Major Facilitator Superfamily Domain-containing Protein Research Articles

Orphan lysosomal solute carrier MFSD1 facilitates highly selective dipeptide transport

Orphan solute carrier (SLC) represents a group of membrane transporters whose exact functions and substrate specificities are not known. Elucidating the function and regulation of orphan SLC transporters is not only crucial for advancing our knowledge of cellular and molecular biology but can potentially lead to the development of new therapeutic strategies. Here, we provide evidence for the biological function of a ubiquitous orphan lysosomal SLC, the Major Facilitator Superfamily Domain-containing Protein 1 (MFSD1), which has remained phylogenetically unassigned. Targeted metabolomics revealed that dipeptides containing either lysine or arginine residues accumulate in lysosomes of cells lacking MFSD1. Whole-cell patch-clamp electrophysiological recordings of HEK293-cells expressing MFSD1 on the cell surface displayed transport affinities for positively charged dipeptides in the lower mM range, while dipeptides that carry a negative net charge were not transported. This was also true for single amino acids and tripeptides, which MFSD1 failed to transport. Our results identify MFSD1 as a highly selective lysosomal lysine/arginine/histidine-containing dipeptide exporter, which functions as a uniporter.

Endothelial and mural laminin-α5 contributes to neurovascular integrity maintenance

BackgroundLaminin-α5, a major component of the basal lamina, is predominantly synthesized by endothelial and mural cells (pericytes and vascular smooth muscle cells) in the CNS. Loss of laminin-α5 in either population fails to induce any abnormalities due to functional redundancy. Thus, the functional significance of laminin-α5 in neurovascular integrity remains unknown. Here, we hypothesize that ablation of laminin-α5 in both endothelial and mural cells increases neurovascular permeability.MethodsThe compound knockout mice were generated by crossing laminin-α5 floxed mice with Tie2-Cre and PDGFRβ-Cre, which target endothelial cells and mural cells, respectively. Neurovascular permeability in these mutants was determined with both exogenous and endogenous tracers. Endothelial paracellular and transcellular permeability was assessed by examining the expression of tight junction proteins and transcytosis-associated proteins. In addition, transmission electron microscopy (TEM) was used to visualize tight junction ultrastructure and endothelial caveolae vesicles. Defects in pericytes and astrocytes were investigated by examining pericyte coverage/contact and astrocyte polarity.ResultsElevated neurovascular permeability was observed in the mutants. Subsequent studies found increased Caveolin-1 and decreased major facilitator superfamily domain-containing protein 2a (MFSD2A) expression, but unaltered Claudin-5 or zonula occludens-1 (ZO-1) expression. Consistent with these results, mutant mice exhibited increased endothelial caveolae vesicle number with intact tight junction structure under TEM. Additionally, pericyte coverage and contact were also decreased in the mutant mice, while astrocyte polarity was unaffected.ConclusionsThese results strongly indicate that endothelial and mural cell-derived laminin-α5 actively maintains neurovascular integrity via the transcellular rather than paracellular mechanism.

The supplementation of a high dose of fish oil during pregnancy and lactation led to an elevation in Mfsd2a expression without any changes in docosahexaenoic acid levels in the retina of healthy 2-month-old mouse offspring.

During fetal development, the proper development of neural and visual systems relies on the maternal supplementation of omega-3 fatty acids through placental transfer. Pregnant women are strongly advised to augment their diet with additional sources of omega-3, such as fish oil (FO). This supplementation has been linked to a reduced risk of preterm birth, pre-eclampsia, and perinatal depression. Recently, higher doses of omega-3 supplementation have been recommended for pregnant women. Considering that omega-3 fatty acids, particularly docosahexaenoic acid (DHA), play a crucial role in maintaining the delicate homeostasis required for the proper functioning of the retina and photoreceptors the effects of high-dose fish oil (FO) supplementation during pregnancy and lactation on the retina and retinal pigmented epithelium (RPE) in healthy offspring warrant better understanding. The fatty acid content and the changes in the expression of the genes regulating cholesterol homeostasis and DHA transport in the retina and RPE were evaluated following the high-dose FO supplementation. Our study demonstrated that despite the high-dose FO treatment during pregnancy and lactation, the rigorous DHA homeostasis in the retina and RPE of the two-month-old offspring remained balanced. Another significant finding of this study is the increase in the expression levels of major facilitator superfamily domain-containing protein (Mfsd2a), a primary DHA transporter. Mfsd2a also serves as a major regulator of transcytosis during development, and a reduction in Mfsd2a levels poses a major risk for the development of leaky blood vessels. Impairment of the blood-retinal barrier (BRB) is associated with the development of numerous ocular diseases, and a better understanding of how to manipulate transcytosis in the BRB during development can enhance drug delivery through the BRB or contribute to the repair of central nervous system (CNS) barriers.

Loss of mfsd8 alters the secretome during Dictyostelium aggregation

Major facilitator superfamily domain-containing protein 8 (MFSD8) is a transmembrane protein that has been reported to function as a lysosomal chloride channel. In humans, homozygous mutations in MFSD8 cause a late-infantile form of neuronal ceroid lipofuscinosis (NCL) called CLN7 disease. In the social amoeba Dictyostelium discoideum, Mfsd8 localizes to cytoplasmic puncta and vesicles, and regulates conserved processes during the organism’s life cycle. Here, we used D. discoideum to examine the effect of mfsd8-deficiency on the secretome during the early stages of multicellular development. Mass spectrometry revealed 61 proteins that were differentially released by cells after 4 and 8 h of starvation. Most proteins were present in increased amounts in mfsd8- conditioned buffer compared to WT indicating that loss of mfsd8 deregulates protein secretion and/or causes the release of proteins not normally secreted by WT cells. GO term enrichment analyses showed that many of the proteins aberrantly released by mfsd8- cells localize to compartments and regions of the cell associated with the endo-lysosomal and secretory pathways. Mass spectrometry also revealed proteins previously known to be impacted by the loss of mfsd8 (e.g., cathepsin D), as well as proteins that may underlie mfsd8-deficiency phenotypes during aggregation. Finally, we show that mfsd8-deficiency reduces intracellular proteasome 20S activity due to the abnormal release of at least one proteasomal subunit. Together, this study reveals the impact of mfsd8 loss on the secretome during D. discoideum aggregation and lays the foundation for follow up work that investigates the role of altered protein release in CLN7 disease.

Marine Fish-Derived Lysophosphatidylcholine: Properties, Extraction, Quantification, and Brain Health Application.

Long-chain omega-3 fatty acids esterified in lysophosphatidylcholine (LPC-omega-3) are the most bioavailable omega-3 fatty acid form and are considered important for brain health. Lysophosphatidylcholine is a hydrolyzed phospholipid that is generated from the action of either phospholipase PLA1 or PLA2. There are two types of LPC; 1-LPC (where the omega-3 fatty acid at the sn-2 position is acylated) and 2-LPC (where the omega-3 fatty acid at the sn-1 position is acylated). The 2-LPC type is more highly bioavailable to the brain than the 1-LPC type. Given the biological and health aspects of LPC types, it is important to understand the structure, properties, extraction, quantification, functional role, and effect of the processing of LPC. This review examines various aspects involved in the extraction, characterization, and quantification of LPC. Further, the effects of processing methods on LPC and the potential biological roles of LPC in health and wellbeing are discussed. DHA-rich-LysoPLs, including LPC, can be enzymatically produced using lipases and phospholipases from wide microbial strains, and the highest yields were obtained by Lipozyme RM-IM®, Lipozyme TL-IM®, and Novozym 435®. Terrestrial-based phospholipids generally contain lower levels of long-chain omega-3 PUFAs, and therefore, they are considered less effective in providing the same health benefits as marine-based LPC. Processing (e.g., thermal, fermentation, and freezing) reduces the PL in fish. LPC containing omega-3 PUFA, mainly DHA (C22:6 omega-3) and eicosapentaenoic acid EPA (C20:5 omega-3) play important role in brain development and neuronal cell growth. Additionally, they have been implicated in supporting treatment programs for depression and Alzheimer's. These activities appear to be facilitated by the acute function of a major facilitator superfamily domain-containing protein 2 (Mfsd2a), expressed in BBB endothelium, as a chief transporter for LPC-DHA uptake to the brain. LPC-based delivery systems also provide the opportunity to improve the properties of some bioactive compounds during storage and absorption. Overall, LPCs have great potential for improving brain health, but their safety and potentially negative effects should also be taken into consideration.

Aging decreases docosahexaenoic acid transport across the blood-brain barrier in C57BL/6J mice.

Nutrients are actively taken up by the brain via various transporters at the blood-brain barrier (BBB). A lack of specific nutrients in the aged brain, including decreased levels of docosahexaenoic acid (DHA), is associated with memory and cognitive dysfunction. To compensate for decreased brain DHA, orally supplied DHA must be transported from the circulating blood to the brain across the BBB through transport carriers, including major facilitator superfamily domain-containing protein 2a (MFSD2A) and fatty acid-binding protein 5 (FABP5) that transport esterified and non-esterified DHA, respectively. Although it is known that the integrity of the BBB is altered during aging, the impact of aging on DHA transport across the BBB has not been fully elucidated. We used 2-, 8-, 12-, and 24-month-old male C57BL/6 mice to evaluate brain uptake of [14C]DHA, as the non-esterified form, using an in situ transcardiac brain perfusion technique. Primary culture of rat brain endothelial cells (RBECs) was used to evaluate the effect of siRNA-mediated MFSD2A knockdown on cellular uptake of [14C]DHA. We observed that the 12- and 24-month-old mice exhibited significant reductions in brain uptake of [14C]DHA and decreased MFSD2A protein expression in the brain microvasculature compared with that of the 2-month-old mice; nevertheless, FABP5 protein expression was up-regulated with age. Brain uptake of [14C]DHA was inhibited by excess unlabeled DHA in 2-month-old mice. Transfection of MFSD2A siRNA into RBECs decreased the MFSD2A protein expression levels by 30% and reduced cellular uptake of [14C]DHA by 20%. These results suggest that MFSD2A is involved in non-esterified DHA transport at the BBB. Therefore, the decreased DHA transport across the BBB that occurs with aging could be due to age-related down-regulation of MFSD2A rather than FABP5.

Esterification of Docosahexaenoic Acid Enhances Its Transport to the Brain and Its Potential Therapeutic Use in Brain Diseases.

Docosahexaenoic acid-containing lysophosphatidylcholine (DHA-LysoPC) is presented as the main transporter of DHA from blood plasma to the brain. This is related to the major facilitator superfamily domain-containing protein 2A (Mfsd2a) symporter expression in the blood-brain barrier that recognizes the various lyso-phospholipids that have choline in their polar head. In order to stabilize the DHA moiety at the sn-2 position of LysoPC, the sn-1 position was esterified by the shortest acetyl chain, creating the structural phospholipid 1-acetyl,2-docosahexaenoyl-glycerophosphocholine (AceDoPC). This small structure modification allows the maintaining of the preferential brain uptake of DHA over non-esterified DHA. Additional properties were found for AceDoPC, such as antioxidant properties, especially due to the aspirin-like acetyl moiety, as well as the capacity to generate acetylcholine in response to the phospholipase D cleavage of the polar head. Esterification of DHA within DHA-LysoPC or AceDoPC could elicit more potent neuroprotective effects against neurological diseases.

The protective effects of hyperoside on Ang II-mediated apoptosis of bEnd.3 cells and injury of blood-brain barrier model in vitro

BackgroundHypertension and its associated dysfunction of the blood-brain barrier (BBB) are considered to contribute to cerebral small vessel disease (cSVD). Angiotensin II (Ang II), as an important vasoactive peptide of the renin-angiotensin system (RAS), is not only a pivotal molecular signal in hypertension, but also causes BBB leakage, cSVD and its related cognitive impair. Hyperoside (Hyp), a flavone glycoside, has antioxidant, antiphlogistic and anti-apoptosis effects. In this study, we investigate the protection of Hyp on apoptosis of bEnd.3 cells and BBB disruption in vitro induced by Ang II.MethodsWe used bEnd.3 cells to imitate a BBB monolayer model and explored the protection of Hyp on Ang II-induced BBB leakage. The apoptotic activity was assessed by TUNEL staining and flow cytometry. The expression of apoptosis pathway related proteins, tight junction proteins and transcytosis related proteins were detected by western blot assay. The BBB model permeability was detected through measuring the flux of sodium fluorescein (Na-F).ResultsWe found that Hyp can not only effectively inhibit the apoptosis of bEnd.3 induced by Ang II, but also protect the structural soundness and functional integrity of BBB model by affecting the expression levels of junctional adhesion molecule A (JAM-A), Claudin-5, zonula occludens-1 (ZO-1), Caveolin-1 (Cav-1) and major facilitator superfamily domain-containing protein 2a (Mfsd2a).ConclusionHyp might be a potent compound for preventing Ang II-induced BBB disruption.

The Solute Carrier MFSD1 Decreases the Activation Status of β1 Integrin and Thus Tumor Metastasis.

Solute carriers are increasingly recognized as participating in a plethora of pathologies, including cancer. We describe here the involvement of the orphan solute carrier Major Facilitator Superfamily Domain-containing protein 1 (MFSD1) in the regulation of tumor cell migration. Loss of MFSD1 enabled higher levels of metastasis in experimental and spontaneous metastasis mouse models. We identified an increased migratory potential in MFSD1−/− tumor cells which was mediated by increased focal adhesion turnover, reduced stability of mature inactive β1 integrin, and the resulting increased integrin activation index. We show that MFSD1 promoted recycling to the cell surface of endocytosed inactive β1 integrin and thereby protected β1 integrin from proteolytic degradation; this led to dampening of the integrin activation index. Furthermore, downregulation of MFSD1 expression was observed during the early steps of tumorigenesis, and higher MFSD1 expression levels correlate with a better cancer patient prognosis. In sum, we describe a requirement for endolysosomal MFSD1 in efficient β1 integrin recycling to suppress tumor cell dissemination.

Overcoming Mfsd2a-Mediated Low Transcytosis to Boost Nanoparticle Delivery to Brain for Chemotherapy of Brain Metastases.

Microvessels of the blood-brain barrier (BBB) exclusively express the major facilitator superfamily domain-containing protein 2a (Mfsd2a), which is the key transporter for docosahexaenoic acid uptake into the brain. Mfsd2a suppresses caveolae-mediated transcytosis to regulate BBB transcellular permeability via controlling lipid composition of BBB endothelial cells. It is speculated that Mfsd2a can restrain BBB crossing efficiency and brain accumulation efficiency of brain-targeting drug delivery systems, which penetrate the BBB often through the receptor-mediated transcytosis pathway. Transcytosis across the BBB is a crucial bottleneck for targeted chemotherapy of brain metastases. To overcome this issue, a pair of priming nanoparticles (NPs) and following drug-loaded NPs are designed. Tunicamycin-(TM)-loaded transcytosis-targeting-peptide-(TTP)-decorated NPs (TM@TTP) are used to boost BBB transcytosis via inhibiting Mfsd2a. Doxorubicin (DOX)-loaded TTP and CD44-specific hyaluronic acid (HA)-comodified NPs (DOX@TTP-HA) are designed as following drug-loaded NPs. The brain accumulation efficacy of following DOX@TTP-HA with priming is 4.30-fold higher than that without priming through the enhanced transcytosis pathway rather than the tight junction opening. Effective BBB crossing and brain accumulation, selective tumor uptake, excellent antitumor efficacy, and low hepatotoxicity are achieved by TM@TTP and DOX@TTP-HA, suggesting this tactic as a significant therapeutic strategy against breast cancer brain metastases.

Wnt signaling activates MFSD2A to suppress vascular endothelial transcytosis and maintain blood-retinal barrier.

Breakdown of the blood-retinal barrier (BRB) causes retinal edema and vision loss. We investigated the role of Wnt signaling in maintaining the BRB by limiting transcytosis. Mice lacking either the Wnt co-receptor low-density lipoprotein receptor-related protein 5 (Lrp5-/- ) or the Wnt ligand Norrin (Ndpy/- ) exhibit increased retinal vascular leakage and enhanced endothelial transcytosis. Wnt signaling directly controls the transcription of an endothelium-specific transcytosis inhibitor, major facilitator superfamily domain-containing protein 2a (MFSD2A), in a β-catenin-dependent manner. MFSD2A overexpression reverses Wnt deficiency-induced transcytosis in endothelial cells and in retinas. Moreover, Wnt signaling mediates MFSD2A-dependent vascular endothelium transcytosis through a caveolin-1 (CAV-1)-positive caveolae pathway. In addition, levels of omega-3 fatty acids are also decreased in Wnt signaling-deficient retinas, reflecting the basic function of MFSD2A as a lipid transporter. Our findings uncovered the Wnt/β-catenin/MFSD2A/CAV-1 axis as a key pathway governing endothelium transcytosis and inner BRB integrity.

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.

The neuronal ceroid lipofuscinosis protein Cln7 functions in the postsynaptic cell to regulate synapse development

The neuronal ceroid lipofuscinoses (NCLs) are a group of fatal, monogenic neurodegenerative disorders with an early onset in infancy or childhood. Despite identification of the genes disrupted in each form of the disease, their normal cellular role and how their deficits lead to disease pathology is not fully understood. Cln7, a major facilitator superfamily domain-containing protein, is affected in a late infantile-onset form of NCL. Cln7 is conserved across species suggesting a common function. Here we demonstrate that Cln7 is required for the normal growth of synapses at the Drosophila larval neuromuscular junction. In a Cln7 mutant, synapses fail to develop fully leading to reduced function and behavioral changes with dysregulation of TOR activity. Cln7 expression is restricted to the post-synaptic cell and the protein localizes to vesicles immediately adjacent to the post-synaptic membrane. Our data suggest an involvement for Cln7 in regulating trans-synaptic communication necessary for normal synapse development.

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.

High‑fat treatment prevents postoperative cognitive dysfunction in a hyperlipidemia model by protecting the blood‑brain barrier via Mfsd2a‑related signaling.

Damage to the blood-brain barrier (BBB) resulting from systemic inflammation caused by surgical trauma is associated with cognitive dysfunction, and individuals with hyperlipidemia are more sensitive to such impairment. The present study was designed to ascertain whether dexmedetomidine (Dex) treatment could reduce the incidence of cognitive dysfunction following surgery in a hyperlipidemia model. Hyperlipidemia was induced in Sprague-Dawley rats (male, 6–7 months old) by consuming a high-fat diet, and rats were divided into three groups (n=10 each) and underwent: exploratory laparotomy to introduce surgical trauma (surgery group), laparotomy and Dex treatment (surgery+Dex group), or sham surgery (sham group). Learning, memory and exploration behavior were assessed using the Morris water maze. Concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-1β, were determined by enzyme-linked immunosorbent assay. BBB permeability was assessed by Evans blue staining. Relative major facilitator superfamily domain-containing protein 2 (Mfsd2a) mRNA expression was determined by quantitative PCR. In the Morris water maze test, the time and distance ratio for the surgery group was significantly lower than those of the sham and surgery+Dex groups (P<0.05). In addition, the TNF-α concentrations in the sham and surgery+Dex groups were lower than that in the surgery group (P<0.05 on days 1 and 3). Evans Blue staining was increased in the surgery group on day 1 (P<0.01). Mfsd2a mRNA expression was higher in the sham and surgery+Dex groups compared with that noted in the surgery group (P<0.05). In conclusion, Dex treatment decreased the incidence of cognitive dysfunction following surgical trauma in a hyperlipidemia rat model. We demonstrated that Dex stabilized BBB integrity through increased Mfsd2a gene expression.

Role of phosphatidylcholine-DHA in preventing APOE4-associated Alzheimer's disease.

Dietary and supplemental intake of the ω-3 fatty acid docosahexaenoic acid (DHA) reduces risk of Alzheimer’s disease (AD) and ameliorates symptoms. The apolipoprotein E (APOE)4 allele is the strongest risk factor for sporadic AD, exclusive of age. APOE4 carriers respond well to the DHA present in fish but do not respond as well to dietary supplements. The mechanisms behind this varied response remain unknown. I posit that the difference is that fish contain DHA in phospholipid form, whereas fish oil supplements do not. This influences whether DHA is metabolized to nonesterified DHA (free DHA) or a phospholipid form called lysophosphatidylcholine DHA (DHA-lysoPC). Free DHA is transported across the outer membrane leaflet of the blood–brain barrier (BBB) via passive diffusion, and DHA-lysoPC is transported across the inner membrane leaflet of the BBB via the major facilitator superfamily domain-containing protein 2A. I propose that APOE4 carriers have impaired brain transport of free DHA but not of DHA-lysoPC, as a consequence of a breakdown in the outer membrane leaflet of the BBB, putting them at increased risk for AD. Dietary sources of DHA in phospholipid form may provide a means to increase plasma levels of DHA-lysoPC, thereby decreasing the risk of AD.—Patrick, R. P. Role of phosphatidylcholine-DHA in preventing APOE4-associated Alzheimer’s disease.

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.

Major Facilitator Superfamily Domain‐containing protein 2a is a novel regulator of hepatic lipid metabolism

Understanding how the body switches between storing and burning energy is a fundamental gap in our ability to better treat metabolic disease. The Major Facilitator Superfamily Domain‐containing protein 2a (MFSD2A) is a newly identified plasma membrane transporter that is nutritionally regulated in liver and brown adipose tissue. MFSD2A protein expression is not detectable in the livers of fed mice, but is highly induced during a fast in a PPARalpha‐ and glucagon receptor‐dependant manner. Additionally, MFSD2A turns over rapidly within 60 minutes, and disappears from the cell surface with similar kinetics. In order to investigate whether MFSD2A plays a role in lipid metabolism, we generated a conventional Mfsd2a knockout mouse model. In the absence of MFSD2A, normal triglyceride accumulation in the liver during a fast was not observed. Additionally, knockout mice exhibited increased energy expenditure and protection from diet‐induced weight gain, without changes to glucose homeostasis. Further data on the mechanism of MFSD2A will be presented. Taken together, our studies indicate that MFSD2A plays an important role in regulation of energy expenditure and liver triglyceride levels.

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

This study describes the identification of Mfsd2a (major facilitator superfamily domain-containing protein 2a), a novel mammalian major facilitator superfamily domain-containing protein, and an additional closely related protein, Mfsd2b. Most intron/exon junctions are conserved between the two genes, suggesting that they are derived from a common ancestor. Mfsd2a and Mfsd2b share a 12 transmembrane alpha-helical domain structure that bears greatest similarity to that of the bacterial Na(+)/melibiose symporters. Confocal microscopy demonstrated that Mfsd2a localizes to the endoplasmic reticulum. Mfsd2a is expressed in many tissues and is highly induced in liver and BAT (brown adipose tissue) during fasting. Mfsd2a displays an oscillatory expression profile in BAT and liver, consistent with a circadian rhythm. Although the basal level of Mfsd2a expression is relatively low in mouse BAT, it is greatly induced during cold-induced thermogenesis and after treatment with betaAR (beta-adrenergic receptor) agonists. This induction is totally abolished in beta-less (betaAR-deficient) mice. These findings indicate that Mfsd2a is greatly up-regulated in BAT during thermogenesis and that its induction is controlled by the betaAR signalling pathway. The observed induction of Mfsd2a expression in cultured BAT cells by dibutyryl-cAMP is in agreement with this conclusion. The present study suggests that Mfsd2a plays a role in adaptive thermogenesis.