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iPSC-derived Lung Cells with Regenerative and Reparative Capabilities

By-line – Review of “Differentiation of Mouse Induced Pluripotent Stem Cells Into Alveolar Epithelial Cells In Vitro for Use In Vivo” from Stem Cell Translational Medicine by Stuart P. Atkinson

Acute and chronic lung diseases often require lung transplants, and while donor organ shortages represent a major problem, other therapeutic avenues are being investigated. Recent advances in induced pluripotent stem cell (iPSC) technologies have led to the in vitro differentiation of alveolar epithelial cells (AECs) from iPSCs [1, 2]. Large flat AEC type I cells are responsible for gas exchange and make up 95% of the alveolar lining, while the cuboidal AEC type II cells make up the remaining 5% [3, 4] and can undergo proliferation and/or differentiation to AEC I cells to repair the alveolar epithelium in the event of lung damage [3, 5, 6]. Now, a group led by Yasuo Saijo from Niigata University Graduate School of Medical and Dental Sciences, Japan have refined the differentiation process of murine iPSCs to AECs and assessed their functionality through seeding of iPSC-derived cells into decellularized mouse lung scaffolds, and through the use of a mouse bleomycin-induced acute lung injury model [7].

Zhou et al began by differentiating miPSCs containing a Nanog-GFP reporter according to the scheme depicted in the adjoining figure, with small-airway basic medium (SABM) supplemented with FGF2 chosen as the most effective media for the second stage of differentiation. Using this scheme, lung epithelial-associated gene expression (SPA, SPB, SPC, SPD, CCSP and TTF-1) was markedly increased, giving a population of around 9% lung progenitor and epithelial cells. Immunofluorescence and flow cytometry confirmed SPC expression in differentiated cells, while transmission electron microscopy found lamellar bodies and microvilli, organelles characteristic of alveolar type 2 cells.

The researchers then assessed iPSC-derived AECs for their ability to recellularise a decellularized mouse lung scaffold [8, 9] in comparison to undifferentiated iPSCs. By the twelfth day of incubation, AECs had integrated into the parenchymal regions and had formed alveolar structures with alveolar epithelial morphology, whereas iPSCs proliferated in the alveolar space and formed masses of cells resembling colonies. Immunofluorescence analysis found strong expression of SPC (an AEC Type II marker) and T1a (an AEC Type I marker), with a greater number of SPC-positive cells compared to in vitro differentiation on day 12. Furthermore, the group found that AECs could ameliorate lung injury in a mouse model while undirected iPSCs could not; the SPC-positive and T1a-positive cell number drop after bleomycin-mediated insult was partly recovered after iPSC-derived AEC treatment 2 days after insult, but not iPSC treatment. Furthermore, iPSC-derived AEC treatment led to the appearance of SPC/PKH26 and T1a/PKH26 double positive cells in lung sections. After 12 days of bleomycin exposure, lung tissues presented with disorganized epithelium, inflammatory cell infiltration, interstitial thickening, collapsed alveolar wall, cystic air spaces and increased collagen deposition (fibrosis). Transplantation of iPSC-derived AECs significantly reduced fibrosis, lung edema and reduced inflammatory cell infiltration and decreased pro-inflammatory cytokine expression to a level similar to saline injected controls. Collagen content was also decreased, although not to basal levels.

Overall, this suggests that iPSC-derived AECs have a significant advantage over undifferentiated iPSCs and display excellent regenerative/reparative potential. To the authors’ knowledge, this is the first report of mouse iPSC-derived cells in the regeneration of a three-dimensional alveolar lung structure and in the treatment of lung injury. However, future studies must further boost the efficiency of differentiation and also assess potential purification strategies so that such cells can be fully appreciated as a clinically applicable strategy.


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