Sweet and low-autoantibodies deny oligodendrocytes their sugar fix.

Pathogenic autoantibodies causing encephalopathy modify the expression of the glucose transporter in oligodendrocytes.

Soluble Uric Acid Is an Intrinsic Negative Regulator of Monocyte Activation in Monosodium Urate Crystal-Induced Tissue Inflammation.

Although monosodium urate (MSU) crystals are known to trigger inflammation, published data on soluble uric acid (sUA) in this context are discrepant. We hypothesized that diverse sUA preparation methods account for this discrepancy and that an animal model with clinically relevant levels of asymptomatic hyperuricemia and gouty arthritis can ultimately clarify this issue. To test this, we cultured human monocytes with different sUA preparation solutions and found that solubilizing uric acid (UA) by prewarming created erroneous results because of UA microcrystal contaminants triggering IL-1ß release. Solubilizing UA with NaOH avoided this artifact, and this microcrystal-free preparation suppressed LPS- or MSU crystal-induced monocyte activation, a process depending on the intracellular uptake of sUA via the urate transporter SLC2A9/GLUT9. CD14+ monocytes isolated from hyperuricemic patients were less responsive to inflammatory stimuli compared with monocytes from healthy individuals. Treatment with plasma from hyperuricemic patients impaired the inflammatory function of CD14+ monocytes, an effect fully reversible by removing sUA from hyperuricemic plasma. Moreover, Alb-creERT2;Glut9 lox/lox mice with hyperuricemia (serum UA of 9-11 mg/dl) showed a suppressed inflammatory response to MSU crystals compared with Glut9 lox/lox controls without hyperuricemia. Taken together, we unravel a technical explanation for discrepancies in the published literature on immune effects of sUA and identify hyperuricemia as an intrinsic suppressor of innate immunity, in which sUA modulates the capacity of monocytes to respond to danger signals. Thus, sUA is not only a substrate for the formation of MSU crystals but also an intrinsic inhibitor of MSU crystal-induced tissue inflammation.

Characterization of Glucose Transporter 6 in Lipopolysaccharide-Induced Bone Marrow-Derived Macrophage Function.

The polarization processes for M1 versus M2 macrophages are quite distinct in the context of changes in cellular metabolism. M1 macrophages are highly glycolytic, whereas M2 macrophages require a more oxidative nutrient metabolism. An important part of M1 polarization involves upregulation of the glucose transporter (GLUT) GLUT1 to facilitate increased glucose uptake and glycolytic metabolism; however, the role of other glucose transporters in this process is largely unknown. In surveying the Functional Annotation of the Mammalian Genome and Gene Expression Omnibus Profiles databases, we discovered that the glucose transporter GLUT6 is highly upregulated in LPS-activated macrophages. In our previous work, we have not detected mouse GLUT6 protein expression in any noncancerous tissue; therefore, in this study, we investigated the expression and significance of GLUT6 in bone marrow-derived macrophages from wild-type and GLUT6 knockout C57BL/6 mice. We show that LPS-induced M1 polarization markedly upregulated GLUT6 protein, whereas naive macrophages and IL-4-induced M2 macrophages do not express GLUT6 protein. However, despite strong upregulation of GLUT6 in M1 macrophages, the absence of GLUT6 did not alter M1 polarization in the context of glucose uptake, glycolytic metabolism, or cytokine production. Collectively, these data show that GLUT6 is dispensable for LPS-induced M1 polarization and function. These findings are important because GLUT6 is an anticancer drug target, and this study suggests that inhibition of GLUT6 may not impart detrimental side effects on macrophage function to interfere with their antitumor properties.

Immunoreactivity of urate transporters, GLUT9 and URAT1, is located in epithelial cells of the choroid plexus of human brains.

It has been suggested that urate plays a protective role in neurons, while hyperuricemia is correlated with atherosclerosis and cardiovascular disease. However, whether there is a system that directly transports urate into the brain remains to be clarified. In this study, the localization of glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1), which are known to be representative reabsorptive urate transporters, was immunohistochemically examined in autopsied human brains. Immunoreactivity of GLUT9 was observed on the apical side of the cytoplasm of epithelial cells in the choroid plexus and in the cilia of ependymal cells of the human brain. Immunoreactivity of URAT1 was observed on the basolateral side of the cytoplasm of epithelial cells in the choroid plexus. In addition, immunoreactivity of GLUT9 and URAT1 was not observed in microvessels of the human brains. The choroid plexus and renal proximal tubule were similar in having a polarized distribution of these two transporters with the two transporters on opposite membranes, but the two transporters' distribution differs between the choroid plexus and the kidney in terms of which membrane (apical/basal) expresses which transporter. These findings support the hypothesis of the direct transport of intravascular urate into the central nervous system through the choroid plexus.

Reduction of Mosquito Survival in Mice Vaccinated with Anopheles stephensi Glucose Transporter.

Despite the fact that recent efforts to control/eradicate malaria have contributed to a significant decrease in the number of cases and deaths, the disease remains a global health challenge. Vaccines based on mosquito salivary gland antigens are a potential approach for reducing vector populations and malaria parasites. The Anopheles AGAP007752 gene encodes for a glucose transporter that is upregulated during Plasmodium infection, and its knockdown decreases the number of sporozoites in mosquito salivary glands. These results together with the fact that glucose is a vital source of energy suggested that a glucose transporter is a candidate protective antigen for the control of mosquito infestations and Plasmodium infection. To address this hypothesis, herein we investigate the effect of mice vaccination with an immunogenic peptide from mosquito glucose transporter on Anopheles stephensi fitness and Plasmodium berghei infection. We showed that vaccination with a peptide of glucose transporter reduced mosquito survival by 5% when compared to controls. However, the reduction in Plasmodium infection was not significant in mosquitoes fed on vaccinated mice. The effect of the peptide vaccination on mosquito survival is important to reduce infestation by malaria vectors. These results support further research on developing glucose transporter-based vaccines to reduce mosquito fitness.

Host programmed death ligand 1 is dominant over programmed death ligand 2 expression in regulating graft-versus-host disease lethality.

Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, play an important role in the maintenance of peripheral tolerance. We explored the role of PD-1 ligands in regulating graft-versus-host disease (GVHD). Both PD-L1 and PD-L2 expression were upregulated in the spleen, liver, colon, and ileum of GVHD mice. Whereas PD-L2 expression was limited to hematopoietic cells, hematopoietic and endothelial cells expressed PD-L1. PD-1/PD-L1, but not PD-1/PD-L2, blockade markedly accelerated GVHD-induced lethality. Chimera studies suggest that PD-L1 expression on host parenchymal cells is more critical than hematopoietic cells in regulating acute GVHD. Rapid mortality onset in PD-L1-deficient hosts was associated with increased gut T-cell homing and loss of intestinal epithelial integrity, along with increased donor T-cell proliferation, activation, Th1 cytokine production, and reduced apoptosis. Bioenergetics profile analysis of proliferating alloreactive donor T-cells demonstrated increased aerobic glycolysis and oxidative phosphorylation in PD-L1-deficient hosts. Donor T-cells exhibited a hyperpolarized mitochondrial membrane potential, increased superoxide production, and increased expression of a glucose transporter in PD-L1-deficient hosts. Taken together, these data provide new insight into the differential roles of host PD-L1 and PD-L2 and their associated cellular and metabolic mechanisms controlling acute GVHD.

Candida albicans Hgt1p, a multifunctional evasion molecule: complement inhibitor, CR3 analogue, and human immunodeficiency virus-binding molecule.

BACKGROUND: The complement system is tightly controlled by several regulators. Two of these, factor H (FH) and C4b-binding protein (C4BP), can be acquired by pathogens conveying resistance to complement attack. The aim of the study was to characterize the FH binding molecule of Candida albicans, a potentially life-threatening yeast. METHODS: The gene coding for this molecule was identified by probing an expression library and homozygous deletion mutants of the respective gene were constructed. Binding and functional assays were undertaken to compare wild-type and knockout strains. RESULTS: The high-affinity glucose transporter 1 (CaHgt1p) was identified as an FH-binding molecule. Homozygous hgt1Δ/Δ deletion mutants, but not the restored strain in which HGT1 was reintegrated, showed a decreased binding of FH and even of C4BP, demonstrating its function as an FH- and C4BP-binding protein. This led to an enhanced terminal complement complex deposition after incubation with human serum; CaHgt1p thus functions as complement inhibitor. hgt1Δ/Δ mutants failed to form rosettes with complement-coated sheep erythrocytes, and show reduced binding to HIV-gp160, implying that a complement receptor 3 (CR3) moiety, known as fungal HIV binding molecule is lacking. CONCLUSIONS: CaHgt1p is a multifunctional evasion molecule, as complement inhibitor, CR3 analogue and HIV receptor.

GLUT8 contains a [DE]XXXL[LI] sorting motif and localizes to a late endosomal/lysosomal compartment.

Glucose transporter 8 (GLUT8) contains a cytoplasmic N-terminal dileucine motif and localizes to a thus far unidentified intracellular compartment. Translocation of GLUT8 to the plasma membrane (PM) was found in insulin-treated mouse blastocysts. Using overexpression of GLUT8 in adipocytes and neuronal cells however, insulin treatment or depolarization of the cells did not lead to GLUT8 PM translocation in other studies. In addition, other experiments showing dynamin-dependent endocytosis of GLUT8 suggested that GLUT8 recycles between an endosomal compartment and the PM. To reveal the functional/physiological role of GLUT8, we studied its subcellular localization in 3T3L1, HEK293 and CHO cells. We show that GLUT8 does not co-localize with GLUT4 and does not redistribute to the PM after treatment with insulin, ionophores or okadaic acid in these cell lines. Once endocytosed, GLUT8 does not recycle to the PM. GLUT8 localizes to late endosomes and lysosomes. An interspecies GLUT8 - sequence alignment revealed the presence of a highly conserved late endosomal/lysosomal-targeting motif ([DE]XXXL[LI]). Changing the glutamate to arginine as found in GLUT4 (RRXXXLL) alters GLUT8 endocytosis and retains the transporter at the PM. Furthermore, sorting GLUT8 to late endosomes/lysosomes does not require prior presence of GLUT8 at the PM followed by its endocytosis. In summary, GLUT8 does not reside in a recycling vesicle pool and is distinct from GLUT4. From our data, we postulate a role for GLUT8 in transport of hexoses across intracellular membranes, for example in specific compartments of GLUT8 expression such as the acrosome of mature spermatozoa or secretory granules in neurons. Furthermore, a role for GLUT8 in hexose transport across the lysosomal membrane, a transport mechanism that has long been suggested but unexplained, is discussed.