Lung diseases can scar the respiratory tissues necessary for oxygen exchange. Without proper oxygen exchange, our cells lack the means to make the energy they so desperately need, and they begin to shut down or even die. Lung diseases such as asthma, emphysema, chronic obstructive pulmonary disease and others can permanently diminish lung capacity, life expectancy and activity levels.
Fortunately, a preclinical study in laboratory animals has suggested a new strategy for treating lung diseases. Carla Kim and Joo-Hyeon Lee of the Stem Cell Research Program at Boston Children’s have described a new lung-specific pathway that is activated by lung injury and directs a resident stem cell population in the lung to proliferate and differentiate into lung-specific cell types.
When Kim and Lee enhanced this pathway in mice, they observed increase production of the cells that line the alveolar sacs where gas exchange occurs. Alveolar cells are irreversibly damaged in emphysema and pulmonary fibrosis.
Inhibition of this same pathway increased stem cell-mediated production of airway epithelial cells, which line the passages that conduct air to the alveolar sacs and are damaged in asthma and bronchiolitis obliterans.
For their experiments, Kim and Lee used a novel culture system called a 3D culture system that mimics the milieu of the lung. This culture system showed that a single bronchioalveolar stem cell could differentiate into both alveolar and bronchiolar epithelial cells. By adding a protein called TSP-1 (thrombospondin-1), the stem cells differentiated into alveolar cells.
Next, Kim and Lee utilized a mouse model of pulmonary fibrosis. However, when they cultured the small endothelial cells that line the many small blood vessels in the lung, which naturally produce TSP-1, and directly injected the culture fluid of these cells into the mice, the noticed these injections reverse the lung damage.
When they used lung endothelial cells that do not produce TSP-1 in 3D cultures, lung-specific stem cells produce more airway cells. in mice that were engineered to not express TSP-1, airway repair was enhanced after lung injury.
Lee explained his results in this way: “When the lung cells are injured, there seems to be a cross talk between the damaged cells, the lung endothelial cells and the stem cells.”
Kim added: “We think that lung endothelial cells produce a lot of repair factors besides TSP-1. We want to find all these molecules, which could provide additional therapeutic targets.”
Even though this work is preclinical in nature, it represents a remarkable way to address the lung damage that debilitates so many people. Hopefully this work is easily translatable to human patients and clinical trials will be in the future. Before that, more confirmation of the role of TSP-1 is required.