To investigate the involvement of transforming growth factor-β1 (TGF-β1) and
tissue inhibitor of metalloproteinase 4 (TIMP-4) in influencing the severity of atrial
fibrosis in
rheumatic heart disease (RHD) patients with
atrial fibrillation (AF). The degree of myocardial
fibrosis was evaluated using Masson staining. The expression levels of TGF-β1, TIMP-4,
matrix metalloproteinase-2 (MMP-2),
type I collagen, and
type III collagen were estimated by Western blot analysis. Additionally, TGF-β1 and TIMP-4
mRNA levels were quantified by qRT-PCR. The effect of TGF-β1 stimulation on TIMP-4 expression was assessed by in vitro stimulation of freshly isolated human atrial fibroblasts with recombinant human TGF-β1, followed by Western blot analysis to detect changes in TIMP-4 levels. Masson
stain revealed that the left atrial diameter and
collagen volume fraction were obviously increased in AF patients, compared to sinus rhythm (SR) controls (both P < 0.05). Western blot analysis showed significantly elevated levels of the AF markers MMP-2,
type I collagen, and
type III collagen in the AF group, in comparison to the SR controls (all P < 0.05). In the AF group, TGF-β1 expression was relatively higher, while TIMP-4 expression was apparently lower than the SR group (all P < 0.05). TIMP-4 expression level showed a negative association with TGF-β1 expression level (r = -0.98, P < 0.01) and TGF-β1 stimulation of atrial fibroblasts led to a sharp decrease in TIMP-4
protein level. Increased TGF-β1 expression and decreased TIMP-4 expression correlated with atrial
fibrosis and ECM changes in the atria of RHD patients with AF. Notably, TGF-β1 suppressed TIMP-4 expression, suggesting that selective TGF-β1 inhibitors may be useful therapeutic agents.