Role Of Circulating Fibrocytes In Mediating Atrial Fibrillation-induced Atrial Fibrosis

Objective: In atrial fibrillation(AF),a more extensively fibrotic atrium represents the substrate for the arrhythmia to persist,and increases risk of recurrence following catheter ablation.Fibrocytes are bone-marrow derived circulating mesenchymal progenitors,and increased fibrocytes have recently been identified in the circulation and fibrotic heart tissues.This study tested the hypothesis that increased circulating fibrocytes are associated with fibrosis area in persistent AF.Methods: Patients with paroxysmal AF(n=16),persistent AF(n=40)or healthy controls(n=28)were recruited in this study.All Patients with AF underwent circumferential pulmonary vein isolation of AF,guided by a CARTO mapping system.The basic clinical paramters,including gender,age,blood pressure,lipid profile,blood routine examination,blood coagulation test,heart rate,ultrasonic cardiogram and drug in use,were recorded.Fresh blood was collected before ablation.Circulating fibrocytes(CD34+/collagen I+)were measured by flow cytometry.Leukocytes were isolated from whole blood and cultured for 12 days and differentiated fibrocytes were changed from round-shape to spindle-shape,and quantitated and sorted by flow cytometry(CD45+/collagen I+).Fibrosis area in left atrium(LA)was measured and analyzed by 3-D CARTO system.Recurrence rate within 30 days in fibrocyte high and low group was recorded.The sorted fibrocytes from healthy controls or persistent AF were used to measure changes in fibroblast activation markers(fibronectin,?-SMA or collagen I) using real-time PCR and immunofluorescence.Results: Persistent AF group had increased circulating fibrocyte number than paroxysmal AF group or healthy controls(3.3±1.3% vs.2.5±0.8%,2.0±0.8%,P<0.05).After leukocyte culture,the percentage of fibrocytes of the remaining adherent cells in culture measured by flow cytometry were also increased in persistent AF group compared with paroxysmal AF group or healthy controls(66±10.1% vs.57±7.9%,48±7.9%,P<0.01).There was also an obvious increase in paroxysmal AF group vs.healthy controls(57±7.9% vs.48±7.9%,P<0.01),these results suggested that leukocytes from persistent AF patients have the enhanced ability to differentiate into fibrocytes.In persistent AF patients,the percentage of fibrocytes has been shown to correlate in a linear fashion with the percentage of atrial fibrosis(R=0.7167,P<0.001).Fibrocyte high group(fibrcoyte%>3.1)presented an increased recurrence rate than fibrocyte low group(fibrcoyte%?3.1%)after 30 days of ablation(56% vs.20%).Expressions of ?-SMA,fibronectin,collagen I and CX3CR1 were enhanced in persistent AF patients compared with healthy controls(P<0.05).Conclusion: In persistent AF,fibrocytes in the circulation was enhanced and displayed a great degree of differentiability into fibroblasts or myofibroblasts,which may contribute to atrial fibrosis and recurrence following ablation.