Mechanisms Of Atrial Fibrosis In Patients With Rheumatic Heart Disease (RHD) And Atrial Fibrillation

Atrial fibrillation (AF) is one of clinical manifestations for many cardiovascular diseases with high morbidity and mortality. But the mechanisms of AF are poorly understood. Recent researches demonstrate that electricity remodeling and tissue structure remodeling were both existing in AF, and atrial fibrosis is the most obvious reflect for atrial tissue structure remodeling in patients with AF. Many factors, such as local rennin angiotensin system (RAS) and cytokines, especially transforming growth factor-beta 1(TGF-β1) and basic fibroblast growth factor (bFGF), regulate the progression of fibrosis diseases. Some researches demonstrate that the high expression of TGF-β1 in pulmonales veins can explain the severe fibrosis in the peripheral zone of pulmonales veins in patients with chronic AF. However, the mechanisms of atrial fibrosis are still incomplete distinct. In domestic, there is no report whether the AngII through AT1-R to adjust the expression of TGF-β1 in patients with AF, and there is little report about the role of TGF-β1 and bFGF in atrial tissure in patients with AF not only in domestic journals but also in international journals.This study was indevided three parts: Section 1 was about the atrial fibrosis change in patients with AF; Section 2 was about the effects of RAS on atrial fibrosis in patients with AF; Section 3 was about the effects of TGF-β1 and bFGF on atrial fibrosis in patients with AF.This study investigated the effects and correlation of RAS and cytokines on the progression of atrial fibrosis by measuring the serum level of angiotensinⅡ, bFGF and TGF-β1; the expression and distribution of collagen, AT1-R, bFGF and TGF-β1; the expression of mRNA or protein of AT1-R, bFGF and TGF-β1, to provid initial experimental evidence for the mechanism of atrial fibrosis.Objectives: 1. to investigate the change of atrial fibrosis in patients with AF by measuring the content and distribution of collagen in atrial tissue.2. to investigate the effect of RAS on atrial fibrosis in patients with AF by detecting the serum level of angiotensinⅡand the expression of mRNA or protein for AT1-R in atrial tissue.3. to investigate the effect of TGF-β1 and bFGF on atrial fibrosis in patients with AF by measuring the serum level and the expression of mRNA and protein for TGF-β1 and bFGF.Methods: 1. Atrial tissue samples, which were obtained from patients received heart operation, were divided into control group (congenital heart disease(CHD) and sinus rhythm) (CHD+ sinus rhythm), and rheumatic heart disease(RHD) group with sinus rhythm (RHD+ sinus rhythm), paroxysm AF (RHD+pAF) or chronic AF (RHD+cAF). The collagen distribution in Atrial tissue was detected with Masson stain, and the content of collagen was detected with hydroxyproline measuring, while the expression of mRNA for collagen typeⅠandⅢwas detected with RT-PCR.2. The serum level of angiotensinⅡwas detected with ELISA, and, the expression and distribution of AT1-R in atrial tissue were detected with immunohistochemistry, while the expression of mRNA for AT1-R with RT-PCR and the expression of protein for AT1-R with Western blot.3. The serum level of TGF-β1 and bFGF were detected with ELISA; the expression and distribution of TGF-β1 and bFGF in atrial tissue were detected with immunohistochemistry; the expression of mRNA for them were detected with RT-PCR; the expression of protein for them were detected with western blot.Results:1. The atrial tissue samples were collected from 48 patients, 8 for RHD+ sinus rhythm group, 10 for RHD+pAF group, 20 for RHD+cAF group, 10 for control CHD+ sinus rhythm group. Clinical data indicated that the left atrial diameter(LAD) of cAF group is larger than that of control group obviously (P < 0.05), other information, including age, gender, left ventricular ejection fraction(LVEF) and valve pathological changes, were not distinct significantly (p>0.05).2. Masson stain demonstrated that the blue collagen fiber located mainly in myocardium matrix, and the expression of collagen fiber was increased gradually in CHD+ sinus rhythm, RHD+ sinus rhythm, RHD+pAF and RHD+cAF group. Meanwhile, the collagen contents detected with Hydroxyproline were increased among these groups gradually. The expression of mRNA for collagen typeⅠandⅢwith RT-PCR was increased gradually among these groups, especially the expression of collagen typeⅠ(P < 0.05).3. The serum level of angiotensinⅡwas increased gradually and markedly in CHD+ sinus rhythm, RHD+ sinus rhythm, RHD+pAF and RHD+cAF group (p<0.05). The brown AT1-R was distributed mainly in membrane and cytoplasm of atrial cardiocytes. The expression of mRNA or protein for AT1-R were decreased gradually in all groups, especially the expression of protein compared between RHD+cAF group and RHD+ sinus rhythm group (p<0.05).4. The Serum level of bFGF was increased gradually and markedly in CHD+ sinus rhythm, RHD+ sinus rhythm, RHD+pAF and RHD+cAF group (p<0.05). The brown bFGF was located mainly in cytoplasm of atrial cardiocytes. The expression of mRNA or protein for bFGF were increased gradually and significantly among these groups (p<0.05). 5. The Serum level of TGF-β1 was increased gradually and significantly in CHD+ sinus rhythm, RHD+ sinus rhythm, RHD+pAF and RHD+cAF group (p<0.05). The brown TGF-β1 was located mainly in cytoplasm of atrial cardiocytes. The expression of mRNA or protein for TGF-β1 were increased gradually and significantly among these groups (p<0.05).Conclusions: 1. The content of collagen was increased gradually among CHD+ sinus rhythm, RHD+ sinus rhythm, RHD+pAF and RHD+cAF group, especially collagen typeⅠ. These implied that the occurrence and maintenance of AF is closely linked with the metabolism of collagen, and the atrial fibrosis is very important structure remolding.2. AngiotensinⅡparticipated in atrial collagen metabolism, which contribute to the occurrence and maintenance of AF. The reverse tendency between the expression of mRNA or protein for AT1-R and the degree of atrial fibrosis may be involved in a feed-back regulation, which needs further research.3. TGF-β1 and bFGF may be both important regulation genes to the metabolism of collagen in atrial fibrosis and may become one of therapy targets for AF.