Alveoli are the gas-exchanging units of the lung and alveolar barrier is often a key battleground that encounters pathogens, allergens, and other insults from the environment. This is seen in the current COVID-19 pandemic, as alveolar epithelium is one of the major targets of SARS-COV-2, the virus that causes COVID-19. Thus, it is essential to understand the mechanisms to maintain the integrity of alveoli epithelium. Alveolar type II (AT2) cells behave as tissue stem cells that repair alveoli epithelium in steady-state replacement and after injury. However, not all AT2 cells are equal in their ability for self-renewal or differentiation. Through marker gene identification, lineage tracing, and single-cell RNA-sequencing (scRNA-seq), distinct subpopulations of AT2 cells have been identified that play the progenitor role in different context. The revelation of AT2 heterogeneity has brought new insights into the role of AT2 cells in various lung disease settings and potentiates the finding of more therapeutics targets. In this mini review, we discussed the recently identified subpopulations of AT2 cells and their functions under steady state, after injury and in pathological conditions.
Heterogeneous groups of alveolar type II cells in lung homeostasis and repair