Henning Warnecke

Oncostatin M Is a Major Mediator of Cardiomyocyte Dedifferentiation and Remodeling

Cardiomyocyte remodeling, which includes partial dedifferentiation of cardiomyocytes, is a process that occurs during both acute and chronic disease processes. Here, we demonstrate that oncostatin M (OSM) is a major mediator of cardiomyocyte dedifferentiation and remodeling during acute myocardial infarction (MI) and in chronic dilated cardiomyopathy (DCM). Patients suffering from DCM show a strong and lasting increase of OSM expression and signaling. OSM treatment induces dedifferentiation of cardiomyocytes and upregulation of stem cell markers and improves cardiac function after MI. Conversely, inhibition of OSM signaling suppresses cardiomyocyte remodeling after MI and in a mouse model of DCM, resulting in deterioration of heart function after MI but improvement of cardiac performance in DCM. We postulate that dedifferentiation of cardiomyocytes initially protects stressed hearts but fails to support cardiac structure and function upon continued activation. Manipulation of OSM signaling provides a means to control the differentiation state of cardiomyocytes and cellular plasticity.

Remodeling and dedifferentiation of adult cardiomyocytes during disease and regeneration

Cardiomyocytes continuously generate the contractile force to circulate blood through the body. Imbalances in contractile performance or energy supply cause adaptive responses of the heart resulting in adverse rearrangement of regular structures, which in turn might lead to heart failure. At the cellular level, cardiomyocyte remodeling includes (1) restructuring of the contractile apparatus; (2) rearrangement of the cytoskeleton; and (3) changes in energy metabolism. Dedifferentiation represents a key feature of cardiomyocyte remodeling. It is characterized by reciprocal changes in the expression pattern of “mature” and “immature” cardiomyocyte-specific genes. Dedifferentiation may enable cardiomyocytes to cope with hypoxic stress by disassembly of the energy demanding contractile machinery and by reduction of the cellular energy demand. Dedifferentiation during myocardial repair might provide cardiomyocytes with additional plasticity, enabling survival under hypoxic conditions and increasing the propensity to enter the cell cycle. Although dedifferentiation of cardiomyocytes has been described during tissue regeneration in zebrafish and newts, little is known about corresponding mechanisms and regulatory circuits in mammals. The recent finding that the cytokine oncostatin M (OSM) is pivotal for cardiomyocyte dedifferentiation and exerts strong protective effects during myocardial infarction highlights the role of cytokines as potent stimulators of cardiac remodeling. Here, we summarize the current knowledge about transient dedifferentiation of cardiomyocytes in the context of myocardial remodeling, and propose a model for the role of OSM in this process.

Oncostatin M Induces FGF23 Expression in Cardiomyocytes

Background: It is well-known that elevated levels of Fibroblast Growth Factor-23 (FGF23), a bone derived hormone, in circulation are associated with renal failure. Recent studies emphasize the correlation between Heart Failure (HF) and FGF23, but the ability of cardiomyocytes themselves to express and secrete this phosphatonin is yet unknown. A further factor involved in HF is the cytokine oncostatin M (OSM). The aims of our study were: 1) to analyze the myocardium of HF patients in terms of FGF23 expression in cardiomyocytes and 2) to assess whether OSM is able to induce FGF23 production in cardiomyocytes. Methods: Cultures of adult cardiomyocytes were treated with OSM and screened for the expression of FGF23 transcripts. FGF23 secretion was determined by Western blot and ELISA of cell culture supernatants. Heart explants of HF patients with Dilated Cardiomyopathy (DCM), Ischemic Cardiomyopathy (ICM) and myocarditis (Myo) were analyzed by immunofluorescence using FGF23 antibodies and compared with healthy controls. FGF23 levels were also determined in mice with a cardiac restricted overexpression of Monocyte Chemotactic Protein-1 (MCP1), which developed an “inflammatory” Heart Failure (iHF) due to macrophage infiltration. Results: OSM massively induced the expression and secretion of FGF23 in cultured adult cardiomyocytes. Confocal microscopy revealed high amounts of FGF23 positive cardiomyocytes in the myocardium of patients with ischemic heart disease (IHD), myocarditis, dilated cardiomyopathy (DCM) and in mice with iHF. Conclusions: The presence of FGF23 in the myocardium of patients with different types of HF and in mice with “inflammatory” HF suggests that macrophages are responsible for the FGF23 expression in cardiomyocytes via OSM. Whether FGF23 acts as a regeneration promoting factor and/or potentially serves as a HF/transplantation marker has to be clarified.

Induction of Smooth Muscle Cell Migration During Arteriogenesis Is Mediated by Rap2

Objective—Collateral artery growth or arteriogenesis is the primary means of the circulatory system to maintain blood flow in the face of major arterial occlusions. Arteriogenesis depends on activation of fibroblast growth factor (FGF) receptors, but relatively little is known about downstream mediators of FGF signaling. Methods and Results—We screened for signaling components that are activated in response to administration of FGF-2 to cultured vascular smooth muscle cells (VSMCs) and detected a significant increase of Rap2 but not of other Ras family members, which corresponded to a strong upregulation of Rap2 and C-Raf in growing collaterals from rabbits with femoral artery occlusion. Small interfering RNAs directed against Rap2 did not affect FGF-2 induced proliferation of VSMC but strongly inhibited their migration. Inhibition of FGF receptor-1 (FGFR1) signaling by infusion of a sulfonic acid polymer or infection with a dominant-negative FGFR1 adenovirus inhibited Rap2 upregulation and collateral vessel growth. Similarly, expression of dominant-negative Rap2 blocked arteriogenesis, whereas constitutive active Rap2 enhanced collateral vessel growth. Conclusion—Rap2 is part of the arteriogenic program and acts downstream of the FGFR1 to stimulate VSMC migration. Specific modulation of Rap2 might be an attractive target to manipulate VSMC migration, which plays a role in numerous pathological processes.

The Janus face of OSM-mediated cardiomyocyte dedifferentiation during cardiac repair and disease.

Dedifferentiation is a common phenomenon among plants but has only been found rarely in vertebrates where it is mostly associated with regenerative responses such as formation of blastemae in amphibians to initiate replacement of lost body parts. Relatively little attention has been paid to dedifferentiation processes in mammals although a decline of differentiated functions and acquisition of immature, embryonic properties is seen in various disease processes. Dedifferentiation of parenchymal cells in mammals might serve multiple purposes including (1) facilitation of tissue regeneration by generation of progenitor-like cells and (2) protection of cells from hypoxia by reduction of ATP consumption due to changes in energy metabolism and/or inactivation of energy-intensive specialized functions. We recently found that an inflammatory cytokine of the interleukin 6 family, oncostatin M (OSM), initiates dedifferentiation of cardiomyocytes both in vitro and in vivo. Interestingly, activation of the OSM signaling pathway protects the heart from acute myocardial ischemia but has a negative impact when continuously activated thereby promoting dilative cardiomyopathy. The strong presence of the OSM receptor on cardiomyocytes and the unique features of the OSM signaling circuit suggest a major role of OSM for cardiac protection and repair. We propose that continuous activation or malfunctions of the cellular dedifferentiation machinery might contribute to different disease conditions.

Mesenchymal stem cells attenuate inflammatory processes in the heart and lung via inhibition of TNF signaling

Mesenchymal stem cells (MSC) have been used to treat different clinical conditions although the mechanisms by which pathogenetic processes are affected are still poorly understood. We have previously analyzed the homing of bone marrow-derived MSC to diseased tissues characterized by a high degree of mononuclear cell infiltration and postulated that MSC might modulate inflammatory responses. Here, we demonstrate that MSC mitigate adverse tissue remodeling, improve organ function, and extend lifespan in a mouse model of inflammatory dilative cardiomyopathy (DCM). Furthermore, MSC attenuate Lipopolysaccharide-induced acute lung injury indicating a general role in the suppression of inflammatory processes. We found that MSC released sTNF-RI, which suppressed activation of the NFκBp65 pathway in cardiomyocytes during DCM in vivo. Substitution of MSC by recombinant soluble TNF-R partially recapitulated the beneficial effects of MSC while knockdown of TNF-R prevented MSC-mediated suppression of the NFκBp65 pathway and improvement of tissue pathology. We conclude that sTNF-RI is a major part of the paracrine machinery by which MSC effect local inflammatory reactions.

Functional Recovery of Chronic Ischemic Myocardium after Surgical Revascularization Correlates with Magnitude of Oxidative Metabolism

Background: The purpose of this study was to validate myocardial microdialysis measurements in patients after myocardial infarction with or without associated postoperative functional recovery in order to develop a highly sensitive tool for real-time in vivo detection of microcellular disorder during cardiac operations. Methods: In 20 patients undergoing coronary artery bypass grafting, microdialysis catheters were implanted into scar or hibernating segments detected by means of magnetic resonance imaging, and into a vital area of the right ventricle (control). Myocardial glucose, lactate and pyruvate were analyzed perioperatively. Myocardial ethanol washout was measured as a sign of recovered local blood flow. Results: After surgical revascularization, improvement of wall motion was found in all hibernating segments compared to the scar segments paralleling an increased glucose delivery to the tissue and increased myocardial tissue flow. The myocardial glucose/lactate ratio and pyruvate also showed significantly higher values. Microdialytic measurements of the viable segments were comparable with those of the right ventricle. Conclusions: Our results indicate that microdialysis measurements parallel magnetic resonance imaging findings in patients with revascularization of chronic ischemic myocardium with dyskinetic segments. The metabolism of those segments is characterized by a significantly increased tissue flow, an increased utilization of glucose and a better oxidative nutrition.

Cardiac biochemical monitoring for the detection of acute myocardial ischemia

Dear Editor: The microdialysis technique allows in vivo sampling and immediate biochemical analysis of interstitial fluid. To our knowledge, the following case is the first to describe in vivo myocardial metabolism in a patient with acute myocardial infarction during and after bypass surgery with lethal complications. A 65-year-old man with acute myocardial infarction received initial but ineffective thrombolysis. Coronary angiogram revealed subtotal stenosis of the right coronary artery and angioplasty led to dissection making necessary surgical rescue intervention. During the operation, a microdialysis catheter was placed directly into the area of infarction and a standard bypass operation was performed uneventfully. Three hours later, the patient developed ventricular fibrillation. Diagnostics showed severe right ventricular infarction. Despite use of an intraaortic balloon pump, NO ventilation, and catecholamine therapy the patient died 9 h postoperatively. The initial ratio of myocardial/systemic (m/s) glucose levels of 0.2 were recorded, indicating profound metabolic disorders of the myocardium (Fig. 1). During surgical intervention, the m/s-glucose ratio rose to 0.95 representing the initial success of the revascularization. Approximately 2 h before the onset of clinical symptoms due to reinfarction, the m/s glucose ratio rapidly declined to 0.3 while clinical symptoms and systemic parameters remained stable. The intramyocardial lactate/pyruvate LP ratio was extremely elevated, up to 800, and constantly decreased during extracorporeal circulation (ECC) before remaining at levels below 20, even during the period of myocardial reinfarction. Microdialysis is already established and clinically used for monitoring. The LP ratio, which describes the myocardial redox state, is accepted as a marker of ischemia [1]. If the tissue is exposed to ischemia the cells take up as much glucose as possible in order to produce adenosine triphosphate (ATP) from the anaerobic part of glycolysis. The decrease in glucose delivery from the capillaries, together with the increase in glucose uptake, leads to a fall in the glucose concentration in the dialysate. The level of glucose is somewhat complicated to interpret as it is affected by changes in the glucose supply to the microdialysis catheter. This supply varies with alterations in local capillary flow

Animal Models and “Omics” Technologies for Identification of Novel Biomarkers and Drug Targets to Prevent Heart Failure

It is now accepted that heart failure (HF) is a complex multifunctional disease rather than simply a hemodynamic dysfunction. Despite its complexity, stressed cardiomyocytes often follow conserved patterns of structural remodelling in order to adapt, survive, and regenerate. When cardiac adaptations cannot cope with mechanical, ischemic, and metabolic loads efficiently or become chronically activated, as, for example, after infection, then the ongoing structural remodelling and dedifferentiation often lead to compromised pump function and patient death. It is, therefore, of major importance to understand key events in the progression from a compensatory left ventricular (LV) systolic dysfunction to a decompensatory LV systolic dysfunction and HF. To achieve this, various animal models in combination with an “omics” toolbox can be used. These approaches will ultimately lead to the identification of an arsenal of biomarkers and therapeutic targets which have the potential to shape the medicine of the future.

Reg proteins direct accumulation of functionally distinct macrophage subsets after myocardial infarction

AimsnMyocardial infarction (MI) causes a massive increase of macrophages in the heart, which serve various non-redundant functions for cardiac repair. The identities of signals controlling recruitment of functionally distinct cardiac macrophages to sites of injury are only partially known. Previous work identified Regenerating islet-derived protein 3 beta (Reg3β) as a novel factor directing macrophages to sites of myocardial injury. Herein, we aim to characterize functionally distinct macrophage subsets and understand the impact of different members of the Reg protein family including Reg3β, Reg3γ, and Reg4 on their accumulation in the infarcted heart.nnnMethods and resultsnWe have determined dynamic changes of three phenotypically distinct tissue macrophage subpopulations in the mouse heart after MI by flow cytometry. RNA sequencing and bioinformatics analysis identified inflammatory gene expression patterns in MHC-IIhi/Ly6Clo and MHC-IIlo/Ly6Clo cardiac tissue macrophages while Ly6Chi cardiac tissue macrophages are characterized by gene activities associated with healing and revascularization of damaged tissue. Loss- and gain-of-function experiments revealed specific roles of Reg proteins for recruitment of cardiac tissue macrophage subpopulations to the site of myocardial injury. We found that expression of Reg3β, Reg3γ, and Reg4 is strongly increased after MI in mouse and human hearts with Reg3β providing the lead, followed by Reg3γ and Reg4. Inactivation of the Reg3β gene prevented the increase of all types of cardiac tissue macrophages shortly after MI whereas local delivery of Reg3β, Reg3γ, and Reg4 selectively stimulated recruitment of MHC-IIhi/Ly6Clo and MHC-IIlo/Ly6Clo but repressed accumulation of Ly6Chi cardiac tissue macrophages.nnnConclusionnWe conclude that distinct cardiac macrophage subpopulations are characterized by substantially different gene expression patterns reflecting their pathophysiological role after MI. We argue that sequential, local production of Reg proteins orchestrates accumulation of macrophage subsets, which seem to act in a parallel or partially overlapping rather than in a successive manner.