SUMMARY The heart has the ability to grow in size in response to exercise, but little is known about the transcriptional mechanisms underlying physiological hypertrophy. Adult cardiomyocytes have also recently been proven to hold the potential for proliferation, a process which could be of great importance for regenerative medicine. Using a unique RT-PCR based screen against all transcriptional components, we showed that C/EBPβ was down-regulated with exercise, while the expression of CITED4 was increased. Reduction of C/EBPβ in vitro and in vivo resulted in a phenocopy of endurance exercise with cardiomyocyte hypertrophy and proliferation. This proliferation was mediated, at least in part by the increased CITED4. Importantly, mice with reduced cardiac C/EBPβ levels displayed substantial resistance to cardiac failure upon pressure overload. These data indicate that C/EBPβ represses cardiomyocyte growth and proliferation in the adult mammalian heart and that reduction in C/EBPβ is a central signal in physiologic hypertrophy and proliferation.

Increased numbers of T lymphocytes are observed in the lungs of patients with chronic obstructive pulmonary disease, but their role in the disease process is not known. We investigated the role of CD8+ T cells in inflammatory cell recruitment and lung destruction in a cigarette smoke-induced murine model of emphysema. In contrast to wild-type C57BL/6J mice that displayed macrophage, lymphocyte, and neutrophil recruitment to the lung followed by emphysema in response to cigarette smoke, CD8+ T cell-deficient (CD8−/−) mice had a blunted inflammatory response and did not develop emphysema when exposed to long-term cigarette smoke. Further studies supported a pathogenetic pathway whereby the CD8+ T cell product, IFN-γ-inducible protein-10, induces production of macrophage elastase (matrix metalloproteinase 12) that degrades elastin, both causing lung destruction directly and generating elastin fragments that serve as monocyte chemokines augmenting macrophage-mediated lung destruction. These studies demonstrate a requirement for CD8+ T cells for the development of cigarette smoke-induced emphysema and they provide a unifying pathway whereby CD8+ T cells are a central regulator of the inflammatory network in chronic obstructive pulmonary disease.

Background Heart failure is a growing cause of morbidity and mortality. Cardiac PI3-kinase signaling promotes cardiomyocyte survival and function but is paradoxically activated in heart failure, suggesting chronic activation of this pathway may become maladaptive. Here we investigated the downstream PI3-kinase effector, SGK1 (serum- and glucocorticoid-regulated kinase-1), in heart failure and its complications. Methods and Results We found that cardiac SGK1 is activated in human and murine heart failure. We investigated the role of SGK1 in the heart using cardiac-specific expression of constitutively-active or dominant-negative SGK1. Cardiac-specific activation of SGK1 in mice increased mortality, cardiac dysfunction, and ventricular arrhythmias. The pro-arrhythmic effects of SGK1 were linked to biochemical and functional changes in the cardiac sodium channel and could be reversed by treatment with ranolazine, a blocker of the late sodium current. Conversely, cardiac-specific inhibition of SGK1 protected mice after hemodynamic stress from fibrosis, heart failure, and sodium channel alterations. Conclusions SGK1 appears both necessary and sufficient for key features of adverse ventricular remodeling and may provide a novel therapeutic target in cardiac disease.

Activin type II receptor (ActRII) ligands have been implicated in muscle wasting in aging and disease. However, the role of these ligands and ActRII signaling in the heart remains unclear. Here, we investigated this catabolic pathway in human aging and heart failure (HF) using circulating follistatin-like 3 (FSTL3) as a potential indicator of systemic ActRII activity. FSTL3 is a downstream regulator of ActRII signaling, whose expression is up-regulated by the major ActRII ligands, activin A, circulating growth differentiation factor-8 (GDF8), and GDF11. In humans, we found that circulating FSTL3 increased with aging, frailty, and HF severity, correlating with an increase in circulating activins. In mice, increasing circulating activin A increased cardiac ActRII signaling and FSTL3 expression, as well as impaired cardiac function. Conversely, ActRII blockade with either clinical-stage inhibitors or genetic ablation reduced cardiac ActRII signaling while restoring or preserving cardiac function in multiple models of HF induced by aging, sarcomere mutation, or pressure overload. Using unbiased RNA sequencing, we show that activin A, GDF8, and GDF11 all induce a similar pathologic profile associated with up-regulation of the proteasome pathway in mammalian cardiomyocytes. The E3 ubiquitin ligase, Smurf1, was identified as a key downstream effector of activin-mediated ActRII signaling, which increased proteasome-dependent degradation of sarcoplasmic reticulum Ca2+ ATPase (SERCA2a), a critical determinant of cardiomyocyte function. Together, our findings suggest that increased activin/ActRII signaling links aging and HF pathobiology and that targeted inhibition of this catabolic pathway holds promise as a therapeutic strategy for multiple forms of HF.

To determine the role of matrix metalloproteinase-8 (MMP-8) in acute lung injury (ALI), we delivered LPS or bleomycin by the intratracheal route to MMP-8−/− mice versus wild-type (WT) mice or subjected the mice to hyperoxia (95% O2) and measured lung inflammation and injury at intervals. MMP-8−/− mice with ALI had greater increases in lung polymorphonuclear neutrophils (PMNs) and macrophage counts, measures of alveolar capillary barrier injury, lung elastance, and mortality than WT mice with ALI. Bronchoalveolar lavage fluid (BALF) from LPS-treated MMP-8−/− mice had more MIP-1α than BALF from LPS-treated WT mice, but similar levels of other pro- and anti-inflammatory mediators. MIP-1α−/− mice with ALI had less acute lung inflammation and injury than WT mice with ALI, confirming that MIP-1α promotes acute lung inflammation and injury in mice. Genetically deleting MIP-1α in MMP-8−/− mice reduced the increased lung inflammation and injury and mortality in MMP-8−/− mice with ALI. Soluble MMP-8 cleaved and inactivated MIP-1α in vitro, but membrane-bound MMP-8 on activated PMNs had greater MIP-1α–degrading activity than soluble MMP-8. High levels of membrane-bound MMP-8 were detected on lung PMNs from LPS-treated WT mice, but soluble, active MMP-8 was not detected in BALF samples. Thus, MMP-8 has novel roles in restraining lung inflammation and in limiting alveolar capillary barrier injury during ALI in mice by inactivating MIP-1α. In addition, membrane-bound MMP-8 on activated lung PMNs is likely to be the key bioactive form of the enzyme that limits lung inflammation and alveolar capillary barrier injury during ALI.

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Matrix metalloproteinase-8 (MMP-8) is a potent interstitial collagenase thought to be expressed mainly by PMNs. To determine whether Mmp-8 regulates lung inflammatory or fibrotic responses to bleomycin, we delivered bleomycin by the intratracheal (IT) route to wild type (WT) vs. Mmp-8−/− mice and quantified Mmp-8 expression, and inflammation and fibrosis in the lung samples. Mmp-8 steady-state mRNA and protein levels increase in whole lung and bronchoalveolar lavage samples when WT mice are treated with bleomycin. Activated murine lung fibroblasts express Mmp-8 in vitro. MMP-8 expression is increased in leukocytes in the lungs of patients with idiopathic pulmonary fibrosis compared with control lung samples. Compared with bleomycin-treated WT mice, bleomycin-treated Mmp-8−/− mice have greater lung inflammation, but reduced lung fibrosis. While bleomycin-treated Mmp-8−/− and WT mice have similar lung levels of several pro- and anti-fibrotic mediators (Tgf-β, Il-13, JE, and Ifn-γ), Mmp-8−/− mice have higher lung levels of Ip-10 and Mip-1α. Genetically deleting either Ip-10 or Mip-1α in Mmp-8−/− mice abrogates their lung inflammatory response to bleomycin but reconstitutes their lung fibrotic response to bleomycin. Studies of bleomycin-treated Mmp-8 bone marrow-chimeric mice show that both leukocytes and lung parenchymal cells are sources of pro-fibrotic Mmp-8 during bleomycin-mediated lung fibrosis. Thus, during bleomycin-mediated lung injury, Mmp-8 dampens the lung acute inflammatory response but promotes lung fibrosis by reducing lung levels of Ip-10 and Mip-1α. These data indicate therapeutic strategies to reduce lung levels of MMP-8 may limit fibroproliferative responses to injury in the human lung.

Background Therapeutic options to treat Non-alcoholic steatohepatitis (NASH) are limited. Mineralocorticoid receptor (MR) activation could play a role in hepatic fibrogenesis and its modulation could be beneficial for NASH. Aim To investigate whether eplerenone, a specific MR antagonist, ameliorates liver damage in experimental NASH. Methods C57bl6 mice were fed a choline-deficient-amino-acid–defined (CDAA) diet for 22 weeks with or without eplerenone supplementation. Serum levels of aminotransferases and aldosterone were measured and hepatic steatosis, inflammation, and fibrosis scored histologically. Hepatic triglyceride content (HTC) and hepatic mRNA levels of pro-inflammatory pro-fibrotic, oxidative stress-associated genes and of MR were also assessed. Results CDAA diet effectively induced fibrotic NASH, and increased the hepatic expression of pro-inflammatory, pro-fibrotic and oxidative stress-associated genes. Hepatic MR mRNA levels significantly correlated with the expression of pro-inflammatory and pro-fibrotic genes and were significantly increased in hepatic stellate cells obtained from CDAA-fed animals. Eplerenone administration was associated to a reduction in histological steatosis and attenuation of liver fibrosis development, which was associated to a significant decrease in the expression of collagen-α1, collagen type III, alpha 1 and Matrix metalloproteinase-2. Conclusion The expression of MR correlates with inflammation and fibrosis development in experimental NASH. Specific MR blockade with eplerenone has hepatic anti-steatotic and anti-fibrotic effects. These data identifies eplerenone as a potential novel therapy for NASH. Considering its safety and FDA-approved status, human studies are warranted