Exercise Training Alleviates Cardiac Fibrosis through Increasing Fibroblast Growth Factor 21 and Regulating TGF-β1-Smad2/3-MMP2/9 Signaling in Mice with Myocardial Infarction

Exercise training has been reported to alleviate cardiac fibrosis and ameliorate heart dysfunction after myocardial infarction (MI), but the molecular mechanism is still not fully clarified. Fibroblast growth factor 21 (FGF21) exerts a protective effect on the infarcted heart. This study investigates whether exercise training could increase FGF21 protein expression and regulate the transforming growth factor-β1 (TGF-β1)-Smad2/3-MMP2/9 signaling pathway to alleviate cardiac fibrosis following MI. Male wild type (WT) C57BL/6J mice and Fgf21 knockout (Fgf21 KO) mice were used to establish the MI model and subjected to five weeks of different types of exercise training. Both aerobic exercise training (AET) and resistance exercise training (RET) significantly alleviated cardiac dysfunction and fibrosis, up-regulated FGF21 protein expression, inhibited the activation of TGF-β1-Smad2/3-MMP2/9 signaling pathway and collagen production, and meanwhile, enhanced antioxidant capacity and reduced cell apoptosis in the infarcted heart. In contrast, knockout of Fgf21 weakened the cardioprotective effects of AET after MI. In vitro, cardiac fibroblasts (CFs) were isolated from neonatal mice hearts and treated with H2O2 (100 μM, 6 h). Recombinant human FGF21 (rhFGF21, 100 ng/mL, 15 h) and/or 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR, 1 mM, 15 h) inhibited H2O2-induced activation of the TGF-β1-Smad2/3-MMP2/9 signaling pathway, promoted CFs apoptosis and reduced collagen production. In conclusion, exercise training increases FGF21 protein expression, inactivates the TGF-β1-Smad2/3-MMP2/9 signaling pathway, alleviates cardiac fibrosis, oxidative stress, and cell apoptosis, and finally improves cardiac function in mice with MI. FGF21 plays an important role in the anti-fibrosis effect of exercise training.

Cardiomyocytes Cellular Phenotypes After Myocardial Infarction

Despite the increasing success of interventional coronary reperfusion strategies, mortality related to acute myocardial infarction (MI) is still substantial. MI is defined as sudden death of myocardial tissue caused by an ischemic episode. Ischaemia leads to adverse remodelling in the affected myocardium, inducing metabolic and ionic perturbations at a single cell level, ultimately leading to cell death. The adult mammalian heart has limited regenerative capacity to replace lost cells. Identifying and enhancing physiological cardioprotective processes may be a promising therapy for patients with MI. Studies report an increasing amount of evidence stating the intricacy of the pathophysiology of the infarcted heart. Besides apoptosis, other cellular phenotypes have emerged as key players in the ischemic myocardium, in particular senescence, inflammation, and dedifferentiation. Furthermore, some cardiomyocytes in the infarct border zone uncouple from the surviving myocardium and dedifferentiate, while other cells become senescent in response to injury and start to produce a pro-inflammatory secretome. Enhancing electric coupling between cardiomyocytes in the border zone, eliminating senescent cells with senolytic compounds, and upregulating cardioprotective cellular processes like autophagy, may increase the number of functional cardiomyocytes and therefore enhance cardiac contractility. This review describes the different cellular phenotypes and pathways implicated in injury, remodelling, and regeneration of the myocardium after MI. Moreover, we discuss implications of the complex pathophysiological attributes of the infarcted heart in designing new therapeutic strategies.

Abstract MP225: Macrophage-specificα5 Integrin Signaling Protects The Infarcted Heart From Adverse Remodeling By Stimulating The Angiogenic Response

Abundant macrophages infiltrate the infarcted heart and play a critical role in repair, remodeling and fibrosis. Macrophages sense changes in the extracellular matrix (ECM) environment through Integrins, thus activating signaling pathways that regulate their function. Analysis of our RNA sequencing data identified integrin α5 (Itgα5) as one of the most upregulated integrin genes in infarct macrophages. Accordingly, we hypothesized that integrin α5 signaling in infarct macrophages transduces ECM-derived signals, regulating responses critical for repair and remodeling of the infarcted heart.In order to study the role of macrophage α5 integrin in the infarcted heart, we generated 2 lines of macrophage-specific α5 integrin KO mice: myeloid cell-specific KOs (Myα5KO, using the lysozyme-M Cre driver) and inducible macrophage-specific α5 KOs (iMaα5KO, using CX3CR1 CreER ). 28 days after infarction, Myα5KO mice had accentuated adverse remodeling, evidenced by increased LVEDV and LVESV, a trend towards reduced ejection fraction. Adverse remodeling in Mya5KO was associated with a marked reduction in microvascular density in the infarct and in the border zone. iMaα5KO mice also exhibited worse remodeling and impaired infarct angiogenesis. A PCR array in infarct macrophages showed that α5 integrin loss was associated with markedly reduced transcription of VEGF-A, and lower levels of the angiogenic CXC chemokines CXCL1 and CXCL2. RNAseq followed by bioinformatic analysis predicted that that Nrf2, Erk5, HIF1a, p38 MAPK, VEGF, RhoA, and PI3K/Akt pathways were inhibited in the absence of α5 signaling in vivo (in infarct macrophages) and in vitro (in bone marrow macrophages undergoing α5 antibody neutralization experiments).In conclusion, α5 integrin promotes an angiogenic VEGF-expressing phenotype in infarct macrophages, protecting the infarcted heart from adverse remodeling. The angiogenic effects of α5 integrin in macrophages may have important therapeutic implications for heart failure patients.

Local Preirradiation of Infarcted Cardiac Tissue Substantially Enhances Cell Engraftment

The success of cell therapy for the treatment of myocardial infarction depends on finding novel approaches that can substantially implement the engraftment of the transplanted cells. In order to enhance cell engraftment, most studies have focused on the pretreatment of transplantable cells. Here we have considered an alternative approach that involves the preconditioning of infarcted heart tissue to reduce endogenous cell activity and thus provide an advantage to our exogenous cells. This treatment is routinely used in other tissues such as bone marrow and skeletal muscle to improve cell engraftment, but it has never been taken in cardiac tissue. To avoid long-term cardiotoxicity induced by full heart irradiation we developed a rat model of a catheter-based heart irradiation system to locally impact a delimited region of the infarcted cardiac tissue. As proof of concept, we transferred ZsGreen+ iPSCs in the infarcted heart, due to their ease of use and detection. We found a very significant increase in cell engraftment in preirradiated rats. In this study, we demonstrate for the first time that preconditioning the infarcted cardiac tissue with local irradiation can substantially enhance cell engraftment.

Pretreatment of cardiac progenitor cells with bradykinin attenuates H2O2-induced cell apoptosis and improves cardiac function in rats by regulating autophagy

Background Previous studies have demonstrated that human cardiac c-Kit+ progenitor cells (hCPCs) can effectively improve ischemic heart disease. However, the major challenge in applying hCPCs to clinical therapy is the low survival rate of graft hCPCs in the host heart, which limited the benefit of transplanted hCPCs. Bradykinin (BK) is a principal active agent of the tissue kinin-kallikrein system. Our previous studies have highlighted that BK mediated the growth and migration of CPCs by regulating Ca2+ influx. However, the protective effect of BK on CPCs, improvement in the survival rate of BK-pretreated hCPCs in the infarcted heart, and the related mechanism remain elusive. Methods HCPCs were treated with H2O2 to induce cell apoptosis and autophagy, and different concentration of BK was applied to rescue the H2O2-induced injury detected by MTT assay, TUNEL staining, flow cytometry, western blotting, and mitoSOX assays. The role of autophagy in the anti-apoptotic effect of BK was chemically activated or inhibited using the autophagy inducer, rapamycin, or the inhibitor, 3-methyladenine (3-MA). To explore the protective effect of BK on hCPCs, 3-MA or BK-pretreated hCPCs were transplanted into the myocardial infarcted rats. An echocardiogram was used to determine cardiac function, H&E and Masson staining were employed to assess pathological characteristics, HLA gene expression was quantified by qRT-PCR, and immunostaining was applied to examine neovascularization using confocal microscopy. Results The in vitro results showed that BK suppressed H2O2-induced hCPCs apoptosis and ROS production in a concentration-dependent manner by promoting pAkt and Bcl-2 expression and reducing cleaved caspase 3 and Bax expression. Moreover, BK restrained the H2O2-induced cell autophagy by decreasing LC3II/I, Beclin1, and ATG5 expression and increasing P62 expression. In the in vivo experiment, the transplanted BK- or 3-MA-treated hCPCs were found to be more effectively improved cardiac function by decreasing cardiomyocyte apoptosis, inflammatory infiltration, and myocardial fibrosis, and promoting neovascularization in the infarcted heart, compared to untreated-hCPCs or c-kit- cardiomyocytes (CPC- cells). Conclusions Our present study established a new method to rescue transplanted hCPCs in the infarcted cardiac area via regulating cell apoptosis and autophagy of hCPCs by pretreatment with BK, providing a new therapeutic option for heart failure.

The impact of myocardial compressibility on organ-level simulations of the normal and infarcted heart

Myocardial infarction (MI) rapidly impairs cardiac contractile function and instigates maladaptive remodeling leading to heart failure. Patient-specific models are a maturing technology for developing and determining therapeutic modalities for MI that require accurate descriptions of myocardial mechanics. While substantial tissue volume reductions of 15–20% during systole have been reported, myocardium is commonly modeled as incompressible. We developed a myocardial model to simulate experimentally-observed systolic volume reductions in an ovine model of MI. Sheep-specific simulations of the cardiac cycle were performed using both incompressible and compressible tissue material models, and with synchronous or measurement-guided contraction. The compressible tissue model with measurement-guided contraction gave best agreement with experimentally measured reductions in tissue volume at peak systole, ventricular kinematics, and wall thickness changes. The incompressible model predicted myofiber peak contractile stresses approximately double the compressible model (182.8 kPa, 107.4 kPa respectively). Compensatory changes in remaining normal myocardium with MI present required less increase of contractile stress in the compressible model than the incompressible model (32.1%, 53.5%, respectively). The compressible model therefore provided more accurate representation of ventricular kinematics and potentially more realistic computed active contraction levels in the simulated infarcted heart. Our findings suggest that myocardial compressibility should be incorporated into future cardiac models for improved accuracy.