The endothelium that lines the normal lung is different from that seen in blood vessels and forms a semi-permeable barrier between the blood and interstitium. Other functions of this endothelial cell monolayer include growth factor production, trafficking of leukocytes, maintaining the vascular tone and signal transduction. As these cells are an important constituent of the alveolar capillaries they are exposed to several stress factors ranging from inflammatory cytokines in the blood to pathogens to mechanical forces and oxidized low-density lipoprotein.
Several diseases are the outcome of damages to these cells. Pulmonary hypertension (PH) is when the systolic pulmonary arterial pressure exceeds 35 mm of Hg. According to data published in the International journal of cardiology in 2016, PH is a reason for sickness and death in patients undergoing haemodialysis. Close to 68% of these patients show PH. While the exact causes of the disease are yet to be explored, loss of function of pulmonary endothelial cells is a major cause of the disease.
Additionally, damage to the endothelial cell barrier increases its permeability to allow the entry of oedematous fluid that is rich in proteins in the airspaces. This, in turn, triggers inflammation that is the cause of acute lung injury (ALI) affecting 200,000 people, according to 2010-published data in the Journal of aerosol medicine and pulmonary drug delivery. This severe disease is yet to see an effective therapy that hence calls for exploring its background.
There have been cell cultures that have used animal sources such as rodents but studies in animals may not reflect what is seen in humans given the species difference. As far as humans are concerned, the use of human umbilical vein provides easy availability and isolation but again the biology of veins becomes a question given the cells we are talking about are capillaries.
A team led by Comhair reported the isolation and primary cultures of pulmonary arterial endothelial cells (PAECs) and microvascular endothelial cells (MVECs) that can offer insights into pulmonary endothelial biology. The former cells were isolated from the elastic and muscular arteries while the latter was obtained from lung tissue. For PAECs, type II collagenase was used to dissociate endothelial cells that were washed and seeded on fibronectin in MCDB-107 medium. For MVECs, lung tissue was treated with type II collagenase and compression with a scalpel. Following two filtration steps, the cells were seeded.
Gene analysis confirmed that the isolated cells were endothelial cells (markers such as eNOS and CD31). Additionally, PAECs and MVECs differed in the expression of genes by 1.1% that was also confirmed by binding to specific lectins. The purity was reported to be 95% while the cells represented that of the lung as also shown by their taking up LDL that reflects their functional activity.
Given the previous use of animal models, such human cell cultures showing makers and functions of pulmonary endothelial cells can allow for detailed research to understand the biology of these sensitive cells and design strategies to treat associated diseases.
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Comhair, S. A., Xu, W., Mavrakis, L., Aldred, M. A., Asosingh, K., & Erzurum, S. C. (2012). Human primary lung endothelial cells in culture. American journal of respiratory cell and molecular biology, 46(6), 723–730.
Marc Humbert, Christophe Guignabert, Sébastien Bonnet, et al. Pathology and pathobiology of pulmonary hypertension: state of the art and research perspectives. European Respiratory Journal 2019, 53 (1) 1801887.