# Cellular and Matrix Organisation of the Human Aortic Valve Interleaflet Triangles

## TL;DR

This study reveals the layered structure and cellular makeup of the human aortic valve interleaflet triangles, offering insights for tissue engineering.

## Contribution

The study identifies up to five distinct tissue layers in interleaflet triangles and their variable composition across different regions of the aortic valve.

## Key findings

- Each interleaflet triangle contains up to five distinct tissue layers with varying composition.
- ILT tissues contain nerve fibers and cells expressing smooth muscle markers.
- The three interleaflet triangles differ in size, appearance, and tissue composition.

## Abstract

The cellular composition and structural components of the valve leaflets, sinus, and annular tissue have all been characterised. In contrast, relatively little is known about the tissue and cellular components of the interleaflet triangles (ILTs). We have used normal human and porcine valves to assess the type of cells present in the different layers and the spatial pattern of the main proteins of the extracellular matrix. We have shown that there are up to five distinct layers of tissue in all the ILTs, and their composition varies between the three ILTs of each aortic valve. This data aids in understanding the functionality of the ILTs and provides essential information when tissue engineering valves.

(1) Background: The sophisticated function of the aortic root relies on the coordinated movement of its constituent components. This study examines the extracellular components of the interleaflet triangles (ILTs) and characterises the cells that are present within this region of the aortic root. (2) Methods: A total of 10 human aortic valves and 6 porcine aortic valves were processed for immunohistochemical staining, scanning, and transmission electron microscopy. (3) Results: The three ILTs differed in size and macroscopic appearance. Each triangle comprised up to five distinct layers of tissue: an innermost endothelial layer, an inner elastin-rich layer, a thicker outer layer comprising densely packed layers of collagen and glycosaminoglycans, and an outer layer of intermingled myocardial and adipose tissue. A band of cells near the luminal surfaces of all ILTs expressed smooth muscle cell α-actin with variable expression of smooth muscle myosin heavy chain. In all the ILTs, there was evidence of neurofilament staining, indicating the presence of nerve fibres. (4) Conclusions: Each ILT is unique in its structure and organisation, with differing amounts of elastin and collagen, as well as myocardial, adipose, and fibrous content. The ILTs contain multiple cell types in varying abundance. Functional studies are required to determine the role of the different cells and their organisation in contributing to the sophisticated, dynamic behaviour of the aortic root.