Title:
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Cellular and Molecular Mechanisms of Aortic Valve Calcification
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Aortic valve calcification is an active inflammatory condition characterised by thickening and
calcification of the leaflets. The cellular and molecular mechanisms of the disease are unknown. We
hypothesised that valve interstitial cells (lCs) playa key role in the calcification process by acting as a
target for inflammatory cytokines that are involved in initiating signalling cascades to promote
osteogenic differentiation of the cells, a mechanism that could be manipulated phannacologically.
Calcified human aortic valve leaflets were characterised with the presence of calcium nodules and
bone lesions. Cultured human aortic valve ICs had the capacity to release a number of inflammatory
cytokines and undergo osteogenic differentiation in response to osteogenic mediators, including bone
morphogenetic proteins (BMPs) and transforming growth factor-beta (TOF-P). In addition,
extracellular nucleotides played an important role in regulating this differentiation process, whereby
ATP increased the expression of osteoblast markers, while adenosine had an opposite effect.
Activation of major signalling pathways including Wnt3a, were partially responsible for promoting
this osteogenic differentiation of valve ICs, leading to upregulation of p-catenin and/or Cbfa-l. These
mechanisms were counteracted by HMO-CoA reductase inhibitors (statins), where atorvastatin
blocked the induction of osteoblast markers in valve ICs and inhibited the effects of Wnt3a on
proliferation and differentiation. In addition, we demonstrated a novel role of pz-adrenergic receptors
(Pz-ARs) in aortic valve calcification, whereby stimulation of pz-ARs prevented osteogenic
differentiation of valve ICs in response to osteogenic medium. Our findings suggests that valve ICs
play an important role in the calcification process and that activation of Wnt3a signalling pathway
may present a possible mechanism for bone fonnation in the valve. This study also identifies potential
pharmacological targets to prevent the onset or progression of aortic valve calcification.
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