Impact of delayed type hypersensitivity arthritis on development of heart failure by aortic constriction in mice.

AIMS: Patients with rheumatoid arthritis (RA) have increased risk of heart failure (HF). The mechanisms and cardiac prerequisites explaining this association remain unresolved. In this study, we sought to determine the potential cardiac impact of an experimental model of RA in mice subjected to HF by constriction of the ascending aorta. METHODS: Aorta was constricted via thoracotomy and placement of o-rings with inner diameter 0.55 mm or 0.66 mm, or sham operated. RA-like phenotype was instigated by delayed-type hypersensitivity arthritis (DTHA) two weeks after surgery and re-iterated after additional 18 days. Cardiac magnetic resonance imaging (MRI) was performed before surgery and at successive time points throughout the study. Six weeks after surgery the mice were euthanized, blood and tissue were collected, organ weights were documented, and expression levels of cardiac foetal genes were analysed. In a supplemental study, DTHA-mice were euthanized throughout 14 days after induction of arthritis, and blood was analysed for important markers and mediators of RA (SAP, TNF-α and IL-6). In order to put the latter findings into clinical context, the same molecules were analysed in serum from untreated RA patients and compared to healthy controls. RESULTS: Significant elevations of inflammatory markers were found in both patient- and murine blood. Furthermore, the DTHA model appeared clinically relevant when compared to the inflammatory responses observed in three prespecified RA severity disease states. Two distinct trajectories of cardiac dysfunction and HF development were found using the two o-ring sizes. These differences were consistent by both MRI, organ weights and cardiac foetal gene expression levels. Still, no difference within the HF groups, nor within the sham groups, could be found when DTHA was induced. CONCLUSION: DTHA mediated systemic inflammation did not cause, nor modify HF caused by aortic constriction. This indicates other prerequisites for RA-induced cardiac dysfunction.

YKL-40 (Chitinase-3-Like Protein 1) Serum Levels in Aortic Stenosis.

BACKGROUND: Identification of novel biomarkers could provide prognostic information and improve risk stratification in patients with aortic stenosis (AS). YKL-40 (chitinase-3-like protein 1), a protein involved in atherogenesis, is upregulated in human calcific aortic valves. We hypothesized that circulating YKL-40 would be elevated and associated with the degree of AS severity and outcome in patients with symptomatic AS. METHODS: Plasma YKL-40 was analyzed in 2 AS populations, one severe AS (n=572) with outcome measures and one with mixed severity (n=67). YKL-40 expression in calcified valves and in an experimental pressure overload model was assessed. RESULTS: We found (1) patients with AS had upregulated circulating YKL-40 compared with healthy controls (median 109 versus 34 ng/mL, P<0.001), but levels were not related to the degree of AS severity. (2) High YKL-40 levels (quartile 4) were associated with long-term (median follow-up 4.7 years) all-cause mortality (adjusted hazard ratio, 1.93 [95% CI, 1.37-2.73], P<0.001). (3) YKL-40 protein expression in human calcific valves co-localized with its putative receptor IL-13rα2 in close proximity to valve interstitial cells. (4) Myocardial YKL-40 increased in experimental pressure overload (6-fold in decompensated versus sham mice). CONCLUSIONS: YKL-40 levels were elevated in AS and associated with mortality but not with other metrics of disease severity including the degree of AS severity. Despite scientific rationale for its role in AS, the clinical utility of circulating YKL-40 as a biomarker is limited. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01794832.

Cardiac sarcoma. / Sarkom i hjertet.

BACKGROUND: Although very rare, cardiac sarcoma is the most common malignant cardiac tumour. Cardiac tumours may present with constitutional symptoms and this can lead to delayed diagnosis. CASE PRESENTATION: A woman in her late twenties was admitted to the acute psychiatric ward with suspected depressive psychosis. Although she presented with insomnia, auditory hallucinosis and paranoid delusions, her main symptoms were dyspnoea, tachycardia and exhaustion. She was discharged after 17 days and admitted directly to the medical ward for further examination. A thorough somatic examination, including diagnostic imaging, revealed a tumour in the left atrium obstructing the mitral ostium in the diastole, resulting in orthopnoea. She had urgent cardiac surgery and the histology was consistent with an intimal sarcoma. INTERPRETATION: This case illustrates a rare disease presenting with atypical symptoms. Her psychiatric symptoms resolved after surgery and oncologic treatment of her cardiac tumour.

Screening for symptoms of depression and anxiety in a cardiology department. / Screening for symptomer på depresjon og angst ved en hjertemedisinsk avdeling.

BACKGROUND: Depression and anxiety are common in patients with cardiac disease and predict a poorer prognosis, increased mortality and reduced compliance with treatment. National and international guidelines recommend procedures for screening, but there is a lack of studies of such practices in Norwegian hospitals. The objective of this study was to implement a simple screening method for symptoms of depression and anxiety in patients with cardiac disease. MATERIAL AND METHOD: Patients in the Department of Cardiology at Diakonhjemmet Hospital who had valvular heart disease, tachyarrhythmia, myocardial infarction or heart failure were screened for symptoms of depression, anxiety and panic attacks with the aid of five questions from the Patient Health Questionnaire-2 (PHQ-2), Generalized Anxiety Disorder Scale-2 (GAD-2) and Patient Health Questionnaire - Somatic, Anxiety, and Depressive Symptom Scales (PHQ-SADS). The patients were recruited from the outpatient clinic or ward at least one month after acute heart disease. RESULTS: A total of 57 of 232 patients reported symptoms of depression or anxiety when screened. The screening method was easy to implement, but time constraints and uncertainty regarding procedures for follow-up and the effect of following up the patients were reported. INTERPRETATION: Good tools and methods are available for screening for symptoms of depression and anxiety and anxiety in patients with cardiac disease. More studies are needed regarding the benefits of screening, at what stage of the disease it should be performed, and whether it should be performed by the primary and/or the specialist health services.

Toll-Like Receptor 9 Promotes Survival in SERCA2a KO Heart Failure Mice.

Aim. Inflammation is important in heart failure (HF). The role of the immune receptor toll-like receptor 9 (TLR9) in HF is not understood and not investigated in diastolic HF. We investigated the role of TLR9 in a murine diastolic HF model caused by cardiomyocyte SERCA2a excision. Methods and Results. We crossed SERCA2a KO and TLR9 KO mice to generate four mouse lines. Tamoxifen-induced cardiomyocyte SERCA2a gene excision was carried out in mice, causing diastolic HF. After 7.6 weeks, cardiac functions and dimensions were analyzed by echocardiography and heart tissues were processed. HF mice depleted of TLR9 demonstrated reduced survival compared to SERC2a KO mice, with a median life expectancy of 58 days compared to 63 days. Both HF groups displayed increased left atrium size, lung weight, fetal gene expressions, monocyte/macrophage infiltration, and fibrosis. However, there were no significant differences between the groups. Conclusion. In mice with SERCA2a KO-induced diastolic HF, the absence of TLR9 reduced median life expectancy. The cause remains elusive, as all investigated HF parameters were unaltered. Still, these findings support a salutary role of TLR9 in some subsets of HF conditions and underline the importance for future studies on the mechanisms of TLR9 in diastolic HF.

NEIL3-Dependent Regulation of Cardiac Fibroblast Proliferation Prevents Myocardial Rupture.

Myocardial infarction (MI) triggers a reparative response involving fibroblast proliferation and differentiation driving extracellular matrix modulation necessary to form a stabilizing scar. Recently, it was shown that a genetic variant of the base excision repair enzyme NEIL3 was associated with increased risk of MI in humans. Here, we report elevated myocardial NEIL3 expression in heart failure patients and marked myocardial upregulation of Neil3 after MI in mice, especially in a fibroblast-enriched cell fraction. Neil3-/- mice show increased mortality after MI caused by myocardial rupture. Genome-wide analysis of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) reveals changes in the cardiac epigenome, including in genes related to the post-MI transcriptional response. Differentially methylated genes are enriched in pathways related to proliferation and myofibroblast differentiation. Accordingly, Neil3-/- ruptured hearts show increased proliferation of fibroblasts and myofibroblasts. We propose that NEIL3-dependent modulation of DNA methylation regulates cardiac fibroblast proliferation and thereby affects extracellular matrix modulation after MI.

Palmitate promotes inflammatory responses and cellular senescence in cardiac fibroblasts.

Palmitate triggers inflammatory responses in several cell types, but its effects on cardiac fibroblasts are at present unknown. The aims of the study were to (1) assess the potential of palmitate to promote inflammatory signaling in cardiac fibroblasts through TLR4 and the NLRP3 inflammasome and (2) characterize the cellular phenotype of cardiac fibroblasts exposed to palmitate. We examined whether palmitate induces inflammatory responses in cardiac fibroblasts from WT, NLRP3-/- and ASC-/-mice (C57BL/6 background). Exposure to palmitate caused production of TNF, IL-6 and CXCL2 via TLR4 activation. NLRP3 inflammasomes are activated in a two-step manner. Whereas palmitate did not prime the NLRP3 inflammasome, it induced activation in LPS-primed cardiac fibroblasts as indicated by IL-1ß, IL-18 production and NLRP3-ASC co-localization. Palmitate-induced NLRP3 inflammasome activation in LPS-primed cardiac fibroblasts was associated with reduced AMPK activity, mitochondrial reactive oxygen species production and mitochondrial dysfunction. The cardiac fibroblast phenotype caused by palmitate, in an LPS and NLRP3 independent manner, was characterized by decreased cellular proliferation, contractility, collagen and MMP-2 expression, as well as increased senescence-associated ß-galactosidase activity, and consistent with a state of cellular senescence. This study establishes that in vitro palmitate exposure of cardiac fibroblasts provides inflammatory responses via TLR4 and NLRP3 inflammasome activation. Palmitate also modulates cardiac fibroblast functionality, in a NLRP3 independent manner, resulting in a phenotype related to cellular senescence. These effects of palmitate could be of importance for myocardial dysfunction in obese and diabetic patients.

Low Circulating Levels of Mitochondrial and High Levels of Nuclear DNA Predict Mortality in Chronic Heart Failure.

BACKGROUND: Mitochondrial DNA (mtDNA) and possibly nuclear DNA (nDNA) are released as danger-associated molecular patterns during cardiac stress, and may activate several innate immune receptors. The purpose of this study was to investigate the regulation of these danger-associated molecular patterns during human heart failure (HF). METHODS AND RESULTS: Plasma levels of mtDNA and nDNA from HF patients (n = 84) were analyzed by reverse transcriptase-polymerase chain reaction and compared with controls (n = 72). Increased levels of mtDNA were found in New York Heart Association (NYHA) I-II and NYHA III-IV. There was evidence of increased nDNA in NYHA III-IV compared with controls and NYHA I-II. Kaplan-Meier analysis revealed higher mortality in patients with high nDNA levels, whereas high levels of mtDNA were associated with survival. CONCLUSIONS: Plasma levels of mtDNA and nDNA are elevated in human HF associated with increased and decreased mortality, respectively. This study may suggest a rationale for exploring interventions within inflammatory signaling pathways activated by nucleic acids as novel targets in treatment of HF.

Sustained Toll-Like Receptor 9 Activation Promotes Systemic and Cardiac Inflammation, and Aggravates Diastolic Heart Failure in SERCA2a KO Mice.

AIM: Cardiac inflammation is important in the pathogenesis of heart failure. However, the consequence of systemic inflammation on concomitant established heart failure, and in particular diastolic heart failure, is less explored. Here we investigated the impact of systemic inflammation, caused by sustained Toll-like receptor 9 activation, on established diastolic heart failure. METHODS AND RESULTS: Diastolic heart failure was established in 8-10 week old cardiomyocyte specific, inducible SERCA2a knock out (i.e., SERCA2a KO) C57Bl/6J mice. Four weeks after conditional KO, mice were randomized to receive Toll-like receptor 9 agonist (CpG B; 2µg/g body weight) or PBS every third day. After additional four weeks, echocardiography, phase contrast magnetic resonance imaging, histology, flow cytometry, and cardiac RNA analyses were performed. A subgroup was followed, registering morbidity and death. Non-heart failure control groups treated with CpG B or PBS served as controls. Our main findings were: (i) Toll-like receptor 9 activation (CpG B) reduced life expectancy in SERCA2a KO mice compared to PBS treated SERCA2a KO mice. (ii) Diastolic function was lower in SERCA2a KO mice with Toll-like receptor 9 activation. (iii) Toll-like receptor 9 stimulated SERCA2a KO mice also had increased cardiac and systemic inflammation. CONCLUSION: Sustained activation of Toll-like receptor 9 causes cardiac and systemic inflammation, and deterioration of SERCA2a depletion-mediated diastolic heart failure.

Toll-like receptor 9 mediated responses in cardiac fibroblasts.

Altered cardiac Toll-like receptor 9 (TLR9) signaling is important in several experimental cardiovascular disorders. These studies have predominantly focused on cardiac myocytes or the heart as a whole. Cardiac fibroblasts have recently been attributed increasing significance in mediating inflammatory signaling. However, putative TLR9-signaling through cardiac fibroblasts remains non-investigated. Thus, our aim was to explore TLR9-signaling in cardiac fibroblasts and investigate the consequence of such receptor activity on classical cardiac fibroblast cellular functions. Cultivated murine cardiac fibroblasts were stimulated with different TLR9 agonists (CpG A, B and C) and assayed for the secretion of inflammatory cytokines (tumor necrosis factor α [TNFα], CXCL2 and interferon α/ß). Expression of functional cardiac fibroblast TLR9 was proven as stimulation with CpG B and -C caused significant CXCL2 and TNFα-release. These responses were TLR9-specific as complete inhibition of receptor-stimulated responses was achieved by co-treatment with a TLR9-antagonist (ODN 2088) or chloroquine diphosphate. TLR9-stimulated responses were also found more potent in cardiac fibroblasts when compared with classical innate immune cells. Stimulation of cardiac fibroblasts TLR9 was also found to attenuate migration and proliferation, but did not influence myofibroblast differentiation in vitro. Finally, results from in vivo TLR9-stimulation with subsequent fractionation of specific cardiac cell-types (cardiac myocytes, CD45+ cells, CD31+ cells and cardiac fibroblast-enriched cell-fractions) corroborated our in vitro data and provided evidence of differentiated cell-specific cardiac responses. Thus, we conclude that cardiac fibroblast may constitute a significant TLR9 responder cell within the myocardium and, further, that such receptor activity may impact important cardiac fibroblast cellular functions.

Toll-like receptor 9-activation during onset of myocardial ischemia does not influence infarct extension.

AIM: Myocardial infarction (MI) remains a major cause of death and disability worldwide, despite available reperfusion therapies. Inflammatory signaling is considered nodal in defining final infarct size. Activation of the innate immune receptor toll-like receptors (TLR) 9 prior to ischemia and reperfusion (I/R) reduces infarct size, but the consequence of TLR9 activation timed to the onset of ischemia is not known. METHODS AND RESULTS: The TLR9-agonist; CpG B was injected i.p. in C57BL/6 mice immediately after induction of ischemia (30 minutes). Final infarct size, as well as area-at-risk, was measured after 24 hours of reperfusion. CpG B injection resulted in a significant increase in circulating granulocytes and monocytes both in sham and I/R mice. Paradoxically, clear evidence of reduced cardiac infiltration of both monocytes and granulocytes could be demonstrated in I/R mice treated with CpG B (immunocytochemistry, myeloperoxidase activity and mRNA expression patterns). In addition, systemic TLR9 activation elicited significant alterations of cardiac inflammatory genes. Despite these biochemical and cellular changes, there was no difference in infarct size between vehicle and CpG B treated I/R mice. CONCLUSION: Systemic TLR9-stimulation upon onset of ischemia and subsequent reperfusion does not alter final infarct size despite causing clear alterations of both systemic and cardiac inflammatory parameters. Our results question the clinical usefulness of TLR9 activation during cardiac I/R.

p38α regulates SERCA2a function.

cAMP-dependent protein kinase (PKA) regulates the L-type calcium channel, the ryanodine receptor, and phospholamban (PLB) thereby increasing inotropy. Cardiac contractility is also regulated by p38 MAPK, which is a negative regulator of cardiac contractile function. The aim of this study was to identify the mechanism mediating the positive inotropic effect of p38 inhibition. Isolated adult and neonatal cardiomyocytes and perfused rat hearts were utilized to investigate the molecular mechanisms regulated by p38. PLB phosphorylation was enhanced in cardiomyocytes by chemical p38 inhibition, by overexpression of dominant negative p38α and by p38α RNAi, but not with dominant negative p38ß. Treatment of cardiomyocytes with dominant negative p38α significantly decreased Ca(2+)-transient decay time indicating enhanced sarco/endoplasmic reticulum Ca(2+)-ATPase function and increased cardiomyocyte contractility. Analysis of signaling mechanisms involved showed that inhibition of p38 decreased the activity of protein phosphatase 2A, which renders protein phosphatase inhibitor-1 phosphorylated and thereby inhibits PP1. In conclusion, inhibition of p38α enhances PLB phosphorylation and diastolic Ca(2+) uptake. Our findings provide evidence for novel mechanism regulating cardiac contractility upon p38 inhibition.

The NLRP3 inflammasome is up-regulated in cardiac fibroblasts and mediates myocardial ischaemia-reperfusion injury.

AIMS: Nucleotide-binding oligomerization domain-Like Receptor with a Pyrin domain 3 (NLRP3) is considered necessary for initiating a profound sterile inflammatory response. NLRP3 forms multi-protein complexes with Apoptosis-associated Speck-like protein containing a Caspase recruitment domain (ASC) and Caspase-1, which activate pro-interleukin-1ß (IL-1ß) and pro-IL-18. The role of NLRP3 in cardiac cells is not known. Thus, we investigated the expression and function of NLRP3 during myocardial ischaemia. METHODS AND RESULTS: Myocardial infarction (MI) was induced in adult C57BL/6 mice and Wistar rats by ligation of the coronary artery. A marked increase in NLRP3, IL-1ß, and IL-18 mRNA expression was found in the left ventricle after MI, primarily located to myocardial fibroblasts. In vitro studies in cells from adult mice showed that myocardial fibroblasts released IL-1ß and IL-18 when primed with lipopolysaccharide and subsequently exposed to the danger signal adenosine triphosphate, a molecule released after tissue damage during MI. When hearts were isolated from NLRP3-deficient mice, perfused and subjected to global ischaemia and reperfusion, a marked improvement of cardiac function and reduction of hypoxic damage was found compared with wild-type hearts. This was not observed in ASC-deficient hearts, potentially reflecting a protective role of other ASC-dependent inflammasomes or inflammasome-independent effects of NLRP3. CONCLUSION: This study shows that the NLRP3 inflammasome is up-regulated in myocardial fibroblasts post-MI, and may be a significant contributor to infarct size development during ischaemia-reperfusion.

Inflammatory cytokines in heart failure: mediators and markers.

Evidence from both experimental and clinical trials indicates that inflammatory mediators are of importance in the pathogenesis of chronic heart failure (HF) contributing to cardiac remodeling and peripheral vascular disturbances. Several studies have shown raised levels of inflammatory cytokines such as tumor necrosis factor (TNF)α, interleukin (IL)-1ß and IL-6 in HF patients in plasma and circulating leukocytes, as well as in the failing myocardium itself. There is strong evidence that these mediators are involved in processes leading to cardiac remodeling such as hypertrophy, fibrosis and apoptosis. Some of these cytokines can also give useful prognostic information as reliable biomarkers in this disorder. In general, immunomodulating treatments have, with a few exceptions, been neutral or even harmful. However, the negative results of anti-TNF studies, for instance, do not necessarily argue against the 'cytokine hypothesis'. These studies just underscore the challenges in developing treatment modalities that can modulate the cytokine network in HF patients and result in beneficial net effects. Future studies should identify the crucial actors and their mechanisms of action in the immunopathogenesis of chronic HF and, in particular, clarify the balance between adaptive and maladaptive effects of these molecules. Such studies are a prerequisite for the development of new treatment strategies that target inflammatory and immunopathogenic mechanisms in HF. In this review article, these issues are thoroughly discussed, and we also argue for the possibility of future therapeutic targets such as mediators in innate immunity, chemokines and mediators in matrix remodeling.

The homeostatic chemokine CCL21 predicts mortality and may play a pathogenic role in heart failure.

BACKGROUND: CCL19 and CCL21, acting through CCR7, are termed homeostatic chemokines. Based on their role in concerting immunological responses and their proposed involvement in tissue remodeling, we hypothesized that these chemokines could play a pathogenic role in heart failure (HF). METHODOLOGY/PRINCIPAL FINDINGS: Our main findings were: (i) Serum levels of CCL19 and particularly CCL21 were markedly raised in patients with chronic HF (n = 150) as compared with healthy controls (n = 20). A CCL21 level above median was independently associated with all-cause mortality. (ii) In patients with HF following acute myocardial infarction (MI; n = 232), high versus low CCL21 levels 1 month post-MI were associated with cardiovascular mortality, even after adjustment for established risk factors. (iii). Explanted failing human LV tissue (n = 29) had markedly increased expression of CCL21 as compared with non-failing myocardium (n = 5). (iv) Our studies in CCR7(-/-) mice showed improved survival and attenuated increase in markers of myocardial dysfunction and wall stress in post-MI HF after 1 week, accompanied by increased myocardial expression of markers of regulatory T cells. (v) Six weeks post-MI, there was an increase in markers of myocardial dysfunction and wall stress in CCR7 deficient mice. CONCLUSIONS/SIGNIFICANCE: High serum levels of CCL21 are independently associated with mortality in chronic and acute post-MI HF. Our findings in CCR7 deficient mice may suggest that CCL21 is not only a marker, but also a mediator of myocardial failure. However, while short term inhibition of CCR7 may be beneficial following MI, a total lack of CCR7 during long-term follow-up could be harmful.

Adrenomedullin is increased in alveolar macrophages and released from the lungs into the circulation in severe heart failure.

Adrenomedullin (AM) is a potent vasorelaxing peptide with natriuretic, diuretic, and growth inhibitory properties. Plasma concentrations and myocardial AM expression are increased in heart failure (HF). Since AM and AM binding sites are abundantly expressed in the lungs, we investigated to what extent pulmonary AM and AM receptor subtypes [CRLR/RAMP2 (AM1) and CRLR/RAMP3 (AM2)] are changed in HF and whether the lungs contribute to the increased plasma concentrations of AM reported in HF. Pulmonary AM mRNA and protein expression were increased by 2.8- and 2.6-fold, respectively, whereas mRNA expression of RAMP2 and CRLR was decreased in rats with HF 7 days after induction of MI compared to sham-operated rats (P < 0.05). Pulmonary AM receptor density was substantially decreased in HF rats compared to sham (3.7 +/-0.6 vs. 29.9 +/- 1.1 fmol/mg membrane protein; P < 0.05). Immunoreactivities against AM and the AM receptor components CRLR, RAMP2, and RAMP3 in the pulmonary tissue were seen in vascular smooth muscle cells, vascular endothelial cells, and in alveolar macrophages. AM mRNA expression in alveolar macrophages obtained from HF rats by bronchoalveolar lavage was 2.9-fold higher than in sham-operated rats (P < 0.05). An even more substantial increase of AM mRNA expression was found in alveolar macrophages from patients with HF (10-fold, P < 0.05), and this increase displayed a negative correlation to left ventricular systolic function (P < 0.05). Furthermore, a net release of AM from the lungs into the circulation was only found in HF patients with the most severe left ventricular systolic dysfunction. Thus, our data demonstrate increased expression and decreased receptor binding of AM in the lungs in severe HF. Furthermore, our data indicate that alveolar macrophages are an important source of pulmonary AM in both experimental and clinical HF. Finally, a net release of AM from the lungs into the circulation was only found in patients with severe systolic dysfunction.

Increased production of CXCL16 in experimental and clinical heart failure: a possible role in extracellular matrix remodeling.

BACKGROUND: Inflammation has been implicated in the pathogenesis of heart failure (HF), but knowledge about the production and role of inflammatory actors remains incomplete. On the basis of its role in vascular inflammation, vascular proliferation, and matrix degradation, we hypothesized a role for the chemokine CXCL16 in the pathogenesis of myocardial remodeling and development of HF. METHODS AND RESULTS: Our main findings were (1) patients with chronic HF (n=188) had increased plasma levels of CXCL16, which correlated with disease severity. (2) Left ventricular tissue from patients with end-stage HF (n=8) showed enhanced CXCL16 levels compared with nonfailing left ventricular (n=6) as assessed by Western blotting. (3) In mice with postmyocardial infarction HF, expression of CXCL16, as assessed by real-time RT-PCR, was increased in the infarcted and the noninfarcted areas of left ventricular 3 and 7 days after coronary ligation, indicating early onset of CXCL16 production. Furthermore, mice exposed to aortic banding had enhanced CXCL16 expression in left ventricular, indicating that CXCL16 expression is not related to ischemia alone. (4) In vitro, CXCL16 promoted proliferation and impaired collagen synthesis in myocardial fibroblasts, and in cardiomyocytes and myocardial fibroblasts, CXCL16 increased matrix metalloproteinase activity, primarily reflecting increased matrix metalloproteinase-2 levels. (5) By using specific inhibitors, we showed that the effect of CXCL16 on fibroblasts involved activation of Jun N-terminal kinase. CONCLUSIONS: We show enhanced myocardial CXCL16 expression in experimental and clinical HF. The effect of CXCL16 on cardiomyocytes and fibroblasts suggests a role for CXCL16 in matrix remodeling and ultimately in the development of HF.