Hypoxia Stimulates Synthesis of Neutrophil Gelatinase-Associated Lipocalin in Aortic Valve Disease

Abstract

Objective: Aortic valve disease is commonly found in the elderly population. It is characterized by dysregulated extracellular matrix remodeling followed by extensive microcalcification of the aortic valve and activation of valve interstitial cells. The mechanism behind these events are largely unknown. Studies have reported expression of hypoxia inducible factor-1 alpha (HIF1α) in calcific nodules in aortic valve disease, therefore we investigated the effect of hypoxia on extracellular matrix remodeling in aged aortic valves.Approach and Results: Western blotting revealed elevated expression of HIF1α and the complex of matrix metalloprotease 9 (MMP9) and neutrophil gelatinase-associated lipocalin (NGAL) in aged porcine aortic valves cultured under hypoxic conditions. Consistently, immunofluorescence staining showed co-expression of MMP9 and NGAL in the fibrosa layer of these porcine hypoxic aortic valves. Gelatinase zymography demonstrated that the activity of MMP9-NGAL complex was significantly increased in aortic valves in 13% O2 compared to 20% O2. Importantly, the presence of ectopic elastic fibers in the fibrosa of hypoxic aortic valves, also detected in human diseased aortic valves, suggests altered elastin homeostasis due to hypoxia.Conclusion: This study demonstrates that hypoxia stimulates pathological extracellular matrix remodeling via expression of NGAL and MMP9 by valve interstitial cells.

Plasma biomarkers associated with adverse outcomes in patients with calcific aortic stenosis

“…8,[16][17][18] Prior studies have also suggested that angiogenesis, possibly facilitated by endostatin, may play a role in AS pathophysiology, 19 and NGAL has also been implicated in adverse extracellular matrix remodeling in valve interstitial cells. 20 These findings raise the possibility of different pathways that can be targeted in the treatment of patients with AS, which should be addressed in future studies. Interestingly, many of these pathways have also been implicated in ischaemic heart disease, suggesting that common pathways are involved in both disease conditions.…”

Extracellular Matrix in Calcific Aortic Valve Disease: Architecture, Dynamic and Perspectives

“…In hypoxic aortic valves the activity of the MMP9–NGAL complex is significantly increased. The presence of ectopic elastic fibers in the fibrosa suggests altered elastin homeostasis [ 89 ]. So, hypoxia play a key role in ECM remodeling by regulating elastin and collagen metabolism.…”

A Novel Ex Vivo Model of Aortic Valve Calcification. A Preliminary Report

“…A series of investigations have used porcine aortic valve leaflets to study the mechanical, biological or contractile properties of valve leaflet tissue (Sauren et al, 1983;Xing et al, 2004;Konduri et al, 2005;Balachandran et al, 2006;Merryman et al, 2007;Chester et al, 2008;El-Hamamsy et al, 2009;Warnock et al, 2011). Grande-Allen's group (Swaminathan et al, 2019) used porcine valve leaflets to study how hypoxia influences extracellular matrix in the leaflets. In one study, porcine leaflets were used to investigate the effects of collagen disruption on spontaneous calcification (Rodriguez et al, 2014).…”