Stem cells of submucosal glands: their function as tissue stem cells and a reserve population for airway repair
In the human lung, SMGs are the main source of mucus, a key component of airway clearance and defence. They are tubuloacinar structures buried in the mesenchyme along the cartilaginous airways and are composed of ciliated ducts, collecting ducts, mucous tubules and many serous acini. The secretory units are surrounded by stellate-shaped cells called myoepithelial cells. The myoepithelial cells and basal cells in the ducts function as stem cells of the SMGs and also contribute to the surface epithelium of the airway after injury. The SMG thereby serves as a reservoir of multipotent stem cells for the lung. SMGs exhibit widespread histological changes including mucous cell hypertrophy and excess mucus production in many muco-obstructive airway diseases including asthma, COPD and CF. Although the molecular mechanisms underlying such changes remain unknown, emerging studies using scRNA-seq are providing insights into SMG-mediated airway injury/repair and disease mechanisms, and may offer therapeutic avenues to treat muco-obstructive diseases.
