Chronic obstructive pulmonary diseases (COPD) have a major public health impact, as evidenced by the 250 million patients affected by these diseases and the 50% 5-year mortality for severe stages of chronic obstructive pulmonary disease (COPD). One pathophysiological mechanism of COPD and emphysema is a depletion of alveolar progenitor cells inducing a loss of alveolar-reparation capacities after an aggression. The genesis of these alterations and the mechanisms involved remain unknown. Alveolar type 2 cells (AT2) are the alveolar epithelial progenitor cells. AT2 proliferate and differentiate into alveolar type 1 cells (AT1) which form the alveolar-capillary barrier, along with endothelial cells, through which respiratory gas exchanges take place. The proliferation and differentiation of AT2 into AT1 are under the control of mesenchymal cells and endothelial cells located in close proximity. Together these cells form the alveolar stem cell niche. The characteristics and interactions of the different cell populations have been well described during lung growth, in the normal adult lung or during pulmonary fibrosis; however, participants are poorly described during smoking exposure and chronic obstructive diseases.
