ATP-binding cassette transporter ABCA2 (ABC2) expression in the developing spinal cord and PNS during myelination

Glyphosate infiltrates the brain and increases pro-inflammatory cytokine TNFα: implications for neurodegenerative disorders

BACKGROUND

Herbicides are environmental contaminants that have gained much attention due to the potential hazards they pose to human health. Glyphosate, the active ingredient in many commercial herbicides, is the most heavily applied herbicide worldwide. The recent rise in glyphosate application to corn and soy crops correlates positively with increased death rates due to Alzheimer's disease and other neurodegenerative disorders. Glyphosate has been shown to cross the blood-brain barrier in in vitro models, but has yet to be verified in vivo. Additionally, reports have shown that glyphosate exposure increases pro-inflammatory cytokines in blood plasma, particularly TNFα.

METHODS

Here, we examined whether glyphosate infiltrates the brain and elevates TNFα levels in 4-month-old C57BL/6J mice. Mice received either 125, 250, or 500 mg/kg/day of glyphosate, or a vehicle via oral gavage for 14 days. Urine, plasma, and brain samples were collected on the final day of dosing for analysis via UPLC-MS and ELISAs. Primary cortical neurons were derived from amyloidogenic APP/PS1 pups to evaluate in vitro changes in Aβ40-42 burden and cytotoxicity. RNA sequencing was performed on C57BL/6J brain samples to determine changes in the transcriptome.

RESULTS

Our analysis revealed that glyphosate infiltrated the brain in a dose-dependent manner and upregulated TNFα in both plasma and brain tissue post-exposure. Notably, glyphosate measures correlated positively with TNFα levels. Glyphosate exposure in APP/PS1 primary cortical neurons increases levels of soluble Aβ40-42 and cytotoxicity. RNAseq revealed over 200 differentially expressed genes in a dose-dependent manner and cell-type-specific deconvolution analysis showed enrichment of key biological processes in oligodendrocytes including myelination, axon ensheathment, glial cell development, and oligodendrocyte development.

CONCLUSIONS

Collectively, these results show for the first time that glyphosate infiltrates the brain, elevates both the expression of TNFα and soluble Aβ, and disrupts the transcriptome in a dose-dependent manner, suggesting that exposure to this herbicide may have detrimental outcomes regarding the health of the general population.

The role of ATP-binding cassette subfamily A in the etiology of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the leading cause of dementia, clinically characterized by memory deficits and progressive cognitive decline. Despite decades of research effective therapies are lacking, and a large part of the genetic heritability remains unidentified. ABCA7 and ABCA1, members of the ATP-binding cassette subfamily A (ABCA), were identified as AD risk genes in genome-wide association studies. Nevertheless, genetic and/or functional studies propose a link between AD and two other members of the ABCA subclass, i.e., ABCA2 and ABCA5.

Main body

Changes in expression or dysfunction of these transporters were found to increase amyloid β levels. This might be related to the common role of ABCA transporters in cellular cholesterol homeostasis, for which a prominent role in AD development has been suggested. In this review, we provide a comprehensive overview and discussion on the contribution of the ABCA subfamily to the etiopathogenesis of AD.

Conclusions

A better understanding of the function and identification of disease-associated genetic variants in ABCA transporters can contribute to the development of novel therapeutic strategies for AD.

Brain Distribution of Drugs: Brain Morphology, Delivery Routes, and Species Differences

Neuropharmacokinetics considers cerebral drug distribution as a critical process for central nervous system drug action as well as for drug penetration through the CNS barriers. Brain distribution of small molecules obeys classical rules of drug partition, permeability, binding to fluid proteins or tissue components, and tissue perfusion. The biodistribution of all drugs, including both small molecules and biologics, may also be influenced by specific brain properties related to brain anatomy and physiological barriers, fluid dynamics, and cellular and biochemical composition, each of which can exhibit significant interspecies differences. All of these properties contribute to select optimal dosing paradigms and routes of drug delivery to reach brain targets for classical small molecule drugs as well as for biologics. The importance of these properties for brain delivery and exposure also highlights the need for efficient new analytical technologies to more comprehensively investigate drug distribution in the CNS, a complex multi-compartmentalized organ system.

ABC efflux transporters at blood-central nervous system barriers and their implications for treating spinal cord disorders

The barriers present in the interfaces between the blood and the central nervous system form a major hurdle for the pharmacological treatment of central nervous system injuries and diseases. The family of ATP-binding cassette (ABC) transporters has been widely studied regarding efflux of medications at blood-central nervous system barriers. These efflux transporters include P-glycoprotein (abcb1), 'breast cancer resistance protein' (abcg2) and the various 'multidrug resistance-associated proteins' (abccs). Understanding which efflux transporters are present at the blood-spinal cord, blood-cerebrospinal fluid and cerebrospinal fluid-spinal cord barriers is necessary to determine their involvement in limiting drug transfer from blood to the spinal cord tissue. Recent developments in the blood-brain barrier field have shown that barrier systems are dynamic and the profile of barrier defenses can alter due to conditions such as age, disease and environmental challenge. This means that a true understanding of ABC efflux transporter expression and localization should not be one static value but instead a range that represents the complex patient subpopulations that exist. In the present review, the blood-central nervous system barrier literature is discussed with a focus on the impact of ABC efflux transporters on: (i) protecting the spinal cord from adverse effects of systemically directed drugs, and (ii) limiting centrally directed drugs from accessing their active sites within the spinal cord.

Ablation of the ATP-binding cassette transporter, Abca2 modifies response to estrogen-based therapies

The ATP-binding cassette transporter 2 (ABCA2) is an endolysosomal protein expressed in oligodendrocytes and Schwann cells, prostate, ovary and macrophages. In cell cultures, ABCA2 over-expression has been linked with resistance to the anticancer agent, estramustine phosphate (EMP; a nor-nitrogen mustard conjugate of estradiol). The present study shows that Abca2 knockout (KO) mice have greater sensitivity to a variety of side effects induced by EMP treatment. Chronic EMP (12×100 mg/kg body weight) produced mortality in 36% of KO mice, but only 7% of age-matched wild type (WT). Side effects of the drug were also more prevalent in the KO mouse. For example, during the first week of EMP treatments, 67% of KO males (compared to 6% of WT males) responded with episodic erectile events. In WT mice, ABCA2 protein localized within pene corpuscles, (which rely on modified Schwann cells for amplification of tactile signals) suggesting that the transporter may function in the erectile process. Endothelial nitric oxide synthase (eNOS; a source of nitric oxide during erectile response) levels were similar in WT and KO male penile tissue. Treatment with 100 mg/kg EMP (once daily for four days) elevated serum estradiol and estrone in both WT and KO. However, the circulating levels of these estrogens were higher in KO mice implying a reduced plasma clearance of estrogens as a consequence of ABCA2 ablation. Consistent with the pro-convulsant effects of estrogens, KO mice also displayed an increased incidence of seizures following EMP (14% vs. 0%). Taken together, these data indicate that ABCA2 deficiency renders mice more sensitive to EMP treatment-induced effects implying that the transporter has a role in regulating EMP transport and/or metabolism.

Developmental expression of orphan G protein-coupled receptor 50 in the mouse brain

Mental disorders have a complex etiology resulting from interactions between multiple genetic risk factors and stressful life events. Orphan G protein-coupled receptor 50 (GPR50) has been identified as a genetic risk factor for bipolar disorder and major depression in women, and there is additional genetic and functional evidence linking GPR50 to neurite outgrowth, lipid metabolism, and adaptive thermogenesis and torpor. However, in the absence of a ligand, a specific function has not been identified. Adult GPR50 expression has previously been reported in brain regions controlling the HPA axis, but its developmental expression is unknown. In this study, we performed extensive expression analysis of GPR50 and three protein interactors using rt-PCR and immunohistochemistry in the developing and adult mouse brain. Gpr50 is expressed at embryonic day 13 (E13), peaks at E18, and is predominantly expressed by neurons. Additionally we identified novel regions of Gpr50 expression, including brain stem nuclei involved in neurotransmitter signaling: the locus coeruleus, substantia nigra, and raphe nuclei, as well as nuclei involved in metabolic homeostasis. Gpr50 colocalizes with yeast-two-hybrid interactors Nogo-A, Abca2, and Cdh8 in the hypothalamus, amygdala, cortex, and selected brain stem nuclei at E18 and in the adult. With this study, we identify a link between GPR50 and neurotransmitter signaling and strengthen a likely role in stress response and energy homeostasis.

A-Subclass ATP-Binding Cassette Proteins in Brain Lipid Homeostasis and Neurodegeneration

The A-subclass of ATP-binding cassette (ABC) transporters comprises 12 structurally related members of the evolutionarily highly conserved superfamily of ABC transporters. ABCA transporters represent a subgroup of "full-size" multispan transporters of which several members have been shown to mediate the transport of a variety of physiologic lipid compounds across membrane barriers. The importance of ABCA transporters in human disease is documented by the observations that so far four members of this protein family (ABCA1, ABCA3, ABCA4, ABCA12) have been causatively linked to monogenetic disorders including familial high-density lipoprotein deficiency, neonatal surfactant deficiency, degenerative retinopathies, and congenital keratinization disorders. Recent research also point to a significant contribution of several A-subfamily ABC transporters to neurodegenerative diseases, in particular Alzheimer's disease (AD). This review will give a summary of our current knowledge of the A-subclass of ABC transporters with a special focus on brain lipid homeostasis and their involvement in AD.

The ATP-binding cassette transporter-2 (ABCA2) regulates cholesterol homeostasis and low-density lipoprotein receptor metabolism in N2a neuroblastoma cells

The ATP-binding cassette transporter-2 (ABCA2) has been identified as a possible regulator of lipid metabolism. ABCA2 is most highly expressed in the brain but its effects on cholesterol homeostasis in neuronal-type cells have not been characterized. It is important to study the role of ABCA2 in regulating cholesterol homeostasis in neuronal-type cells because ABCA2 has been identified as a possible genetic risk factor for Alzheimer's disease. In this study, the effects of ABCA2 expression on cholesterol homeostasis were examined in mouse N2a neuroblastoma cells. ABCA2 reduced total, free- and esterified cholesterol levels as well as membrane cholesterol but did not perturb cholesterol distribution in organelle or lipid raft compartments. ABCA2 did not modulate de novo cholesterol biosynthesis from acetate. Cholesterol trafficking to the plasma membrane was not affected by ABCA2 but efflux to the physiological acceptor ApoE3 and mobilization of plasma membrane cholesterol to the endoplasmic reticulum for esterification were reduced by ABCA2. ABCA2 reduced esterification of serum and low-density lipoprotein-derived cholesterol but not 25-hydroxycholesterol. ABCA2 decreased low-density lipoprotein receptor (LDLR) mRNA and protein levels and increased its turnover rate. The surface expression of LDLR as well as the uptake of fluroresecent DiI-LDL was also reduced by ABCA2. Reduction of endogenous ABCA2 expression by RNAi treatment of N2a cells and rat primary cortical neurons produced the opposite effects of over-expression of ABCA2, increasing LDLR protein levels. This report identifies ABCA2 as a key regulator of cholesterol homeostasis and LDLR metabolism in neuronal cells.

ABCA2 as a therapeutic target in cancer and nervous system disorders

BACKGROUND

Overexpression of ATP-binding cassette (ABC) transporters is a major adaptive advantage used by tumor cells to evade the accumulation of cytotoxic agents. ABCA2, a transporter highly expressed in the cells of the nervous and haematopoetic systems, is associated with lipid transport and drug resistance in cancer cells, including tumor stem cells. Recently, a single nucleotide polymorphism (SNP) in Abca2 was linked to early onset Alzheimer's disease (AD). The characterization of two independent knockout mouse models has shed light on putative in vivo functions of this transporter in the development and maintenance of myelin membrane lipids in the CNS.

OBJECTIVE

The objective of this review is to guide the reader through the existing scope of literature on the ABCA2 transporter, focusing on its potential as a future target in human pathologies, specifically cancer and neurological disease.

METHODS

An NCBI PubMed literature search was conducted to address the growing body of ABCA2 literature that, at the time of publication, included 39 reports. From these, we focused on papers that provided insight into the functional importance of this transporter in tumor stem cells, cancer, drug resistance, Alzheimer's disease and myelination.

RESULTS/CONCLUSION

These studies have implicated ABCA2 as a therapeutic target in modulating the drug resistance phenotype prevalent in human cancers and in the treatment of neuropathies, including Alzheimer's disease and myelin-related disorders.

ABCA2 Deficiency Results in Abnormal Sphingolipid Metabolism in Mouse Brain

ABCA2, a member of the ATP-binding cassette (ABC) transporter family, is localized mainly to late endosome/lysosomes of oligodendrocytes in brain, but the physiological role and function of ABCA2 are unknown. In this study, we generated mutant mice (ABCA2-null) by targeting the abca2 gene. ABCA2-null mice exhibited a phenotype including lower pregnancy rate and body weight, shorter latency period on the balance beam, and sensitization to environmental stress compared with wild type mice but no abnormality in the cytoarchitectonic and compact myelin structure or oligodendroglial differentiation. Lipid analysis of brain from 11 days to 64 weeks of age revealed significant accumulation of gangliosides along with reduced sphingomyelin (SM) from 4 weeks to 64 weeks of age and accumulation of cerebrosides and sulfatides at 64 weeks of age in ABCA2-null mice compared with wild type mice. In addition, a significant accumulation of the major ganglioside GM1 and reduced SM was detected in the myelin fraction of ABCA2-null brain. Comparison of ABCA2-null and wild type mice revealed weak ABCA2 immunoreactivity in some large pyramidal cells of wild type brain. These results suggest that ABCA2 is involved in the intracellular metabolism of sphingolipids in the brain, particularly SM and gangliosides in oligodendrocytes and certain neurons.

CLINICAL SIGNIFICANCE OF ABCA2, A POSSIBLE MOLECULAR MARKER FOR OLIGODENDROGLIOMAS

OBJECTIVE

ABCA2 is a member of the adenosine triphosphate-binding cassette transporter superfamily and is proposed to exert critical functions in the transmembrane transport of endogenous lipids such as myelin. It is expressed predominantly in the cytoplasm of oligodendrocytes and Schwann cells, the myelin-forming cells in the brain and peripheral nerves. Recently, it has been shown that it may be a useful marker for the cellular characterization of vestibular schwannomas.

METHODS

To determine whether or not ABCA2 can distinguish oligodendrogliomas from astrocytic tumors, the authors investigated the expression of ABCA2 in a panel of 55 glioma tissues (13 oligodendrogliomas, nine anaplastic oligodendrogliomas, 12 anaplastic astrocytomas, and 21 glioblastomas) using real-time reverse-transcriptase polymerase chain reaction analysis, immunoblot analysis, and immunohistochemistry analysis. The authors also compared the expression of Olig2, a recently identified marker for oligodendroglioma.

RESULTS

The relative expression level of ABCA2 messenger ribonucleic acid determined by real-time quantitative polymerase chain reaction is significantly higher (by a factor of five) in oligodendroglioma than in anaplastic astrocytoma or glioblastoma. It was moderately increased in anaplastic oligodendrogliomas. In immunohistochemical analysis, ABCA2 exhibited remarkable immunopositivity in 11 out of 13 oligodendrogliomas showing a granular pattern in the cytoplasm of tumor cells. However, ABCA2 was completely negative in most anaplastic astrocytomas (75%) and glioblastomas (76%). Anaplastic oligodendroglioma showed an intermediate pattern: strongly positive in two out of nine samples and negative in seven out of nine samples. However, Olig2 was strongly positive in most anaplastic astrocytomas (83%) and glioblastomas (71%). Although there was no difference in the detection of oligodendroglial tumors, the specificity (negative in astrocytic tumor) was significantly higher in ABCA2 than in Olig2.

CONCLUSION

These lines of evidence suggest that ABCA2 could be a molecular marker for oligodendroglioma.

Expression of ABCA2 protein in both non-myelin-forming and myelin-forming Schwann cells in the rodent peripheral nerve

We previously reported that ABCA2, of the A subclass of the ATP-binding cassette (ABC) transporter superfamily, is expressed in mature oligodendrocytes and Schwann cells, the cells responsible for myelination in the brain and the peripheral nerve, respectively. However, unidentified cells expressing ABCA2 also were found. Here, we provide evidence for the expression of ABCA2 in the rodent sciatic nerve not only in Schwann cells, which express the Schwann cell marker S100beta and a zinc finger transcription factor Krox20 (a marker for myelin-forming Schwann cells), but also in Krox20-negative cells, which express glial fibrillary acidic protein (GFAP), a cell adhesion molecule L1, and S100beta weekly. We also analyzed developmental changes in ABCA2 expression in Schwann cells. The expression of ABCA2 in Krox20+/S100beta+ Schwann cells was found initially in rat facial nerve at postnatal day (PD) 8, in half (52.4%) of the cells showing myelinization at PD 14, and in all of the cells in the adult stage. These results demonstrate that ABCA2 is expressed in non-myelin-forming as well as in myelin-forming Schwann cells, and that ABCA2 may be involved in transport of a substance associated with cellular maturation rather than initial myelin formation in both types of Schwann cells.

"Skittish" Abca2 knockout mice display tremor, hyperactivity, and abnormal myelin ultrastructure in the central nervous system

The ATP-binding cassette transporter 2 (ABCA2) is an endolysosomal protein most highly expressed in the central and peripheral nervous system tissues and macrophages. Previous studies indicated its role in cholesterol/steroid (estramustine, estradiol, and progesterone) trafficking/sequestration, oxidative stress response, and Alzheimer's disease. Developmental studies have shown its expression during macrophage and oligodendrocyte differentiation, processes requiring membrane growth. To determine the in vivo function(s) of this transporter, we generated a knockout mouse from a gene-targeted disruption of the murine ABCA2 gene. Knockout males and females are viable and fertile. However, a non-Mendelian inheritance pattern was shown among male progeny of heterozygous crosses. Compared to wild-type and heterozygous littermates, knockout mice displayed a tremor without ataxia, hyperactivity, and reduced body weight; the latter two phenotypes were more marked in females than in males. This sexual disparity suggests a role for ABCA2 in hormone-dependent neurological and/or developmental pathways. Myelin sheath thickness in the spinal cords of knockout mice was greatly increased compared to that in wild-type mice, while a significant reduction in myelin membrane periodicity (compaction) was observed in both spinal cords and cerebra of knockout mice. Loss of ABCA2 function in vivo resulted in abnormal myelin compaction in spinal cord and cerebrum, an ultrastructural defect that we propose to be the cause of the phenotypic tremor.

The ABCA subfamily--gene and protein structures, functions and associated hereditary diseases

To date, 12 members of the human ABCA subfamily are identified. They share a high degree of sequence conservation and have been mostly related with lipid trafficking in a wide range of body locations. Mutations in some of these genes have been described to cause severe hereditary diseases related with lipid transport, such as fatal surfactant deficiency or harlequin ichthyosis. In addition, most of them are hypothesized to participate in the subcellular sequestration of drugs, thereby being responsible for the resistance of several carcinoma cell lines against drug treatment. The objective of this review is to summarize the literature for this subfamily of ABC transporter proteins, excluding ABCA1 and ABCA4, which will be discussed in other chapters of this issue.

ABCA2 is a marker of neural progenitors and neuronal subsets in the adult rodent brain

The notion that the ATP-binding cassette transporter-A2 (ABCA2) may be involved in brain sterol homeostasis and is associated with early onset Alzheimer's disease led us to explore its neural expression. Our data support and extend the previous reports on ABCA2 expression by oligodendrocytes. They evidence that ABCA2 (i) is located in intracellular vesicles, identified in transfected cells as lysosome-related organelles only partially overlapping with classical endolysosomes; (ii) is a marker of neural progenitors as it is expressed in the subventricular zone of the lateral ventricle and the dentate gyrus of the hippocampal formation, sites of continual neurogenesis in the adult brain, and in nestin(+) cells differentiated in vitro from embryonic stem cells; (iii) persists, in the adult rodent brain, in a subset of GABAergic and glutamatergic neurons. Considering that the latter are targets of Alzheimer's lesions, these data provide a new rationale to explore the neuropathological consequences of ABCA2 functional dysregulations.

Peripheral neuropathy in genetic mitochondrial diseases

Peripheral neuropathy is an underrecognized but common occurrence in genetic mitochondrial disorders. To gain insight into the frequency and clinical presentation of this complication, nerve conduction studies were performed on 43 subjects with congenital lactic acidosis enrolled in a controlled clinical trial of oral dichloroacetate. Median and peroneal motor conduction studies and median and sural sensory conduction studies were performed on each patient. The mean amplitude of the peroneal motor nerve (P < 0.001) and the conduction velocities of the median (P < 0.001) and peroneal (P < 0.001) motor nerves were uniformly lower in our subjects than in healthy literature control subjects. There were no significant differences in sensory nerve conduction studies. A generalized reduction in motor nerve conduction velocity was the dominant electrophysiological abnormality in the patients in this study and was independent of age, sex, or congenital mitochondrial disorder. We postulate that cellular energy failure is the most likely common cause of peripheral neuropathy in patients with genetic mitochondrial diseases, owing to the high demand for adenosine triphosphate via aerobic carbohydrate metabolism by nerve tissue.

Protective effects of a peroxisome proliferator-activated receptor-beta/delta agonist in experimental autoimmune encephalomyelitis

Agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma) exert anti-inflammatory and anti-proliferative effects which led to testing of these drugs in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. In contrast, the effect of PPARdelta (PPARdelta) agonists in EAE is not yet known. We show that oral administration of the selective PPARdelta agonist GW0742 reduced clinical symptoms in C57BL/6 mice that had been immunized with encephalitogenic myelin oligodendrocyte glycoprotein (MOG) peptide. In contrast to previous results with PPARgamma agonists, GW0742 only modestly attenuated clinical symptoms when the drug was provided simultaneously with immunization, but a greater reduction was observed if administered during disease progression. Reduced clinical symptoms were accompanied by a reduction in the appearance of new cortical lesions, however cerebellar lesion load was not reduced. Treatment of T-cells with GW0742 either in vivo or in vitro did not reduce IFNgamma production; however GW0742 reduced astroglial and microglial inflammatory activation and IL-1beta levels in EAE brain. RTPCR analysis showed that GW0742 increased expression of some myelin genes. These data demonstrate that PPARdelta agonists, like other PPAR ligands, can exert protective actions in an autoimmune model of demyelinating disease.

Expression of ABCA2 protein in human vestibular schwannoma and peripheral nerve

ABCA2, which belongs to the A subclass of the ATP-binding cassette (ABC) transporter superfamily, is predominantly expressed in the cytoplasm of oligodendrocytes and Schwann cells, the myelin-forming cells in brain and peripheral nerve, respectively. Here, we demonstrate by immunoblot and immunohistochemistry that ABCA2 is expressed in benign vestibular schwannomas, which contain neither axons nor compact myelin. The expression patterns of ABCA2 in combination with other markers showed phenotypic heterogeneity in schwannomas. The majority of cells in fascicular Antoni type A areas coexpressed ABCA2, Ca2+-binding protein S100beta, and p75 nerve growth factor receptor. In contrast, considerably varied expression levels of ABCA2 and p75 were more prominent in hypocellular type B areas than in type A areas. These data suggest that ABCA2 may be useful as a marker for cellular characterization of schwannomas.

ATP binding cassette transporter ABC1 is required for the release of interleukin-1beta by P2X7-stimulated and lipopolysaccharide-primed mouse Schwann cells

Schwann cells are best known as myelinating glial cells of the peripheral nervous system, but they also participate actively in the sphere of immunity by producing pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta). In a previous study, we demonstrated that posttranslational processing of IL-1beta by immune-challenged Schwann cells required the P2X7 receptor. Remarkably, the release of IL-1beta was not associated with cell death, indicating the involvement of an active mechanism. ATP binding cassette (ABC) transporters are known to transport leaderless secretory proteins, such as IL-1beta; therefore, we investigated whether such transporters were at work in Schwann cells. Mouse Schwann cells expressed ABC1 transporter mRNA and displayed the functional protein. Glybenclamide and diisothiocyanato-stilbene-disulfonic acid (DIDS), two blockers of chloride fluxes that drive the export activity of ABC1 transporters, inhibited IL-1beta release without altering its intracellular processing. Enhancing chloride efflux potentiated the release of IL-1beta, while decreasing it led to a strong reduction in its release. Because the stimulation of the P2X7 receptor also activates a chloride conductance, we investigated the possibility of a sole anionic pathway mobilized by the P2X7 receptor and ABC1. Glybenclamide and DIDS had no significant effects on the P2X7-activated chloride current suggesting therefore the existence of two different pathways. In summary, ABC1 transporters are required for the release of IL-1beta by mouse Schwann cells. Being associated together with chloride conductance, P2X7 receptors and ABC1 transporters delineate a subtle and complex regulation of IL-1beta production in mammalian Schwann cells. Furthermore, ABC1 transporters could be a target of therapeutic interest for regulating IL-1beta activity in neuroinflammation disorders.

Identification of genetic networks

In this report, we propose the use of structural equations as a tool for identifying and modeling genetic networks and genetic algorithms for searching the most likely genetic networks that best fit the data. After genetic networks are identified, it is fundamental to identify those networks influencing cell phenotypes. To accomplish this task we extend the concept of differential expression of the genes, widely used in gene expression data analysis, to genetic networks. We propose a definition for the differential expression of a genetic network and use the generalized T2 statistic to measure the ability of genetic networks to distinguish different phenotypes. However, describing the differential expression of genetic networks is not enough for understanding biological systems because differences in the expression of genetic networks do not directly reflect regulatory strength between gene activities. Therefore, in this report we also introduce the concept of differentially regulated genetic networks, which has the potential to assess changes of gene regulation in response to perturbation in the environment and may provide new insights into the mechanism of diseases and biological processes. We propose five novel statistics to measure the differences in regulation of genetic networks. To illustrate the concepts and methods for reconstruction of genetic networks and identification of association of genetic networks with function, we applied the proposed models and algorithms to three data sets.

Human ATP-binding cassette transporter-2 (ABCA2) positively regulates low-density lipoprotein receptor expression and negatively regulates cholesterol esterification in Chinese hamster ovary cells

We present evidence that the ATP binding-cassette transporter-2 (ABCA2) is a sterol-responsive gene that has a role in the trafficking of low-density lipoprotein-derived free cholesterol (LDL-FC). In HepG2 cells ABCA2 was coordinately expressed with other sterol-responsive genes. Stable constitutive expression of ABCA2 in Chinese hamster ovary cells (CHOA2) was accompanied by an increase the expression of the low-density lipoprotein receptor (LDLR) and other genes involved in the regulation of cholesterol homeostasis. LDLR mRNA was elevated greater than ninefold and 3-hydroxy-3-methylglutaryl CoA synthase (HMGCoA S) expression was elevated sevenfold in CHOA2 cells. The increase in LDLR expression was regulated at the level of transcription; however, culture of CHO and CHOA2 cells in medium containing lipoprotein-deficient serum (LPDS) results in similar levels of LDLR promoter expression. No differences were measured in the dose-dependent uptake of fluorescently labeled 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchorate-LDL (DiI-LDL) between CHO and CHOA2 cells cultured in medium containing LPDS. Ultraviolet microscopy revealed a similar distribution of the DiI-LDL label in cytoplasmic vesicles. We measured an LDL dose-dependent reduction in esterification of LDL-FC in intact CHOA2 cells cultured in medium containing LPDS, however, no significant difference was measured in acylcoenzyme A:cholesterol acyltransferase (ACAT) activity in cell-free extracts of CHO and CHOA2 cells. CHO cells or CHOA2 cells treated with the hydrophobic amine, U18666A, showed similar filipin staining of unesterified cholesterol in cytoplasmic vesicles. Addition of progesterone or U18666A to CHO cells elevated ABCA2 expression. Finally, we found that ABCA2 expression was elevated in Niemann-Pick type C1 (NPC1) fibroblasts and in Familial Hypercholesterolemia (FHC) fibroblasts.

Association of ABCA2 expression with determinants of Alzheimer's disease

With the use of a novel method for detecting differential gene expression, alterations in functional gene clusters related to transport or oxidative stress response and beta-amyloid (Abeta) peptide metabolism were identified in a HEK293 cell line engineered to overexpress the human ATP binding cassette transporter ABCA2. These included fatty acid binding protein, phospholipid binding protein, phospholipid synthesis protein, transporter cofactors, seladin-1, Abeta precursor protein (APP), vimentin, and low-density lipoprotein receptor-related protein. ABCA2 was highly expressed in neuroblastoma cells and colocalized with Abeta and APP. Additionally, increased APP protein levels were detected within ABCA2/APP double-transfected cells, and increased Abeta was detected in the media of ABCA2-transfected cells relative to controls. The transporter was abundant in the temporal and frontal regions of both normal and Alzheimer's disease (AD) brain but was detected at lower concentrations in the parietal, occipital, and cerebellar regions. The ABCA2 transfected cell line expressed resistance to a free radical initiator, confirming involvement in protection against reactive oxygen species and suggesting a further possible link to AD.

Identification of Genetic Networks

In this report, we propose the use of structural equations as a tool for identifying and modeling genetic networks and genetic algorithms for searching the most likely genetic networks that best fit the data. After genetic networks are identified, it is fundamental to identify those networks influencing cell phenotypes. To accomplish this task we extend the concept of differential expression of the genes, widely used in gene expression data analysis, to genetic networks. We propose a definition for the differential expression of a genetic network and use the generalized T  2 statistic to measure the ability of genetic networks to distinguish different phenotypes. However, describing the differential expression of genetic networks is not enough for understanding biological systems because differences in the expression of genetic networks do not directly reflect regulatory strength between gene activities. Therefore, in this report we also introduce the concept of differentially regulated genetic networks, which has the potential to assess changes of gene regulation in response to perturbation in the environment and may provide new insights into the mechanism of diseases and biological processes. We propose five novel statistics to measure the differences in regulation of genetic networks. To illustrate the concepts and methods for reconstruction of genetic networks and identification of association of genetic networks with function, we applied the proposed models and algorithms to three data sets.