Engineering three-dimensional pulmonary tissue constructs

In this paper, we report on engineering 3-D pulmonary tissue constructs in vitro. Primary isolates of murine embryonic day 18 fetal pulmonary cells (FPC) were comprised of a mixed population of epithelial, mesenchymal, and endothelial cells as assessed by immunohistochemistry and RT-PCR of 2-D cultures. The alveolar type II (AE2) cell phenotype in 2-D and 3-D cultures was confirmed by detection of SpC gene expression and presence of the gene product prosurfactant protein C. Three-dimensional constructs of FPC were generated utilizing Matrigel hydrogel and synthetic polymer scaffolds of poly-lactic-co-glycolic acid (PLGA) and poly-L-lactic-acid (PLLA) fabricated into porous foams and nanofibrous matrices, respectively. Three-dimensional Matrigel constructs contained alveolar forming units (AFU) comprised of cells displaying AE2 cellular ultrastructure while expressing the SpC gene and gene product. The addition of tissue-specific growth factors induced formation of branching, sacculated epithelial structures reminiscent of the distal lung architecture. Importantly, 3-D culture was necessary for inducing expression of the morphogenesis-associated distal epithelial gene fibroblast growth factor receptor 2 (FGFr2). PLGA foams and PLLA nanofiber scaffolds facilitated ingrowth of FPC, as evidenced by histology. However, these matrices did not support the survival of distal lung epithelial cells, despite the presence of tissue-specific growth factors. Our results may provide the first step on the long road toward engineering distal pulmonary tissue for augmenting and/or replacing dysfunctional native lung in diseases, such as neonatal pulmonary hypoplasia.