Rationale: Changes in redox potentials of cardiac myocytes are linked to several cardiovascular diseases. Redox alterations are currently mostly described qualitatively using chemical sensors, which however do not allow quantifying redox potentials, lack specificity, and the possibility to analyze subcellular domains. Recent advances to quantitatively describe defined redox changes include the application of genetically encoded redox biosensors. Objective: Establishment of mouse models, which allow the quantification of the glutathione redox potential ( E GSH ) in the cytoplasm and the mitochondrial matrix of isolated cardiac myocytes and in Langendorff-perfused hearts based on the use of the redox-sensitive green fluorescent protein 2, coupled to the glutaredoxin 1 (Grx1-roGFP2). Methods and Results: We generated transgenic mice with cardiac myocyte–restricted expression of Grx1-roGFP2 targeted either to the mitochondrial matrix or to the cytoplasm. The response of the roGFP2 toward H 2 O 2 , diamide, and dithiothreitol was titrated and used to determine the E GSH in isolated cardiac myocytes and in Langendorff-perfused hearts. Distinct E GSH were observed in the cytoplasm and the mitochondrial matrix. Stimulation of the cardiac myocytes with isoprenaline, angiotensin II, or exposure to hypoxia/reoxygenation additionally underscored that these compartments responded independently. A compartment-specific response was also observed 3 to 14 days after myocardial infarction. Conclusions: We introduce redox biosensor mice as a new tool, which allows quantification of defined alterations of E GSH in the cytoplasm and the mitochondrial matrix in cardiac myocytes and can be exploited to answer questions in basic and translational cardiovascular research.

On a molecular level, cells sense changes in oxygen availability through the PHDs, which regulate the protein stability of the α-subunit of the transcription factor HIF. Especially, PHD3 has been additionally associated with apoptotic cell death. We hypothesized that PHD3 plays a role in cell-fate decisions in macrophages. Therefore, myeloid-specific PHD3(-/-) mice were created and analyzed. PHD3(-/-) BMDM showed no altered HIF-1α or HIF-2α stabilization or increased HIF target gene expression in normoxia or hypoxia. Macrophage M1 and M2 polarization was unchanged likewise. Compared with macrophages from WT littermates, PHD3(-/-) BMDM exhibited a significant reduction in TUNEL-positive cells after serum withdrawal or treatment with stauro and SNAP. Under the same conditions, PHD3(-/-) BMDM also showed less Annexin V staining, which is representative for membrane disruption, and indicated a reduced early apoptosis. In an unbiased transcriptome screen, we found that Angptl2 expression was reduced in PHD3(-/-) BMDM under stress conditions. Addition of rAngptl2 rescued the antiapoptotic phenotype, demonstrating that it is involved in the PHD3-mediated response toward apoptotic stimuli in macrophages.

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BackgroundUnloading the left ventricle and delaying reperfusion reduces infarct size in preclinical models of acute myocardial infarction. We hypothesized that a potential explanation for this effect is that left ventricular (LV) unloading before reperfusion increases collateral blood flow to ischemic myocardium.Methods and ResultsAcute myocardial infarction was induced by balloon occlusion of the left anterior descending artery for 120 minutes in adult swine, followed by reperfusion for 180 minutes. After 90 minutes of occlusion, animals were assigned to 30 minutes of continued occlusion (n=6) or to 30 minutes of support with either an Impella CP (n=4) or venoarterial extracorporeal membrane oxygenation (n=5) with persistent occlusion. The primary end point was measures of microcirculatory blood flow including the collateral flow index (CFI) during left anterior descending artery occlusion as (Pw−RA)/(Pa−RA), where Pa, Pw, and RA are aortic, coronary wedge, and right atrial pressure, respectively. Infarct size was quantified using triphenyltetrazolium chloride. Compared with continued occlusion, Impella, not venoarterial extracorporeal membrane oxygenation, reduced infarct size relative to the area at risk. Before reperfusion, Impella reduced LV stroke work by 25% and increased the CFI by 75%, but venoarterial extracorporeal membrane oxygenation did not. Among all groups, the change in CFI between 90 and 120 minutes correlated inversely with the change in LV stroke work (r 2=0.44, P=0.01) and infarct size (r 2=0.41, P=0.02).ConclusionsWe report for the first time that 30 minutes of LV unloading during coronary occlusion increases the CFI, which correlates inversely with LV stroke work and infarct size. Venoarterial extracorporeal membrane oxygenation failed to increase the CFI and did not reduce infarct size.

The prolyl-4-hydroxylase domain (PHD) enzymes are regarded as the molecular oxygen sensors. There is an interplay between oxygen availability and cellular metabolism, which in turn has significant effects on the functionality of innate immune cells, such as macrophages. However, if and how PHD enzymes affect macrophage metabolism are enigmatic. We hypothesized that macrophage metabolism and function can be controlled via manipulation of PHD2. We characterized the metabolic phenotypes of PHD2-deficient RAW cells and primary PHD2 knockout bone marrow-derived macrophages (BMDM). Both showed typical features of anaerobic glycolysis, which were paralleled by increased pyruvate dehydrogenase kinase 1 (PDK1) protein levels and a decreased pyruvate dehydrogenase enzyme activity. Metabolic alterations were associated with an impaired cellular functionality. Inhibition of PDK1 or knockout of hypoxia-inducible factor 1␣ (HIF-1␣) reversed the metabolic phenotype and impaired the functionality of the PHD2-deficient RAW cells and BMDM. Taking these results together, we identified a critical role of PHD2 for a reversible glycolytic reprogramming in macrophages with a direct impact on their function. We suggest that PHD2 serves as an adjustable switch to control macrophage behavior.KEYWORDS PDK, prolyl-4-hydroxylase domain, dioxygenases, hypoxia, macrophages M acrophages are an essential component of innate immunity and are well recognized to play critical roles in inflammation, tumor progression, and tissue repair, for example, after an ischemic insult (1). Under aerobic conditions, the oxidative breakdown of pyruvate within the mitochondria is the prevalent source of energy in most cells. Upon a decrease in oxygen availability, cells shift the metabolism toward anaerobic glycolysis. In line with this, macrophages can use aerobic or anaerobic glycolysis for energy production, depending on the context. There is a growing understanding that macrophage function can be altered by cellular metabolism (2). One of the key factors in switching aerobic to anaerobic metabolism at the transcriptional level is the hypoxia-inducible factor (HIF). HIF comprises two subunits: the constitutively regulated HIF␤ subunit and one of three oxygen-regulated HIF␣ subunits (HIF-1␣, HIF-2␣, or HIF-3␣) (3). The protein stability of HIF␣ is regulated by the three prolyl-4-hydroxylase domain (PHD) enzymes, PHD1, -2, and -3, which hydroxylate HIF␣ in an oxygen-dependent manner (for a review, see references 4 and 5). The hydroxylated product is recognized by the pVHL protein, which results in ubiquitination and proteasomal degradation of the ␣-subunit. In hypoxia, the hydroxylation and degra-

Macrophages are essential for the inflammatory response after an ischemic insult and thereby influence tissue recovery. For the oxygen sensing prolyl-4-hydroxylase domain enzyme (PHD) 2 a clear impact on the macrophage-mediated arteriogenic response after hind-limb ischemia has been demonstrated previously, which involves fine tuning a M2-like macrophage population. To analyze the role of PHD3 in macrophages, we performed hind-limb ischemia (ligation and excision of the femoral artery) in myeloid-specific PHD3 knockout mice (PHD3−/−) and analyzed the inflammatory cell invasion, reperfusion recovery and fibrosis in the ischemic muscle post-surgery. In contrast to PHD2, reperfusion recovery and angiogenesis was unaltered in PHD3−/− compared to WT mice. Macrophages from PHD3−/− mice showed, however, a dampened inflammatory reaction in the affected skeletal muscle tissues compared to WT controls. This was associated with a decrease in fibrosis and an anti-inflammatory phenotype of the PHD3−/− macrophages, as well as decreased expression of Cyp2s1 and increased PGE2-secretion, which could be mimicked by PHD3−/− bone marrow-derived macrophages in serum starvation.

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