Lef-1 controls cell cycle progression in airway basal cells to regulate proliferation and differentiation

The maintenance of a fully differentiated airway epithelium requires populations of epithelial progenitor cells to continuously replenish damaged and aging cells. Airway basal cells are one type of progenitor in the large airways. Basal cells are anchored to the basal lamina via desmosomes and, as a result, are located deeper in the epithelium where they are more protected from the external environment. There is now good experimental evidence indicating that airway basal cells are a population of multipotent stem cells that regulate both homeostasis of the normal epithelium and its orderly regeneration after injury. Because basal cells are a stem cell population, alterations in their genomes through mutations or epigenetic modifications induced by environmental agents or pathogens might affect the long-term susceptibility of individuals to respiratory disease. Thus, a greater understanding of basal cell behavior is potentially of clinical relevance. For example, therapies aimed at regulating basal cell proliferation and inducing their differentiation towards specific lineages might help to restore a normal phenotype in a disease context. The importance of restoring pulmonary function after lung damage is recently highlighted in the Coronavirus disease 2019 pandemic, which has infected nearly half a billion people and induced lung epithelial and endothelial damage. Another important life-limiting hereditary lung disease is cystic fibrosis, where cell-based therapies could theoretically cure cystic fibrosis lung disease.

Lymphoid enhancer-binding factor 1 (LEF1), a member of the T-cell factor (TCF)/LEF1 family of high mobility transcription factors, is predominantly involved in the Wnt/β-catenin signaling pathway. As a downstream mediator of the Wnt signaling pathway, LEF1 is also essential for stem cell maintenance and organ development in addition to its role in epithelial-mesenchymal transition by activating the transcription of proteins integral to these processes. It has also been shown that Lef-1 is responsible for the survival and progression of several cancers. Therefore, its complex and context-dependent impact on airway basal cell behavior requires a closer look. The overexpression of Lef-1 in myoepithelial cells of the submucosal glands can result in a spontaneous lineage commitment towards a basal cell phenotype with a capacity for airway regeneration. Therefore, Lef-1 could play a critical role in airway basal cell self-renewal, though this hasn’t been formally investigated.

With this realization, University of Iowa researchers: Chandler Jensen-Cody, Adrianne Crooke, Dr. Pavana Rotti, Vitaly Ievlev, Weam Shahin, Soo-Yeun Park, Dr. Thomas Lynch, and led by Professor John Engelhardt investigated the role of Lef-1 within the basal cell compartment of the surface airway epithelium. Their research work is published in the journal Stem Cells. Professor John Engelhardt and his research team are well known in exploring innovative strategies for the treatment of cystic fibrosis via gene and cell therapy.

The research team observed that Lef-1 controls the differentiation and proliferation of mouse tracheal basal cells. They demonstrated that deletion of Lef-1 inhibited basal cell proliferation at the G1/S transition of the cell cycle. Lef-1 KO basal cells could not maintain all of the major luminal tracheal cell types in air-liquid interface culture. The authors dissected the molecular mechanism of regulating self-renewal and differentiation by conducting RNA sequencing analysis, where they demonstrated that Lef-1 KO led to the downregulation of critical cell cycle progression and DNA damage response genes. One important finding is the role of the kinase Chek1, for which its inhibition disabled basal cell self-renewal in a fashion similar to Lef-1 deletion. Lef-1 KO imposed a transient cell cycle block in vitro, but eventually basal cells compensated to normal proliferation via a Chek1-independent pathway. In contrast, in vivo studies revealed that Lef-1 KO basal cells were unable to properly regenerate tracheal epithelium after injury.

The research team demonstrated that Lef-1 is necessary for proper basal cell function through interactions/cross-talk between Wnt signaling and other genetic pathways that play a role in proliferating and lineage-commitment of the basal cells to differentiated progeny. Therefore, regulating its function could present potential therapeutic target for regenerative medicine.