Upregulation of the 5-Lipoxygenase Pathway in Human Aortic Valves Correlates With Severity of Stenosis and Leads to Leukotriene-Induced Effects on Valvular Myofibroblasts

Abstract

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 Pϭ0.03), its activating protein (5-lipoxygenase activating protein; rϭϪ0.39; Pϭ0.02), and LTA 4 hydrolase (rϭϪ0.48; Pϭ0.01) 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 (rϭϪ0.52; Pϭ0.007). 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. (Circulation. 2011;123:1316-1325.)Key Words: aortic valve stenosis Ⅲ echocardiography Ⅲ inflammation Ⅲ leukotrienes Ⅲ myofibroblasts A lthough the primary risk factor for developing aortic stenosis is increasing age, 1 stenotic aortic valves share morphological characteristics with atherosclerotic lesions. For example, in the active disease process, lipid accumulation, 2 inflammatory infiltration, 3-5 neovascularization, 6,7 extracellular matrix degradation, 8 -10 and extensive calcification 3,5,11 take place, which eventually cause the aortic valve to narrow. However, attempts to inhibit the hemodynamic progression of aortic stenosis using lipid-lowering drugs have not been successful. [12][13][14] The poor prognosis and increased mortality from aortic stenosis after the onset of symptoms in the absence of surgical valve replacement 15 provide a rationale for the pursuit of a medical treatment that impedes the hemodynamic progression of aortic valve disease. Clinical Perspective on p 1325Inflammatory infiltration of activated macrophages and T-cells, as well as cytokine release, has been described in human s...

International Union of Basic and Clinical Pharmacology. LXXXIV: Leukotriene Receptor Nomenclature, Distribution, and Pathophysiological Functions

“…These authors also demonstrated that a nuclear localization sequence (localized in the C tail) is essential for the receptor translocation to the nucleus, as already demonstrated for other GPCRs (Boivin et al, 2008) as well as for other proteins that normally target the nucleus, such as 5-LO (Hanaka et al, 2002). Finally, CysLT 1 R expression in myofibroblasts derived from human heart valves exhibits a perinuclear pattern, and LTC 4 increased nuclear [Ca 2ϩ ] in those cells (Nagy et al, 2011).…”

The Expression of Groups IIE and V Phospholipase A2 is Associated with an Increased Expression of Osteogenic Molecules in Human Calcified Aortic Valves

“…Because these molecules were found to be co-localized with PLA2-IIE and -V in the aortic valves in the present study, eicosanoids may be produced within valve tissue and/or play a role in the development of valve calcification 1) . In line with the present findings, a previous report showed that the 5-LOX expression is increased in calcified human aortic valves and that the incubation of myofibroblast cultures with LTC4, a 5-LOX metabolite, induces calcium nodule formation 2) . In cultures of tendon stem cells, serotonergic receptor signals have been shown to stimulate tissuenonspecific ALP through the actions of eicosanoids produced via the PLA2 pathway 17) .…”

“…Another report showed that PGE2 stimulates the osteogenic differentiation of cultured tendon stem cells via BMP-2 induction 18) . Taken together, these previous reports 2,17,18) appear to support the hypothesis that eicosanoids produced via the PLA2 pathway contribute to the process of ectopic osteogenesis in cardiac valves.…”

“…Eicosanoids and fatty acids play important roles in osteogenesis 1) , and a recent report showed that eicosanoids contribute to the genesis of human aortic valve calcification 2) . These lipid mediators are produced by the hydrolysis of membrane phospholipids via the catalytic activity of phospholipase A2 (PLA2) [3][4][5][6][7][8] .…”

Aortic Stenosis - New Insights in Stenosis Progression and in Prevention

“…Moreover they showed that leukotriene C4 (LTC4) increased intracellular calcium, enhanced reactive oxygen species production, reduced the mitochondrial membrane potential, and led to morphological cell cytoplasm changes and calcification. This data suggest the up-regulation of the pathway LT and the potentially detrimental LT-induced effects on valvular myofibroblasts as possible role in the development of aortic stenosi and induce to considerate innovative therapeutic interventions (42). The first landmark randomized, prospective trial published in this field, Scottish Aortic Stenosis and Lipid Lowering Trial, Impact on Regression (SALTIRE), (43) demonstrated, however, that high-dose atorvastatin does not slow the progression of this disease.…”