The Effects of Oxygen-Derived Free-Radical Scavengers During Normothermic Ex-Situ Heart Perfusion.

Oxidative stress occurs during ex-situ heart perfusion (ESHP) and may negatively affect functional preservation of the heart. We sought to assess the status of key antioxidant enzymes during ESHP, and the effects of augmenting these antioxidants on the attenuation of oxidative stress and improvement of myocardial and endothelial preservation in ESHP. Porcine hearts were perfused for 6 hours with oxygen-derived free-radical scavengers polyethylene glycol (PEG)-catalase or PEG-superoxide dismutase (SOD) or with naive perfusate (control). The oxidative stress-related modifications were determined in the myocardium and coronary vasculature, and contractile function, injury, and endothelial integrity were compared between the groups. The activity of key antioxidant enzymes decreased and adding catalase and SOD restored the enzyme activity. Cardiac function and endothelial integrity were preserved better with restored catalase activity. Catalase and SOD both decreased myocardial injury and catalase reduced ROS production and oxidative modification of proteins in the myocardium and coronary vasculature. The activity of antioxidant enzymes decrease in ESHP. Catalase may improve the preservation of cardiac function and endothelial integrity during ESHP. While catalase and SOD may both exert cardioprotective effects, unbalanced SOD and catalase activity may paradoxically increase the production of reactive species during ESHP.

The Effects of Oxygen-Derived Free-Radical Scavengers During Normothermic Ex-Situ Heart Perfusion.

Oxidative stress occurs during ex-situ heart perfusion (ESHP) and may negatively affect functional preservation of the heart. We sought to assess the status of key antioxidant enzymes during ESHP, and the effects of augmenting these antioxidants on the attenuation of oxidative stress and improvement of myocardial and endothelial preservation in ESHP. Porcine hearts were perfused for 6 hours with oxygen-derived free-radical scavengers polyethylene glycol (PEG)-catalase or PEG-superoxide dismutase (SOD) or with naive perfusate (control). The oxidative stress-related modifications were determined in the myocardium and coronary vasculature, and contractile function, injury, and endothelial integrity were compared between the groups. The activity of key antioxidant enzymes decreased and adding catalase and SOD restored the enzyme activity. Cardiac function and endothelial integrity were preserved better with restored catalase activity. Catalase and SOD both decreased myocardial injury and catalase reduced ROS production and oxidative modification of proteins in the myocardium and coronary vasculature. The activity of antioxidant enzymes decrease in ESHP. Catalase may improve the preservation of cardiac function and endothelial integrity during ESHP. While catalase and SOD may both exert cardioprotective effects, unbalanced SOD and catalase activity may paradoxically increase the production of reactive species during ESHP.

TRIM35-mediated degradation of nuclear PKM2 destabilizes GATA4/6 and induces P53 in cardiomyocytes to promote heart failure.

Pyruvate kinase M2 (PKM2) is a glycolytic enzyme that translocates to the nucleus to regulate transcription factors in different tissues or pathologic states. Although studied extensively in cancer, its biological role in the heart remains unresolved. PKM1 is more abundant than the PKM2 isoform in cardiomyocytes, and thus, we speculated that PKM2 is not genetically redundant to PKM1 and may be critical in regulating cardiomyocyte-specific transcription factors important for cardiac survival. Here, we showed that nuclear PKM2 (S37P-PKM2) in cardiomyocytes interacts with prosurvival and proapoptotic transcription factors, including GATA4, GATA6, and P53. Cardiomyocyte-specific PKM2-deficient mice (Pkm2 Mut Cre+) developed age-dependent dilated cardiac dysfunction and had decreased amounts of GATA4 and GATA6 (GATA4/6) but increased amounts of P53 compared to Control Cre+ hearts. Nuclear PKM2 prevented caspase-1-dependent cleavage and degradation of GATA4/6 while also providing a molecular platform for MDM2-mediated reduction of P53. In a preclinical heart failure mouse model, nuclear PKM2 and GATA4/6 were decreased, whereas P53 was increased in cardiomyocytes. Loss of nuclear PKM2 was ubiquitination dependent and associated with the induction of the E3 ubiquitin ligase TRIM35. In mice, cardiomyocyte-specific TRIM35 overexpression resulted in decreased S37P-PKM2 and GATA4/6 along with increased P53 in cardiomyocytes compared to littermate controls and similar cardiac dysfunction to Pkm2 Mut Cre+ mice. In patients with dilated left ventricles, increase in TRIM35 was associated with decreased S37P-PKM2 and GATA4/6 and increased P53. This study supports a previously unrecognized role for PKM2 as a molecular platform that mediates cell signaling events essential for cardiac survival.

Loss of the fructose transporter SLC2A5 inhibits cancer cell migration.

Metastasis is the primary cause of cancer patient death and the elevation of SLC2A5 gene expression is often observed in metastatic cancer cells. Here we evaluated the importance of SLC2A5 in cancer cell motility by silencing its gene. We discovered that CRISPR/Cas9-mediated inactivation of the SLC2A5 gene inhibited cancer cell proliferation and migration in vitro as well as metastases in vivo in several animal models. Moreover, SLC2A5-attenuated cancer cells exhibited dramatic alterations in mitochondrial architecture and localization, uncovering the importance of SLC2A5 in directing mitochondrial function for cancer cell motility and migration. The direct association of increased abundance of SLC2A5 in cancer cells with metastatic risk in several types of cancers identifies SLC2A5 as an important therapeutic target to reduce or prevent cancer metastasis.

A reversible metabolic stress-sensitive regulation of CRMP2A orchestrates EMT/stemness and increases metastatic potential in cancer.

An epithelial-to-mesenchymal transition (EMT) phenotype with cancer stem cell-like properties is a critical feature of aggressive/metastatic tumors, but the mechanism(s) that promote it and its relation to metabolic stress remain unknown. Here we show that Collapsin Response Mediator Protein 2A (CRMP2A) is unexpectedly and reversibly induced in cancer cells in response to multiple metabolic stresses, including low glucose and hypoxia, and inhibits EMT/stemness. Loss of CRMP2A, when metabolic stress decreases (e.g., around blood vessels in vivo) or by gene deletion, induces extensive microtubule remodeling, increased glutamine utilization toward pyrimidine synthesis, and an EMT/stemness phenotype with increased migration, chemoresistance, tumor initiation capacity/growth, and metastatic potential. In a cohort of 27 prostate cancer patients with biopsies from primary tumors and distant metastases, CRMP2A expression decreases in the metastatic versus primary tumors. CRMP2A is an endogenous molecular brake on cancer EMT/stemness and its loss increases the aggressiveness and metastatic potential of tumors.

MFN2-driven mitochondria-to-nucleus tethering allows a non-canonical nuclear entry pathway of the mitochondrial pyruvate dehydrogenase complex.

The mitochondrial pyruvate dehydrogenase complex (PDC) translocates into the nucleus, facilitating histone acetylation by producing acetyl-CoA. We describe a noncanonical pathway for nuclear PDC (nPDC) import that does not involve nuclear pore complexes (NPCs). Mitochondria cluster around the nucleus in response to proliferative stimuli and tether onto the nuclear envelope (NE) via mitofusin-2 (MFN2)-enriched contact points. A decrease in nuclear MFN2 levels decreases mitochondria tethering and nPDC levels. Mitochondrial PDC crosses the NE and interacts with lamin A, forming a ring below the NE before crossing through the lamin layer into the nucleoplasm, in areas away from NPCs. Effective blockage of NPC trafficking does not decrease nPDC levels. The PDC-lamin interaction is maintained during cell division, when lamin depolymerizes and disassembles before reforming daughter nuclear envelopes, providing another pathway for nPDC entry during mitosis. Our work provides a different angle to understanding mitochondria-to-nucleus communication and nuclear metabolism.

SNPs for Genes Encoding the Mitochondrial Proteins Sirtuin3 and Uncoupling Protein 2 Are Associated With Disease Severity, Type 2 Diabetes, and Outcomes in Patients With Pulmonary Arterial Hypertension and This Is Recapitulated in a New Mouse Model Lacking Both Genes.

Background Isolated loss-of-function single nucleotide polymorphisms (SNPs) for SIRT3 (a mitochondrial deacetylase) and UCP2 (an atypical uncoupling protein enabling mitochondrial calcium entry) have been associated with both pulmonary arterial hypertension (PAH) and insulin resistance, but their collective role in animal models and patients is unknown. Methods and Results In a prospective cohort of patients with PAH (n=60), we measured SNPs for both SIRT3 and UCP2, along with several clinical features (including invasive hemodynamic data) and outcomes. We found SIRT3 and UCP2 SNPs often both in the same patient in a homozygous or heterozygous manner, correlating positively with PAH severity and associated with the presence of type 2 diabetes and 10-year outcomes (death and transplantation). To explore this mechanistically, we generated double knockout mice for Sirt3 and Ucp2 and found increasing severity of PAH (mean pulmonary artery pressure, right ventricular hypertrophy/dilatation and extensive vascular remodeling, including inflammatory plexogenic lesions, in a gene dose-dependent manner), along with insulin resistance, compared with wild-type mice. The suppressed mitochondrial function (decreased respiration, increased mitochondrial membrane potential) in the double knockout pulmonary artery smooth muscle cells was associated with apoptosis resistance and increased proliferation, compared with wild-type mice. Conclusions Our work supports the metabolic theory of PAH and shows that these mice exhibit spontaneous severe PAH (without environmental or chemical triggers) that mimics human PAH and may explain the findings in our patient cohort. Our study offers a new mouse model of PAH, with several features of human disease that are typically absent in other PAH mouse models.

Interaction with p53 explains a pro-proliferative function for VHL in cancer.

The von Hippel-Lindau (VHL) protein binds and degrades hypoxia-inducible factors (HIF) hydroxylated by prolyl-hydroxylases under normoxia. Although originally described as a tumor suppressor, there is growing evidence that VHL may paradoxically promote tumor growth. The significance of its described interactions with many other proteins remains unclear. We found that VHL interacts with p53, preventing its tetramerization, promoter binding and expression of its target genes p21, PUMA, and Bax. VHL limited the decrease in proliferation and increase in apoptosis caused by p53 activation, independent of prolyl-hydroxylation and HIF activity, and its presence in tumors caused a resistance to p53-inducing chemotherapy in vivo. We propose that VHL has both anti-tumor function, via HIF degradation, and a new pro-tumor function via p53 target (p21, PUMA, Bax) inhibition. Because p53 plays a critical role in tumor biology, is activated by many chemotherapies, and because VHL levels vary among different tumors and its function can even be lost by mutations in some tumors, our results have important clinical applications. KEY MESSAGES: VHL and p53 physically interact and VHL inhibits p53 activity by limiting the formation of p53 tetramers. VHL attenuates the expression of p53 target genes in response to p53 stimuli. The inhibition of p53 by VHL is independent of HIF and prolyl-hydroxylation.

Pimozide Alleviates Hyperglycemia in Diet-Induced Obesity by Inhibiting Skeletal Muscle Ketone Oxidation.

Perturbations in carbohydrate, lipid, and protein metabolism contribute to obesity-induced type 2 diabetes (T2D), though whether alterations in ketone body metabolism influence T2D pathology is unknown. We report here that activity of the rate-limiting enzyme for ketone body oxidation, succinyl-CoA:3-ketoacid-CoA transferase (SCOT/Oxct1), is increased in muscles of obese mice. We also found that the diphenylbutylpiperidine pimozide, which is approved to suppress tics in individuals with Tourette syndrome, is a SCOT antagonist. Pimozide treatment reversed obesity-induced hyperglycemia in mice, which was phenocopied in mice with muscle-specific Oxct1/SCOT deficiency. These actions were dependent on pyruvate dehydrogenase (PDH/Pdha1) activity, the rate-limiting enzyme of glucose oxidation, as pimozide failed to alleviate hyperglycemia in obese mice with a muscle-specific Pdha1/PDH deficiency. This work defines a fundamental contribution of enhanced ketone body oxidation to the pathology of obesity-induced T2D, while suggesting pharmacological SCOT inhibition as a new class of anti-diabetes therapy.

Tissue-specific regulation of p53 by PKM2 is redox dependent and provides a therapeutic target for anthracycline-induced cardiotoxicity.

Chemotherapy-induced cardiotoxicity (CIC) is a common clinical problem that compromises effective anticancer therapies. Many chemotherapeutics (including anthracyclines, such as doxorubicin) induce the proapoptotic transcription factor p53 in the tumor and nonspecifically in the heart, promoting heart failure. Although inhibition of p53 shows benefit in preclinical heart failure models, it would not be an attractive adjuvant therapy for CIC, because it would prevent tumor regression. A p53-targeting therapy that would decrease chemotherapy-induced apoptosis in the myocardium and, at the same time, enhance apoptosis in the tumor would be ideal. Here, we propose that differences in oxygen tension between the myocardium and the tumor could provide a platform for redox-dependent tissue-specific therapies. We show by coimmunoprecipitation and mass spectrometry that the redox-regulated pyruvate kinase muscle 2 (PKM2) directly binds with p53 and that the redox status of cysteine-423 of tetrameric (but not monomeric) PKM2 is critical for the differential regulation of p53 transcriptional activity. Tetrameric PKM2 suppresses p53 transcriptional activity and apoptosis in a high oxidation state but enhances them in a low oxidation one. We show that the oxidation state (along with cysteine-423 oxidation) is higher in the heart compared to the tumor of the same animal. Treatment with TEPP-46 (a compound that stabilizes tetrameric PKM2) suppressed doxorubicin-induced cardiomyocyte apoptosis, preventing cardiac dysfunction, but enhanced cancer cell apoptosis and tumor regression in the same animals in lung cancer models. Thus, our work suggests that redox-dependent differences in common proteins expressed in the myocardium and tumor can be exploited therapeutically for tissue selectivity in CIC.

The antianginal ranolazine mitigates obesity-induced nonalcoholic fatty liver disease and increases hepatic pyruvate dehydrogenase activity.

Obese individuals are often at risk for nonalcoholic fatty liver disease (NAFLD), insulin resistance, type 2 diabetes (T2D), and cardiovascular diseases such as angina, thereby requiring combination therapies for their comorbidities. Ranolazine is a second-line antianginal agent that also improves glycemia, and our aim was to determine whether ranolazine modifies the progression of obesity-induced NAFLD. Twelve-week-old C57BL/6J male mice were fed a low-fat or high-fat diet for 10 weeks and then treated for 30 days with either vehicle control or ranolazine (50 mg/kg via daily s.c. injection). Glycemia was monitored via glucose/pyruvate/insulin tolerance testing, whereas in vivo metabolism was assessed via indirect calorimetry. Hepatic triacylglycerol content was quantified via the Bligh and Dyer method. Consistent with previous reports, ranolazine treatment reversed obesity-induced glucose intolerance, which was associated with reduced body weight and hepatic steatosis, as well as increased hepatic pyruvate dehydrogenase (PDH) activity. Ranolazine's actions on hepatic PDH activity may be directly mediated, as ranolazine treatment reduced PDH phosphorylation (indicative of increased PDH activity) in HepG2 cells. Therefore, in addition to mitigating angina, ranolazine also reverses NAFLD, which may contribute to its documented glucose-lowering actions, situating ranolazine as an ideal antianginal therapy for obese patients comorbid for NAFLD and T2D.

FoxO1 regulates myocardial glucose oxidation rates via transcriptional control of pyruvate dehydrogenase kinase 4 expression.

Pyruvate dehydrogenase (PDH) is the rate-limiting enzyme for glucose oxidation and a critical regulator of metabolic flexibility during the fasting to feeding transition. PDH is regulated via both PDH kinases (PDHK) and PDH phosphatases, which phosphorylate/inactivate and dephosphorylate/activate PDH, respectively. Our goal was to determine whether the transcription factor forkhead box O1 (FoxO1) regulates PDH activity and glucose oxidation in the heart via increasing the expression of Pdk4, the gene encoding PDHK4. To address this question, we differentiated H9c2 myoblasts into cardiac myocytes and modulated FoxO1 activity, after which Pdk4/PDHK4 expression and PDH phosphorylation/activity were assessed. We assessed binding of FoxO1 to the Pdk4 promoter in cardiac myocytes in conjunction with measuring the role of FoxO1 on glucose oxidation in the isolated working heart. Both pharmacological (1 µM AS1842856) and genetic (siRNA mediated) inhibition of FoxO1 decreased Pdk4/PDHK4 expression and subsequent PDH phosphorylation in H9c2 cardiac myocytes, whereas 10 µM dexamethasone-induced Pdk4/PDHK4 expression was abolished via pretreatment with 1 µM AS1842856. Furthermore, transfection of H9c2 cardiac myocytes with a vector expressing FoxO1 increased luciferase activity driven by a Pdk4 promoter construct containing the FoxO1 DNA-binding element region, but not in a Pdk4 promoter construct lacking this region. Finally, AS1842856 treatment in fasted mice enhanced glucose oxidation rates during aerobic isolated working heart perfusions. Taken together, FoxO1 directly regulates Pdk4 transcription in the heart, thereby controlling PDH activity and subsequent glucose oxidation rates.NEW & NOTEWORTHY Although studies have shown an association between FoxO1 activity and pyruvate dehydrogenase kinase 4 expression, our study demonstrated that pyruvate dehydrogenase kinase 4 is a direct transcriptional target of FoxO1 (but not FoxO3/FoxO4) in the heart. Furthermore, we report here, for the first time, that FoxO1 inhibition increases glucose oxidation in the isolated working mouse heart.

Metabolic Modulation of Clear-cell Renal Cell Carcinoma with Dichloroacetate, an Inhibitor of Pyruvate Dehydrogenase Kinase.

BACKGROUND: Clear-cell renal cell carcinoma (ccRCC) exhibits suppressed mitochondrial function and preferential use of glycolysis even in normoxia, promoting proliferation and suppressing apoptosis. ccRCC resistance to therapy is driven by constitutive hypoxia-inducible factor (HIF) expression due to genetic loss of von Hippel-Lindau factor. In addition to promoting angiogenesis, HIF suppresses mitochondrial function by inducing pyruvate dehydrogenase kinase (PDK), a gatekeeping enzyme for mitochondrial glucose oxidation. OBJECTIVE: To reverse mitochondrial suppression of ccRCC using the PDK inhibitor dichloroacetate (DCA). DESIGN, SETTING, AND PARTICIPANTS: Radical nephrectomy specimens from patients with ccRCC were assessed for PDK expression. The 786-O ccRCC line and two animal models (chicken in ovo and murine xenografts) were used for mechanistic studies. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Mitochondrial function, proliferation, apoptosis, HIF transcriptional activity, angiogenesis, and tumor size were measured in vitro and in vivo. Independent-sample t-tests and analysis of variance were used for statistical analyses. RESULTS: PDK was elevated in 786-O cells and in ccRCC compared to normal kidney tissue from the same patient. DCA reactivated mitochondrial function (increased respiration, Krebs cycle metabolites such as α-ketoglutarate [cofactor of factor inhibiting HIF], and mitochondrial reactive oxygen species), increased p53 activity and apoptosis, and decreased proliferation in 786-O cells. DCA reduced HIF transcriptional activity in an FIH-dependent manner, inhibiting angiogenesis in vitro. DCA reduced tumor size and angiogenesis in vivo in both animal models. CONCLUSIONS: DCA can reverse the mitochondrial suppression of ccRCC and decrease HIF transcriptional activity, bypassing its constitutive expression. Its previous clinical use in humans makes it an attractive candidate for translation to ccRCC patients. PATIENT SUMMARY: We show that an energy-boosting drug decreases tumor growth and tumor blood vessels in animals carrying human kidney cancer cells. This generic drug has been used in patients for other conditions and thus could be tested in kidney cancer that remains incurable.