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Winkler et al . show that the glucose transporter GLUT1 in brain endothelium is necessary for the maintenance of proper brain capillary networks and blood-brain barrier integrity. The study also shows that loss of GLUT1 in a mouse model of Alzheimer's disease accelerates BBB breakdown, perfusion and metabolic stress resulting in behavioral deficits, elevated amyloid beta levels and neurodegeneration. The glucose transporter GLUT1 at the blood-brain barrier (BBB) mediates glucose transport into the brain. Alzheimer's disease is characterized by early reductions in glucose transport associated with diminished GLUT1 expression at the BBB. Whether GLUT1 reduction influences disease pathogenesis remains, however, elusive. Here we show that GLUT1 deficiency in mice overexpressing amyloid β-peptide (Aβ) precursor protein leads to early cerebral microvascular degeneration, blood flow reductions and dysregulation and BBB breakdown, and to accelerated amyloid β-peptide (Aβ) pathology, reduced Aβ clearance, diminished neuronal activity, behavioral deficits, and progressive neuronal loss and neurodegeneration that develop after initial cerebrovascular degenerative changes. We also show that GLUT1 deficiency in endothelium, but not in astrocytes, initiates the vascular phenotype as shown by BBB breakdown. Thus, reduced BBB GLUT1 expression worsens Alzheimer's disease cerebrovascular degeneration, neuropathology and cognitive function, suggesting that GLUT1 may represent a therapeutic target for Alzheimer's disease vasculo-neuronal dysfunction and degeneration.

In patients with congenital heart disease, the development of pulmonary arterial hypertension (PAH) is based on vascular exposure to abnormal hemodynamic forces. In our work using a large animal model of increased pulmonary blood flow and pressure, we have previously described a pattern of alterations to vascular cell metabolism, mitochondrial function, and mitochondrial redox signaling, paralleling changes in advanced pulmonary vasculopathy states. Based on our findings and emerging literature, we believe that endothelial mitochondria play a central role in integrating and relaying pathologic mechanotransductive signals in abnormal pulmonary hemodynamics. In this manuscript, we demonstrate that exposure of the pulmonary vascular endothelium to aberrant mechanical forces increases production of mitochondrial reactive oxygen species (ROS) and stabilizes the transcription factor Hypoxia Inducible Factor-1α (HIF-1α), and that these changes are associated with impaired endothelial production of Nitric Oxide (NO). We validate that the mitochondrial antioxidant 10-(6′-ubiquinonyl)decyltriphenylphosphonium bromide (MitoQ) can reverse these alterations in vitro, and evaluate the effects of MitoQ treatment in vivo utilizing our large animal shunt model. We find that MitoQ therapy in pulmonary overcirculation decreases the production of mitochondrial ROS, diminishes the mechanically-induced stabilization of HIF-1α, and partially restores vascular reactivity by rescuing endothelial NO production. These findings raise exciting prospects concerning shared pathophysiologic mechanisms and possible common therapeutic targets amongst PAH etiologies.

Tissue-Specific Remodeling of the Mitochondrial Proteome in Type 1 Diabetic Akita Mice Heiko Bugger 1 , Dong Chen 2 , 3 , Christian Riehle 1 , Jamie Soto 1 , Heather A. Theobald 1 , Xiao X. Hu 1 , Balasubramanian Ganesan 2 , 3 , Bart C. Weimer 2 , 3 and E. Dale Abel 1 1 Division of Endocrinology, Metabolism and Diabetes, and Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, Utah; 2 Department of Nutrition and Food Sciences, Utah State University, Logan, Utah; 3 Center for Integrated BioSystems, Utah State University, Logan, Utah. Corresponding author: E. Dale Abel, dale.abel{at}hmbg.utah.edu . Abstract OBJECTIVE To elucidate the molecular basis for mitochondrial dysfunction, which has been implicated in the pathogenesis of diabetes complications. RESEARCH DESIGN AND METHODS Mitochondrial matrix and membrane fractions were generated from liver, brain, heart, and kidney of wild-type and type 1 diabetic Akita mice. Comparative proteomics was performed using label-free proteome expression analysis. Mitochondrial state 3 respirations and ATP synthesis were measured, and mitochondrial morphology was evaluated by electron microscopy. Expression of genes that regulate mitochondrial biogenesis, substrate utilization, and oxidative phosphorylation (OXPHOS) were determined. RESULTS In diabetic mice, fatty acid oxidation (FAO) proteins were less abundant in liver mitochondria, whereas FAO protein content was induced in mitochondria from all other tissues. Kidney mitochondria showed coordinate induction of tricarboxylic acid (TCA) cycle enzymes, whereas TCA cycle proteins were repressed in cardiac mitochondria. Levels of OXPHOS subunits were coordinately increased in liver mitochondria, whereas mitochondria of other tissues were unaffected. Mitochondrial respiration, ATP synthesis, and morphology were unaffected in liver and kidney mitochondria. In contrast, state 3 respirations, ATP synthesis, and mitochondrial cristae density were decreased in cardiac mitochondria and were accompanied by coordinate repression of OXPHOS and peroxisome proliferator–activated receptor (PPAR)-γ coactivator (PGC)-1α transcripts. CONCLUSIONS Type 1 diabetes causes tissue-specific remodeling of the mitochondrial proteome. Preservation of mitochondrial function in kidney, brain, and liver, versus mitochondrial dysfunction in the heart, supports a central role for mitochondrial dysfunction in diabetic cardiomyopathy. Footnotes B.C.W. is currently affiliated with University of California Davis, School of Veterinary Medicine, Department of Population Health and Reproduction, Davis, California. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received February 20, 2009. Accepted June 3, 2009. © 2009 by the American Diabetes Association.

Excess tissue iron levels are a risk factor for diabetes, but the mechanisms underlying the association are incompletely understood. We previously published that mice and humans with a form of hereditary iron overload, hemochromatosis, exhibit loss of β-cell mass. This effect by itself is not sufficient, however, to fully explain the diabetes risk phenotype associated with all forms of iron overload. We therefore examined glucose and fatty acid metabolism and hepatic glucose production in vivo and in vitro in a mouse model of hemochromatosis in which the gene most often mutated in the human disease, HFE, has been deleted (Hfe⁻(/)⁻). Although Hfe⁻(/)⁻ mice exhibit increased glucose uptake in skeletal muscle, glucose oxidation is decreased and the ratio of fatty acid to glucose oxidation is increased. On a high-fat diet, the Hfe⁻(/)⁻ mice exhibit increased fatty acid oxidation and are hypermetabolic. The decreased glucose oxidation in skeletal muscle is due to decreased pyruvate dehydrogenase (PDH) enzyme activity related, in turn, to increased expression of PDH kinase 4 (pdk4). Increased substrate recycling to liver contributes to elevated hepatic glucose production in the Hfe⁻(/)⁻ mice. Increased hepatic glucose production and metabolic inflexibility, both of which are characteristics of type 2 diabetes, may contribute to the risk of diabetes with excessive tissue iron.

ob/ob and db/db mice manifest myocardial hypertrophy, insulin resistance, altered substrate utilization, mitochondrial dysfunction, and lipid accumulation. This study was designed to determine the contribution of central and peripheral leptin signaling to myocardial metabolism and function in ob/ob and db/db mice in the absence of diabetes and morbid obesity. Male ob/ob mice (aged 4 weeks) were caloric restricted by pairfeeding to a leptin-treated ob/ob group. In addition to determining glucose tolerance and circulating lipid concentrations, myocardial substrate metabolism and mitochondrial function were determined in saponin-permeabilized cardiac fibers. Second, experiments were performed to determine whether leptin treatment by intraperitoneal injection or intracerebroventricular infusion could normalize myocardial palmitate oxidation in caloric-restricted ob/ob mouse hearts. Despite normalizing body weight and glucose tolerance, fat mass and circulating lipid levels remained increased in caloric-restricted ob/ob animals. Palmitate oxidation remained elevated in caloric-restricted ob/ob hearts and was normalized by intraperitoneal or intracerebroventricular leptin. Intraperitoneal and intracerebroventricular treatment also normalized circulating free fatty acid levels, myocardial fatty acid oxidation gene expression, and myocardial insulin sensitivity. These data suggest that impaired hypothalamic leptin signaling is sufficient to increase myocardial fatty acid oxidation by increasing delivery of free fatty acid substrates and peroxisome proliferator-activated receptor-α ligands to the heart.

To identify metabolic pathways that may underlie susceptibility or resistance to high-fat diet-induced hepatic steatosis. We performed comparative transcriptomic analysis of the livers of A/J and C57Bl/6 mice, which are, respectively, resistant and susceptible to high-fat diet-induced hepatosteatosis and obesity. Mice from both strains were fed a normal chow or a high-fat diet for 2, 10, and 30 days, and transcriptomic data were analyzed by time-dependent gene set enrichment analysis. Biochemical analysis of mitochondrial respiration was performed to confirm the transcriptomic analysis. Time-dependent gene set enrichment analysis revealed a rapid, transient, and coordinate upregulation of 13 oxidative phosphorylation genes after initiation of high-fat diet feeding in the A/J, but not in the C57Bl/6, mouse livers. Biochemical analysis using liver mitochondria from both strains of mice confirmed a rapid increase by high-fat diet feeding of the respiration rate in A/J but not C57Bl/6 mice. Importantly, ATP production was the same in both types of mitochondria, indicating increased uncoupling of the A/J mitochondria. Together with previous data showing increased expression of mitochondrial β-oxidation genes in C57Bl/6 but not A/J mouse livers, our present study suggests that an important aspect of the adaptation of livers to high-fat diet feeding is to increase the activity of the oxidative phosphorylation chain and its uncoupling to dissipate the excess of incoming metabolic energy and to reduce the production of reactive oxygen species. The flexibility in oxidative phosphorylation activity may thus participate in the protection of A/J mouse livers against the initial damages induced by high-fat diet feeding that may lead to hepatosteatosis.

Insulin/IGF-I signaling regulates the metabolism of most mammalian tissues including pancreatic islets. To dissect the mechanisms linking insulin signaling with mitochondrial function, we first identified a mitochondria-tethering complex in beta-cells that included glucokinase (GK), and the pro-apoptotic protein, BAD(S). Mitochondria isolated from beta-cells derived from beta-cell specific insulin receptor knockout (betaIRKO) mice exhibited reduced BAD(S), GK and protein kinase A in the complex, and attenuated function. Similar alterations were evident in islets from patients with type 2 diabetes. Decreased mitochondrial GK activity in betaIRKOs could be explained, in part, by reduced expression and altered phosphorylation of BAD(S). The elevated phosphorylation of p70S6K and JNK1 was likely due to compensatory increase in IGF-1 receptor expression. Re-expression of insulin receptors in betaIRKO cells partially restored the stoichiometry of the complex and mitochondrial function. These data indicate that insulin signaling regulates mitochondrial function and have implications for beta-cell dysfunction in type 2 diabetes.

Mitochondrial targeting of antioxidants has been an area of interest due to the mitochondria's role in producing and metabolizing reactive oxygen species. Antioxidants, especially vitamin E (α-tocopherol), have been conjugated to lipophilic cations to increase their mitochondrial targeting. Synthetic vitamin E analogues have also been produced as an alternative to α-tocopherol. In this paper, we investigated the mitochondrial targeting of a vitamin E metabolite, 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (α-CEHC), which is similar in structure to vitamin E analogues. We report a fast and efficient method to conjugate the water-soluble metabolite, α-CEHC, to triphenylphosphonium cation via a lysine linker using solid phase synthesis. The efficacy of the final product (MitoCEHC) to lower oxidative stress was tested in bovine aortic endothelial cells. In addition the ability of MitoCEHC to target the mitochondria was examined in type 2 diabetes db/db mice. The results showed mitochondrial accumulation in vivo and oxidative stress decrease in vitro.

The disruption of mitochondrial dynamics has been identified in cardiovascular diseases, including pulmonary hypertension (PH), ischemia-reperfusion injury, heart failure, and cardiomyopathy. Mitofusin 2 (Mfn2) is abundantly expressed in heart and pulmonary vasculature cells at the outer mitochondrial membrane to modulate fusion. Previously, we have reported reduced levels of Mfn2 and fragmented mitochondria in pulmonary arterial endothelial cells (PAECs) isolated from a sheep model of PH induced by pulmonary over-circulation and restoring Mfn2 normalized mitochondrial function. In this study, we assessed the effect of increased expression of Mfn2 on mitochondrial metabolism, bioenergetics, reactive oxygen species production, and mitochondrial membrane potential in control PAECs. Using an adenoviral expression system to overexpress Mfn2 in PAECs and utilizing 13C labeled substrates, we assessed the levels of TCA cycle metabolites. We identified increased pyruvate and lactate production in cells, revealing a glycolytic phenotype (Warburg phenotype). Mfn2 overexpression decreased the mitochondrial ATP production rate, increased the rate of glycolytic ATP production, and disrupted mitochondrial bioenergetics. The increase in glycolysis was linked to increased hypoxia-inducible factor 1α (HIF-1α) protein levels, elevated mitochondrial reactive oxygen species (mt-ROS), and decreased mitochondrial membrane potential. Our data suggest that disrupting the mitochondrial fusion/fission balance to favor hyperfusion leads to a metabolic shift that promotes aerobic glycolysis. Thus, therapies designed to increase mitochondrial fusion should be approached with caution.

It is well-established that mitochondrial dysfunction plays a critical role in the development of pulmonary hypertension (PH). However, the molecular mechanisms and how the individual electron transport complexes (ETC) may be affected are poorly understood. In this study, we identified decreased ETC Complex I activity and assembly and linked these changes to disrupted mitochondrial bioenergetics in pulmonary arterial endothelial cells (PAECs) isolated from a lamb model of PH with increased pulmonary blood flow (Shunt). These derangements were associated with decreased mitochondrial activity of the protein tyrosine kinase, pp60Src. Treating Control PAECs with either the Src family kinase inhibitor, PP2, or the siRNA-mediated knockdown of pp60Src was able to recapitulate the adverse effects on ETC Complex I activity and assembly and mitochondrial bioenergetics. Conversely, restoring pp60Src activity in lamb PH PAECs re-established ETC Complex I activity, improved ETC Complex I assembly and enhanced mitochondrial bioenergetics. Phosphoprotein enrichment followed by two-dimensional gel electrophoresis and tandem mass spectrometry was used to identify three ETC Complex I subunits (NDUFS1, NDUFAF5, and NDUFV2) as pp60Src substrates. Finally, we demonstrated that the pY levels of NDUFS1, NDUFAF5, and NDUFV2 are decreased in lamb PH PAECs. Enhancing mitochondrial pp60Src activity could be a therapeutic strategy to reverse PH-related mitochondrial dysfunction.