GLUT5: structure, functions, diseases and potential applications

Role of fructose in renal cell carcinoma progression

Renal cell carcinoma (RCC) is a highly malignant tumor with a poor prognosis, underscoring the urgent need for novel therapeutic strategies. RCC cells exhibit rapid proliferation and high metabolic demands, leading to hypoglycemic and hypoxic conditions within the tumor microenvironment (TME). Our study reveals that the fructose transporter Glut5 is prominently expressed in RCC, facilitating increased fructose uptake. This compensatory mechanism supports RCC survival under glucose deprivation and hypoxia. Fructose utilization sustains RCC proliferation, migration, and colony formation in vitro, significantly reduces apoptosis, and accelerates renal cancer growth in vivo. Mechanistically, fructose activates the cAMP/PKA signaling pathway, driving metabolic reprogramming and promoting tumor progression. Furthermore, 2,5-dehydro-D-mannitol (2,5-AM), a competitive inhibitor of fructose transport, significantly inhibits RCC growth both in vivo and in vitro. These findings provide new insights into the role of fructose metabolism in RCC progression and suggest potential therapeutic targets.

Hepatic and Pancreatic Cellular Response to Early Life Nutritional Mismatch

To determine the basis for perinatal nutritional mismatch causing metabolic dysfunction-associated steatotic liver disease and diabetes mellitus, we examined adult phenotype, hepatic transcriptome, and pancreatic β-islet function. In prenatal caloric-restricted rats with intrauterine growth restriction (IUGR) and postnatal exposure to high fat with fructose (HFhf) or high carbohydrate, we investigated male and female IUGR-HFhf and IUGR-high carbohydrate, vs HFhf and control offspring. Males more than females displayed adiposity, glucose intolerance, insulin resistance, hyperlipidemia, and hepatomegaly with hepatic steatosis. Male hepatic triglyceride synthesis, de novo lipogenesis genes increased, while female lipolysis, β-oxidation, fatty acid efflux, and FGF21 genes increased. IUGR-HFhf males demonstrated reduced β-islet insulin and humanin, and type 1 diabetes mellitus human amniotic fluid increased humanin. Humanin suppression disabled glucose stimulated insulin, ATP production, with apoptotic diminished β-islet viability. Humanin and FGF21 may reverse perinatal nutritional mismatched phenotype by restoring functional β islets and preventing metabolic dysfunction-associated steatotic liver disease and diabetes mellitus.

New insights into the mechanisms of iron absorption: Iron dextran uptake in the intestines of weaned pigs through glucose transporter 5 (GLUT5) and divalent metal transporter 1 (DMT1) transporters

The purpose of this study was to gain insight into the mechanism of iron dextran (DexFe) absorption in the intestines. A total of 72 piglets (average BW = 7.12 ± 0.75 kg, male to female ratio = 1:1) weaned at 28 d of age were randomly divided into two treatment groups with six replicates for each group. The experimental diets included the basal diet supplemented with 100 mg/kg iron dextran (DexFe group) and the basal diet supplemented with 100 mg/kg FeSO4·H2O (CON group). The experiment lasted for 28 d. The piglets' intestinal iron transport was measured in vitro using an Ussing chamber. Porcine intestinal epithelial cell line (IPEC-J2) cells were used to develop a monolayer cell model that explored the molecular mechanism of DexFe absorption. Results showed that compared to the CON group, the ADG of pigs in the DexFe group was improved (P = 0.022), while the F/G was decreased (P = 0.015). The serum iron concentration, apparent iron digestibility, and iron deposition in the duodenum, jejunum, and ileum were increased (P < 0.05) by dietary DexFe supplementation. Piglets in the DexFe group had higher serum red blood count, hemoglobin, serum iron content, serum ferritin and transferrin levels and lower total iron binding capacity (P < 0.05). In the Ussing chamber test, the iron absorption rate of the DexFe group was greater (P < 0.001) than the CON group, and there was no significant difference between the DexFe group and the glucose group (P > 0.05). Furthermore, when compared to the CON group, DexFe administration improved (P < 0.05) SLC2A5 gene and glucose transporter 5 (GLUT5) protein expression but had no effect (P > 0.05) on SLC11A2 gene or divalent metal transporter 1 (DMT1) protein expression. Once the GLUT5 protein was suppressed, the iron transport rate and apparent permeability coefficient were decreased (P < 0.05) in IPEC-J2 monolayer cell models. The findings suggest the effectiveness of DexFe application in weaned piglets and revealed for the first time that DexFe absorption in the intestine is closely related to the glucose transporter GLUT5 protein channel.

Interactions between glucagon like peptide 1 (GLP-1) and estrogens regulates lipid metabolism

Obesity, characterized by excessive fat accumulation in white adipose tissue (WAT), is linked to numerous health issues, including insulin resistance (IR), and type 2 diabetes mellitus (DM2). The distribution of adipose tissue differs by sex, with men typically exhibiting android adiposity and pre-menopausal women displaying gynecoid adiposity. After menopause, women have an increased risk of developing android-type obesity, IR, and DM2. Glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) are important in treating obesity and DM2 by regulating insulin secretion, impacting glucose and lipid metabolism. GLP-1Rs are found in various tissues including the pancreas, brain, and adipose tissue. Studies suggest GLP-1RAs and estrogen replacement therapies have similar effects on tissues like the liver, central nervous system, and WAT, probably by converging pathways involving protein kinases. To investigate these interactions, female rats underwent ovariectomy (OVR) to promote a state of estrogen deficiency. After 20 days, the rats were euthanized and the tissues were incubated with 10 μM of liraglutide, a GLP-1RA. Results showed significant changes in metabolic parameters: OVR increased lipid catabolism in perirenal WAT and basal lipolysis in subcutaneous WAT, while liraglutide treatment enhanced stimulated lipolysis in subcutaneous WAT. Liver responses included increased stimulated lipolysis with liraglutide. Transcriptome analysis revealed distinct gene expression patterns in WAT of OVR rats and those treated with GLP-1RA, highlighting pathways related to lipid and glucose metabolism. Functional enrichment analysis showed estrogen's pivotal role in these pathways, influencing genes involved in lipid metabolism regulation. Overall, the study underscores GLP-1RA acting directly on adipose tissues and highlights the complex interactions between GLP-1 and estrogen in regulating metabolism, suggesting potential synergistic therapeutic effects in treating metabolic disorders like obesity and DM2.

Suitability of red fox (Vulpes vulpes) and golden jackal (Canis aureus) as hosts of Echinococcus multilocularis based on egg production characteristics and literature data on the intestinal ecosystems of carnivores

Echinococcus multilocularis is the most important food-borne parasite in Europe. Its natural definitive host is the red fox (Vulpes vulpes) while other canid species play a secondary role in the maintenance of its endemics. However, recent studies call attention to the potential of golden jackal (Canis aureus) as a suitable definitive host for E. multilocularis. Our study aimed to evaluate the quantitative and qualitative egg production traits of adult E. multilocularis in different hosts as an indicator of reproductive success. Investigation of 111 and 82 parasites from 33 red foxes and 29 golden jackals, respectively, we ascertained that the proportion of worms with mature eggs was significantly lower in golden jackals than in red foxes. Those worms, which produced mature eggs in golden jackal hosts, originated from less crowded infrapopulations than their fox-originated counterparts. Other characteristics of the parasite's reproductive ability, such as the proportion of fertile worms, and mean egg production were similar in the two hosts. Comparing these findings to evolutionary data on different canid taxa, we hypothesised that the mutual presence of red fox and a differently evolved host of E. multilocularis might contribute to the formation of stable parasite circulation in these multi-host systems.

Renal Sugar Metabolites and mRNA Expression of Glucose Transporters in Meat-Type Chickens with Differing Residual Water Intake

Molecular differences exist between birds with high residual water intake (HRWI) compared to those with low residual water intake (LRWI). Residual water intake (RWI) is defined as the difference between the water intake of a bird and the expected water intake corrected for metabolic body weight, feed intake, and body weight gain. Tissue metabolomic analysis revealed significantly increased kidney glucose, fructose, and arabitol in the LRWI group compared to the HRWI group. mRNA expression analysis of apical sodium glucose cotransporters SGLT1, SGLT4, SGLT5, and SGLT6 showed decreased expression of SGLTs 1, 5, and 6 in LRWI birds (p < 0.05), whereas SGLT4 expression was increased compared with HRWI birds (p < 0.01). An analysis of basal glucose transporters GLUT1, GLUT2, GLUT5, and GLUT9 showed significantly increased GLUT2 expression in LRWI birds compared with HRWI birds (p < 0.01). We postulate that SGLT4 is the main apical transporter in chicken kidneys and that its increased expression reduces these birds' need for water, resulting in less drinking. This is balanced by the increased expression of the basal transporter GLUT2, indicating better glucose retention, which may partly explain the physiological mechanism behind why these birds drink less water. Innately driven broiler water intake could therefore be influenced by the expression of kidney solute transporters.

Glucose transporters and their energy homeostasis function in various organs

Glucose transporters (GLUTs) belong to a membrane-protein family that essentially participates in easing the transportation and absorption of glucose molecules throughout the cellular membranes. From the brain to the eyes, each section delves into the intricate mechanisms of glucose uptake and utilization, shedding light on the unique adaptations and regulatory pathways in different anatomical structures. Beginning with the brain, known for its high energy demands, the chapter explicates the specialized GLUT expression patterns crucial for neuronal function and synaptic transmission. Moving to metabolic powerhouses like the liver, muscles, and adipose tissue, it elucidates the dynamic interplay of GLUT isoforms in energy storage, mobilization, and insulin responsiveness. Furthermore, the chapter navigates through the kidneys, lungs, skin, and reproductive organs, unveiling the diverse roles of GLUTs in renal glucose reabsorption, pulmonary-epithelial transportation, skin barrier associated functions, and gonadal development. It also explores the significance of placental GLUTs in fatal nutrient supply and the implications of cardiac GLUTs in myocardial energy metabolism. Additionally, it examines the intricate regulation of GLUTs at key barriers like the BBB (Blood-Brain Barrier) and placenta, as well as in endocrine glands such as the pancreas, adrenal medulla and thyroid. Moreover, it further elucidates the less-explored territories of GLUT expression in the bones, gastrointestinal tract, and ocular tissues like the retina, unraveling their implications in immune function, bone metabolism, intestinal glucose-sensing, and retinal physiology.

It's a Trap! Aldolase-Prescribed C4 Deoxyradiofluorination Affords Intracellular Trapping and the Tracing of Fructose Metabolism by PET

Fructose metabolism has been implicated in various diseases, including metabolic disorders, neurodegenerative disorders, cardiac disorders, and cancer. However, the limited availability of a quantitative imaging radiotracer has hindered its exploration in pathology and diagnostic imaging. Methods: We adopted a molecular design strategy based on the catalytic mechanism of aldolase, a key enzyme in fructolysis. We successfully synthesized a radiodeoxyfluorinated fructose analog, [18F]4-fluoro-4-deoxyfructose ([18F]4-FDF), in high molar activity. Results: Through heavy isotope tracing by mass spectrometry, we demonstrated that C4-deoxyfluorination of fructose led to effective trapping as fluorodeoxysorbitol and fluorodeoxyfructose-1-phosphate in vitro, unlike C1- and C6-fluorinated analogs that resulted in fluorolactate accumulation. This observation was consistent in vivo, where [18F]6-fluoro-6-deoxyfructose displayed substantial bone uptake due to metabolic processing whereas [18F]4-FDF did not. Importantly, [18F]4-FDF exhibited low uptake in healthy brain and heart tissues, known for their high glycolytic activity and background levels of [18F]FDG uptake. [18F]4-FDF PET/CT allowed for sensitive mapping of neuro- and cardioinflammatory responses to systemic lipopolysaccharide administration. Conclusion: Our study highlights the significance of aldolase-guided C4 radiodeoxyfluorination of fructose in enabling effective radiotracer trapping, overcoming limitations of C1 and C6 radioanalogs toward a clinically viable tool for imaging fructolysis in highly glycolytic tissues.

Bridging the gap: glucose transporters, Alzheimer's, and future therapeutic prospects

Glucose is the major source of chemical energy for cell functions in living organisms. The aim of this mini-review is to provide a clearer and simpler picture of the fundamentals of glucose transporters as well as the relationship of these transporters to Alzheimer's disease. This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Electronic databases (PubMed and ScienceDirect) were used to search for relevant studies mainly published during the period 2018-2023. This mini-review covers the two main types of glucose transporters, facilitated glucose transporters (GLUTs) and sodium-glucose linked transporters (SGLTs). The main difference between these two types is that the first type works through passive transport across the glucose concentration gradient. The second type works through active co-transportation to transport glucose against its chemical gradient. Fluctuation in glucose transporters translates into a disturbance of normal functioning, such as Alzheimer's disease, which may be caused by a significant downregulation of GLUTs most closely associated with insulin resistance in the brain. The first sign of Alzheimer's is a lack of GLUT4 translocation. The second sign is tau hyperphosphorylation, which is caused by GLUT1 and 3 being strongly upregulated. The current study focuses on the use of glucose transporters in treating diseases because of their proven therapeutic potential. Despite this, studies remain insufficient and inconclusive due to the complex and intertwined nature of glucose transport processes. This study recommends further understanding of the mechanisms related to these vectors for promising future therapies.