Chapter 5 - Proteoglycans in the Lung

Abstract

Proteoglycans (PGs) are integral components of the extracellular matrix (ECM) and are present throughout the lung. PGs are macromolecules consisting of a protein core and glycosaminoglycan (GAG) side chains. The GAG side chains include chondroitin sulfate, keratin sulfate, heparan sulfate, dermatin sulfate, and hyaluronic acid, a GAG that is not bound to a protein core. Different subclasses of PGs have been described, and include large, aggregating PGs such as versican and aggrecan; small leucine-rich repeat PGs such as decorin, biglycan, lumican, and fibromodulin; basement membrane PGs such as perlecan; and cell surface PGs such as syndecan. Members of all these PG families have been identified in the lung. PGs form a key component of the lung ECM. They contribute to the structural integrity of the fiber network and are critical determinants of the mechanical properties of the lung tissues. They have important influences on various biological processes, including cell proliferation and responses to cytokines and chemokines, and participate in various autocrine pathways. Their involvement in different disease processes is currently being investigated; PGs potentially contribute to any disease in which the lung matrix is affected. Defining the role of PGs in disease biology is especially important as these molecules offer new, putative therapeutic targets.