Mfsd2a encodes a novel major facilitator superfamily domain-containing protein highly induced in brown adipose tissue during fasting and adaptive thermogenesis

Interaction of major facilitator superfamily domain containing 2A with the blood-brain barrier

The functional and structural integrity of the blood-brain barrier is crucial in maintaining homeostasis in the brain microenvironment; however, the molecular mechanisms underlying the formation and function of the blood-brain barrier remain poorly understood. The major facilitator superfamily domain containing 2A has been identified as a key regulator of blood-brain barrier function. It plays a critical role in promoting and maintaining the formation and functional stability of the blood-brain barrier, in addition to the transport of lipids, such as docosahexaenoic acid, across the blood-brain barrier. Furthermore, an increasing number of studies have suggested that major facilitator superfamily domain containing 2A is involved in the molecular mechanisms of blood-brain barrier dysfunction in a variety of neurological diseases; however, little is known regarding the mechanisms by which major facilitator superfamily domain containing 2A affects the blood-brain barrier. This paper provides a comprehensive and systematic review of the close relationship between major facilitator superfamily domain containing 2A proteins and the blood-brain barrier, including their basic structures and functions, cross-linking between major facilitator superfamily domain containing 2A and the blood-brain barrier, and the in-depth studies on lipid transport and the regulation of blood-brain barrier permeability. This comprehensive systematic review contributes to an in-depth understanding of the important role of major facilitator superfamily domain containing 2A proteins in maintaining the structure and function of the blood-brain barrier and the research progress to date. This will not only help to elucidate the pathogenesis of neurological diseases, improve the accuracy of laboratory diagnosis, and optimize clinical treatment strategies, but it may also play an important role in prognostic monitoring. In addition, the effects of major facilitator superfamily domain containing 2A on blood-brain barrier leakage in various diseases and the research progress on cross-blood-brain barrier drug delivery are summarized. This review may contribute to the development of new approaches for the treatment of neurological diseases.

Blood-derived lysophospholipid sustains hepatic phospholipids and fat storage necessary for hepatoprotection in overnutrition

The liver has a high demand for phosphatidylcholine (PC), particularly in overnutrition, where reduced phospholipid levels have been implicated in the development of nonalcoholic fatty liver disease (NAFLD). Whether other pathways exist in addition to de novo PC synthesis that contribute to hepatic PC pools remains unknown. Here, we identified the lysophosphatidylcholine (LPC) transporter major facilitator superfamily domain containing 2A (Mfsd2a) as critical for maintaining hepatic phospholipid pools. Hepatic Mfsd2a expression was induced in patients having NAFLD and in mice in response to dietary fat via glucocorticoid receptor action. Mfsd2a liver-specific deficiency in mice (L2aKO) led to a robust nonalcoholic steatohepatitis-like (NASH-like) phenotype within just 2 weeks of dietary fat challenge associated with reduced hepatic phospholipids containing linoleic acid. Reducing dietary choline intake in L2aKO mice exacerbated liver pathology and deficiency of liver phospholipids containing polyunsaturated fatty acids (PUFAs). Treating hepatocytes with LPCs containing oleate and linoleate, two abundant blood-derived LPCs, specifically induced lipid droplet biogenesis and contributed to phospholipid pools, while LPC containing the omega-3 fatty acid docosahexaenoic acid (DHA) promoted lipid droplet formation and suppressed lipogenesis. This study revealed that PUFA-containing LPCs drive hepatic lipid droplet formation, suppress lipogenesis, and sustain hepatic phospholipid pools - processes that are critical for protecting the liver from excess dietary fat.

Circadian Dysfunction in Adipose Tissue: Chronotherapy in Metabolic Diseases

Essential for survival and reproduction, the circadian timing system (CTS) regulates adaptation to cyclical changes such as the light/dark cycle, temperature change, and food availability. The regulation of energy homeostasis possesses rhythmic properties that correspond to constantly fluctuating needs for energy production and consumption. Adipose tissue is mainly responsible for energy storage and, thus, operates as one of the principal components of energy homeostasis regulation. In accordance with its roles in energy homeostasis, alterations in adipose tissue's physiological processes are associated with numerous pathologies, such as obesity and type 2 diabetes. These alterations also include changes in circadian rhythm. In the current review, we aim to summarize the current knowledge regarding the circadian rhythmicity of adipogenesis, lipolysis, adipokine secretion, browning, and non-shivering thermogenesis in adipose tissue and to evaluate possible links between those alterations and metabolic diseases. Based on this evaluation, potential therapeutic approaches, as well as clock genes as potential therapeutic targets, are also discussed in the context of chronotherapy.

The Role of Major Facilitator Superfamily Domain-Containing 2a in the Central Nervous System

Major facilitator superfamily-domain containing 2a (Mfsd2a) is selectively expressed in vascular endotheliocytes and plays a crucial role in maintaining the integrity of the blood‒brain barrier and the transport of docosahexaenoic acid. It is currently recognized as the only molecule that inhibits endocytosis mediated by caveolae in brain endothelial cells. Mfsd2a gene knockout leads to an increase in the permeability of the blood-brain barrier from embryonic stages to adulthood while maintaining the normal pattern of the vascular network. In Mfsd2a knockout mice, the docosahexaenoic acid content is significantly reduced and associated with neuron loss, resulting in microcephaly and cognitive impairment. Based on the role of Mfsd2a in the central nervous system, it has been preliminarily suggested as a potential therapeutic target for drug delivery to the central nervous system. This paper reviews the current progress in Mfsd2a research and summarizes the physiological functions of Mfsd2a in the central nervous system and its role in the occurrence and development of a variety of neurological diseases.

Phosphatidylcholine Liposomes Reprogram Macrophages toward an Inflammatory Phenotype

Phospholipids are the major components of cellular membranes and cell-derived vesicles such as exosomes. They are also key components of artificial lipid nanoparticles, allowing the encapsulation and transport of various biological or chemical cargos. Both artificial and natural vesicles could be captured by cells delivering important information that could modulate cellular functions. However, the potential contribution of phospholipids within vesicles altering cellular physiology has been largely underestimated. Here, we showed that macrophages exposed to liposomes made exclusively with palmitoyl oleoyl phosphatidylcholine (POPC) in vivo resulted in a dramatic alteration of the transcriptome profile. Differential gene expression analysis indicated that the exposure to POPC liposomes resulted in a change in the expression of 1598 genes. Moreover, 146 genes were upregulated, and 69 genes were downregulated by incubation with POPC liposomes in contrast to palmitoyl oleoyl phosphatidylserine (POPS) exposure. Signaling pathway impact analysis revealed that 24 signaling pathways were significantly modulated after exposure to POPC liposomes, including the activation of the NF-κB pathway. Indeed, the expression of several cytokines (TNF-α, IL-6, and IL-10) and chemokines (Cxcl1 and Cxcl2) were increased. These observations were validated by the exposure of macrophages to POPC liposomes in culture conditions. In addition, the proteomic analysis of peritoneal cells exposed to POPC liposomes performed by mass spectrometry revealed that the expression of 107 proteins was downregulated after POPC exposure, whereas the expression of 12 proteins was significantly upregulated by this treatment, including seven proteins involved in the neutrophil degranulation pathway. This observation was confirmed by flow cytometry analysis showing the rapid recruitment of neutrophils into the peritoneal cavity after POPC exposure. Overall, these findings demonstrate that the presence of phospholipids within artificial and natural vesicles could be responsible for changes in the function of target cells.

The effects of rhein on D-GalN/LPS-induced acute liver injury in mice: Results from gut microbiome-metabolomics and host transcriptome analysis

Background

Rhubarb is an important traditional Chinese medicine, and rhein is one of its most important active ingredients. Studies have found that rhein can improve ulcerative colitis by regulating gut microbes, but there are few reports on its effects on liver diseases. Therefore, this study aims to investigate these effects and underlying mechanisms.

Methods

Mice were given rhein (100 mg/kg), with both a normal control group and a model group receiving the same amount of normal saline for one week. Acute liver injury was induced in mice by intraperitoneal injection of D-GalN (800 mg/kg)/LPS (10 ug/kg). Samples (blood, liver, and stool) were then collected and assessed for histological lesions and used for 16S rRNA gene sequencing, high-performance liquid chromatography-mass spectrometry (LC-MS) and RNA-seq analysis.

Results

The levels of ALT and AST in the Model group were abnormal higher compared to the normal control group, and the levels of ALT and AST were significantly relieved in the rhein group. Hepatic HE staining showed that the degree of liver injury in the rhein group was lighter than that in the model group, and microbiological results showed that norank_o:Clostridia_UCG-014, Lachnoclostridium, and Roseburia were more abundant in the model group compared to the normal control group. Notably, the rhein treatment group showed reshaped disturbance of intestinal microbial community by D-GalN/LPS and these mice also had higher levels of Verrucomicrobia, Akkermansiaceae and Bacteroidetes. Additionally, There were multiple metabolites that were significantly different between the normal control group and the model group, such as L-α-amino acid, ofloxacin-N-oxide, 1-hydroxy-1,3-diphenylpropan-2-one,and L-4-hydroxyglutamate semialdehyde, but that returned to normal levels after rhein treatment. The gene expression level in the model group also changed significantly, various genes such as Cxcl2, S100a9, Tnf, Ereg, and IL-10 were up-regulated, while Mfsd2a and Bhlhe41 were down-regulated, which were recovered after rhein treatment.

Conclusion

Overall, our results show that rhein alleviated D-GalN/LPS-induced acute liver injury in mice. It may help modulate gut microbiota in mice, thereby changing metabolism in the intestine. Meanwhile, rhein also may help regulate genes expression level to alleviate D-GalN/LPS-induced acute liver injury.

Association of cluster determinant 36, scavenger receptor class B type 1, and major facilitator superfamily domain containing the 2a genetic polymorphism with serum lipid profile in aging population with type 2 diabetes mellitus

Background

Lipid metabolism disorder commonly happens in subjects with Type 2 diabetes mellitus (T2DM) which may be linked to genetic variants of lipid metabolism-related genes. However, few studies have explored the relationship between lipid metabolism-related gene polymorphism and serum lipid profile in aging subjects with T2DM. The present study was designed to explore the impact of genetic polymorphism of cluster determinant 36 (CD36) (rs1049673, rs1054516, rs2151916), scavenger receptor class B type 1 (SCARB1) (rs5888), and major facilitator superfamily domain containing the 2a (MFSD2A) (rs12083239, rs4233508, rs12072037) on the relationship between circulating lipids in aging subjects with T2DM.

Methods

205 T2DM patients and 205 age and gender matched control subjects were recruited. Information on demographic characteristics was collected by using a self-administered questionnaire. Fasting venous blood samples were taken for lipid-related gene genotyping and serum lipid profile measurement. The Chi-square test was used to compare percentage differences and to calculate P-value for Hardy-Weinberg equilibrium. Logistic regression and multiple linear regression were used to explore the risk or correlation between variables, and general linear model (GLM) was used to compare the means of serum lipids between the groups.

Results

In T2DM group, CD36 rs1054516 and MFSD2A rs12072037 were correlated with serum TC level. In control group, CD36 rs1049673 was correlated with serum HDL-C level. Meanwhile, T2DM subjects with MFSD2A rs12083239 (CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (AA) had higher TG level than control subjects. T2DM subjects with CD36 rs1049673 (CG, GG), CD36 rs1054516 (CT), CD36 rs2151916 (TT, CT), SCARB1 rs5888 (GG), MFSD2A rs12083239 (GG, CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (CA, AA) had lower HDL-C level than control subjects. T2DM subjects with MFSD2A rs12072037 (AA) had lower LDL-C level than control subjects. In dominant model, major genotype (GG) of SCARB1 gene was associated with the risk of T2DM (OR = 0.636, P = 0.032).

Conclusion

The genetic polymorphism of CD36 (rs1049673, rs1054516, rs2151916), SCARB1 (rs5888), and MFSD2A (rs12083239, rs4233508, rs12072037) were associated with serum lipids in T2DM subjects. The SCARB1 rs5888 major genotype (GG) was a protective factor for T2DM. Large scale cohort study is required to determine the relationship between lipid metabolism-related gene polymorphism, serum lipid profile and T2DM in aging subjects.

Evidence for a trap-and-flip mechanism in a proton-dependent lipid transporter

Transport of lipids across membranes is fundamental for diverse biological pathways in cells. Multiple ion-coupled transporters take part in lipid translocation, but their mechanisms remain largely unknown. Major facilitator superfamily (MFS) lipid transporters play central roles in cell wall synthesis, brain development and function, lipids recycling, and cell signaling. Recent structures of MFS lipid transporters revealed overlapping architectural features pointing towards a common mechanism. Here we used cysteine disulfide trapping, molecular dynamics simulations, mutagenesis analysis, and transport assays in vitro and in vivo, to investigate the mechanism of LtaA, a proton-dependent MFS lipid transporter essential for lipoteichoic acid synthesis in the pathogen Staphylococcus aureus. We reveal that LtaA displays asymmetric lateral openings with distinct functional relevance and that cycling through outward- and inward-facing conformations is essential for transport activity. We demonstrate that while the entire amphipathic central cavity of LtaA contributes to lipid binding, its hydrophilic pocket dictates substrate specificity. We propose that LtaA catalyzes lipid translocation by a ‘trap-and-flip’ mechanism that might be shared among MFS lipid transporters.

LtaA catalyzes glycolipid translocation by a ‘trap-and-flip’ mechanism, pointing to a shared mechanistic model among MFS lipid transporters. Asymmetric lateral openings allow access of the entire lipid substrate to the amphipathic central cavity.

Comparative Transcriptome Profiling of Young and Old Brown Adipose Tissue Thermogenesis

Brown adipose tissue (BAT) is a major site for uncoupling protein 1 (UCP1)-mediated non-shivering thermogenesis. BAT dissipates energy via heat generation to maintain the optimal body temperature and increases energy expenditure. These energetic processes in BAT use large amounts of glucose and fatty acid. Therefore, the thermogenesis of BAT may be harnessed to treat obesity and related diseases. In mice and humans, BAT levels decrease with aging, and the underlying mechanism is elusive. Here, we compared the transcriptomic profiles of both young and aged BAT in response to thermogenic stimuli. The profiles were extracted from the GEO database. Intriguingly, aging does not cause transcriptional changes in thermogenic genes but upregulates several pathways related to the immune response and downregulates metabolic pathways. Acute severe CE upregulates several pathways related to protein folding. Chronic mild CE upregulates metabolic pathways, especially related to carbohydrate metabolism. Our findings provide a better understanding of the effects of aging and metabolic responses to thermogenic stimuli in BAT at the transcriptome level.

The Blood-Brain Barrier: Much More Than a Selective Access to the Brain

The blood-brain barrier is a dynamic structure, collectively referred to as the neurovascular unit. It is responsible for the exchange of blood, oxygen, ions, and other molecules between the peripheral circulation and the brain compartment. It is the main entrance to the central nervous system and as such critical for the maintenance of its homeostasis. Dysfunction of the blood-brain barrier is a characteristic of several neurovascular pathologies. Moreover, physiological changes, environmental factors, nutritional habits, and psychological stress can modulate the tightness of the barrier. In this contribution, we summarize our current understanding of structure and function of this important component of the brain. We also describe the neurological deficits associated with its damage. A special emphasis is placed in the effect of the exposure to xenobiotics and pollutants in the permeability of the barrier. Finally, current protective strategies as well as the culture models to study this fascinating structure are discussed.

The Role of Mfsd2a in Nervous System Diseases

Major facilitator superfamily (MFS) is the maximum and most diversified membrane transporter, acting as uniporters, symporters and antiporters. MFS is considered to have a good development potential in the transport of drugs for the treatment of brain diseases. The major facilitator superfamily domain containing protein 2a (Mfsd2a) is a member of MFS. Mfsd2a-knockout mice have shown a marked decrease of docosahexaenoic acid (DHA) level in brain, exhibiting neuron loss, microcephaly and cognitive deficits, as DHA acts essentially in brain growth and integrity. Mfsd2a has attracted more and more attention in the study of nervous system diseases because of its critical role in maintaining the integrity of the blood-brain barrier (BBB) and transporting DHA, including inhibiting cell transport in central nervous system endothelial cells, alleviating BBB injury, avoiding BBB injury in cerebral hemorrhage model, acting as a carrier etc. Up to now, the clinical research of Mfsd2a in nervous system diseases is rare. This article reviewed the current research progress of Mfsd2a in nervous system diseases. It summarized the physiological functions of Mfsd2a in the occurrence and development of intracranial hemorrhage (ICH), Alzheimer's disease (AD), sepsis-associated encephalopathy (SAE), autosomal recessive primary microcephaly (MCPH) and intracranial tumor, aiming to provide ideas for the basic research and clinical application of Mfsd2a.

MFSD2A-associated primary microcephaly - Expanding the clinical and mutational spectrum of this ultra-rare disease

MFSD2A, a member of the major facilitator superfamily (MFS), is a transmembrane transporter responsible for the uptake of specific essential fatty acids through the blood-brain barrier (BBB) to the brain. The transporter is crucial for early embryonic brain development and a major factor in the formation and maintenance of the BBB. Mfsd2a-knockout mice show a leakage of the BBB in early embryonic stages and develop a phenotype characterized by microcephaly, cognitive impairment, and anxiety. So far, homozygous or compound heterozygous MFSD2A mutations in humans have only been reported in 13 different families with a total of 28 affected individuals. The phenotypical spectrum of patients with MFSD2A variants is rather broad but all patients present with microcephaly and severe intellectual disability, absent or limited speech, and walking difficulties. Severely affected patients develop seizures and show brain malformations and have, above all, a profound developmental delay hardly reaching any developmental motor milestones. Here, we report on two unrelated individuals with novel homozygous variants in the MFSD2A gene, presenting with severe primary microcephaly, brain malformations, profound developmental delay, and epilepsy, including hypsarrhythmia. Our findings extend the mutational spectrum of the bi-allelic MFSD2A variants causing autosomal recessive primary microcephaly type 15 and broaden the phenotypic spectrum associated with these pathogenic variants emphasizing the role of MFSD2A in early brain development.

Novel neuroclinical findings of autosomal recessive primary microcephaly 15 in a consanguineous Iranian family

Major facilitator superfamily domain-containing 2A (MFSD2A) is required for brain uptake of Docosahexaenoic acid and Lysophosphatidylcholine, both are essential for the normal neural development and function. Mutations in MFSD2A dysregulate the activity of this transporter in brain endothelial cells and can lead to microcephaly. In this study, we describe an 11-year-old male who is affected by autosomal recessive primary microcephaly 15. This patient also shows severe intellectual disability, recurrent respiratory and renal infections, low birth weight, and developmental delay. After doing clinical and neuroimaging evaluations, due to heterogeneity of neurogenetic disorders, no narrow clinical diagnosis was possible, therefore, we utilized targeted-exome sequencing to identify any causative genetic factors. This revealed a homozygous in-frame deletion (NM_001136493.1: c.241_243del; p.(Val81del)) in the MFSD2A gene as the most likely disease-susceptibility variant which was confirmed by Sanger sequencing. Neuroimaging revealed lateral ventricular asymmetry, corpus callosum hypoplasia, type B of cisterna magna, and widening of Sylvian fissures. All of these novel phenotypes are associated with autosomal recessive primary microcephaly-15 (MCPH15). According to the genotype-phenotype data, p.(Val81del) can be considered a likely pathogenic variant leading to non-lethal microcephaly. However, further cumulative data and molecular approaches are required to accurately identify genotype-phenotype correlations in MFSD2A.

Perspective: The Potential Role of Circulating Lysophosphatidylcholine in Neuroprotection against Alzheimer Disease

Alzheimer disease (AD), the most common cause of dementia, is a progressive disorder involving cognitive impairment, loss of learning and memory, and neurodegeneration affecting wide areas of the cerebral cortex and hippocampus. AD is characterized by altered lipid metabolism in the brain. Lower concentrations of long-chain PUFAs have been described in the frontal cortex, entorhinal cortex, and hippocampus in the brain in AD. The brain can synthesize only a few fatty acids; thus, most fatty acids must enter the brain from the blood. Recent studies show that PUFAs such as DHA (22:6) are transported across the blood-brain barrier (BBB) in the form of lysophosphatidylcholine (LPC) via a specific LPC receptor at the BBB known as the sodium-dependent LPC symporter 1 (MFSD2A). Higher dietary PUFA intake is associated with decreased risk of cognitive decline and dementia in observational studies; however, PUFA supplementation, with fatty acids esterified in triacylglycerols did not prevent cognitive decline in clinical trials. Recent studies show that LPC is the preferred carrier of PUFAs across the BBB into the brain. An insufficient pool of circulating LPC containing long-chain fatty acids could potentially limit the supply of long-chain fatty acids to the brain, including PUFAs such as DHA, and play a role in the pathobiology of AD. Whether adults with low serum LPC concentrations are at greater risk of developing cognitive decline and AD remains a major gap in knowledge. Preventing and treating cognitive decline and the development of AD remain a major challenge. The LPC pathway is a promising area for future investigators to identify modifiable risk factors for AD.

Mfsd2a Reverses Spatial Learning and Memory Impairment Caused by Chronic Cerebral Hypoperfusion via Protection of the Blood-Brain Barrier

Disruption of the blood–brain barrier (BBB) can lead to cognitive impairment. Major facilitator superfamily domain-containing protein 2a (Mfsd2a) is a newly discovered protein that is essential for maintaining BBB integrity. However, the role of Mfsd2a in vascular cognitive impairment has not been explored yet. In this study, a rat model of chronic cerebral hypoperfusion (CCH) was established by producing permanent bilateral common carotid artery occlusion (2VO) in rats. We found that after the 2VO procedure, the rats exhibited cognitive impairment, showed increased BBB leakage within the hippocampus, and had reduced expression of the Mfsd2a protein. The overexpression of Mfsd2a in the rat hippocampus reversed these changes. Further investigations using transmission electron microscopy revealed a significantly increased rate of vesicular transcytosis in the BBB of the hippocampus of the CCH rats; the rate reduced after overexpression of Mfsd2a. Moreover, Mfsd2a overexpression did not cause changes in the expression of tight junction-associated proteins and in the ultrastructures of the tight junctions. In conclusion, Mfsd2a attenuated BBB damage and ameliorated cognitive impairment in CCH rats, and its protective effect on the BBB was achieved via inhibition of vesicular transcytosis.

Overexpression of Mfsd2a attenuates blood brain barrier dysfunction via Cav-1/Keap-1/Nrf-2/HO-1 pathway in a rat model of surgical brain injury

INTRODUCTION

Disruption of the blood brain barrier (BBB) and subsequent cerebral edema formation is one of the major adverse effects of brain surgery, leading to postoperative neurological dysfunction. Recently, Mfsd2a has been shown to have a crucial role for the maintenance of BBB functions. In this study, we aimed to evaluate the role of Mfsd2a on BBB disruption following surgical brain injury (SBI) in rats.

MATERIALS AND METHODS

Rats were subjected to SBI by partial resection of the right frontal lobe. To evaluate the effect of Mfsd2a on BBB permeability and neurobehavior outcome following SBI, Mfsd2a was either overexpressed or downregulated in the brain by administering Mfsd2a CRISPR activation or knockout plasmids, respectively. The potential mechanism of Mfsd2a-mediated BBB protection through the cav-1/Nrf-2/HO-1 signaling pathway was evaluated.

RESULTS

Mfsd2a levels were significantly decreased while cav-1, Nrf-2 and HO-1 levels were increased in the right frontal perisurgical area following SBI. When overexpressed, Mfsd2a attenuated brain edema and abolished neurologic impairment caused by SBI while downregulation of Mfsd2a expression further deteriorated BBB functions and worsened neurologic performance following SBI. The beneficial effect of Mfsd2a overexpression on BBB functions was associated with diminished expression of cav-1, increased Keap-1/Nrf-2 dissociation and further augmented levels of Nrf-2 and HO-1 in the right frontal perisurgical area, leading to enhanced levels of tight junction proteins following SBI. The BBB protective effect of Mfsd2a was blocked by selective inhibitors of Nrf-2 and HO-1.

CONCLUSIONS

Mfsd2a attenuates BBB disruption through cav-1/Nrf-2/HO-1 signaling pathway in rats subjected to experimental SBI.

Probable role for major facilitator superfamily domain containing 6 (MFSD6) in the brain during variable energy consumption

Purpose: The major facilitator superfamily (MFS) is known as the largest and most diverse superfamily containing human transporters, and these transporters are essential as they sustain the homeostasis within cellular compartments by moving substances over lipid membranes.Methods: We have identified a novel MFS protein, named Major facilitator superfamily domain containing 6 (MFSD6), and confirmed that it is phylogenetically related to the human Solute Carrier (SLC) transporter family. A homology model of MFSD6 revealed 12 predicted transmembrane segments (TMS) with the classical MFS fold between TMS 6 and 7.Results: Immunohistological analyses showed specific MFSD6 staining in neurons of wildtype mouse brain tissue, but no expression in astrocytes. Furthermore, we explored expression and probable function(s) of MFSD6 in relation to its phylogenetically related proteins, major facilitator superfamily domain containing 8 (MFSD8) and 10 (MFSD10), which is of interest as both these proteins are involved in diseases.Conclusions: We showed that expression levels of Mfsd6 and Mfsd10 were decreased with elevated or depleted energy consumption, while that of Mfsd8 remained unaffected.

Mfsd2a: A Physiologically Important Lysolipid Transporter in the Brain and Eye

Lipids and essential fatty acids are required for normal brain development and continued photoreceptor membrane biogenesis for the maintenance of vision. The blood-brain barrier and blood-eye barriers prohibit the free diffusion of solutes into the brain and eye so that transporter-mediated uptake predominates at these barriers. The major facilitator superfamily of transporters constitutes one of the largest families of facilitative transporters across all domains of life. A unique family member, major facilitator superfamily domain containing 2a (Mfsd2a) is a lysophosphatidylcholine (LPC) transporter expressed at the blood-brain and blood-retinal barriers and demonstrated to be the major pathway for brain and eye accretion of docosahexaenoic acid (DHA) as an LPC. In addition to LPC-DHA, Mfsd2a can transport other LPCs containing mono- and polyunsaturated fatty acids. Mfsd2a deficiency in mouse and humans results in severe microcephaly, underscoring the importance of LPC transport in brain development. Beyond its role in brain development, LPC-DHA uptake in the brain and eye negatively regulates de novo lipogenesis. This review focuses on the current understanding of the physiological roles of Mfsd2a in the brain and eye and the proposed transport mechanism of Mfsd2a.

The Mitotic Apparatus and Kinetochores in Microcephaly and Neurodevelopmental Diseases

Regulators of mitotic division, when dysfunctional or expressed in a deregulated manner (over- or underexpressed) in somatic cells, cause chromosome instability, which is a predisposing condition to cancer that is associated with unrestricted proliferation. Genes encoding mitotic regulators are growingly implicated in neurodevelopmental diseases. Here, we briefly summarize existing knowledge on how microcephaly-related mitotic genes operate in the control of chromosome segregation during mitosis in somatic cells, with a special focus on the role of kinetochore factors. Then, we review evidence implicating mitotic apparatus- and kinetochore-resident factors in the origin of congenital microcephaly. We discuss data emerging from these works, which suggest a critical role of correct mitotic division in controlling neuronal cell proliferation and shaping the architecture of the central nervous system.

Reproductive state and choline intake influence enrichment of plasma lysophosphatidylcholine-DHA: a post hoc analysis of a controlled feeding trial

The major facilitator superfamily domain 2a protein was identified recently as a lysophosphatidylcholine (LPC) symporter with high affinity for LPC species enriched with DHA (LPC-DHA). To test the hypothesis that reproductive state and choline intake influence plasma LPC-DHA, we performed a post hoc analysis of samples available through 10 weeks of a previously conducted feeding study, which provided two doses of choline (480 and 930 mg/d) to non-pregnant (n 21), third-trimester pregnant (n 26), and lactating (n 24) women; all participants consumed 200 mg of supplemental DHA and 22 % of their daily choline intake as 2H-labelled choline. The effects of reproductive state and choline intake on total LPC-DHA (expressed as a percentage of LPC) and plasma enrichments of labelled LPC and LPC-DHA were assessed using mixed and generalised linear models. Reproductive state interacted with time (P = 0·001) to influence total LPC-DHA, which significantly increased by week 10 in non-pregnant women, but not in pregnant or lactating women. Contrary to total LPC-DHA, patterns of labelled LPC-DHA enrichments were discordant between pregnant and lactating women (P < 0·05), suggestive of unique, reproductive state-specific mechanisms that result in reduced production and/or enhanced clearance of LPC-DHA during pregnancy and lactation. Regardless of the reproductive state, women consuming 930 v. 480 mg choline per d exhibited no change in total LPC-DHA but higher d3-LPC-DHA (P = 0·02), indicating that higher choline intakes favour the production of LPC-DHA from the phosphatidylethanolamine N-methyltransferase pathway of phosphatidylcholine biosynthesis. Our results warrant further investigation into the effect of reproductive state and dietary choline on LPC-DHA dynamics and its contribution to DHA status.

The prognostic value of major facilitator superfamily domain-containing protein 2A in patients with hepatocellular carcinoma

INTRODUCTION

We aimed to characterize the expression of major facilitator superfamily domain-containing protein 2A (MFSD2A) in hepatocellular carcinoma (HCC) patients and analyze its prognostic value.

RESULTS

Immunohistochemistry revealed that low expression of MFSD2A was present in 37 of 79 cases (46.84%), which was significantly correlated with poor histological differentiation (P = 0.012). The plasma MFSD2A level in HCC patients was significantly lower than in healthy controls (P = 0.0079) and controls with chronic hepatitis B virus (HBV) infection (P = 0.0430). Moreover, patients with lower MFSD2A expression had shorter survival than higher expression (P = 0.021). Multivariate analysis revealed that MFSD2A was an independent prognostic predictor for HCC patients (P = 0.027).

CONCLUSION

The current study indicate MFSD2A may be an optimal diagnostic and prognostic biomarker for HCC.

METHODS

First, we examined MFSD2A expression in 24 paired HCC and nontumorous tissues by real-time quantitative PCR (RT-qPCR). Second, the protein levels of MFSD2A in 11 paired HCC and nontumorous tissues were investigated by western blotting (WB). Moreover, MFSD2A protein expression was evaluated by immunohistochemistry in 79 HCC patients. In addition, we detected the plasma level of MFSD2A in HCC patients and healthy individuals and investigated the relationship between MFSD2A expression and clinicopathological parameters or prognosis of HCC patients.

SEC24A identified as an essential mediator of thapsigargin-induced cell death in a genome-wide CRISPR/Cas9 screen

Endoplasmic reticulum (ER) stress from accumulated misfolded proteins in the ER can activate the unfolded protein response (UPR). The UPR acts either to restore proteostasis or to activate cell death pathways if the stress cannot be resolved. The key downstream effectors in these pathways have been studied extensively. However, in comparison, stressor-specific key mediators are not as well characterized. In this study, we sought to identify and compare the genes that are necessary for cell death induced by three classic pharmacological ER stressors with different mechanisms of action: thapsigargin, tunicamycin, and brefeldin A. We conducted genome-wide CRISPR/Cas9-based loss-of-function screens against these agents in HAP1 cells, which are a near-haploid cell line. Our screens confirmed that MFSD2A and ARF4, which were identified in previous screens, are necessary for tunicamycin- and brefeldin A-induced cytotoxicity, respectively. We identified a novel gene, SEC24A, as an essential gene for thapsigargin-induced cytotoxicity in HAP1 cells. Further experiments showed that the ability of SEC24A to facilitate ER stress-induced cell death is specific to thapsigargin and that SEC24A acts upstream of the UPR. These findings show that the genes required for ER stress-induced cell death are specific to the agent used to induce ER stress and that the resident ER cargo receptor protein SEC24A is an essential mediator of thapsigargin-induced UPR and cell death.

Insights into major facilitator superfamily domain-containing protein-2a (Mfsd2a) in physiology and pathophysiology. What do we know so far?

Major facilitator superfamily domain-containing protein-2a (Mfsd2a) which was considered as an orphan transporter has recently gained attention for its regulatory role in the maintenance of proper functioning of the blood-brain barrier. Besides the major role of Mfsd2a in maintaining the barrier function, increasing evidence has emerged with regard to the contributions of Mfsd2a to various biological processes such as transport, cell fusion, cell cycle, inflammation and regeneration, managing tumor growth, functioning of other organs with barrier functions or responses to injury. The purpose of this article is to review the different roles of Mfsd2a and its involvement in the physiological and pathophysiological processes primarily in the central nervous system and throughout the mammalian body under the lights of the current literature.

MFSD2A expression predicts better prognosis in gastric cancer

Major facilitator superfamily domain containing-2A (MFSD2A) is reported to correlated with some tumors, but its clinical significance in gastric cancer (GC) is still unknown. The expression of MFSD2A and CD34 were examined on tissue microarrays of 170 set of GC and adjacent normal tissue (ANT) by immunohistochemistry. The relationship of MFSD2A with microvessel density (MVD) and clinicopathological characteristics was also investigated. MFSD2A expression is lower in GC tissue (35.3%) than in ANT (78.2%, P < 0.01). Mean MVD was higher in cancer tissue (49.7 ± 5.46) than in ANT (19.3 ± 2.19, P < 0.01), and higher in MFSD2A^- GC (56.5 ± 7.27), than in MFSD2A⁺ GC (24.8 ± 4.31, P < 0.01). MFSD2A expression was significantly higher in moderately/well differentiated GC (47.4%) than in poorly differentiated GC (25.0%, P < 0.01) and in early-stage GC (46.4%) than in advanced GC (27.7%, P = 0.012). Patients with MFSD2A⁺ specimens (n = 60) had significantly better prognoses than the MFSD2A^- group (n = 110; P < 0.0001). These results suggest that MFSD2A might affect angiogenesis and inhibit GC development and progression. MFSD2A may help predict prognosis and could be a therapeutic target in GC.

Fatty acid transporting proteins: Roles in brain development, aging, and stroke

Polyunsaturated fatty acids are required for the brain development and significantly impact aging and stroke. Due to the hydrophobicity of fatty acids, fatty acids transportation related proteins that include fatty acid binding proteins (FABPs), long chain acyl-coA synthase (ACS), fatty acid transportation proteins (FATPs), fatty acid translocase (FAT/CD36) and newly reported major facilitator superfamily domain-containing protein (Mfsd2a) play critical roles in the uptake of various fatty acids, especially polyunsaturated fatty acids. They are not only involved in neurodevelopment, but also have great impact on neurological disease, such as aging related dementia and stroke.

Insights into the role of hepatocyte PPARα activity in response to fasting

The liver plays a central role in the regulation of fatty acid metabolism. Hepatocytes are highly sensitive to nutrients and hormones that drive extensive transcriptional responses. Nuclear hormone receptors are key transcription factors involved in this process. Among these factors, PPARα is a critical regulator of hepatic lipid catabolism during fasting. This study aimed to analyse the wide array of hepatic PPARα-dependent transcriptional responses during fasting. We compared gene expression in male mice with a hepatocyte specific deletion of PPARα and their wild-type littermates in the fed (ad libitum) and 24-h fasted states. Liver samples were acquired, and transcriptome and lipidome analyses were performed. Our data extended and confirmed the critical role of hepatocyte PPARα as a central for regulator of gene expression during starvation. Interestingly, we identified novel PPARα-sensitive genes, including Cxcl-10, Rab30, and Krt23. We also found that liver phospholipid remodelling was a novel fasting-sensitive pathway regulated by PPARα. These results may contribute to investigations on transcriptional control in hepatic physiology and underscore the clinical relevance of drugs that target PPARα in liver pathologies, such as non-alcoholic fatty liver disease.

Metastatic Brain Tumors Disrupt the Blood-Brain Barrier and Alter Lipid Metabolism by Inhibiting Expression of the Endothelial Cell Fatty Acid Transporter Mfsd2a

Disruption of the blood-brain barrier (BBB) by cancer cells is linked to metastatic tumor initiation and progression; however, the pathways that drive these events remain poorly understood. Here, we have developed novel patient-derived xenograft (PDX) models of brain metastases that recapitulate pathological growth features found in original patient samples, thus allowing for analysis of BBB disruption by tumor cells. We report that the BBB is selectively disrupted in brain metastases, in part, via inhibition of the endothelial cell-expressed docosahexaenoic acid (DHA) transporter, major facilitator superfamily domain 2a (Mfsd2a). Loss of Mfsd2a expression in the tumor endothelium results in enhanced BBB leakage, but reduced DHA transport and altered lipid metabolism within metastases. Mfsd2a expression in normal cerebral endothelial cells is cooperatively regulated by TGFβ and bFGF signaling pathways, and these pathways are pathologically diminished in the brain metastasis endothelium. These results not only reveal a fundamental pathway underlying BBB disruption by metastatic cancer cells, but also suggest that restoring DHA metabolism in the brain tumor microenvironment may be a novel therapeutic strategy to block metastatic cell growth and survival.

Characteristics of 29 novel atypical solute carriers of major facilitator superfamily type: evolutionary conservation, predicted structure and neuronal co-expression

Solute carriers (SLCs) are vital as they are responsible for a major part of the molecular transport over lipid bilayers. At present, there are 430 identified SLCs, of which 28 are called atypical SLCs of major facilitator superfamily (MFS) type. These are MFSD1, 2A, 2B, 3, 4A, 4B, 5, 6, 6 L, 7, 8, 9, 10, 11, 12, 13A, 14A and 14B; SV2A, SV2B and SV2C; SVOP and SVOPL; SPNS1, SPNS2 and SPNS3; and UNC93A and UNC93B1. We studied their fundamental properties, and we also included CLN3, an atypical SLC not yet belonging to any protein family (Pfam) clan, because its involvement in the same neuronal degenerative disorders as MFSD8. With phylogenetic analyses and bioinformatic sequence comparisons, the proteins were divided into 15 families, denoted atypical MFS transporter families (AMTF1-15). Hidden Markov models were used to identify orthologues from human to Drosophila melanogaster and Caenorhabditis elegans Topology predictions revealed 12 transmembrane segments (for all except CLN3), corresponding to the common MFS structure. With single-cell RNA sequencing and in situ proximity ligation assay on brain cells, co-expressions of several atypical SLCs were identified. Finally, the transcription levels of all genes were analysed in the hypothalamic N25/2 cell line after complete amino acid starvation, showing altered expression levels for several atypical SLCs.

MFSD2B is a sphingosine 1-phosphate transporter in erythroid cells

Sphingosine 1-phosphate (S1P) is an intercellular signaling molecule present in blood. Erythrocytes have a central role in maintaining the S1P concentration in the blood stream. We previously demonstrated that S1P is exported from erythrocytes by a glyburide-sensitive S1P transporter. However, the gene encoding the S1P transporter in erythrocytes is unknown. In this study, we found that the mouse erythroid cell line, MEDEP-E14, has S1P export activity and exhibits properties that are consistent with those of erythrocytes. Using microarray analysis of MEDEP-E14 cells and its parental cell line, E14TG2a, we identified several candidate genes for S1P export activity. Of those genes, only one gene, Mfsd2b, showed S1P transport activity. The properties of S1P release by MFSD2B were similar to those in erythrocytes. Moreover, knockout of MFSD2B in MEDEP-E14 cells decreased S1P export from the cells. These results strongly suggest that MFSD2B is a novel S1P transporter in erythroid cells.

Multi-tissue transcriptomic study reveals the main role of liver in the chicken adaptive response to a switch in dietary energy source through the transcriptional regulation of lipogenesis

Background

Because the cost of cereals is unstable and represents a large part of production charges for meat-type chicken, there is an urge to formulate alternative diets from more cost-effective feedstuff. We have recently shown that meat-type chicken source is prone to adapt to dietary starch substitution with fat and fiber. The aim of this study was to better understand the molecular mechanisms of this adaptation to changes in dietary energy sources through the fine characterization of transcriptomic changes occurring in three major metabolic tissues – liver, adipose tissue and muscle – as well as in circulating blood cells.

Results

We revealed the fine-tuned regulation of many hepatic genes encoding key enzymes driving glycogenesis and de novo fatty acid synthesis pathways and of some genes participating in oxidation. Among the genes expressed upon consumption of a high-fat, high-fiber diet, we highlighted CPT1A, which encodes a key enzyme in the regulation of fatty acid oxidation. Conversely, the repression of lipogenic genes by the high-fat diet was clearly associated with the down-regulation of SREBF1 transcripts but was not associated with the transcript regulation of MLXIPL and NR1H3, which are both transcription factors. This result suggests a pivotal role for SREBF1 in lipogenesis regulation in response to a decrease in dietary starch and an increase in dietary PUFA. Other prospective regulators of de novo hepatic lipogenesis were suggested, such as PPARD, JUN, TADA2A and KAT2B, the last two genes belonging to the lysine acetyl transferase (KAT) complex family regulating histone and non-histone protein acetylation. Hepatic glycogenic genes were also down-regulated in chickens fed a high-fat, high-fiber diet compared to those in chickens fed a starch-based diet. No significant dietary-associated variations in gene expression profiles was observed in the other studied tissues, suggesting that the liver mainly contributed to the adaptation of birds to changes in energy source and nutrients in their diets, at least at the transcriptional level. Moreover, we showed that PUFA deposition observed in the different tissues may not rely on transcriptional changes.

Conclusion

We showed the major role of the liver, at the gene expression level, in the adaptive response of chicken to dietary starch substitution with fat and fiber.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4520-5) contains supplementary material, which is available to authorized users.

Structural prediction of two novel human atypical SLC transporters, MFSD4A and MFSD9, and their neuroanatomical distribution in mice

Out of the 430 known solute carriers (SLC) in humans, 30% are still orphan transporters regarding structure, distribution or function. Approximately one third of all SLCs belong to the evolutionary conserved and functionally diverse Major Facilitator Superfamily (MFS). Here, we studied the orphan proteins, MFSD4A and MFSD9, which are atypical SLCs of MFS type. Hidden Markov Models were used to identify orthologues in several vertebrates, and human MFSD4A and MFSD9 share high sequence identity with their identified orthologues. MFSD4A and MFSD9 also shared more than 20% sequence identity with other phylogenetically related SLC and MFSD proteins, allowing new family clustering. Homology models displayed 12 transmembrane segments for both proteins, which were predicted to fold into a transporter-shaped structure. Furthermore, we analysed the location of MFSD4A and MFSD9 in adult mouse brain using immunohistochemistry, showing abundant neuronal protein staining. As MFSD4A and MFSD9 are plausible transporters expressed in food regulatory brain areas, we monitored transcriptional changes in several mouse brain areas after 24 hours food-deprivation and eight weeks of high-fat diet, showing that both genes were affected by altered food intake in vivo. In conclusion, we propose MFSD4A and MFSD9 to be novel transporters, belonging to disparate SLC families. Both proteins were located to neurons in mouse brain, and their mRNA expression levels were affected by the diet.

Metabolism and functions of docosahexaenoic acid-containing membrane glycerophospholipids

Omega‐3 (ω‐3) fatty acids (FAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are known to have important roles in human health and disease. Besides being utilized as fuel, ω‐3 FAs have specific functions based on their structural characteristics. These functions include serving as ligands for several receptors, precursors of lipid mediators, and components of membrane glycerophospholipids (GPLs). Since ω‐3 FAs (especially DHA) are highly flexible, the levels of DHA in GPLs may affect membrane biophysical properties such as fluidity, flexibility, and thickness. Here, we summarize some of the cellular mechanisms for incorporating DHA into membrane GPLs and propose biological effects and functions of DHA‐containing membranes of several cell and tissue types.

Synthesis and Identification of AceDoxyPC, a Protectin-Containing Structured Phospholipid, Using Liquid Chromatography/Mass Spectrometry

Fatty acids have many health benefits in a great variety of diseases ranging from cardiovascular to cerebral diseases. For instance, docosahexaenoic acid (DHA), which is highly enriched in brain phospholipids, plays a major role in anti-inflammatory or neuroprotective pathways. Its effects are thought to be due, in part, to its conversion into derived mediators such as protectins. 1-Lyso,2-docosahexaenoyl-glycerophosphocholine (LysoPtdCho-DHA) is one of the physiological carrier of DHA to the brain. We previously synthesized a structured phosphatidylcholine to mimic 1-lyso,2-docosahexaenoyl-glycerophosphocholine, named AceDoPC® (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that is considered as a stabilized form of the physiological LysoPtdCho-DHA and that is neuroprotective in experimental ischemic stroke. Considering these, the current study aimed at enzymatically oxygenate DHA contained within AceDoPC® to synthesize a readily structured oxidized phospholipid containing protectin DX (PDX), thereafter named AceDoxyPC (1-acetyl,2-PDX-glycerophosphocholine). Identification of this product was performed using liquid chromatography/tandem mass spectrometry. Such molecule could be used as a bioactive mediator for therapy against neurodegenerative diseases and stroke.

Both maternal and offspring Elovl2 genotypes determine systemic DHA levels in perinatal mice

The molecular details relevant to dietary supplementation of the omega-3 fatty acid DHA in mothers as well as in their offspring are not clear. The PUFA elongase, elongation of very long-chain fatty acid (ELOVL)2, is a critical enzyme in the formation of DHA in mammals. In order to address the question regarding the origin of DHA during perinatal life, we have used DHA-deficient Elovl2-ablated mice as a model system to analyze the maternal impact on the DHA level in their offspring of various genotypes. Elovl2^-/- mothers maintained on control diet had significantly lower systemic levels of DHA compared with the Elovl2^+/- and Elovl2^+/+ mothers. Dietary DHA administration during the pregnancy and lactation periods led to increased DHA accretion in maternal tissues and serum of all genotypes. The proportion of DHA in the liver and serum of the Elovl2^-/- offspring was significantly lower than in the Elovl2^+/+ offspring. Remarkably, the DHA level in the Elovl2^+/- offspring nursed by DHA-free-fed Elovl2^-/- mothers was almost as high as in +/+ pups delivered by +/+ mothers, suggesting that endogenous synthesis in the offspring can compensate for maternal DHA deficiency. Maternal DHA supplementation had a strong impact on offspring hepatic gene expression, especially of the fatty acid transporter, Mfsd2a, suggesting a dynamic interplay between DHA synthesis and DHA uptake in the control of systemic levels in the offspring.

Structural Insights into the Transport Mechanism of the Human Sodium-dependent Lysophosphatidylcholine Transporter MFSD2A

Major facilitator superfamily domain containing 2A (MFSD2A) was recently characterized as a sodium-dependent lysophosphatidylcholine transporter expressed at the blood-brain barrier endothelium. It is the primary route for importation of docosohexaenoic acid and other long-chain fatty acids into fetal and adult brain and is essential for mouse and human brain growth and function. Remarkably, MFSD2A is the first identified major facilitator superfamily member that uniquely transports lipids, implying that MFSD2A harbors unique structural features and transport mechanism. Here, we present three three-dimensional structural models of human MFSD2A derived by homology modeling using MelB- and LacY-based crystal structures and refined by biochemical analysis. All models revealed 12 transmembrane helices and connecting loops and represented the partially outward-open, outward-partially occluded, and inward-open states of the transport cycle. In addition to a conserved sodium-binding site, three unique structural features were identified as follows: a phosphate headgroup binding site, a hydrophobic cleft to accommodate a hydrophobic hydrocarbon tail, and three sets of ionic locks that stabilize the outward-open conformation. Ligand docking studies and biochemical assays identified Lys-436 as a key residue for transport. It is seen forming a salt bridge with the negative charge on the phosphate headgroup. Importantly, MFSD2A transported structurally related acylcarnitines but not a lysolipid without a negative charge, demonstrating the necessity of a negatively charged headgroup interaction with Lys-436 for transport. These findings support a novel transport mechanism by which lysophosphatidylcholines are "flipped" within the transporter cavity by pivoting about Lys-436 leading to net transport from the outer to the inner leaflet of the plasma membrane.

The Melibiose Transporter of Escherichia coli: CRITICAL CONTRIBUTION OF LYS-377 TO THE STRUCTURAL ORGANIZATION OF THE INTERACTING SUBSTRATE BINDING SITES

We examine the role of Lys-377, the only charged residue in helix XI, on the functional mechanism of the Na(+)-sugar melibiose symporter from Escherichia coli. Intrinsic fluorescence, FRET, and Fourier transform infrared difference spectroscopy reveal that replacement of Lys-377 with either Cys, Val, Arg, or Asp disables both Na(+) and melibiose binding. On the other hand, molecular dynamics simulations extending up to 200-330 ns reveal that Lys-377 (helix XI) interacts with the anionic side chains of two of the three putative ligands for cation binding (Asp-55 and Asp-59 in helix II). When Asp-59 is protonated during the simulations, Lys-377 preferentially interacts with Asp-55. Interestingly, when a Na(+) ion is positioned in the Asp-55-Asp-59 environment, Asp-124 in helix IV (a residue essential for melibiose binding) reorients and approximates the Asp-55-Asp-59 pair, and all three acidic side chains act as Na(+) ligands. Under these conditions, the side chain of Lys-377 interacts with the carboxylic moiety of these three Asp residues. These data highlight the crucial role of the Lys-377 residue in the spatial organization of the Na(+) binding site. Finally, the analysis of the second-site revertants of K377C reveals that mutation of Ile-22 (in helix I) preserves Na(+) binding, whereas that of melibiose is largely abolished according to spectroscopic measurements. This amino acid is located in the border of the sugar-binding site and might participate in sugar binding through apolar interactions.

Dysregulated expression of lipid storage and membrane dynamics factors in Tia1 knockout mouse nervous tissue

During cell stress, the transcription and translation of immediate early genes are prioritized, while most other messenger RNAs (mRNAs) are stored away in stress granules or degraded in processing bodies (P-bodies). TIA-1 is an mRNA-binding protein that needs to translocate from the nucleus to seed the formation of stress granules in the cytoplasm. Because other stress granule components such as TDP-43, FUS, ATXN2, SMN, MAPT, HNRNPA2B1, and HNRNPA1 are crucial for the motor neuron diseases amyotrophic lateral sclerosis (ALS)/spinal muscular atrophy (SMA) and for the frontotemporal dementia (FTD), here we studied mouse nervous tissue to identify mRNAs with selective dependence on Tia1 deletion. Transcriptome profiling with oligonucleotide microarrays in comparison of spinal cord and cerebellum, together with independent validation in quantitative reverse transcriptase PCR and immunoblots demonstrated several strong and consistent dysregulations. In agreement with previously reported TIA1 knock down effects, cell cycle and apoptosis regulators were affected markedly with expression changes up to +2-fold, exhibiting increased levels for Cdkn1a, Ccnf, and Tprkb vs. decreased levels for Bid and Inca1 transcripts. Novel and surprisingly strong expression alterations were detected for fat storage and membrane trafficking factors, with prominent +3-fold upregulations of Plin4, Wdfy1, Tbc1d24, and Pnpla2 vs. a −2.4-fold downregulation of Cntn4 transcript, encoding an axonal membrane adhesion factor with established haploinsufficiency. In comparison, subtle effects on the RNA processing machinery included up to 1.2-fold upregulations of Dcp1b and Tial1. The effect on lipid dynamics factors is noteworthy, since also the gene deletion of Tardbp (encoding TDP-43) and Atxn2 led to fat metabolism phenotypes in mouse. In conclusion, genetic ablation of the stress granule nucleator TIA-1 has a novel major effect on mRNAs encoding lipid homeostasis factors in the brain, similar to the fasting effect.

Gene expression in superior temporal cortex of schizophrenia patients

We investigated gene expression pattern obtained from microarray data of 10 schizophrenia patients and 10 control subjects. Brain tissue samples were obtained postmortem; thus, the different ages of the patients at death also allowed a study of the dynamic behavior of the expression patterns over a time frame of many years. We used statistical tests and dimensionality reduction methods to characterize the subset of genes differentially expressed in the two groups. A set of 10 genes were significantly downregulated, and a larger set of 40 genes were upregulated in the schizophrenia patients. Interestingly, the set of upregulated genes includes a large number of genes associated with gene transcription (zinc finger proteins and histone methylation) and apoptosis. We furthermore identified genes with a significant trend correlating with age in the control (MLL3) or the schizophrenia group (SOX5, CTRL). Assessments of correlations of other genes with the disorder (RRM1) or with the duration of medication could not be resolved, because all patients were medicated. This hypothesis-free approach uncovered a series of genes differentially expressed in schizophrenia that belong to a number of distinct cell functions, such as apoptosis, transcriptional regulation, cell motility, energy metabolism and hypoxia.

Association of polymorphisms and haplotype in the region of TRIT1, MYCL1 and MFSD2A with the risk and clinicopathological features of gastric cancer in a southeast Chinese population

To explore the association of polymorphisms in the region of three neighboring genes TRIT1, MYCL1 and MFSD2A with risk and clinicopathological features of gastric cancer, 19 tagging SNPs in this region were genotyped using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in a case-control study of 610 Chinese gastric cancer patients and 608 cancer-free controls. MFSD2A rs4233508 T>C CC genotype was associated with an increased risk of gastric cancer in younger patients and an increased risk of moderately/well-differentiated intestinal-type gastric cancer (adjusted odds ratio [OR], 1.74 and 1.50, respectively). TRIT1 rs11581557 T>G TG was associated with lymph node metastasis (TG versus TT/GG, adjusted OR, 1.64). MFSD2A rs12083239 GC genotype and TRIT1 rs2172362 or rs230310 homozygous genotype were associated with Lauren's classification (GC versus GG, adjusted OR, 1.69; GC versus GG/CC, adjusted OR, 1.74) and tumor site (rs2172362: CC versus CT, adjusted OR, 1.71; CC/TT versus CT, adjusted OR, 1.62; rs230310: CC versus CT, adjusted OR, 1.75; CC/TT versus CT, adjusted OR, 1.67) of gastric cancer, respectively. One TRIT1 haplotype, CCGT, was associated with lymph node metastasis and tumor site of gastric cancer (CCGT versus TTTT, adjusted OR, 1.91 and 1.55). This is believed to be the first report that several tagging SNPs and haplotypes in TRIT1, MYCL1 and MFSD2A region are significantly associated with risk and clinicopathological features of gastric cancer in a Chinese population. The findings might be useful for risk assessment and prognosis prediction of gastric cancer.

Influence of maternal low protein diet during pregnancy on hepatic gene expression signature in juvenile female porcine offspring

SCOPE

Epidemiological and experimental evidence indicates that maternal nutrition status contributes to long-term changes in the metabolic phenotype of the offspring, a process known as fetal programming.

METHODS AND RESULTS

We have used a swine model (Sus scrofa) to analyze consequences of a maternal low protein diet (about 50% of control) during pregnancy on hepatic lipid metabolism and genome-wide hepatic gene expression profile of juvenile female offspring (mean age 85 days). We found 318 S. scrofa genes to be differentially expressed in the liver at age 85 days. In the low protein offspring group key genes of fatty acid de novo synthesis were downregulated whereas several genes of lipolysis and phospholipid biosynthesis were upregulated. qRT-PCR analysis of selected genes verified microarray data and revealed linear correlations between gene expression levels and slaughter weight. Hepatic cholesterol 7α hydroxylase protein expression tended to be lower in the low protein group. Total lipid and triglyceride content and fatty acid composition of total lipids were not different between groups.

CONCLUSION

A maternal low protein diet during pregnancy induces a distinct hepatic gene expression signature in juvenile female pigs which was not translated into phenotypical changes of liver lipid metabolism.

Major facilitator superfamily domain-containing protein 2a (MFSD2A) has roles in body growth, motor function, and lipid metabolism

The metabolic adaptations to fasting in the liver are largely controlled by the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARα), where PPARα upregulates genes encoding the biochemical pathway for β-oxidation of fatty acids and ketogenesis. As part of an effort to identify and characterize nutritionally regulated genes that play physiological roles in the adaptation to fasting, we identified Major facilitator superfamily domain-containing protein 2a (Mfsd2a) as a fasting-induced gene regulated by both PPARα and glucagon signaling in the liver. MFSD2A is a cell-surface protein homologous to bacterial sodium-melibiose transporters. Hepatic expression and turnover of MFSD2A is acutely regulated by fasting/refeeding, but expression in the brain is constitutive. Relative to wildtype mice, gene-targeted Mfsd2a knockout mice are smaller, leaner, and have decreased serum, liver and brown adipose triglycerides. Mfsd2a knockout mice have normal liver lipid metabolism but increased whole body energy expenditure, likely due to increased β-oxidation in brown adipose tissue and significantly increased voluntary movement, but surprisingly exhibited a form of ataxia. Together, these results indicate that MFSD2A is a nutritionally regulated gene that plays myriad roles in body growth and development, motor function, and lipid metabolism. Moreover, these data suggest that the ligand(s) that are transported by MFSD2A play important roles in these physiological processes and await future identification.

MFSD2a, the Syncytin-2 receptor, is important for trophoblast fusion

The syncytiotrophoblast is formed at the placental periphery through cytotrophoblast fusion, which depends on Human Endogenous Retrovirus-encoded Envelope proteins Syncytin-1 and Syncytin-2. In the current study, the role of Major Facilitator Superfamily Domain Containing 2A (MFSD2a), the Syncytin-2 receptor, in trophoblast fusion and its expression in normal vs. pre-eclampsia placentas were studied. Forskolin-induced fusion of BeWo cells first parallelled an increase in MFSD2a expression. The MFSD2a signal localized in the cytoplasm and at the plasma membrane. Knockdown of MFSD2a expression confirmed its importance in BeWo fusion. Furthermore, reduced MFSD2a expression was noted in severe pre-eclamptic placentas. These data thus support the importance of MFSD2a in trophoblast fusion and placenta development.

Brain-specific rescue of Clock reveals system-driven transcriptional rhythms in peripheral tissue

The circadian regulatory network is organized in a hierarchical fashion, with a central oscillator in the suprachiasmatic nuclei (SCN) orchestrating circadian oscillations in peripheral tissues. The nature of the relationship between central and peripheral oscillators, however, is poorly understood. We used the tetOFF expression system to specifically restore Clock function in the brains of Clock(Δ19) mice, which have compromised circadian clocks. Rescued mice showed normal locomotor rhythms in constant darkness, with activity period lengths approximating wildtype controls. We used microarray analysis to assess whether brain-specific rescue of circadian rhythmicity was sufficient to restore circadian transcriptional output in the liver. Compared to Clock mutants, Clock-rescue mice showed significantly larger numbers of cycling transcripts with appropriate phase and period lengths, including many components of the core circadian oscillator. This indicates that the SCN oscillator overcomes local circadian defects and signals directly to the molecular clock. Interestingly, the vast majority of core clock genes in liver were responsive to Clock expression in the SCN, suggesting that core clock genes in peripheral tissues are intrinsically sensitive to SCN cues. Nevertheless, most circadian output in the liver was absent or severely low-amplitude in Clock-rescue animals, demonstrating that the majority of peripheral transcriptional rhythms depend on a fully functional local circadian oscillator. We identified several new system-driven rhythmic genes in the liver, including Alas1 and Mfsd2. Finally, we show that 12-hour transcriptional rhythms (i.e., circadian "harmonics") are disrupted by Clock loss-of-function. Brain-specific rescue of Clock converted 12-hour rhythms into 24-hour rhythms, suggesting that signaling via the central circadian oscillator is required to generate one of the two daily peaks of expression. Based on these data, we conclude that 12-hour rhythms are driven by interactions between central and peripheral circadian oscillators.