Age-Related Changes in Aortic Valve Hemostatic Protein Regulation

Abstract

Objective While valvular endothelial cells (VECs) have unique responses compared to vascular ECs, valvular regulation of hemostasis is not well understood. Heart valves remodel throughout a person's lifetime, resulting in changes in extracellular matrix (ECM) composition and tissue mechanical properties that may affect VEC hemostatic function. This work assessed VEC regulation of hemostasis in situ and in vitro as a function of specimen age. Approach and Results Porcine aortic valves (PAV) were assigned into one of three age groups: YNG (6 weeks), ADT (6 months), or OLD (2 years). Histology of valves showed that secreted thrombotic/anti-thrombotic proteins localize at the valve endothelium, and tissue interior. Gene expression and immunostains for von Willebrand factor (VWF), tissue factor pathway inhibitor, and tissue plasminogen activator in YNG PAVECs was higher than in OLD, while plasminogen activator inhibitor-1 levels in OLD were higher than in YNG and ADT. Histamine stimulated YNG PAVECs released higher concentrations of VWF proteins than OLD, while the fraction of cleaved VWF-140 fragments were not different between age groups. A CAVD in vitro model using valvular interstitial cells (VICs) confirmed that VWF in culture significantly increased VIC nodule formation and calcification. Conclusions Hemostatic protein regulation in AV tissues and VECs changes with age. The presence of VWF and other potential hemostatic proteins increase VIC calcification in vitro. Therefore, the increased capacity of elderly valves to sequester the hemostatic proteins, together with age-associated loss of ECM organization warrants investigation into potential roles for these proteins in the formation of calcific nodules.

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