MicroRNAs (miRNAs) are a class of small noncoding RNAs that have gained status as important regulators of gene expression. Here, we investigated the function and molecular mechanisms of the miR-208 family of miRNAs in adult mouse heart physiology. We found that miR-208a, which is encoded within an intron of α-cardiac muscle myosin heavy chain gene (Myh6), was actually a member of a miRNA family that also included miR-208b, which was determined to be encoded within an intron of β-cardiac muscle myosin heavy chain gene (Myh7). These miRNAs were differentially expressed in the mouse heart, paralleling the expression of their host genes. Transgenic overexpression of miR-208a in the heart was sufficient to induce hypertrophic growth in mice, which resulted in pronounced repression of the miR-208 regulatory targets thyroid hormone-associated protein 1 and myostatin, 2 negative regulators of muscle growth and hypertrophy. Studies of the miR-208a Tg mice indicated that miR-208a expression was sufficient to induce arrhythmias. Furthermore, analysis of mice lacking miR-208a indicated that miR-208a was required for proper cardiac conduction and expression of the cardiac transcription factors homeodomain-only protein and GATA4 and the gap junction protein connexin 40. Together, our studies uncover what we believe are novel miRNA-dependent mechanisms that modulate cardiac hypertrophy and electrical conduction.

Cardiovascular disease is the leading cause of human morbidity and mortality. Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy associated with heart failure. Here, we report that cardiac-specific knockout of Dicer, a gene encoding a RNase III endonuclease essential for microRNA (miRNA) processing, leads to rapidly progressive DCM, heart failure, and postnatal lethality. Dicer mutant mice show misexpression of cardiac contractile proteins and profound sarcomere disarray. Functional analyses indicate significantly reduced heart rates and decreased fractional shortening of Dicer mutant hearts. Consistent with the role of Dicer in animal hearts, Dicer expression was decreased in end-stage human DCM and failing hearts and, most importantly, a significant increase of Dicer expression was observed in those hearts after left ventricle assist devices were inserted to improve cardiac function. Together, our studies demonstrate essential roles for Dicer in cardiac contraction and indicate that miRNAs play critical roles in normal cardiac function and under pathological conditions. cardiac function ͉ microRNA T he heart is the first organ to form and to function during vertebrate embryogenesis (1). Perturbations in normal cardiac development and function result in a variety of cardiovascular diseases, the overall leading cause of death in developed countries (2, 3). Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy, in which the heart becomes weakened and affects the ability of the cardiovascular system to meet the metabolic demands of the body. DCM, characterized by cardiac chamber dilation and systolic impairment, has been associated with mutation of specific contractile proteins and components of stress sensor machinery (2, 4). However, the regulatory events required for appropriate coordination of contractile function are still elusive.MicroRNAs (miRNAs) are a class of recently discovered Ϸ22-nt regulatory RNAs that posttranscriptionally regulate gene expression (5). Despite the large number of miRNAs identified thus far, the biological roles of most miRNAs and the molecular mechanisms underlying their function remain largely unknown. Emerging evidence suggests that miRNAs play important roles in a variety of biological processes, including cancer and stem cell biology (6, 7). Recent studies uncovered the involvement of several musclespecific miRNAs, miR-1, -133, and -208 in particular, in the regulation of cardiac and skeletal muscle gene expression and muscle proliferation and differentiation (8-11). Specifically, gene targeting studies demonstrate that miR-1 and -208 are required for proper cardiac development and/or function (9,10).In this study, we took a global approach to study cardiac miRNAs by deleting Dicer, an endonuclease required for the processing of all miRNAs, in the heart. Here we report that loss of Dicer results in a dramatic decrease in the level of mature miRNAs. All Dicer mutant mice die postnatally due to severe DCM and heart failure.Furthermore, we have ...

Paradigm shifting studies in the mouse have identified tissue macrophage heterogeneity as a critical determinant of immune responses. In contrast, surprisingly little is known regarding macrophage heterogeneity in humans. Macrophages within the mouse heart are partitioned into CCR2- and CCR2+ subsets with divergent origins, repopulation mechanisms, and functions. Here we demonstrate that the human myocardium also contains distinct subsets of CCR2- and CCR2+ macrophages. Analysis of sex mismatched heart transplant recipients revealed that CCR2- macrophages are a tissue-resident population exclusively replenished through local proliferation, whereas CCR2+ macrophages are maintained through monocyte recruitment and proliferation. Moreover, CCR2- and CCR2+ macrophages have distinct functional properties, analogous to reparative CCR2- and inflammatory CCR2+ macrophages in the mouse heart. Clinically, CCR2+ macrophage abundance is associated with LV remodeling and systolic function in heart failure patients. Collectively, these observations provide initial evidence for the functional importance of macrophage heterogeneity in the human heart.

Isolated iliac artery aneurysms can be managed with much lower mortality and morbidity rates than aneurysm previously been reported by using a systematic operative approach. Percutaneous techniques may be less durable and effective than direct surgical repair.

Fibrin is essential for hemostasis; however, abnormal fibrin formation is hypothesized to increase thrombotic risk. We previously showed that in situ thrombin generation on a cell's surface modulates the 3-dimensional structure and stability of the fibrin network. Currently, we compared the abilities of extravascular and intravascular cells to support fibrin formation, structure, and stability. Extravascular cells (fibroblasts, smooth muscle) supported formation of dense fibrin networks that resisted fibrinolysis, whereas unstimulated intravascular (endothelial) cells produced coarse networks that were susceptible to fibrinolysis. All 3 cell types produced a fibrin structural gradient, with a denser network near, versus distal to, the cell surface. Although fibrin structure depended on cellular procoagulant activity, it did not reflect interactions between integrins and fibrin. These findings contrasted with those on platelets, which influenced fibrin structure via interactions between ␤3 integrins and fibrin. Inflammatory cytokines that induced prothrombotic activity on endothelial cells caused the production of abnormally dense fibrin networks that resisted fibrinolysis. Blocking tissue factor activity significantly reduced the density and stability of fibrin networks produced by cytokine-stimulated endothelial cells. Together, these findings indicate fibrin structure and stability reflect the procoagulant phenotype of the endogenous cells, and suggest abnormal fibrin structure is a novel link between inflammation and thrombosis. (Blood. 2009;114:4886-4896)

The incidence of cardiac recovery is higher in patients implanted with an a priori BTR strategy. We developed a simple tool to help identify patients in whom recovery is feasible. In BTR patients with favorable characteristics, I-CARS suggests a 24% probability of successful LVAD explantation. Large-scale studies to better address post-explantation outcomes are warranted.

No abstract

Background: Left ventricular assist device (LVAD) unloading and hemodynamic support in patients with advanced chronic heart failure can result in significant improvement in cardiac function allowing LVAD removal, however the rate of this is generally considered to be low. This prospective multicenter non-randomized study (RESTAGE-HF) investigated whether a protocol of optimized LVAD mechanical unloading, combined with standardized specific pharmacological therapy to induce reverse remodeling and regular testing of underlying myocardial function, could produce a higher incidence of LVAD explantation. Methods: Forty patients with chronic advanced heart failure from non-ischemic cardiomyopathy receiving the Heartmate II LVAD were enrolled from 6 centers. LVAD speed was optimized with an aggressive pharmacological regimen and regular echocardiograms were performed at reduced LVAD speed (6000rpm, no net flow) to test underlying myocardial function. The primary endpoint was the proportion of patients with sufficient improvement of myocardial function to reach criteria for explantation within 18 months with sustained remission from HF (freedom from transplant/VAD/death) at 12 months. Results: Prior to LVAD age was 35.1±10.8 years, 67.5% were male, heart failure mean duration was 20.8±20.6 months, 95% required inotropic and 20% temporary mechanical support, left ventricular ejection fraction (LVEF) was 14.5±5.3%, end-diastolic diameter (LVEDD) 7.33±0.89cm, end-systolic diameter (LVESD) 6.74±0.88cm, PA saturations were 46.7±9.2% and pulmonary capillary wedge pressure (PCWP) was 26.2±7.6mmHg. Four enrolled patients did not undergo the protocol due to medical complications unrelated to the study procedures. Overall 40% of all enrolled (16/40) patients achieved the primary endpoint, p<0.0001, with 50% (18/36) of patients receiving the protocol being explanted within 18 months (pre-explant LVEF 57±8%; LVEDD 4.81±0.58cm; LVESD 3.53±0.51cm; PCWP 8.1±3.1mmHg; PA sats 63.6±6.8% at 6000rpm). Overall 19 patients were explanted (19/36, 52.3% of those receiving the protocol). The fifteen ongoing explanted patients are now 2.26±0.97years post explant. Post-explantation survival free from LVAD or transplantation was 90% at 1-year and 77% at 2 and 3 years. Conclusions: In this multicenter prospective study, this strategy of LVAD support combined with a standardized pharmacologic and cardiac function monitoring protocol resulted in a high rate of LVAD explantation and was feasible and reproducible with explants occurred in all six participating sites.