Self-assembling peptides and peptide derivatives bearing cell-binding ligands are increasingly being investigated as defined cell culture matrices and as scaffolds for regenerative medicine. In order to systematically refine such scaffolds to elicit specific desired cell behaviors, ligand display should ideally be achieved without inadvertently altering other physicochemical properties such as viscoelasticity. Moreover, for in vivo applications, self-assembled biomaterials must exhibit low immunogenicity. In the present study, multi-peptide co-assembling hydrogels based on the beta-sheet fibrillizing peptide Q11 (QQKFQFQFEQQ) were designed such that they presented RGDS or IKVAV ligands on their fibril surfaces. In co-assemblies of the ligand-bearing peptides with Q11, ligand incorporation levels capable of influencing the attachment, spreading, morphology, and growth of human umbilical vein endothelial cells (HUVECs) did not significantly alter the materials' fibrillization, beta-turn secondary structure, or stiffness. RGDS-Q11 specifically increased HUVEC attachment, spreading, and growth when co-assembled into Q11 gels, whereas IKVAV-Q11 exerted a more subtle influence on attachment and morphology. Additionally, Q11 and RGDS-Q11 were minimally immunogenic in mice, making Q11-based biomaterials attractive candidates for further investigation as defined, modular extracellular matrices for applications in vitro and in vivo.

Despite modern treatments, congenital diaphragmatic hernia (CDH) remains associated with variable survival and significant morbidity. The associated pulmonary hypoplasia is a major determinant of outcome. To develop better treatments, improved comprehension of the pathogenesis of lung hypoplasia is warranted. We developed an in vitro cell recombinant model to mimic pulmonary hypoplasia and specifically to investigate epithelial-mesenchymal interactions and to decipher which tissue layer is primarily defective in nitrofen-induced CDH-associated lung hypoplasia. Epithelial cells (E) and fibroblasts (F) were isolated from E19 control ((C)) and nitrofen-induced hypoplastic rat lungs ((N)). Cells were recombined and cultured as either homotypic [(F(C))(E(C)) and (F(N))(E(N))] or heterotypic [(F(C))(E(N)) and (F(N))(E(C))] recombinants. Recombinants containing F(N) fibroblasts had a thickened fibroblast tissue layer and there were fewer organized alveolar-like epithelial structures compared with those in control (F(C))(E(C)) recombinants. These F(N) recombinants exhibited a decrease in terminal deoxynucleotidyl transferase dUTP nick end labeling and cleaved caspase-3 positive cells. Cell proliferation was arrested in recombinants containing F(N) fibroblasts, which also exhibited increased p27(Kip1) and p57(Kip2) expression. In conclusion, fibroblasts, and not epithelial cells, appear to be the defective cell type in nitrofen-induced hypoplastic lungs due to a decreased ability to undergo apoptosis and maintain overall proliferation. This may explain the characteristic pulmonary interstitial thickening and hypoplasia observed in both nitrofen-induced hypoplastic lungs as well as human hypoplastic CDH lungs.

Respiratory diseases of the newborn can arise from the disruption of essential angiogenic pathways. Neuropilin-1 (NRP1), which is a critical receptor implicated in systemic vascular growth and remodeling, binds two distinct ligand families: vascular endothelial growth factor (VEGF) and class 3 semaphorins (SEMA3). Although the function of VEGF-NRP1 interactions in vascular development is well described, the importance of SEMA3-NRP1 signaling in systemic or pulmonary vascular morphogenesis is debated. We sought to characterize the effect of deficient SEMA3-NRP1 signaling on fetal pulmonary vascular development in a mouse model. Temporospatial expression of Nrp1 and Sema3 mRNA and protein during murine fetal lung development was investigated, and the development of the pulmonary vasculature in transgenic mice deficient in Sema3-Nrp1 signaling was examined by histology, immunostaining, and electron microscopy. Loss of Sema3-Nrp1 signaling resulted in acute respiratory distress and high neonatal mortality. Pathohistological examination of mutants revealed immature and atelectatic regions in the lung, severely reduced capillary density, thickened alveolar septa containing centrally located dilated capillaries, hypertensive changes in arteriolar walls, anomalous and misaligned pulmonary veins, and reduced pulmonary surfactant secretion. Notably, many features are reminiscent of the fatal pulmonary disorder alveolar capillary dysplasia. These findings indicate a critical role for Sema3-Nrp1 signaling in fetal pulmonary development, which may have clinical relevance for treatment of various neonatal respiratory disorders, including alveolar capillary dysplasia.

Reciprocal signaling between the lung mesenchyme and epithelium is crucial for differentiation and branching morphogenesis. We hypothesized that the combination of signaling pathways comprising early epithelialmesenchymal interactions and a 3D spatial environment are necessary for an efficient induction of embryonic and induced pluripotent stem cells (ESCs and iPSCs) into a lung cell phenotype with hallmarks of the distal niche. Aggregating early, but not late, embryonic lung mesenchyme with endoderm-induced mouse ESCs and iPSCs for 6 days resulted in organization into tubular structures and differentiation of the tubular lining cells to an NKX2-1 + /SOX2 -/SOX9 + /proSFTPC + lineage. Over 80% of the endoderm-induced cells committed to an NKX2-1 + lineage. Electron microscopy analysis demonstrated numerous multivesicular bodies and glycogen deposits in the tubular lining cells, characteristic features of type II epithelial cell progenitors. Using soluble FGFR2 receptor antagonists, we demonstrate that reciprocal fibroblast growth factor (FGF) 2, 7, and 10 signaling is essential for differentiation of endoderm-induced cells to an NKX2-1 + /proSFTPC + phenotype within 3D aggregates. Only FGF2 was able to commit endoderm-induced cells in monolayer cultures to an NKX2-1 + lineage, however with a significant lower efficiency (*16%) than seen with mesenchyme. Thus, while FGF2 signaling alone can induce a primed population of ESCs and iPSCs, the cells do not differentiate to distal lung epithelial progenitors with the same efficiency and level of maturity that is achieved when the complex tissue and 3D environment of the developing lung is more accurately recapitulated.