Human Aortic Valve Calcification Is Associated With an Osteoblast Phenotype

Abstract

Background-Calcific aortic stenosis is the third most common cardiovascular disease in the United States. We hypothesized that the mechanism for aortic valve calcification is similar to skeletal bone formation and that this process is mediated by an osteoblast-like phenotype. Methods and Results-To test this hypothesis, we examined calcified human aortic valves replaced at surgery (nϭ22) and normal human valves (nϭ20) removed at time of cardiac transplantation. Contact microradiography and microcomputerized tomography were used to assess the 2-dimensional and 3-dimensional extent of mineralization. Mineralization borders were identified with von Kossa and Goldner's stains. Electron microscopy and energy-dispersive spectroscopy were performed for identification of bone ultrastructure and CaPO 4 composition. To analyze for the osteoblast and bone markers, reverse transcriptase-polymerase chain reaction was performed on calcified versus normal human valves for osteopontin, bone sialoprotein, osteocalcin, alkaline phosphatase, and the osteoblast-specific transcription factor Cbfa1. Microradiography and micro-computerized tomography confirmed the presence of calcification in the valve. Special stains for hydroxyapatite and CaPO 4 were positive in calcification margins. Electron microscopy identified mineralization, whereas energy-dispersive spectroscopy confirmed the presence of elemental CaPO 4 . Reverse transcriptase-polymerase chain reaction revealed increased mRNA levels of osteopontin, bone sialoprotein, osteocalcin, and Cbfa1 in the calcified valves. There was no change in alkaline phosphatase mRNA level but an increase in the protein expression in the diseased valves. Conclusions-These findings support the concept that aortic valve calcification is not a random degenerative process but an active regulated process associated with an osteoblast-like phenotype.

Pathogenesis of Calcific Aortic Valve Disease

“…RANK is expressed in normal valve leaflets, but is downregulated in aortic valve lesions. 65 The osteoblast-specific transcription factor, Runx2/Cbfa1, has been detected in rabbit models of experimental aortic valve disease, 16,17,27 and osteoblast-like cells have been identified both in a rabbit model 17 and in calcified human valves. 15 Finally, a subset of end-stage human aortic valve lesions contain heterotopic bone, 15 further confirming the dysregulated nature of aortic valvular calcification.…”

“…The first was the long-held notion that calcific aortic valve disease was a "degenerative," and therefore unmodifiable, condition. 6 However, more recent studies have demonstrated convincingly that calcific aortic valve lesions have many features characteristic of an active pathobiological process, including chronic inflammation, [7][8][9] lipoprotein deposition, 10 -12 active calcification, [13][14][15][16][17][18] and renin-angiotensin system activation. 19,20 These features are present in both trileaflet and bileaflet aortic valve lesions.…”

“…Recently, rabbit models been developed, 16,26,27 with that of Rajamannan and colleagues already providing a number of novel insights. 16 -18,28,29 In particular, these models have implicated the Wnt 18 and Runx2/ Cbfa1 16,17,27 signaling pathways in disease pathogenesis. Only very recently has a purported mouse model of calcific aortic valve disease been described.…”

Molecular-Genetic Factors, Associated With Aortic Stenosis Development

“…В экспериментах in vivo было показано, что в стенотически измененных клапанах фибробласты приобретают свойства плюрипотент-ных клеток, способных к остеобластической диффе- ренцировке. "Активированные" фибробласты (или миофибробласты) имеют сходные свойства с остео-бластами костной ткани и обладают возможностью синтезировать остеогенные медиаторы [7]. Наиболее изученными регуляторными путями экспрессии остеогенных медиаторов "активирован-ными фибробластами" являются: пути трансформи-рующих факторов роста (TGFβ1 и β3), в том числе костных морфогенетических белков (bone morphogenetic protein -BMP), Wnt, RANK/RANKL и Notch1 пути.…”

The role of statin treatment in valvular heart disease: is the jury still out?

“…Over the last ten years, the scientific progress in the field of calcific AS progression has been substantial 6,7 . Historically, calcific AS has been associated with passive, age-related valve degeneration.…”