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Background: In the past years, several studies investigated how distinct immune cell subsets affects post–myocardial infarction repair. However, whether and how the tissue environment controls these local immune responses has remained poorly understood. We sought to investigate how antigen-specific T-helper cells differentiate under myocardial milieu’s influence. Methods: We used a transgenic T cell receptor (TCR-M) model and major histocompatibility complex-II tetramers, both myosin-specific, combined with single-cell transcriptomics (single-cell RNA sequencing [scRNA-seq]) and functional phenotyping to elucidate how the antigen-specific CD4 + T cells differentiate in the murine infarcted myocardium and influence tissue repair. Additionally, we transferred proinflammatory versus regulatory predifferentiated TCR-M-cells to dissect how they specially contribute to post–myocardial infarction inflammation. Results: Flow cytometry and scRNA-/TCR-seq analyses revealed that transferred TCR-M cells acquired an induced regulatory phenotype (induced regulatory T cell) in the infarcted myocardium and blunted local inflammation. Myocardial TCR-M cells differentiated into 2 main lineages enriched with either cell activation and profibrotic transcripts (eg, Tgfb1 ) or suppressor immune checkpoints (eg, Pdcd1 ), which we also found in human myocardial tissue. These cells produced high levels of LAP (latency-associated peptide) and inhibited IL-17 (interleukin-17) responses. Endogenous myosin-specific T-helper cells, identified using genetically barcoded tetramers, also accumulated in infarcted hearts and exhibited a regulatory phenotype. Notably, TCR-M cells that were predifferentiated toward a regulatory phenotype in vitro maintained stable in vivo FOXP3 (Forkhead box P3) expression and anti-inflammatory activity whereas T H 17 partially converted toward a regulatory phenotype in the injured myocardium. Overall, the myosin-specific Tregs dampened post–myocardial infarction inflammation, suppressed neighboring T cells, and were associated with improved cardiac function. Conclusions: These findings provide novel evidence that the heart and its draining lymph nodes actively shape local immune responses by promoting the differentiation of antigen-specific Tregs poised with suppressive function.

Rationale: Approximately 50% of heart failure patients are diagnosed with Heart Failure with preserved Ejection Fraction (HFpEF), but there are currently no effective treatments. Hypothesis: Treatment of a feline HFpEF animal model with a pan HDAC inhibitor, SAHA, will improve the cardiopulmonary phenotype and mediate changes in the metabolome and skeletal muscle composition. Methods and results: Male domestic short hair cats (n=21, age 2mo) underwent either a sham procedure (n=5) or aortic constriction (n=16) using a customized pre-shaped band causing slow progressive pressure overload during maturation. At 2-months post-banding, banded animals received either daily treatment with 10mg/kg SAHA (b+SAHA) (n=8) or vehicle (b+veh) (n=8) for 2 months. At 4 months post-banding, b+ SAHA animals had significantly reduced LV wall thickness, LA size (LA/Ao), and improved LA function (LA EF) vs. b+ veh animals (fig). Invasive hemodynamics and lung mechanics were performed after 2 months of treatment. Banded animals had significantly increased filling pressures (LVEDP), increased pulmonary arterial pressures (mPAP), decreased lung compliance and arterial oxygenation (A-aDO 2 ). SAHA significantly reduced LVEDP, mPAP, and A-aDO 2 and increased lung compliance (fig). b+SAHA animals had an increase in the percentage of type 1 muscle fibers (increased oxidative capacity) compared to type 2 (fig). Blood-based metabolomics revealed SAHA-induced a metabolic shift towards increased lipolysis and mitochondrial oxidation. Conclusion: Treatment with SAHA improved cardiopulmonary structure and function in banded animals and caused changes in the metabolome and skeletal muscle.

Rationale: Wound healing after myocardial infarction involves a highly regulated inflammatory response that is initiated by the appearance of neutrophils to clear out dead cells and matrix debris. Neutrophil infiltration is controlled by multiple secreted factors, including the master regulator transforming growth factor β (TGFβ). Broad inhibition of TGFβ early postinfarction has worsened post–myocardial infarction remodeling; however, this signaling displays potent cell specificity, and targeted suppression particularly in the myocyte could be beneficial. Objective: Our aims were to test the hypothesis that targeted suppression of myocyte TGFβ signaling ameliorates postinfarct remodeling and inflammatory modulation and to identify mechanisms by which this may be achieved. Methods and Results: Mice with TGFβ receptor–coupled signaling genetically suppressed only in cardiac myocytes (conditional TGFβ receptor 1 or 2 knockout) displayed marked declines in neutrophil recruitment and accompanying metalloproteinase 9 activation after infarction and were protected against early-onset mortality due to wall rupture. This is a cell-specific effect, because broader inhibition of TGFβ signaling led to 100% early mortality due to rupture. Rather than by altering fibrosis or reducing the generation of proinflammatory cytokines/chemokines, myocyte-selective TGFβ inhibition augmented the synthesis of a constellation of highly protective cardiokines. These included thrombospondin 4 with associated endoplasmic reticulum stress responses, interleukin-33, follistatin-like 1, and growth and differentiation factor 15, which is an inhibitor of neutrophil integrin activation and tissue migration. Conclusions: These data reveal a novel role of myocyte TGFβ signaling as a potent regulator of protective cardiokine and neutrophil-mediated infarct remodeling.

As Drs. Villa-Abrille, Perez, and Cingolani correctly point out,1 the behavior whereby cardiac muscle is subjected to abruptly increased systolic load and then manifests a gradual rise in contractility has been recognized for over a century. First credited to Gleb (not Glen) von Anrep,2 its name has morphed over the decades along with the types of experiments used to generate it. The name, slow force response (SFR), has indeed been adapted by many to describe this behavior, but we feel the term is far less universal than the writers suggest, and also believe it obfuscates the mechanistic concepts behind it. What is slow—force or response? What is the response to and what …

Introduction Coronary artery disease is the leading cause of death and myocardial infarction (MI) its most severe manifestation.TGFb is a major switch governing the myocardial response to injury and global inhibition is detrimental following MI. Recently, cell-specific gene manipulation models have enabled investigation of cardiomyocyte (CM) versus non-CM TGFb signaling on maladaptive remodeling. We found CM TGFb to be central to pressure-overload disease. Here, we tested the hypothesis that CM TGFb modifies acute post-MI remodeling, and thus benefits rather than worsens outcome as observed with antibody-based inhibition that primarily targets interstitial/vascular cells. Methods Mice with cardiac-specific conditional knockdown of TgfbR1 or 2 (aMHC - MCM TgfbR fl/fl) or injection of TGFb-neutralizing antibody were subjected to proximal LAD-ligation and followed by echocardiography and continuous ECG monitoring. Expression and activity of the major matrix metalloproteinases MMP2/MMP9 and TIMP1 were assessed by qRT-PCR, immunoblot, and zymography, respectively. Only mice surviving >24h after surgery (>90%) were included in analyses. Results LAD ligation decreased fractional shortening on day 1 to 18±2% (61±1% in sham animals) with no differences between genotypes (n≥8). Similarly, echocardiographic parameters of myocardial dimensions and function did not differ at weeks 1 or 3. Early mortality (day 4 - 10) was strikingly lower in knockdown mice as compared to controls (10% vs 48%, p Conclusion TGFb inhibition exhibits differential effects in wound healing following MI. Where global inhibition is deleterious, CM-targeted knockdown powerfully protects the heart from rupture. This highlights potent cross-talk between the CM TGFb signal and matrix remodeling and the importance of targeted inhibition to benefit cardiac disease.