Fig. 9

Schematic alveolar representation and suggested model for type IV collagen during alveologenesis. a Normal alveolar septum in which type I (ATI) and II pneumocytes (ATII) cover the alveolar surface with the blood capillaries in close association. Alveolar myofibroblast progenitors localized at the base of the septum proliferate, differentiate into alveolar myofibroblast, and migrate where they synthesize elastin. Lipofibroblasts are localized close to ATII. b Type IV collagen mutations cause abnormal septum formation. Type IV collagen lungs have increased cells with lipid content (ATII and lipofibroblasts), and abnormal capillary formation. Alveolar myofibroblasts fail to proliferate, differentiate and migrate, causing defects in elastin deposition. c Suggested model for type IV collagen, basement membrane and septal myofibroblast development. Type IV collagen is a central player in myofibroblast progenitor proliferation, differentiation and mobilization to the tip of the septum