Novel acyl-CoA synthetase in adrenoleukodystrophy target tissues

Role of ACSBG1 in brain lipid metabolism and X-linked adrenoleukodystrophy pathogenesis: Insights from a knockout mouse model

The "bubblegum" acyl-CoA synthetase (ACSBG1) is a pivotal player in lipid metabolism during the development of the mouse brain, facilitating the activation of long-chain fatty acids (LCFAs) and their integration into essential lipid species crucial for brain function. Through its enzymatic activity, ACSBG1 converts LCFAs into acyl-CoA derivatives, supporting vital processes like membrane formation, myelination, and energy production. Its regulatory role significantly influences neuronal growth, synaptic plasticity, and overall brain development, highlighting its importance in maintaining lipid homeostasis and proper brain function. Originally discovered in the fruit fly brain, ACSBG1 attracted attention for its potential implication in X-linked adrenoleukodystrophy (XALD) pathogenesis. Studies using Drosophila melanogaster lacking the ACSBG1 homolog, bubblegum, revealed adult neurodegeneration with elevated levels of very long-chain fatty acids (VLCFA). To explore ACSBG1's role in fatty acid (FA) metabolism and its relevance to XALD, we created an ACSBG1 knockout (Acsbg1-/-) mouse model and examined its impact on lipid metabolism during mouse brain development. Phenotypically, Acsbg1-/- mice resembled wild type (w.t.) mice. Despite its primary expression in tissues affected by XALD, brain, adrenal gland and testis, ACSBG1 depletion did not significantly reduce total ACS enzyme activity in these tissues when using LCFA or VLCFA as substrates. However, analysis unveiled intriguing developmental and compositional changes in FA levels associated with ACSBG1 deficiency. In the adult mouse brain, ACSBG1 expression peaked in the cerebellum, with lower levels observed in other brain regions. Developmentally, ACSBG1 expression in the cerebellum was initially low during the first week of life but increased dramatically thereafter. Cerebellar FA levels were assessed in both w.t. and Acsbg1-/- mouse brains throughout development, revealing notable differences. While saturated VLCFA levels were typically high in XALD tissues and in fruit flies lacking ACSBG1, cerebella from Acsbg1-/- mice displayed lower saturated VLCFA levels, especially after about 8 days of age. Additionally, monounsaturated ω9 FA levels exhibited a similar trend as saturated VLCFA, while ω3 polyunsaturated FA levels were elevated in Acsbg1-/- mice. Further analysis of specific FA levels provided additional insights into potential roles for ACSBG1. Notably, the decreased VLCFA levels in Acsbg1-/- mice primarily stemmed from changes in C24:0 and C26:0, while reduced ω9 FA levels were mainly observed in C18:1 and C24:1. ACSBG1 depletion had minimal effects on saturated long-chain FA or ω6 polyunsaturated FA levels but led to significant increases in specific ω3 FA, such as C20:5 and C22:5. Moreover, the impact of ACSBG1 deficiency on the developmental expression of several cerebellar FA metabolism enzymes, including those required for synthesis of ω3 polyunsaturated FA, was assessed; these FA can potentially be converted into bioactive signaling molecules like eicosanoids and docosanoids. In conclusion, despite compelling circumstantial evidence, it is unlikely that ACSBG1 directly contributes to the pathology of XALD. Instead, the effects of ACSBG1 knockout on processes regulated by eicosanoids and/or docosanoids should be further investigated.

Characterization of the Bubblegum acyl-CoA synthetase of Microchloropsis gaditana

The metabolic pathways of glycerolipids are well described in cells containing chloroplasts limited by a two-membrane envelope but not in cells containing plastids limited by four membranes, including heterokonts. Fatty acids (FAs) produced in the plastid, palmitic and palmitoleic acids (16:0 and 16:1), are used in the cytosol for the synthesis of glycerolipids via various routes, requiring multiple acyl-Coenzyme A (CoA) synthetases (ACS). Here, we characterized an ACS of the Bubblegum subfamily in the photosynthetic eukaryote Microchloropsis gaditana, an oleaginous heterokont used for the production of lipids for multiple applications. Genome engineering with TALE-N allowed the generation of MgACSBG point mutations, but no knockout was obtained. Point mutations triggered an overall decrease of 16:1 in lipids, a specific increase of unsaturated 18-carbon acyls in phosphatidylcholine and decrease of 20-carbon acyls in the betaine lipid diacylglyceryl-trimethyl-homoserine. The profile of acyl-CoAs highlighted a decrease in 16:1-CoA and 18:3-CoA. Structural modeling supported that mutations affect accessibility of FA to the MgACSBG reaction site. Expression in yeast defective in acyl-CoA biosynthesis further confirmed that point mutations affect ACSBG activity. Altogether, this study supports a critical role of heterokont MgACSBG in the production of 16:1-CoA and 18:3-CoA. In M. gaditana mutants, the excess saturated and monounsaturated FAs were diverted to triacylglycerol, thus suggesting strategies to improve the oil content in this microalga.

Effects of miR-125b-5p on Preadipocyte Proliferation and Differentiation in Chicken

Our previous studies have shown that miR-125b-5p was highly expressed and significantly upregulated during abdominal fat deposition in chickens. However, the role of miR-125b in the regulation of adipogenesis is not clear in chickens. Therefore, we evaluated the effects of miR-125b-5p on preadipocyte proliferation and differentiation and the interaction between miR-125b-5p and the acyl-CoA synthetase bubblegum family member 2 (ACSBG2) gene in adipogenesis in chicken abdominal adipose tissue. Here, transfection tests of miR-125b-5p mimic/inhibitor were performed in preadipocytes, and the effects of miR-125b-5p on preadipocytes proliferation and differentiation were analyzed. The target site of miR-125b-5p in the 3'UTR (untranslated region) of ACSBG2 were verified by a luciferase reporter assay. Our results showed that miR-125b-5p overexpression inhibited proliferation and reduced the number of cells in S phase and G2/M phase in preadipocytes; conversely, miR-125b-5p inhibition promoted the proliferation and increased the number of cells in S phase and G2/M phase. In adipocytes after induction, miR-125b-5p overexpression led to a notable increase in the accumulation of lipid droplets as well as in the concentration of triglycerides, while miR-125b-5p inhibition had the opposite effect. Furthermore, miR-125b-5p could directly bind to the 3'UTR of ACSBG2, and its overexpression could significantly repress the mRNA and protein expression of ACSBG2. These results indicate that miR-125b-5p can inhibit preadipocyte proliferation and can promote preadipocyte differentiation to affect adipogenesis in chicken abdominal adipose tissues, at least partially by downregulating ACSBG2.

MiRNAs and mRNAs Analysis during Abdominal Preadipocyte Differentiation in Chickens

Simple Summary

We sequenced the miRNAs and mRNAs of preabdominal fat cells and differentiated adipocytes, and target genes of miRNA combined with mRNA transcriptome data jointly. We found that the MAPK signal pathway, insulin signal pathway, fatty acid metabolism, ECM( extracellular matrix)–receptor interaction, and other signal pathways were involved in the differentiation of preabdominal fat cells. In addition, we found that some miRNAs–mRNAs combinations were strongly related to the differentiation of fat cells (miR-214−ACSBG2, NFKB2, CAMK2A, ACLY, CCND3, PLK3, ITGB2; miR-148a-5p−ROCK2; miR-10a-5p−ELOVL5; miR-146b-5p−LAMA4; miR-6615-5p−FLNB; miR-1774−COL6A1). Our findings provide important resources for the study of adipocyte differentiation.

Abstract

The excessive deposition of abdominal fat has become an important factor in restricting the production efficiency of chickens, so reducing abdominal fat deposition is important for improving growth rate. It has been proven that miRNAs play an important role in regulating many physiological processes of organisms. In this study, we constructed a model of adipogenesis by isolating preadipocytes (Ab-Pre) derived from abdominal adipose tissue and differentiated adipocytes (Ab-Ad) in vitro. Deep sequencing of miRNAs and mRNAs expressed in Ab-Pre and Ab-Ad groups was conducted to explore the effect of miRNAs and mRNAs on fat deposition. We identified 80 differentially expressed miRNAs (DEMs) candidates, 58 of which were up-regulated and 22 down-regulated. Furthermore, six miRNAs and six mRNAs were verified by qRT-PCR, and the results showed that the expression of the DEMs and differentially expressed genes (DEGs) in the two groups was consistent with our sequencing results. When target genes of miRNA were combined with mRNA transcriptome data, a total of 891 intersection genes were obtained, we predicted the signal pathways of cross genes enrichment to the MAPK signal pathway, insulin signal pathway, fatty acid metabolism, and ECM–receptor interaction. Meanwhile, we constructed miRNA and negatively correlated mRNA target networks, including 12 miRNA–mRNAs pairs, which showed a strong association with the abdominal adipocyte differentiation (miR-214−ACSBG2, NFKB2, CAMK2A, ACLY, CCND3, PLK3, ITGB2; miR-148a-5p−ROCK2; miR-10a-5p−ELOVL5; miR-146b-5p−LAMA4; miR-6615-5p−FLNB; miR-1774−COL6A1). Overall, these findings provide a background for further research on lipid metabolism. Thus, we can better understand the molecular genetic mechanism of chicken abdominal fat deposition.

Expansion, retention and loss in the Acyl-CoA synthetase "Bubblegum" (Acsbg) gene family in vertebrate history

Fatty acids (FAs) constitute a considerable fraction of all lipid molecules with a fundamental role in numerous physiological processes. In animals, the majority of complex lipid molecules are derived from the transformation of FAs through several biochemical pathways. Yet, for FAs to enroll in these pathways they require an activation step. FA activation is catalyzed by the rate limiting action of Acyl-CoA synthases. Several Acyl-CoA enzyme families have been previously described and classified according to the chain length of FAs they process. Here, we address the evolutionary history of the ACSBG gene family which activates, FAs with >16 carbons. Currently, two different ACSBG gene families, ACSBG1 and ACSBG2, are recognized in vertebrates. We provide evidence that a wider and unequal ACSBG gene repertoire is present in vertebrate lineages. We identify a novel ACSBG-like gene lineage which occurs specifically in amphibians, ray finned fishes, coelacanths and cartilaginous fishes named ACSBG3. Also, we show that the ACSBG2 gene lineage duplicated in the Theria ancestor. Our findings, thus offer a far richer understanding on FA activation in vertebrates and provide key insights into the relevance of comparative and functional analysis to perceive physiological differences, namely those related with lipid metabolic pathways.

Phosphoprotein network analysis of white adipose tissues unveils deregulated pathways in response to high-fat diet

Despite efforts in the last decade, signaling aberrations associated with obesity remain poorly understood. To dissect molecular mechanisms that define this complex metabolic disorder, we carried out global phosphoproteomic analysis of white adipose tissue (WAT) from mice fed on low-fat diet (LFD) and high-fat diet (HFD). We quantified phosphorylation levels on 7696 peptides, and found significant differential phosphorylation levels in 282 phosphosites from 191 proteins, including various insulin-responsive proteins and metabolic enzymes involved in lipid homeostasis in response to high-fat feeding. Kinase-substrate prediction and integrated network analysis of the altered phosphoproteins revealed underlying signaling modulations during HFD-induced obesity, and suggested deregulation of lipogenic and lipolytic pathways. Mutation of the differentially-regulated novel phosphosite on cytoplasmic acetyl-coA forming enzyme ACSS2 (S263A) upon HFD-induced obesity led to accumulation of serum triglycerides and reduced insulin-responsive AKT phosphorylation as compared to wild type ACSS2, thus highlighting its role in obesity. Altogether, our study presents a comprehensive map of adipose tissue phosphoproteome in obesity and reveals many previously unknown candidate phosphorylation sites for future functional investigation.

Lessons from the gonadotropin-regulated long chain acyl-CoA synthetase (GR-LACS) null mouse model: a role in steroidogenesis, but not result in X-ALD phenotype

Gonadotropin-regulated long chain fatty acid Acyl-CoA synthetase (GR-LACS), is a member of the LACS family that is regulated by gonadotropin in the rat Leydig cell (LC). Its mouse/human homologs, lipidosin/bubblegum, have been suggested to participate in X-linked adrenoleukodystrophy (X-ALD), an adreno/neurodegenerative disorder with accumulation of very long chain fatty acids (VLCFA) in tissues and plasma. To further gain insights into its regulatory function, a GR-LACS/lipidosin null mouse was generated. No apparent phenotypic abnormalities were observed in the X-ALD target tissues (brain, testis, adrenal). Nuclear inclusions seen in mice >15 month-old, were present in LC of 9 month-old GR-LACS(-/-) mice. LC of the null mice showed refractoriness to the gonadotropin-induced desensitization of testosterone production that is observed in adult animals. LCFAs were moderately increased in the testis, ovary and brain, but not in the adrenal gland of GR-LACS(-/-) mice, with no major changes in VLCFA. No change in LACS activity was observed in these tissues, suggesting a compensatory mechanism exhibited by other LACS members. The GR-LACS(-/-) model did not support its association with X-ALD. These studies revealed a role of GR-LACS in reducing the aging process of the LC, and its participation in gonadotropin-induced testicular desensitization of testosterone production.

Long-chain acyl-CoA synthetases and fatty acid channeling

Thirteen homologous proteins comprise the long-chain acyl-CoA synthetase (ACSL), fatty acid transport protein (FATP), and bubblegum (ACSBG) subfamilies that activate long-chain and very-long-chain fatty acids to form acyl-CoAs. Gain- and loss-of-function studies show marked differences in the ability of these enzymes to channel fatty acids into different pathways of complex lipid synthesis. Further, the ability of the ACSLs and FATPs to enhance cellular FA uptake does not always require these proteins to be present on the plasma membrane; instead, FA uptake can be increased by enhancing its conversion to acyl-CoA and its metabolism in downstream pathways. Since altered fatty acid metabolism is a hallmark of numerous metabolic diseases and pathological conditions, the ACSL, FATP and ACSBG isoforms are likely to play important roles in disease etiology.

Expression of an acyl-CoA synthetase, lipidosin, in astrocytes of the murine brain and its up-regulation during remyelination following cuprizone-induced demyelination

Lipidosin is an 80-kDa protein with long-chain acyl-CoA synthetase activity expressed in the brain, adrenal gland, testis, and ovary, which are selectively damaged in X-linked adrenoleukodystrophy (X-ALD). Western blot analysis of the cerebrum and cerebellum revealed a gradual increase in the expression of lipidosin postnatally. Light microscopic immunohistochemistry using a panel of specific monoclonal antibodies showed that the lipidosin-immunopositive cells were ubiquitously distributed in the brain and were denser in the gray matter than in the white matter. Lipidosin immunoreactivity was colocalized with GFAP immunoreactivity but not with ubiquitin C-terminal hydrolase 1 (= PGP9.5) immunoreactivity, a neuronal marker, and lipidosin-producing cells detected by an antisense probe specific for lipidosin mRNA were also GFAP immunopositive. These data together with Western blot analysis of primary cultured astrocytes indicate that lipidosin is expressed in astrocytes. Immunoelectron microscopic analysis revealed that lipidosin immunoreactivity was widely distributed from perivascular endfeet to perisynaptic processes without being limited to peroxisomes. Lipidosin immunoreactivity was greatly increased in astrocytes in the area of remyelination following experimental demyelination induced by the administration of cuprizone to mice. These data suggest that lipidosin was involved in fatty acid metabolism during reconstruction of the myelin sheath.

X-linked adrenoleukodystrophy: clinical, biochemical and pathogenetic aspects

X-linked adrenoleukodystrophy (X-ALD) is a clinically heterogeneous disorder ranging from the severe childhood cerebral form to asymptomatic persons. The overall incidence is 1:16,800 including hemizygotes as well as heterozygotes. The principal molecular defect is due to inborn mutations in the ABCD1 gene encoding the adrenoleukodystrophy protein (ALDP), a transporter in the peroxisome membrane. ALDP is involved in the transport of substrates from the cytoplasm into the peroxisomal lumen. ALDP defects lead to characteristic accumulation of saturated very long-chain fatty acids, the diagnostic disease marker. The pathogenesis is unclear. Different molecular mechanisms seem to induce inflammatory demyelination, neurodegeneration and adrenocortical insufficiency involving the primary ABCD1 defect, environmental factors and modifier genes. Important information has been derived from the X-ALD mouse models; species differences however complicate the interpretation of results. So far, bone marrow transplantation is the only effective long-term treatment for childhood cerebral X-ALD, however, only when performed at an early-stage of disease. Urgently needed novel therapeutic strategies are under consideration ranging from dietary approaches to gene therapy.

A novel mammalian bubblegum-related acyl-CoA synthetase restricted to testes and possibly involved in spermatogenesis

We have characterized a new, membrane-associated acyl-CoA synthetase (ACS), termed bubblegum-related protein (BGR), which upon functional analysis demonstrated ACS activity capable of activating long- and very long-chain fatty acids. By multiple tissue RNA array and Northern blot analyses, human BGR mRNA was exclusively detected in testes. Murine Bgr mRNA was specifically expressed in pubertal and adult testes and was further demonstrated to be enriched in germ cells and Sertoli cells while present at a lower level in Leydig cells both by in situ hybridization and cell type fractionation. The complex 5'-end of the BGR mRNA appears to underlie translational control leading to differential utilization of alternative translation start sites. Thus, the BGR gene expands the bubblegum ACS family with a testes-specific, developmentally regulated member that may play a role in spermatogenesis.

Tissue-cell- and species-specific expression of gonadotropin-regulated long chain acyl-CoA synthetase (GR-LACS) in gonads, adrenal and brain. Identification of novel forms in the brain

Gonadotropin-regulated long chain acyl-CoA synthetase (GR-LACS) is a novel hormonally regulated fatty acyl-CoA synthetase (FACS) with activity for long-chain fatty acids. The presence of this enzyme in the Leydig cells of the mature rat testis and its mode of regulation suggest that it participates in testicular steroidogenesis. This study demonstrates that GR-LACS expression is tissue, cell and species-specific. The 79 kDa GR-LACS protein is expressed in rodent gonads and brain, and only in the mouse in the adrenal cortex. In the ovary of both species it is associated with follicles undergoing atresia. It is present in the newborn and immature testis tubules and after puberty only in the Leydig cells. A distinct GR-LACS protein species of 64 kDa that was more abundant than the 79 kDa long form was found in the rat brain. Also, a minor 73 kDa form was observed in the rat brain and mouse ovary. Two novel species resulting from alternatively splicing of the GR-LACS gene were identified in a rat brain cDNA library: a short form 1 (S1) lacking exon 8 and short form 2 (S2) lacking exons 6-8. Expression studies revealed that the sizes of the S1/S2 proteins are comparable to those of the endogenous variant species. Neither S form contains FACSs activity, suggesting that exon 8 is essential for the enzymatic function. GR-LACS variants exhibit small but significant dominant negative effects on the FACS activity of the long form. GR-LACS variants may regulate the long form's activity in the brain.

The second member of the human and murine bubblegum family is a testis- and brainstem-specific acyl-CoA synthetase

Acyl-CoA synthetases that activate fatty acids to their CoA derivatives play a central role in fatty acid metabolism. ACSBG1, an acyl-CoA synthetase originally identified in the fruit fly mutant bubblegum, was hypothesized to contribute to the biochemical pathology of X-linked adrenoleukodystrophy. We looked for homologous proteins and identified ACSBG2 in humans, mice, and rats. Human ACSBG1 and ACSBG2 amino acid sequences are 50% identical. ACSBG2 expression was confined to the testis and brainstem. Immunohistochemistry and in situ hybridization studies further localized ACSBG2 expression to testicular Sertoli cells and large motoneurons in the medulla oblongata and cervical spinal cord. Full-length cDNA encoding human and mouse ACSBG2 was cloned. In transfected COS-1 cells, both human and murine ACSBG2 were detected as 75- to 80-kDa proteins by Western blot. Cells overexpressing ACSBG2 had increased ability to activate oleic acid (C18:1omega9) and linoleic acid (C18:2omega6) but not other fatty acid substrates tested. Within a highly conserved motif known to be important for catalysis, human ACSBG2 contains a histidine residue where all other known acyl-CoA synthetases, including mouse and rat ACSBG2, contain an arginine. This substitution resulted in a shift of the human ACSBG2 pH optimum to a more acidic pH. Mutation of this histidine to arginine improved catalytic function at neutral pH by shifting the pH profile without affecting substrate specificity. Although the role of ACSBG2 in testicular and neuronal lipid metabolism remains unclear, the limited tissue expression pattern and limited substrate specificity rule out a likely role for this enzyme in X-linked adrenoleukodystrophy pathology.

The gonadotropin-regulated long-chain acyl CoA synthetase gene: A novel downstream Sp1/Sp3 binding element critical for transcriptional promoter activity

The 79 kD gonadotropin-regulated testicular long chain acyl-CoA synthetase gene (GR-LACS) is a hormone-regulated member of the acyl-CoA synthetase family that is expressed abundantly in Leydig cells and to a lesser extent in germinal cells of the adult testis. GR-LACS possesses an ATP/AMP binding domain and the fatty acyl-CoA synthetase (FACS) signature motif. To gain insights into the transcriptional regulation of GR-LACS in gonadal cells, we determined the genomic organization of the gene, including the upstream flanking sequences. The mouse GR-LACS gene spans over at least 45 kb and the coding region is encoded by exons 1-14. All exon-intron junction sites correspond to the consensus splice sequence GT-AG. Exon 7 and 11 comprise the conserved ATP/AMP binding domain and the FACS signature motif, respectively. Primer extension and S1 nuclease analyses demonstrated four transcriptional start sites located at -266/-216 bp 5' to the ATG codon. The minimal promoter domain resides within -254/-217 bp 5' to ATG codon, and upstream sequences to -404 bp (-1035/-405 bp) contribute to the inhibition of transcription in the expressing mouse Leydig tumor cells. Removal of -217/-1 bp, containing a 23 nt GC rich sequence (-112/-90) with an Sp1/Sp3 binding element, within the 1st exon of this TATA-less promoter, significantly reduced GR-LACS gene transcription. Transcriptional activity was abolished by a 2 nt mutation of this element. Thus, functional analyses of this promoter domain indicate that transcription of GR-LACS gene requires an Sp1/Sp3 binding element downstream of the transcriptional start sites which is essential for basal promoter activity.

Identification and characterization of the BGR-like gene with a potential role in human testicular development/spermatogenesis

AIM

To investigate the roles of the BGR-like gene in testicular development/spermatogenesis.

METHODS

A human testis cDNA microarray was hybridized with probes from human adult testes and embryo testes. The differentially expressed clones were sequenced and analyzed. Expression of the BGR-like gene was analyzed by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

A new gene exhibiting 50-fold difference in expression level between adult and fetal human testes was cloned and named the BGR-like gene. The cDNA consisted of 2500 nucleotides and had an open reading frame of 1437 nucleotides encoding a putative protein of 497 amino acid residues. Homologous comparison showed that the BGR-like gene was a new alternative splicing variant of the BGR gene and had sequence homology with the bubblegum gene of human, mouse, rat and Drosophila. Protein motif analysis of the BGR-like gene revealed that it contained a conserved adenosine monophosphate (AMP)-binding domain and a fatty acyl-CoA synthetase signature motif which existed in all acyl-CoA synthetases. The BGR-like gene transcript was imperceptibly expressed in human fetal testes, highly in human adult testes and moderately in elderly testes and human Leydig cells. RT-PCR-based tissue distribution experiments showed that the BGR-like gene was exclusively expressed in testes and was a testes-specific isoform of the BGR gene. A BGR-like gene transcript was not detected in some azoospermic testes.

CONCLUSION

The BGR-like gene may play an important role in spermatogenesis/testicular development and may be correlated with male infertility.

Mouse very long-chain Acyl-CoA synthetase 3/fatty acid transport protein 3 catalyzes fatty acid activation but not fatty acid transport in MA-10 cells

The family of proteins that includes very long-chain acyl-CoA synthetases (ACSVL) consists of six members. These enzymes have also been designated fatty acid transport proteins. We cloned full-length mouse Acsvl3 cDNA and characterized its protein product ACSVL3/fatty acid transport protein 3. The predicted amino acid sequence contains two highly conserved motifs characteristic of acyl-CoA synthetases. Northern blot analysis revealed that the mouse Acsvl3 mRNA is highly expressed in adrenal gland, testis, and ovary, with lower expression in the brain of adult mice. A developmental Northern blot revealed that Acsvl3 mRNA levels were significantly higher in embryonic mouse brain (embryonic days 12-14) than in newborn or adult mice, suggesting a possible role in nervous system development. Immunohistochemistry revealed high ACSVL3 expression in adrenal cortical cells, spermatocytes and interstitial cells of the testis, theca cells of the ovary, cerebral cortical neurons, and cerebellar Purkinje cells. Endogenous ACSVL3 was found primarily in mitochondria of MA-10 and Neuro2a cells by both Western blot analysis of subcellular fractions and immunofluorescence analysis. In MA-10 cells, loss-of-function studies using RNA interference confirmed that endogenous ACSVL3 is an acyl-CoA synthetase capable of activating both long-chain (C16:0) and very long-chain (C24:0) fatty acids. However, despite decreased acyl-CoA synthetase activity, initial rates of fatty acid uptake were unaffected by knockdown of Acsvl3 expression in MA-10 cells. These studies cast doubt on the designation of ACSVL3 as a fatty acid transport protein.

X-linked adrenoleukodystrophy: role of very long-chain acyl-CoA synthetases

The principal biochemical abnormality in the neurodegenerative disorder X-linked adrenoleukodystrophy (X-ALD) is elevated plasma and tissue levels of very long-chain fatty acids (VLCFA). Enzymes with very long-chain acyl-CoA synthetase (VLACS) activity are required for VLCFA metabolism, including degradation by peroxisomal beta-oxidation or incorporation into complex lipids, and may also participate in VLCFA synthesis. Two enzymes with VLACS activity, ACSVL1 and BG1, were investigated for their potential role in X-ALD biochemical pathology. Skin fibroblast mRNA levels for ACSVL1, an enzyme previously shown to be in peroxisomes and to participate in VLCFA beta-oxidation, were not significantly different between normal controls, patients with childhood cerebral X-ALD, and patients with adrenomyeloneuropathy. Similar results were obtained with mRNA for BG1, a non-peroxisomal enzyme that is highly expressed in nervous system, adrenal gland, and testis, the principal tissues pathologically affected in X-ALD. No significant differences in the immunohistochemical staining patterns of tissues expressing either ACSVL1 or BG1 were observed when wild-type and X-ALD mice were compared. Western blot analysis of BG1 protein levels showed no differences between fibroblasts from controls, cerebral X-ALD, or adrenomyeloneuropathy patients. BG1 protein levels were similar in wild-type and X-ALD mouse brain, spinal cord, testis, and adrenal gland. We hypothesized that one function of BG1 was to direct VLCFA into the cholesterol ester synthesis pathway. However, BG1 depletion in Neuro2a cells using RNA interference did not decrease incorporation of labeled VLCFA into cholesterol esters. We conclude that the role, if any, of ACSVL1 and BG1 in X-ALD biochemical pathology is indirect.

Nutritional significance and metabolism of very long chain fatty alcohols and acids from dietary waxes

Very long chain fatty alcohols obtained from plant waxes and beeswax have been reported to lower plasma cholesterol in humans. This review discusses nutritional or regulatory effects produced by wax esters or aliphatic acids and alcohols found in unrefined cereal grains, beeswax, and many plant-derived foods. Reports suggest that 5-20 mg per day of mixed C24-C34 alcohols, including octacosanol and triacontanol, lower low-density lipoprotein (LDL) cholesterol by 21%-29% and raise high-density lipoprotein cholesterol by 8%-15%. Wax esters are hydrolyzed by a bile salt-dependent pancreatic carboxyl esterase, releasing long chain alcohols and fatty acids that are absorbed in the gastrointestinal tract. Studies of fatty alcohol metabolism in fibroblasts suggest that very long chain fatty alcohols, fatty aldehydes, and fatty acids are reversibly inter-converted in a fatty alcohol cycle. The metabolism of these compounds is impaired in several inherited human peroxisomal disorders, including adrenoleukodystrophy and Sjögren-Larsson syndrome. Reports on dietary management of these diseases confirm that very long chain fatty acids (VLCFA) are normal constituents of the human diet and are synthesized endogenously. Concentrations of VLCFA in blood plasma increase during fasting and when children are placed on ketogenic diets to suppress seizures. Existing data support the hypothesis that VLCFA exert regulatory roles in cholesterol metabolism in the peroxisome and also alter LDL uptake and metabolism.

Murine bubblegum orthologue is a microsomal very long-chain acyl-CoA synthetase

It has been suggested that a gene termed bubblegum (Bgm), encoding an acyl-CoA synthetase, could be involved in the pathogenesis of the inherited neurodegenerative disorder X-ALD (X-linked adrenoleukodystrophy). The precise function of the ALDP (ALD protein) still remains unclear. Aldp deficiency in mammals and Bgm deficiency in Drosophila led to accumulation of VLCFAs (very long-chain fatty acids). As a first step towards studying this interaction in wild-type versus Aldp-deficient mice, we analysed the expression pattern of the murine orthologue of the Bgm gene. In contrast with the ubiquitously expressed Ald gene, Bgm expression is restricted to the tissues that are affected by X-ALD such as brain, testis and adrenals. During mouse brain development, Bgm mRNA was first detected by Northern-blot analysis on embryonic day 18 and increased steadily towards adulthood, whereas the highest level of Ald mRNA was found on embryonic day 12 and decreased gradually during differentiation. Protein fractionation and confocal laser imaging of Bgm-green fluorescent protein fusion proteins revealed a microsomal localization that was different from peroxisomes (where Aldp is detected), endoplasmic reticulum and Golgi. Mouse Bgm showed acyl-CoA synthetase activity towards a VLCFA substrate in addition to LCFAs, and this activity was enriched in the microsomal compartment. Speculating that Bgm expression could be regulated by Ald deficiency, we compared the abundance of Bgm mRNA in wild-type and Ald knockout mice but observed no difference. Although mouse Bgm is capable of activating VLCFA, we conclude that a direct interaction between the mouse Bgm and the Aldp seems unlikely.

The acyl-CoA synthetase "bubblegum" (lipidosin): further characterization and role in neuronal fatty acid beta-oxidation

Acyl-CoA synthetases play a pivotal role in fatty acid metabolism, providing activated substrates for fatty acid catabolic and anabolic pathways. Acyl-CoA synthetases comprise numerous proteins with diverse substrate specificities, tissue expression patterns, and subcellular localizations, suggesting that each enzyme directs fatty acids toward a specific metabolic fate. We reported that hBG1, the human homolog of the acyl-CoA synthetase mutated in the Drosophila mutant "bubblegum," belongs to a previously unidentified enzyme family and is capable of activating both long- and very long-chain fatty acid substrates. We now report that when overexpressed, hBG1 can activate diverse saturated, monosaturated, and polyunsaturated fatty acids. Using in situ hybridization and immunohistochemistry, we detected expression of mBG1, the mouse homolog of hBG1, in cerebral cortical and cerebellar neurons and in steroidogenic cells of the adrenal gland, testis, and ovary. The expression pattern and ability of BG1 to activate very long-chain fatty acids implicates this enzyme in the pathogenesis of X-linked adrenoleukodystrophy. In neuron-derived Neuro2a cells, mBG1 co-sedimented with mitochondria and was found in small vesicular structures located in close proximity to mitochondria. RNA interference was used to decrease mBG1 expression in Neuro2a cells and led to a 30-35% decrease in activation and beta-oxidation of the long-chain fatty acid, palmitate. These results suggest that in Neuro2a cells, mBG1-activated long-chain fatty acids are directed toward mitochondrial degradation. mBG1 appears to play a minor role in very long-chain fatty acid activation in these cells, indicating that other acyl-CoA synthetases are necessary for very long-chain fatty acid metabolism in Neuro2a cells.

A novel murine long-chain acyl-CoA synthetase expressed in brain participates in neuronal cell proliferation

Refsum disease (RfD) is an autosomal recessive neurologic disorder of the lipid metabolism. We have identified a novel murine long-chain acyl-CoA synthetase (mLACS) associated with the RfD gene using yeast two-hybrid assay. Northern blot analyses revealed that mLACS was expressed mainly in the brain and testis. mLACS was highly expressed in the brain at 2 weeks after birth and maintained through adult life. Expressions of the brain-specific LACS family increased in the PC12 cells undergoing neurite outgrowth by nerve growth factor. mLACS preferentially catalyzed the formation of arachidonoyl-CoA more than palmitoyl-CoA or oleoyl-CoA in PC12 cells. Triacsin C, an inhibitor of LACS, suppressed the cell proliferation and decreased mLACS expression in parent PC12 cells, but not in stably anti-sense mLACS cDNA-transfected cells. Our results indicate that mLACS participates in neuronal cell proliferation and differentiation, and interaction of the RfD gene with brain-selective mLACS may be involved in the pathogenesis of RfD.