William E. Stansfield

Myocardin inhibits cellular proliferation by inhibiting NF-κB(p65)-dependent cell cycle progression

We previously reported the importance of the serum response factor (SRF) cofactor myocardin in controlling muscle gene expression as well as the fundamental role for the inflammatory transcription factor NF-κB in governing cellular fate. Inactivation of myocardin has been implicated in malignant tumor growth. However, the underlying mechanism of myocardin regulation of cellular growth remains unclear. Here we show that NF-κB(p65) represses myocardin activation of cardiac and smooth muscle genes in a CArG-box-dependent manner. Consistent with their functional interaction, p65 directly interacts with myocardin and inhibits the formation of the myocardin/SRF/CArG ternary complex in vitro and in vivo. Conversely, myocardin decreases p65-mediated target gene activation by interfering with p65 DNA binding and abrogates LPS-induced TNF-α expression. Importantly, myocardin inhibits cellular proliferation by interfering with NF-κB-dependent cell-cycle regulation. Cumulatively, these findings identify a function for myocardin as an SRF-independent transcriptional repressor and cell-cycle regulator and provide a molecular mechanism by which interaction between NF-κB and myocardin plays a central role in modulating cellular proliferation and differentiation.

Muscle ring finger 1 mediates cardiac atrophy in vivo

Pathological cardiac hypertrophy, induced by various etiologies such as high blood pressure and aortic stenosis, develops in response to increased afterload and represents a common intermediary in the development of heart failure. Understandably then, the reversal of pathological cardiac hypertrophy is associated with a significant reduction in cardiovascular event risk and represents an important, yet underdeveloped, target of therapeutic research. Recently, we determined that muscle ring finger-1 (MuRF1), a muscle-specific protein, inhibits the development of experimentally induced pathological; cardiac hypertrophy. We now demonstrate that therapeutic cardiac atrophy induced in patients after left ventricular assist device placement is associated with an increase in cardiac MuRF1 expression. This prompted us to investigate the role of MuRF1 in two independent mouse models of cardiac atrophy: 1) cardiac hypertrophy regression after reversal of transaortic constriction (TAC) reversal and 2) dexamethasone-induced atrophy. Using echocardiographic, histological, and gene expression analyses, we found that upon TAC release, cardiac mass and cardiomyocyte cross-sectional areas in MuRF1(-/-) mice decreased approximately 70% less than in wild type mice in the 4 wk after release. This was in striking contrast to wild-type mice, who returned to baseline cardiac mass and cardiomyocyte size within 4 days of TAC release. Despite these differences in atrophic remodeling, the transcriptional activation of cardiac hypertrophy measured by beta-myosin heavy chain, smooth muscle actin, and brain natriuretic peptide was attenuated similarly in both MuRF1(-/-) and wild-type hearts after TAC release. In the second model, MuRF1(-/-) mice also displayed resistance to dexamethasone-induced cardiac atrophy, as determined by echocardiographic analysis. This study demonstrates, for the first time, that MuRF1 is essential for cardiac atrophy in vivo, both in the setting of therapeutic regression of cardiac hypertrophy and dexamethasone-induced atrophy.

Periostin Is a Novel Factor in Cardiac Remodeling After Experimental and Clinical Unloading of the Failing Heart

BACKGROUND Maladaptive left ventricular hypertrophy (LVH) remains a prevalent and highly morbid condition associated with end-stage heart disease. Originally evaluated in the context of bone development, periostin is important in endocardial cushion formation and has recently been implicated in heart failure. Because of its potential role in cardiovascular development, we sought to establish the role of periostin after relief of pressure overload in animal and human models. METHODS Pressure overload induction of LVH was performed by minimally invasive aortic arch banding of C57Bl6 mice. Bands were removed 1 month later to allow regression. Cardiac tissue was procured in paired samples of patients receiving LV assist devices (LVAD), with subsequent reanalysis at the time of explant for transplantation. RESULTS One week after debanding, heart weight/body weight ratios and echocardiography confirmed decreased LV mass relative to hypertrophied animals. Gene and protein expression of periostin was measured by real-time polymerase chain reaction and Western blot, and was similarly decreased compared with LVH mice. Immunohistochemical localization of periostin showed it was exclusively in the extracellular matrix of the myocardium. The decrease in periostin with pressure relief paralleled changes in interstitial fibrosis observed by picrosirius red staining. Corroborating the murine data, periostin expression was significantly reduced after LVAD-afforded pressure relief in patients. CONCLUSIONS Periostin is closely associated with pressure overload-induced LVH and LVH regression in both animal and human models. The magnitude of expression changes and the consistent nature of these changes indicate that periostin may be a mediator of cardiac remodeling.

Regression of pressure-induced left ventricular hypertrophy is characterized by a distinct gene expression profile.

OBJECTIVE Left ventricular hypertrophy is a highly prevalent and robust predictor of cardiovascular morbidity and mortality. Existing studies have finely detailed mechanisms involved with its development, yet clinical translation of these findings remains unsatisfactory. We propose an alternative strategy focusing on mechanisms of left ventricular hypertrophy regression rather than its progression and hypothesize that left ventricular hypertrophy regression is associated with a distinct genomic profile. METHODS Minimally invasive transverse arch banding and debanding (or their respective sham procedures) were performed in C57Bl6 male mice. Left ventricular hypertrophy was assessed physiologically by means of transthoracic echocardiographic analysis, structurally by means of histology, and molecularly by means of real-time polymerase chain reaction. Mouse hearts were genomically analyzed with Agilent (Santa Clara, Calif) mouse 44k developmental gene chips. RESULTS Compared with control animals, animals banded for 28 days had a robust hypertrophic response, as determined by means of heart weight/body weight ratio, histologic analysis, echocardiographic analysis, and fetal gene expression. These parameters were reversed within 1 week of debanding. Whole-genome arrays on left ventricular tissue revealed 288 genes differentially expressed during progression, 265 genes differentially expressed with regression, and only 23 genes shared by both processes. Signaling-related expression patterns were more prevalent with regression rather than the structure-related patterns associated with left ventricular hypertrophy progression. In addition, regressed hearts showed comparatively more changes in energy metabolism and protein production. CONCLUSIONS This study demonstrates an effective model for characterizing left ventricular hypertrophy and reveals that regression is genomically distinct from its development. Further examination of these expression profiles will broaden our understanding of left ventricular hypertrophy and provide a novel therapeutic paradigm focused on promoting regression of left ventricular hypertrophy and not just halting its progression.

MuRF2 regulates PPARγ1 activity to protect against diabetic cardiomyopathy and enhance weight gain induced by a high fat diet.

BackgroundIn diabetes mellitus the morbidity and mortality of cardiovascular disease is increased and represents an important independent mechanism by which heart disease is exacerbated. The pathogenesis of diabetic cardiomyopathy involves the enhanced activation of PPAR transcription factors, including PPARα, and to a lesser degree PPARβ and PPARγ1. How these transcription factors are regulated in the heart is largely unknown. Recent studies have described post-translational ubiquitination of PPARs as ways in which PPAR activity is inhibited in cancer. However, specific mechanisms in the heart have not previously been described. Recent studies have implicated the muscle-specific ubiquitin ligase muscle ring finger-2 (MuRF2) in inhibiting the nuclear transcription factor SRF. Initial studies of MuRF2−/− hearts revealed enhanced PPAR activity, leading to the hypothesis that MuRF2 regulates PPAR activity by post-translational ubiquitination.MethodsMuRF2−/− mice were challenged with a 26-week 60% fat diet designed to simulate obesity-mediated insulin resistance and diabetic cardiomyopathy. Mice were followed by conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1-regulated mRNA expression.ResultsMuRF2 protein levels increase ~20% during the development of diabetic cardiomyopathy induced by high fat diet. Compared to littermate wildtype hearts, MuRF2−/− hearts exhibit an exaggerated diabetic cardiomyopathy, characterized by an early onset systolic dysfunction, larger left ventricular mass, and higher heart weight. MuRF2−/− hearts had significantly increased PPARα- and PPARγ1-regulated gene expression by RT-qPCR, consistent with MuRF2’s regulation of these transcription factors in vivo. Mechanistically, MuRF2 mono-ubiquitinated PPARα and PPARγ1 in vitro, consistent with its non-degradatory role in diabetic cardiomyopathy. However, increasing MuRF2:PPARγ1 (>5:1) beyond physiological levels drove poly-ubiquitin-mediated degradation of PPARγ1 in vitro, indicating large MuRF2 increases may lead to PPAR degradation if found in other disease states.ConclusionsMutations in MuRF2 have been described to contribute to the severity of familial hypertrophic cardiomyopathy. The present study suggests that the lack of MuRF2, as found in these patients, can result in an exaggerated diabetic cardiomyopathy. These studies also identify MuRF2 as the first ubiquitin ligase to regulate cardiac PPARα and PPARγ1 activities in vivo via post-translational modification without degradation.

Inhibitory kappa B kinase-β is a target for specific nuclear factor kappa B-mediated delayed cardioprotection

OBJECTIVE Myocardial ischemia/reperfusion injury remains a vexing problem. Translating experimental strategies that deliver protective agents before the ischemic insult limits clinical applicability. We targeted 2 proteins in the nuclear factor-kappaB pathway, inhibitory kappa B kinase-beta, and 26S cardiac proteasome to determine their cardioprotective effects when delivered during reperfusion. METHODS C57BL/6 mice underwent left anterior descending artery occlusion for 30 minutes. An inhibitory kappa B kinase-beta inhibitor (Compound A), a proteasome inhibitor (PS-519), or vehicle was administered at left anterior descending artery release or 2 hours afterward. Infarct size was analyzed 24 hours later. Pressure-volume loops were performed at 72 hours. Serum and left ventricular tissue were collected 1 hour after injury to examine protein expression by enzyme-linked immunosorbent assay and Western blot. RESULTS Inhibitory kappa B kinase-beta and proteasome inhibition significantly attenuated infarct size and preserved ejection fraction compared with the vehicle groups. When delivered even 2 hours after reperfusion, Compound A, but not PS-519, still decreased infarct size in mice. Finally, when delivered at reperfusion, successful inhibition of phosphorylated-p65 and decreased interleukin-6 and tumor necrosis factor-alpha levels occurred in mice given the inhibitory kappa B kinase-beta inhibitor, but not in mice with proteasome inhibition. CONCLUSION Although inhibitory kappa B kinase-beta and proteasome inhibition at reperfusion attenuated infarct size after acute ischemia/reperfusion, only inhibitory kappa B kinase-beta inhibition provided cardioprotection through specific suppression of nuclear factor-kappaB signaling. This feature of highly targeted nuclear factor-kappaB inhibition might account for its delayed protective effects, providing a clinically relevant option for treating myocardial ischemia/reperfusion associated with unknown periods of ischemia and reperfusion as seen in cardiac surgery and acute coronary syndromes.

Recovery from decompensated heart failure is associated with a distinct, phase-dependent, gene expression profile

BACKGROUND Clinical and experimental studies have traditionally focused on understanding the mechanisms for why a heart fails. We hypothesize that the pathways involved with myocardial recovery are not simply the reverse of those that cause heart failure. However, determining when and how a decompensated heart can recover remains unknown. METHODS Male C57BL/6 mice underwent minimally invasive aortic banding for 3, 4, or 6 wk with or without subsequent band removal for 1 wk (debanding). Physiologic and genomic characterization was performed with intracardiac pressure-volume recordings, rt-PCR, and microarray analysis. RESULTS Heart weight/body weight ratios and PV loops demonstrated a transition from compensated left ventricular hypertrophy to decompensated heart failure between 3 and 4 wk. Pressure-relief afforded by debanding allowed functional recovery and normalization of LVH after both 3 and 4, but not 6 wk of banding. Whole genome microarrays demonstrated 397 genes differentially expressed in recovered hearts, 250 genes differentially expressed in the nonrecoverable (6 wk) hearts, and only 10 genes shared by both processes. In particular, altered expression patterns of apoptotic and metalloproteinase genes correlated with the hearts ability to functionally recover. CONCLUSIONS This clinically-relevant model (1) allows us to temporally and mechanistically characterize the failing heart, (2) demonstrates a unique genomic signature that may predict when a failing heart can recover following pressure relief, and (3) will prove useful as a template for testing therapeutic strategies aimed at recovery of the failing heart.

Tricuspid Valve Annular Dilation as a Predictor of Right Ventricular Failure After Implantation of a Left Ventricular Assist Device.

Tricuspid annular (TA) dilation has been suggested as a more reliable marker of concomitant advanced right ventricular failure (RVF) than severity of tricuspid regurgitation (TR). Our objective was to examine the impact of TA dilation on occurrence of RVF and in‐hospital mortality following left ventricular assist device (LVAD) implant.

The Pathophysiology of Cardiac Hypertrophy and Heart Failure

Abstract Left ventricular hypertrophy (LVH) is one of the most common cardiovascular diseases; the estimated prevalence is 20% in the general population. In spite of being one of the greatest independent risk factors for cardiovascular morbidity and mortality, it remains essentially untreated. In this chapter, we review the complex interplay of physiologic systems that give rise to pathologic hypertrophy and heart failure. We explore the hierarchy of intra- and intercellular signaling systems that converge to produce the hypertrophic phenotype. Lastly, we consider novel access points within these systems that may represent new therapeutic windows for pharmacologic intervention.

Pulmonary and atrial resection and reconstruction for sarcoma with intracardiac extension

From the Divisions of Thoracic Surgery and Cardiac Surgery, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada. K.H. is supported by a fellowship grant from the Mitsukoshi Health, Welfare Foundation, Tokyo, Japan, and the Ishidsu Shun Memorial Scholarship, Tokyo. Read at the American Association of Thoracic Surgery 2015 Focus on Thoracic Surgery: Technical Challenges and Complication, Boston, Massachusetts, October 23-24, 2015. Disclosures: Authors have nothing to disclose with regard to commercial support. Received for publication Aug 1, 2016; revisions received Nov 15, 2016; accepted for publication Dec 4, 2016; available ahead of print Jan 12, 2017. Address for reprints: Shaf Keshavjee,MD, Division of Thoracic Surgery, Toronto General Hospital, 190 Elizabeth St, RFE 1-408, Toronto, Ontario M5G 2C4, Canada (E-mail: Shaf.Keshavjee@uhn.ca). J Thorac Cardiovasc Surg 2017;153:e61-3 0022-5223/