Jochen Pöling

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.

Myocardial healing requires Reg3β-dependent accumulation of macrophages in the ischemic heart

Cardiac healing after myocardial ischemia depends on the recruitment and local expansion of myeloid cells, particularly macrophages. Here we identify Reg3β as an essential regulator of macrophage trafficking to the damaged heart. Using mass spectrometry–based secretome analysis, we found that dedifferentiating cardiomyocytes release Reg3β in response to the cytokine OSM, which signals through Jak1 and Stat3. Loss of Reg3β led to a large decrease in the number of macrophages in the ischemic heart, accompanied by increased ventricular dilatation and insufficient removal of neutrophils. This defect in neutrophil removal in turn caused enhanced matrix degradation, delayed collagen deposition and increased susceptibility to cardiac rupture. Our data indicate that OSM, acting through distinct intracellular pathways, regulates both cardiomyocyte dedifferentiation and cardiomyocyte-dependent regulation of macrophage trafficking. Release of OSM from infiltrating neutrophils and macrophages initiates a positive feedback loop in which OSM-induced production of Reg3β in cardiomyocytes attracts additional OSM-secreting macrophages. The activity of the feedback loop controls the degree of macrophage accumulation in the heart, which is instrumental in myocardial healing.

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.

Therapeutic targeting of the oncostatin M receptor-β prevents inflammatory heart failure

Abstract Heart failure (HF) is a common and potentially deadly condition, which frequently develops as a consequence of various diseases of the heart. The incidence of heart failure continuously increases in aging societies illustrating the need for new therapeutic approaches. We recently discovered that continuous activation of oncostatin M (OSM), a cytokine of the interleukin-6 family that induces dedifferentiation of cardiomyocytes, promotes progression of heart failure in dilative cardiomyopathy. To evaluate whether inhibition of OSM signaling represents a meaningful therapeutic approach to prevent heart failure we attenuated OSM-receptor (Oβ) signaling in a mouse model of inflammatory dilative cardiomyopathy. We found that administration of an antibody directed against the extracellular domain of Oβ or genetic inactivation of a single allele of the Oβ gene reduced cardiomyocyte remodeling and dedifferentiation resulting in improved cardiac performance and increased survival. We conclude that pharmacological attenuation of long-lasting Oβ signaling is a promising strategy to treat different types and stages of HF that go along with infiltration by OSM-releasing inflammatory cells.

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.

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.

Hyperacute rejection in ex vivo-perfused porcine lungs transgenic for human complement regulatory proteins

Inhibition of complement activation via human membrane‐associated complement regulators is known to prevent hyperacute rejection in heart and kidney pig‐to‐primate transplantation. The protective effect of such strategies in pulmonary xenografts, however, seems to be insufficient. In an ex vivo perfusion, model lungs from donor pigs transgenic for human CD55 (n = 6) or human CD59 (n = 5) were perfused with fresh human blood and compared with nontransgenic organs (n = 6). In addition, a soluble complement component 1 esterase inhibitor (C1‐Inh) was applied in h‐CD55 transgenic lungs (n = 3). In the h‐CD55 transgenic group, survival was prolonged (P < 0.05), quality and maximal time of oxygenation significantly improved and pulmonary vascular resistance reduced compared with the control group. There was a decreased sequestration of platelets, less parenchymal injury and reduced deposition of C5b−9 in the h‐CD55 transgenic group. Additional soluble complement inhibition (C1‐Inh) did not prolong survival of h‐CD55 transgenic lungs. Survival and pulmonary function in lungs expressing h‐CD59 was not significantly different from parameters observed in nontransgenic lungs. In this ex vivo model of pig‐to‐primate lung transplantation, membrane‐based complement inhibition resulted in significantly improved pulmonary function. However, minor histopathological injuries observed in these transgenic xenografts suggested only partial protection from pulmonary dysfunction by complement inhibition alone.

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.

Analysis of the myocardial metabolism by microdialysis during open beating heart surgery

Objectives. Microdialysis allows the in vivo biochemical analysis of interstitial fluids. Our aim was to reveal in vivo reliable data of the myocardium during open beating heart surgery. Design. In ten patients undergoing routine beating coronary artery bypass grafting a microdialysis catheter was inserted into the left ventricle. Measurements were performed up to 45 min after anastomosis. Data were retrospectively compared with standard on-pump procedures. Results. The myocardial lactate remained stable during anastomosis, followed by a significant decrease of lactate after revascularisation. Myocardial glucose levels showed a slight decrease, followed by a significant increase after revascularisation. Myocardial purines showed a slight increase during anastomosis, followed by a sharp decrease during reperfusion period. Conclusions. In contrast to on-pump procedures myocardial lactate and purines showed less increasing trend during the ischemic period, while myocardial glucose remained stable as a sign of preserved tissue blood flow. Myocardial microdialysis showed different values compared to the elective on-pump CABG and previous animal studies. This technique allows bedside monitoring of biochemical changes, suggesting its possible role as a clinical monitoring tool.