages are believed to represent phases of the disease in which the beginning neurodegeneration can be compensated by plastic reorganization.

Age-dependent resistance to lethal alphavirus encephalitis in mice: analysis of gene expression in the central nervous system and identification of a novel interferon-inducible protective gene, mouse ISG12

Several different mammalian neurotropic viruses produce an age-dependent encephalitis characterized by more severe disease in younger hosts. To elucidate potential factors that contribute to age-dependent resistance to lethal viral encephalitis, we compared central nervous system (CNS) gene expression in neonatal and weanling mice that were either mock infected or infected intracerebrally with a recombinant strain, dsTE12Q, of the prototype alphavirus Sindbis virus. In 1-day-old mice, infection with dsTE12Q resulted in rapidly fatal disease associated with high CNS viral titers and extensive CNS apoptosis, whereas in 4-week-old mice, dsTE12Q infection resulted in asymptomatic infection with lower CNS virus titers and undetectable CNS apoptosis. GeneChip expression comparisons of mock-infected neonatal and weanling mouse brains revealed developmental regulation of the mRNA expression of numerous genes, including some apoptosis regulatory genes, such as the proapoptotic molecules caspase-3 and TRAF4, which are downregulated during development, and the neuroprotective chemokine, fractalkine, which is upregulated during postnatal development. In parallel with increased neurovirulence and increased viral replication, Sindbis virus infection in 1-day-old mice resulted in both a greater number of host inflammatory genes with altered expression and greater changes in levels of host inflammatory gene expression than infection in 4-week-old mice. Only one inflammatory response gene, an expressed sequence tag similar to human ISG12, increased by a greater magnitude in infected 4-week-old mouse brains than in infected 1-day-old mouse brains. Furthermore, we found that enforced neuronal ISG12 expression results in a significant delay in Sindbis virus-induced death in neonatal mice. Together, our data identify genes that are developmentally regulated in the CNS and genes that are differentially regulated in the brains of different aged mice in response to Sindbis virus infection.

Plasticity-associated molecular and structural events in the injured brain

Injury to the brain appears to create a fertile ground for functional and structural plasticity that is, at least partly, responsible for functional recovery. Increases in dendritic arborization, spine density, and synaptogenesis in both peri-injury and intact cortical areas are the potential morphological strategies that enable the brain to reorganize its neuronal circuits. These injury-initiated alterations are time-dependent and frequently proceed in interaction with behavior-related signals. A complex concert of a variety of genes/proteins is required to tightly control these changes. Two broad categories of molecules appear to be involved. First, regulatory molecules or effector molecules with regulatory function, such as immediate early genes/transcription factors, kinase network proteins, growth factors, and neurotransmitter receptors, and second, structural proteins, such as adhesion molecules and compounds of synapses, growth cones, and cytoskeleton. A better understanding of the processes contributing to postinjury plasticity may be an advantage for developing new and more effective therapeutic approaches. This knowledge might also shed light on other forms of brain plasticity, such as those involved in learning processes or ontogeny.

Modulation of apolipoprotein D and apolipoprotein E mRNA expression by growth arrest and identification of key elements in the promoter

Apolipoprotein D (apoD) and apolipoprotein E (apoE) are co-expressed in many tissues, and, in certain neuropathological situations, their expression appears to be under coordinate regulation. We have previously shown that apoD gene expression in cultured human fibroblasts is up-regulated when the cells undergo growth arrest. Here, we demonstrate that, starting around day 2 of growth arrest, both apoD and apoE mRNA levels increase between 1.5- and 27-fold in other cell types, including mouse primary fibroblasts and fibroblast-like and human astrocytoma cell lines. To understand the regulatory mechanisms of apoD expression, we have used apoD promoter-luciferase reporter constructs to compare gene expression in growing cells and in cells that have undergone growth arrest. Analysis of gene expression in cells transfected with constructs with deletions and mutations in the apoD promoter and constructs with artificial promoters demonstrated that the region between nucleotides -174 and -4 is fully responsible for the basal gene expression, whereas the region from -558 to -179 is implicated in the induction of apoD expression following growth arrest. Within this region, an alternating purine-pyrimidine stretch and a pair of serum-responsive elements (SRE) were found to be major determinants of growth arrest-induced apoD gene expression. Evidence is also presented that SREs in the apoE promoter may contribute to the up-regulation of apoE gene expression following growth arrest.

Gene expression profiling in perilesional and contralateral areas after ischemia in rat brain

Structural and functional reorganization in the vicinity of damaged neocortex and other connected brain areas seems to be responsible for postlesional functional recovery. To better understand the molecular mechanisms underlying this type of plasticity, gene expression patterns were analyzed by using DNA macroarrays comprising 1176 genes. Circumscribed unilateral infarcts consistently affecting the forelimb area of the motor cortex were induced photochemically in adult rats. Ten days after lesioning, cortical gene expression fingerprints were evaluated from an area adjacent to the lesion as well as two contralateral areas of motor and somatosensory cortex. Discrete regions showed distinct expression patterns. Upregulation was observed of different members of transcription factors, immediate early genes, neuronal signaling as well as neuronal growth and structure-associated genes, ipsilaterally (six genes) and/or contralaterally (eight genes in the motor and seven in the somatosensory cortex). In contrast, downregulations were restricted to ipsilateral areas and included genes coding for ion channels, transport proteins, mediators of metabolic pathways, and intracellular transducers (14 genes). A subset of these regulations were further confirmed by real-time polymerase chain reaction (TaqMan assay). At least part of the detected regulations, in particular those of the contralateral hemisphere, are likely to underlie plasticity processes.