Opisthorchis viverrini excretory-secretory products suppress GLUT8 of cholangiocytes

Opisthorchis viverrini infection and the subsequent bile duct cancer it induces remains a significant public health problem in Southeast Asia. Opisthorchiasis has been reported to cause reduced plasma glucose levels among infected patients. The underlying mechanism for this phenomenon is unclear. In the present study, evidence is presented to support the hypothesis that O. viverrini exploits host cholangiocyte glucose transporters (GLUTs) in a similar manner to that of rodent intestinal nematodes, to feed on unabsorbed glucose in the bile for survival. GLUT levels in a cholangiocyte H69 cell line co-cultured with excretory-secretory products of O. viverrini were examined using qPCR and immunoblotting. GLUT 8 mRNA and expressed proteins were found to be downregulated in H69 cells in the presence of O. viverrini. This suggests that O. viverrini alters glucose metabolism in cells within its vicinity by limiting transporter expression resulting in increased bile glucose that it can utilize and potentially explains the previously reported anti-insulin effect of opisthorchiasis.

The Impact of SLC2A8 RNA Interference on Glucose Uptake and the Transcriptome of Human Trophoblast Cells

While glucose is the primary fuel for fetal growth, the placenta utilizes the majority of glucose taken up from the maternal circulation. Of the facilitative glucose transporters in the placenta, SLC2A8 (GLUT8) is thought to primarily function as an intracellular glucose transporter; however, its function in trophoblast cells has not been determined. To gain insight into the function of SLC2A8 in the placenta, lentiviral-mediated RNA interference (RNAi) was performed in the human first-trimester trophoblast cell line ACH-3P. Non-targeting sequence controls (NTS RNAi; n = 4) and SLC2A8 RNAi (n = 4) infected ACH-3P cells were compared. A 79% reduction in SLC2A8 mRNA concentration was associated with an 11% reduction (p ≤ 0.05) in ACH-3P glucose uptake. NTS RNAi and SLC2A8 RNAi ACH-3P mRNA were subjected to RNAseq, identifying 1525 transcripts that were differentially expressed (|log2FC| > 1 and adjusted p-value < 0.05), with 273 transcripts derived from protein-coding genes, and the change in 10 of these mRNAs was validated by real-time qPCR. Additionally, there were 147 differentially expressed long non-coding RNAs. Functional analyses revealed differentially expressed genes involved in various metabolic pathways associated with cellular respiration, oxidative phosphorylation, and ATP synthesis. Collectively, these data indicate that SLC2A8 deficiency may impact placental uptake of glucose, but that its likely primary function in trophoblast cells is to support cellular respiration. Since the placenta oxidizes the majority of the glucose it takes up to support its own metabolic needs, impairment of SLC2A8 function could set the stage for functional placental insufficiency.

Alternative Splicing and Cleavage of GLUT8

The GLUT (SLC2) family of membrane-associated transporters are described as glucose transporters. However, this family is divided into three classes and, though the regulated transporter activity of class I proteins is becoming better understood, class III protein functions continue to be obscure. We have cataloged the relative expression and splicing of SLC2 mRNA isomers in tumors and normal tissues, with a focus on breast tumors and cell lines. mRNA for the class III protein GLUT8 is the predominant SLC2 species expressed alongside GLUT1 in many tissues, but GLUT8 mRNA exists mostly as an untranslated splice form in tumors. We confirm that GLUT8 is not presented at the cell surface and does not transport glucose directly. However, we reveal a lysosome-dependent reaction that cleaves the GLUT8 protein and releases the carboxy-terminal peptide to a separate vesicle population. Given the localization of GLUT8 at a major metabolic hub (the late endosomal/lysosomal interface) and its regulated cleavage reaction, we evaluated TXNIP-mediated hexosamine homeostasis and speculate that GLUT8 may function as a sensory component of this reaction.

Trehalose intake and exercise upregulate a glucose transporter, GLUT8, in the brain

Physical exercise influences cognitive function through a cascade of cellular processes that promote angiogenesis and neurogenesis. Autophagy is a cellular degradation system that is capable of producing energy in response to various conditions such as starvation, physical exercise and several treatments. Our previous report demonstrated that a disaccharide, trehalose, induced autophagy in the brain and reduced the levels of potentially toxic proteins. To achieve more efficient induction of autophagy in the brain, in this study, we examined the effect of disaccharide intake combined with exercise on autophagy in vivo. Consistent with the results of previous studies, our biochemical analyses demonstrated that trehalose increased the level of lipidated LC3 (LC3II) in the brain and liver of adult mice. However, contrary to our expectation, treadmill exercise reduced the level of LC3II in the brain and liver. Interestingly, glycogen storage was preserved in the liver of trehalose-intake mice even after exercise. Moreover, the trehalose transporter GLUT8 was increased in the liver by trehalose or in the brain by trehalose together with exercise. In contrast, the level of GLUT4 remained stable in the liver and brain even after exercise. These findings suggest that trehalose and GLUT8 coordinately contribute to energy supply in the brain.

Expression of glucose transporter 8 (GLUT8) in spermatogenesis of adult boar testes

The present study was designed to investigate the glucose transporter 8 (GLUT8) expression and localization in adult boar testis. Localization and expression of GLUT8 were conducted with Western Blotting, immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) methods GLUT8 protein and mRNA were expressed in the boar testes. The results of Western Blotting analysis showed specificity of the antibody for protein of boar testes. The immunohistochemistry results showed that GLUT8 protein mainly localized in spermatocytes, round spermatids and elongated spermatids of the seminiferous tubules in the adult boar testes. And the GLUT8 expression persists during eight stages of boar spermatogenesis. GLUT8 may mainly provide glucose for the later stage of germ cell differentiation in adluminal compartment in adult boar testes. These results suggested that GLUT8 is important for the spermatogenesis in the adult boar testes.

Glucose transporter 8 immunoreactivity in astrocytic and microglial cells in subependymal areas of human brains

Glucose transporter 8 (GLUT8), a glucose/fructose transporter, has been shown to be expressed in neuronal cells in several brain areas. A recent immunohistochemical study has shown the presence of GLUT8 in the cytoplasm of epithelial cells of the choroid plexus and ependymal cells. In this study, localization of GLUT8 in glial cells was investigated using immunohistochemical methods. Immunoreactivity for GLUT8 was observed in cells showing astrocytic or microglial structural features located around the lateral ventricles. Confocal microscopic examination revealed that subependymal GLUT8-positive cells with large amounts of cytoplasm mainly show clear immunoreactivity for vimentin, while they were also colocalized with weak immunoreactivity for glial fibrillary acidic protein (GFAP) within the cytoplasm of some cells. In addition, some GLUT8-positive cells with small amounts of cytoplasm and small nuclei showed CD68 or HLA-DR immunoreactivity, indicating them to be cells of microglia/macrophage lineage. These findings suggest that glucose/fructose is transported into the cytoplasm of vimentin- or GFAP-positive astrocytic and CD68- or HLA-DR-positive microglial cells located around the lateral ventricle.

Immunoreactivity of glucose transporter 8 is localized in the epithelial cells of the choroid plexus and in ependymal cells

High fructose intake is known to be associated with increased plasma triglyceride concentration, impaired glucose tolerance, insulin resistance, and high blood pressure. In addition, excess fructose intake is also thought to be a risk factor for dementia. Previous immunohistochemical studies have shown the presence of glucose transporter 5 (GLUT5), a major transporter of fructose, in the epithelial cells of the choroid plexus and ependymal cells in the brains of humans, rats, and mice, while GLUT2, a minor transporter of fructose, was localized in the ependymal cells of rat brain. In this study, immunoreactivity for the fructose transporter GLUT8 was observed in the cytoplasm of the epithelial cells in the choroid plexus and in the ependymal cells of the brains of humans and mice. These structures were not immunoreactive for GLUT7, GLUT11, and GLUT12. Our findings support the hypothesis of the transport of intravascular fructose through the epithelial cells of the choroid plexus and the ependymal cells.

Possible Role of GnIH as a Mediator between Adiposity and Impaired Testicular Function

The aim of the present study was to evaluate the roles of gonadotropin-inhibitory hormone (GnIH) as an endocrine link between increasing adiposity and impaired testicular function in mice. To achieve this, the effect of GnIH on changes in nutrients uptake and hormonal synthesis/action in the adipose tissue and testis was investigated simultaneously by in vivo study and separately by in vitro study. Mice were treated in vivo with different doses of GnIH for 8 days. In the in vitro study, adipose tissue and testes of mice were cultured with different doses of GnIH with or without insulin or LH for 24 h at 37°C. The GnIH treatment in vivo showed increased food intake, upregulation of glucose transporter 4 (GLUT4), and increased uptake of triglycerides (TGs) in the adipose tissue. These changes may be responsible for increased accumulation of fat in white adipose tissue, resulting in increase in the body mass. Contrary to the adipose tissue, treatment with GnIH both in vivo and in vitro showed decreased uptake of glucose by downregulation of glucose transporter 8 (GLUT8) expressions in the testis, which in turn resulted in the decreased synthesis of testosterone. The GnIH treatment in vivo also showed the decreased expression of insulin receptor protein in the testis, which may also be responsible for the decreased testicular activity in the mice. These findings thus suggest that GnIH increases the uptake of glucose and TGs in the adipose tissue, resulting in increased accumulation of fat, whereas simultaneously in the testis, GnIH suppressed the GLUT8-mediated glucose uptake, which in turn may be responsible for decreased testosterone synthesis. This study thus demonstrates GnIH as mediator of increasing adiposity and impaired testicular function in mice.