Fractalkine depresses cardiomyocyte contractility

Prostaglandin E2 affects mitochondrial function in adult mouse cardiomyocytes and hearts

Prostaglandin E2 (PGE2) signals differently through 4 receptor subtypes (EP1-EP4) to elicit diverse physiologic/pathologic effects. We previously reported that PGE2 via its EP3 receptor reduces cardiac contractility and male mice with cardiomyocyte-specific deletion of the EP4 receptor (EP4 KO) develop dilated cardiomyopathy. The aim of this study was to identify pathways responsible for this phenotype. We performed ingenuity pathway analysis (IPA) and found that genes differentiating WT mice and EP4 KO mice were significantly overrepresented in mitochondrial (adj. p value = 6.28 × 10-26) and oxidative phosphorylation (adj. p value = 1.58 × 10-27) pathways. Electron microscopy from the EP4 KO hearts show substantial mitochondrial disarray and disordered cristae. Not surprisingly, isolated adult mouse cardiomyocytes (AVM) from these mice have reduced ATP levels compared to their WT littermates and reduced expression of key genes involved in the electron transport chain (ETC) in older mice. Moreover, treatment of AVM from C57Bl/6 mice with PGE2 or the EP3 agonist sulprostone resulted in changes of various genes involved in the ETC, measured by the Mitochondrial Energy Metabolism RT2-profiler assay. Lastly, the EP4 KO mice have reduced expression of superoxide dismuatse-2 (SOD2), whereas treatment of AVM with PGE2 or sulprostone increase superoxide production, suggesting increased oxidative stress levels in these EP4 KO mice. Altogether the current study supports the premise that PGE2 acting via its EP4 receptor is protective, while signaling through its other receptors, likely EP3, is deleterious.

CX3CL1 represses autophagy via CX3CR1/ CaMKIIδ/HDAC4/Rubicon axis and exacerbates chronic intermittent hypoxia induced Kupffer cell apoptosis

BACKGROUND

Nocturnal hypoxemia is an established factor in the pathogenesis and exacerbation of term metabolic (dysfunction) associated fatty liver disease (MAFLD). Kupffer cells (KCs) are resident macrophages in the liver, and their activity is closely related to the progress of MAFLD. KC insufficient autophagy is involved in MAFLD pathogenesis. Herein, the regulatory mechanism of KC autophagy under chronic intermittent hypoxia (CIH) condition was investigated.

METHODS

Primary KCs and hepatic stellate cells (HSCs) were isolated from mouse liver. Immunofluorescence was employed to detect immunofluorescence intensity of LC3 protein and HDAC4 distribution. KC apoptosis was measured by TUNEL staining. Dual-luciferase reporter and ChIP assays were performed to analyze the interactions between HDAC4, MEF2C and RUBCN.

RESULTS

Herein, our results revealed that CIH-induced increased CX3CL1 in HSCs inhibited KC autophagy and promoted cell apoptosis by interacting with CX3CR1. Meanwhile, CX3CL1 treatment inhibited KC autophagy (p < 0.001, fold change: 0.059) and promoted cell apoptosis (p < 0.001, fold change: 8.18). Rubicon knockdown promoted KC autophagy (p < 0.001, fold change: 2.90) and inhibited cell apoptosis (p < 0.05, fold change: 0.23), while these effects were reversed by CX3CL1 treatment (p < 0.01, fold change: 6.59; p < 0.001, fold change: 0.35). Our mechanistic experiments demonstrated that HDAC4 overexpression transcriptionally inhibited RUBCN expression by interacting with MEF2C, thereby promoting KC autophagy and inhibiting cell apoptosis. Moreover, CaMKIIδ inhibition promoted the translocation of HDAC4 from the cytosol to the nucleus to promote KC autophagy and inhibit the apoptosis.

CONCLUSION

Taken together, CIH-induced increased CX3CL1 expression in HSCs inhibited KC autophagy and promoted apoptosis by regulating the CX3CR1/ CaMKIIδ/HDAC4/Rubicon axis.

Mitochondria as a Cellular Hub in Infection and Inflammation

Mitochondria are the energy center of the cell. They are found in the cell cytoplasm as dynamic networks where they adapt energy production based on the cell’s needs. They are also at the center of the proinflammatory response and have essential roles in the response against pathogenic infections. Mitochondria are a major site for production of Reactive Oxygen Species (ROS; or free radicals), which are essential to fight infection. However, excessive and uncontrolled production can become deleterious to the cell, leading to mitochondrial and tissue damage. Pathogens exploit the role of mitochondria during infection by affecting the oxidative phosphorylation mechanism (OXPHOS), mitochondrial network and disrupting the communication between the nucleus and the mitochondria. The role of mitochondria in these biological processes makes these organelle good targets for the development of therapeutic strategies. In this review, we presented a summary of the endosymbiotic origin of mitochondria and their involvement in the pathogen response, as well as the potential promising mitochondrial targets for the fight against infectious diseases and chronic inflammatory diseases.

Pro-inflammatory Cytokines in Acute Coronary Syndromes

BACKGROUND

Over the last decades, the role of inflammation and immune system activation in the initiation and progression of coronary artery disease (CAD) has been established.

OBJECTIVES

The study aimed to present the interplay between cytokines and their actions preceding and shortly after ACS.

METHODS

We searched in a systemic manner the most relevant articles to the topic of inflammation, cytokines, vulnerable plaque and myocardial infarction in MEDLINE, COCHRANE and EMBASE databases.

RESULTS

Different classes of cytokines (intereleukin [IL]-1 family, Tumor necrosis factor-alpha (TNF-α) family, chemokines, adipokines, interferons) are implicated in the entire process leading to destabilization of the atherosclerotic plaque, and consequently, to the incidence of myocardial infarction. Especially IL-1 and TNF-α family are involved in inflammatory cell accumulation, vulnerable plaque formation, platelet aggregation, cardiomyocyte apoptosis and adverse remodeling following the myocardial infarction. Several cytokines such as IL-6, adiponectin, interferon-γ, appear with significant prognostic value in ACS patients. Thus, research interest focuses on the modulation of inflammation in ACS to improve clinical outcomes.

CONCLUSION

Understanding the unique characteristics that accompany each cytokine-cytokine receptor interaction could illuminate the signaling pathways involved in plaque destabilization and indicate future treatment strategies to improve cardiovascular prognosis in ACS patients.

Cardiomyopathy Associated with Diabetes: The Central Role of the Cardiomyocyte

The term diabetic cardiomyopathy (DCM) labels an abnormal cardiac structure and performance due to intrinsic heart muscle malfunction, independently of other vascular co-morbidity. DCM, accounting for 50%–80% of deaths in diabetic patients, represents a worldwide problem for human health and related economics. Optimal glycemic control is not sufficient to prevent DCM, which derives from heart remodeling and geometrical changes, with both consequences of critical events initially occurring at the cardiomyocyte level. Cardiac cells, under hyperglycemia, very early undergo metabolic abnormalities and contribute to T helper (Th)-driven inflammatory perturbation, behaving as immunoactive units capable of releasing critical biomediators, such as cytokines and chemokines. This paper aims to focus onto the role of cardiomyocytes, no longer considered as “passive” targets but as “active” units participating in the inflammatory dialogue between local and systemic counterparts underlying DCM development and maintenance. Some of the main biomolecular/metabolic/inflammatory processes triggered within cardiac cells by high glucose are overviewed; particular attention is addressed to early inflammatory cytokines and chemokines, representing potential therapeutic targets for a prompt early intervention when no signs or symptoms of DCM are manifesting yet. DCM clinical management still represents a challenge and further translational investigations, including studies at female/male cell level, are warranted.

Increased Plasma Soluble Fractalkine in Patients with Chronic Heart Failure and Its Clinical Significance

Fractalkine has been reported to play an important role in the pathophysiology of various cardiovascular disorders. This research aims to study the change of soluble fractalkine (sFKN) in plasma level of patients with chronic heart failure (CHF) and evaluate its prognostic value.A total of 96 patients with CHF and 45 healthy subjects were included in this study. The plasma levels of sFKN, brain natriuretic peptide (BNP), and Interleukin-18 (IL-18) were determined by ELISA kits when they were first admitted to the hospital. Left ventricular ejection fraction (LVEF) was measured by echocardiogram. Rehospitalization status within 1 year after the first hospitalization was also recorded.The plasma levels of sFKN, BNP, and IL-18 in patients with CHF were significantly higher than in the control group (P < 0.05). The concentrations of sFKN and BNP were increased with the severity of heart failure classified by NYHA classification (P < 0.05). There were no statistical differences among all CHF subgroups classified by etiology (P > 0.05). Plasma sFKN level in CHF group was positively correlated with BNP (r = 0.441, P < 0.001) and IL-18 (r = 0.592, P < 0.001). Receiver operating characteristic curve analysis showed that area under the curve values of FKN, BNP, and IL-18 were 0.885 (95%CI: 0.810 to 0.960, P < 0.001), 0.889 (95%CI: 0.842 to 0.956, P < 0.001), and 0.878 (95%CI: 0.801-0.954, P < 0.001), respectively. The concentrations of sFKN and BNP were increased in patients readmitted more than once within 1 year (P < 0.05).

The Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid (SAHA) Restores Cardiomyocyte Contractility in a Rat Model of Early Diabetes

In early diabetes, hyperglycemia and the associated metabolic dysregulation promote early changes in the functional properties of cardiomyocytes, progressively leading to the appearance of the diabetic cardiomyopathy phenotype. Recently, the interplay between histone acetyltransferases (HAT) and histone deacetylases (HDAC) has emerged as a crucial factor in the development of cardiac disorders. The present study evaluates whether HDAC inhibition can prevent the development of cardiomyocyte contractile dysfunction induced by a short period of hyperglycemia, with focus on the potential underlying mechanisms. Cell contractility and calcium dynamics were measured in unloaded ventricular myocytes isolated from the heart of control and diabetic rats. Cardiomyocytes were either untreated or exposed to the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) for 90 min. Then, a fraction of each group of cells was used to evaluate the expression levels of proteins involved in the excitation-contraction coupling, and the cardiomyocyte metabolic activity, ATP content, and reactive oxygen species levels. SAHA treatment was able to counteract the initial functional derangement in cardiomyocytes by reducing cell oxidative damage. These findings suggest that early HDAC inhibition could be a promising adjuvant approach for preventing diabetes-induced cardiomyocyte oxidative damage, which triggers the pro-inflammatory signal cascade, mitochondrial damage, and ventricular dysfunction.

Trimethylamine-N-Oxide (TMAO)-Induced Impairment of Cardiomyocyte Function and the Protective Role of Urolithin B-Glucuronide

One of the most recently proposed candidates as a potential trigger for cardiovascular diseases is trimethylamine-N-oxide (TMAO). Possible direct effects of TMAO on myocardial tissue, independent of vascular damage, have been only partially explored so far. In the present study, we assessed the detrimental direct effects of TMAO on cardiomyocyte contractility and intracellular calcium dynamics, and the ability of urolithin B-glucuronide (Uro B-gluc) in counteracting TMAO-induced cell damage. Cell mechanics and calcium transients were measured, and ultrastructural analysis was performed in ventricular cardiomyocytes isolated from the heart of normal adult rats. Cells were either untreated, exposed to TMAO, or to TMAO and Uro B-gluc. TMAO exposure worsened cardiomyocyte mechanics and intracellular calcium handling, as documented by the decrease in the fraction of shortening (FS) and the maximal rate of shortening and re-lengthening, associated with reduced efficiency in the intracellular calcium removal. Ultrastructurally, TMAO-treated cardiomyocytes also exhibited glycogen accumulation, a higher number of mitochondria and lipofuscin-like pigment deposition, suggesting an altered cellular energetic metabolism and a higher rate of protein oxidative damage, respectively. Uro B-gluc led to a complete recovery of cellular contractility and calcium dynamics, and morphologically to a reduced glycogen accumulation. We demonstrated for the first time a direct negative role of TMAO on cardiomyocyte functional properties and the ability of Uro B-gluc in counteracting these detrimental effects.

C1q/tumor necrosis factor-related protein-3 enhances the contractility of cardiomyocyte by increasing calcium sensitivity

C1q/tumor necrosis factor-related protein-3 (CTRP3) is an adipokine that protects against myocardial infarction-induced cardiac dysfunction through its pro-angiogenic, anti-apoptotic, and anti-fibrotic effects. However, whether CTRP3 can directly affect the systolic and diastolic function of cardiomyocytes remains unknown. Adult rat cardiomyocytes were isolated and loaded with Fura-2AM. The contraction and Ca²⁺ transient data was collected and analyzed by IonOptix system. 1 and 2μg/ml CTRP3 significantly increased the contraction of cardiomyocytes. However, CTRP3 did not alter the diastolic Ca²⁺ content, systolic Ca²⁺ content, Ca²⁺ transient amplitude, and L-type Ca²⁺ channel current. To reveal whether CTRP3 affects the Ca²⁺ sensitivity of cardiomyocytes, the typical phase-plane diagrams of sarcomere length vs. Fura-2 ratio was performed. We observed a left-ward shifting of the late relaxation trajectory after CTRP3 perfusion, as quantified by decreased Ca²⁺ content at 50% sarcomere relaxation, and increased mean gradient (μm/Fura-2 ratio) during 500-600ms (-0.163 vs. -0.279), 500-700ms (-0.159 vs. -0.248), and 500-800ms (-0.148 vs. -0.243). Consistently, the phosphorylation level of cardiac troponin I at Ser23/24 was reduced by CTRP3, which could be eliminated by preincubation of okadaic acid, a type 2A protein phosphatase inhibitor. In summary, CTRP3 increases the contraction of cardiomyocytes by increasing the myofilament Ca²⁺ sensitivity. CTRP3 might be a potential endogenous Ca²⁺ sensitizer that modulates the contractility of cardiomyocytes.

In vivo administration of urolithin A and B prevents the occurrence of cardiac dysfunction in streptozotocin-induced diabetic rats

Background

Emerging evidence suggests that specific (poly)phenols may constitute new preventative strategies to counteract cell oxidative stress and myocardial tissue inflammation, which have a key role in the patho-physiology of diabetic cardiomyopathy. In a rat model of early diabetes, we evaluated whether in vivo administration of urolithin A (UA) or urolithin B (UB), the main gut microbiota phenolic metabolites of ellagitannin-rich foods, can reduce diabetes-induced microenvironmental changes in myocardial tissue, preventing cardiac functional impairment.

Methods

Adult Wistar rats with streptozotocin-induced type-1 diabetes (n = 29) were studied in comparison with 10 control animals. Diabetic rats were either untreated (n  =  9) or subjected to daily i.p. injection of UA (n = 10) or UB (n = 10). After 3 weeks of hyperglycaemia, hemodynamics, cardiomyocyte contractile properties and calcium transients were measured to assess cardiac performance. The myocardial expression of the pro-inflammatory cytokine fractalkine and proteins involved in calcium dynamics (sarcoplasmic reticulum calcium ATPase, phospholamban and phosphorylated phospholamban) were evaluated by immunoblotting. Plasma, urine and tissue distribution of UA, UB and their phase II metabolites were determined.

Results

In vivo urolithin treatment reduced by approximately 30% the myocardial expression of the pro-inflammatory cytokine fractalkine, preventing the early inflammatory response of cardiac cells to hyperglycaemia. The improvement in myocardial microenvironment had a functional counterpart, as documented by the increase in the maximal rate of ventricular pressure rise compared to diabetic group (+18% and +31% in UA and UB treated rats, respectively), and the parallel reduction in the isovolumic contraction time (−12%). In line with hemodynamic data, both urolithins induced a recovery of cardiomyocyte contractility and calcium dynamics, leading to a higher re-lengthening rate (+21%, on average), lower re-lengthening times (−56%), and a more efficient cytosolic calcium clearing (−32% in tau values). UB treatment also increased the velocity of shortening (+27%). Urolithin metabolites accumulated in the myocardium, with a higher concentration of UB and UB-sulphate, potentially explaining the slightly higher efficacy of UB administration.

Conclusions

In vivo urolithin administration may be able to prevent the initial inflammatory response of myocardial tissue to hyperglycaemia and the negative impact of the altered diabetic milieu on cardiac performance.

Prostaglandin E2 Reduces Cardiac Contractility via EP3 Receptor

BACKGROUND

Prostaglandin E2 (PGE2) EP receptors EP3 and EP4 signal via decreased and increased cAMP production, respectively. Previously, we reported that cardiomyocyte-specific EP4 knockout mice develop dilated cardiomyopathy with reduced ejection fraction. Thus, we hypothesized that PGE2 increases contractility via EP4 but decreases contractility via EP3.

METHODS AND RESULTS

The effects of PGE2 and the EP1/EP3 agonist sulprostone on contractility were examined in the mouse Langendorff preparation and in adult mouse cardiomyocytes. Isolated hearts of adult male C57Bl/6 mice were perfused with PGE2 (10(-6) M) or sulprostone (10(-6) M) and compared with vehicle. Both PGE2 and sulprostone decreased +dp/dt (P<0.01) and left ventricular developed pressure (P<0.001) with reversal by an EP3 antagonist. In contrast, the EP4 agonist had the opposite effect. Adult mouse cardiomyocytes contractility was also reduced after treatment with either PGE2 or sulprostone for 10 minutes. We then examined the acute effects of PGE2, sulprostone, and the EP4 agonist on expression of phosphorylated phospholamban and sarcoendoplasmic reticulum Ca(2+)-ATPase 2a in adult mouse cardiomyocytes using Western blot. Treatment with either PGE2 or sulprostone decreased expression of phosphorylated phospholamban corrected to total phospholamban, whereas treatment with the EP4 agonist had the opposite effect. Sarcoendoplasmic reticulum Ca(2+)-ATPase 2a expression was unaffected. Finally, we examined the effect of these compounds in vivo using pressure-volume loops. Both PGE2 and sulprostone decreased +dp/dt, whereas the EP4 agonist increased +dp/dt.

CONCLUSIONS

Contractility is reduced via the EP3 receptor but increased via EP4. These effects may be mediated through changes in phospholamban phosphorylation and has relevance to detrimental effects of inflammation.

Molecular Characterization of Pediatric Restrictive Cardiomyopathy from Integrative Genomics

Pediatric restrictive cardiomyopathy (RCM) is a genetically heterogeneous heart disease with limited therapeutic options. RCM cases are largely idiopathic; however, even within families with a known genetic cause for cardiomyopathy, there is striking variability in disease severity. Although accumulating evidence implicates both gene expression and alternative splicing in development of dilated cardiomyopathy (DCM), there have been no detailed molecular characterizations of underlying pathways dysregulated in RCM. RNA-Seq on a cohort of pediatric RCM patients compared to other forms of adult cardiomyopathy and controls identified transcriptional differences highly common to the cardiomyopathies, as well as those unique to RCM. Transcripts selectively induced in RCM include many known and novel G-protein coupled receptors linked to calcium handling and contractile regulation. In-depth comparisons of alternative splicing revealed splicing events shared among cardiomyopathy subtypes, as well as those linked solely to RCM. Genes identified with altered alternative splicing implicate RBM20, a DCM splicing factor, as a potential mediator of alternative splicing in RCM. We present the first comprehensive report on molecular pathways dysregulated in pediatric RCM including unique/shared pathways identified compared to other cardiomyopathy subtypes and demonstrate that disruption of alternative splicing patterns in pediatric RCM occurs in the inverse direction as DCM.

Parenchymal and Stromal Cells Contribute to Pro-Inflammatory Myocardial Environment at Early Stages of Diabetes: Protective Role of Resveratrol

Background: Little information is currently available concerning the relative contribution of cardiac parenchymal and stromal cells in the activation of the pro-inflammatory signal cascade, at the initial stages of diabetes. Similarly, the effects of early resveratrol (RSV) treatment on the negative impact of diabetes on the different myocardial cell compartments remain to be defined. Methods: In vitro challenge of neonatal cardiomyocytes and fibroblasts to high glucose and in vivo/ex vivo experiments on a rat model of Streptozotocin-induced diabetes were used to specifically address these issues. Results: In vitro data indicated that, besides cardiomyocytes, neonatal fibroblasts contribute to generating initial changes in the myocardial environment, in terms of pro-inflammatory cytokine expression. These findings were mostly confirmed at the myocardial tissue level in diabetic rats, after three weeks of hyperglycemia. Specifically, monocyte chemoattractant protein-1 and Fractalkine were up-regulated and initial abnormalities in cardiomyocyte contractility occurred. At later stages of diabetes, a selective enhancement of pro-inflammatory macrophage M1 phenotype and a parallel reduction of anti-inflammatory macrophage M2 phenotype were associated with a marked disorganization of cardiomyocyte ultrastructural properties. RSV treatment inhibited pro-inflammatory cytokine production, leading to a recovery of cardiomyocyte contractile efficiency and a reduced inflammatory cell recruitment. Conclusion: Early RSV administration could inhibit the pro-inflammatory diabetic milieu sustained by different cardiac cell types.

Cardiac-restricted Overexpression of TRAF3 Interacting Protein 2 (TRAF3IP2) Results in Spontaneous Development of Myocardial Hypertrophy, Fibrosis, and Dysfunction

TRAF3IP2 (TRAF3 interacting protein 2; previously known as CIKS or Act1) is a key intermediate in the normal inflammatory response and the pathogenesis of various autoimmune and inflammatory diseases. Induction of TRAF3IP2 activates IκB kinase (IKK)/NF-κB, JNK/AP-1, and c/EBPβ and stimulates the expression of various inflammatory mediators with negative myocardial inotropic effects. To investigate the role of TRAF3IP2 in heart disease, we generated a transgenic mouse model with cardiomyocyte-specific TRAF3IP2 overexpression (TRAF3IP2-Tg). Echocardiography, magnetic resonance imaging, and pressure-volume conductance catheterization revealed impaired cardiac function in 2-month-old male transgenic (Tg) mice as evidenced by decreased ejection fraction, stroke volume, cardiac output, and peak ejection rate. Moreover, the male Tg mice spontaneously developed myocardial hypertrophy (increased heart/body weight ratio, cardiomyocyte cross-sectional area, GATA4 induction, and fetal gene re-expression). Furthermore, TRAF3IP2 overexpression resulted in the activation of IKK/NF-κB, JNK/AP-1, c/EBPβ, and p38 MAPK and induction of proinflammatory cytokines, chemokines, and extracellular matrix proteins in the heart. Although myocardial hypertrophy decreased with age, cardiac fibrosis (increased number of myofibroblasts and enhanced expression and deposition of fibrillar collagens) increased progressively. Despite these adverse changes, TRAF3IP2 overexpression did not result in cell death at any time period. Interestingly, despite increased mRNA expression, TRAF3IP2 protein levels and activation of its downstream signaling intermediates remained unchanged in the hearts of female Tg mice. The female Tg mice also failed to develop myocardial hypertrophy. In summary, these results demonstrate that overexpression of TRAF3IP2 in male mice is sufficient to induce myocardial hypertrophy, cardiac fibrosis, and contractile dysfunction.

Fractalkine neutralization improves cardiac function after myocardial infarction

NEW FINDINGS

What is the central question of this study? What is the cardioprotective role of fractalkine neutralization in heart failure and what are the mechanisms responsible? What is the main finding and its importance? The concentration of fractalkine is increased in the left ventricle of mice with myocardial infarction, similar to the increases in plasma from heart failure patients. The present study shows a clear beneficial effect of neutralizing fractalkine in a model of myocardial infarction, which results in increased survival. Such an approach may be worthwhile in human patients. Concentrations of the chemokine fractalkine (FKN) are increased in patients with chronic heart failure, and our previous studies show that aged mice lacking the prostaglandin E2 EP4 receptor subtype (EP4-KO) have increased cardiac FKN, with a phenotype of dilated cardiomyopathy. However, how FKN participates in the pathogenesis of heart failure has rarely been studied. We hypothesized that FKN contributes to the pathogenesis of heart failure and that anti-FKN treatment prevents heart failure induced by myocardial infarction (MI) more effectively in EP4-KO mice. Male EP4-KO mice and wild-type littermates underwent sham or MI surgery and were treated with an anti-FKN antibody or control IgG. At 2 weeks post-MI, echocardiography was performed and hearts were excised for determination of infarct size, immunohistochemistry and Western blot of signalling molecules. Given that FKN protein levels in the left ventricle were increased to a similar extent in both strains after MI and that anti-FKN treatment improved survival and cardiac function in both strains, we subsequently used only wild-type mice to examine the mechanisms whereby anti-FKN is cardioprotective. Myocyte cross-sectional area and interstitial collagen fraction were reduced after anti-FKN treatment, as were macrophage migration and gelatinase activity. Activation of ERK1/2 and p38 MAPK were reduced after neutralization of FKN. In vitro, FKN increased fibroblast proliferation. In conclusion, increased FKN contributes to heart failure after MI. This effect is not exacerbated in EP4-KO mice, suggesting that there is no link between FKN and lack of EP4. Overall, inhibition of FKN may be important to preserve cardiac function post-MI.