Fibrosis In Atrial Fibrillation Research Articles

The correlation between left atrium voltage mapping and 3D late gadolinium enhancement cardiac magnetic resonance imaging findings in naive AF ablation candidate

Abstract Introduction The extent of the efficacy of late gadolinium enhancement cardiac MR (LGE-CMR) in depicting left atrial (LA) fibrosis in atrial fibrillation (AF) patients, compared to invasive Electroanatomical Mapping (EAM), is ongoing research field, while the highest degree of accuracy found when using ADAS program. Earlier studies focused mainly on post-ablation patients, employing segmentation (quality) and point-by-point (PBP) comparison methods. The non-invasive LGE-CMR-based fibrosis map shows promise for preprocedural planning and real-time guidance. Aim Evaluate LGE-CMR-based LA fibrosis precision in ablation-naïve AF patients using ADAS software, comparing it to the gold standard EAM using CARTO-3, in both qualitative and quantitative methods. Methods Patients planned for first CARTO-based AF ablation, undergoing pre-ablation LGE-CMR. 3D substrate atrial maps were generated via ADAS based on LGE-CMR (CMR-fib) and via CARTO as EAM. Normal range LA voltage was defined by Image Intensity Ratio of 1.2-1.32 on ADAS and by 0.2-0.5mV on Carto. Comparison methods, qualitative segmentation and PBP quantitative, with EAM serving as the gold standard. Results 24 naive patients included in the study (mean age 63.5 ± 10.9 yrs; 7 females, 15 paroxysmal AF, 17 maps during sinus). Segmental qualitative analysis (384 segments) showed 77% scarred segments, predominantly small scars (up to ⅓ segment). Compared with EAM, the CMR had 68.4% agreement, with 80.4% sensitivity, 78% PPV, 36.6% specificity, 32.6% NPV , kappa 0.139 AUC 0.567. Better agreement was found for dense scar. PBP quantitative comparison (41,345 points) demonstrated 50% scarred points, with 89% accuracy between EAM and CMR, with 49.6% sensitivity, 99.7% specificity, 99.5% PPV, and 73.5% NPV kappa 0.53, AUC 0.747. In both methods, agreement was worse for LA roof and best for AP and septal wall. Conclusion LGE-CMR tends to underestimate scar presence in naive patients compared to EAM, potentially due to baseline voltage scars, which are less dense compared to iatrogenic scar, the voltage criteria for scar in literature. Sensitivity is higher in segmental comparison, while specificity is superior in PBP, consistent with expectations of minimizing the size of comparison (from a segment to point). Hence, qualitative segmental method is better when assessing overall scarring, while PBP for assessing smaller specific areas. PBP comparisons exhibit less bias than segmental comparisons, which are overly sensitive to small scars. The diminished reliability of the LA roof is probably due to the margin of the CMR scan. Our study result regarding low sensitivity and high specificity of PBP aligns with a prior study investigating naïve patients through PBP comparisons, highlighting the need for a larger-scale study to assess LGE-CMR accuracy, considering various wall thicknesses and establishing scar thresholds on ADAS and CARTO software, for ablation-naïve patients with LA body scars.PBP projection on LA bodyAUC for PBP comprasion

Primary cilia suppress the fibrotic activity of atrial fibroblasts from patients with atrial fibrillation in vitro

Atrial fibrosis serves as an arrhythmogenic substrate in atrial fibrillation (AF) and contributes to AF persistence. Treating atrial fibrosis is challenging because atrial fibroblast activity is multifactorial. We hypothesized that the primary cilium regulates the profibrotic response of AF atrial fibroblasts, and explored therapeutic potentials of targeting primary cilia to treat fibrosis in AF. We included 25 patients without AF (non-AF) and 26 persistent AF patients (AF). Immunohistochemistry using a subset of the patients (non-AF: n = 10, AF: n = 10) showed less ciliated fibroblasts in AF versus non-AF. Acetylated α-tubulin protein levels were decreased in AF, while the gene expressions of AURKA and NEDD9 were highly increased in AF patients’ left atrium. Loss of primary cilia in human atrial fibroblasts through IFT88 knockdown enhanced expression of ECM genes, including FN1 and COL1A1. Remarkably, restoration or elongation of primary cilia by an AURKA selective inhibitor or lithium chloride, respectively, prevented the increased expression of ECM genes induced by different profibrotic cytokines in atrial fibroblasts of AF patients. Our data reveal a novel mechanism underlying fibrotic substrate formation via primary cilia loss in AF atrial fibroblasts and suggest a therapeutic potential for abrogating atrial fibrosis by restoring primary cilia.

Impact of iNAV and dNAV 3D LGE-CMR on the assessment of atrial fibrosis in atrial fibrillation patients

Abstract Background Late gadolinium enhanced (LGE) cardiac magnetic resonance (CMR) imaging serves as a valuable non-invasive tool for visualizing and quantifying left atrial (LA) fibrosis in atrial fibrillation (AF) patients. The extent of pre-procedural LA-LGE, indicative of native atrial fibrosis, has proven to be a predictor of AF recurrence risk following AF ablation. Consequently, assessing the LA fibrotic burden has emerged as a potential guide for personalized patient management. Currently, most centers engaged in LA-LGE image acquisition apply a scan protocol based on a diaphragmatic navigator-gated 3D image strategy (dNAV). Recently introduced image navigated (iNAV) 3D LGE strategies are proposed to outperform the dNAV strategy. This advancement involves the dynamic tracking of the heart's respiratory position with an image reconstruction algorithm, yielding motion-compensated images in significantly reduced and more consistent scan durations. We performed an evaluation of the novel image navigated (iNAV) 3D LGE-CMR imaging strategy in comparison to the conventional diaphragm navigated (dNAV) 3D LGE-CMR strategy. Methods In twenty-six consecutive AF patients, both imaging techniques (i.e. iNAV and dNAV) were performed subsequently, with equivalent spatial resolution and timing in the cardiac cycle. Patients were randomized in the acquisition order of iNAV and dNAV. LA fibrosis was quantified (percentage of atrial fibrosis using image intensity ratio threshold 1.2) and overlap in atrial fibrosis areas was tested between the two methods. Results Acquisition time of iNAV was significantly lower compared to dNAV (5±1 minutes vs. 12±4 minutes, p<0.001, respectively). There was a significant correlation between the iNAV and dNAV LA fibrotic burden (r=0.69, p<0.001). LA fibrosis scores were lower for iNAV compared to dNAV (12±8% vs. 20±12%, p<0.001, respectively). Spatial correspondence between the atrial fibrosis maps was modest (Dice similarity coefficient 0.43±0.15). Notably, 13/23 (56%) patients underwent a shift in their UTAH fibrosis stage classification, depending on the chosen imaging strategy. Conclusion iNAV acquisition was more than twice as fast as dNAV, and iNAV resulted in a lower atrial fibrosis score as compared to dNAV. More than half of the patients were reclassified into a different UTAH fibrosis stage depending on the employed imaging strategy. This underscores the critical importance of recognizing that the choice of imaging strategy significantly impacts the categorization of patients into their respective fibrosis stages. This distinction carries potential clinical implications when evaluating the utility of UTAH fibrosis stages in the context of AF management and therapeutic decision-making, as patients in lower fibrosis stages are generally regarded as more suitable candidates for ablation, while those categorized in higher fibrosis stages face an increased risk of arrhythmia recurrence following PVI.Figure 1Figure 2

PET-MRI Imaging to assess severity and distribution of atrial fibrosis in atrial fibrillation

Abstract Background Atrial fibrosis is a major determinant of atrial fibrillation (AF) susceptibility and ablation targeting fibrotic areas to suppress AF revealed by magnetic resonance imaging (MRI) was considered a promising approach to treat persistent AF; however, its outcome has been disappointing. We sought to develop a new imaging modality to detect the severity and distribution of atrial fibrosis. Methods This study enrolled 19 healthy volunteers and 85 patients with various cardiovascular (CV) diseases of whom 22 had persistent AF. Each patient underwent 18F-labeled aluminum fluoride targeting fibroblast activation protein inhibitor (18F-AlF-FAPI)-positron emission tomography - magnetic resonance imaging (PET-MRI). Left atrial appendage tissue biopsied at 18F-FAPI-uptake positive and negative sites was stained with Masson trichome to detect fibrosis (N=10). We compared cardiac atrial 18F-AlF-FAPI-PET-MRI imaging among healthy individuals, patients without AF and patients with persistent AF as well as patients developing and not developing postoperative AF (POAF). Results Degree of fibrosis based on Masson staining was consistent with 18F-FAPI-uptake (P<0.05). Whereas 18F-FAPI uptake was essentially undetectable in healthy volunteers, in patients with CV diseases, 18F-FAPI uptake was present in all atrial chambers. Patients with persistent AF had the greatest and most widespread uptake (P<0.001), including left atrium (P=0.001), right atrium (P<0.001), left atrial appendage (P=0.007), right atrial appendage (P<0.001), and left atrial posterior wall (P=0.004). 18F-FAPI-uptake did not differ between those with versus without POAF. Conclusions 18F-AlF-FAPI-PET-MRI imaging detected atrial fibrosis in patients with various CV diseases; patients with persistent AF exhibit severe and widespread fibrosis, while POAF is not associated with increased 18F-FAPI uptake.

Systematic in-silico evaluation of fibrosis effects on re-entrant wave dynamics in atrial tissue.

Despite the key role of fibrosis in atrial fibrillation (AF), the effects of different spatial distributions and textures of fibrosis on wave propagation mechanisms in AF are not fully understood. To clarify these aspects, we performed a systematic computational study to assess fibrosis effects on the characteristics and stability of re-entrant waves in electrically-remodelled atrial tissues. A stochastic algorithm, which generated fibrotic distributions with controlled overall amount, average size, and orientation of fibrosis elements, was implemented on a monolayer spheric atrial model. 245 simulations were run at changing fibrosis parameters. The emerging propagation patterns were quantified in terms of rate, regularity, and coupling by frequency-domain analysis of correspondent synthetic bipolar electrograms. At the increase of fibrosis amount, the rate of reentrant waves significantly decreased and higher levels of regularity and coupling were observed (p < 0.0001). Higher spatial variability and pattern stochasticity over repetitions was observed for larger amount of fibrosis, especially in the presence of patchy and compact fibrosis. Overall, propagation slowing and organization led to higher stability of re-entrant waves. These results strengthen the evidence that the amount and spatial distribution of fibrosis concur in dictating re-entry dynamics in remodeled tissue and represent key factors in AF maintenance.

Inhibitory effects of propylene glycol alginate sodium sulfate derivatives on atrial fibrosis in atrial fibrillation

Atrial fibrosis is the hallmark of structural remodeling in the pathogenesis of atrial fibrillation (AF). Meanwhile, AF causes a hypercoagulable state, and then provokes pro-fibrotic response. To discover a potential effective AF treatment targeting both coagulation and atrial fibrosis, this study investigated the structure–activity relationship of propylene glycol alginate sodium sulfate (PSS) derivatives with heparin-like activity on TGF-β1-induced atrial fibrosis. We found that PSS derivatives had significantly inhibitory effects on proliferation, migration, phenotypic transformation, and secretion/deposition of extracellular matrix of atrial fibroblasts. Among them, PGGS showed the optimal anti-atrial fibrotic activity by suppressing TGF-β1-induced activation of Smad2/3 signaling pathway. Furthermore, the study in vivo indicated that PGGS treatment displayed a reduced atrial fibrosis and AF inducibility, and attenuated the hypercoagulable state by decreasing D-dimer level and thrombin (FIIa) activity in MHC-TGF-β1 cys33ser transgenic mice, which had increased fibrosis in atrium but not in the ventricles. Our results demonstrated that PSS derivatives, especially PGGS, were potential anti-atrial fibrosis and anti-coagulant agents for AF prevention. Our study is beneficial in extending the current understandings of the function of PSS on atrial fibrosis and vulnerability to AF.

Ion channel dysfunction and fibrosis in atrial fibrillation: Two sides of the same coin.

Atrial fibrillation (AF) is a common heart rhythm disorder that is associated with an increased risk of stroke and heart failure (HF). Initially, an association between AF and ion channel dysfunction was identified, classifying the pathology as a predominantly electrical disease. More recently it has been recognized that fibrosis and structural atrial remodeling play a driving role in the development of this arrhythmia also in these cases. Understanding the role of fibrosis in genetic determined AF could be important to better comprise the pathophysiology of this arrhythmia and to refine its management also in nongenetic forms. In this review we analyze genetic and epigenetic mechanisms responsible for AF and their link with atrial fibrosis, then we will consider analogies with the pathophysiological mechanism in nongenetic AF, and discuss consequent therapeutic options.

LncRNA LENGA sponges miR-378 to promote myocardial fibrosis in atrial fibrillation.

miR-378 is known to suppress myocardial fibrosis, while its upstream regulators have not been identified. lncRNA LENGA is a recently identified lncRNA in cancer biology. We observed the altered expression of LENGA in atrial fibrillation (AF) patients and predicted its interaction with miR-378. We then explored the interaction between LENGA and miR-378 in AF. Angiotensin-II (Ang-II)-induced human atrial cardiac fibroblasts and human atrial muscle tissues were collected and the expression of LENGA and miR-378 was determined by RT-qPCR. The interaction between LENGA and miR-378 was analyzed through bioinformatics analysis and confirmed by RNA pulldown assay. Cell proliferation and collagen production were analyzed through in vitro assay to analyze the role of LENGA and miR-378 in MF. AF patients showed increased expression of LENGA and deceased expression of miR-378 compared to the sinus rhythm group. LENGA and miR-378 interacted with each other, while they are not closely correlated with each other. Overexpression assay showed that LENGA and miR-378 overexpression failed to affect each other's expression. LENGA promoted collagen production and proliferation of Ang-II-induced atrial fibroblasts, while miR-378 played opposite roles. Moreover, LENGA suppressed the function of miR-378. Therefore, LENGA may sponge miR-378 to promote MF in AF.

Left atrial fibrosis-guided ablation in patients with atrial fibrillation: a systematic review and meta-analysis of randomized trials

Abstract Background Left atrial fibrosis is related to atrial fibrillation (AF) recurrence after AF ablation. However, the benefit of patient-specific substrate modification guided by fibrosis delineated on voltage mapping or magnetic resonance imaging (MRI) is conflicting. Objective To compare the efficacy and safety of additional modification of left atrial fibrosis [identified by low-voltage area (LVA) or late gadolinium-enhancement on MRI] vs. circumferential pulmonary vein isolation (PVI) with or without stepwise ablation not targeting fibrosis in AF. Methods A systematic search of PubMed, EMBASE, and Cochrane Central Register of Controlled Trials was performed from inception to November 2022. Only randomized studies investigating the utility of fibrosis-guided substrate modification beyond conventional PVI were included. The primary outcome was a recurrence of any atrial arrhythmia. Major adverse events and procedural, fluoroscopic, and total ablation time were defined as secondary outcomes. We calculated pooled estimates of the outcomes by a random-effect model and reported them as risk ratio (RRs) and 95% confidence interval (CI). Results A total of 9 studies (8 randomized controlled clinical trials and 1 randomized design within a prospective study) and 2135 patients with AF were included. The atrial arrhythmia recurrence was lower in the additional fibrosis-guided ablation group (RR 0.82; 95% CI 0.71-0.94; p=0.006) (Figure 1A). No differences were found between fibrosis-guided substrate modification and conventional PVI group in major adverse events [RR 1.25 (0.55-2.81), p=0.598)] and mean differences of procedural time [-2.88 (-40.34 to 34.57) min], fluoroscopic time [1.82 (-1.86 to 5.49) min], and total ablation time [-14.28 (-48.70 to 20.14) min]. In the stratified analyses, there were no interactions of the lower atrial arrhythmia recurrences within the modality of fibrosis identification (LVA vs. delayed enhancement on MRI), type of AF (paroxysmal vs. persistent), the burden of LVA (no or low vs. high), and strategy of the control group (PVI only vs. PVI plus stepwise ablation) (Figure 1B). Conclusion By incorporating two modalities of left atrial substrate evaluation – voltage mapping and MRI – we conclude that the individually tailored fibrosis-guided ablation in AF is associated with a lower recurrence after catheter ablation.

SHP-1 alleviates atrial fibrosis in atrial fibrillation by modulating STAT3 activation.

Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) has a well-established role in myocardial infarction, yet its involvement in atrial fibrosis and atrial fibrillation (AF) has not been elucidated. As cardiac arrhythmias caused by AF are a major global health concern, we investigated whether SHP-1 modulates AF development. The degree of atrial fibrosis was examined using Masson's trichrome staining, and SHP-1 expression in the human atrium was assessed using quantitative polymerase chain reaction (qPCR), immunohistochemistry (IHC), and western blotting (WB). We also examined SHP-1 expression in cardiac tissue from an AF mouse model, as well as in angiotensin II (Ang II)-treated mouse atrial myocytes and fibroblasts. We found that SHP-1 expression was reduced with the aggravation of atrial fibrosis in clinical samples of patients with AF. SHP-1 was also downregulated in the heart tissue of AF mice and Ang II-treated myocytes and fibroblasts, compared with that in the control groups. Next, we demonstrated that SHP-1 overexpression alleviated AF severity in mice by injecting a lentiviral vector into the pericardial space. In Ang II-treated myocytes and fibroblasts, we observed excessive extracellular matrix (ECM) deposition, reactive oxygen species (ROS) generation, and transforming growth factor beta 1 (TGF-β1)/mothers against decapentaplegic homolog 2 (SMAD2) pathway activation, all of which were counteracted by the overexpression of SHP-1. Our WB data showed that STAT3 activation was inversely correlated with SHP-1 expression in samples from patients with AF, AF mice, and Ang II-treated cells. Furthermore, administration of colivelin, a STAT3 agonist, in SHP-1-overexpressing, Ang II-treated myocytes and fibroblasts resulted in higher levels of ECM deposition, ROS generation, and TGF-β1/SMAD2 activation. These findings indicate that SHP-1 regulates AF fibrosis progression by modulating STAT3 activation and is thus a potential treatment target for atrial fibrosis and AF.

Construction and integrated analysis of the ceRNA network hsa_circ_0000672/miR-516a-5p/TRAF6 and its potential function in atrial fibrillation

Atrial fibrosis is a crucial contributor to initiation and perpetuation of atrial fibrillation (AF). This study aimed to identify a circRNA-miRNA-mRNA competitive endogenous RNA (ceRNA) regulatory network related to atrial fibrosis in AF, especially to validate hsa_circ_0000672/hsa_miR-516a-5p/TRAF6 ceRNA axis in AF preliminarily. The circRNA-miRNA-mRNA ceRNA network associated with AF fibrosis was constructed using bioinformatic tools and literature reviews. Left atrium (LA) low voltage was used to represent LA fibrosis by using LA voltage matrix mapping. Ten controls with sinus rhythm (SR), and 20 patients with persistent AF including 12 patients with LA low voltage and 8 patients with LA normal voltage were enrolled in this study. The ceRNA regulatory network associated with atrial fibrosis was successfully constructed, which included up-regulated hsa_circ_0000672 and hsa_circ_0003916, down-regulated miR-516a-5p and five up-regulated hub genes (KRAS, SMAD2, TRAF6, MAPK11 and SMURF1). In addition, according to the results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, these hub genes were clustered in TGF-beta and MAPK signaling pathway. In the patients with persistent AF, hsa_circ_0000672 expression in peripheral blood monocytes was significantly higher than those in controls with SR by quantitative real-time polymerase chain reaction (p-value < 0.001). Furthermore, hsa_circ_0000672 expression was higher in peripheral blood monocytes of persistent AF patients with LA low voltage than those with LA normal voltage (p-value = 0.002). The dual-luciferase activity assay confirmed that hsa_circ_0000672 exerted biological functions as a sponge of miR-516a-5p to regulate expression of its target gene TRAF6. Hsa_circ_0000672 expression in peripheral blood monocytes may be associated with atrial fibrosis. The hsa_circ_0000672 may be involved in atrial fibrosis by indirectly regulating TRAF6 as a ceRNA by sponging miR-516a-5p.

SGLT2i alleviates epicardial adipose tissue inflammation by modulating ketone body-glyceraldehyde-3-phosphate dehydrogenase malonylation pathway.

Inflammation in the epicardial adipose tissue (EAT) is a contributor to atrial fibrillation. Studies have reported that sodium glucose co-transporter 2 inhibitor (SGLT2i) can alleviate EAT inflammation. However, the mechanism remains elusive. This study aims to investigate the molecular mechanism of SGLT2i in reducing EAT inflammation and to explore the effects of SGLT2i on atrial fibrosis in atrial fibrillation. Sprague-Dawley rats were injected with angiotensin II to induce atrial fibrillation and randomly assigned to receive SGLT2i ( n = 6) or vehicle ( n = 6). Macrophages (RAW264.7) were treated with ketone bodies; ACC1 knockdown/overexpression and malonyl-CoA overexpression were performed in vitro . The levels of inflammatory cytokines, ACC1, and malonyl-CoA were examined by ELISA. GAPDH malonylation was measured by co-immunoprecipitation. In atrial fibrillation rats, SGLT2i increased the ketone body levels and decreased the expression of ACC1 and alleviated EAT inflammation and atrial fibrosis. In RAW264.7 cells, ketone bodies decreased the levels of ACC1, malonyl-CoA, and GAPDH malonylation, accompanied by reduced inflammatory cytokines. ACC1 knockdown decreased the expression of malonyl-CoA and GAPDH malonylation and alleviated lipopolysaccharide (LPS)-induced macrophage inflammation; these effects were inhibited by malonyl-CoA overexpression. Furthermore, the protective effects of ketone bodies on macrophage inflammation were abrogated by ACC1 overexpression. SGLT2i alleviates EAT inflammation by reducing GAPDH malonylation via downregulating the expression of ACC1 through increasing ketone bodies, thus attenuating atrial fibrosis.

The emerging role of ferroptosis in myocardial fibrosis of atrial fibrillation.

The aim of this study was to investigate the relationship between ferroptosis and myocardial fibrosis in atrial fibrillation (AF). The patient's left atrial appendage tissue was obtained in cardiac surgery. Sirius red staining, Prussian blue and Western blot were used to detect staining to assess histological fibrosis and ferroptosis changes. There is a certain correlation between the degree of tissue fibrosis and ferroptosis in AF (r = 0.7763, p = 0.0004). The key proteins related to the regulation of ferroptosis were significantly abnormal in the AF group. Ferroptosis is involved in myocardial fibrosis of AF and is a potential target for the diagnosis, prevention and treatment of AF.

Relationship Between Periodontitis and Atrial Fibrosis in Atrial Fibrillation: Histological Evaluation of Left Atrial Appendages.

Atrial fibrosis contributes to the onset and persistence of atrial fibrillation (AF) and AF-related stroke.Periodontitis, a common infectious and inflammatory disease, aggravates some systemic diseases. However, theassociation of periodontitis with AF and with atrial fibrosis has remained unclarified. The authors aimed to elucidate the relationship between periodontitis and atrial fibrosis by studying resected left atrial appendages (LAAs). Seventy-six patients with AF (55 with nonparoxysmal AF, 25 with mitral valve regurgitation, 18 with LAA thrombus) who were scheduled to undergo LAA excision during cardiac surgery were prospectively enrolled. All patients underwent an oral examination, and the remaining number of teeth, bleeding on probing, periodontal probing depth, and periodontal inflamed surface area (PISA) were evaluated as parameters of periodontitis. The degree of fibrosis in each LAA was quantified by Azan-Mallory staining. Bleeding on probing (R=0.48; P< 0.0001), periodontal probing depth of≥4mm (R=0.26; P=0.02), and PISA (R=0.46; P< 0.0001) were positively correlated with atrial fibrosis. Among patients with >10 remaining teeth, PISA was positively and strongly correlated with atrial fibrosis (R=0.57; P< 0.0001). After adjustments for age, AF duration, BMI, mitral valve regurgitation, and CHADS₂ (congestive heart failure, hypertension, age, diabetes, previous stroke/transient ischemic attack) score, PISA was significantly associated with atrial fibrosis (β=0.016; P=0.0002). The authors histologically revealed the association of periodontitis with atrial fibrosis. This indicates that periodontitis, which is modifiable, is likely a risk factor for AF.

Abstract 11717: Expression of Tumor Endothelial Marker 1 in Cardiac Fibroblasts is Associated With Atrial Fibrosis and Regulates Cell Behaviors of Cardiac Fibroblasts

Background: Tumor endothelial marker 1 (TEM1 or CD248) is a transmembrane protein that expresses in mesenchymal lineage-derived cells only during embryogenesis. Re-upregulation of TEM1 in fibroblasts has been found in hepatic fibrosis, renal fibrosis and wound healing. Atrial fibrosis plays an important role in atrial fibrillation (AF) and stroke. We evaluated TEM1 expression in atrial fibrosis and its physiological significance. Methods and Results: All data were presented as mean ± standard error. In 10 patients (pts) with AF undergoing indicated cardiac surgery and Maze procedure, left atrial (LA) appendage was excised. Immunofluorescence staining showed TEM1 expressed in LA cardiac fibroblasts (CFs) in AF pts but not in normal LA tissue purchased from the US Biomax, Inc. Sirius Red staining showed more LA fibrosis in AF than normal LA tissue (7.51±0.40% vs. 3.80±0.51%, p&lt;0.01). In AF pts, higher LA TEM1 expression detected by western blotting was associated with larger LA fibrosis. In 20 AF pts (15 men, mean age 57.5 ± 2.8 yrs) undergoing catheter ablation, LA blood samples were taken and soluble TEM1 (sTEM1) was measured by ELISA. Peak atrial longitudinal strain (PALS) measured by speckle tracking echocardiography before ablation was used as an atrial fibrosis marker. There was a significantly negative correlation of the sTEM1 levels in LA with PALS (ρ=-0.453, p&lt;0.05) indicating increased sTEM1 was associated with atrial fibrosis. In vitro study showed recombinant TEM1 protein (rTEM1) increased proliferation of cultured CFs (saline vs rTEM1 10, 50 and 100 nM, BrdU absorbance: 0.55±0.02 vs. 0.62±0.04 vs. 0.73±0.04 vs. 0.74±0.04, p&lt;0.05) and reduced starvation-induced apoptosis (cell death ELISA absorbance: 1.06±0.09 vs. 0.61±0.05 vs. 0.49±0.11 vs. 0.33±0.02, p&lt;0.05). Transwell assay showed rTEM1 induced increased CFs migration. Conclusions: The study results indicate that TEM1 upregulation in CFs is associated with atrial fibrosis and TEM1 changes the cell behaviors of CFs. Further studies are undergoing to clarify if TEM1 knockdown could alleviate atrial fibrosis.

Abstract 11201: Relationship Between Periodontitis and Atrial Fibrosis in Atrial Fibrillation: Histological Evaluation of Left Atrial Appendages

Introduction: Atrial fibrosis contributes to the onset and persistence of atrial fibrillation (AF) and AF-related stroke. Periodontitis, a common infectious and inflammatory disease, aggravates some systemic diseases. However, the association of periodontitis with AF and with atrial fibrosis has remained unclarified. Hypothesis: We hypothesized that periodontitis aggravates atrial fibrosis and conducted a histological study using resected left atrial appendages (LAAs). Methods: Seventy-six patients with AF (55 with nonparoxysmal AF, 25 with mitral valve regurgitation [MR], 18 with LAA thrombus) who were scheduled to undergo LAA excision during cardiac surgery were prospectively enrolled. All patients underwent an oral examination, and remaining number of teeth, bleeding on probing (BOP), periodontal probing depth (PPD), and periodontal inflamed surface area (PISA) were evaluated as parameters of periodontitis. The degree of fibrosis in each LAA was quantified by Azan-Mallory staining. Results: BOP ( R = 0.48, P &lt; 0.0001), PPD of &gt; 4 mm ( R = 0.26, P = 0.02), and PISA ( R = 0.46, P &lt; 0.0001) were positively correlated with atrial fibrosis. Among patients with &gt;10 remaining teeth, PISA was positively and strongly correlated with atrial fibrosis ( R = 0.57, P &lt; 0.0001; Figure). After adjustments for age, AF duration, BMI, MR, and CHADS 2 (congestive heart failure, hypertension, age, diabetes, previous stroke/transient ischemic attack) score, PISA was significantly associated with atrial fibrosis ( β = 0.016, P = 0.0002). Conclusions: We histologically revealed the association of periodontitis with atrial fibrosis. This indicates that periodontitis, which is modifiable, is a risk factor for AF.

Atrial myocyte-derived exosomal microRNA contributes to atrial fibrosis in atrial fibrillation

BackgroundAtrial fibrosis plays a critical role in the development of atrial fibrillation (AF). Exosomes are a promising cell-free therapeutic approach for the treatment of AF. The purposes of this study were to explore the mechanisms by which exosomes derived from atrial myocytes regulate atrial remodeling and to determine whether their manipulation facilitates the therapeutic modulation of potential fibrotic abnormalities during AF.MethodsWe isolated exosomes from atrial myocytes and patient serum, and microRNA (miRNA) sequencing was used to analyze exosomal miRNAs in exosomes derived from atrial myocytes and patient serum. mRNA sequencing and bioinformatics analyses corroborated the key genes that were direct targets of miR-210-3p.ResultsThe miRNA sequencing analysis identified that miR-210-3p expression was significantly increased in exosomes from tachypacing atrial myocytes and serum from patients with AF. In vitro, the miR-210-3p inhibitor reversed tachypacing-induced proliferation and collagen synthesis in atrial fibroblasts. Accordingly, miR-210-3p knock out (KO) reduced the incidence of AF and ameliorated atrial fibrosis induced by Ang II. The mRNA sequencing analysis and dual-luciferase reporter assay showed that glycerol-3-phosphate dehydrogenase 1-like (GPD1L) is a potential target gene of miR-210-3p. The functional analysis suggested that GPD1L regulated atrial fibrosis via the PI3K/AKT signaling pathway. In addition, silencing GPD1L in atrial fibroblasts induced cell proliferation, and these effects were reversed by a PI3K inhibitor (LY294002).ConclusionsAtrial myocyte-derived exosomal miR-210-3p promoted cell proliferation and collagen synthesis by inhibiting GPD1L in atrial fibroblasts. Preventing pathological crosstalk between atrial myocytes and fibroblasts may be a novel target to ameliorate atrial fibrosis in patients with AF.Graphical

Liraglutide inhibits AngII-induced cardiac fibroblast proliferation and ECM deposition through regulating miR-21/PTEN/PI3K pathway.

Cardiac fibrosis characterized with the aberrant proliferation of cardiac fibroblasts and extracellular matrix (ECM) deposition is a major pathophysiological feature of atrial fibrillation (AF). Liraglutide has exerted an alleviative role in various cardiovascular diseases, and can also regulate the level of microRNAs (miRNAs). It has been reported that miR-21 modulated cardiac fibrosis in AF. However, the regulative effect of liraglutide on atrial fibrosis via miR-21 and the underlying mechanism are still unclear. The atrial fibroblasts were isolated from the heart of C57BL/6 mice, and treated with Angiotensin II (AngII) and liraglutide. The proliferation, migration, and ECM deposition were determined by cell counting Kit-8 (CCK-8), Brdu, transwell assay, cell scratch, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blot and immunofluorescence. The underlying mechanism was explored after transfection of miR-21 mimics into cells. Liraglutide inhibited proliferation, migration, invasion of fibroblast cell and ECM deposition in AngII-stimulated cardiac fibroblasts. Additionally, liraglutide decreased the AngII-induced increase in the expression level of miR-21, but enhanced the expression of phosphatase and tensin homolog (PTEN), a target of miR-21, thereby suppressing the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway. Rescue assay confirmed that overexpression of miR-21 counteracted the ameliorative effect of liraglutide on the proliferation, migration, invasion and ECM deposition in fibroblasts stimulated by AngII. Liraglutide dampened AngII-induced proliferation and migration, and ECM deposition of cardiac fibroblast via modulating miR-21/PTEN/PI3K pathway.

LncRNA HOTAIR promotes myocardial fibrosis in atrial fibrillation through binding with PTBP1 to increase the stability of Wnt5a

BackgroundAtrial fibrillation (AF) is one of the most common arrhythmia in clinical practice, and atrial fibrosis is the important mediator in AF. LncRNA HOTAIR was reported to be up-regulated in AF, while the underlying mechanism of HOTAIR in AF remains unclear. MethodsIn vitro and in vivo AF model was established. qRT-PCR and Western blotting were used to assess the mRNA expression (HOTAIR, Wnt5a and PTBP1) and protein levels (Wnt5a, collagen I/III, α-SMA, CTGF, p-ERK, ERK, p-JNK, and JNK), respectively. MTT, CCK8, transwell assay was used to test cell viability, proliferation and migration, respectively. RIP assay assessed the correlation among HOTAIR, PTBP1 and Wnt5a. The level of α-SMA was detected by immunofluorescence. HE and Masson staining detected the histological changes and fibrosis in mouse heart tissues. ResultsAng II significantly increased the viability of atrial fibroblasts. The levels of HOTAIR and Wnt5a in fibroblasts were up-regulated by Ang II. HOTAIR silencing or Wnt5a significantly inhibited Ang II-induced proliferation, migration and fibrosis in fibroblasts. HOTAIR silencing repressed Wnt5a-mediated ERK and JNK signaling pathway, and Wnt5a partially abolished the effect of HOTAIR silencing on cell proliferation, migration and fibrosis. Meanwhile, HOTAIR could increase the mRNA stability of Wnt5a via recruiting PTBP1. Furthermore, HOTAIR knockdown notably inhibited the fibrosis in heart tissues of AF mice via regulation of Wnt signaling. ConclusionHOTAIR could promote atrial fibrosis in AF through binding with PTBP1 to increase Wnt5a stability. Our study might shed new insights on exploring new strategies against AF.

TGF-β1-induced endothelial-mesenchymal transition: a potential contributor to fibrotic remodeling in atrial fibrillation?

Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide, with an unmet therapeutic need. Fibrotic remodeling, in which collagen-producing atrial fibroblasts play a crucial role, substantially contributes to arrhythmia promotion and progression. In this issue of the JCI, Lai, Tsai, and co-authors reveal that TGF-β1 promoted endothelial-mesenchymal transition during AF and put forward the notion that, in the adult heart, atrial fibroblasts can originate from different cellular sources. These important findings extend our understanding of the origin, biology, and function of fibroblasts and offer possibilities for therapeutic targeting of fibrosis in AF.