Elastic fibers in the aortic valve spongiosa: A fresh perspective on its structure and role in overall tissue function

This study characterizes the elastic fiber structure within the aortic valve spongiosa, the middle layer of the tri-laminate leaflet. The layer is rich in glycosaminoglycans and proteoglycans, through which it resists compression and lubricates shear between the outer layers. Elastin in this layer forms a fine, interweaving structure, yet it is unclear how this particular structure, which uses elasticity to preload the leaflet, assists spongiosa function. In this study, immunohistochemistry (IHC) and scanning electron microscopy (SEM) are used to characterize spongiosa elastin, as well as investigate regional differences in structure. IHC for elastin highlights an intermediate structure which varies in thickness and density between regions. In particular, the spongiosa elastin is thicker in the hinge and coaptation region than in the belly. SEM of NaOH-digested leaflets shows a rectilinear pattern of elastic fibers in the hinge and coaptation region, as opposed to a radially oriented stripe pattern in the belly. In conclusion, elastic fibers in the spongiosa connect the two outer layers and vary regionally in structure, while possibly playing a role in responding to regionally specific loading patterns.