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-β1 (TGF-β1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-β1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-β1-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-β1-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-β1 and mitochondrial associated redox signaling.

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.

No abstract

Chronic inflammation contributes significantly to disease progression in heart failure (HF), and is characterized by expansion of activated macrophages, dendritic cells, and T cells in the failing heart. Neutrophils play a well-known role as the initial drivers of inflammatory response to myocardial infarction (MI), thereby providing the platform for the subsequent recruitment of macrophages and T cells. However, whether and how neutrophils contribute to inflammation and adverse LV remodeling in chronic HF are unknown. We tested the hypothesis that activated neutrophils are required for tissue remodeling and disease progression in HF. Male C57Bl/6 mice were studied 4 and 8 weeks after left coronary artery ligation during established ischemic HF (sham-operated controls). As assessed by flow cytometry, CD11b + Ly6G + neutrophils were expanded in the peripheral blood (4 w post-MI), and in the bone marrow, spleen, and heart at 8 w post-MI. Immunostaining revealed that in the failing heart, neutrophils were primarily localized to the MI border zone, but also augmented in remote zone myocardium. CXCL1 and CXCL5 chemokine expression was increased in the failing heart, consistent with chemotactic signals for myocardial neutrophil recruitment. Isolated naïve neutrophils also exhibited increased chemotaxis in response to plasma from HF mice (versus plasma from naïve mice), as assessed by time-lapse video microscopy. Moreover, blood neutrophils isolated from HF mice exhibited significantly increased neutrophil extracellular trap (NET) production as compared to control neutrophils, whereas plasma NETs (histone-DNA complexes) were increased in HF mice. Finally, the in vivo role of neutrophils in chronic HF (8 w post-MI) was determined via depletion studies using genetic (Ly6G-diptheria toxin receptor mice) and antibody (1A8) based approaches. In both models, 2 and 4 w of neutrophil depletion, respectively, significantly improved LV systolic function and reduced end systolic volume. 1A8 treated HF mice also exhibited reduced remote zone fibrosis. We conclude: neutrophil expansion and activation are important components of the chronic inflammatory response in HF, and play an obligatory role in the progression of LV remodeling in ischemic cardiomyopathy.

No abstract