Glucose Transporter GLUT4 Research Articles

Sexual and Metabolic Differences in Hippocampal Evolution: Alzheimer’s Disease Implications

Sex differences in brain metabolism and their relationship to neurodegenerative diseases like Alzheimer’s are an important emerging topic in neuroscience. Intrinsic anatomic and metabolic differences related to male and female physiology have been described, underscoring the importance of considering biological sex in studying brain metabolism and associated pathologies. The hippocampus is a key structure exhibiting sex differences in volume and connectivity. Adult neurogenesis in the dentate gyrus, dendritic spine density, and electrophysiological plasticity contribute to the hippocampus’ remarkable plasticity. Glucose transporters GLUT3 and GLUT4 are expressed in human hippocampal neurons, with proper glucose metabolism being crucial for learning and memory. Sex hormones play a major role, with the aromatase enzyme that generates estradiol increasing in neurons and astrocytes as an endogenous neuroprotective mechanism. Inhibition of aromatase increases gliosis and neurodegeneration after brain injury. Genetic variants of aromatase may confer higher Alzheimer’s risk. Estrogen replacement therapy in postmenopausal women prevents hippocampal hypometabolism and preserves memory. Insulin is also a key regulator of hippocampal glucose metabolism and cognitive processes. Dysregulation of the insulin-sensitive glucose transporter GLUT4 may explain the comorbidity between type II diabetes and Alzheimer’s. GLUT4 colocalizes with the insulin-regulated aminopeptidase IRAP in neuronal vesicles, suggesting an activity-dependent glucose uptake mechanism. Sex differences in brain metabolism are an important factor in understanding neurodegenerative diseases, and future research must elucidate the underlying mechanisms and potential therapeutic implications of these differences.

4-Furanylvinylquinoline derivative as a new scaffold for the design of oxidative stress initiator and glucose transporter inhibitor drugs

In the present study, a detailed analysis of the effect of a substitution at the C4 position of the quinoline ring by styryl or furanylvinyl substituents on the structure-antitumour activity relationship was conducted. After analysing a library of derivatives from the styrylquinoline and furanylvinylquinoline groups, we selected the most active (IC50 below 100 nM) derivative 13, which contained the strongly electron-withdrawing nitro group in the furan substituent. The mechanism of action of this compound was studied on cell lines that differed in their p53 protein status. For this derivative, both cell cycle arrest (in G2/M phase in both HCT 116 cell lines and S phase for U-251 cell line) and the induction of apoptosis (up to 66% for U-251 cell line) were revealed. These studies were then confirmed by other methods at the gene and protein levels. Interestingly, we observed differences in the mechanism of action depending on the presence and mutation of the p53 protein, thus confirming its key role in cellular processes. Incubation with derivative 13 resulted in the induction of oxidative stress and triggered a cascade of cellular defence proteins that failed in the face of such an active compound. In addition, the results showed an inhibition of the GLUT-1 glucose transporter, which is extremely important in the context of anti-cancer activity.

Rg3-lipo biomimetic delivery of paclitaxel enhances targeting of tumors and myeloid-derived suppressor cells.

Liposomal drug delivery systems have revolutionized traditional cytotoxic drugs. However, the relative instability and toxicity of the existing liposomal drug delivery systems compromised their efficacy. Herein, we present Rg3-lipo, an innovative drug delivery system using a glycosyl moiety-enriched ginsenoside (Rg3). This system is distinguished by its glycosyl moieties exposed on the liposomal surface. These moieties imitate human cell membranes to stabilize and evade phagocytic clearance. The Rg3-lipo system loaded with paclitaxel (PTX-Rg3-lipo) demonstrated favorable bioavailability and safety in Sprague-Dawley rats, beagle dogs, and cynomolgus monkeys. With its glycosyl moieties recognizing tumor cells via the glucose transporter Glut1, PTX-Rg3-lipo inhibited gastric, breast, and esophageal cancers in human cancer cell lines, tumor-bearing mice, and patient-derived xenograft models. These glycosyl moieties selectively targeted myeloid-derived suppressor cells (MDSCs) through the glucose transporter Glut3 to attenuate their immunosuppressive effect. The mechanism study revealed that Rg3-lipo suppressed glycolysis and downregulated the transcription factors c-Maf and Mafb overcoming the MDSC-mediated immunosuppressive microenvironment and enhancing PTX-Rg3-lipo's antitumor effect. Taken together, we supply substantial evidence for its advantageous bioavailability and safety in multiple animal models, including nonhuman primates, and Rg3-lipo's dual targeting of cancer cells and MDSCs. Further investigation regarding Rg3-lipo's druggability will be conducted in clinical trials.

IMMU-21. OVEREXPRESSING CAR T-CELL GLUCOSE TRANSPORTER TO ENHANCE ANTI-TUMOR ACTIVITY IN GLIOBLASTOMA

Abstract INTRODUCTION Despite aggressive interventions, Glioblastoma (GBM) remains as a challenge for neuro-oncologists. Standard treatments are often followed by disease recurrence. Adoptive cell therapies have emerged as a viable therapeutic for brain malignancies. CAR-T cell therapy has generated substantial interest because of its efficacy and specificity in treating various cancers. Despite these efficacies, studies reveal limitations of CAR-T therapy due to the altered metabolic environment in GBM. GBM tumors shift towards aerobic glycolysis, regardless of oxygen availability leading to massive glucose consumption. This results in impeding T-cell glycolysis and activation. OBJECTIVE The GBM microenvironment provides local restraints via metabolic competition suppressing antitumor immunity, specifically inhibiting infiltration and tumoricidal functions of host and adoptively transferred tumor-reactive T-cells. In our study, we manipulated the metabolic fitness of the therapeutic T-cells to enhance their tumoricidal activity, by overexpressing glucose transporter GLUT1 and GLUT3. We show that this manipulation can enhance their anti-tumor activity. METHODS The T-cell glucose metabolic pathway was modulated via glucose transporter overexpression. The functionality of metabolically modified T-cells was investigated in murine and human models. RESULTS We demonstrated that tumor cells impose glucose restriction when competing for glucose with T-cells leading to T-cell hypo responsiveness. Overexpression of glucose transporters such as Glut1 and Glut3 increased T-cell glucose utilization and provide survival advantage leading to enhanced T-cell activation in glucose-restricted conditions. The metabolic modifications regulate T-cell efficacy by enhancing intra-tumoral trafficking. We tested this approach in the context of CD70CAR T cell therapy. It was established that glucose transporter overexpression in CD70 CAR T-cells not only improves intracranial tumor invasion but also elicit functional anti-tumor cell response thus improving survival. CONCLUSIONS This study integrates fundamental concepts of tumor and immune metabolism in the design of immunotherapy and confirms that immunometabolism represents a viable target for new cancer therapy to treat brain tumors.

Skeletal muscle from TBC1D4 p.Arg684Ter variant carriers is severely insulin resistant but exhibits normal metabolic responses during exercise.

In the Greenlandic Inuit population, 4% are homozygous carriers of a genetic nonsense TBC1D4 p.Arg684Ter variant leading to loss of the muscle-specific isoform of TBC1D4 and an approximately tenfold increased risk of type 2 diabetes1. Here we show the metabolic consequences of this variant in four female and four male homozygous carriers and matched controls. An extended glucose tolerance test reveals prolonged hyperglycaemia followed by reactive hypoglycaemia in the carriers. Whole-body glucose disposal is impaired during euglycaemic-hyperinsulinaemic clamp conditions and associates with severe insulin resistance in skeletal muscle only. Notably, a marked reduction in muscle glucose transporter GLUT4 and associated proteins is observed. While metabolic regulation during exercise remains normal, the insulin-sensitizing effect of a single exercise bout is compromised. Thus, loss of the muscle-specific isoform of TBC1D4 causes severe skeletal muscle insulin resistance without baseline hyperinsulinaemia. However, physical activity can ameliorate this condition. These observations offer avenues for personalized interventions and targeted preventive strategies.

Glut3 promotes cellular O-GlcNAcylation as a distinctive tumor-supportive feature in Treg cells.

Regulatory T cells (Tregs) establish dominant immune tolerance but obstruct tumor immune surveillance, warranting context-specific mechanistic insights into the functions of tumor-infiltrating Tregs (TIL-Tregs). We show that enhanced posttranslational O-linked N-acetylglucosamine modification(O-GlcNAcylation) of cellular factors is a molecular feature that promotes a tumor-specific gene expression signature and distinguishes TIL-Tregs from their systemic counterparts. We found that altered glucose utilization through the glucose transporter Glut3 is a major facilitator of this process. Treg-specific deletion of Glut3 abrogates tumor immune tolerance, while steady-state immune homeostasis remains largely unaffected in mice. Furthermore, by employing mouse tumor models and human clinical data, we identified the NF-κB subunit c-Rel as one such factor that, through Glut3-dependent O-GlcNAcylation, functionally orchestrates gene expression in Tregs at tumor sites. Together, these results not only identify immunometabolic alterations and molecular events contributing to fundamental aspects of Treg biology, specifically at tumor sites but also reveal tumor-specific cellular properties that can aid in the development of Treg-targeted cancer immunotherapies.

Viral interactions with host factors (TIM-1, TAM -receptors, Glut-1) are related to the disruption of glucose and ascorbate transport and homeostasis, causing the haemorrhagic manifestations of viral haemorrhagic fevers.

The haemorrhagic features of viral haemorrhagic fevers may be caused by common patterns of metabolic disturbances of the glucose and ascorbate homeostasis. Haemorrhages and vasculature disfunctions are a clinical feature not only of viral haemorrhagic fevers, but also in scurvy, diabetes and thrombotic microangiopathic haemolytic anaemia. Interestingly, the expression of glucose and ascorbate transporter Glut-1 on the erythrocyte membrane is associated with the inability to synthesize ascorbate and is restricted to that very species that are susceptible to filoviruses (primates, humans and fruit bats). Glut-1 may play a pivotal role in haemorrhagic fever pathogenesis. TIM-1 and TAM receptors have been recognized to enhance entry of Ebola, Lassa and Dengue viruses and viral interferences with TIM-1 could disturb its function, disturbing the expression of Glut-1. In those species not able to synthesize ascorbate and expressing Glut-1 on erythrocytes virus could interact with Glut-1 or other functionally related protein, and the influx of glucose into the cells would be severely impaired. As a consequence, transient hyperglycemia and a marked oxidative stress coupled with the high levels of glucose in plasma would be established, and then promote the activation of NF–κB transcription, exacerbating a pro-inflammatory response mediated by cytokines and chemokines: The inability to synthesize ascorbate is an Achilles Heel when trying to counteract the oxidative stress.

Calcium ATPase (PMCA) and GLUT-4 Upregulation in the Transverse Tubule Membrane of Skeletal Muscle from a Rat Model of Chronic Heart Failure.

Intolerance to exercise is a symptom associated with chronic heart failure (CHF) resulting in SM waste and weakness in humans. The effect of CHF on skeletal muscle (SM) arose from experimental evidence in rat models to explain the underlying mechanism. We investigated SM mechanical and metabolic properties in sham rats and with coronary ligation-induced CHF. After twelve weeks of CHF, rats were catheterized to measure right auricular pressure, SM mechanical properties, SERCA-ATPase activity and plasma membrane Ca2+-ATPase (PMCA) hydrolytic activity in isolated sarcoplasmic reticulum (SR) and transverse tubule (TT membrane), respectively, in the sham and CHF. The right auricular pressure and plasma nitrite concentration in CHF increased two-fold with respect to the sham. Pleural effusion and ascites were detected in CHF, confirming CHF. SERCA activity was conserved in CHF. In TT membranes from CHF, the glucose transporter GLUT4 increased seven-fold, and the PMCA hydrolytic activity increased five-fold, but in isolated muscle, the mechanical properties were unaffected. The absence of a deleterious effect of coronary ligation-induced CHF in the rat model on SM could be explained by the increased activity of PMCA and increased presence of GLUT-4 on the TT membrane, which may be involved in the mechanical outcome of the EDL.

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.

GLUT1 overexpression in CAR-T cells induces metabolic reprogramming and enhances potency

The intensive nutrient requirements needed to sustain T cell activation and proliferation, combined with competition for nutrients within the tumor microenvironment, raise the prospect that glucose availability may limit CAR-T cell function. Here, we seek to test the hypothesis that stable overexpression (OE) of the glucose transporter GLUT1 in primary human CAR-T cells would improve their function and antitumor potency. We observe that GLUT1OE in CAR-T cells increases glucose consumption, glycolysis, glycolytic reserve, and oxidative phosphorylation, and these effects are associated with decreased T cell exhaustion and increased Th17 differentiation. GLUT1OE also induces broad metabolic reprogramming associated with increased glutathione-mediated resistance to reactive oxygen species, and increased inosine accumulation. When challenged with tumors, GLUT1OE CAR-T cells secrete more proinflammatory cytokines and show enhanced cytotoxicity in vitro, and demonstrate superior tumor control and persistence in mouse models. Our collective findings support a paradigm wherein glucose availability is rate limiting for effector CAR-T cell function and demonstrate that enhancing glucose availability via GLUT1OE could augment antitumor immune function.

7284 Ablation of hexose-6-phosphate dehydrogenase in mice causes skeletal muscle atrophy and dramatically impairs exercise capacity

Abstract Disclosure: M. Zogg: None. A.D. Grötsch: None. J. Birk: None. P. Pelczar: None. J. Bouitbir: None. A. Odermatt: None. Hexose-6-phosphate dehydrogenase (H6PD) catalyzes the first two steps of the pentose-phosphate pathway (PPP) within the endoplasmic reticulum (ER), generating the redox equivalent NADPH. It has been shown that mice lacking H6PD develop defects mainly in skeletal muscles [1]. Nevertheless, the mechanisms underlying the myopathy in H6PD KO mice is unknown. Here, we further assessed muscle responses to H6PD deficiency and aimed to uncover the mechanisms that may cause myopathy in mice. We conducted a detailed characterization of the muscle structure and function as well as energy metabolism in oxidative and glycolytic muscles of H6PD KO mice. At the age of 15 weeks, H6PD KO mice displayed lower body weight than WT mice, despite similar food and water intake. Grip strength was significantly lower in H6PD KO than in WT mice. This was associated with decreased weight of the mixed (gastrocnemius, quadriceps) and fast fiber type rich muscles of the hind leg (extensor digitorum longus, tibialis anterior) in H6PD KO animals. Atrogin1 and Murf1 mRNA expression, markers of atrophy, increased only in the white (glycolytic) quadriceps. In this context, fast-twitch fibers in WT mice displayed higher H6pd mRNA expression than slow-twitch fibers. Electron microscopy analysis of red and white gastrocnemius muscles displayed the presence of large intramyofibrillar vacuoles, and morphologic changes of the sarcoplasmic reticulum and mitochondria in H6PD KO muscle. Metabolically, H6PD KO muscles presented an accumulation of glycogen granules and significantly decreased mRNA expression of glucose transporter Glut4, glucose-6-phosphate transporter G6pt and glycogen phosphorylase Pygm. The exercise capacity, measured by maximal running distance, decreased by more than 50% in H6PD KO mice. Upon exercise, both WT and H6PD KO animals were able to mobilize the majority of glycogen stored in their muscles. However, immediately after exercise, there was a significant increase in plasma lactate and glucose levels in H6PD KO animals. Disturbances in glucose metabolism were further supported by in vitro experiments using stable C2C12 H6PD KO myoblasts, revealing a shift in basal state mitochondrial fuel oxidation usage from glucose to fatty acid and glutamine in metabolic dependency assays. In conclusion, our findings revealed that H6PD seems to play a key role in proper function and energy metabolism of skeletal muscles.

12527 Determining The Impact Of Dampened Oxidative Stress On Islet Function And Gene Expression During Diabetes Onset In NOD Mice

Abstract Disclosure: K.V. Coutinho: None. H. Shinde: None. J. Feduska: None. K. Burnette: None. S.O. Poole: None. H.M. Tse: None. C.S. Hunter: None. Type 1 diabetes (T1D) arises from autoimmune destruction of insulin-producing pancreatic β-cells. Revealing the mechanisms underlying T1D onset are critical for therapeutic development but not completely understood. NADPH oxidase (NOX) generates superoxide, a precursor of reactive oxygen species (ROS), to regulate cell survival, differentiation, signaling, and autoimmune responses in T1D. NOD (Non-Obese Diabetic) mice spontaneously develop T1D, featuring increased cytokine/chemokine synthesis, inflammatory responsive macrophages and T cells, and ROS. Here, we harness NOD mice deficient in NOX-derived superoxide (NOD.Ncf1m[1]J), which have significantly lower T1D incidence. However, the impacts on islet β-cells in this T1D resistant model are unknown. We assessed a time course of glucose homeostasis between 6-20 weeks (W), spanning the onset T1D in NOD mice. Surprisingly, comparative glucose tolerance testing (GTT) in NOD.Ncf1m[1]J mice revealed increased glucose intolerance at 10W with no differences at 6, 14, and 20W as compared to NOD. Insulin tolerance was similar between the two models at all stages examined. This suggests superoxide production is necessary for β-cell function, despite that NOD.Ncf1m[1]J mice are T1D resistant. To understand islet transcriptomic changes between NOD and NOD.Ncf1m[1]J mice, we conducted comparative bulk islet RNA sequencing from 6 to 20W. Principal component analysis was applied to ensure differences between genotypes at each timepoint. Quality control methods within the Nextflow core pipeline were used to ensure sample quality. As expected, NOD.Ncf1m[1]J mice had decreased Ncf1 and immune response-related mRNA levels. Expression of T-cell exhaustion (Pdcd1, Lag3, and Tigit) genes remained level in NOD mice, but had significantly lower expression at 6W in NOD.Ncf1m[1]J mice. Interestingly, Ctla4, encoding a gene product that inhibits T-cell function, was upregulated at 14W in NOD.Ncf1m[1]J mice. Furthermore, GO analysis of downregulated NOD.Ncf1m[1]J gene sets include T-cell activation, response to IFN-β and IFN-γ at 6W, and decreased cytokine production at 20W. Supporting the dysregulation of β-cell function, Bace2, encoding a protease that limits β-cell function and mass, was upregulated with NOD. Ncf1m[1]J. Additionally, 14W β-cell function gene expression was decreased in the NOD.Ncf1m[1]J mice, including Slc2a2, which encodes the β-cell GLUT2 glucose transporter, and Glp1r, which is involved in preserving β-cell mass and function. Taken together, NOX-derived superoxide, whose loss decreases T1D incidence, may also dampen β-cell gene expression and function. Future directions will include comparative NOD and NOD.Ncf1m[1]J single cell transcriptomics to determine cell type specific transcriptional signatures between islet and immune cell subtypes. Presentation: 6/2/2024

Development of a Competitive Nutrient-Based T-Cell Immunotherapy Designed to Block the Adaptive Warburg Effect in Acute Myeloid Leukemia.

Background: T-cell-based adoptive cell therapies have emerged at the forefront of cancer immunotherapies; however, failed long-term survival and inevitable exhaustion of transplanted T lymphocytes in vivo limits clinical efficacy. Leukemia blasts possess enhanced glycolysis (Warburg effect), exploiting their microenvironment to deprive nutrients (e.g., glucose) from T cells, leading to T-cell dysfunction and leukemia progression. Methods: Thus, we explored whether genetic reprogramming of T-cell metabolism could improve their survival and empower T cells with a competitive glucose-uptake advantage against blasts and inhibit their uncontrolled proliferation. Results: Here, we discovered that high-glucose concentration reduced the T-cell expression of glucose transporter GLUT1 (SLC2A1) and TFAM (mitochondrion transcription factor A), an essential transcriptional regulator of mitochondrial biogenesis, leading to their impaired expansion ex vivo. To overcome the glucose-induced genetic deficiency in metabolism, we engineered T cells with lentiviral overexpression of SLC2A1 and/or TFAM transgene. Multi-omics analyses revealed that metabolic reprogramming promoted T-cell proliferation by increasing IL-2 release and reducing exhaustion. Moreover, the engineered T cells competitively deprived glucose from allogenic blasts and lessened leukemia burden in vitro. Conclusions: Our findings propose a novel T-cell immunotherapy that utilizes a dual strategy of starving blasts and cytotoxicity for preventing uncontrolled leukemia proliferation.

CRISPR–Cas9 screens reveal regulators of ageing in neural stem cells

Ageing impairs the ability of neural stem cells (NSCs) to transition from quiescence to proliferation in the adult mammalian brain. Functional decline of NSCs results in the decreased production of new neurons and defective regeneration following injury during ageing1–4. Several genetic interventions have been found to ameliorate old brain function5–8, but systematic functional testing of genes in old NSCs—and more generally in old cells—has not been done. Here we develop in vitro and in vivo high-throughput CRISPR–Cas9 screening platforms to systematically uncover gene knockouts that boost NSC activation in old mice. Our genome-wide screens in primary cultures of young and old NSCs uncovered more than 300 gene knockouts that specifically restore the activation of old NSCs. The top gene knockouts are involved in cilium organization and glucose import. We also establish a scalable CRISPR–Cas9 screening platform in vivo, which identified 24 gene knockouts that boost NSC activation and the production of new neurons in old brains. Notably, the knockout of Slc2a4, which encodes the GLUT4 glucose transporter, is a top intervention that improves the function of old NSCs. Glucose uptake increases in NSCs during ageing, and transient glucose starvation restores the ability of old NSCs to activate. Thus, an increase in glucose uptake may contribute to the decline in NSC activation with age. Our work provides scalable platforms to systematically identify genetic interventions that boost the function of old NSCs, including in vivo, with important implications for countering regenerative decline during ageing.

Comment on, "Hypoxia preconditioning protects neuronal cells against traumatic brain injury through stimulation of glucose transport mediated by HIF-1α/GLUTs signaling pathway in rat".

Wu et al. (2021) investigated the neuroprotective effects of hypoxia preconditioning (HPC) in a rat model of traumatic brain injury (TBI). The study demonstrated that HPC enhances brain resilience to TBI by upregulating glucose transporters GLUT1 and GLUT3 through the HIF-1α signaling pathway. Comprehensive molecular and histological analyses confirmed increased expression of these transporters, correlating with reduced neuronal apoptosis and cerebral edema. The robust methodology, including rigorous statistical validation and time-course assessments, underscores HPC's potential therapeutic role in mitigating neuronal loss and improving glucose transport post-injury. However, the study could be strengthened by incorporating additional preconditioning controls, comparative analyses with other neuroprotective strategies, and exploring downstream metabolic effects in greater detail. Furthermore, expanding the research to include diverse animal models and examining sex-dependent responses would enhance the generalizability and translational relevance of the findings. Future studies should also integrate metabolic flux analysis and advanced imaging techniques to further elucidate HPC's mechanisms of action.

Oligodendroglial fatty acid metabolism as a central nervous system energy reserve

Brain function requires a constant supply of glucose. However, the brain has no known energy stores, except for glycogen granules in astrocytes. In the present study, we report that continuous oligodendroglial lipid metabolism provides an energy reserve in white matter tracts. In the isolated optic nerve from young adult mice of both sexes, oligodendrocytes survive glucose deprivation better than astrocytes. Under low glucose, both axonal ATP levels and action potentials become dependent on fatty acid β-oxidation. Importantly, ongoing oligodendroglial lipid degradation feeds rapidly into white matter energy metabolism. Although not supporting high-frequency spiking, fatty acid β-oxidation in mitochondria and oligodendroglial peroxisomes protects axons from conduction blocks when glucose is limiting. Disruption of the glucose transporter GLUT1 expression in oligodendrocytes of adult mice perturbs myelin homeostasis in vivo and causes gradual demyelination without behavioral signs. This further suggests that the imbalance of myelin synthesis and degradation can underlie myelin thinning in aging and disease.

Exercise performance and health: Role of GLUT4

The glucose transporter GLUT4 is integral for optimal skeletal muscle performance during exercise, as well as for metabolic health. Physiological regulation of GLUT4 translocation during exercise and increased GLUT4 expression following exercise involves multiple, redundant signalling pathways. These include effects of reactive oxygen species (ROS). ROS contribute to GLUT4 translocation that increases skeletal muscle glucose uptake during exercise and stimulate signalling pathways that increase GLUT4 expression. Conversely, ROS can also inhibit GLUT4 translocation and expression in metabolic disease states. The opposing roles of ROS in GLUT4 regulation are ultimately linked to the metabolic state of skeletal muscle and the intricate mechanisms involved give insights into pathways critical for exercise performance and implicated in metabolic health and disease.

Pharmacologic LDH inhibition redirects intratumoral glucose uptake and improves antitumor immunity in solid tumor models.

Tumor reliance on glycolysis is a hallmark of cancer. Immunotherapy is more effective in controlling glycolysis-low tumors lacking lactate dehydrogenase (LDH) due to reduced tumor lactate efflux and enhanced glucose availability within the tumor microenvironment (TME). LDH inhibitors (LDHi) reduce glucose uptake and tumor growth in preclinical models, but their impact on tumor-infiltrating T cells is not fully elucidated. Tumor cells have higher basal LDH expression and glycolysis levels compared with infiltrating T cells, creating a therapeutic opportunity for tumor-specific targeting of glycolysis. We demonstrate that LDHi treatment (a) decreases tumor cell glucose uptake, expression of the glucose transporter GLUT1, and tumor cell proliferation while (b) increasing glucose uptake, GLUT1 expression, and proliferation of tumor-infiltrating T cells. Accordingly, increasing glucose availability in the microenvironment via LDH inhibition leads to improved tumor-killing T cell function and impaired Treg immunosuppressive activity in vitro. Moreover, combining LDH inhibition with immune checkpoint blockade therapy effectively controls murine melanoma and colon cancer progression by promoting effector T cell infiltration and activation while destabilizing Tregs. Our results establish LDH inhibition as an effective strategy for rebalancing glucose availability for T cells within the TME, which can enhance T cell function and antitumor immunity.

Picalm, a novel regulator of GLUT4-trafficking in adipose tissue

ObjectivePicalm (phosphatidylinositol-binding clathrin assembly protein), a ubiquitously expressed clathrin-adapter protein, is a well-known susceptibility gene for Alzheimer's disease, but its role in white adipose tissue (WAT) function has not yet been studied. Transcriptome analysis revealed differential expression of Picalm in WAT of diabetes-prone and diabetes-resistant mice, hence we aimed to investigate the potential link between Picalm expression and glucose homeostasis, obesity-related metabolic phenotypes, and its specific role in insulin-regulated GLUT4 trafficking in adipocytes. MethodsPicalm expression and epigenetic regulation by microRNAs (miRNAs) and DNA methylation were analyzed in WAT of diabetes-resistant (DR) and diabetes-prone (DP) female New Zealand Obese (NZO) mice and in male NZO after time-restricted feeding (TRF) and alternate-day fasting (ADF). PICALM expression in human WAT was evaluated in a cross-sectional cohort and assessed before and after weight loss induced by bariatric surgery. siRNA-mediated knockdown of Picalm in 3T3-L1-cells was performed to elucidate functional outcomes on GLUT4-translocation as well as insulin signaling and adipogenesis. ResultsPicalm expression in WAT was significantly lower in DR compared to DP female mice, as well as in insulin-sensitive vs. resistant NZO males, and was also reduced in NZO males following TRF and ADF. Four miRNAs (let-7c, miR-30c, miR-335, miR-344) were identified as potential mediators of diabetes susceptibility-related differences in Picalm expression, while 11 miRNAs (including miR-23a, miR-29b, and miR-101a) were implicated in TRF and ADF effects. Human PICALM expression in adipose tissue was lower in individuals without obesity vs. with obesity and associated with weight-loss outcomes post-bariatric surgery. siRNA-mediated knockdown of Picalm in mature 3T3-L1-adipocytes resulted in amplified insulin-stimulated translocation of the endogenous glucose transporter GLUT4 to the plasma membrane and increased phosphorylation of Akt and Tbc1d4. Moreover, depleting Picalm before and during 3T3-L1 differentiation significantly suppressed adipogenesis, suggesting that Picalm may have distinct roles in the biology of pre- and mature adipocytes. ConclusionsPicalm is a novel regulator of GLUT4-translocation in WAT, with its expression modulated by both genetic predisposition to diabetes and dietary interventions. These findings suggest a potential role for Picalm in improving glucose homeostasis and highlight its relevance as a therapeutic target for metabolic disorders.

Misprogramming of glucose metabolism impairs recovery of hippocampal slices from neuronal GLT-1 knockout mice and contributes to excitotoxic injury through mitochondrial superoxide production.

We have previously reported a failure of recovery of synaptic function in the CA1 region of acute hippocampal slices from mice with a conditional neuronal knockout (KO) of GLT-1 (EAAT2, Slc1A2) driven by synapsin-Cre (synGLT-1 KO). The failure of recovery of synaptic function is due to excitotoxic injury. We hypothesized that changes in mitochondrial metabolism contribute to the heightened vulnerability to excitotoxicity in the synGLT-1 KO mice. We found impaired flux of carbon from 13C-glucose into the tricarboxylic acid cycle in synGLT-1 KO cortical and hippocampal slices compared with wild-type (WT) slices. In addition, we found downregulation of the neuronal glucose transporter GLUT3 in both genotypes. Flux of carbon from [1,2-13C]acetate, thought to be astrocyte-specific, was increased in the synGLT-KO hippocampal slices but not cortical slices. Glycogen stores, predominantly localized to astrocytes, are rapidly depleted in slices after cutting, and are replenished during exvivo incubation. In the synGLT-1 KO, replenishment of glycogen stores during exvivo incubation was compromised. These results suggest both neuronal and astrocytic metabolic perturbations in the synGLT-1 KO slices. Supplementing incubation medium during recovery with 20 mM D-glucose normalized glycogen replenishment but had no effect on recovery of synaptic function. In contrast, 20 mM non-metabolizable L-glucose substantially improved recovery of synaptic function, suggesting that D-glucose metabolism contributes to the excitotoxic injury in the synGLT-1 KO slices. L-lactate substitution for D-glucose did not promote recovery of synaptic function, implicating mitochondrial metabolism. Consistent with this hypothesis, phosphorylation of pyruvate dehydrogenase, which decreases enzyme activity, was increased in WT slices during the recovery period, but not in synGLT-1 KO slices. Since metabolism of glucose by the mitochondrial electron transport chain is associated with superoxide production, we tested the effect of drugs that scavenge and prevent superoxide production. The superoxide dismutase/catalase mimic EUK-134 conferred complete protection and full recovery of synaptic function. A site-specific inhibitor of complex III superoxide production, S3QEL-2, was also protective, but inhibitors of NADPH oxidase were not. In summary, we find that the failure of recovery of synaptic function in hippocampal slices from the synGLT-1 KO mouse, previously shown to be due to excitotoxic injury, is caused by production of superoxide by mitochondrial metabolism.