Peroxisomal defects in microglial cells induce a disease-associated microglial signature.

Microglial cells ensure essential roles in brain homeostasis. In pathological condition, microglia adopt a common signature, called disease-associated microglial (DAM) signature, characterized by the loss of homeostatic genes and the induction of disease-associated genes. In X-linked adrenoleukodystrophy (X-ALD), the most common peroxisomal disease, microglial defect has been shown to precede myelin degradation and may actively contribute to the neurodegenerative process. We previously established BV-2 microglial cell models bearing mutations in peroxisomal genes that recapitulate some of the hallmarks of the peroxisomal ß-oxidation defects such as very long-chain fatty acid (VLCFA) accumulation. In these cell lines, we used RNA-sequencing and identified large-scale reprogramming for genes involved in lipid metabolism, immune response, cell signaling, lysosome and autophagy, as well as a DAM-like signature. We highlighted cholesterol accumulation in plasma membranes and observed autophagy patterns in the cell mutants. We confirmed the upregulation or downregulation at the protein level for a few selected genes that mostly corroborated our observations and clearly demonstrated increased expression and secretion of DAM proteins in the BV-2 mutant cells. In conclusion, the peroxisomal defects in microglial cells not only impact on VLCFA metabolism but also force microglial cells to adopt a pathological phenotype likely representing a key contributor to the pathogenesis of peroxisomal disorders.

Immune response of BV-2 microglial cells is impacted by peroxisomal beta-oxidation.

Microglia are crucial for brain homeostasis, and dysfunction of these cells is a key driver in most neurodegenerative diseases, including peroxisomal leukodystrophies. In X-linked adrenoleukodystrophy (X-ALD), a neuroinflammatory disorder, very long-chain fatty acid (VLCFA) accumulation due to impaired degradation within peroxisomes results in microglial defects, but the underlying mechanisms remain unclear. Using CRISPR/Cas9 gene editing of key genes in peroxisomal VLCFA breakdown (Abcd1, Abcd2, and Acox1), we recently established easily accessible microglial BV-2 cell models to study the impact of dysfunctional peroxisomal ß-oxidation and revealed a disease-associated microglial-like signature in these cell lines. Transcriptomic analysis suggested consequences on the immune response. To clarify how impaired lipid degradation impacts the immune function of microglia, we here used RNA-sequencing and functional assays related to the immune response to compare wild-type and mutant BV-2 cell lines under basal conditions and upon pro-inflammatory lipopolysaccharide (LPS) activation. A majority of genes encoding proinflammatory cytokines, as well as genes involved in phagocytosis, antigen presentation, and co-stimulation of T lymphocytes, were found differentially overexpressed. The transcriptomic alterations were reflected by altered phagocytic capacity, inflammasome activation, increased release of inflammatory cytokines, including TNF, and upregulated response of T lymphocytes primed by mutant BV-2 cells presenting peptides. Together, the present study shows that peroxisomal ß-oxidation defects resulting in lipid alterations, including VLCFA accumulation, directly reprogram the main cellular functions of microglia. The elucidation of this link between lipid metabolism and the immune response of microglia will help to better understand the pathogenesis of peroxisomal leukodystrophies.

Microgliosis: a double-edged sword in the control of food intake.

Maintaining energy balance is essential for survival and health. This physiological function is controlled by the brain, which adapts food intake to energy needs. Indeed, the brain constantly receives a multitude of biological signals that are derived from digested foods or that originate from the gastrointestinal tract, energy stores (liver and adipose tissues) and other metabolically active organs (muscles). These signals, which include circulating nutrients, hormones and neuronal inputs from the periphery, collectively provide information on the overall energy status of the body. In the brain, several neuronal populations can specifically detect these signals. Nutrient-sensing neurons are found in discrete brain areas and are highly enriched in the hypothalamus. In turn, specialized brain circuits coordinate homeostatic responses acting mainly on appetite, peripheral metabolism, activity and arousal. Accumulating evidence shows that hypothalamic microglial cells located at the vicinity of these circuits can influence the brain control of energy balance. However, microglial cells could have opposite effects on energy balance, that is homeostatic or detrimental, and the conditions for this shift are not totally understood yet. One hypothesis relies on the extent of microglial activation, and nutritional lipids can considerably change it.

Evidence for Constitutive Microbiota-Dependent Short-Term Control of Food Intake in Mice: Is There a Link with Inflammation, Oxidative Stress, Endotoxemia, and GLP-1?

Aims: Although prebiotics, probiotics, and fecal transplantation can alter the sensation of hunger and/or feeding behavior, the role of the constitutive gut microbiota in the short-term regulation of food intake during normal physiology is still unclear. Results: An antibiotic-induced microbiota depletion study was designed to compare feeding behavior in conventional and microbiota-depleted mice. Tissues were sampled to characterize the time profile of microbiota-derived signals in mice during consumption of either standard or high-fat food for 1 h. Pharmacological and genetic tools were used to evaluate the contribution of postprandial endotoxemia and inflammatory responses in the short-term regulation of food intake. We observed constitutive microbial and macronutrient-dependent control of food intake at the time scale of a meal; that is, within 1 h of food introduction. Specifically, microbiota depletion increased food intake, and the microbiota-derived anorectic effect became significant during the consumption of high-fat but not standard food. This anorectic effect correlated with a specific postprandial microbial metabolic signature, and did not require postprandial endotoxemia or an NOD-, LRR-, and Pyrin domain-containing protein 3-inflammasome-mediated inflammatory response. Innovation and Conclusion: These findings show that the gut microbiota controls host appetite at the time scale of a meal under normal physiology. Interestingly, a microbiota-derived anorectic effect develops specifically with a high-fat meal, indicating that gut microbiota activity is involved in the satietogenic properties of foods. Antioxid. Redox Signal. 37, 349-369.

Peroxisomal ABC Transporters: An Update.

ATP-binding cassette (ABC) transporters constitute one of the largest superfamilies of conserved proteins from bacteria to mammals. In humans, three members of this family are expressed in the peroxisomal membrane and belong to the subfamily D: ABCD1 (ALDP), ABCD2 (ALDRP), and ABCD3 (PMP70). These half-transporters must dimerize to form a functional transporter, but they are thought to exist primarily as tetramers. They possess overlapping but specific substrate specificity, allowing the transport of various lipids into the peroxisomal matrix. The defects of ABCD1 and ABCD3 are responsible for two genetic disorders called X-linked adrenoleukodystrophy and congenital bile acid synthesis defect 5, respectively. In addition to their role in peroxisome metabolism, it has recently been proposed that peroxisomal ABC transporters participate in cell signaling and cell control, particularly in cancer. This review presents an overview of the knowledge on the structure, function, and mechanisms involving these proteins and their link to pathologies. We summarize the different in vitro and in vivo models existing across the species to study peroxisomal ABC transporters and the consequences of their defects. Finally, an overview of the known and possible interactome involving these proteins, which reveal putative and unexpected new functions, is shown and discussed.

Peroxisomes in Immune Response and Inflammation.

The immune response is essential to protect organisms from infection and an altered self. An organism's overall metabolic status is now recognized as an important and long-overlooked mediator of immunity and has spurred new explorations of immune-related metabolic abnormalities. Peroxisomes are essential metabolic organelles with a central role in the synthesis and turnover of complex lipids and reactive species. Peroxisomes have recently been identified as pivotal regulators of immune functions and inflammation in the development and during infection, defining a new branch of immunometabolism. This review summarizes the current evidence that has helped to identify peroxisomes as central regulators of immunity and highlights the peroxisomal proteins and metabolites that have acquired relevance in human pathologies for their link to the development of inflammation, neuropathies, aging and cancer. This review then describes how peroxisomes govern immune signaling strategies such as phagocytosis and cytokine production and their relevance in fighting bacterial and viral infections. The mechanisms by which peroxisomes either control the activation of the immune response or trigger cellular metabolic changes that activate and resolve immune responses are also described.

Predictive Structure and Topology of Peroxisomal ATP-Binding Cassette (ABC) Transporters.

The peroxisomal ATP-binding Cassette (ABC) transporters, which are called ABCD1, ABCD2 and ABCD3, are transmembrane proteins involved in the transport of various lipids that allow their degradation inside the organelle. Defective ABCD1 leads to the accumulation of very long-chain fatty acids and is associated with a complex and severe neurodegenerative disorder called X-linked adrenoleukodystrophy (X-ALD). Although the nucleotide-binding domain is highly conserved and characterized within the ABC transporters family, solid data are missing for the transmembrane domain (TMD) of ABCD proteins. The lack of a clear consensus on the secondary and tertiary structure of the TMDs weakens any structure-function hypothesis based on the very diverse ABCD1 mutations found in X-ALD patients. Therefore, we first reinvestigated thoroughly the structure-function data available and performed refined alignments of ABCD protein sequences. Based on the 2.85 Å resolution crystal structure of the mitochondrial ABC transporter ABCB10, here we propose a structural model of peroxisomal ABCD proteins that specifies the position of the transmembrane and coupling helices, and highlight functional motifs and putative important amino acid residues.

Flow Cytometric Analysis of the Expression Pattern of Peroxisomal Proteins, Abcd1, Abcd2, and Abcd3 in BV-2 Murine Microglial Cells.

Microglial cells play important roles in neurodegenerative diseases including peroxisomal leukodystrophies. The BV-2 murine immortalized cells are widely used in the context of neurodegenerative researches. It is therefore important to establish the expression pattern of peroxisomal proteins by flow cytometry in these cells. So, the expression pattern of various peroxisomal transporters (Abcd1, Abcd2, Abcd3) contributing to peroxisomal ß-oxidation was evaluated on BV-2 cells by flow cytometry and complementary methods (fluorescence microscopy, and RT-qPCR). By flow cytometry a strong expression of peroxisomal proteins (Abcd1, Abcd2, Abcd3) was observed. These data were in agreement with those obtained by fluorescence microscopy (presence of numerous fluorescent dots in the cytoplasm characteristic of a peroxisomal staining pattern) and RT-qPCR (high levels of Abcd1, Abcd2, and Abcd3 mRNAs). Thus, the peroxisomal proteins (Abcd1, Abcd2, Abcd3) are expressed in BV-2 cells, and can be analyzed by flow cytometry.

Peroxisomal ATP-binding cassette transporters form mainly tetramers.

ABCD1 and its homolog ABCD2 are peroxisomal ATP-binding cassette (ABC) half-transporters of fatty acyl-CoAs with both distinct and overlapping substrate specificities. Although it is established that ABC half-transporters have at least to dimerize to generate a functional unit, functional equivalents of tetramers (i.e. dimers of full-length transporters) have also been reported. However, oligomerization of peroxisomal ABCD transporters is incompletely understood but is of potential significance because more complex oligomerization might lead to differences in substrate specificity. In this work, we have characterized the quaternary structure of the ABCD1 and ABCD2 proteins in the peroxisomal membrane. Using various biochemical approaches, we clearly demonstrate that both transporters exist as both homo- and heterotetramers, with a predominance of homotetramers. In addition to tetramers, some larger molecular ABCD assemblies were also found but represented only a minor fraction. By using quantitative co-immunoprecipitation assays coupled with tandem mass spectrometry, we identified potential binding partners of ABCD2 involved in polyunsaturated fatty-acid metabolism. Interestingly, we identified calcium ATPases as ABCD2-binding partners, suggesting a role of ABCD2 in calcium signaling. In conclusion, we have shown here that ABCD1 and its homolog ABCD2 exist mainly as homotetramers in the peroxisomal membrane.

Attenuation of 7-ketocholesterol-induced overproduction of reactive oxygen species, apoptosis, and autophagy by dimethyl fumarate on 158N murine oligodendrocytes.

Mitochondrial dysfunctions and oxidative stress are involved in several non demyelinating or demyelinating neurodegenerative diseases. Some of them, including multiple sclerosis (MS), are associated with lipid peroxidation processes leading to increased levels of 7-ketocholesterol (7KC). So, the eventual protective effect of dimethylfumarate (DMF), which is used for the treatment of MS, was evaluated on 7KC-treated oligodendrocytes, which are myelin synthesizing cells. To this end, murine oligodendrocytes 158N were exposed to 7KC (25, 50µM) for 24h without or with DMF (1, 25, 50µM). The biological activities of DMF associated or not with 7KC were evaluated by phase contrast microscopy, crystal violet and MTT tests. The impact on transmembrane mitochondrial potential (ΔYm), O2- and H2O2 production, apoptosis and autophagy was measured by microscopical and flow cytometric methods by staining with DiOC6(3), dihydroethidine and dihydrorhodamine 123, Hoechst 33342, and by Western blotting with the use of specific antibodies raised against uncleaved and cleaved caspase-3 and PARP, and LC3-I/II. DMF attenuates the different effects of 7KC, namely: cell growth inhibition and/or loss of cell adhesion, decrease of ΔΨm, O2- and H2O2 overproduction, PARP and caspase-3 cleavage, nuclear condensation and fragmentation, and activation of LC3-I into LC3-II. The ability of DMF to attenuate 7KC-induced reactive oxygen species overproduction, apoptosis, and autophagy on oligodendrocytes reinforces the interest for this molecule for the treatment of MS or other demyelinating diseases.

Structure-function analysis of peroxisomal ATP-binding cassette transporters using chimeric dimers.

ABCD1 and ABCD2 are two closely related ATP-binding cassette half-transporters predicted to homodimerize and form peroxisomal importers for fatty acyl-CoAs. Available evidence has shown that ABCD1 and ABCD2 display a distinct but overlapping substrate specificity, although much remains to be learned in this respect as well as in their capability to form functional heterodimers. Using a cell model expressing an ABCD2-EGFP fusion protein, we first demonstrated by proximity ligation assay and co-immunoprecipitation assay that ABCD1 interacts with ABCD2. Next, we tested in the pxa1/pxa2Δ yeast mutant the functionality of ABCD1/ABCD2 dimers by expressing chimeric proteins mimicking homo- or heterodimers. For further structure-function analysis of ABCD1/ABCD2 dimers, we expressed chimeric dimers fused to enhanced GFP in human skin fibroblasts of X-linked adrenoleukodystrophy patients. These cells are devoid of ABCD1 and accumulate very long-chain fatty acids (C26:0 and C26:1). We checked that the chimeric proteins were correctly expressed and targeted to the peroxisomes. Very long-chain fatty acid levels were partially restored in transfected X-linked adrenoleukodystrophy fibroblasts regardless of the chimeric construct used, thus demonstrating functionality of both homo- and heterodimers. Interestingly, the level of C24:6 n-3, the immediate precursor of docosahexaenoic acid, was decreased in cells expressing chimeric proteins containing at least one ABCD2 moiety. Our data demonstrate for the first time that both homo- and heterodimers of ABCD1 and ABCD2 are functionally active. Interestingly, the role of ABCD2 (in homo- and heterodimeric forms) in the metabolism of polyunsaturated fatty acids is clearly evidenced, and the chimeric dimers provide a novel tool to study substrate specificity of peroxisomal ATP-binding cassette transporters.

Regulation of the adrenoleukodystrophy-related gene (ABCD2): focus on oxysterols and LXR antagonists.

The regulation of the ABCD2 gene is recognized as a possible therapeutic target for X-linked adrenoleukodystrophy, a rare neurodegenerative disease caused by mutations in the ABCD1 gene. Up-regulation of ABCD2 expression has indeed been demonstrated to compensate for ABCD1 deficiency, restoring peroxisomal ß-oxidation of very-long-chain fatty acids. Besides the known inducers of the ABCD2 gene (phenylbutyrate and histone deacetylase inhibitors, fibrates, dehydroepiandrosterone, thyroid hormone and thyromimetics), this review will focus on LXR antagonists and 22S-hydroxycholesterol, recently described as inducers of ABCD2 expression. Several LXR antagonists have been identified and their possible indication for neurodegenerative disorders will be discussed.

LXR antagonists induce ABCD2 expression.

X-linked adrenoleukodystrophy (X-ALD) is a rare neurodegenerative disorder characterized by the accumulation of very-long-chain fatty acids resulting from a beta-oxidation defect. Oxidative stress and inflammation are also key components of the pathogenesis. X-ALD is caused by mutations in the ABCDI gene, which encodes for a peroxisomal half ABC transporter predicted to participate in the entry of VLCFA-CoA into the peroxisome, the unique site of their beta-oxidation. Two homologous peroxisomal ABC transporters, ABCD2 and ABCD3 have been proven to compensate for ABCD1 deficiency when overexpressed. Pharmacological induction of these target genes could therefore represent an alternative therapy for X-ALD patients. Since LXR activation was shown to repress ABCD2 expression, we investigated the effects of LXR antagonists in different cell lines. Cells were treated with GSK(17) (a LXR antagonist recently discovered from the GlaxoSmithKline compound collection), 22(S)-hydroxycholesterol (22S-HC, another LXR antagonist) and 22R-HC (an endogenous LXR agonist). We observed up-regulation of ABCD2,ABCD3 and CTNNB1 (the gene encoding for beta-catenin, which was recently demonstrated to induce ABCD2 expression) in human HepG2 hepatoma cells and in X-ALD skin fibroblasts treated with LXR antagonists. Interestingly, induction in X-ALD fibroblasts was concomitant with a decrease in oxidative stress. Rats treated with 22S-HC showed hepatic induction of the 3 genes of interest. In human, we show by multiple tissue expression array that expression of ABCD2 appears to be inversely correlated with NR1H3 (LXRalpha) expression. Altogether, antagonists of LXR that are currently developed in the context of dyslipidemia may find another indication with X-ALD.

Fatty acids - induced lipotoxicity and inflammation.

Fatty acids are known to serve as energetic substrates, key components of membrane lipids, and as substrates for the synthesis of signaling molecules and complex lipids. They are also known to be ligands either of membrane receptors involved in cell signaling or of nuclear receptors mediating gene regulation. Accumulation of fatty acids due to altered metabolism and/or unbalanced diet has been described to be toxic for several tissues, especially liver. In numerous cell types, cell death, cytokine secretion and activation of inflammatory processes appear to be a consequence of fatty acid accumulation. This review presents the different classes of fatty acids known to trigger toxic effects and inflammation, the cellular and subcellular targets of these fatty acids in the context of non-alcoholic fatty liver disease (NAFLD), and the mechanisms by which these effects are mediated.

[Peroxisomal ABC transporters and X-linked adrenoleukodystrophy]. / Transporteurs ABC peroxysomaux et adrénoleucodystrophie liée au chromosome X.

X-linked adrenoleukodystrophy (X-ALD) is a complex neurodegenerative disease associated with mutations in the ABCD1 gene, which encodes for a peroxisomal ABC transporter. Thanks to the efforts of the ELA foundation and to the recent successes of gene therapy published in Science in 2009, X-ALD is better known but still remains poorly understood. The exact role of ABCD1 and its homologs, as well as the exact link between the biochemical and metabolic peroxisomal defects and the clinical symptoms of the disease remain to be elucidated. This review summarizes the knowledge concerning the subfamily D of the ABC transporter family and concerning X-ALD, the most frequent peroxisomal disorder.

Substrate specificity overlap and interaction between adrenoleukodystrophy protein (ALDP/ABCD1) and adrenoleukodystrophy-related protein (ALDRP/ABCD2).

X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder caused by mutations in the ABCD1 gene, which encodes a peroxisomal member of the ATP-binding cassette (ABC) transporter subfamily D called ALDP. ALDP is supposed to function as a homodimer allowing the entry of CoA-esters of very-long chain fatty acids (VLCFA) into the peroxisome, the unique site of their ß-oxidation. ALDP deficiency can be corrected by overexpression of ALDRP, its closest homolog. However, the exact nature of the substrates transported by ALDRP and its relationships with ALDP still remain unclear. To gain insight into the function of ALDRP, we used cell models allowing the induction in a dose-dependent manner of a wild type or a mutated non-functional ALDRP-EGFP fusion protein. We explored the consequences of the changes of ALDRP expression levels on the fatty acid content (saturated, monounsaturated, and polyunsaturated fatty acids) in phospholipids as well as on the levels of ß-oxidation of 3 suspected substrates: C26:0, C24:0, and C22:6n-3 (DHA). We found an inverse correlation between the fatty acid content of saturated (C26:0, C24:0) and monounsaturated (C26:1, C24:1) VLCFA and the expression level of ALDRP. Interestingly, we obtained a transdominant-negative effect of the inactive ALDRP-EGFP on ALDP function. This effect is due to a physical interaction between ALDRP and ALDP that we evidenced by proximity ligation assays and coimmunoprecipitation. Finally, the ß-oxidation assays demonstrate a role of ALDRP in the metabolism of saturated VLCFA (redundant with that of ALDP) but also a specific involvement of ALDRP in the metabolism of DHA.

Iodination of verapamil for a stronger induction of death, through GSH efflux, of cancer cells overexpressing MRP1.

The multidrug resistance protein 1 (MRP1), involved in multidrug resistance (MDR) of cancer cells, was found to be modulated by verapamil, through stimulation of GSH transport, leading to apoptosis of MRP1-overexpressing cells. In this study, various iodinated derivatives of verapamil were synthesized, including iodination on the B ring, known to be involved in verapamil cardiotoxicity, and assayed for the stimulation of GSH efflux by MRP1. The iodination, for nearly all compounds, led to a higher stimulation of GSH efflux. However, determination of concomitant cytotoxicity is also important for selecting the best compound, which was found to be 10-fold more potent than verapamil. This will then allow us to design original anti-cancer compounds which could specifically kill the resistant cancer cells.

Peroxisomal and mitochondrial status of two murine oligodendrocytic cell lines (158N, 158JP): potential models for the study of peroxisomal disorders associated with dysmyelination processes.

In some neurodegenerative disorders (leukodystrophies) characterized by myelin alterations, the defect of peroxisomal functions on myelin-producing cells (oligodendrocytes) are poorly understood. The development of in vitro models is fundamental to understanding the physiopathogenesis of these diseases. We characterized two immortalized murine oligodendrocyte cell lines: a normal (158N) and a jimpy (158JP) cell line mutated for the proteolipid protein PLP/DM20. Fluorescence microscopy, flow cytometry, and western blotting analysis allow to identify major myelin proteins (PLP colocalizing with mitochondria; myelin basic protein), oligodendrocyte (CNPase and myelin oligodendrocyte glycoprotein), and peroxisomal markers [adrenoleukodystrophy protein, PMP70, acyl-CoA oxidase 1 (ACOX1), l-peroxisomal bifunctional enzyme, and catalase]. Using electron microscopy, peroxisomes were identified in the two cell lines. Gene expression (ATP-binding cassette, Abcd1, Abcd2, Abcd3, and Acox1) involved in peroxisomal transport or beta-oxidation of fatty acids was evaluated using quantitative PCR. 4-phenylbutyrate treatment increases expression of ACOX1, l-peroxisomal bifunctional enzyme, PLP, myelin oligodendrocyte glycoprotein, and CNPase, mainly in 158N cells. In both cell lines, 4-phenylbutyrate-induced ACOX1 and catalase activities while only Abcd2 gene was up-regulated in 158JP. Moreover, the higher mitochondrial activity and content observed in 158JP were associated with higher glutathione content and increased basal production of reactive oxygen species revealing different redox statuses. Altogether, 158N and 158JP cells will permit studying the relationships between peroxisomal defects, mitochondrial activity, and oligodendrocyte functions.

Induction of the adrenoleukodystrophy-related gene (ABCD2) by thyromimetics.

X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder caused by mutations in the ABCD1 (ALD) gene. The ABCD2 gene, its closest homolog, has been shown to compensate for ABCD1 deficiency when overexpressed. We previously demonstrated that the ABCD2 promoter contains a functional thyroid hormone response element. Thyroid hormone (T3) through its receptor TRbeta can induce hepatic Abcd2 expression in rodents and transiently normalize the VLCFA level in fibroblasts of Abcd1 null mice. In a therapeutic perspective, the use of selective agonists of TRbeta should present the advantage to be devoid of side effects, at least concerning the cardiotoxicity associated to TRalpha activation. In this study, we compared the effects of T3 with those of two thyromimetics (GC-1 and CGS 23425) specific of TRbeta. Using a gene reporter assay, we demonstrated that the rat Abcd2 promoter responds to the thyromimetics in a dose-dependent way similar to what is observed with T3. We then investigated the effects of 2-, 4- and 10-day treatments on the expression of ABCD2 and its paralogs ABCD3 and ABCD4 in human cell lines by RT-qPCR. Both thyromimetics trigger up-regulation of ABCD2-4 genes in HepG2 cells and X-ALD fibroblasts. Interestingly, in X-ALD fibroblasts, while T3 is associated with a transient induction of ABCD2 and ABCD3, the treatments with thyromimetics allow the induction to be maintained until 10 days. Further in vivo experiments in Abcd1 null mice with these thyromimetics should confirm the therapeutic potentialities of these molecules.

ATP-binding cassette transporter A1 is significantly involved in the intestinal absorption of alpha- and gamma-tocopherol but not in that of retinyl palmitate in mice.

BACKGROUND: It has long been assumed that newly absorbed vitamin A and E enter the body only via enterocyte-produced chylomicrons. However, recent results in cell cultures have shown that a fraction of alpha-tocopherol is secreted with intestinal HDL. OBJECTIVES: The aims of this study were to identify this transporter and to assess whether it is significantly implicated in the in vivo intestinal absorption of the 2 main dietary forms of vitamin E (ie, alpha- and gamma-tocopherol) and in that of retinyl palmitate (vitamin A). DESIGN: Having performed preliminary experiments in the Caco-2 cell model, we compared fasting and postprandial plasma concentrations of vitamins A and E in mice deficient in ATP-binding cassette A1 (ABCA1) transporter and in wild-type mice. RESULTS: A substantial efflux of alpha- and gamma-tocopherol, but not of retinyl esters, was induced by the presence of apolipoprotein A-I at the basolateral side of Caco-2 monolayers. The efflux of alpha- and gamma-tocopherol was also impaired by glyburide and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The postprandial response of plasma gamma-tocopherol was 4-fold lower in ABCA1(-/-) mice (P = 0.025) than in wild-type mice, whereas no significant difference was observed for retinyl esters. Fasting plasma alpha-tocopherol, but not vitamin A, concentrations were lower in mice bearing the genetic deletion. CONCLUSIONS: ABCA1 is the transporter responsible for the in vivo secretion of alpha- and gamma-tocopherol with intestinal HDL, and this pathway is significantly implicated in the intestinal absorption and plasma status of vitamin E but not of vitamin A.