The extracellular matrix of the lung: The forgotten friend!

Abstract

The extracellular matrix represents the three-dimensional scaffold of the alveolar wall, which is composed of a layer of epithelial and endothelial cells, their basement membrane, and a thin layer of interstitial space lying between the capillary endothelium and the alveolar epithelium [1]. In the segment where the epithelial and endothelial basement membranes are not fused, the interstitium is composed of cells, a macromolecular fibrous component, and the fluid phase of the extracellular matrix, functioning as a three dimensional mechanical scaffold characterized by a fibrous mesh consisting mainly of collagen types I and III, which provides tensile strength, and elastin conveying an elastic recoil [2, 3]. The three-dimensional fiber mesh is filled with other macromolecules, mainly glycosaminoglycans (GAGs), which are the major components of the non-fibrillar compartment of the interstitium [4]. In the lung, the extracellular matrix plays several roles, providing: a) mechanical tensile and compressive strength and elasticity; b) a low mechanical tissue compliance, thus contributing to the maintenance of normal interstitial fluid dynamics [5]; c) low resistive pathway for effective gas exchange [2]; d) control of cell behavior by binding of growth factors, chemokines, cytokines, and interaction with cell-surface receptors [6]. © 2007 Springer Science + Business Media Inc.