The expression of transforming growth factor-β1 and α-smooth muscle actin is increased in the human myxomatous valve

Background: In vitro experimental studies have reported that transforming growth factor-β1 (TGF-β1) stimulates the production of α-smooth muscle actin (α-SMA) in porcine valves. However, the relation between TGF-β1 and α-SMA in myxomatous valves has not been elucidated. Methods: We classified 27 subjects into two groups: 1) myxomatous group (M:F=11:12, mean age=55±15 years) and 2) rheumatic group (M:F=3:1, mean age=41±17 years) according to preoperative echocardiographic and postoperative histologic findings. Twenty-seven valve specimens from the patients who underwent valve replacement were obtained. Tissue samples were analyzed by immunohistochemistry for TGF-β1 and α-SMA. The positively stained areas were measured using an image analysis program (Image Pro-Plus 4.5), and then the TGF-β1 volume fraction (TGF-VF) and α-SMA volume fraction (α-SMA-VF) were calculated. Results: TGF-VF in myxomatous valves was higher than in rheumatic valves (2,759±2,294 vs 864±276, p=0.04). α-SMA-VF in myxomatous valves was higher than in rheumatic valves (4,122±2,275 vs 2,421±844, p=0.002). There was a significant correlation between TGF-β1 and α-SMA in myxomatous valves (r=0.38, p=0.04). There was no significant correlation between TGF-β1 and α-SMA in rheumatic valves (r=-0.50, p=0.67). Conclusions: TGF-β1 and α-SMA may be related to the pathogenesis of myxomatous valves. The activation of TGF-β1 might increase the expression of α-SMA in human myxomatous valves.