Advancements in gene therapy approaches for atrial fibrillation: Targeted delivery, mechanistic insights and future prospects

Atrial fibrillation (AF) remains a complex and challenging arrhythmia to treat, necessitating innovative therapeutic strategies. This review explores the evolving landscape of gene therapy for AF, focusing on targeted delivery methods, mechanistic insights, and future prospects. Direct myocardial injection, reversible electroporation, and gene painting techniques are discussed as effective means of delivering therapeutic genes, emphasizing their potential to modulate both structural and electrical aspects of the AF substrate. The importance of identifying precise targets for gene therapy, particularly in the context of AF-associated genetic, structural, and electrical abnormalities, is highlighted. Current studies employing animal models, such as mice and large animals, provide valuable insights into the efficacy and limitations of gene therapy approaches. The significance of imaging methods for detecting atrial fibrosis and guiding targeted gene delivery is underscored. Activation mapping techniques offer a nuanced understanding of AF-specific mechanisms, enabling tailored gene therapy interventions. Future prospects include the integration of advanced imaging, activation mapping, and percutaneous catheter-based techniques to refine transendocardial gene delivery, with potential applications in both ventricular and atrial contexts. As gene therapy for AF progresses, bridging the translational gap between preclinical models and clinical applications is imperative for the successful implementation of these promising approaches.

Angiotensin-receptor blocker losartan alleviates atrial fibrillation in rats by downregulating frizzled 8 and inhibiting the activation of WNT-5A pathway

Atrial fibrillation (AF) is a common arrhythmia. Angiotensin-receptor blocker (ARB) is related to AF treatment. This study explored the mechanism of ARB in AF. AF rat models were established by Ach-CaCl2 mixed solution injection. Rats were treated with ARB by gavage and injected with pcDNA3.1-based frizzled homolog 8 (FZD8) overexpression plasmids (oe-FZD8) through the tail vein. The 12-lead electrocardiogram was recorded by biological signal acquisition and processing system and AF duration was recorded, and atrial effective refractory period (AERP) was monitored by electrophysiology. Atrial fibrosis degree, FZD8 messenger RNA and protein levels, collagen I, collagen III, transforming growth factor β1 (TGF-β1), fibronectin, α smooth muscle actin (α-SMA), WBT-5B, and p-JNK1/2 levels, interleukin 1 β (IL-1β) and interleukin 6 (IL-6) levels were detected by Masson staining, reverse transcription quantitative polymerase chain reaction, western blot assay, immunohistochemistry, and enzyme-linked immunosorbent assay. ACh-CaCl2-induced AF rats showed a large area of fused necrosis, abnormal collagen fibre proliferation, high atrial fibrosis degree, and increased atrial fibrosis area in atrial interstitium, elevated collagen I, collagen III, TGF-β1, fibronectin, α-SMA, IL-1β, and IL-6 levels, whereas these trends were averted by ARB treatment. FZD8 was highly expressed in AF rat myocardium. ARB repressed FZD8 expression, prolonged AERP and reduced AF incidence. FZD8 overexpression annulled the effects of ARB on improving AF rat myocardial fibrosis. ARB inactivated the WNT-5A pathway by suppressing FZD8. ARB inactivated the WNT-5A pathway by silencing FZD8, therefore, alleviating AF rat atrial fibrosis.

miR-29b ameliorates atrial fibrosis in rats with atrial fibrillation by targeting TGFβRΙ and inhibiting the activation of Smad-2/3 pathway

OBJECTIVE

Atrial fibrillation (AF) is a major cause of stroke with lifetime risks. microRNAs (miRNAs) are associated with AF attenuation, yet the mechanism remains unknown. This study investigated the functional mechanism of miR-29b in atrial fibrosis in AF.

METHODS

The AF rat model was established by a 7-day intravenous injection of Ach-CaCl₂ mixture. AF rats were injected with adeno-associated virus (AAv)-miR-29b and TGFβRΙ overexpression plasmid. AF duration was recorded by electrocardiogram. Atrial fibrosis was observed by Masson staining. Expressions of COL1A1, COL3A1, TGFβRΙ, TGFβΙ, miR-29b and Smad-2/3 pathway-related proteins in atrial tissues were detected by RT-qPCR and Western blot. Binding sites of miR-29b and TGFβRΙ were predicted and their target relationship was verified by dual-luciferase reporter assay.

RESULTS

miR-29b was poorly expressed and expressions of COL1A1, COL3A1, TGFβRΙ, and TGFβ1 were increased in atrial tissues of AF rats. miR-29b overexpression alleviated atrial fibrosis, reduced expressions of COL1A1, COL3A1, and TGFβ1, and shortened AF duration in AF rats. TGFβRΙ was highly expressed in atrial tissues of AF rats. miR-29b targeted TGFβRΙ. TGFβRΙ overexpression overcame the improving effect of miR-29b overexpression on AF. miR-29b overexpression decreased ratios of p-Smad-2/3 and Smad-2/3 and inhibited the Smad-2/3 pathway.

CONCLUSION

miR-29b might mitigate atrial fibrosis in AF rats by targeting TGFβRΙ and inhibiting the Smad-2/3 pathway.

Atrial fibrillation and cardiac fibrosis

The understanding of atrial fibrillation (AF) evolved from a sole rhythm disturbance towards the complex concept of a cardiomyopathy based on arrhythmia substrates. There is evidence that atrial fibrosis can be visualized using late gadolinium enhancement cardiac magnetic resonance imaging and that it is a powerful predictor for the outcome of AF interventions. However, a strategy of an individual and fibrosis guided management of AF looks promising but results from prospective multicentre trials are pending. This review gives an overview about the relationship between cardiac fibrosis and AF focusing on translational aspects, clinical observations, and fibrosis imaging to emphasize the concept of personalized paths in AF management taking into account the individual amount and distribution of fibrosis.

Atrial fibrosis underlying atrial fibrillation (Review)

Atrial fibrillation (AF) is one of the most common tachyarrhythmias observed in the clinic and is characterized by structural and electrical remodelling. Atrial fibrosis, an emblem of atrial structural remodelling, is a complex multifactorial and patient-specific process involved in the occurrence and maintenance of AF. Whilst there is already considerable knowledge regarding the association between AF and fibrosis, this process is extremely complex, involving intricate neurohumoral and cellular and molecular interactions, and it is not limited to the atrium. Current technological advances have made the non-invasive evaluation of fibrosis in the atria and ventricles possible, facilitating the selection of patient-specific ablation strategies and upstream treatment regimens. An improved understanding of the mechanisms and roles of fibrosis in the context of AF is of great clinical significance for the development of treatment strategies targeting the fibrous region. In the present review, a focus was placed on the atrial fibrosis underlying AF, outlining its role in the occurrence and perpetuation of AF, by reviewing recent evaluations and potential treatment strategies targeting areas of fibrosis, with the aim of providing a novel perspective on the management and prevention of AF.

How transforming growth factor contributes to atrial fibrillation?

Atrial fibrillation (AF) is the most common clinically significant arrhythmia. There are four fundamental pathophysiological mechanisms of AF including: electrical remodeling, structural remodeling, autonomic nervous system changes, and Ca2+ handling abnormalities. The transforming growth factor-β (TGF-β) superfamily are cytokines that have the ability to regulate numerous cell functions including proliferation, differentiation, apoptosis, epithelial-mesenchymal transition, and production of extracellular matrix. During the last decade numerous studies have demonstrated that TGF-β affects the architecture of the heart. TGF-β1 has been shown to be involved in the development and propagation of atrial fibrillation (AF). Investigators have studied TGF-β signaling in AF with the aim of discovering potential therapeutic agents. In this review we discuss the role of TGF-β in atrial fibrillation and specifically its role in atrial structural and electrical remodeling.

Atrial matrix remodeling in atrial fibrillation patients with aortic stenosis

BACKGROUND

This study aimed to evaluate atrium extracellular matrix remodeling in atrial fibrillation (AF) patients with severe aortic stenosis, through histological fibrosis quantification and extracellular matrix gene expression analysis, as well as serum quantification of selected protein targets.

METHODS

A posthoc analysis of a prospective study was performed in a cohort of aortic stenosis patients. Between 2014 and 2019, 56 patients with severe aortic stenosis submitted to aortic valve replacement surgery in a tertiary hospital were selected.

RESULTS

Fibrosis was significantly increased in the AF group when compared to sinus rhythm (SR) patients (p = 0.024). Moreover, cardiomyocyte area was significantly higher in AF patients versus SR patients (p = 0.008). Conversely, collagen III gene expression was increased in AF patients (p = 0.038). TIMP1 was less expressed in the atria of AF patients. MMP16/TIMP4 ratio was significantly decreased in AF patients (p = 0.006). TIMP1 (p = 0.004) and TIMP2 (p = 0.012) were significantly increased in the serum of AF patients. Aortic valve maximum (p = 0.0159) and mean (p = 0.031) gradients demonstrated a negative association with serum TIMP1.

CONCLUSIONS

Atrial fibrillation patients with severe aortic stenosis present increased atrial fibrosis and collagen type III synthesis, with extracellular matrix remodelling demonstrated by a decrease in the MMP16/TIMP4 ratio, along with an increased serum TIMP1 and TIMP2 proteins.

Relationship Between 25-Hydroxyvitamin D, Renin, and Collagen Remodeling Biomarkers in Atrial Fibrillation

The interplay between vitamin D, the renin-angiotensin system (RAS), and collagen remodeling has been implicated in the pathogenesis of various cardiovascular diseases. This study sought to explore this relationship in atrial fibrillation (AF) by profiling plasma levels of 25-hydroxyvitamin D, RAS biomarkers, and collagen remodeling biomarkers using the enzyme-linked immunosorbent assay method. We hypothesized that 25-hydroxyvitamin D levels would inversely correlate with RAS biomarkers and that levels of RAS and collagen remodeling biomarkers would positively correlate with each other. Although our AF cohort (n = 37) did not exhibit decreased 25-hydroxyvitamin D levels compared to normal controls (n = 26), these levels inversely correlated with renin (Spearman r = -0.57, P = 0.005). Renin levels were elevated in patients with AF compared to normal controls (1233 ± 238 ng/mL vs 401 ± 27 ng/mL, P = 0.0002) and positively correlated with levels of matrix metalloproteinase 1 (MMP-1; Spearman r = 0.89, P = 0.01) and MMP-2 (Spearman r = 0.82, P = 0.03). These data suggest that 25-hydroxyvitamin D may influence RAS activation, and renin may help mediate the collagen remodeling process in AF. Understanding mediators of RAS dysregulation in AF may elucidate targets for therapeutic intervention to prevent collagen remodeling.

Useful applications of growth factors for cardiovascular regenerative medicine

Novel advances for cardiovascular diseases (CVDs) include regenerative approaches for fibrosis, hypertrophy, and neoangiogenesis. Studies indicate that growth factor (GF) signaling could promote heart repair since most of the evidence is derived from preclinical models. Observational studies have evaluated GF serum/plasma levels as feasible biomarkers for risk stratification of CVDs. Noteworthy, two clinical interventional published studies showed that the administration of growth factors (GFs) induced beneficial effect on left ventricular ejection fraction (LVEF), myocardial perfusion, end-systolic volume index (ESVI). To date, large scale ongoing studies are in Phase I-II and mostly focussed on intramyocardial (IM), intracoronary (IC) or intravenous (IV) administration of vascular endothelial growth factor (VEGF) and fibroblast growth factor-23 (FGF-23) which result in the most investigated GFs in the last 10 years. Future data of ongoing randomized controlled studies will be crucial in understanding whether GF-based protocols could be in a concrete way effective in the clinical setting.

Gene therapy for atrial fibrillation - How close to clinical implementation?

In this review we examine the current state of gene therapy for the treatment of cardiac arrhythmias. We describe advances and challenges in successfully creating and incorporating gene vectors into the myocardium. After summarizing the current scientific research in gene transfer technology we then focus on the most promising areas of gene therapy, the treatment of atrial fibrillation and ventricular tachyarrhythmias. We review the scientific literature to determine how gene therapy could potentially be used to treat patients with cardiac arrhythmias.

Longitudinal study of electrical, functional and structural remodelling in an equine model of atrial fibrillation

Background

Large animal models are important in atrial fibrillation (AF) research, as they can be used to study the pathophysiology of AF and new therapeutic approaches. Unlike other animal models, horses spontaneously develop AF and could therefore serve as a bona fide model in AF research. We therefore aimed to study the electrical, functional and structural remodelling caused by chronic AF in a horse model.

Method

Nine female horses were included in the study, with six horses tachypaced into self-sustained AF and three that served as a time-matched sham-operated control group. Acceleration in atrial fibrillatory rate (AFR), changes in electrocardiographic and echocardiographic variables and response to medical treatment (flecainide 2 mg/kg) were recorded over a period of 2 months. At the end of the study, changes in ion channel expression and fibrosis were measured and compared between the two groups.

Results

AFR increased from 299 ± 33 fibrillations per minute (fpm) to 376 ± 12 fpm (p < 0.05) and atrial function (active left atrial fractional area change) decreased significantly during the study (p < 0.05). No changes were observed in heart rate or ventricular function. The AF group had more atrial fibrosis compared to the control group (p < 0.05). No differences in ion channel expression were observed.

Conclusion

Horses with induced AF show signs of atrial remodelling that are similar to humans and other animal models.

Alteration in the expression of the renin-angiotensin system in the myocardium of mice conceived by in vitro fertilization

Epidemiological studies have revealed that offspring conceived by in vitro fertilization (IVF) have an elevated risk of cardiovascular malformations at birth, and are more predisposed to cardiovascular diseases. The renin-angiotensin system (RAS) plays an essential role in both the pathogenesis of congenital heart disease in fetuses and cardiovascular dysfunction in adults. This study aimed to assess the relative expression levels of genes in the RAS pathway in mice conceived using IVF, compared to natural mating with superovulation. Results demonstrated that expression of the angiotensin II receptor type 1 (AGTR1), connective tissue growth factor (CTGF), and collagen 3 (COL3), in the myocardial tissue of IVF-conceived mice, was elevated at 3 weeks, 10 weeks, and 1.5 years of age, when compared to their non-IVF counterparts. These data were supported by microRNA microarray analysis of the myocardial tissue of aged IVF-conceived mice, where miR-100, miR-297, and miR-758, which interact with COL3, AGTR1, and COL1 respectively, were upregulated when compared to naturally mated mice of the same age. Interestingly, bisulfite sequencing data indicated that IVF-conceived mice exhibited decreased methylation of CpG sites in Col1. In support of our in vivo investigations, miR-297 overexpression was shown to upregulate AGTR1 and CTGF, and increased cell proliferation in cultured H9c2 cardiomyocytes. These findings indicate that the altered expression of RAS in myocardial tissue might contribute to cardiovascular malformation and/or dysfunction in IVF-conceived offspring. Furthermore, these cardiovascular abnormalities might be the result of altered DNA methylation and abnormal regulation of microRNAs.

Synergistic effects of sulfur dioxide and polycyclic aromatic hydrocarbons on pulmonary pro-fibrosis via mir-30c-1-3p/ transforming growth factor β type II receptor axis

SO₂ and PAHs are well-known pollutants of coal burning and significant contributors to haze episodes. The purpose of the study is to determine whether the combined effects of SO₂ and BaP are synergetic and to investigate the pro-fibrotic influences and possible mechanism from the aspect of microRNAs. In the present study cellular metabolic activity of BEAS-2B was assessed using MTT probe. C57BL/6 mice were exposed to BaP (40 mg/kg b.w.) for 5 days or SO₂ (7 mg/m³) inhalation for 4 weeks alone or together. Lung tissues were processed for histology to assess pulmonary fibrosis. The protein level of pulmonary pro-fibrotic genes (Col1a1, Col3a1, alpha-SMA, fibronectin) and TGFβR2 were analyzed by Western blot and immunofluorescence in vivo and in vitro. Furthermore, we clarified that the microRNA expression of mir-30c-1-3p by real-time RT-PCR. The luciferase reporter assay was used to determine the binding sites of mir-30c-1-3p in the 3'-UTR of TGFβR2. It was confirmed that SO₂ and BaP acted together to produce synergistic effects in cellular metabolic activity. Coexisting of SO₂ and BaP increased the protein expression of pro-fibrotic genes and TGFβR2 and decreased mir-30c-1-3p in vivo and in vitro. Dual-luciferase reporter gene assays showed that TGFβR2 was a validated target of mir-30c-1-3p. All above results demonstrated that mir-30c-1-3p was involved in the synergistic pro-fibrotic effects of SO₂ and BaP in lung via targeting TGFβR2. This work implies the potential risk of pulmonary fibrosis from the co-existence of SO₂ and PAHs and provides new insights into the molecular markers for relevant diseases.

Association of Autoantibodies against M2-Muscarinic Acetylcholine Receptor with Atrial Fibrosis in Atrial Fibrillation Patients

Objectives

To investigate the association of serum autoantibodies against M2-muscarinic acetylcholine receptor (anti-M2-R) with atrial fibrosis in long-standing persistent atrial fibrillation (AF) patients.

Methods

Twenty-four long-standing persistent AF patients, scheduled to undergo hybrid ablation surgery, were enrolled in the study. Twenty-six patients with sinus rhythm, scheduled to undergo coronary artery bypass grafting surgery, were enrolled into the non-AF group. We detected serum anti-M2-R levels. Left atrial appendages were subjected to histological and molecular biological assays. Patients in the AF group received follow-up for two years.

Results

The AF group showed significantly higher serum anti-M2-R levels compared to the non-AF group (496.2 ± 232.5 vs. 86.3 ± 25.7 pmol/L, p < 0.001). The AF group exhibited severe fibrosis in the left atrial appendages, as indicated by increased collagen volume fraction (45.2 ± 4.7% vs. 27.6 ± 8.3%, p < 0.001), and higher levels of collagen I (0.52 ± 0.04 vs. 0.24 ± 0.06, p < 0.001) and collagen III (0.51 ± 0.07 vs. 0.36 ± 0.09, p < 0.001). TGF-β1 and CTGF were also upregulated in the AF group. A positive correlation between serum anti-M2-R levels and fibrosis of the left atrial appendage and fibrogenic indexes was observed.

Conclusions

Serum anti-M2-R levels are higher in AF patients and are associated with the severity of atrial fibrosis. In addition, serum anti-M2-R levels are positively correlated to TGF-β1 and CTGF expression in the left atrial appendage.

Oral administration of alcalase potato protein hydrolysate-APPH attenuates high fat diet-induced cardiac complications via TGF-β/GSN axis in aging rats

Consumption of high fat diet (HFD) is associated with increased cardiovascular risk factors among elderly people. Aging and obesity induced-cardiac remodeling includes hypertrophy and fibrosis. Gelsolin (GSN) induces cardiac hypertrophy and TGF-β, a key cytokine, which induces fibrosis. The relationship between TGF-β and GSN in aging induced cardiac remodeling is still unknown. We evaluated the expressions of TGF-β and GSN in HFD fed 22 months old aging SD rats, followed by the administration of either probucol or alcalase potato protein hydrolysate (APPH). Western blotting and Masson trichrome staining showed that APPH (45 and 75 mg/kg/day) and probucol (500 mg/kg/day) treatments significantly reduced the aging and HFD-induced hypertrophy and fibrosis. Echocardiograph showed that the performance of the hearts was improved in APPH, and probucol treated HFD aging rats. Serum from all rats was collected and H9c2 cells were cultured with collected serums separately. The GSN dependent hypertrophy was inhibited with an exogenous TGF-β in H9c2 cells cultured in HFD+ APPH treated serum. Thus, we propose that along with its role in cardiac fibrosis, TGF-β also acts as an upstream activator of GSN dependent hypertrophy. Hence, TGF-β in serum could be a promising therapeutic target for cardiac remodeling in aging and/or obese subjects.

Gene Therapy for the Treatment of Cardiac Arrhythmias: Current and Emerging Applications

In this review, we examine the current state of gene therapy for the treatment of cardiac arrhythmias. We describe advances and challenges in successfully creating and incorporating gene vectors into the myocardium. After summarizing the current scientific research in gene transfer technology, we then focus on the most promising areas of gene therapy at this time, which is the treatment of atrial fibrillation and ventricular tachyarrhythmias. We also review the scientific literature to determine how gene therapy could potentially be used to treat patients with cardiac arrhythmias.

Salvianolic Acid B-Alleviated Angiotensin II Induces Cardiac Fibrosis by Suppressing NF-κB Pathway In Vitro

BACKGROUND Salvianolic acid B (SalB) is the representative component of phenolic acids derived from the roots and rhizomes of Salvia miltiorrhiza Bge (Labiatae), which has been used widely in Asian countries for clinical therapy of various cardiovascular dysfunction-related diseases. However, cardiac protection effects and the underlying mechanism for clinical application are still poorly understood. Here, we investigated the potential anti-myocardial fibrosis effect and mechanism of SalB on Angiotensin II (Ang II)-induced cardiac fibrosis in vitro. MATERIAL AND METHODS The proliferation and migration capacity of cardiac fibroblasts (CFBs) were measured by MTT assay and scratch analysis, respectively. The colorimetric assay determined the hydroxyproline content in medium. Western blotting detected the protein expressions of nuclear transcription factor-kappa B (NF-κB) pathway-associated proteins, fibronectin (FN), collagen type I (Coll I), α-smooth muscle actin (α-SMA), and connective tissue growth factor (CTGF). The expression of α-SMA protein was observed by immunofluorescence staining. qRT-PCR detected the mRNA expression of NF-κB. RESULTS SalB attenuated Ang II-induced the proliferation and the migration ability of CFBs. Ang II-induced the extracellular matrix protein Coll I, FN, and α-SMA, the pro-fibrotic cytokine CTGF protein expression was inhibited, and the nuclear translocation of NF-κB p65 subunit was reduced by SalB. Western blotting and qRT-PCR confirmed that SalB blocked the activation of NF-κB induced by Ang II. PDTC (the NF-κB inhibitor) also inhibited proliferation of CFBs and reduced α-SMA and Coll I expression induced by Ang II. CONCLUSIONS SalB can alleviate Ang II-induced cardiac fibrosis via suppressing the NF-κB pathway in vitro.

MicroRNA-30c suppresses the pro-fibrogenic effects of cardiac fibroblasts induced by TGF-β1 and prevents atrial fibrosis by targeting TGFβRII

Atrial fibrosis serves as an important contributor to atrial fibrillation (AF). Recent data have suggested that microRNA-30c (miR-30c) is involved in fibrotic remodelling and cancer development, but the specific role of miR-30c in atrial fibrosis remains unclear. The purpose of this study was to investigate the role of miR-30c in atrial fibrosis and its underlying mechanisms through in vivo and in vitro experiments. Our results indicate that miR-30c is significantly down-regulated in the rat abdominal aortic constriction (AAC) model and in the cellular model of fibrosis induced by transforming growth factor-β1 (TGF-β1). Overexpression of miR-30c in cardiac fibroblasts (CFs) markedly inhibits CF proliferation, differentiation, migration and collagen production, whereas decrease in miR-30c leads to the opposite results. Moreover, we identified TGFβRII as a target of miR-30c. Finally, transferring adeno-associated virus 9 (AAV9)-miR-30c into the inferior vena cava of rats attenuated fibrosis in the left atrium following AAC. These data indicate that miR-30c attenuates atrial fibrosis via inhibition of CF proliferation, differentiation, migration and collagen production by targeting TGFβRII, suggesting that miR-30c might be a novel potential therapeutic target for preventing atrial fibrosis.

Human Epicardial Adipose Tissue cTGF Expression is an Independent Risk Factor for Atrial Fibrillation and Highly Associated with Atrial Fibrosis

Epicardial adipose tissue (EAT) is associated with the incidence, perpetuation, and recurrence of atrial fibrillation (AF), with elusive underlying mechanisms. We analyzed adipokine expression in samples from 20 patients with sinus rhythm (SR) and 16 with AF. Quantitative real-time PCR showed that connective tissue growth factor (cTGF) expression was significantly higher in EAT than in subcutaneous adipose tissue (SAT) or paracardial adipose tissue (PAT) from patients with AF, and in EAT from patients with SR (P < 0.001). Galectin-3 expression was significantly higher in EAT than in SAT or PAT (P < 0.001), with no significant differences between patients with AF and SR (P > 0.05). Leptin and vaspin expression were lower in EAT than in PAT (P < 0.001). Trichrome staining showed that the fibrosis was much more severe in patients with AF than SR (P < 0.001). We found a linear relationship between cTGF mRNA expression level and collagen volume fraction (y = 1.471x + 27.330, P < 0.001), and logistic regression showed that cTGF level was an independent risk factor for AF (OR 2.369, P = 0.027). In conclusion, highly expressed in EAT, cTGF is associated with atrial fibrosis, and can be an important risk factor for AF.

Biological therapies targeting arrhythmias: are cells and genes the answer?

INTRODUCTION

Arrhythmias can cause symptoms ranging from simple dizziness to life-threatening circulatory collapse. Current management includes medical therapy and procedures such as catheter ablation or device implantation. However, these strategies still pose a risk of serious side effects, and some patients remain symptomatic. Advancement in our understanding of how arrhythmias develop on the cellular level has made more targeted approaches possible. In addition, contemporary studies have found that several genes are involved in the pathogenesis of arrhythmias.

AREAS COVERED

In the present review, the authors explore the cellular and genetic mechanisms leading to arrhythmias as well as the progress that has been made in using both gene and cell therapy to treat tachy- and bradyarrhythmias. They also consider why gene and cell therapy has resulted into a few clinical trials with promising results, however still not applicable in routine clinical practice.

EXPERT OPINION

The question currently is whether such biological therapies could replace current established approaches. The contemporary evidence suggests that despite recent advances in this field, it will need more work in experimental models before this is applied into clinical practice. Gene and cell studies targeting conduction and repolarization are promising, but still not ready for use in the clinical setting.

Role of serum TGF-β1 level in atrial fibrosis and outcome after catheter ablation for paroxysmal atrial fibrillation

This study aimed to evaluate the relationship between serum transforming growth factor-β1 (TGF-β1) concentration and atrial fibrosis and to determine whether plasma TGF-β1 concentration is an independent predictor of atrial fibrillation (AF) recurrence after catheter ablation.We included 98 consecutive patients who underwent catheter ablation, including 38 with paroxysmal AF (AF group) and 60 with paroxysmal supraventricular tachycardia (control group). We compared their preablation serum concentration of biomarkers and clinical and echocardiographic findings.Serum TGF-β1 concentrations, type-III procollagen N-terminal peptides (PIIINP), type-IV procollagen (IV-C), and laminin (LN) were significantly higher in the AF group than in the control group; however, there was no correlation between their concentrations and left atrial diameter (LAD). The area of the low-voltage zone positively correlated with TGF-β1 and PIIINP concentrations, but not with LAD. Atrial tachyarrhythmia (AF and AFL/AT) recurrence was observed in 15 patients (39.4%) at mean 241.4 ± 68.5 days of follow-up 12 months after ablation. Regression analysis revealed that TGF-β1 was a major risk factor for AF recurrence (odds ratio, 1.14; 95% confidence interval, 1.11-1.17; P = .02).Serum TGF-β1 concentration is an independent predictor of AF recurrence in patients with paroxysmal AF and may help identify patients likely to have better outcomes after catheter ablation.

Buccal Mucosal Epithelial Cells Downregulate CTGF Expression in Buccal Submucosal Fibrosis Fibroblasts

Introduction

Oral submucosal fibrosis (OSMF) is a chronic debilitating fibrotic disease of the oral cavity and is a serious health hazard in south Asia and, increasingly, the rest of the world. The molecular basis behind various treatment modalities to treat OSMF still remains unclear. In this study, we have investigated the in vitro ability of the buccal mucosal cells to reduce the proliferation of the fibroblasts of the fibrotic area in co-culture of cells and also at the molecular levels to reduce the level of connective tissue growth factor (CTGF) in the OSMF fibroblasts (SMF-F).

Materials and Methods

The study compares isolation, morphological and proliferation kinetics of SMF-F and BMF cells with and without co-culturing with BMEs. In addition, we have compared the mRNA expression levels of CTGF in SMF-F co-cultured BME and non-co-cultured SMF-F cells using validated real-time quantitative PCR (RT-qPCR) method.

Results

The basic morphological characteristics of SMF-F were similar to BMF, but the former cells had higher proliferation rate in early passages compared to late passage state. We also observed that the CTGF expression levels in SMF-F under co-culture conditions of BME were consistently and significantly downregulated in all four different SMF-F-derived cells from four different patients.

Conclusion

Rapid proliferation and collagen synthesis in SMF-F as against BMF cells are the factors that confirm the innate nature of fibrosis fibroblasts (SMF-F). Further, the CTGF expression level in SMF-F was significantly suppressed by BME in co-culture conditions against controls (BMF). Considered together, this suggests that the cell therapeutic candidate of BME could be used in treating OSMF.

Circulating Biomarkers Predictive of Postoperative Atrial Fibrillation

Postoperative atrial fibrillation (PoAF), a common complication of cardiac surgery, contributes significantly to morbidity, mortality, and increasing healthcare costs. Despite advances in surgical and medical management, the overall incidence of PoAF has not changed significantly, partly because of the limited understanding of mechanisms underlying acute surgery-related factors, such as myocardial injury, inflammation, sympathetic activation, and oxidative stress, which play an important role in the initiation of PoAF, whereas a preexisting atrial substrate appears to be more important in the maintenance of this dysrhythmia. Thus, in a majority of patients, PoAF becomes a manifestation of an underlying arrhythmogenic substrate that is unmasked after acute surgical stress. As such, the ability to identify which patients have this proarrhythmic substrate and are, therefore, at high risk for developing AF postoperatively, is important for the improved selection for prophylactic interventions, closer monitoring for complications, and establishing the probability of AF in the long term. This review highlights the role of the underlying substrate in promoting PoAF, proposed mechanisms, and the potential role of serum biomarkers to identify patients at risk for PoAF.

Constitutive Expression of a Dominant-Negative TGF-β Type II Receptor in the Posterior Left Atrium Leads to Beneficial Remodeling of Atrial Fibrillation Substrate

RATIONALE

Fibrosis is an important structural contributor to formation of atrial fibrillation (AF) substrate in heart failure. Transforming growth factor-β (TGF-β) signaling is thought to be intricately involved in creation of atrial fibrosis.

OBJECTIVE

We hypothesized that gene-based expression of dominant-negative type II TGF-β receptor (TGF-β-RII-DN) in the posterior left atrium in a canine heart failure model will sufficiently attenuate fibrosis-induced changes in atrial conduction and restitution to decrease AF. Because AF electrograms are thought to reflect AF substrate, we further hypothesized that TGF-β-RII-DN would lead to increased fractionation and decreased organization of AF electrograms.

METHODS AND RESULTS

Twenty-one dogs underwent injection+electroporation in the posterior left atrium of plasmid expressing a dominant-negative TGF-β type II receptor (pUBc-TGFβ-DN-RII; n=9) or control vector (pUBc-LacZ; n=12), followed by 3 to 4 weeks of right ventricular tachypacing (240 bpm). Compared with controls, dogs treated with pUBC-TGFβ-DN-RII demonstrated an attenuated increase in conduction inhomogeneity, flattening of restitution slope and decreased duration of induced AF, with AF electrograms being more fractionated and less organized in pUBc-TGFβ-DN-RII versus pUBc-LacZ dogs. Tissue analysis revealed a significant decrease in replacement/interstitial fibrosis, p-SMAD2/3 and p-ERK1/2.

CONCLUSIONS

Targeted gene-based reduction of TGF-β signaling in the posterior left atrium-with resulting decrease in replacement fibrosis-led to beneficial remodeling of both conduction and restitution characteristics of the posterior left atrium, translating into a decrease in AF and increased complexity of AF electrograms. In addition to providing mechanistic insights, this data may have important diagnostic and therapeutic implications for AF.

Atrial fibrillation: mechanisms, therapeutics, and future directions

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting 1% to 2% of the general population. It is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes. AF is associated with increased morbidity and mortality and is a risk factor for embolic stroke and worsening heart failure. Current research on AF support and explore the hypothesis that initiation and maintenance of AF require pathophysiological remodeling of the atria, either specifically as in lone AF or secondary to other heart disease as in heart failure-associated AF. Remodeling in AF can be grouped into three categories that include: (i) electrical remodeling, which includes modulation of L-type Ca(2+) current, various K(+) currents and gap junction function; (ii) structural remodeling, which includes changes in tissues properties, size, and ultrastructure; and (iii) autonomic remodeling, including altered sympathovagal activity and hyperinnervation. Electrical, structural, and autonomic remodeling all contribute to creating an AF-prone substrate which is able to produce AF-associated electrical phenomena including a rapidly firing focus, complex multiple reentrant circuit or rotors. Although various remodeling events occur in AF, current AF therapies focus on ventricular rate and rhythm control strategies using pharmacotherapy and surgical interventions. Recent progress in the field has started to focus on the underlying substrate that drives and maintains AF (termed upstream therapies); however, much work is needed in this area. Here, we review current knowledge of AF mechanisms, therapies, and new areas of investigation.

Cardiac Fibrosis in Patients With Atrial Fibrillation: Mechanisms and Clinical Implications

Atrial fibrillation (AF) is associated with structural, electrical, and contractile remodeling of the atria. Development and progression of atrial fibrosis is the hallmark of structural remodeling in AF and is considered the substrate for AF perpetuation. In contrast, experimental and clinical data on the effect of ventricular fibrotic processes in the pathogenesis of AF and its complications are controversial. Ventricular fibrosis seems to contribute to abnormalities in cardiac relaxation and contractility and to the development of heart failure, a common finding in AF. Given that AF and heart failure frequently coexist and that both conditions affect patient prognosis, a better understanding of the mutual effect of fibrosis in AF and heart failure is of particular interest. In this review paper, we provide an overview of the general mechanisms of cardiac fibrosis in AF, differences between fibrotic processes in atria and ventricles, and the clinical and prognostic significance of cardiac fibrosis in AF.

A functional polymorphism C-509T in TGFβ-1 promoter contributes to susceptibility and prognosis of lone atrial fibrillation in Chinese population

Transforming growth factor-β1 (TGF-β1) is an important mediator of atrial fibrosis and atrial fibrillation (AF). But the involved genetic mechanism is unknown. Herein, the TGF-β1 C-509 T polymorphism (rs1800469) was genotyped in a case-control study of 840 patients and 845 controls in Chinese population to explore the association between the polymorphism and susceptibility and prognosis of lone AF. As a result, the CT and/or TT genotypes had an increased lone AF risk [adjusted odds ratio (OR) = 1.50 for CT, OR = 3.72 for TT, and OR = 2.15 for CT/TT], compared with the TGF-β1CC genotype. Moreover, patients carrying CT/TT genotypes showed a higher possibility of AF recurrence after catheter ablation, compared with patients carrying CC genotype. In a genotype-phenotype correlation analysis using 24 normal left atrial appendage samples, increasing gradients of atrial TGF-β1 expression levels positively correlated with atrial collagen volume fraction were identified in samples with CC, CT and TT genotypes. The in vitro luciferase assays also showed a higher luciferase activity of the -509 T allele than that of the -509 C allele. In conclusion, the TGF-β1 C-509 T polymorphism is involved in the etiology of lone AF and thus may be a marker for genetic susceptibility to lone AF and predicting prognosis after catheter ablation in Chinese populations. Therefore, we provide new information about treatment strategies and our understanding of TGF-β1 in AF.

TGF-β1 signal pathway in the regulation of inflammation in patients with atrial fibrillation

OBJECTIVE

To observe the expression changes of inflammatory markers TGF-β1, Smad3 and IL-6 in patients with atrial fibrillation (AF), and to explore the significance of TGF-β1 signaling pathway in the structural remodeling of AF.

METHODS

The expression of TGF-β1, Smad3 and IL-6 in 50 cases with AF and 30 normal cases were detected by RT-PCR and ELISA.

RESULTS

The TGF-β1, Smad3 and IL-6 mRNA and protein expression levels in patients with AF were significantly higher than that in the control group (P<0.05), but there was no significantly different between the paroxysmal AF group and the persistent AF group (P>0.05). The TGF-β1mRNA expression in the ⩾ 50 years subgroup was significantly higher than that in the <50 years subgroups, and it was higher in the NYHA III subgroup than in the I/II grade subgroup. It was also higher in the left ventricular ejection fraction (LVEF) <50% subgroup than in LVEF ⩾ 50% group, and it was significantly higher in the AF time ⩾ 36 months subgroup than that in <36 months subgroup (P<0.05). The Smad3 and IL-6 expressions in the in the LVEF <50% subgroup were both high that than that in LVEF ⩾ 50% group, and higher in the AF time ⩾ 36 months subgroup than that in <36 months subgroup (P<0.05). There were a positive correlation between TGF-β1, Smad3 and IL-6 (r=0.687, r=0.547). There were also a positive correlation between Smad3 and IL-6 mRNA (r=0.823).

CONCLUSIONS

AF is associated with inflammation, and the inflammation is also involved in the fibrillation and sustain of AF. The TGF-β1 signal pathway may be involved in the process of atrial structural remodeling in patients with AF, and iss related with the occurrence and maintenance of AF.

NF-κB-mediated integrin-linked kinase regulation in angiotensin II-induced pro-fibrotic process in cardiac fibroblasts

AIMS

Cardiac fibrosis is a final outcome of many clinical conditions that lead to cardiac failure and is characterized by a progressive substitution of cellular elements by extracellular-matrix proteins, such as collagen type I, collagen type II, connective tissue growth factor (CTGF), etc. The aim of this study was to identify the mechanisms responsible for angiotensin II (Ang II)-stimulated cardiac fibrosis using rat neonatal cardiac fibroblasts.

MAIN METHODS

Neonatal fibroblasts were transfected with IκBα mutant, constitutively active (ca) integrin-linked kinase (ILK), dominant negative of ILK and small interfering RNA (siRNA) of ILK in the presence and absence of Ang-II stimulation. The pro-fibrotic gene expression and protein levels were determined by quantitative real time PCR and western blotting using their specific probes and antibodies. NF-κB translocation was determined by immunocytochemistry and confocal microscopy images were analyzed.

KEY FINDINGS

Our results indicate that overexpression of ILK promotes a pro-fibrotic process by upregulating collagen type I and CTGF genes via activation of nuclear factor-κB (NF-κB) in cardiac fibroblasts. Inactivation of either NF-κB by the super-repressor IκBα or ILK by siRNA significantly attenuates the pro-fibrotic process. Moreover, ILK overexpression triggers NF-κB-p65 translocation to the nucleus, and ILK inhibition prevents the translocation in cardiac fibroblasts stimulated with Ang II.

SIGNIFICANCE

Our data suggest that the Ang II-stimulated pro-fibrotic process is regulated by a complex mechanism involving crosstalk between ILK and NF-κB activation. This dual mechanism may play a critical role in the progression of cardiac fibrosis.