Background Hypoxic vasodilation is a physiological response to low oxygen (O2) tension that increases blood supply to match metabolic demands. While this response has been characterized for more than 100 years, the underlying hypoxic sensing and effector signaling mechanisms remain uncertain. We have shown that deoxygenated myoglobin (deoxyMb) in the heart can reduce nitrite to nitric oxide (NO˙) and thereby contribute to cardiomyocyte NO˙ signaling during ischemia. Based on recent observations that Mb is expressed in the vasculature of hypoxia-tolerant fish, we hypothesized that endogenous nitrite may contribute to physiological hypoxic vasodilation via reactions with vascular Mb to form NO˙. Methods and Results We here show that Mb is expressed in vascular smooth muscle and contributes significantly to nitrite-dependent hypoxic vasodilation in vivo and ex vivo. The generation of NO˙ from nitrite reduction by deoxyMb activates canonical soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) signaling pathways. In vivo and ex vivo vasodilation responses, the reduction of nitrite to NO˙ and the subsequent signal transduction mechanisms were all significantly impaired in mice without myoglobin (Mb−/−). Hypoxic vasodilation studies in Mb, endothelial and inducible NO synthase knockout models (eNOS−/−, iNOS−/−) suggest that only Mb contributes to systemic hypoxic vasodilatory responses in mice. Conclusions Endogenous nitrite is a physiological effector of hypoxic vasodilation. Its reduction to NO˙ via the heme globin Mb enhances blood flow and matches O2 supply to increased metabolic demands under hypoxic conditions.

Lyme disease is a tick-borne spirochetal infection that may affect the heart. Cardiac manifestations include conduction disturbances and other pathologies of the heart. We report on a 37-year old male, who was admitted to the emergency department because of dizziness and generalized tiredness. Physical examination and the initial laboratory values revealed no abnormalities. The patient's electrocardiogram on admission revealed newly diagnosed bradycardia due to atrioventricular heart block. The ventricular heart rate was 35/min. The patient was admitted to the ICU. Lyme serology and Western blot were positive for Borrelia antibodies. After institution of antibiotic therapy with ceftriaxone, atrioventricular heart block resolved rapidly. We therefore have to assume that in this patient Lyme carditis was the cause of third-degree AV block.

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Ischemic heart diseases are the most frequent diseases in the western world. Apart from Interleukin (IL-)1, inflammatory therapeutic targets in the clinic are still missing. Interestingly, opposing roles of the pro-inflammatory cytokine IL-23 have been described in cardiac ischemia in mice. IL-23 is a composite cytokine consisting of p19 and p40 which binds to IL-23R and IL-12Rβ1 to initiate signal transduction characterized by activation of the Jak/STAT, PI3K and Ras/Raf/MAPK pathways. Here, we generate IL-23R-Y416FΔICD signaling deficient mice and challenged these mice in close- and open-chest left anterior descending coronary arteria ischemia/reperfusion experiments. Our experiments showed only minimal changes in all assayed parameters in IL-23R signaling deficient mice compared to wild-type mice in ischemia and for up to four weeks of reperfusion, including ejection fraction, endsystolic volume, enddiastolic volume, infarct size, gene regulation and α smooth muscle actin (αSMA) and Hyaluronic acid (HA) protein expression. Moreover, injection of IL-23 in wild-type mice after LAD ischemia/reperfusion had also no influence on the outcome of the healing phase. Our data showed that IL-23R deficiency has no effects in myocardial I/R.

The incidence of heart failure after myocardial infarction (MI) remains high and the underlying causes are incompletely understood. The crosstalk between heart and adipose tissue and stimulated lipolysis has been identified as potential driver of heart failure. Lipolysis is also activated acutely in response to MI. However, the role in the post-ischemic remodeling process and the contribution of different depots of adipose tissue is unclear. Here, we employ a mouse model of 60 min cardiac ischemia and reperfusion (I/R) to monitor morphology, cellular infiltrates and gene expression of visceral and subcutaneous white adipose tissue depots (VAT and SAT) for up to 28 days post ischemia. We found that in SAT but not VAT, adipocyte size gradually decreased over the course of reperfusion and that these changes were associated with upregulation of UCP1 protein, indicating white adipocyte conversion to the so-called ‘brown-in-white’ phenotype. While this phenomenon is generally associated with beneficial metabolic consequences, its role in the context of MI is unknown. We further measured decreased lipogenesis in SAT together with enhanced infiltration of MAC-2+ macrophages. Finally, quantitative PCR analysis revealed transient downregulation of the adipokines adiponectin, leptin and resistin in SAT. While adiponectin and leptin have been shown to be cardioprotective, the role of resistin after MI needs further investigation. Importantly, all significant changes were identified in SAT, while VAT was largely unaffected by MI. We conclude that targeted interference with lipolysis in SAT may be a promising approach to promote cardiac healing after ischemia.

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Obesity is one of the major risk factors that can lead to a myocardial infarction and can negatively influence subsequent cardiac remodeling. The onset of obesity is related to different genetic variants of the fat mass and obesity associated gene (Fto). Fto deficient mice were protected from obesity and showed an improved glucose tolerance under a high fat diet. In addition, it is known that Fto acts as an m6A RNA demethylase, whereby it can influence mRNA stability and translation. In a first approach, we used Fto deficient mice to perform an ischemic/reperfusion (I/R) model. At 24 h after reperfusion, Fto deficient mice already had a smaller infarct size compared to their wild type littermates. Over a time period of three weeks, the heart function was investigated by echocardiography. Three weeks after reperfusion, Fto deficient mice showed a preserved heart function and had reduced collagen scar formation compared to wild‐type control mice. Initial molecular studies indicated a reduction of the mTORC1 pathway and consequently a down regulation of S6K phosphorylation. For a first approach of therapeutic intervention, we used the Fto inhibitor rhein, which binds the active center of Fto and thereby inhibits its demethylase activity. Wild type mice were pre‐treated with rhein or the solvent over three weeks before the I/R procedure was performed. The rhein‐treated mice showed a significant reduction in the infarct size compared to the solvent treated littermates. In this study, we demonstrated that Fto deficiency can modulate the outcome of a myocardial infarction by improving left ventricular function and reduction of the infarct size.Support or Funding InformationSupported by the Deutsche Forschung Gesellschaft (DFG) as Part of the SFB 1116 (project number 236177352)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.