Valvular endothelial cells (VEC)
Valvular endothelial cells (VEC) represent the cell layer that covers
the leaflets, in line with the endothelium from the entire
cardiovascular system. However, VEC are phenotypically different from
other cardiovascular endothelial cells, probably due to the fact that
they interact with VIC to maintain the integrity of valve tissues and
potentially, also to mediate disease (26). They are highly specialized
endothelial cells: usually endothelial cells in vascular tissues are
typically elongated in the direction of blood flow, but on the leaflets
they have a circumferential arrangement to support leaflet stresses and
mechanical forces (30). As all endothelial cells, VEC are crucial to
function as a barrier, regulating interactions between blood flow and
VICs, including metabolic and inflammatory processes (31).
VEC may also exhibit differences phenotypes depending on their location
on the valve leaflets (32). Endothelial cell production of nitric oxide
(NO) is an important crosstalk to maintain VIC quiescent and endothelial
injury has been proposed to be an initiating factor for calcified aortic
valve disease (33). VEC are also responsible for the non-thrombogenic
proprieties of the leaflets, playing an important immune and
inflammatory role (34). VEC are also capable of responding to mechanical
stimuli, with a flow-mediating mechanotransduction process being
responsible for the activation of protective or pathological pathways
(35).