Oxygen is critical for survival, and without lungs, it is impossible for that life-saving gas to enter the human body (Hsia et al., 2016). When the lungs are filled with fresh air, oxygen diffuses through the epithelium into blood vessels. To make this process more efficient, evolution has increased the surface of the lung. If you add up the area of the alveoli, you will get a surface of approximately 100 square meters. This enhances blood oxygenation in the lungs.
The heart and lungs share a close relationship, because the cardiovascular system distributes blood that has been enriched with oxygen (Forfia et al., 2013). This is particularly important when one of these two organs is not working properly. Cell culture offers the opportunity to understand disease mechanisms of these closely associated organs at a cellular level, and to specifically target pathogenic processes using therapeutic compounds.
In vitro assays with lung cells allow for toxicological testing of various substances such as nanoparticles (Fröhlich and Salar-Behzadi et al., 2014). Toxic compounds from tobacco smoke can lead to chronic respiratory diseases, including chronic obstructive pulmonary disease (COPD), or asthma (Holtzman et al., 2014). Worldwide, more than three million deaths result from COPD annually, according to the World Health Organization. The key players in pathogenesis are innate immune cells and epithelial cells.
Hypertension can cause an inflammatory state of alveolar vessels and ultimately lead to irreversible vascular remodeling (Pugliese et al., 2014). Remodeling of the complete lung tissue is a hallmark of another disease, pulmonary fibrosis (Todd et al., 2012). This disease leads to altered lung fibroblasts, loss of epithelial cells in the alveoli, and the accumulation of extracellular matrix.
Airway epithelia are unique, as they build the interface between air and liquid in the body. These cells require particular culture conditions. This is why the transcriptional profile of such cells most closely resembles the conditions in vivo when an air-liquid interface exists in the culture (Pezzulo et al., 2011).
Another critical cell type for healthy as well as diseased lungs are endothelial cells. These cells can be isolated from the lung and kept in culture, which allows scientists to study their biology and epithelial disease mechanisms (Comhair et al., 2012). Smooth muscle cells control the airflow into the respiratory system. During development, differentiation and disease-related remodeling the cells migrate, a process that scientists can also investigate in vitro (Gerthoffer, 2008).