DHHC9-mediated GLUT1 S-palmitoylation promotes glioblastoma glycolysis and tumorigenesis

Glucose transporter GLUT1 is a transmembrane protein responsible for the uptake of glucose into the cells of many tissues through facilitative diffusion. Plasma membrane (PM) localization is essential for glucose uptake by GLUT1. However, the mechanism underlying GLUT1 PM localization remains enigmatic. We find that GLUT1 is palmitoylated at Cys207, and S-palmitoylation is required for maintaining GLUT1 PM localization. Furthermore, we identify DHHC9 as the palmitoyl transferase responsible for this critical posttranslational modification. Knockout of DHHC9 or mutation of GLUT1 Cys207 to serine abrogates palmitoylation and PM distribution of GLUT1, and impairs glycolysis, cell proliferation, and glioblastoma (GBM) tumorigenesis. In addition, DHHC9 expression positively correlates with GLUT1 PM localization in GBM specimens and indicates a poor prognosis in GBM patients. These findings underscore that DHHC9-mediated GLUT1 S-palmitoylation is critical for glucose supply during GBM tumorigenesis.

Placental mitochondrial function, nutrient transporters, metabolic signalling and steroid metabolism relate to fetal size and sex in mice

Fetal growth depends on placental function, which requires energy supplied by mitochondria. Here we investigated whether mitochondrial function in the placenta relates to growth of the lightest and heaviest fetuses of each sex within the litter of mice. Placentas from the lightest and heaviest fetuses were taken to evaluate placenta morphology (stereology), mitochondrial energetics (high-resolution respirometry), and mitochondrial regulators, nutrient transporters, hormone handling and signalling pathways (qPCR and western blotting). We found that mitochondrial complex I and II oxygen consumption rate was greater for placentas supporting the lightest female fetuses, although placental complex I abundance of the lightest females and complexes III and V of the lightest males were decreased compared to their heaviest counterparts. Expression of mitochondrial biogenesis (Nrf1) and fission (Drp1 and Fis1) genes was lower in the placenta from the lightest females, whilst biogenesis-related gene Tfam was greater in the placenta of the lightest male fetuses. Additionally, placental morphology and steroidogenic gene (Cyp17a1 and Cyp11a1) expression were aberrant for the lightest females, but glucose transporter (Glut1) expression lower in only the lightest males versus their heaviest counterparts. Differences in intra-litter placental phenotype were related to sex-dependent changes in the expression of hormone responsive (androgen receptor) and metabolic signalling pathways (AMPK, AKT, PPARγ). Thus, in normal mouse pregnancy, placental structure, function and mitochondrial phenotype are differentially responsive to growth of the female and the male fetus. This study may inform the design of sex-specific therapies for placental insufficiency and fetal growth abnormalities with life-long benefits for the offspring.

SLC2A1 and Its Related Epileptic Phenotypes

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is caused by heterozygous, mostly de novo, mutations in SLC2A1 gene encoding the glucose transporter GLUT1, the most relevant energy transporter in the blood–brain barrier. GLUT1DS includes a broad spectrum of neurologic disturbances, from severe encephalopathy with developmental delay, to epilepsy, movement disorders, acquired microcephaly and atypical mild forms. For diagnosis, lumbar puncture and genetic analysis are necessary and complementary; an immediate response to ketogenic diet supports the diagnosis in case of high suspicion of disease and negative exams. The ketogenic diet is the first-line treatment and should be established at the initial stages of disease.

Starvation-induced regulation of carbohydrate transport at the blood–brain barrier is TGF-β-signaling dependent

During hunger or malnutrition, animals prioritize alimentation of the brain over other organs to ensure its function and, thus, their survival. This protection, also-called brain sparing, is described from Drosophila to humans. However, little is known about the molecular mechanisms adapting carbohydrate transport. Here, we used Drosophila genetics to unravel the mechanisms operating at the blood–brain barrier (BBB) under nutrient restriction. During starvation, expression of the carbohydrate transporter Tret1-1 is increased to provide more efficient carbohydrate uptake. Two mechanisms are responsible for this increase. Similar to the regulation of mammalian GLUT4, Rab-dependent intracellular shuttling is needed for Tret1-1 integration into the plasma membrane; even though Tret1-1 regulation is independent of insulin signaling. In addition, starvation induces transcriptional upregulation that is controlled by TGF-β signaling. Considering TGF-β-dependent regulation of the glucose transporter GLUT1 in murine chondrocytes, our study reveals an evolutionarily conserved regulatory paradigm adapting the expression of sugar transporters at the BBB.

LncRNA HOTAIR regulates glucose transporter Glut1 expression and glucose uptake in macrophages during inflammation

Inflammation plays central roles in the immune response. Inflammatory response normally requires higher energy and therefore is associated with glucose metabolism. Our recent study demonstrates that lncRNA HOTAIR plays key roles in NF-kB activation, cytokine expression, and inflammation. Here, we investigated if HOTAIR plays any role in the regulation of glucose metabolism in immune cells during inflammation. Our results demonstrate that LPS-induced inflammation induces the expression of glucose transporter isoform 1 (Glut1) which controls the glucose uptake in macrophages. LPS-induced Glut1 expression is regulated via NF-kB activation. Importantly, siRNA-mediated knockdown of HOTAIR suppressed the LPS-induced expression of Glut1 suggesting key roles of HOTAIR in LPS-induced Glut1 expression in macrophage. HOTAIR induces NF-kB activation, which in turn increases Glut1 expression in response to LPS. We also found that HOTAIR regulates glucose uptake in macrophages during LPS-induced inflammation and its knockdown decreases LPS-induced increased glucose uptake. HOTAIR also regulates other upstream regulators of glucose metabolism such as PTEN and HIF1α, suggesting its multimodal functions in glucose metabolism. Overall, our study demonstrated that lncRNA HOTAIR plays key roles in LPS-induced Glut1 expression and glucose uptake by activating NF-kB and hence HOTAIR regulates metabolic programming in immune cells potentially to meet the energy needs during the immune response.

Monosomy-3 Alters the Expression Profile of the Glucose Transporters GLUT1-3 in Uveal Melanoma

Monosomy-3 in uveal melanoma (UM) cells increases the risk of fatal metastases. The gene encoding the low-affinity glucose transporter GLUT2 resides on chromosome 3q26.2. Here, we analyzed the expression of the glucose transporters GLUT1, GLUT2, and GLUT3 with regard to the histological and clinical factors by performing immunohistochemistry on the primary tumors of n = 33 UM patients. UMs with monosomy-3 exhibited a 57% lower immunoreactivity for GLUT2 and a 1.8×-fold higher ratio of GLUT1 to total GLUT1-3. The combined levels of GLUT1-3 proteins were reduced in the irradiated but not the non-irradiated tumors with monosomy-3. GLUT3 expression was stronger in the irradiated samples with disomy-3 versus monosomy-3, but the ratio of the GLUT3 isoform to total GLUT1-3 did not differ with regard to the monosomy-3 status in the irradiated or non-irradiated subgroups. Systemic metastases were associated with the presence of monosomy-3 in the primary and circulating tumor cells as well as a higher GLUT1 ratio. Upregulation of the high-affinity glucose transporter GLUT1 possibly as a compensation for the low-affinity isoform GLUT2 may be enhancing the basal glucose uptake in the UM cells with monosomy-3. Prevention of hyperglycemia might, therefore, be a valuable approach to delay the lethal UM metastases.

Starvation-induced regulation of carbohydrate transport at the blood-brain barrier is TGF-β-signaling dependent

During hunger or malnutrition animals prioritize alimentation of the brain over other organs to ensure its function and thus their survival. This so-called brain sparing is described from Drosophila to humans. However, little is known about the molecular mechanisms adapting carbohydrate transport. Here, we used Drosophila genetics to unravel the mechanisms operating at the blood-brain barrier (BBB) under nutrient restriction. During starvation, expression of the carbohydrate transporter Tret1-1 is increased to provide more efficient carbohydrate uptake. Two mechanisms are responsible for this increase. Similarly to the regulation of mammalian GLUT4, Rab-dependent intracellular shuttling is needed for Tret1-1 integration into the plasma membrane, even though Tret1-1 regulation is independent of insulin signaling. In addition, starvation induces transcriptional upregulation controlled by TGF-β signaling. Considering TGF-β-dependent regulation of the glucose transporter GLUT1 in murine chondrocytes, our study reveals an evolutionarily conserved regulatory paradigm adapting the expression of sugar transporters at the BBB.