Takotsubo syndrome (TTS) is a conundrum without consensus about the cause. In a murine model of coronary microvascular dysfunction (CMD), abnormalities in myocardial perfusion played a key role in the development of TTS. Vascular Kv1.5 channels connect coronary blood flow to myocardial metabolism and their deletion mimics the phenotype of CMD. To determine if TTS is related to CMD, wild-type (WT), Kv1.5^−/−, and TgKv1.5^−/− (Kv1.5^−/− with smooth muscle-specific expression Kv1.5 channels) mice were studied following transaortic constriction (TAC). Measurements of left ventricular (LV) fractional shortening (FS) in base and apex, and myocardial blood flow (MBF) were completed with standard and contrast echocardiography. Ribonucleic Acid deep sequencing was performed on LV apex and base from WT and Kv1.5^−/− (control and TAC). Changes in gene expression were confirmed by real-time-polymerase chain reaction. MBF was increased with chromonar or by smooth muscle expression of Kv1.5 channels in the TgKv1.5^−/−. TAC-induced systolic apical ballooning in Kv1.5^−/−, shown as negative FS (P < 0.05 vs. base), which was not observed in WT, Kv1.5^−/− with chromonar, or TgKv1.5^−/−. Following TAC in Kv1.5^−/−, MBF was lower in LV apex than in base. Increasing MBF with either chromonar or in TgKv1.5^−/− normalized perfusion and function between LV apex and base (P = NS). Some genetic changes during TTS were reversed by chromonar, suggesting these were independent of TAC and more related to TTS. Abnormalities in flow regulation between the LV apex and base cause TTS. When perfusion is normalized between the two regions, normal ventricular function is restored. This pictorial summary of our study represents the induction of Takotsubo Syndrome by stress resulting in tissue hypoxia in the apex compared to the base of the left ventricle as shown by the blue color. The cause of this difference in tissue hypoxia is related to the lower myocardial blood flow (MBF) in the apex compared to the base. These changes in perfusion and the resultant hypoxia in the apex led to a drastic change in gene expression. The array shown reveals the dramatic changes between control and Takotsubo hearts, in which the expression of several genes appears to be ‘flipped’ between the two conditions with red–brown color indicating higher expression (Control vs. Takotsubo) and the blue the reverse. The summary also shows the effects of chromonar, a coronary-specific vasodilator, in term of restoring myocardial blood flow to the apex and restoration of normal function.

Diabetes is a risk factor for worse outcomes following acute myocardial infarction (AMI). In this study, we tested the hypothesis that SDF-1:CXCR4 expression is compromised in post-AMI in diabetes, and that reversal of this defect can reverse the adverse effects of diabetes. Mesenchymal stem cells (MSC) isolated from green fluorescent protein (GFP) transgenic mice (control MSC) were induced to overexpress stromal cell-derived factor-1 (SDF-1). SDF-1 expression in control MSC and SDF-1-overexpressing MSC (SDF-1:MSC) were quantified using enzyme-linked immunosorbent assay (ELISA). AMI was induced on db/db and control mice. Mice were randomly selected to receive infusion of control MSC, SDF-1:MSC, or saline into the border zone after AMI. Serial echocardiography was used to assess cardiac function. SDF-1 and CXCR4 mRNA expression in the infarct zone of db/db mice and control mice were quantified. Compared to control mice, SDF-1 levels were decreased 82%, 91%, and 45% at baseline, 1 day and 3 days post-AMI in db/db mice, respectively. CXCR4 levels are increased 233% at baseline and 54% 5 days post-AMI in db/db mice. Administration of control MSC led to a significant improvement in ejection fraction (EF) in control mice but not in db/db mice 21 days after AMI. In contrast, administration of SDF-1:MSC produced a significant improvement in EF in both control mice and db/db mice 21 days after AMI. The SDF-1:CXCR4 axis is compromised in diabetes, which appears to augment the deleterious consequences of AMI. Over-express of SDF-1 expression in diabetes rescues cardiac function post AMI. Our results suggest that modulation of SDF-1 may improve post-AMI cardiac repair in diabetes.

The aim of this review is to summarize recent findings of endogenous cell-based tissue repair triggered by a multitude of approaches, especially stem cell therapy. The emerging evidence has demonstrated that an important role of transplanted cells is to act as an initiator to trigger endogenous stem cell-mediated tissue repair after injury. Multiple approaches may orchestrate endogenous regeneration. The low efficacy of endogenous stem cells may be due to deficiency of cytokines to activate and induce endogenous stem cell homing, relatively insufficient endogenous stem cell pool, diseases or aging-related dysfunction of endogenous stem cells, and hostile microenvironments that limit the capacity of endogenous stem cells to repair damaged tissue. In certain situations, external stimulation and/or exogenous stem cells may be required to catalyze the repair. Endogenous stem cells are playing an important role in tissue repair. An important role of transplanted cells is to act as an initiator to trigger endogenous stem cell-based tissue repair.

Cardiovascular diseases (CVDs) are the leading cause of death worldwide, and effectively repairing the heart following myocardial injuries remains a significant challenge. Research has increasingly shown that exosomes derived from mesenchymal stem cells (MSC-Exo) can ameliorate myocardial injuries and improve outcomes after such injuries. The therapeutic benefits of MSC-Exo are largely due to their capacity to deliver specific cargo, including microRNAs and proteins. MSC-Exo can modulate various signaling pathways and provide several beneficial effects, including cytoprotection, inflammation modulation, and angiogenesis promotion to help repair the damaged myocardium. In this review, we summarize the cardioprotective effects of MSC-Exo in myocardial injury, the underlying molecular mechanism involved in the process, and various approaches studied to enhance their efficacy based on recent findings.

The stromal cell-derived factor-1 (SDF-1):CXCR4 is important in myocardial repair. In this study we tested the hypothesis that early upregulation of cardiomyocyte CXCR4 (CM-CXCR4) at a time of high myocardial SDF-1 expression could be a strategy to engage the SDF-1:CXCR4 axis and improve cardiac repair. The effects of the hypoxia inducible factor (HIF) hydroxylase inhibitor dimethyloxalylglycine (DMOG) on CXCR4 expression was tested on H9c2 cells. In mice a myocardial infarction (MI) was produced in CM-CXCR4 null and wild-type controls. Mice were randomized to receive injection of DMOG (DMOG group) or saline (Saline group) into the border zone after MI. Protein and mRNA expression of CM-CXCR4 were quantified. Echocardiography was used to assess cardiac function. During hypoxia, DMOG treatment increased CXCR4 expression of H9c2 cells by 29 and 42% at 15 and 24 h, respectively. In vivo DMOG treatment increased CM-CXCR4 expression at 15 h post-MI in control mice but not in CM-CXCR4 null mice. DMOG resulted in increased ejection fraction in control mice but not in CM-CXCR4 null mice 21 days after MI. Consistent with greater cardiomyocyte survival with DMOG treatment, we observed a significant increase in cardiac myosin-positive area within the infarct zone after DMOG treatment in control mice, but no increase in CM-CXCR4 null mice. Inhibition of cardiomyocyte death in MI through the stabilization of HIF-1α requires downstream CM-CXCR4 expression. These data suggest that engagement of the SDF-1:CXCR4 axis through the early upregulation of CM-CXCR4 is a strategy for improving cardiac repair after MI.

Background: CXCL12/CXCR4 signaling is essential in cardiac development and repair, however, its contribution to aortic valve stenosis (AVS) remains unclear. In this study, we tested the role of endothelial CXCR4 on the development of AVS.Materials and methods: We generated CXCR4 endothelial cell-specific knockout mice (EC CXCR4 KO) by crossing CXCR4^fl/fl mice with Tie2-Cre mice to study the role of endothelial cell CXCR4 in AVS. CXCR4^fl/fl mice were used as controls. Echocardiography was used to assess the aortic valve and cardiac function. Heart samples containing the aortic valve were stained using Alizarin Red for detection of calcification. Masson’s trichrome staining was used for the detection of fibrosis. The apex of the heart samples was stained with wheat germ agglutinin (WGA) to visualize ventricular hypertrophy.Results: Compared with the control group, the deletion of CXCR4 in endothelial cells led to significantly increased aortic valve peak velocity and aortic valve peak pressure gradient, with decreased aortic valve area and ejection fraction. EC CXCR4 KO mice also developed cardiac hypertrophy as evidenced by increased diastolic and systolic left ventricle posterior wall thickness (LVPW), cardiac myocyte size, and heart weight (HW) to body weight (BW) ratio. Our data also confirmed increased microcalcifications, interstitial fibrosis, and thickened valvular leaflets of the EC CXCR4 KO mice.Conclusion: The data collected throughout this study suggest the deletion of CXCR4 in endothelial cells is linked to the development of aortic valve stenosis and left ventricular hypertrophy. The statistically significant parameters measured indicate that endothelial cell CXCR4 plays an important role in aortic valve development and function. We have compiled compelling evidence that EC CXCR4 KO mice can be used as a novel model for AVS.