GLUT1-deficient mice exhibit impaired endothelium-dependent vascular relaxation

Chronic β3 adrenergic agonist treatment improves brain microvascular endothelial function and cognition in aged mice

Microvascular endothelial dysfunction, characterized by impaired neurovascular coupling, reduced glucose uptake, blood-brain barrier disruption, and microvascular rarefaction, plays a critical role in the pathogenesis of age-related vascular cognitive impairment (VCI). Emerging evidence points to non-cell autonomous mechanisms mediated by adverse circulating milieu (an increased ratio of pro-geronic to anti-geronic circulating factors) in the pathogenesis of endothelial dysfunction leading to impaired cerebral blood flow and cognitive decline in the aging population. In particular, age-related adipose dysfunction contributes, at least in part, to an unfavorable systemic milieu characterized by chronic hyperglycemia, hyperinsulinemia, dyslipidemia, and altered adipokine profile, which together contribute to microvascular endothelial dysfunction. Hence, in the present study, we aimed to test whether thermogenic stimulation, an intervention known to improve adipose and systemic metabolism by increasing cellular energy expenditure, could mitigate brain endothelial dysfunction and improve cognition in the aging population. Eighteen-month-old old C57BL/6J mice were treated with saline or CL (β3-adrenergic agonist) for 6 weeks followed by functional analysis to assess endothelial function and cognition. CL treatment improved neurovascular coupling responses and rescued brain glucose uptake in aged animals. In addition, CL treatment also attenuated blood-brain barrier leakage and associated neuroinflammation in the cortex of aged animals. More importantly, these beneficial changes in microvascular function translated to improved cognitive performance in radial arm water maze and Y-maze tests. Our results suggest that β3-adrenergic agonist treatment improves multiple aspects of brain microvascular endothelial function and can be potentially repurposed for treating age-associated cognitive decline.

The protective role of endothelial GLUT1 in ischemic stroke

OBJECTIVE

To provide thorough insight on the protective role of endothelial glucose transporter 1 (GLUT1) in ischemic stroke.

METHODS

We comprehensively review the role of endothelial GLUT1 in ischemic stroke by narrating the findings concerning biological characteristics of GLUT1 in brain in depth, summarizing the changes of endothelial GLUT1 expression and activity during ischemic stroke, discussing how GLUT1 achieves its neuroprotective effect via maintaining endothelial function, and identifying some outstanding blind spots in current studies.

RESULTS

Endothelial GLUT1 maintains persistent high glucose and energy requirements of the brain by transporting glucose through the blood-brain barrier, which preserves endothelial function and is beneficial to stroke prognosis.

CONCLUSION

This review underscores the potential involvement of GLUT1 trafficking, activity modulation, and degradation, and we look forward to more clinical and animal studies to illuminate these mechanisms.

Tanshinone IIA regulates expression of glucose transporter 1 via activation of the HIF‑1α signaling pathway

Tanshinone IIA (Tan 2A) is a lipid‑soluble compound extracted from the Chinese herb Danshen (Salvia miltiorrhiza Bunge). It protects neuron and microvascular endothelial cells against hypoxia/ischemia both in vitro and in vivo however the mechanism is not fully known. Glucose transporter 1 (GLUT‑1) is ubiquitously expressed in all types of tissue in the human body and serves important physiological functions due to its glucose uptake ability. The present study evaluated the role of Tan 2A in regulating GLUT‑1 expression and its potential mechanism. RT‑PCR and western Blot were used to detect the expression of GLUT‑1. Si RNA mediated knockdown and CHIP assay were used to explore the mechanism of Tan 2A on GLUT‑1expression. Tan 2A treatment induced expression of GLUT‑1 and subsequently increased glucose uptake in endothelial cells (ECs). Furthermore, mRNA expression levels of vascular endothelial cell growth factor, BCL2 interacting protein 3 and enolase 2, which are target genes for hypoxia‑inducible factor‑1α (HIF‑1α), were significantly upregulated by Tan 2A. Co‑immunoprecipitation demonstrated that Tan 2A markedly increased the association of HIF‑1α with recombination signal‑binding protein for immunoglobulin κJ region (RBPJκ). Moreover, knockdown of HIF‑1α and RBPJκ significantly reversed the regulatory effect of Tan 2A on mRNA expression levels of these genes in ECs. The results of the present study suggested that HIF‑1α partially mediated the regulatory effect of Tan 2A on GLUT‑1 expression in ECs. Therefore, GLUT‑1 may be a potential therapeutic target for Tan 2A.

The proteasome activator REGγ promotes diabetic endothelial impairment by inhibiting HMGA2-GLUT1 pathway

Diabetic vascular endothelial impairment is one of the main causes of death in patients with diabetes lacking adequately defined mechanisms or effective treatments. REGγ, the 11S proteasome activator known to promote the degradation of cellular proteins in a ubiquitin- and ATP-independent manner, emerges as a new regulator in the cardiovascular system. Here, we found that REGγ was upregulated in streptozocin (STZ)-induced diabetic mouse aortic endothelium in vivo and high glucose (HG)-treated vascular endothelial cells (ECs) in vitro. REGγ deficiency ameliorated endothelial impairment in STZ-induced diabetic mice by protecting against a decline in cellular glucose uptake and associated vascular ECs dysfunction by suppressing high mobility group AT-hook 2 (HMGA2) decay. Mechanically, REGγ interacted with and degraded the transcription factor HMGA2 directly, leading to decreased HMGA2 transcriptional activity, subsequently lowered expression of glucose transporter type 1 (GLUT1), and reduced cellular glucose uptake, vascular endothelial dysfunction, and impaired diabetic endothelium. Ablation of endogenous GLUT1 or HMGA2 or overexpressing exogenous HMGA2 in vascular ECs significantly blocked or reestablished the REGγ-dependent action on cellular glucose uptake and vascular endothelial functions of HG stimulation in vitro. Furthermore, exogenously introducing HMGA2 improved diabetic mice endothelial impairment features caused by REGγ in vivo, thereby substantiating a REGγ-HMGA2-GLUT1 pathway in diabetic endothelial impairment. Our findings indicate that modulating REGγ-proteasome activity may be a potential therapeutic approach for diabetic disorders with endothelial impairment.

Endothelial TFEB (Transcription Factor EB) Improves Glucose Tolerance via Upregulation of IRS (Insulin Receptor Substrate) 1 and IRS2

OBJECTIVE

Vascular endothelial cells (ECs) play a critical role in maintaining vascular homeostasis. Aberrant EC metabolism leads to vascular dysfunction and metabolic diseases. TFEB (transcription factor EB), a master regulator of lysosome biogenesis and autophagy, has protective effects on vascular inflammation and atherosclerosis. However, the role of endothelial TFEB in metabolism remains to be explored. In this study, we sought to investigate the role of endothelial TFEB in glucose metabolism and underlying molecular mechanisms. Approach and Results: To determine whether endothelial TFEB is critical for glucose metabolism in vivo, we utilized EC-selective TFEB knockout and EC-selective TFEB transgenic mice fed a high-fat diet. EC-selective TFEB knockout mice exhibited significantly impaired glucose tolerance compared with control mice. Consistently, EC-selective TFEB transgenic mice showed improved glucose tolerance. In primary human ECs, small interfering RNA-mediated TFEB knockdown blunts Akt (AKT serine/threonine kinase) signaling. Adenovirus-mediated overexpression of TFEB consistently activates Akt and significantly increases glucose uptake in ECs. Mechanistically, TFEB upregulates IRS1 and IRS2 (insulin receptor substrate 1 and 2). TFEB increases IRS2 transcription measured by reporter gene and chromatin immunoprecipitation assays. Furthermore, we found that TFEB increases IRS1 protein via downregulation of microRNAs (miR-335, miR-495, and miR-548o). In vivo, Akt signaling in the skeletal muscle and adipose tissue was significantly impaired in EC-selective TFEB knockout mice and consistently improved in EC-selective TFEB transgenic mice on high-fat diet.

CONCLUSIONS

Our data revealed a critical role of TFEB in endothelial metabolism and suggest that TFEB constitutes a potential molecular target for the treatment of vascular and metabolic diseases.

Polygonum perfoliatum L., an Excellent Herbal Medicine Widely Used in China: A Review

Polygonum perfoliatum L. (synonym: Polygonum knotweed L.; Persicaria perfoliata; family: Polygonaceae) is a kind of folk traditional Chinese medicine with a long history of wide use in the treatment of ancient internal, surgical, and gynecological diseases. At present, 80 chemical constituents have been isolated from P. perfoliatum, including flavonoids, anthraquinones, terpenoids, phenolic acids, phenylpropanoids, and alkaloids, among which flavonoids are the main active components. Modern studies have shown that P. perfoliatum has pharmacological activities such as anti-inflammatory, anti-bacterial, antiviral, anti-liver fibrosis, antitussive and expectorant, anti-tumor, anti-oxidation, and so on. By consulting and sorting out a large number of related literatures at home and abroad in recent years, this paper systematically reviewed the botany, traditional uses, phytochemistry, pharmacological activities, and quality control of P. perfoliatum, and discussed its development potential in new drug research and clinical application in the future, in order to provide a reference basis for further research and promote the in-depth development and utilization.

Lupus-prone New Zealand Black/New Zealand White F1 mice display endothelial dysfunction and abnormal phenotype and function of endothelial progenitor cells

Patients with systemic lupus erythematosus (SLE) have an impairment in phenotype and function of endothelial progenitor cells (EPCs) which is mediated by interferon alpha (IFN-alpha). We assessed whether murine lupus models also exhibit vasculogenesis abnormalities and their potential association with endothelial dysfunction. Phenotype and function of EPCs and type I IFN gene signatures in EPC compartments were assessed in female New Zealand Black/New Zealand White F(1) (NZB/W), B6.MRL-Fas(lpr)/J (B6/lpr) and control mice. Thoracic aorta endothelial and smooth muscle function were measured in response to acetylcholine or sodium nitropruside, respectively. NZB/W mice displayed reduced numbers, increased apoptosis and impaired function of EPCs. These abnormalities correlated with significant decreases in endothelium-dependent vasomotor responses and with increased type I IFN signatures in EPC compartments. In contrast, B6/lpr mice showed improvement in endothelium-dependent and endothelial-independent responses, no abnormalities in EPC phenotype or function and downregulation of type I IFN signatures in EPC compartments. These results indicate that NZB/W mice represent a good model to study the mechanisms leading to endothelial dysfunction and abnormal vasculogenesis in lupus. These results further support the hypothesis that type I IFNs may play an important role in premature vascular damage and, potentially, atherosclerosis development in SLE.

Will the original glucose transporter isoform please stand up!

Monosaccharides enter cells by slow translipid bilayer diffusion by rapid, protein-mediated, cation-dependent cotransport and by rapid, protein-mediated equilibrative transport. This review addresses protein-mediated, equilibrative glucose transport catalyzed by GLUT1, the first equilibrative glucose transporter to be identified, purified, and cloned. GLUT1 is a polytopic, membrane-spanning protein that is one of 13 members of the human equilibrative glucose transport protein family. We review GLUT1 catalytic and ligand-binding properties and interpret these behaviors in the context of several putative mechanisms for protein-mediated transport. We conclude that no single model satisfactorily explains GLUT1 behavior. We then review GLUT1 topology, subunit architecture, and oligomeric structure and examine a new model for sugar transport that combines structural and kinetic analyses to satisfactorily reproduce GLUT1 behavior in human erythrocytes. We next review GLUT1 cell biology and the transcriptional and posttranscriptional regulation of GLUT1 expression in the context of development and in response to glucose perturbations and hypoxia in blood-tissue barriers. Emphasis is placed on transgenic GLUT1 overexpression and null mutant model systems, the latter serving as surrogates for the human GLUT1 deficiency syndrome. Finally, we review the role of GLUT1 in the absence or deficiency of a related isoform, GLUT3, toward establishing the physiological significance of coordination between these two isoforms.

The peroxisome proliferator-activated receptor gamma agonist pioglitazone improves cardiometabolic risk and renal inflammation in murine lupus

Individuals with systemic lupus erythematosus (SLE) have a striking increase in the risk of premature atherosclerosis, a complication preceded by significant subclinical vascular damage. A proposed mechanism leading to accelerated vascular disease in SLE is an imbalance between vascular damage and repair, as patients with this disease display significant abnormalities in phenotype and function of endothelial progenitor cells. In addition, individuals with SLE have a higher incidence of insulin resistance which may further contribute to the increased cardiovascular risk. This study examined the role of the peroxisome proliferator activated receptor gamma agonist pioglitazone in improving endothelial function, endothelial progenitor cell numbers and functional capacity, metabolic parameters, and disease activity in the lupus-prone murine model New Zealand Black/New Zealand White (NZB x NZW)F(1). Ten-week-old prenephritic female NZB/NZW F(1) mice were exposed to 10 or 25 mg/kg/day of oral pioglitazone or vehicle for 15 or 24 wk. Mice exposed to pioglitazone exhibited pronounced enhancement in endothelial-dependent vasorelaxation of thoracic aortas and in endothelial progenitor cell function, as assessed by the capacity of bone marrow-derived endothelial progenitor cells to differentiate into mature endothelial cells. Pioglitazone-treated mice showed improvement in insulin resistance, adipokine, and lipid profile. Kidneys from pioglitazone-treated mice showed significant decreases in immune complex deposition, renal inflammation, T cell glomerular infiltration, and intrarenal synthesis of TNF-alpha, IL-1beta, and VCAM-1. These results indicate that peroxisome proliferator-activated receptor gamma agonists could serve as important tools in the prevention of premature cardiovascular disease and organ damage in SLE.

Reduced NO synthesis and eNOS mRNA expression in endothelial cells from newborns with a strong family history of type 2 diabetes

BACKGROUND

A deficient synthesis of nitric oxide (NO) may play a role in the early endothelial dysfunction of healthy humans with a strong family history of type 2 diabetes (DM2). In this study, we evaluate the intracellular synthesis of NO and the expression of eNOS transcripts in human umbilical vein endothelial cells (HUVECs), exposed to high glucose concentrations, of healthy newborns with (experimental) and without (control) a strong family history of DM2.

METHODS

HUVECs were incubated in M-199 culture media (containing a 5 mmol/L physiological glucose concentration) or supraphysiological glucose concentrations (15 or 30 mmol/L), for 48 h. Flow cytometry, reactive of Griess and RT-PCR were used to determine intracellular NO synthesis, presence of NO metabolites, and expression of eNOS, GLUT1 or p53 transcripts.

RESULTS

NO synthesis in experimental HUVECs showed a progressive reduction in the presence of increasing glucose concentration (11% for 5 mmol to 8% for 30 mmol; p < 0.01), whereas control HUVECs showed an increase in NO synthesis (3% for 5 mmol to 31% for 30 mmol; p < 0.001). In experimental HUVECs, we found a diminished expression of eNOS and p53, and also an enhanced expression of GLUT1 mRNA transcripts. Control HUVECs showed an increase in eNOS, and no modifications in p53 or GLUT1 mRNA transcripts.

CONCLUSIONS

Our results show how HUVECs, isolated from healthy newborns with a strong family history of DM2, have an abnormal intracellular synthesis of NO and an impaired expression of eNOS, GLUT1 and p53 genes, all associated with NO synthesis.

GLUT1 deficiency syndrome--2007 update

GLUT1 deficiency syndrome (GLUT1DS, OMIM 606777) is a treatable epileptic encephalopathy resulting from impaired glucose transport into the brain. The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid (CSF; hypoglycorrhachia; mean 1.7 [SD 0.3mmol/L]) in the setting of normoglycaemia. CSF lactate is normal. Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder. Hypotonic, ataxic, and dystonic features are most prominent. Speech is often severely affected. Some patients develop spasticity and secondary microcephaly. The phenotype is highly variable ranging from severe impairment to children without seizures. Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake. Neuroimaging is uninformative. Most patients carry heterozygous de novo mutations in the GLUT1 gene (OMIM 138140, gene map locus 1p35-31.3). Autosomal dominant transmission and several mutational hot spots have been identified, but phenotype-genotype correlations are not yet apparent. Homozygous GLUT1 mutations presumably are lethal. The ketogenic diet is the treatment of choice as it provides an alternative fuel to the brain. It should be introduced early and maintained into puberty. Seizures are effectively controlled with the onset of ketosis, but might recur and require comedication. The effect on neurodevelopment appears less impressive. The increasing number of patients, molecular and biochemical analysis, recent research into ketogenic diet mechanisms, and the development of animal models for GLUT1DS have brought substantial insights in disease manifestations and mechanisms. This review summarizes data on 84 published cases and highlights recent advances in understanding this entity.