Development of a decellularized lung bioreactor system for bioengineering the lung: the matrix reloaded

We developed a decellularized murine lung matrix bioreactor system that could be used to evaluate the potential of stem cells to regenerate lung tissue. Lungs from 2-3-month-old C57BL/6 female mice were excised en bloc with the trachea and heart, and decellularized with sequential solutions of distilled water, detergents, NaCl, and porcine pancreatic DNase. The remaining matrix was cannulated and suspended in small airway growth medium, attached to a ventilator to simulate normal, murine breathing-induced stretch. After 7 days in an incubator, lung matrices were analyzed histologically. Scanning electron microscopy and histochemical staining demonstrated that the pulmonary matrix was intact and that the geographic placement of the proximal and distal airways, alveoli and vessels, and the basement membrane of these structures all remained intact. Decellularization was confirmed by the absence of nuclear 4',6-diamidino-2-phenylindole staining and negative polymerase chain reaction for genomic DNA. Collagen content was maintained at normal levels. Elastin, laminin, and glycosaminglycans were also present, although at lower levels compared to nondecellularized lungs. The decellularized lung matrix bioreactor was capable of supporting growth of fetal alveolar type II cells. Analysis of day 7 cryosections of fetal-cell-injected lung matrices showed pro-Sp-C, cytokeratin 18, and 4',6-diamidino-2-phenylindole-positive cells lining alveolar areas that appeared to be attached to the matrix. These data illustrate the potential of using decellularized lungs as a natural three-dimensional bioengineering matrix as well as provide a model for the study of lung regeneration from pulmonary stem cells.