Extracellular matrix

This chapter reviews the extracellular matrix constituents of the respiratory system. Until recently the extracellular matrix was thought of solely as a static structural support network. Now it is knows that the extracellular matrix is comprised by a large and varied group of dynamic macromolecules and their regulatory factors, which provides structural support and is a physical barrier. However, it also elicits cellular responses and its interactions are involved in development and organ formation. Disruption of normal extracellular matrix during disease processes can lead to an inflammatory response that exacerbates aberrant remodeling of the lung. The biomechanical properties of the lung are primarily determined by the extracellular matrix components that comprise the tissue. In the lung they can be largely categorized into four groups: the collagens, proteoglycans, elastic fibers, and non-collagenous proteins. The matrix of the normal lung imparts the strength and resilience for the continuous cycling of inspiration and expiration. For proper gas exchange, the components of the extracellular matrix are distributed in a fashion to reduce the boundary between erythrocytes and oxygen. When the exquisite balance of matrix glycoprotein is disturbed, the consequences on the lung are manifested by pathology. Heritable disorders of connective tissue (HDCT) are a series of disorders caused by mutations in structural or modifying components of the extracellular matrix. Since most of these gene products are expressed in multiple tissues, pleiotropic manifestations are observed in most HDCT. Alterations in connective tissue likely play key roles in the pathogenesis of both asthma and COPD.