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88 Tissue Engineering and Nanotheranostics
mucous that impedes airway function. Unlike the pancreatic and
hepatic lineages which derive from the posterior foregut or hindgut
endodermal tissues, cells comprising the lungs originate from the
anterior foregut endodermal tissue.^47 Lineages from the anterior fore-
gut endoderm have proved more challenging to differentially reca-
pitulate using directed in vitro culture techniques. Additionally,
minimal knowledge exists about cell specific markers for lung epithe-
lial cells or lung progenitor cells. One known progenitor marker is
transcriptional regulator Nkx2-1; however, Nkx2-1 is also found in
thyroid and fore brain tissue and is therefore not lung tissue
specific.47–49 This further complicates the isolation and characteriza-
tion of lung progenitors in a differentiation culture.
Like pancreatic and hepatic differentiations, the first step requires
definitive endodermal induction. This can be done with Activin A;
however this approach has been shown to prefer posterior foregut and
hindgut lineages with further differentiation.^48 In 2011, Green et al.
determined that following Activin A treatment with inhibition of
both BMP and TGF-β signaling, using Noggin and SB-431542,
induced an enriched population of anterior foregut endodermal cells
from the definitive endoderm population.^48 Using this strategy to
derive anterior foregut endodermal cells from murine ESCs, Longmire
et al. showed that subsequent stimulation of BMP and FGF signaling
resulted in promotion of Nkx2-1 positive lung and thyroid progenitor
cells with minimal neuro-ectoderm induction.^49 They activated BMP
and FGF signaling by addition of FGF2, Wnt3a, FGF10, KGF,
BMP4, EGF, and heparin to the culture.^49
Mou et al. used a similar stepwise approach to differentiate lung
progenitors in both murine ESCs and human iPSCs.^50 By addition of
BMP4, FGF2, FGF10, Wnt ligands, and retinoic acid they further
differentiated multipotent lung progenitors from anterior foregut
endodermal cells.^50 The differentiation strategies from Longmire
et al. and Mou et al. reported relatively low efficiencies with no more
than 21% of the desired cell type obtained.49,50 This leaves room for
future work to refine and improve lung progenitor and lung epithelial
cell differentiation. One interesting factor in the work conducted by
Mou et al. was the use of an iPSC line derived from a CF patient; this
