Person:

Mou, Hongmei

Summary Cellular plasticity contributes to the regenerative capacity of plants, invertebrates, teleost fishes, and amphibians. In vertebrates, differentiated cells are known to revert into replicating progenitors, but these cells do not persist as stable stem cells. We now present evidence that differentiated airway epithelial cells can revert into stable and functional stem cells in vivo. Following the ablation of airway stem cells, we observed a surprising increase in the proliferation of committed secretory cells. Subsequent lineage tracing demonstrated that the luminal secretory cells had dedifferentiated into basal stem cells. Dedifferentiated cells were morphologically indistinguishable from stem cells and they functioned as well as their endogenous counterparts to repair epithelial injury. Indeed, single secretory cells clonally dedifferentiated into multipotent stem cells when they were cultured ex vivo without basal stem cells. In contrast, direct contact with a single basal stem cell was sufficient to prevent secretory cell dedifferentiation. In analogy to classical descriptions of amphibian nuclear reprogramming, the propensity of committed cells to dedifferentiate was inversely correlated to their state of maturity. This capacity of committed cells to dedifferentiate into stem cells may play a more general role in the regeneration of many tissues and in multiple disease states, notably cancer.

Deriving lung progenitors from patient-specific pluripotent cells is a key step in producing differentiated lung epithelium for disease modeling and transplantation. By mimicking the signaling events that occur during mouse lung development, we generated murine lung progenitors in a series of discrete steps. Definitive endoderm derived from mouse embryonic stem cells (ESCs) was converted into foregut endoderm, then into replicating Nkx2.1+ lung endoderm, and finally into multipotent embryonic lung progenitor and airway progenitor cells. We demonstrated that precisely-timed BMP, FGF, and WNT signaling are required for NKX2.1 induction. Mouse ESC-derived Nkx2.1+ progenitor cells formed respiratory epithelium (tracheospheres) when transplanted subcutaneously into mice. We then adapted this strategy to produce disease-specific lung progenitor cells from human Cystic Fibrosis induced pluripotent stem cells (iPSCs), creating a platform for dissecting human lung disease. These disease-specific human lung progenitors formed respiratory epithelium when subcutaneously engrafted into immunodeficient mice.

Neutrophil breach of the mucosal surface is a common pathological consequence of infection. We present an advanced co-culture model to explore neutrophil transepithelial migration utilizing airway mucosal barriers differentiated from primary human airway basal cells and examined by advanced imaging. Human airway basal cells were differentiated and cultured at air-liquid interface (ALI) on the underside of 3 µm pore-sized transwells, compatible with the study of transmigrating neutrophils. Inverted ALIs exhibit beating cilia and mucus production, consistent with conventional ALIs, as visualized by micro-optical coherence tomography (µOCT). µOCT is a recently developed imaging modality with the capacity for real time two- and three-dimensional analysis of cellular events in marked detail, including neutrophil transmigratory dynamics. Further, the newly devised and imaged primary co-culture model recapitulates key molecular mechanisms that underlie bacteria-induced neutrophil transepithelial migration previously characterized using cell line-based models. Neutrophils respond to imposed chemotactic gradients, and migrate in response to Pseudomonas aeruginosa infection of primary ALI barriers through a hepoxilin A3-directed mechanism. This primary cell-based co-culture system combined with µOCT imaging offers significant opportunity to probe, in great detail, micro-anatomical and mechanistic features of bacteria-induced neutrophil transepithelial migration and other important immunological and physiological processes at the mucosal surface.