Publications by authors named "Melroy X Miranda"

8 Publications

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Sirtuin 5 promotes arterial thrombosis by blunting the fibrinolytic system.

Cardiovasc Res 2020 Sep 15. Epub 2020 Sep 15.

Center for Molecular Cardiology, Schlieren Campus, University of Zurich, Wagistrasse 12, Schlieren, Switzerland.

Aims: Arterial thrombosis as a result of plaque rupture or erosion is a key event in acute cardiovascular events. Sirtuin 5 (SIRT5) belongs to the lifespan-regulating sirtuin superfamily and has been implicated in acute ischemic stroke and cardiac hypertrophy. This project aims at investigating the role of SIRT5 in arterial thrombus formation.

Methods And Results: Sirt5 transgenic (Sirt5Tg/0) as well as knock-out (Sirt5-/-) mice underwent photochemically-induced carotid endothelial injury to trigger arterial thrombosis. Primary human aortic endothelial cells (HAECs) treated with SIRT5 silencing-RNA (si-SIRT5) as well as peripheral blood mononuclear cells (PBMCs) from acute coronary syndrome (ACS) patients and non-ACS controls (case-control study, total n = 171) were used to increase the translational relevance of our data. Compared to WT controls, Sirt5Tg/0 mice displayed accelerated arterial thrombus formation following endothelial-specific damage. Conversely, in Sirt5-/-mice arterial thrombosis was blunted. Platelet function was unaltered, as assessed by ex vivo collagen-induced aggregometry. Similarly, activation of the coagulation cascade as assessed by vascular and plasma tissue factor (TF) and TF pathway inhibitor (TFPI) expression was unaltered. Increased thrombus embolization episodes and circulating D-dimer levels suggested augmented activation of the fibrinolytic system in Sirt5-/- mice. Accordingly, Sirt5-/- mice showed reduced plasma and vascular expression of the fibrinolysis inhibitor plasminogen activator inhibitor (PAI)-1. In HAECs, SIRT5-silencing inhibited PAI-1 gene and protein expression in response to TNF-α. This effect was mediated by increased AMPK activation and reduced phosphorylation of the MAP kinase ERK 1/2, but not JNK and p38 as shown both in vivo and in vitro. Lastly, both PAI-1 and SIRT5 gene expression are increased in ACS patients compared to non-ACS controls after adjustment for cardiovascular risk factors, while PAI-1 expression increased across tertiles of SIRT5.

Conclusions: SIRT5 promotes arterial thrombosis by modulating fibrinolysis through endothelial PAI-1 expression. Hence, SIRT5 may be an interesting therapeutic target in the context of atherothrombotic events.

Translational Perspectives: This study illustrates a novel role for Sirtuin 5 in arterial thrombosis by regulating fibrinolysis through plasminogen activator inhibitor 1 (PAI-1). These results shed new light onto the pathophysiology of arterial thrombus formation which underlies most of the acute atherosclerotic complications. Also, they further affirm the intrinsic relationship between lifespan regulating genes, vascular dysfunction and age-related cardiovascular disease, thus indicating these genes as potential targets for cardiovascular prevention and therapy. Further studies will be needed to assess the predictive ability of SIRT5 in patients with acute cardiovascular or cerebrovascular events. Also, the design of specific SIRT5 inhibitors will allow trials aiming at investigating the efficacy of SIRT5 blockage in the clinical setting.
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http://dx.doi.org/10.1093/cvr/cvaa268DOI Listing
September 2020

Sirt6 deletion in bone marrow-derived cells increases atherosclerosis - Central role of macrophage scavenger receptor 1.

J Mol Cell Cardiol 2020 02 21;139:24-32. Epub 2020 Jan 21.

Center for Molecular Cardiology, University of Zurich, Zurich, Switzerland; Department of Cardiology, University Heart Center, Zurich University Hospital, Zurich, Switzerland. Electronic address:

Aims: Sirtuin 6 (Sirt6) is a NAD-dependent deacetylase that plays a key role in DNA repair, inflammation and lipid regulation. Sirt6-null mice show severe metabolic defects and accelerated aging. Macrophage-foam cell formation via scavenger receptors is a key step in atherogenesis. We determined the effects of bone marrow-restricted Sirt6 deletion on foam cell formation and atherogenesis using a mouse model.

Methods And Results: Sirt6 deletion in bone marrow-derived cells increased aortic plaques, lipid content and macrophage numbers in recipient Apoe mice fed a high-cholesterol diet for 12 weeks (n = 12-14, p < .001). In RAW macrophages, Sirt6 overexpression reduced oxidized low-density lipoprotein (oxLDL) uptake, Sirt6 knockdown enhanced it and increased mRNA and protein levels of macrophage scavenger receptor 1 (Msr1), whereas levels of other oxLDL uptake and efflux transporters remained unchanged. Similarly, in human primary macrophages, Sirt6 knockdown increased MSR1 protein levels and oxLDL uptake. Double knockdown of Sirt6 and Msr1 abolished the increase in oxLDL uptake observed upon Sirt6 single knockdown. FACS analyses of macrophages from aortic plaques of Sirt6-deficient bone marrow-transplanted mice showed increased MSR1 protein expression. Double knockdown of Sirt6 and the transcription factor c-Myc in RAW cells abolished the increase in Msr1 mRNA and protein levels; c-Myc overexpression increased Msr1 mRNA and protein levels.

Conclusions: Loss of Sirt6 in bone marrow-derived cells is proatherogenic; hereby macrophages play an important role given a c-Myc-dependent increase in MSR1 protein expression and an enhanced oxLDL uptake in human and murine macrophages. These findings assign endogenous SIRT6 in macrophages an important atheroprotective role.
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http://dx.doi.org/10.1016/j.yjmcc.2020.01.002DOI Listing
February 2020

Gut microbiota-dependent trimethylamine N-oxide in acute coronary syndromes: a prognostic marker for incident cardiovascular events beyond traditional risk factors.

Eur Heart J 2017 Mar;38(11):814-824

Department of Cardiology, University Heart Center, University Hospital Zurich, Switzerland.

Aims: Systemic levels of trimethylamine N-oxide (TMAO), a pro-atherogenic and pro-thrombotic metabolite produced from gut microbiota metabolism of dietary trimethylamine (TMA)-containing nutrients such as choline or carnitine, predict incident cardiovascular event risks in stable primary and secondary prevention subjects. However, the prognostic value of TMAO in the setting of acute coronary syndromes (ACS) remains unknown.

Methods And Results: We investigated the relationship of TMAO levels with incident cardiovascular risks among sequential patients presenting with ACS in two independent cohorts. In the Cleveland Cohort, comprised of sequential subjects (n = 530) presenting to the Emergency Department (ED) with chest pain of suspected cardiac origin, an elevated plasma TMAO level at presentation was independently associated with risk of major adverse cardiac events (MACE, including myocardial infarction, stroke, need for revascularization, or death) over the ensuing 30-day (4th quartile (Q4) adjusted odds ratio (OR) 6.30, 95% confidence interval (CI), 1.89-21.0, P < 0.01) and 6-month (Q4 adjusted OR 5.65, 95%CI, 1.91-16.7; P < 0.01) intervals. TMAO levels were also a significant predictor of the long term (7-year) mortality (Q4 adjusted HR 1.81, 95%CI, 1.04-3.15; P < 0.05). Interestingly, TMAO level at initial presentation predicted risk of incident MACE over the near-term (30 days and 6 months) even among subjects who were initially negative for troponin T (< 0.1 ng/mL) (30 days, Q4 adjusted OR 5.83, 95%CI, 1.79-19.03; P < 0.01). The prognostic value of TMAO was also assessed in an independent multicentre Swiss Cohort of ACS patients (n = 1683) who underwent coronary angiography. Trimethylamine N-oxide again predicted enhanced MACE risk (1-year) (adjusted Q4 hazard ratios: 1.57, 95% CI, 1.03-2.41; P <0.05).

Conclusion: Plasma TMAO levels among patients presenting with chest pain predict both near- and long-term risks of incident cardiovascular events, and may thus provide clinical utility in risk stratification among subjects presenting with suspected ACS.
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http://dx.doi.org/10.1093/eurheartj/ehw582DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837488PMC
March 2017

The Sirt1 activator SRT3025 provides atheroprotection in Apoe-/- mice by reducing hepatic Pcsk9 secretion and enhancing Ldlr expression.

Eur Heart J 2015 Jan 6;36(1):51-9. Epub 2014 Mar 6.

Cardiovascular Research, Institute of Physiology, University of Zurich and University Heart Center, Cardiology, University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland Zurich Center of Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland

Aims: The deacetylase sirtuin 1 (Sirt1) exerts beneficial effects on lipid metabolism, but its roles in plasma LDL-cholesterol regulation and atherosclerosis are controversial. Thus, we applied the pharmacological Sirt1 activator SRT3025 in a mouse model of atherosclerosis and in hepatocyte culture.

Methods And Results: Apolipoprotein E-deficient (Apoe(-/-)) mice were fed a high-cholesterol diet (1.25% w/w) supplemented with SRT3025 (3.18 g kg(-1) diet) for 12 weeks. In vitro, the drug activated wild-type Sirt1 protein, but not the activation-resistant Sirt1 mutant; in vivo, it increased deacetylation of hepatic p65 and skeletal muscle Foxo1. SRT3025 treatment decreased plasma levels of LDL-cholesterol and total cholesterol and reduced atherosclerosis. Drug treatment did not change mRNA expression of hepatic LDL receptor (Ldlr) and proprotein convertase subtilisin/kexin type 9 (Pcsk9), but increased their protein expression indicating post-translational effects. Consistent with hepatocyte Ldlr and Pcsk9 accumulation, we found reduced plasma levels of Pcsk9 after pharmacological Sirt1 activation. In vitro administration of SRT3025 to cultured AML12 hepatocytes attenuated Pcsk9 secretion and its binding to Ldlr, thereby reducing Pcsk9-mediated Ldlr degradation and increasing Ldlr expression and LDL uptake. Co-administration of exogenous Pcsk9 with SRT3025 blunted these effects. Sirt1 activation with SRT3025 in Ldlr(-/-) mice reduced neither plasma Pcsk9, nor LDL-cholesterol levels, nor atherosclerosis.

Conclusion: We identify reduction in Pcsk9 secretion as a novel effect of Sirt1 activity and uncover Ldlr as a prerequisite for Sirt1-mediated atheroprotection in mice. Pharmacological activation of Sirt1 appears promising to be tested in patients for its effects on plasma Pcsk9, LDL-cholesterol, and atherosclerosis.
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http://dx.doi.org/10.1093/eurheartj/ehu095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4286317PMC
January 2015

Deletion of Sirt3 does not affect atherosclerosis but accelerates weight gain and impairs rapid metabolic adaptation in LDL receptor knockout mice: implications for cardiovascular risk factor development.

Basic Res Cardiol 2014 Jan 27;109(1):399. Epub 2013 Dec 27.

Division of Cardiology, Department of Medicine, University Hospital Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland,

Sirt3 is a mitochondrial NAD(+)-dependent deacetylase that governs mitochondrial metabolism and reactive oxygen species homeostasis. Sirt3 deficiency has been reported to accelerate the development of the metabolic syndrome. However, the role of Sirt3 in atherosclerosis remains enigmatic. We aimed to investigate whether Sirt3 deficiency affects atherosclerosis, plaque vulnerability, and metabolic homeostasis. Low-density lipoprotein receptor knockout (LDLR(-/-)) and LDLR/Sirt3 double-knockout (Sirt3(-/-)LDLR(-/-)) mice were fed a high-cholesterol diet (1.25 % w/w) for 12 weeks. Atherosclerosis was assessed en face in thoraco-abdominal aortae and in cross sections of aortic roots. Sirt3 deletion led to hepatic mitochondrial protein hyperacetylation. Unexpectedly, though plasma malondialdehyde levels were elevated in Sirt3-deficient mice, Sirt3 deletion affected neither plaque burden nor features of plaque vulnerability (i.e., fibrous cap thickness and necrotic core diameter). Likewise, plaque macrophage and T cell infiltration as well as endothelial activation remained unaltered. Electron microscopy of aortic walls revealed no difference in mitochondrial microarchitecture between both groups. Interestingly, loss of Sirt3 was associated with accelerated weight gain and an impaired capacity to cope with rapid changes in nutrient supply as assessed by indirect calorimetry. Serum lipid levels and glucose tolerance were unaffected by Sirt3 deletion in LDLR(-/-) mice. Sirt3 deficiency does not affect atherosclerosis in LDLR(-/-) mice. However, Sirt3 controls systemic levels of oxidative stress, limits expedited weight gain, and allows rapid metabolic adaptation. Thus, Sirt3 may contribute to postponing cardiovascular risk factor development.
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http://dx.doi.org/10.1007/s00395-013-0399-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3898152PMC
January 2014

Endothelial mineralocorticoid receptor activation mediates endothelial dysfunction in diet-induced obesity.

Eur Heart J 2013 Dec 17;34(45):3515-24. Epub 2013 Apr 17.

Institute of Physiology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.

Aims: Aldosterone plays a crucial role in cardiovascular disease. 'Systemic' inhibition of its mineralocorticoid receptor (MR) decreases atherosclerosis by reducing inflammation and oxidative stress. Obesity, an important cardiovascular risk factor, is an inflammatory disease associated with increased plasma aldosterone levels. We have investigated the role of the 'endothelial' MR in obesity-induced endothelial dysfunction, the earliest stage in atherogenesis.

Methods And Results: C57BL/6 mice were exposed to a normal chow diet (ND) or a high-fat diet (HFD) alone or in combination with the MR antagonist eplerenone (200 mg/kg/day) for 14 weeks. Diet-induced obesity impaired endothelium-dependent relaxation in response to acetylcholine, whereas eplerenone treatment of obese mice prevented this. Expression analyses in aortic endothelial cells isolated from these mice revealed that eplerenone attenuated expression of pro-oxidative NADPH oxidase (subunits p22phox, p40phox) and increased expression of antioxidative genes (glutathione peroxidase-1, superoxide dismutase-1 and -3) in obesity. Eplerenone did not affect obesity-induced upregulation of cyclooxygenase (COX)-1 or prostacyclin synthase. Endothelial-specific MR deletion prevented endothelial dysfunction in obese (exhibiting high 'endogenous' aldosterone) and in 'exogenous' aldosterone-infused lean mice. Pre-incubation of aortic rings from aldosterone-treated animals with the COX-inhibitor indomethacin restored endothelial function. Exogenous aldosterone administration induced endothelial expression of p22phox in the presence, but not in the absence of the endothelial MR.

Conclusion: Obesity-induced endothelial dysfunction depends on the 'endothelial' MR and is mediated by an imbalance of oxidative stress-modulating mechanisms. Therefore, MR antagonists may represent an attractive therapeutic strategy in the increasing population of obese patients to decrease vascular dysfunction and subsequent atherosclerotic complications.
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http://dx.doi.org/10.1093/eurheartj/eht095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3844149PMC
December 2013

The FIH hydroxylase is a cellular peroxide sensor that modulates HIF transcriptional activity.

EMBO Rep 2012 Mar 1;13(3):251-7. Epub 2012 Mar 1.

Henry Wellcome Building for Molecular Physiology, University of Oxford, Oxford OX3 7BN, UK.

Hypoxic and oxidant stresses can coexist in biological systems, and oxidant stress has been proposed to activate hypoxia pathways through the inactivation of the 'oxygen-sensing' hypoxia-inducible factor (HIF) prolyl and asparaginyl hydroxylases. Here, we show that despite reduced sensitivity to cellular hypoxia, the HIF asparaginyl hydroxylase--known as FIH, factor inhibiting HIF--is strikingly more sensitive to peroxide than the HIF prolyl hydroxylases. These contrasting sensitivities indicate that oxidant stress is unlikely to signal hypoxia directly to the HIF system, but that hypoxia and oxidant stress can interact functionally as distinct regulators of HIF transcriptional output.
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http://dx.doi.org/10.1038/embor.2012.9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3323130PMC
March 2012

Dysregulation of hypoxia pathways in fumarate hydratase-deficient cells is independent of defective mitochondrial metabolism.

Hum Mol Genet 2010 Oct 21;19(19):3844-51. Epub 2010 Jul 21.

Henry Wellcome Building for Molecular Physiology, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.

Mutations in the gene encoding the Krebs cycle enzyme fumarate hydratase (FH) predispose to hereditary leiomyomatosis and renal cell cancer in affected individuals. FH-associated neoplasia is characterized by defective mitochondrial function and by upregulation of transcriptional pathways mediated by hypoxia-inducible factor (HIF), although whether and by what means these processes are linked has been disputed. We analysed the HIF pathway in Fh1-/- mouse embryonic fibroblasts (MEFs), in FH-defective neoplastic tissues and in Fh1-/- MEFs re-expressing either wild-type or an extra-mitochondrial restricted form of FH. These experiments demonstrated that upregulation of HIF-1alpha occurs as a direct consequence of FH inactivation. Fh1-/- cells accumulated intracellular fumarate and manifested severe impairment of HIF prolyl but not asparaginyl hydroxylation which was corrected by provision of exogenous 2-oxoglutarate (2-OG). Re-expression of the extra-mitochondrial form of FH in Fh1-/- cells was sufficient to reduce intracellular fumarate and to correct dysregulation of the HIF pathway completely, even in cells that remained profoundly defective in mitochondrial energy metabolism. The findings indicate that upregulation of HIF-1alpha arises from competitive inhibition of the 2-OG-dependent HIF hydroxylases by fumarate and not from disruption of mitochondrial energy metabolism.
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http://dx.doi.org/10.1093/hmg/ddq305DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2935862PMC
October 2010