Rationale The role of mononuclear phagocytes in chronic heart failure (HF) is unknown. Objective Our aim was to delineate monocyte, macrophage, and dendritic cell trafficking in HF and define the contribution of the spleen to cardiac remodeling. Methods and Results We evaluated C57Bl/6 mice with chronic HF 8 weeks after coronary ligation. As compared with sham-operated controls, HF mice exhibited: (1) increased proinflammatory CD11b+F4/80+CD206− macrophages and CD11b+F4/80+Gr-1hi monocytes in the heart and peripheral blood, respectively, and reduced CD11b+F4/80+Gr-1hi monocytes in the spleen; (2) significantly increased CD11c+B220− classical dendritic cells and CD11c+/lowB220+ plasmacytoid dendritic cells in both the heart and spleen, and increased classic dendritic cells and plasmacytoid dendritic cells in peripheral blood and bone marrow, respectively; (3) increased CD4+ helper and CD8+ cytotoxic T-cells in the spleen; and (4) profound splenic remodeling with abundant white pulp follicles, markedly increased size of the marginal zone and germinal centers, and increased expression of alarmins. Splenectomy in mice with established HF reversed pathological cardiac remodeling and inflammation. Splenocytes adoptively transferred from mice with HF, but not from sham-operated mice, homed to the heart and induced long-term left ventricular dilatation, dysfunction, and fibrosis in naive recipients. Recipient mice also exhibited monocyte activation and splenic remodeling similar to HF mice. Conclusions Activation of mononuclear phagocytes is central to the progression of cardiac remodeling in HF, and heightened antigen processing in the spleen plays a critical role in this process. Splenocytes (presumably splenic monocytes and dendritic cells) promote immune-mediated injurious responses in the failing heart and retain this memory on adoptive transfer.

Background Inappropriately sustained inflammation is a hallmark of chronic ischemic heart failure (HF); however, the pathophysiological role of T-lymphocytes is unclear. Methods and Results Permanent coronary ligation was performed in adult C57BL/6 mice. As compared with sham-operated mice, mice with HF (8 w after ligation) exhibited the following features: 1) significant (p<0.05) expansion of circulating CD3+CD8+ cytotoxic and CD3+CD4+ helper (Th) T-lymphocytes, together with increased Th1, Th2, Th17, and regulatory T-cell (Treg) CD4+ subsets; 2) significant expansion of CD8+ and CD4+ T-cells in failing myocardium, with increased Th1, Th2, Th17, and Treg CD4+ subsets, marked reduction of the Th1/Th2 ratio, augmentation of the Th17/Treg ratio, and upregulation of Th2 cytokines; and 3) significantly increased Th1, Th2, Th17 cells, and Tregs, in the spleen and mediastinal lymph nodes, with increased expansion of splenic antigen-experienced effector and memory CD4+ T cells. Antibody-mediated CD4+ T-cell depletion in HF mice (starting 4 w after ligation) reduced cardiac infiltration of CD4+ T-cells and prevented progressive LV dilatation and hypertrophy whereas adoptive transfer of splenic CD4+ T-cells (and, to a lesser extent, cardiac CD3+ T-cells) from donor mice with HF induced long-term LV dysfunction, fibrosis, and hypertrophy in naïve recipient mice. Conclusions CD4+ T-lymphocytes are globally expanded and activated in chronic ischemic HF, with Th2 (vs Th1) and Th17 (vs Treg) predominance in failing hearts, and with expansion of memory T-cells in the spleen. Cardiac and splenic T-cells in HF are primed to induce cardiac injury and remodeling, and retain this memory upon adoptive transfer.

Visual Abstract

Background. Heart failure (HF) is a state of inappropriately sustained inflammation, suggesting the loss of normal immunosuppressive mechanisms. Regulatory T-lymphocytes (Tregs) are considered key suppressors of immune responses; however, their role in HF is unknown. We hypothesized that Tregs are dysfunctional in ischemic cardiomyopathy and HF, and promote immune activation and left ventricular (LV) remodeling. Methods. Adult male wild-type (WT) C57BL/6 mice, Foxp3-diptheria toxin receptor(DTR) transgenic mice, and tumor necrosis factor(TNF)α receptor-1(TNFR1)−/− mice underwent non-reperfused myocardial infarction (MI) to induce HF, or sham operation. LV remodeling was assessed by echocardiography, and histological and molecular phenotyping. Alterations in Treg profile and function were examined by flow cytometry, immunostaining, and in vitro cell assays. Results. As compared with WT sham mice, CD4+Foxp3+ Tregs in WT HF mice robustly expanded in the heart, circulation, spleen, and lymph nodes in a phasic manner after MI, beyond the early phase of wound healing, and exhibited pro-inflammatory Th1-type features with interferon-γ, TNFα, and TNFR1 expression, loss of immunomodulatory capacity, heightened proliferation, and potentiated anti-angiogenic and pro-fibrotic properties. Selective Treg ablation in Foxp3-DTR mice with ischemic cardiomyopathy reversed LV remodeling and dysfunction, alleviating hypertrophy and fibrosis, while suppressing circulating CD4+ T-cells and systemic inflammation, and enhancing tissue neovascularization. Importantly, Tregs reconstituted after ablation exhibited restoration of immunosuppressive capacity and normalized TNFR1 expression. Treg dysfunction was also tightly coupled to Treg-endothelial cell contact- and TNFR1-dependent inhibition of angiogenesis, and the mobilization and tissue infiltration of CD34+Flk1+ circulating angiogenic cells in a CCL5/CCR5-dependent manner. Anti-CD25-mediated Treg depletion in WT mice imparted similar benefits on LV remodeling, CACs, and tissue neovascularization. Conclusions. Pro-inflammatory and anti-angiogenic Tregs play an essential pathogenetic role in chronic ischemic HF to promote immune activation and pathological LV remodeling. The restoration of normal Treg function may be a viable approach to therapeutic immunomodulation in this disease.

Environmental triggers of dilated cardiomyopathy are poorly understood. Acute exposure to acrolein, a ubiquitous aldehyde pollutant, impairs cardiac function and cardioprotective responses in mice. Here, we tested the hypothesis that chronic oral exposure to acrolein induces inflammation and cardiomyopathy. C57BL/6 mice were gavage-fed acrolein (1 mg/kg) or water (vehicle) daily for 48 days. The dose was chosen based on estimates of human daily unsaturated aldehyde consumption. Compared with vehicle-fed mice, acrolein-fed mice exhibited significant (P < 0.05) left ventricular (LV) dilatation (LV end-diastolic volume 36 ± 8 vs. 17 ± 5 μl), contractile dysfunction (dP/dt(max) 4,697 ± 1,498 vs. 7,016 ± 1,757 mmHg/s), and impaired relaxation (tau 15.4 ± 4.3 vs. 10.4 ± 2.2 ms). Histological and biochemical evaluation revealed myocardial oxidative stress (membrane-localized protein-4-hydroxy-trans-2-nonenal adducts) and nitrative stress (increased protein-nitrotyrosine) and varying degrees of plasma and myocardial protein-acrolein adduct formation indicative of physical translocation of ingested acrolein to the heart. Acrolein also induced myocyte hypertrophy (~2.2-fold increased myocyte area, P < 0.05), increased apoptosis (~7.5-fold), and disrupted endothelial nitric oxide synthase in the heart. DNA binding studies, immunohistochemistry, and PCR revealed significant (P < 0.05) activation of nuclear factor-κB in acrolein-exposed hearts, along with upregulated gene expression of proinflammatory cytokines tumor necrosis factor-α and interleukin-1β. Long-term oral exposure to acrolein, at an amount within the range of human unsaturated aldehyde intake, induces a phenotype of dilated cardiomyopathy in the mouse. Human exposure to acrolein may have analogous effects and raise consideration of an environmental, aldehyde-mediated basis for heart failure.

Physiological heart development and cardiac function rely on the response of cardiac cells to mechanical stress during hemodynamic loading and unloading. These stresses, especially if sustained, can induce changes in cell structure, contractile function, and gene expression. Current cell culture techniques commonly fail to adequately replicate physical loading observed in the native heart. Therefore, there is a need for physiologically relevant in vitro models that recreate mechanical loading conditions seen in both normal and pathological conditions. To fulfill this need, we have developed a microfluidic cardiac cell culture model (μCCCM) that for the first time allows in vitro hemodynamic stimulation of cardiomyocytes by directly coupling cell structure and function with fluid induced loading. Cells are cultured in a small (1 cm diameter) cell culture chamber on a thin flexible silicone membrane. Integrating the cell culture chamber with a pump, collapsible pulsatile valve and an adjustable resistance element (hemostatic valve) in series allow replication of various loading conditions experienced in the heart. This paper details the design, modeling, fabrication and characterization of fluid flow, pressure and stretch generated at various frequencies to mimic hemodynamic conditions associated with the normal and failing heart. Proof-of-concept studies demonstrate successful culture of an embryonic cardiomyoblast line (H9c2 cells) and establishment of an in vivo like phenotype within this system.

BackgroundAlthough cardiac and splenic mononuclear phagocytes (MPs), i.e., monocytes, macrophages and dendritic cells (DCs), are key contributors to cardiac remodeling after myocardial infarction, their role in pressure-overload remodeling is unclear. We tested the hypothesis that these immune cells are required for the progression of remodeling in pressure-overload heart failure (HF), and that MP depletion would ameliorate remodeling.Methods and ResultsC57BL/6 mice were subjected to transverse aortic constriction (TAC) or sham operation, and assessed for alterations in MPs. As compared with sham, TAC mice exhibited expansion of circulating LyC6hi monocytes and pro-inflammatory CD206− cardiac macrophages early (1 w) after pressure-overload, prior to significant hypertrophy and systolic dysfunction, with subsequent resolution during chronic HF. In contrast, classical DCs were expanded in the heart in a biphasic manner, with peaks both early, analogous to macrophages, and late (8 w), during established HF. There was no significant expansion of circulating DCs, or Ly6C+ monocytes and DCs in the spleen. Periodic systemic MP depletion from 2 to 16 w after TAC in macrophage Fas-induced apoptosis (MaFIA) transgenic mice did not alter cardiac remodeling progression, nor did splenectomy in mice with established HF after TAC. Lastly, adoptive transfer of splenocytes from TAC HF mice into naïve recipients did not induce immediate or long-term cardiac dysfunction in recipient mice.ConclusionsMononuclear phagocytes populations expand in a phasic manner in the heart during pressure-overload. However, they are dispensable for the progression of remodeling and failure once significant hypertrophy is evident and blood monocytosis has normalized.

In the failing heart, iNOS is expressed by both macrophages and cardiomyocytes. We hypothesized that inflammatory cell-localized iNOS exacerbates left ventricular (LV) remodeling. Wild-type (WT) C57BL/6 mice underwent total body irradiation and reconstitution with bone marrow from iNOS−/− mice (iNOS−/−c) or WT mice (WTc). Chi-meric mice underwent coronary ligation to induce large infarction and ischemic heart failure (HF), or sham surgery. After 28 days, as compared with WTc sham mice, WTc HF mice exhibited significant (p < 0.05) mortality, LV dysfunction, hypertrophy, fibrosis, oxidative/nitrative stress, inflammatory activation, and iNOS upregulation. These mice also exhibited a ∼twofold increase in circulating Ly6Chi pro-inflammatory monocytes, and ∼sevenfold higher cardiac M1 macrophages, which were primarily CCR2– cells. In contrast, as compared with WTc HF mice, iNOS−/− c HF mice exhibited significantly improved survival, LV function, hypertrophy, fibrosis, oxidative/nitrative stress, and inflammatory activation, without differences in overall cardiac iNOS expression. Moreover, iNOS−/−c HF mice exhibited lower circulating Ly6Chi monocytes, and augmented cardiac M2 macrophages, but with greater infiltrating monocyte-derived CCR2+ macrophages vs. WTc HF mice. Lastly, upon cell-to-cell contact with naïve cardiomyocytes, peritoneal macrophages from WT HF mice depressed contraction, and augmented cardiomy-ocyte oxygen free radicals and peroxynitrite. These effects were not observed upon contact with macrophages from iNOS−/− HF mice. We conclude that leukocyte iNOS is obligatory for local and systemic inflammatory activation and cardiac remodeling in ischemic HF. Activated macrophages in HF may directly induce cardiomyocyte contractile dysfunction and oxidant stress upon cell-to-cell contact; this juxtacrine response requires macrophage-localized iNOS.