The myocardial matrix and the development and progression of ventricular remodeling

Mechanism of heart failure after myocardial infarction

Despite the widespread use of early revascularization and drugs to regulate the neuroendocrine system, the impact of such measures on alleviating the development of heart failure (HF) after myocardial infarction (MI) remains limited. Therefore, it is important to discuss the development of new therapeutic strategies to prevent or reverse HF after MI. This requires a better understanding of the potential mechanisms involved. HF after MI is the result of complex pathophysiological processes, with adverse ventricular remodeling playing a major role. Adverse ventricular remodeling refers to the heart's adaptation in terms of changes in ventricular size, shape, and function under the influence of various regulatory factors, including the mechanical, neurohormonal, and cardiac inflammatory immune environments; ischemia/reperfusion injury; energy metabolism; and genetic correlation factors. Additionally, unique right ventricular dysfunction can occur secondary to ischemic shock in the surviving myocardium. HF after MI may also be influenced by other factors. This review summarizes the main pathophysiological mechanisms of HF after MI and highlights sex-related differences in the prognosis of patients with acute MI. These findings provide new insights for guiding the development of targeted treatments to delay the progression of HF after MI and offering incremental benefits to existing therapies.

FOSL2 participates in renal fibrosis via SGK1-mediated epithelial-mesenchymal transition of proximal tubular epithelial cells

Background

Fos-related antigen 2 (FOSL2) plays a facilitative role in fibrotic disease; however, its role in renal fibrosis remains unclear. This study aimed to clarify the role and underlying mechanisms of FOSL2 in renal fibrosis.

Methods

Upregulated genes in unilateral ureteral obstruction (UUO)-injured kidneys were screened in Gene Expression Omnibus (GEO) databases, and overlapping genes were identified using Venn diagram software. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed for these genes. The UUO-induced mouse model and transforming growth factor-β1 (TGF-β1)-induced cell model were used for the in vivo and in vitro studies.

Results

A total of 43 commonly upregulated genes were identified. GO and KEGG pathway analyses indicated that FOSL2 may be involved in fibrosis. Furthermore, FOSL2 was confirmed to be upregulated in UUO-injured kidneys and TGF-β1-induced cells. Knockdown of FOSL2 ameliorated interstitial fibrosis, extracellular matrix deposition, and epithelial-mesenchymal transition via the downregulation of fibronectin, α-smooth muscle actin (α-SMA), collagen type I (Col1a1 and Col1a2), and Col5a1 and upregulation of E-cadherin. Bioinformatics analysis revealed that serum/glucocorticoid regulated kinase 1 (SGK1) may be regulated by FOSL2 and involved in renal fibrosis. Further experiments confirmed that TGF-β1 enhanced SGK1 expression and transcription, which were reversed by FOSL2 silencing. Moreover, FOSL2 was bound to the SGK1 promoter, and SGK1 overexpression reversed the effects of FOSL2 silencing in TGF-β1-induced cells.

Conclusion

FOSL2 plays an essential role in promoting renal fibrosis in an SGK1-dependent manner, and targeting the FOSL2/SGK1 signaling axis may offer a potential strategy for the treatment of renal fibrosis.

Global historical retrospect and future prospects on biomarkers of heart failure: A bibliometric analysis and science mapping

Introduction

Heart failure is a rapidly growing public health problem and has become a major cause of hospitalization in middle-aged and older adults. Biomarkers are clinically important in managing heart failure and have attracted more attention from researchers in recent years. This study aimed to evaluate the global research of heart failure biomarkers by bibliometrics and to identify the hot spots and perspectives for further advancement.

Methods

Selection of relevant documents was from the Web of Science Core Collection. Microsoft Excel, VOSviewer, SciMA, and CiteSpace software were used for bibliometric analysis.

Results

As of October 29, 2021, 5,978 documents for heart failure biomarkers have been identified from 1989 to 2021. European Journal of Heart Failure and Circulation respectively ranked first in terms of the number of publications and the number of co-citations. A total of 5,698 institutions from 90 countries participated in these publications, with the USA leading with 2,045 documents. The most productive institution was Harvard University. Januzzi, J.L. and Maisel, A.S. were the most productive and most cited authors respectively. Natriuretic peptide, copeptin, valsartan, ferric carboxymaltose, empagliflozin, preserved ejection fraction, myocardial fibrosis, and heart transplantation were hot themes.

Conclusions

Extensive national and inter-institutional collaboration should be enhanced to bridge the gap between developed and less developed countries in heart failure biomarkers research. The research in this field seems to have reached a relatively mature stage, with a decrease in research fervor in recent years. The study of the natriuretic peptide family still has high centrality, with advances in the study of expression products and inflammatory markers. Cardiac fibrosis, cardiac remodeling, and therapies regarding heart failure have become hot spots.

A strategic expression method of miR-29b and its anti-fibrotic effect based on RNA-sequencing analysis

Tissue fibrosis is a significant health issue associated with organ dysfunction and failure. Increased deposition of collagen and other extracellular matrix (ECM) proteins in the interstitial area is a major process in tissue fibrosis. The microRNA-29 (miR-29) family has been demonstrated as anti-fibrotic microRNAs. Our recent work showed that dysregulation of miR-29 contributes to the formation of cardiac fibrosis in animal models of uremic cardiomyopathy, whereas replenishing miR-29 attenuated cardiac fibrosis in these animals. However, excessive overexpression of miR-29 is a concern because microRNAs usually have multiple targets, which could result in unknown and unexpected side effect. In the current study, we constructed a novel Col1a1-miR-29b vector using collagen 1a1 (Col1a1) promoter, which can strategically express miR-29b-3p (miR-29b) in response to increased collagen synthesis and reach a dynamic balance between collagen and miR-29b. Our experimental results showed that in mouse embryonic fibroblasts (MEF cells) transfected with Col1a1-miR-29b vector, the miR-29b expression is about 1000 times less than that in cells transfected with CMV-miR-29b vector, which uses cytomegalovirus (CMV) as a promoter for miR-29b expression. Moreover, TGF-β treatment increased the miR-29b expression by about 20 times in cells transfected with Col1a1-miR-29b, suggesting a dynamic response to fibrotic stimulation. Western blot using cell lysates and culture media demonstrated that transfection of Col1a1-miR-29b vector significantly reduced TGF-β induced collagen synthesis and secretion, and the effect was as effective as the CMV-miR-29b vector. Using RNA-sequencing analysis, we found that 249 genes were significantly altered (180 upregulated and 69 downregulated, at least 2-fold change and adjusted p-value <0.05) after TGF-β treatment in MEF cells transfected with empty vector. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis using GAGE R-package showed that the top 5 upregulated pathways after TGF-β treatment were mostly fibrosis-related, including focal adhesion, ECM reaction, and TGF-β signaling pathways. As expected, transfection of Col1a1-miR-29b or CMV-miR-29b vector partially reversed the activation of these pathways. We also analyzed the expression pattern of the top 100 miR-29b targeting genes in these cells using the RNA-sequencing data. We identified that miR-29b targeted a broad spectrum of ECM genes, but the inhibition effect is mostly moderate. In summary, our work demonstrated that the Col1a1-miR-29b vector can be used as a dynamic regulator of collagen and other ECM protein expression in response to fibrotic stimulation, which could potentially reduce unnecessary side effect due to excessive miR-29b levels while remaining an effective potential therapeutic approach for fibrosis.

Atrial fibrillation and cardiac fibrosis: A review on the potential of extracellular matrix proteins as biomarkers

The involvement of fibrosis as an underlying pathology in heart diseases is becoming increasingly clear. In recent years, fibrosis has been granted a causative role in heart diseases and is now emerging as a major contributor to Atrial Fibrillation (AF) pathogenesis. AF is the most common arrhythmia encountered in the clinic, but the substrate for AF is still being debated. Consensus in the field is a combination of cardiac tissue remodeling, inflammation and genetic predisposition. The extracellular matrix (ECM) is subject of growing investigation, since measuring circulatory biomarkers of ECM formation and degradation provides both diagnostic and prognostic information. However, fibrosis is not just fibrosis. Each specific collagen biomarker holds information on regulatory mechanisms, as well as information about which section of the ECM is being remodeled, providing a detailed description of cardiac tissue homeostasis. This review entails an overview of the implication of fibrosis in AF, the different collagens and their significance, and the potential of using biomarkers of ECM remodeling as tools for understanding AF pathogenesis and identifying patients at risk for further disease progression.

Modulation of miR-10a-mediated TGF-β1/Smads signaling affects atrial fibrillation-induced cardiac fibrosis and cardiac fibroblast proliferation

Atrial fibrillation (AF) rat models and rat cardiac fibroblasts (CFs) with overexpressed or inhibited miR-10a were used to investigate the possible role of miR-10a-mediated transforming growth factor-β (TGF-β1)/Smads signaling in cardiac fibrosis and fibroblast proliferation in rats with AF. Gene ontology and pathway enrichment analyses were used to identify the possible function of miR-10a in cardiac fibrosis. The results showed that overexpressed miR-10a significantly prolonged the duration of AF, further elevated the collagen volume fraction (CVF), and increased the viability of CFs in AF rats; these findings were in contrast with the findings for rats with inhibition of miR-10a (all P<0.05). Moreover, miR-10a overexpression could promote miR-10a, collagen-I, collagen III, α-SMA, and TGF-β1 protein expression and increase the levels of hydroxyproline but reduced Smad7 protein expression in atrial tissues and CFs in AF rats. Not surprisingly, inhibiting miR-10a led to completely contrasting results (all P<0.05). Moreover, TGF-β1 treatment could reverse the inhibitory effect of miR-10a down-regulation on cardiac fibrosis in CFs. Bioinformatics analysis and luciferase reporter assay results demonstrated that miR-10a bound directly to the 3′-UTR of BCL6, which is involved in cell growth and proliferation. Thus, our study indicate that down-regulation of miR-10a may inhibit collagen formation, reduce atrial structure remodeling, and decrease proliferation of CFs, eventually suppressing cardiac fibrosis in AF rats via inhibition of the TGF-β1/Smads signaling pathway.

The prothrombotic state in atrial fibrillation: pathophysiological and management implications

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia and is associated with significant morbidity and mortality. There is plenty of evidence available to support the presence of a prothrombotic or hypercoagulable state in AF, but the contributory factors are multifactorial and cannot simply be explained by blood stasis. Abnormal changes in atrial wall (anatomical and structural, as ‘vessel wall abnormalities’), the presence of spontaneous echo contrast to signify abnormal changes in flow and stasis (‘flow abnormalities’), and abnormal changes in coagulation, platelet, and other pathophysiologic pathways (‘abnormalities of blood constituents’) are well documented in AF. The presence of these components therefore fulfils Virchow’s triad for thrombogenesis. In this review, we present an overview of the established and professed pathophysiological mechanisms for thrombogenesis in AF and its management implications.

The relationship between myocardial fibrosis and myocardial microRNAs in dilated cardiomyopathy: A link between mir-133a and cardiovascular events

It is unknown whether fibrosis‐associated microRNAs: miR‐21, miR‐26, miR‐29, miR‐30 and miR‐133a are linked to cardiovascular (CV) outcome. The study evaluated the levels of extracellular matrix (ECM) fibrosis and the prevalence of particular microRNAs in patients with dilated cardiomyopathy (DCM) to investigate any correlation with CV events. Methods: Seventy DCM patients (48 ± 12 years, EF 24.4 ± 7.4%) underwent right ventricular biopsy. The control group was comprised of 7 patients with CAD who underwent CABG and intraoperative biopsy. MicroRNAs were measured in blood and myocardial tissue via qPCR. The end‐point was a combination of CV death and urgent HF hospitalization at the end of 12 months. There were differential levels of circulating and myocardial miR‐26 and miR‐29 as well as myocardial miR‐133a when the DCM and CABG groups were compared. Corresponding circulating and myocardial microRNAs did not correlate with one another. There was no correlation between microRNA and ECM fibrosis. By the end of the 12‐month period of the study, CV death had occurred in 6 patients, and a further 19 patients required urgent HF hospitalization. None of the circulating microRNAs was a predictor of the combined end‐point; however, myocardial miR‐133a was an independent predictor in unadjusted models (HR 1.53; 95% CI 1.14‐2.05; P < .004) and adjusted models (HR 1.57; 95% CI 1.14‐2.17; P < .005). The best cut‐off value for the miR‐133a level for the prediction of the combined end‐point was 0.74 ΔCq, with an AUC of 0.67. The absence of a correlation between the corresponding circulating and myocardial microRNAs calls into question their cellular source. This study sheds new light on the role of microRNAs in ECM fibrosis in DCM, which warrants further exploration.

SHIP, a novel factor to ameliorate extracellular matrix accumulation via suppressing PI3K/Akt/CTGF signaling in diabetic kidney disease

Tubular interstitial extracellular matrix accumulation, which plays a key role in the pathogenesis and progression of diabetic kidney disease (DKD), is believed to be mediated by activation of PI3K/Akt signal pathway. However, it is still not clear whether SH2 domain-containing inositol 5'-phosphatase (SHIP), known as a negative regulator of PI3K/Akt pathway is also involved in extracellular matrix metabolism of diabetic kidney. In the present study, decreased SHIP and increased phospho-Akt (Ser 473, Thr 308) were found in renal tubular cells of diabetic mice accompanied by overexpression of connective tissue growth factor (CTGF) and extracellular matrix deposition versus normal mice. Again, high glucose attenuated SHIP expression in a time-dependent manner, concomitant with activation of PI3K/Akt signaling and extracellular matrix production in human renal proximal tubular epithelial cells (HK2) cultured in vitro, which was significantly prevented by transfection of M90-SHIP vector. Furthermore, in vivo delivery of rAd-INPP5D vector (SHIP expression vector) via intraperitoneal injection in diabetic mice increased SHIP expression by 3.36 times followed by 65.26%, 70.38% and 46.71% decreases of phospho-Akt (Ser 473), phospho-Akt (Thr 308) and CTGF expression versus diabetic mice receiving rAd-EGFP vector. Meanwhile, increased renal extracellular matrix accumulation of diabetic mice was also inhibited with intraperitoneal injection of rAd-INPP5D vector. These above data suggested that overexpression of SHIP might be a potent method to lessen renal extracellular matrix accumulation via inactivation of PI3K/Akt pathway and suppression of CTGF expression in DKD.

Fibrosis of extracellular matrix is related to the duration of the disease but is unrelated to the dynamics of collagen metabolism in dilated cardiomyopathy

Background

Fibrosis of extracellular matrix (ECM) in dilated cardiomyopathy (DCM) corresponds to the myocardial over-production of various types of collagens. However, mechanism of this process is poorly understood.

Objective

To investigate whether enhanced metabolism of ECM occur in DCM.

Methods

Seventy consecutive DCM patients (pts) (48 ± 12.1 years, EF 24.4 ± 7.4 %) and 20 healthy volunteers were studied. Based on symptoms duration, pts were divided into new-onset (n = 35, 6 months) and chronic DCM (n = 35, >6 months). Markers of collagen type I and III synthesis-procollagen type I carboxy- and amino-terminal peptides (PICP and PINP) and procollagen type III carboxy- and amino-terminal peptides (PIIICP and PIIINP), collagen 1 (col-1), ECM metabolism controlling factors—tumor growth factor beta-1 (TGF1-β), connective tissue growth factor (CTGF), and ECM degradation enzymes—matrix metalloproteinases (MMP-2, MMP-9) and their tissue inhibitor (TIMP-1) were measured in serum. All pts underwent right ventricular endomyocardial biopsy to study ECM fibrosis.

Results

The presence of fibrosis was detected in 24 (34.3 %) pts and was more prevalent in chronic DCM [17 (48.6 %) vs. 7 (20 %), p < 0.01]. The levels of PIIINP [4.41 (2.17–6.08) vs. 3.32 (1.69–5.02) ng/ml, p < 0.001], CTGF [3.82 (0.48–23.87) vs. 2.37 (0.51–25.32) ng/ml, p < 0.01], MMP-2 [6.06 (2.72–14.8) vs. 4.43 (2.27–7.4) ng/ml, p < 0.001], MMP-9 [1.98 (0.28–9.25) vs. 1.01 (0.29–3.59) ng/ml, p < 0.002)], and TIMP-1 [15.29 (1.8–36.17) vs. 2.61 (1.65–24.09) ng/ml, p < 0.004] were significantly higher in DCM, whereas levels of col-1 [57.7 (23.1–233.4) vs. 159.4 (31.2–512.9) pg/ml, p < 0.001] were significantly lower in DCM compared to controls. There were no differences in all measured serum markers of ECM metabolism between newonset and chronic DCM and as well as fibrosis positive and negative pts. Fibrosis was weakly correlated only with the duration of DCM (r = 0.23, p < 0.05), however, not a single serum marker of fibrosis correlated with fibrosis. Neither unadjusted nor adjusted models, constructed from serum markers of ECM metabolism, predicted the probability of myocardial fibrosis.

Conclusions

Dynamics of ECM turnover in DCM is high, which is reflected by the increased levels CTGF and degradation enzymes. Synthesis of collagen type III prevailed over collagen type I. ECM metabolism was not different in DCM regardless of the duration of the disease and status of myocardial fibrosis. Serum markers of ECM metabolism were found not to be useful for the prediction of myocardial fibrosis in DCM.

Extracellular matrix biomarker, fibulin-1, is closely related to NT-proBNP and soluble urokinase plasminogen activator receptor in patients with aortic valve stenosis (the SEAS study)

Background

Fibulin-1, a circulating extracellular matrix glycoprotein, has been associated with arterial disease and elevated N-terminal prohormone B-type natriuretic peptide (NT-proBNP) in diabetes. Soluble urokinase plasminogen activator receptor (suPAR), a marker of inflammation, has been associated with subclinical atherosclerosis. Therefore, we aimed to explore the interplay between these biomarkers and mild to moderate aortic valve stenosis (AS).

Methods

In 374 patients with mild to moderate AS, we investigated the relationship of fibulin-1 with NT-proBNP, levels of suPAR and the degree of AS at baseline and after one and four years of treatment with Simvastatin 40 mg and Ezetimibe 10 mg or placebo.

Results

During treatment, fibulin-1 became more closely associated with NT-proBNP (β_year0 = 0.10, p = 0.08, β_year1 = 0.16, p = 0.005, β_year4 = 0.22, p<0.001) and suPAR (β_year0 = 0.05, p = 0.34, β_year1 = 0.16, p = 0.006, β_year4 = 0.13, p = 0.03) at the expense of the association to aortic valve area index (AVAI) (β_year0 = −0.14, p = 0.005, β_year1 = −0.08, p = 0.11, β_year4 = −0.06, p = 0.22) independently of age, gender, creatinine, and serum aspartate aminotransferase (Adj.R_year0² = 0.19, Adj.R_year1² = 0.22, Adj.R_year4² = 0.27). Fibulin-1 was unrelated to aortic regurgitation, left ventricular mass, and ejection fraction. In patients with baseline AVAI<0.58 cm²/m² (median value), fibulin-1 was more closely associated to NT-proBNP (β_year0 = 0.25, β_year1 = 0.21, β_year4 = 0.22, all p<0.01), and suPAR (β_year0 = 0.09, p = 0.26, β_year1 = 0.23, β_year4 = 0.21, both p<0.01) independently of age, gender, AST and treatment allocation.

Conclusions

Increased levels of fibulin-1 were independently associated with higher levels of suPAR and NT-proBNP especially in patients with lower AVAI, suggesting that fibulin-1 may be an early marker of AS as well as cardiac fibrosis secondarily to elevated left ventricular hemodynamic load.

NT-proBNP, C-reactive protein and soluble uPAR in a bi-ethnic male population: the SAfrEIC study

Objective and design

This cross-sectional study aimed to investigate associations between a marker of cardiac strain, the N-terminal prohormone B-type natriuretic peptide (NT-proBNP), and inflammation as reflected by either a conventional or novel inflammatory marker in a bi-ethnic South African cohort.

Methods and subjects

We measured NT-proBNP, C-reactive protein (CRP) and plasma-soluble urokinase plasminogen activator receptor (suPAR) levels along with conventional biomarkers in black (n = 117) and white (n = 116) men.

Results

NT-proBNP, CRP and suPAR levels were higher in black compared to white men. NT-proBNP was significantly associated with both CRP (r = 0.38; p = 0.001) and suPAR (r = 0.42; p<0.001) in black men only. After full adjustment in multiple regression analyses, the above associations of NT-proBNP with CRP (β = 0.199; p = 0.018) and suPAR (β = 0.257; p<0.01) were confirmed in black men.

Conclusion

These results suggest that a low-grade inflammatory state as reflected by both a conventional and novel marker of inflammation may contribute to higher cardiovascular risk as reflected by the associations obtained with a marker of cardiac strain in black South African men.

NT-proBNP is associated with fibulin-1 in Africans: the SAfrEIC study

OBJECTIVES

The N-terminal prohormone B-type natriuretic peptide (NT-proBNP) is involved in the regulation of volume load and secreted when systemic cardiac overload occurs. Fibulin-1 on the other hand is a component of many extracellular matrix proteins including those present in atherosclerotic lesions, expressed in elastin-containing fibres of blood vessels, and also in the heart. Due to an alarming prevalence of hypertensive heart disease in black South Africans, we investigated the associations of NT-proBNP with fibulin-1 and markers of arterial stiffness in Africans and Caucasians.

METHODS

We included 231 Africans and 238 Caucasians from South Africa aged 22-77 years. Serum NT-proBNP and fibulin-1 levels were determined, and arterial compliance and pulse wave velocity were measured.

RESULTS

Africans had significantly higher blood pressure and NT-proBNP levels than Caucasians and African men had higher fibulin-1 levels than Caucasian men. In single regression analysis, NT-proBNP was significantly associated with fibulin-1 in African men and Caucasian women. NT-proBNP correlated negatively with arterial compliance in all groups except Caucasian women. After partial adjustments, the association between NT-proBNP and fibulin-1 strengthened in African men only. After full adjustment in multiple regression analysis, the association of NT-proBNP with fibulin-1 was confirmed in African men (R(2)=0.41; β=0.26; p<0.01) and also in younger women (R(2)=0.34; β=0.251; p=0.012).

CONCLUSIONS

Only Africans indicated a significant independent association between NT-proBNP and fibulin-1, suggesting that cardiovascular alterations are already present in this relatively young African population as opposed to Caucasians.

Mechanisms of thrombogenesis in atrial fibrillation: Virchow's triad revisited

Atrial fibrillation is the most common sustained cardiac arrhythmia, which is associated with a high risk of stroke and thromboembolism. Increasing evidence suggests that the thrombogenic tendency in atrial fibrillation is related to several underlying pathophysiological mechanisms. Abnormal changes in flow are evident by stasis in the left atrium, and seen as spontaneous echocontrast. Abnormal changes in vessel walls-essentially, anatomical and structural defects-include progressive atrial dilatation, endocardial denudation, and oedematous or fibroelastic infiltration of the extracellular matrix. Additionally, abnormal changes in blood constituents are well described, and include haemostatic and platelet activation, as well as inflammation and growth factor changes. These changes result in the fulfilment of Virchow's triad for thrombogenesis, and accord with a prothrombotic or hypercoagulable state in this arrhythmia. In this Review, we present an overview of the established and purported mechanisms for thrombogenesis in atrial fibrillation.

Increased expression of extracellular matrix proteins in rapid atrial pacing-induced atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is characterized by structural remodeling of the extracellular matrix (ECM) in cardiac atrium.

OBJECTIVE

The purpose of this study was to gain further insight into atrial ECM remodeling at the molecular level and to test whether altered expression of ECM proteins was associated with the disease.

METHODS

Sustained AF was induced in nine adult pigs after 3-4 weeks of continuous rapid atrial pacing at a rate of 600 bpm. Histologic studies and immunohistochemical stain were performed to identify the potential pathologic substrate underlying abnormalities in atrial tissues with sustained AF.

RESULTS

In the pathologic findings, the fraction of myocardial ECM (ECM%) was measured, with a significantly greater ECM% found in the AF group compared with the sham operated group (n = 6; i.e., pigs with normal sinus rhythm [SR]). A set of 9,182 genes was screened with cDNA microarray analysis. In AF animals, expression of 121 genes increased and 24 genes decreased by > or =1.75-fold compared with SR animals. Significant up-regulation of fibronectin-1 (4.9-fold), fibrillin-1 (3.1-fold), and fibromodulin (1.9-fold) in the fibrillating atria was confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction. Western blot analysis revealed significantly increased atrial fibronectin-1, fibrillin-1, and fibromodulin in the AF group compared with the SR group (1.5-, 2.7-, and 2.1-fold, respectively). Immunohistochemical staining of AF tissue displayed increased accumulation of fibronectin-1 and fibrillin-1 in the atrial interstitial space.

CONCLUSION

Increased expression of ECM proteins in fibrillating atria supports the hypothesis that ECM metabolism contributes to the development of AF.

Novel and potential future biomarkers for assessment of the severity and prognosis of chronic heart failure

Over the last two decades, the pathophysiology and biomolecular basis of heart failure syndrome has reached sound and more comprehensive understanding. This knowledge has allowed expert researchers and clinicians to explore an entirely new spectrum of potential biochemical markers derived from different cellular and signaling pathways that lead to myocardial hypertrophy, chronic damage of the myocyte, apoptosis, and, ultimately, myocardial remodeling. Indeed, the link between myocardial remodeling and adverse outcomes, as well as the recognition of the myocardial interstitium as a multifunctional dynamic entity strongly influenced by systemic neurohormonal and inflammatory activation, has provided a solid ground for research of biomarkers that might correlate with severity and prognostication in chronic heart failure. This paper reviews and summarize recent literature on some of the most interesting circulating biomarkers with potential use for the stratification of patients with chronic heart failure.

Atrial Extracellular Matrix Remodeling and the Maintenance of Atrial Fibrillation

Background— Remodeling occurs in both ventricle and atrium in dilated cardiomyopathy and heart failure. However, the alteration of atrial extracellular matrix components during remodeling and its effect on the electrical remodeling and atrial arrhythmia have never been explored.

Methods and Results— Atrial tissue samples of 53 explanted hearts from patients with dilated cardiomyopathy and end-stage heart failure who underwent heart transplantation were examined. Nineteen patients had permanent atrial fibrillation (PmAF), 18 had persistent AF (PsAF), and 16 had no documented AF (NAF). Sixteen donor left atria (LA) were used as controls (CNs). Western Blot analysis revealed a selective downregulation of tissue inhibitor of metalloproteinase (TIMP)-2 in PmAF and PsAF groups compared with the NAF and CN groups and an upregulation of atrial metalloproteinase (MMP)-2 that was most pronounced in the PmAF group followed by the PsAF and NAF groups. Immunofluorescent staining revealed that in the LA, type I collagen volume fraction (CVF-I) increased significantly in the PmAF group followed by the PsAF and NAF groups compared with that in CN. LA CVF-I significantly correlated with LA dimension and TIMP-2 to MMP-2 ratio. In the PsAF group, CVF-I/CVF-III ratio was significantly correlated with AF duration and the frequency of AF recurrence.

Conclusions— Atrial extracellular matrix remodeling manifested by the selective downregulation of TIMP-2 along with upregulation of MMP-2 and CVF-I in the atrium is associated with the development of sustained atrial fibrillation in patients with cardiomyopathy and heart failure.

Matrix metalloproteinases: regulation and dysregulation in the failing heart

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes responsible for myocardial extracellular protein degradation. Several MMP species identified within the human myocardium may be dysregulated in congestive heart failure (CHF). For example, MMPs that are expressed at very low levels in normal myocardium, such as collagenase-3 (MMP-13) and the membrane-type-1 MMPs, are substantially upregulated in CHF. However, MMP species are not uniformly increased in patients with end-stage CHF, suggesting that a specific portfolio of MMPs are expressed in the failing myocardium. With the use of animal models of CHF, a mechanistic relationship has been demonstrated with respect to myocardial MMP expression and the left ventricular (LV) remodeling process. The tissue inhibitors of the MMPs (TIMPs) are locally synthesized proteins that bind to active MMPs and thereby regulate net proteolytic activity. However, there does not appear to be a concomitant increase in myocardial TIMPs during the LV remodeling process and progression to CHF. This disparity between MMP and TIMP levels favors a persistent MMP activation state within the myocardium and likely contributes to the LV remodeling process in the setting of developing CHF. The elucidation of upstream signaling mechanisms that contribute to the selective induction of MMP species within the myocardium as well as strategies to normalize the balance between MMPs and TIMPs may yield some therapeutic strategies by which to control myocardial extracellular remodeling and thereby slow the progression of the CHF process.