A comparison of left and right atrial fibroblasts reveals different collagen production activity and stress-induced mitogen-activated protein kinase signalling in rats

Defining Transcriptomic Heterogeneity between Left and Right Ventricle-Derived Cardiac Fibroblasts

Cardiac fibrosis is a key aspect of heart failure, leading to reduced ventricular compliance and impaired electrical conduction in the myocardium. Various pathophysiologic conditions can lead to fibrosis in the left ventricle (LV) and/or right ventricle (RV). Despite growing evidence to support the transcriptomic heterogeneity of cardiac fibroblasts (CFs) in healthy and diseased states, there have been no direct comparisons of CFs in the LV and RV. Given the distinct natures of the ventricles, we hypothesized that LV- and RV-derived CFs would display baseline transcriptomic differences that influence their proliferation and differentiation following injury. Bulk RNA sequencing of CFs isolated from healthy murine left and right ventricles indicated that LV-derived CFs may be further along the myofibroblast transdifferentiation trajectory than cells isolated from the RV. Single-cell RNA-sequencing analysis of the two populations confirmed that Postn+ CFs were more enriched in the LV, whereas Igfbp3+ CFs were enriched in the RV at baseline. Notably, following pressure overload injury, the LV developed a larger subpopulation of pro-fibrotic Thbs4+/Cthrc1+ injury-induced CFs, while the RV showed a unique expansion of two less-well-characterized CF subpopulations (Igfbp3+ and Inmt+). These findings demonstrate that LV- and RV-derived CFs display baseline subpopulation differences that may dictate their diverging responses to pressure overload injury. Further study of these subpopulations will elucidate their role in the development of fibrosis and inform on whether LV and RV fibrosis require distinct treatments.

Epigallocatechin-3-Gallate Inhibits Atrial Fibrosis and Reduces the Occurrence and Maintenance of Atrial Fibrillation and its Possible Mechanisms

BACKGROUND

Atrial fibrosis is one of the main causes of the onset and recurrence of atrial fibrillation (AF), for which there is no effective treatment. The aim of this study was to investigate the effect and mechanism of epigallocatechin-3-gallate (EGCG) on AF in rats.

METHODS

The rat model of AF was established by rapid pacing induction after angiotensin-II (Ang-II) induced atrial fibrosis to verify the relationship between atrial fibrosis and the AF. The expression levels of TGF-β/Smad3 pathway molecules and lysyl oxidase (LOX) in AF were detected. Subsequently, EGCG was used to intervene Ang-II-induced atrial fibrosis to explore the role of EGCG in the treatment of AF and its inhibitory mechanism on fibrosis. It was further verified that EGCG inhibited the production of collagen and the expression of LOX through the TGF-β/Smad3 pathway at the cellular level.

RESULTS

The results showed that the induction rate and maintenance time of AF in rats increased with the increase of the degree of atrial fibrosis. Meanwhile, the expressions of Col I, Col III, molecules related to TGF-β/Smad3 pathway, and LOX increased significantly in the atrial tissues of rats in the Ang-II induced group. EGCG could reduce the occurrence and maintenance time of AF by inhibiting the degree of Ang-induced rat atrial fibrosis. Cell experiments confirmed that EGCG could reduce the synthesis of collagen and the expression of LOX in cardiac fibroblast induced by Ang-II. The possible mechanism is to down-regulate the expression of genes and proteins related to the TGF-β/Smad3 pathway.

CONCLUSION

EGCG could downregulate the expression levels of collagen and LOX by inhibiting the TGF-β/Smad3 signaling pathway, alleviating Ang-II-induced atrial fibrosis, which in turn inhibited the occurrence and curtailed the duration of AF.

Inhibition of transglutaminase 2 (TG2) ameliorates ventricular fibrosis in isoproterenol-induced heart failure in rats

AIMS

Transglutaminase (TG) inhibitors represent promising therapeutic interventions in cardiac fibrosis and related dysfunctions. However, it remains unknown how TG inhibition, TG2 in particular, affects the signaling systems that drive pathological fibrosis. This study aimed to examine the effect TG inhibition by cystamine on the progression of isoproterenol (ISO)-induced cardiac fibrosis and dysfunction in rats.

MATERIALS AND METHODS

Cardiac fibrosis was established by intraperitoneal injection of ISO to rats (ISO group), followed by 6 weeks of cystamine injection (ISO + Cys group). The control groups were administered normal saline alone or with cystamine. Hemodynamics, lipid profile, liver enzymes, urea, and creatinine were assessed in conjunction with heart failure markers (serum NT-proANP and cTnI). Left ventricular (LV) and atrial (LA) fibrosis, total collagen content, and mRNA expression of profibrotic markers including TG2 were quantified by Masson's trichrome staining, LC-MS/MS and quantitative PCR, respectively.

KEY FINDINGS

Cystamine administration to ISO rats significantly decreased diastolic and mean arterial pressures, total cholesterol, triglycerides, LDL, liver enzymes, urea, and creatinine levels, while increasing HDL. NT-proANP and cTnI serum levels remained unchanged. In LV tissues, significant reductions in ISO-induced fibrosis and elevated total collagen content were achieved after cystamine treatment, together with a reduction in TG2 concentration. Reduced mRNA expression of several profibrotic genes (COL1A1, FN1, MMP-2, CTGF, periostin, CX43) was also evidenced in LV tissues of ISO rats upon cystamine administration, whereas TGF-β1 expression was depressed in LA tissues. Cystamine decreased TG2 mRNA expression in the LV of control rats, while LV expression of TG2 was relatively low in ISO rats irrespective of cystamine treatment.

SIGNIFICANCE

TG2 inhibition by cystamine in vivo exerted cardioprotective effects against ISO-induced cardiac fibrosis in rats decreasing the LV abundance of several profibrotic markers and the content of TG2 and collagen, suggesting that TG2 pharmacological inhibition could be beneficial to alleviate cardiac fibrosis.

Empagliflozin suppressed cardiac fibrogenesis through sodium-hydrogen exchanger inhibition and modulation of the calcium homeostasis

BACKGROUND

The novel sodium-glucose co-transporter 2 inhibitor (SGLT2i) potentially ameliorates heart failure and reduces cardiac arrhythmia. Cardiac fibrosis plays a pivotal role in the pathophysiology of HF and atrial myopathy, but the effect of SGLT2i on fibrogenesis remains to be elucidated. This study investigated whether SGLT2i directly modulates fibroblast activities and its underlying mechanisms.

METHODS AND RESULTS

Migration, proliferation analyses, intracellular pH assay, intracellular inositol triphosphate (IP3) assay, Ca²⁺ fluorescence imaging, and Western blotting were applied to human atrial fibroblasts. Empagliflozin (an SGLT2i, 1, or 5 μmol/L) reduced migration capability and collagen type I, and III production. Compared with control cells, empagliflozin (1 μmol/L)- treated atrial fibroblasts exhibited lower endoplasmic reticulum (ER) Ca²⁺ leakage, Ca²⁺ entry, inositol trisphosphate (IP3), lower expression of phosphorylated phospholipase C (PLC), and lower intracellular pH. In the presence of cariporide (an Na⁺-H⁺ exchanger (NHE) inhibitor, 10 μmol/L), control and empagliflozin (1 μmol/L)-treated atrial fibroblasts revealed similar intracellular pH, ER Ca²⁺ leakage, Ca²⁺ entry, phosphorylated PLC, pro-collagen type I, type III protein expression, and migration capability. Moreover, empagliflozin (10 mg/kg/day orally for 28 consecutive days) significantly increased left ventricle systolic function, ß-hydroxybutyrate and decreased atrial fibrosis, in isoproterenol (100 mg/kg, subcutaneous injection)-induced HF rats.

CONCLUSIONS

By inhibiting NHE, empagliflozin decreases the expression of phosphorylated PLC and IP3 production, thereby reducing ER Ca²⁺ release, extracellular Ca²⁺ entry and the profibrotic activities of atrial fibroblasts.

Inhibition of the cardiac fibroblast-enriched histone methyltransferase Dot1L prevents cardiac fibrosis and cardiac dysfunction

Background

Cardiac fibrosis is characterized by excessive extracellular matrix deposition that contributes to compromised cardiac function and potentially heart failure. Disruptor of telomeric silencing 1-like (Dot1L) is the catalytic enzyme required for histone H3K79 methylation which has been demonstrated to play a role in transcriptional activation. However, the functions of Dot1L in the process of cardiac fibrosis still remain unknown.

Results

In the present study, we found that endogenous Dot1L is upregulated in cardiac fibroblasts (CFs) treated with angiotensin II (Ang II) or transforming growth factor (TGF)-β1, along with elevated extracellular matrix (ECM) such as fibronectin, collagen I and III. Silencing or inhibiting Dot1L mitigated Ang II-induced myofibroblast generation and fibrogenesis. We identified the transcription factor-forkhead box O (FoxO) 3a as a novel substrate of Dot1L, the transcriptional activating mark H3K79me3 level on the promoter of FoxO3a was increase in activated-CFs, and inhibition of Dot1L markedly decreased FoxO3a transcription accompanied by a significant decrease in the expression of fibrogenic gene. Knockdown of FoxO3a could alleviate ECM deposition induced by Ang II, on the contrary, overexpression FoxO3a resulting in CFs activation. Consistently, in vivo Dot1L ablation rescued myocardial ischemia-induced cardiac fibrosis and improved cardiac function.

Conclusions

Our findings conclude that upregulation of Dot1L results in activation of the cardiac fibroblasts to promote profibrotic gene, eventually causes cardiac fibrosis. Pharmacological targeting for Dot1L might represent a promising therapeutic approach for the treatment of human cardiac fibrosis and other fibrotic diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00877-5.

Regional Diversities in Fibrogenesis Weighed as a Key Determinant for Atrial Arrhythmogenesis

Atrial fibrosis plays a key role in atrial myopathy, resulting in the genesis of atrial fibrillation (AF). The abnormal distribution of fibrotic tissue, electrical coupling, paracrine interactions, and biomechanical–electrical interactions have all been suggested as causes of fibrosis-related arrhythmogenesis. Moreover, the regional difference in fibrogenesis, specifically the left atrium (LA) exhibiting a higher arrhythmogenesis and level of fibrosis than the right atrium (RA) in AF, is a key contributor to atrial arrhythmogenesis. LA fibroblasts have greater profibrotic cellular activities than RA fibroblasts, but knowledge about the regional diversity of atrial regional fibrogenesis remains limited. This article provides a comprehensive review of research findings on the association between fibrogenesis and arrhythmogenesis from laboratory to clinical evidence and updates the current understanding of the potential mechanism underlying the difference in fibrogenesis between the LA and RA.

Calcium Regulation on the Atrial Regional Difference of Collagen Production Activity in Atrial Fibrogenesis

Background: Atrial fibrosis plays an important role in the genesis of heart failure and atrial fibrillation. The left atrium (LA) exhibits a higher level of fibrosis than the right atrium (RA) in heart failure and atrial arrhythmia. However, the mechanism for the high fibrogenic potential of the LA fibroblasts remains unclear. Calcium (Ca²⁺) signaling contributes to the pro-fibrotic activities of fibroblasts. This study investigated whether differences in Ca²⁺ homeostasis contribute to differential fibrogenesis in LA and RA fibroblasts. Methods: Ca²⁺ imaging, a patch clamp assay and Western blotting were performed in isolated rat LA and RA fibroblasts. Results: The LA fibroblasts exhibited a higher Ca²⁺ entry and gadolinium-sensitive current compared with the RA fibroblasts. The LA fibroblasts exhibited greater pro-collagen type I, type III, phosphorylated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), phosphorylated phospholipase C (PLC), stromal interaction molecule 1 (STIM1) and transient receptor potential canonical (TRPC) 3 protein expression compared with RA fibroblasts. In the presence of 1 mmol/L ethylene glycol tetra-acetic acid (EGTA, Ca²⁺ chelator), the LA fibroblasts had similar pro-collagen type I, type III and phosphorylated CaMKII expression compared with RA fibroblasts. Moreover, in the presence of KN93 (a CaMKII inhibitor, 10 μmol/L), the LA fibroblasts had similar pro-collagen type I and type III compared with RA fibroblasts. Conclusion: The discrepancy of phosphorylated PLC signaling and gadolinium-sensitive Ca²⁺ channels in LA and RA fibroblasts induces different levels of Ca²⁺ influx, phosphorylated CaMKII expression and collagen production.

Physiological testosterone attenuates profibrotic activities of rat cardiac fibroblasts through modulation of nitric oxide and calcium homeostasis

Testosterone deficiency is associated with poor prognosis among patients with chronic heart failure (HF). Physiological testosterone improves the exercise capacity of patients with HF. In this study, we evaluated whether treatment with physiological testosterone contributes to anti-fibrogenesis by modifying calcium homeostasis in cardiac fibroblasts and we studied the underlying mechanisms. Nitric oxide (NO) analyses, calcium (Ca²⁺) fluorescence, and Western blotting were performed in primary isolated rat cardiac fibroblasts with or without (control cells) testosterone (10, 100, 1,000 nmol/L) treatment for 48 hours. Physiological testosterone (10 nmol/L) increased NO production and phosphorylation at the inhibitory site of the inositol trisphosphate (IP3) receptor, thereby reducing Ca²⁺ entry, phosphorylated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) expression, type I and type III pro-collagen production. Non-physiological testosterone-treated fibroblasts exhibited similar NO and collagen production capabilities as compared to control (testosterone deficient) fibroblasts. These effects were blocked by co-treatment with NO inhibitor (L-NG-nitro arginine methyl ester [L-NAME], 100 μmol/L). In the presence of the IP3 receptor inhibitor (2-aminoethyl diphenylborinate [2-APB], 50 μmol/L), testosterone-deficient and physiological testosterone-treated fibroblasts exhibited similar phosphorylated CaMKII expression. When treated with 2-APB or CaMKII inhibitor (KN93, 10 μmol/L), testosterone-deficient and physiological testosterone-treated fibroblasts exhibited similar type I, and type III collagen production. In conclusion, physiological testosterone activates NO production, and attenuates the IP3 receptor/Ca²⁺ entry/CaMKII signaling pathway, thereby inhibiting the collagen production capability of cardiac fibroblasts.

Atorvastatin attenuates TGF‑β1‑induced fibrogenesis by inhibiting Smad3 and MAPK signaling in human ventricular fibroblasts

Excessive proliferation and myofibroblasts transformation of cardiac fibroblasts play a critical role in the process of cardiac fibrosis. Atorvastatin (ATV), a 3‑hydroxy‑3‑methyl‑glutaryl‑coenzyme A reductase inhibitor, is commonly used to treat hypercholesterolemia. It has previously been shown that ATV has potential anti‑fibrotic effects. However, the underlying mechanisms of ATV against cardiac fibrosis remain to be fully elucidated, and to the best of our knowledge, there are no reports focusing on the effects of ATV on transforming growth factor‑β1 (TGF‑β1)‑induced human ventricular fibroblasts (hVFs) activation. In the present study, hVFs were stimulated with TGF‑β1 with or without pretreatment with ATV. Subsequently, hVF proliferation, cytotoxicity, myofibroblast differentiation and pro‑fibrotic gene expression were assessed. Canonical and non‑canonical signaling downstream of TGF‑β1, such as Smad3 and mitogen‑activated protein kinase (MAPK) signaling, were investigated by evaluating the phosphorylation levels of Smad3, extracellular signal‑regulated kinase 1/2, p38 MAPK and c‑Jun N‑terminal kinase. The results indicated that ATV significantly prevented TGF‑β1‑induced cell proliferation, myofibroblast differentiation and production of extracellular matrix proteins, such as matrix metalloproteinase‑2, collagen I and collagen III, in hVFs. Furthermore, ATV effectively inhibited TGF‑β1‑induced activation of Smad3 and MAPK signaling in hVFs. In conclusion, the present results demonstrated that ATV prevented TGF‑β1‑induced fibrogenesis in hVFs, at least in part by inhibiting the Smad3 and MAPK signaling pathways. Therefore, these results imply that ATV may be a promising agent to treat myocardial fibrosis.

Vascular endothelial growth factor enhances profibrotic activities through modulation of calcium homeostasis in human atrial fibroblasts

Vascular endothelial growth factor (VEGF), a pivotal activator of angiogenesis and calcium (Ca²⁺) signaling in endothelial cells, was shown to increase collagen production in atrial fibroblasts. In this study, we evaluated whether VEGF may regulate Ca²⁺ homeostasis in atrial fibroblasts and contribute to its profibrogenesis. Migration, and proliferation analyses, patch-clamp assay, Ca²⁺ fluorescence imaging, and western blotting were performed using VEGF-treated (300 pg/mL or 1000 pg/mL) human atrial fibroblasts with or without coadministration of Ethylene glycol tetra-acetic acid (EGTA, 1 mmol/L), or KN93 (a Ca²⁺/calmodulin-dependent protein kinase II [CaMKII] inhibitor, 10 μmol/L). VEGF (1000 pg/mL) increased migration, myofibroblast differentiation, pro-collagen type I, pro-collagen type III production, and phosphorylated VEGF receptor 1 expression of fibroblasts. VEGF (1000 pg/mL) increased the nonselective cation current (I_NSC) of transient receptor potential (TRP) channels and potassium current of intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels thereby upregulating Ca²⁺ entry. VEGF upregulated phosphorylated ERK expression. An ERK inhibitor (PD98059, 50 μmol/L) attenuated VEGF-activated I_NSC of TRP channels. The presence of EGTA attenuated the profibrotic effects of VEGF on pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and migratory capabilities of fibroblasts. VEGF upregulated the expression of phosphorylated CaMKII in fibroblasts, which was attenuated by EGTA. In addition, KN93 reduced VEGF-increased pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and the migratory capabilities of fibroblasts. In conclusion, we found that VEGF increases atrial fibroblast activity through CaMKII signaling by enhancing Ca²⁺ entry. Our findings provide benchside evidence leading to a potential novel strategy targeting atrial myopathy and arrhythmofibrosis.

MFGE8 attenuates Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation through inhibition of TGF-β1/Smad2/3 pathway

Atrial fibrillation (AF) is characterized by potentiated growth of atrial fibroblasts and excessive deposition of the extracellular matrix. Atrial fibrosis has emerged as a hallmark of atrial structural remodeling linked to AF. Nonetheless, the specific mechanism underlying the progression of atrial fibrosis to AF is still largely unknown. MFGE8 (milk fat globule-EGF factor 8) is a soluble glycoprotein associated with many human diseases. Recently, a number of studies revealed that MFGE8 plays a crucial role in heart disease. Yet, MFGE8 regulation and function in the process of atrial fibrosis and vulnerability to AF remain unexplored. In this study, we found that the expression of MFGE8 was downregulated in the atriums of patients with AF compared with individuals without AF. In addition, the expression of MFGE8 was lower in atriums of angiotensin II (Ang-II)-stimulated rats as compared with the sham group. In vitro, silencing of MFGE8 by small interfering RNA significantly increased Ang-II-induced atrial fibrosis, whereas administration of recombinant human MFGE8 (rhMFGE8) attenuated the atrial fibrosis. Moreover, we found that the activated TGF-β1/Smad2/3 pathway after Ang-II treatment was significantly potentiated by the MFGE8 knockdown but inhibited by rhMFGE8 in vitro. Inhibition of integrin β3 which is the receptor for MFGE8, suppressed the TGF-β1/Smad2/3 activating effects of the MFGE8 knockdown in Ang-II-treated rat atrial fibroblasts. Finally, we administered rhMFGE8 to rats; it attenuated atrial fibrosis and remodeling and further reduced AF vulnerability induced by Ang-II, indicating that MFGE8 might have the potential both as a novel biomarker and as a therapeutic target in atrial fibrosis and AF.

Does an imbalance in circulating vascular endothelial growth factors (VEGFs) cause atrial fibrillation in patients with valvular heart disease?

Background

The pathogenesis of atrial fibrillation (AF) remains unclear. Vascular endothelial growth factors (VEGFs) can stimulate fibrosis within the atrium and ventricle. We hypothesized that there is a relationship between the serum VEGFs/soluble vascular endothelial growth factor receptor (sVEGFRs) levels and AF in patients with valvular heart disease (VHD). This provides a new paradigm for studying AF.

Methods

The plasma levels of VEGF-A, VEGF-C, sVEGFR-1 and sVEGFR-2 were detected by enzyme-linked immunosorbent assay (ELISA). A total of 100 people, consisting of AF patients (long-standing, persistent AF; n=49), sinus rhythm (SR) patients (n=31) and healthy controls (n=20), were included in this study.

Results

The plasma levels of VEGF-A were significantly higher in AF patients compared to healthy control (P<0.05). The plasma levels of sVEGFR-1 were significantly higher in AF compared to SR (P<0.05). The plasma levels of sVEGFR-2 were significantly lower in AF patients compared to SR patients and healthy controls (both P<0.05). There was a significant and negative correlation between AF and the sVEGFR-2 levels in the groups (r=-0.432, P=0.000).

Conclusions

An imbalance in VEGFs and sVEGFRs may contribute to AF by breaking the balance of angiogenesis and lymphangiogenesis. Additionally, sVEGFR-2 may be an important biomarker of AF.

MK5 haplodeficiency decreases collagen deposition and scar size during post-myocardial infarction wound repair

MK5 is a protein serine/threonine kinase activated by p38, ERK3, and ERK4 MAPKs. MK5 mRNA and immunoreactivity are detected in mouse cardiac fibroblasts, and MK5 haplodeficiency attenuates the increase in collagen 1-α1 mRNA evoked by pressure overload. The present study examined the effect of MK5 haplodeficiency on reparative fibrosis following myocardial infarction (MI). Twelve-week-old MK5^+/- and wild-type littermate (MK5^+/+) mice underwent ligation of the left anterior descending coronary artery (LADL). Surviving mice were euthanized 8 or 21 days post-MI. Survival rates did not differ significantly between MK5^+/+ and MK5^+/- mice, with rupture of the LV wall being the primary cause of death. Echocardiographic imaging revealed similar increases in LV end-diastolic diameter, myocardial performance index, and wall motion score index in LADL-MK5^+/+ and LADL-MK5^+/- mice. Area at risk did not differ between LADL-MK5^+/+ and LADL-MK5^+/- hearts. In contrast, infarct size, scar area, and scar collagen content were reduced in LADL-MK5^+/- hearts. Immunohistochemical analysis of mice experiencing heart rupture revealed increased MMP-9 immunoreactivity in the infarct border zone of LADL-MK5^+/- hearts compared with LADL-MK5^+/+. Although inflammatory cell infiltration was similar in LADL-MK5^+/+ and LADL-MK5^+/- hearts, angiogenesis was more pronounced in the infarct border zone of LADL-MK5^+/- mice. Characterization of ventricular fibroblasts revealed reduced motility and proliferation in fibroblasts isolated from MK5^-/- mice compared with those from both wild-type and haplodeficient mice. siRNA-mediated knockdown of MK5 in fibroblasts from wild-type mice also impaired motility. Hence, reduced MK5 expression alters fibroblast function and scar morphology but not mortality post-MI. NEW & NOTEWORTHY MK5/PRAK is a protein serine/threonine kinase activated by p38 MAPK and/or atypical MAPKs ERK3/4. MK5 haplodeficiency reduced infarct size, scar area, and scar collagen content post-myocardial infarction. Motility and proliferation were reduced in cultured MK5-null cardiac myofibroblasts.

Factor Xa inhibition by rivaroxaban regulates fibrogenesis in human atrial fibroblasts with modulation of nitric oxide synthesis and calcium homeostasis

BACKGROUND

Rivaroxaban, a widely used factor Xa inhibitor in reducing stroke in atrial fibrillation (AF) patients has multiple biological effects with activation of protease-activated receptor (PAR) signaling. Atrial fibrosis plays a critical role in the pathophysiology of AF. In this study, we evaluated whether rivaroxaban regulates atrial fibroblast activity and its underlying mechanisms.

METHODS AND RESULTS

Migration, proliferation analyses, nitric oxide (NO) production assay, calcium fluorescence imaging, and western blots were conducted in human atrial fibroblasts with or without rivaroxaban (100 nmol/L or 300 nmol/L) and co-administration of L-NAME (L-NG-nitro arginine methyl ester, 100 μmol/L), EGTA (Ethylene glycol tetra-acetic acid, 1 mmol/L), thrombin (0.5 U/mL), PAR1 agonist peptide (TFLLR-NH2, 100 μmol/L), PAR1 inhibitor (SCH79797, 0.5 μmol/L) and PAR2 inhibitor (GB83, 10 μmol/L). Atrial fibrosis was examined in isoproterenol (100 mg/kg, subcutaneous injection)-treated rats with or without rivaroxaban (10 mg/kg/day orally for 14 consecutive days). Rivaroxaban reduced the migration, pro-collagen type I production, and proliferation of atrial fibroblasts. Rivaroxaban decreased phosphorylated endothelial NO synthase (eNOS) (Thr 495, an inhibitory phosphorylated site of eNOS), and calcium (Ca²⁺) entry, and increased NO production. Moreover, L-NAME blocked the effects of rivaroxaban on fibroblast collagen and NO production. In the presence of EGTA, the migratory capability was similarly decreased in atrial fibroblasts with and without treatment with rivaroxaban (100 nmol/L), which suggests that rivaroxaban decreases migratory capability of atrial fibroblasts by inhibiting Ca²⁺ entry. Additionally, rivaroxaban significantly attenuated the effects of thrombin, and TFLLR-NH2 on migratory, proliferative, and pro-collagen type I production capability in atrial fibroblasts. SCH79797 or GB83 decreased pro-collagen type I production, migration, and proliferation capability in fibroblasts, but combined SCH79797 or GB83 with and without rivaroxaban had similar fibroblast activity. Moreover, rivaroxaban significantly decreased atrial fibrosis in isoproterenol-treated rats.

CONCLUSIONS

Rivaroxaban (100-300 nmol/L) regulates atrial fibroblast activity and atrial fibrosis by increasing NO production and decreasing Ca²⁺ entry through inhibition of PAR signaling.