Neutrophils are indispensable for adverse cardiac remodeling in heart failure.

Persistent immune activation contributes significantly to left ventricular (LV) dysfunction and adverse remodeling in heart failure (HF). In contrast to their well-known essential role in acute myocardial infarction (MI) as first responders that clear dead cells and facilitate subsequent reparative macrophage polarization, the role of neutrophils in the pathobiology of chronic ischemic HF is poorly defined. To determine the importance of neutrophils in the progression of ischemic cardiomyopathy, we measured their production, levels, and activation in a mouse model of chronic HF 8 weeks after permanent coronary artery ligation and large MI. In HF mice, neutrophils were more abundant both locally in failing myocardium (more in the border zone) and systemically in the blood, spleen, and bone marrow, together with increased BM granulopoiesis. There were heightened stimuli for neutrophil recruitment and trafficking in HF, with increased myocardial expression of the neutrophil chemoattract chemokines CXCL1 and CXCL5, and increased neutrophil chemotactic factors in the circulation. HF neutrophil NETotic activity was increased in vitro with coordinate increases in circulating neutrophil extracellular traps (NETs) in vivo. Neutrophil depletion with either antibody-based or genetic approaches abrogated the progression of LV remodeling and fibrosis at both intermediate and late stages of HF. Moreover, analogous to murine HF, the plasma milieu in human acute decompensated HF strongly promoted neutrophil trafficking. Collectively, these results support a key tissue-injurious role for neutrophils and their associated cytotoxic products in ischemic cardiomyopathy and suggest that neutrophils are potential targets for therapeutic immunomodulation in this disease.

Cardiac Mesenchymal Stem Cells Promote Fibrosis and Remodeling in Heart Failure: Role of PDGF Signaling.

Heart failure (HF) is characterized by progressive fibrosis. Both fibroblasts and mesenchymal stem cells (MSCs) can differentiate into pro-fibrotic myofibroblasts. MSCs secrete and express platelet-derived growth factor (PDGF) and its receptors. We hypothesized that PDGF signaling in cardiac MSCs (cMSCs) promotes their myofibroblast differentiation and aggravates post-myocardial infarction left ventricular remodeling and fibrosis. We show that cMSCs from failing hearts post-myocardial infarction exhibit an altered phenotype. Inhibition of PDGF signaling in vitro inhibited cMSC-myofibroblast differentiation, whereas in vivo inhibition during established ischemic HF alleviated left ventricular remodeling and function, and decreased myocardial fibrosis, hypertrophy, and inflammation. Modulating cMSC PDGF receptor expression may thus represent a novel approach to limit pathologic cardiac fibrosis in HF.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice.

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-ß1 (TGF-ß1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-ß1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-ß1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-ß1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-ß1 and mitochondrial associated redox signaling.

Reduction of myocardial infarct size by doxycycline: a role for plasmin inhibition.

Myocardial ischemia-reperfusion (I/R) is associated with the activation of matrix metalloproteinases (MMPs) and serine proteases. We hypothesized that activation of MMPs and the serine protease plasmin contribute to early cardiac myocyte death following I/R and that broad-spectrum protease inhibition with doxycycline (DOX) preserves myocyte viability. Rats treated daily with or without DOX beginning 48 h prior to experimentation were subjected to 30 min of coronary occlusion and 2 days of reperfusion. DOX pre-treatment reduced infarct size by 37%. DOX attenuated increases in MMP-9 and plasmin levels as determined by gelatin zymography and immunoblot, respectively. Neutrophil extravasation was unaltered by DOX as assessed by myeloperoxidase (MPO) activity. To examine the contribution of MMP-9 and plasmin to myocyte injury, cultures of neonatal rat ventricular myocytes (NRVMs) were treated for 48 h with 83 kDa MMP-9 or plasminogen in the presence or absence of DOX. MMP-9 treatment did not affect myocyte viability. Plasminogen treatment led to increased plasmin activity, resulting in loss of beta1-integrin, NRVM detachment and apoptosis. DOX co-treatment inhibited plasmin activity and preserved NRVM attachment, whereas co-treatment with the broad-spectrum MMP inhibitor GM6001 had no effect. These results indicate that plasmin causes disruption of myocyte attachment and viability independently of MMP activation in vitro and that inhibition of plasmin by DOX may reduce I/R-induced myocyte death in vivo through the inhibition of plasmin.