Proteoglycans and Normal Lung Structure

PGs are critical components of the lung ECM, and all subclasses of PGs are present in the normal lung. The load-bearing components of the lung scaffold include collagen and elastic fibers, and PGs, which represent the ground substance within the fiber network. PGs are divided into subclasses, essentially based on 

Dcn+I+ (C) mice. Note the heterogeneity in size and irregularity of fibrils from Dcn-I- 

Lung parenchymal tissues display prominent viscoelastic behavior. The lung tissue matrix represents a composite of collagen and elastic fibers, PGs, and GAGs. 

Mechanotransduction describes the biological phenomenon wherein cells can alter protein metabohsm in response to mechanical stimuli (40). The effect of mechanical strain on cellular systems has been a recent focus of research interest a number of studies have examined the effects of mechanical forces on ECM remodeling (41). The effects of excessive mechanical strain on ECM production have been studied using experimental systems that either stretch cell monolayers or strain three-dimensional gels of mixed cell cultures. Xu et al. (42,43) have documented that cychc mechanical strain of mixed fetal lung cell cultures resulted in a modest 

Lung diseases characterized by remodeling of the lung parenchyma or airway wall involve alterations in PGs. Changes in PGs have been best characterized in pulmonary fibrosis and, to a lesser extent, in asthma. Their roles in such diseases as emphysema, lung cancer, and ventilation-induced lung injury have not been as well defined. 

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