Mechanism Research Of MCP-1 On Atrial Fibrosis In Ageing Atrial Fibrillation

Objective:The aim of this study was to investigate the relationship between MCP-1 and age-related atrial fibrillation and to elucidate the underlying mechanism of MCP-1 promoting atrial fibrosis.In vitro,age-related characteristic changes of the electrical remodeling and structural reconstruction were testified,and further steps were adapted to analyze the expression of MCP-1 and fibrosis related indicators to clarify the interact between the age and fibrosis.In vivo,canine fibroblasts were isolated,purified and identified from left atrial.MCP-1 and MCP-1 receptor antagonists(CCR2-Block)were used to investigate whether MCP-1/CCR2 pathway could influence the ability of fibroblasts in cardiac interstitium.This study was performed as follows: Establishing a canine model of atrial fibrillation to compare the electrical remodeling and histological remodeling in different age-related atrial fibrillation groups.Analyze the difference role of MCP-1 and fibrosis markers in age-related atrial fibrillation.Primary canine fibroblasts were isolated from the left atrial of adult canine and treated with MCP-1 and CCR2 receptor antagonists to investigate the effects and mechanisms of MCP-1/CCR2 on aging-related myocardial remodeling.Methods:Part I: The establishment of different age with or without atrial fibrillation canine model in vivo.Echocardiography,histological detection and electricity physiological test was performed to explore the morphological changes and electrophysiological changes in different groups.Part II: The protein content and mRNA of MCP-1,extracellular matrix components of atrial myocytes and other related cytokines were detected by Western blot and qRT-PCR.The levels of collagen metabolism markers,cytokines(MCP-1,TGF-β1)in serum were detected by ELISA,and the electrical remodeling and structural remodeling caused by aging were identified.Part III: Canine atrial fibroblasts were isolated,respectively,control,MCP-1 at different concentrations,at different time points to clarify the MCP-1 on fibroblast secretion and activation function.The primary atrial fibroblasts were treated with control,MCP-1,MCP-1 + CCR2 antagonist and other groups.The expressions of MCP-1,MMP2,TIMP-s and TGF-β1 were tested to explore the clear MCP-1/CCR2 pathway on the secretion and activator function of fibroblast.Results:Part I: Compared with the adult control group,left atrial expansion,left ventricular end-diastolic volume,and shortening of left ventricular long axis significantly decreased(P<0.05).The AERP of adult AF group was shorter than that of adult control group.The shorter the S1 stimulation circumference,the shorter the shortening of AERP(P<0.05);however,the AERP of left atria was gradually prolonged in aged AF group compared with the control group and AF duration increased(P<0.05).Visible collagen network is widely distributed in posterior left atrial wall with atrial fibrillation.Part II: The levels of MCP-1 and CCR2 from peripheral blood of elderly patients with AF were increase significantly compared with other groups.QRT-PCR and western blot detect that MCP-1,CCR2 expression was significantly increase in aged group and atrial fibrillation groups.The levels of MMP2 and MMP-9 increased in elderly patients with atrial fibrillation,while the expressions of TIMP-1 and TIMP-2 showed a decreasing trend.Part III: MCP-1 can stimulate canine primary fibroblasts proliferation,activation,secretion.MCP-1 affect the ability of fibroblasts to secrete CCR2,α-SMA,COL-Ⅰ,TGF-β1 and so on.Interfere the MCP-1/CCR2 pathway can reduce the activation of myofibroblasts.There exists feedback loop in the MCP-1/CCR2/TGF-β1 pathway to affect the fibroblast activate and secrete ability.Conclusions:Model established by left atrial appendage pacing provide a reliable animal model to study the age-related atrial fibrillation.In vitro,it is found that age-related atrial fibrillation is more prone to electrical remodeling and structural remodeling,and fibrosis plays an important role in the maintenance of elderly atrial fibrillation.MCP-1 is closely related to aging and atrial fibrillation.In vivo,MCP-1 can affect activity,secretion and activation ability of the fibroblast cell.The MCP-1/CCR2 pathway may affect myocardial fibrosis through its effects on fibroblasts.The underly procedure as follows: MCP-1 stimulates fibroblasts to secrete collagen directly to induce the fibrosis process in myocardium;MCP-1 stimulates fibroblasts to secrete pro-fibrogenic factors such as TGF-β1;MCP-1 affects fibroblast differentiation into myofibroblasts and exerts fibrogenic activity.Blocking the MCP-1/CCR2 pathway can block the effect of MCP-1 on fibroblast activity.