I2-Imidazoline Ligand CR4056 Improves Memory, Increases ApoE Expression and Reduces BBB Leakage in 5xFAD Mice.

Recent evidence suggests that I2-imidazoline ligands have neuroprotective properties in animal models of neurodegeneration, such as Alzheimer's disease (AD). We recently demonstrated that the I2-ligand BU224 reversed memory impairments in AD transgenic mice and this effect was not because of reductions in amyloid-ß (Aß) deposition. In this study, our aim was to determine the therapeutic potential of the powerful analgesic I2-imidazoline ligand CR4056 in the 5xFAD model of AD, since this ligand has been proven to be safely tolerated in humans. Sub-chronic oral administration of CR4056 (30 mg/kg for 10 days) led to an improvement in recognition memory in 6-month-old 5xFAD mice, but not in wild-type littermates, without affecting Aß levels or deposition. Our results also revealed a change in the profile of microglia by CR4056, resulting in a suppression of pro-inflammatory activated microglia, but increased the density of astrocytes and the expression of ApoE, which is mainly produced by these glial cells. In addition, CR4056 restored fibrinogen extravasation, affecting the distribution of markers of astrocytic end feet in blood vessels. Therefore, these results suggest that CR4056 protects against Aß-mediated neuroinflammation and vascular damage, and offers therapeutic potential at any stage of AD.

ApoE (Apolipoprotein E) in Brain Pericytes Regulates Endothelial Function in an Isoform-Dependent Manner by Modulating Basement Membrane Components.

OBJECTIVE: The ε4 allele of the APOE gene (APOE4) is the strongest genetic risk factor for Alzheimer disease when compared with the common ε3 allele. Although there has been significant progress in understanding how apoE4 (apolipoprotein E4) drives amyloid pathology, its effects on amyloid-independent pathways, in particular cerebrovascular integrity and function, are less clear. Approach and Results: Here, we show that brain pericytes, the mural cells of the capillary walls, differentially modulate endothelial cell phenotype in an apoE isoform-dependent manner. Extracellular matrix protein induction, tube-like structure formation, and barrier formation were lower with endothelial cells cocultured with pericytes isolated from apoE4-targeted replacement (TR) mice compared with those from apoE3-TR mice. Importantly, aged apoE4-targeted replacement mice had decreased extracellular matrix protein expression and increased plasma protein leakages compared with apoE3-TR mice. CONCLUSIONS: ApoE4 impairs pericyte-mediated basement membrane formation, potentially contributing to the cerebrovascular effects of apoE4.

Brain-derived neurotrophic factor modulates cholesterol homeostasis and Apolipoprotein E synthesis in human cell models of astrocytes and neurons.

In the central nervous system, cholesterol is critical to maintain membrane plasticity, cellular function, and synaptic integrity. In recent years, much attention was focused on the role of cholesterol in brain since a breakdown of cholesterol metabolism has been associated with different diseases. Brain-derived neurotrophic factor (BDNF) was previously reported to elicit cholesterol biosynthesis and promote the accumulation of presynaptic proteins in cholesterol-rich lipid rafts, but no data are available on its ability to modulate physiological mechanisms involved in cholesterol homeostasis. Major aim of this research was to investigate whether BDNF influences cholesterol homeostasis, focusing on the effect of the neurotrophin on Apolipoprotein E (ApoE) synthesis, cholesterol efflux from astrocytes and cholesterol incorporation into neurons. Our results show that BDNF significantly stimulates cholesterol efflux by astrocytes, as well as ATP binding cassette A1 (ABCA1) transporter and ApoE expression. Conversely, cholesterol uptake in neurons was downregulated by BDNF. This effect was associated with the increase of Liver X Receptor (LXR)-beta expression in neuron exposed to BDNF. The level of apoptosis markers, that is, cleaved caspase 3 and poly ADP ribose polymerase (PARP), was found increased in neurons treated with high cholesterol, but significantly lower when the cells were exposed to cholesterol in the presence of BDNF, thus suggesting a neuroprotective role of the neurotrophin, likely through its reducing effect of neuronal cholesterol uptake. Interestingly, cholesterol stimulates BDNF production by neurons. Overall, our findings evidenced a novel role of BDNF in the modulation of ApoE and cholesterol homeostasis in glial and neuronal cells.

ABCA1/ApoE/HDL Pathway Mediates GW3965-Induced Neurorestoration After Stroke.

BACKGROUND AND PURPOSE: ATP-binding cassette transporter A1 (ABCA1) is a major reverse cholesterol transporter and plays critical role in the formation of brain high-density lipoprotein (HDL) cholesterol. Apolipoprotein E (ApoE) is the most abundant apolipoprotein and transports cholesterol into cells in brain. ABCA1 and ApoE are upregulated by liver-X receptors. Activation of liver-X receptors has neurorestorative benefit for stroke. The current study investigates whether ABCA1/ApoE/HDL pathway mediates GW3965, a synthetic dual liver-X receptor agonist, induced neurorestoration after stroke. METHODS: Middle-aged male specific brain ABCA1-deficient (ABCA1-B/-B) and floxed-control (ABCA1fl/fl) mice were subjected to distal middle-cerebral artery occlusion (dMCAo) and gavaged with saline or GW3965 (10 mg/kg) or intracerebral infusion of artificial cerebrospinal fluid or human plasma HDL3 in ABCA1-B/-B stroke mice, starting 24 hours after dMCAo and daily until euthanization 14 days after dMCAo. RESULTS: No differences in the blood level of total cholesterol and triglyceride and lesion volume were found among the groups. Compared with ABCA1fl/fl ischemic mice, ABCA1-B/-B ischemic mice exhibited impairment functional outcome and decreased ABCA1/ApoE expression and decreased gray/white matter densities in the ischemic boundary zone 14 days after dMCAo. GW3965 treatment of ABCA1fl/fl ischemic mice led to increased brain ABCA1/ApoE expression, concomitantly to increased blood HDL, gray/white matter densities and oligodendrocyte progenitor cell numbers in the ischemic boundary zone, as well as improved functional outcome 14 days after dMCAo. GW3965 treatment had negligible beneficial effects in ABCA1-B/-B ischemic mice. However, intracerebral infusion of human plasma HDL3 significantly attenuated ABCA1-B/-B-induced deficits. In vitro, GW3965 treatment (5 µM) increased ABCA1/synaptophysin level and neurite/axonal outgrowth in primary cortical neurons derived from ABCA1fl/fl embryos, but not in neurons derived from ABCA1-B/-B embryos. HDL treatment (80 µg/mL) attenuated the reduction of neurite/axonal outgrowth in neurons derived from ABCA1-B/-B embryos. CONCLUSIONS: ABCA1/ApoE/HDL pathway, at least partially, contributes to GW3965-induced neurorestoration after stroke.

Epigenetic Control of Apolipoprotein E Expression Mediates Gender-Specific Hematopoietic Regulation.

Epigenetic alterations play a central role in the control of normal and malignant blood cell development. We demonstrate here that expression of a truncated DNA methyltransferase 3B isoform DNMT3B7, which has been shown to alter cellular epigenetic patterns, decreases the overall number of hematopoietic stem and progenitor cells (HSPCs), and markedly diminishes blood cell reconstitution within the female hormonal microenvironment. Gene expression profiling of HSPCs isolated from DNMT3B7 transgenic embryos identified Apolipoprotein E (Apoe) as overexpressed. The CpG island controlling Apoe expression had lower levels of modified cytosines in DNMT3B7 transgenic HSPCs, corresponding with the observed increase in gene expression. Furthermore, we observed that spleens and bone marrows of female mice transplanted with DNMT3B7 transgenic HSPCs express very high levels of Apoe. Finally, the introduction of Apoe-overexpressing HSPCs into male recipients decreased bone marrow engraftment, recapitulating our original observations in female recipients. Our work reveals a dynamic interplay between the intrinsic epigenetic changes in HSPCs and extrinsic endocrine factors acting on these cells to regulate the efficiency of HSPC engraftment and reconstitution. We have identified a novel mechanism by which gender-specific hormones modulate HSPC function, which could serve as a target for augmenting hematopoiesis in cases with limited HSC functionality.

Overexpression of full-length cholesteryl ester transfer protein in SW872 cells reduces lipid accumulation.

Cells produce two cholesteryl ester transfer protein (CETP) isoforms, full-length and a shorter variant produced by alternative splicing. Blocking synthesis of both isoforms disrupts lipid metabolism and storage. To further define the role of CETP in cellular lipid metabolism, we stably overexpressed full-length CETP in SW872 cells. These CETP(+) cells had several-fold higher intracellular CETP and accumulated 50% less TG due to a 26% decrease in TG synthesis and 2.5-fold higher TG turnover rate. Reduced TG synthesis was due to decreased fatty acid uptake and impaired conversion of diglyceride to TG even though diacylglycerol acyltransferase activity was normal. Sterol-regulatory element binding protein 1 mRNA levels were normal, and although PPARγ expression was reduced, the expression of several of its target genes including adipocyte triglyceride lipase, FASN, and APOE was normal. CETP(+) cells contained smaller lipid droplets, consistent with their higher levels of perilipin protein family (PLIN) 3 compared with PLIN1 and PLIN2. Intracellular CETP was mostly associated with the endoplasmic reticulum, although CETP near lipid droplets poorly colocalized with this membrane. A small pool of CETP resided in the cytoplasm, and a subfraction coisolated with lipid droplets. These data show that overexpression of full-length CETP disrupts lipid homeostasis resulting in the formation of smaller, more metabolically active lipid droplets.

Macrophage-derived apoESendai suppresses atherosclerosis while causing lipoprotein glomerulopathy in hyperlipidemic mice.

Lipoprotein glomerulopathy (LPG) is a renal disease often accompanied by dyslipidemia and increased serum apoE levels. apoESendai (Arg145Pro), a rare mutant based on the apoE3 sequence carrying an apoE2 charge, causes LPG in humans and transgenic mice, but its effects on the artery wall are unknown. Macrophage expression of apoESendai may also directly influence renal and arterial homeostasis. We investigated the effects of macrophage-expressed apoESendai in apoE(-/-) mice with or without LDL receptor (LDLR). Murine bone marrow transduced to express apoE2, apoE3, or apoESendai was transplanted into lethally irradiated mice. Macrophage apoESendai expression reduced aortic lesion size and inflammation by 32 and 28%, respectively, compared with apoE2 in apoE(-/-) recipients. No differences in lesion size or inflammation were found between apoESendai and apoE3 in apoE(-/-) recipients. Macrophage apoESendai expression also reduced aortic lesion size by 18% and inflammation by 29% compared with apoE2 in apoE(-/-)/LDLR(-/-) recipients. Glomerular lesions compatible with LPG with increased mesangial matrix, extracellular lipid accumulation, and focal mesangiolysis were only observed in apoE(-/-)/LDLR(-/-) mice expressing apoESendai. Thus, macrophage expression of apoESendai protects against atherosclerosis while causing lipoprotein glomerulopathy. This is the first demonstration of an apoprotein variant having opposing effects on vascular and renal homeostasis.

Nuclear receptor 4 group A member 1 determines hepatitis C virus entry efficiency through the regulation of cellular receptor and apolipoprotein E expression.

Orphan nuclear receptor subfamily 4 group A member 1 (NR4A1) is a transcription factor stimulated by many factors and plays pivotal roles in metabolism, proliferation and apoptosis. In this study, the expression of NR4A1 in Huh7.5.1 cells was significantly upregulated by hepatitis C virus (HCV) infection. The silencing of NR4A1 inhibited the entry of HCV and reduced the specific infectivity of secreted HCV particles but had only minor or no effect on the genome replication and translation, virion assembly and virus release steps of the virus life cycle. Further experiments demonstrated that the silencing of NR4A1 affected virus entry through pan-downregulation of the expression of HCV receptors scavenger receptor BI, occludin, claudin-1 and epidermal growth factor receptor but not CD81. The reduced specific infectivity of HCV in the knockdown cells was due to decreased apolipoprotein E (ApoE) expression. These results explain the delayed spread of HCV in NR4A1 knockdown Huh7.5.1 cells. Thus, NR4A1 plays a role in HCV replication through regulating the expression of HCV receptors and ApoE, and facilitates HCV entry and spread.

Apolipoprotein E synthesized by adipocyte and apolipoprotein E carried on lipoproteins modulate adipocyte triglyceride content.

Excessive energy storage of adipose tissue makes contribution to the occurrence and progression of obesity, which accompanies with multiple adverse complications, such as metabolic syndrome, cardiovascular diseases. It is well known that apolipoprotein E, as a component of lipoproteins, performs a key role in maintaining plasma lipoproteins homeostasis. Interestingly, apolipoprotein E is highly expressed in adipocyte and has positive relation with body fat mass. Apolipoprotein E knock-out mice show small fat mass compared to wild type mice. Moreover, adipocyte deficiency in apolipoprotein E shows impaired lipoproeteins internalization and triglyceride accumulation. Apolipopreotein E-deficient lipoproteins can not induce preadipocyte to form round full-lipid adipocyte, whereas apolipoprotein E-containing lipoproteins can. This article mainly reviews the modulation of apolipoprotein E synthesized by adipocyte and apolipoprotein E carried on lipoproteins in adipocyte triglyceride content.

Strong reduction of low-density lipoprotein receptor/apolipoprotein E expressions by telmisartan in cerebral cortex and hippocampus of stroke resistant spontaneously hypertensive rats.

BACKGROUND: Telmisartan is a unique angiotensin II type 1 receptor blocker with a partial peroxisome proliferator-activated receptor-γ (PPARγ) agonistic property to exert not only antihypertensive effect but also antimetabolic syndrome effect. METHODS: We examined the long-term effect of telmisartan on cholesterol transport-related proteins (low-density lipoprotein receptor [LDL-R]/apolipoprotein E [ApoE]) and microtubule-associated proteins 2 (MAP2) in the brains of stroke resistant spontaneously hypertensive rats (SHR-SRs), which were divided into 3 experiment groups including vehicle group (SHR/Ve), low-dose telmisartan group (SHR/Low, .3 mg/kg/day), and high-dose telmisartan group (SHR/High, 3 mg/kg/day). RESULTS: The numbers of LDL-R- and immuno-ApoE-positive neurons increased in both cerebral cortex and hippocampus of SHR/Ve throughout 6, 12, and 18 months of age, compared with age-matched normotensive Wistar rats. On the other hand, telmisartan significantly reduced the numbers of LDL-R- and ApoE immuno-positive neurons in both cerebral cortex and hippocampus, with similar effectiveness in the SHR/Low group without blood pressure (BP) lowering to BP lowering (SHR/High). The decrease of MAP2-positive neuron in SHR/Ve was recovered by telmisartan in both cerebral cortex and hippocampus. CONCLUSIONS: These findings suggest that a long-term treatment with telmisartan directly improved neuronal lipid metabolism in the cerebral cortex and hippocampus of SHR-SR, mainly improving LDL-R and ApoE metabolism (SHR/Low) with a small additive benefit by BP lowering (SHR/High), which could provide a preventative approach in patients with hypertension at risk of Alzheimer disease.

ApoE derived from adipose tissue does not suppress atherosclerosis or correct hyperlipidemia in apoE knockout mice.

The synthesis of apoE by adipocytes has profound effects on adipose tissue lipid flux and gene expression. Using adipose tissue transplantation from wild-type (WT) to apoE knockout (EKO) mice, we show that adipose tissue also contributes to circulating apoE. Different from circulating apoE produced by bone marrow transplantation (BMT), however, adipose tissue-derived apoE does not correct hyperlipidemia or suppress atherosclerosis. ApoE secreted by macrophages has a more acidic isoform distribution, and it increases binding of reconstituted VLDL particles to hepatocytes and fibroblasts more effectively than apoE secreted by adipocytes. The incremental binding can be entirely accounted for by binding to the LDL receptor. After BMT into EKO hosts, plasma cholesterol and macrophage-derived apoE are largely within IDL/LDL- and HDL-sized particles. After adipose tissue transplantation, most cholesterol and adipocyte apoE remain in VLDL. After BMT, circulating apoE no longer demonstrates predominance of acidic isoforms compared with that circulating after fat transplantation. In conclusion, fat transplantation provides circulating apoE levels similar to those provided by bone marrow transplantation, but it does not suppress hyperlipidemia or atherosclerosis. A potential mechanism contributing to this difference is differential binding to cell surface lipoprotein receptors.

Arctigenin promotes cholesterol efflux from THP-1 macrophages through PPAR-γ/LXR-α signaling pathway.

Cholesterol efflux from macrophages is a critical mechanism to prevent the development of atherosclerosis. Here, we sought to investigate the effects of arctigenin, a bioactive component of Arctium lappa, on the cholesterol efflux in oxidized low-density lipoprotein (oxLDL)-loaded THP-1 macrophages. Our data showed that arctigenin significantly accelerated apolipoprotein A-I- and high-density lipoprotein-induced cholesterol efflux in both dose- and time-dependent manners. Moreover, arctigenin treatment enhanced the expression of ATP binding cassette transporter A1 (ABCA1), ABCG1, and apoE, all of which are key molecules in the initial step of cholesterol efflux, at both mRNA and protein levels. Arctigenin also caused a concentration-dependent elevation in the expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ) and liver X receptor-alpha (LXR-α). The arctigenin-mediated induction of ABCA1, ABCG1, and apoE was abolished by specific inhibition of PPAR-γ or LXR-α using small interfering RNA technology. Our results collectively indicate that arctigenin promotes cholesterol efflux in oxLDL-loaded THP-1 macrophages through upregulation of ABCA1, ABCG1 and apoE, which is dependent on the enhanced expression of PPAR-γ and LXR-α.

Expression of adhesion, attachment and invasion markers in eutopic and ectopic endometrium: a link to the aetiology of endometriosis.

BACKGROUND: Cell properties, such as attachment, adhesion and invasion, are important for the normal function of the endometrium. However, it is believed that the same properties may also be involved in the development of gynaecological diseases, such as endometriosis. Endometrial cells, shed by retrograde menstruation, may have an aberrant expression of molecules involved in these functions, leading to endometriosis. Therefore, the aim of this study was to investigate the expression of proteins involved in adhesion, attachment and invasion in eutopic and ectopic endometrium. METHODS: Endometrial biopsy specimens were collected from healthy volunteers (controls: proliferative phase, n = 10; secretory phase, n = 15) and from endometriosis patients (proliferative phase: n = 9, secretory phase: n = 10). Biopsy specimens from endometriomas were also collected (proliferative phase: n = 9, secretory phase: n = 10). Expression of apolipoprotein E (ApoE), integrin ß-2 (ITGB2), integrin ß-7 (ITGB7), Laminin γ-1 (LAMC1), CD24 molecule (CD24) and junctional adhesion molecule-1 (JAM-1) was evaluated with real-time reverse transcriptase polymerase chain reaction and immunohistochemistry. RESULTS: The endometrium from controls and women with endometriosis expressed ApoE, ITGB2, ITGB7, LAMC1, CD24 and JAM-1. Gene expression of ApoE and JAM-1 was decreased in both proliferative and secretory phase in the endometrium from women with endometriosis compared with control endometrium. Also, mRNA expression of LAMC1 was reduced in the endometrium from endometriosis patients compared with controls in the proliferative phase. An altered gene expression of CD24 was seen between the endometrium from endometriosis patients and endometriomas in the secretory phase. The ITGB2 protein expression was altered in epithelia cells between the endometrium from healthy volunteers and endometriosis patients in the secretory phase. CONCLUSIONS: We have shown differential expression of adhesion, attachment and invasion proteins in proliferative and secretory endometrium from controls and endometriosis patients and in endometriomas. This study suggests that molecules with these properties may have a role in the anchoring of endometrial cells at ectopic sites, thus initiating the development of endometriosis.

Molecular signatures in post-mortem brain tissue of younger individuals at high risk for Alzheimer's disease as based on APOE genotype.

Alzheimer's disease (AD) is a neurodegenerative condition characterized histopathologically by neuritic plaques and neurofibrillary tangles. The objective of this transcriptional profiling study was to identify both neurosusceptibility and intrinsic neuroprotective factors at the molecular level, not confounded by the downstream consequences of pathology. We thus studied post-mortem cortical tissue in 28 cases that were non-APOE4 carriers (called the APOE3 group) and 13 cases that were APOE4 carriers. As APOE genotype is the major genetic risk factor for late-onset AD, the former group was at low risk for development of the disease and the latter group was at high risk for the disease. Mean age at death was 42 years and none of the brains had histopathology diagnostic of AD at the time of death. We first derived interregional difference scores in expression between cortical tissue from a region relatively invulnerable to AD (primary somatosensory cortex, BA 1/2/3) and an area known to be susceptible to AD pathology (middle temporal gyrus, BA 21). We then contrasted the magnitude of these interregional differences in between-group comparisons of the APOE3 (low risk) and APOE4 (high risk) genotype groups. We identified 70 transcripts that differed significantly between the groups. These included EGFR, CNTFR, CASP6, GRIA2, CTNNB1, FKBPL, LGALS1 and PSMC5. Using real-time quantitative PCR, we validated these findings. In addition, we found regional differences in the expression of APOE itself. We also identified multiple Kyoto pathways that were disrupted in the APOE4 group, including those involved in mitochondrial function, calcium regulation and cell-cycle reentry. To determine the functional significance of our transcriptional findings, we used bioinformatics pathway analyses to demonstrate that the molecules listed above comprised a network of connections with each other, APOE, and APP and MAPT. Overall, our results indicated that the abnormalities that we observed in single transcripts and in signaling pathways were not the consequences of diagnostic plaque and tangle pathology, but preceded it and thus may be a causative link in the long molecular prodrome that results in clinical AD.

Design, synthesis and identification of a new class of triarylmethyl amine compounds as inhibitors of apolipoprotein E production.

We have identified a new class of triarylmethyl amine compounds that can inhibit apolipoprotein E (apoE) production. ApoE is a cholesterol- and lipid-carrier protein implicated in aging, atherosclerosis, Alzheimer's Disease (AD), and other neurological and lipid-related disorders. Attenuation of apoE production is generally considered to be of therapeutic value. A majority of the apoE in the brain is produced by astrocytes. Here, we describe the design, synthesis, and biological screening of a small library of compounds that led to the identification of four triarylmethyl amines as potent inhibitors of apoE production in CCF-STTG1 astrocytoma cells.

Apolipoprotein E expression is elevated by interleukin 1 and other interleukin 1-induced factors.

BACKGROUND: We have previously outlined functional interactions, including feedback cycles, between several of the gene products implicated in the pathogenesis of Alzheimer's disease. A number of Alzheimer-related stressors induce neuronal expression of apolipoprotein E (ApoE), ß-amyloid precursor protein (ßAPP), and fragments of the latter such as amyloid ß-peptide (Aß) and secreted APP (sAPP). These stressors include interleukin-1 (IL-1)-mediated neuroinflammation and glutamate-mediated excitotoxicity. Such circumstances are especially powerful when they transpire in the context of an APOE ε4 allele. METHODS: Semi-quantitative immunofluorescence imaging was used to analyze rat brains implanted with IL-1ß slow-release pellets, sham pellets, or no pellets. Primary neuronal or NT2 cell cultures were treated with IL-1ß, glutamate, Aß, or sAPP; relative levels of ApoE mRNA and protein were measured by RT-PCR, qRT-PCR, and western immunoblot analysis. Cultures were also treated with inhibitors of multi-lineage kinases--in particular MAPK-p38 (SB203580), ERK (U0126), or JNK (SP600125)--prior to exposure of cultures to IL-1ß, Aß, sAPP, or glutamate. RESULTS: Immunofluorescence of tissue sections from pellet-implanted rats showed that IL-1ß induces expression of ßAPP, IL-1α, and ApoE; the latter was confirmed by western blot analysis. These protein changes were mirrored by increases in their mRNAs, as well as in those encoding IL-1ß, IL-1ß-converting enzyme (ICE), and tumor necrosis factor (TNF). IL-1ß also increased ApoE expression in neuronal cultures. It stimulated release of sAPP and glutamate in these cultures too, and both of these agents--as well as Aß--stimulated ApoE expression themselves, suggesting that they may contribute to the effect of IL-1ß on ApoE levels. Inhibitors of MAPK-p38, ERK, and JNK inhibited ApoE induction by all these agents except glutamate, which was sensitive only to inhibitors of ERK and JNK. CONCLUSION: Conditions of glial activation and hyperexcitation can elevate proinflammatory cytokines, ApoE, glutamate, ßAPP, and its secreted fragments. Because each of these factors promotes glial activation and neuronal hyperexcitation, these relationships have the potential to sustain self-propagating neurodegenerative cycles that could culminate in a progressive neurodegenerative disorder such as Alzheimer's disease.

Microarray analysis of cultured rat hippocampal neurons treated with brain derived neurotrophic factor.

Brain derived neurotrophic factor (BDNF) has been shown to exert multiple actions on neurons. It plays a role in neuronal growth and maintenance and use-dependent plasticity, such as long-term potentiation and learning. This neurotrophin is believed to regulate neuronal plasticity by modifying neuronal excitability and morphology. There is experimental evidence for both an acute and a long-term effect of BDNF on synaptic transmission and structure but the molecular mechanisms underlying these events have not been completely clarified. In order to study the BDNF-induced molecular changes, the set of genes modulated in cultured hippocampal neurons by BDNF treatment was investigated after subchronic treatment with the neurotrophin. Microarray analysis performed with these cells, revealed increased expression of mRNA encoding the neuropeptides neuropeptide Y and somatostatin, and of the secreted peptide VGF (non acronymic), all of which participate in neurotransmission. In addition, the expression of genes apolipoprotein E (ApoE), delta-6 fatty acid desaturase (Fads2) and matrix metalloproteinase 14 (Mmp14), which play a role in neuronal remodelling, was also enhanced. More studies are needed to investigate and confirm the role of these genes in synaptic plasticity, but the results reported in this paper show that microarray analysis of hippocampal cultures can be used to expand our current knowledge of the molecular events triggered by BDNF in the hippocampus.

Neuronal ApoE upregulates MHC-I expression to drive selective neurodegeneration in Alzheimer's disease.

Selective neurodegeneration is a critical causal factor in Alzheimer's disease (AD); however, the mechanisms that lead some neurons to perish, whereas others remain resilient, are unknown. We sought potential drivers of this selective vulnerability using single-nucleus RNA sequencing and discovered that ApoE expression level is a substantial driver of neuronal variability. Strikingly, neuronal expression of ApoE-which has a robust genetic linkage to AD-correlated strongly, on a cell-by-cell basis, with immune response pathways in neurons in the brains of wild-type mice, human ApoE knock-in mice and humans with or without AD. Elimination or over-expression of neuronal ApoE revealed a causal relationship among ApoE expression, neuronal MHC-I expression, tau pathology and neurodegeneration. Functional reduction of MHC-I ameliorated tau pathology in ApoE4-expressing primary neurons and in mouse hippocampi expressing pathological tau. These findings suggest a mechanism linking neuronal ApoE expression to MHC-I expression and, subsequently, to tau pathology and selective neurodegeneration.

Hyperglycemia and advanced glycosylation end products suppress adipocyte apoE expression: implications for adipocyte triglyceride metabolism.

Endogenous adipocyte apolipoprotein E (apoE) plays an important role in adipocyte lipoprotein metabolism and lipid flux. A potential role for hyperglycemia in regulating adipocyte apoE expression and triglyceride metabolism was examined. Exposure of adipocytes to high glucose or advanced glycosylation end product-BSA significantly suppressed apoE mRNA and protein levels. This suppression was significantly attenuated by antioxidants or inhibitors of the NF-κB transcription pathway. Hyperglycemia in vivo led to adipose tissue oxidant stress and significant reduction in adipose tissue and adipocyte apoE mRNA level. Incubation with antioxidant in organ culture completely reversed this suppression. Hyperglycemia also reduced adipocyte triglyceride synthesis, and this could be completely reversed by adenoviral-mediated increases in apoE. To more specifically evaluate an in vivo role for adipocyte apoE expression on organismal triglyceride distribution in vivo, WT or apoE knockout (EKO) adipose tissue was transplanted in EKO recipient mice. After 12 wk, WT adipocytes transplanted in EKO mice accumulated more triglyceride compared with transplanted EKO adipocytes. In addition, EKO recipients of WT adipose tissue had reduced hepatic triglyceride content compared with EKO recipients transplanted with EKO adipose tissue. Our results demonstrate that hyperglycemia and advanced glycosylation end products suppress the expression of adipocyte apoE in vitro and in vivo and thereby reduce adipocyte triglyceride synthesis. In vivo results using adipose tissue transplantation suggest that reduction of adipocyte apoE, and subsequent reduction of adipocyte triglyceride accumulation, could influence lipid accumulation in nonadipose tissue.

Factor B, the complement alternative pathway serine proteinase, is a major constitutive protein synthesized and secreted by resident and elicited mouse macrophages.

Factor B, the complement alternative pathway serine proteinase, a class III gene product of the major histocompatibility complex, is a major constitutive secretion product of mouse mononuclear phagocytes. This glycoprotein was synthesized and secreted by macrophages as a doublet of Mr 90,000 and 93,000 polypeptides that were immunoprecipitable with antibodies raised to human serum factor B, and that were indistinguishable from plasma factor B by immunoreactivity, peptide mapping, and molecular weight. Macrophage factor B was cleaved and activated to factor Bb- and Ba-like fragments by factor D and cobra venom factor. Some conversion of macrophage factor B to Bb-sized fragments occurred spontaneously in the conditioned culture medium after several hours. Factor B represented approximately 0.5% of newly synthesized protein and 4-6% of the secreted protein of resident peritoneal macrophages and macrophages elicited with thioglycollate broth, pyran copolymer, NaIO4, bacillus Calmette-Guerin, or Corynebacterium parvum. We detected synthesis of factor B immediately upon explanting these macrophages in culture; synthesis continued for several days in culture. The rate of secretion of factor B, as a proportion of total protein secretion in culture, remained constant with time. By radioimmunoassay, factor B antigens accumulated in the 24-h macrophage-conditioned culture medium at 2-10 nM, and was present in cell lysates at 4-8 nmol per 10(6) cells. We detected synthesis of factor B in bone marrow-derived macrophages as early as 5 d of culture. The P388D1 macrophage line synthesized factor B, but mouse L cells did not. In contrast, apolipoprotein E, another secreted protein of macrophages, was secreted by resident and thioglycollate-elicited macrophages but not by freshly harvested pyran copolymer-activated macrophages. Its synthesis was initiated at day 9 in culture of bone marrow-derived macrophages. These data support the classification of factor B as a constitutive biosynthetic and secreted protein of immature and mature macrophages in various states of activation. Production of factor B was modulated by treatment of macrophages in vivo or in culture with bacterial lipopolysaccharide endotoxin, which increased the synthesis, secretion, and accumulation of factor B up to 11-fold.