Upregulation of the 5-lipoxygenase pathway in human aortic valves correlates with severity of stenosis and leads to leukotriene-induced effects on valvular myofibroblasts.

BACKGROUND

The development of aortic valve stenosis is not only associated with calcification and extracellular matrix remodeling, but also with inflammation. The aim of this study was to determine the role of proinflammatory signaling through the leukotriene (LT) pathway in aortic stenosis.

METHODS AND RESULTS

After macroscopic dissection of surgically removed human aortic valves, RNA was extracted from 311 preparations derived from 68 patients to differentiate normal, thickened, and calcified areas from each cusp. Subsequently, quantitative polymerase chain reaction analysis was used to correlate gene expression patterns with preoperative echocardiographic parameters. The messenger RNA levels of the LT-forming enzyme 5-lipoxygenase increased 1.6- and 2.2-fold in thickened and calcified tissue, respectively, compared with normal areas of the same valves. In thickened tissues, messenger RNA levels for 5-lipoxygenase (r= -0.35; P=0.03), its activating protein (5-lipoxygenase activating protein; r= -0.39; P=0.02), and LTA(4) hydrolase (r= -0.48; P=0.01) correlated inversely with the velocity-time integral ratio. In addition, leukotriene A(4) hydrolase transcripts correlated inversely with aortic valve area, indexed for body surface area (r= -0.52; P=0.007). Immunohistochemical stainings revealed LT receptor expression on valvular myofibroblasts. In primary cultures of human myofibroblasts derived from stenotic aortic valves, Leukotriene C(4) (LTC(4)) increased intracellular calcium, enhanced reactive oxygen species production, reduced the mitochondrial membrane potential, and led to morphological cell cytoplasm changes and calcification.

CONCLUSIONS

The upregulation of the LT pathway in human aortic valve stenosis and its correlation with clinical stenosis severity, taken together with the potentially detrimental LT-induced effects on valvular myofibroblasts, suggests one possible role of inflammation in the development of aortic stenosis.