Benjamin Vogel

Foxp3+ CD4+ T Cells Improve Healing After Myocardial Infarction by Modulating Monocyte/Macrophage Differentiation

Rationale: An exaggerated or persistent inflammatory activation after myocardial infarction (MI) leads to maladaptive healing and subsequent remodeling of the left ventricle. Foxp3+ CD4+ regulatory T cells (Treg cells) contribute to inflammation resolution. Therefore, Treg cells might influence cardiac healing post-MI. Objective: Our aim was to study the functional role of Treg cells in wound healing post-MI in a mouse model of permanent left coronary artery ligation. Methods and Results: Using a model of genetic Treg-cell ablation (Foxp3DTR mice), we depleted the Treg-cell compartment before MI induction, resulting in aggravated cardiac inflammation and deteriorated clinical outcome. Mechanistically, Treg-cell depletion was associated with M1-like macrophage polarization, characterized by decreased expression of inflammation-resolving and healing-promoting factors. The phenotype of exacerbated cardiac inflammation and outcome in Treg-cell–ablated mice could be confirmed in a mouse model of anti-CD25 monoclonal antibody–mediated depletion. In contrast, therapeutic Treg-cell activation by superagonistic anti-CD28 monoclonal antibody administration 2 days after MI led to improved healing and survival. Compared with control animals, CD28-SA–treated mice showed increased collagen de novo expression within the scar, correlating with decreased rates of left ventricular ruptures. Therapeutic Treg-cell activation induced an M2-like macrophage differentiation within the healing myocardium, associated with myofibroblast activation and increased expression of monocyte/macrophage-derived proteins fostering wound healing. Conclusions: Our data indicate that Treg cells beneficially influence wound healing after MI by modulating monocyte/macrophage differentiation. Moreover, therapeutic activation of Treg cells constitutes a novel approach to improve healing post-MI.

Determination of collagen content within picrosirius red stained paraffin-embedded tissue sections using fluorescence microscopy

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Interleukin-13 Deficiency Aggravates Healing and Remodeling in Male Mice After Experimental Myocardial Infarction

Background—Activation of innate immunity, especially infiltration of monocytes, is critical for proper wound healing and scar formation after myocardial infarction (MI). Therefore, we tested the hypothesis that interleukin-13 (IL-13), which influences the differentiation of monocytes/macrophages and has profibrotic properties, modulates wound healing and remodeling after MI. Methods and Results—MI was induced by permanent ligation of the left coronary artery in both male and female wild-type (WT)/IL-13−/− mice. Real-time polymerase chain reaction demonstrated that expression of IL-13 was induced in left and right ventricular myocardium of WT mice within days in response to MI. Fifty-six–day survival was significantly impaired (65% in WT versus 34% in IL-13−/−) in male but not female IL-13−/− (55% in WT versus 54% in IL-13−/−) mice. Serial echocardiography showed significantly increased left ventricular dilation in male IL-13−/− compared with WT mice starting from day 1 after MI, despite comparable infarct size. Fluorescence-activated cell sorter analysis revealed less leukocyte infiltration in male IL-13−/− mice on day 3. Real-time polymerase chain reaction analysis demonstrated reduced expression of marker genes of alternative activation in monocytes sorted from the infarct zone of male IL-13−/− in comparison with WT mice on day 3 after MI. Conclusions—Genetic deficiency of IL-13 worsens outcome after MI in male mice. Our data indicate that IL-13 regulates leukocyte recruitment and induces M2-like monocyte/macrophage differentiation, which modifies wound healing within the infarct zone.

5-Lipoxygenase facilitates healing after myocardial infarction

Early healing after myocardial infarction (MI) is characterized by a strong inflammatory reaction. Most leukotrienes are pro-inflammatory and are therefore potential mediators of healing and remodeling after myocardial ischemia. The enzyme 5-lipoxygenase (5-LOX) has a key role in the transformation of arachidonic acid in leukotrienes. Thus, we tested the effect of 5-LOX on healing after MI. After chronic coronary artery ligation, early mortality was significantly increased in 5-LOX−/− when compared to matching wildtype (WT) mice due to left ventricular rupture. This effect could be reproduced in mice treated with the 5-LOX inhibitor Zileuton. A perfusion mismatch due to the vasoactive potential of leukotrienes is not responsible for left ventricular rupture since local blood flow assessed by magnetic resonance perfusion measurements was not different. However, after MI, there was an accentuation of the inflammatory reaction with an increase of pro-inflammatory macrophages. Yet, mortality was not changed in chimeric mice (WT vs. 5-LOX−/− bone marrow in 5-LOX−/− animals), indicating that an altered function of 5-LOX−/− inflammatory cells is not responsible for the phenotype. Collagen production and accumulation of fibroblasts were significantly reduced in 5-LOX−/− mice in vivo after MI. This might be due to an impaired migration of 5-LOX−/− fibroblasts, as shown in vitro to serum. In conclusion, a lack or inhibition of 5-LOX increases mortality after MI because of healing defects. This is not mediated by a change in local blood flow, but through an altered inflammation and/or fibroblast function.

HMGA1 down-regulation is crucial for chromatin composition and a gene expression profile permitting myogenic differentiation

BackgroundHigh mobility group A (HMGA) proteins regulate gene transcription through architectural modulation of chromatin and the formation of multi-protein complexes on promoter/enhancer regions. Differential expression of HMGA variants has been found to be important for distinct differentiation processes and deregulated expression was linked to several disorders. Here we used mouse C2C12 myoblasts and C2C12 cells stably over-expressing HMGA1a-eGFP to study the impact of deregulated HMGA1 expression levels on cellular differentiation.ResultsWe found that induction of the myogenic or osteogenic program of C2C12 cells caused an immediate down-regulation of HMGA1. In contrast to wild type C2C12 cells, an engineered cell line with stable over-expression of HMGA1a-eGFP failed to differentiate into myotubes. Immunolocalization studies demonstrated that sustained HMGA1a-eGFP expression prevented myotube formation and chromatin reorganization that normally accompanies differentiation. Western Blot analyses showed that elevated HMGA1a-eGFP levels affected chromatin composition through either down-regulation of histone H1 or premature expression of MeCP2. RT-PCR analyses further revealed that sustained HMGA1a expression also affected myogenic gene expression and caused either down-regulation of genes such as MyoD, myogenin, Igf1, Igf2, Igfbp1-3 or up-regulation of the transcriptional repressor Msx1. Interestingly, siRNA experiments demonstrated that knock-down of HMGA1a was required and sufficient to reactivate the myogenic program in induced HMGA1a over-expressing cells.ConclusionsOur data demonstrate that HMGA1 down-regulation after induction is required to initiate the myogenic program in C2C12 cells. Sustained HMGA1a expression after induction prevents expression of key myogenic factors. This may be due to specific gene regulation and/or global effects on chromatin. Our data further corroborate that altered HMGA1 levels influence the expression of other chromatin proteins. Thus, HMGA1 is able to establish a specific chromatin composition. This work contributes to the understanding of how differential HMGA1 expression is involved in chromatin organization during cellular differentiation processes and it may help to comprehend effects of HMGA1 over-expression occurring in malign or benign tumours.

Cross-linking of DNA through HMGA1 suggests a DNA scaffold

Binding of proteins to DNA is usually considered 1D with one protein bound to one DNA molecule. In principle, proteins with multiple DNA binding domains could also bind to and thereby cross-link different DNA molecules. We have investigated this possibility using high-mobility group A1 (HMGA1) proteins, which are architectural elements of chromatin and are involved in the regulation of multiple DNA-dependent processes. Using direct stochastic optical reconstruction microscopy (dSTORM), we could show that overexpression of HMGA1a-eGFP in Cos-7 cells leads to chromatin aggregation. To investigate if HMGA1a is directly responsible for this chromatin compaction we developed a DNA cross-linking assay. We were able to show for the first time that HMGA1a can cross-link DNA directly. Detailed analysis using point mutated proteins revealed a novel DNA cross-linking domain. Electron microscopy indicates that HMGA1 proteins are able to create DNA loops and supercoils in linearized DNA confirming the cross-linking ability of HMGA1a. This capacity has profound implications for the spatial organization of DNA in the cell nucleus and suggests cross-linking activities for additional nuclear proteins.

Touch-free measurement of body temperature using close-up thermography of the ocular surface

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Determination of DNase activity by degradation of ethidium bromide–DNA complexes using a fluorescence plate reader

The long known toxicity of free chromatin mediated by histones regained attention after discovery of neutrophil extracellular traps (NETs). Free histones from necrotic cells or NETs can damage prokaryotic and eukaryotic cells and are responsible for the aggravation of a growing list of diseases. DNases degrade the toxic chromatin polymer to nucleosomes and efficiently reduce local high histone concentrations. Therefore, DNase activity as a biomarker is of growing interest in basic and clinical research. Here a detailed one-step protocol is presented that allows rapid and sensitive detection of DNases down to 400 fg/μl per reaction based on the detection of fluorescent ethidium bromide/DNA complexes in a 96-well plate reader. The flexible protocol uses an internal standard for background correction and allows convenient and reliable data analysis using common laboratory equipment and chemicals without elaborate preparations. The DNase activity of a sample is clearly defined by substrate amount, incubation time, and (if appropriate) a DNase standard for absolute quantification in Kunitz units per milligram sample protein. Quantitative kinetic determination is possible within less than 1h down to 5 pg DNases/μl per reaction.