Extracellular Matrix

Basement membranes (BMs) are thin sheets of specialized extracellular matrix that underlie endothelial and epithelial cells and surround all muscle cells, fat cells, and peripheral nerves. They play important roles in filtration, in compartmentalization within tissues, and in maintenance of epithelial integrity, and they influence cell proliferation, differentiation, migration, and survival. In the lung, BMs are associated with bronchial and vascular smooth muscle cells, bronchial epithelium, nerve, and pleura, and they are part of the air-blood barrier between microvascular endothelial cells and alveolar epithelial cells. Collagen IV and laminin are the major components of all BMs which also contain entactin/nidogen and various heparan sulfate proteoglycans, including perlecan. Two collagen IV heterotrimeric protomers, (α1) ₂α2 and α3 α4 α5, are found in alveolar basement membranes, but the latter does not appear to have an important function in the lung. However, the α3 chain contains the epitope that is attacked in Goodpasture's syndrome, an autoimmune disease characterized by pulmonary hemorrhage and glomerulonephritis. Laminins containing the α5 chain are widespread in both developing and adult lung. Preventing expression of laminin α5 via targeted mutagenesis interferes with lung lobe septation and maturation of the lung parenchyma.