The Role of SO2 in Pulmonary Vascular Remodeling
Chronic obstructive pulmonary disease (COPD) is the third most common cause of death in the United States. The incidence of aging and age-related cardiopulmonary diseases like COPD has become more prevalent over the years as the average life expectancy has increased in the population.
COPD is characterized by chronic inflammation that restricts airflow in the lungs creating low-oxygen conditions in the tissues, which can result in hypoxia-induced pulmonary vascular remodeling (PVR). PVR plays a critical role in many cardio-pulmonary disorders and is characterized by pulmonary artery endothelial cell (PAEC) dysfunction, uncontrolled proliferation of pulmonary artery smooth muscle cells (PASMCs), hypertrophy, and collagen accumulation in the vascular walls.
A better understanding of the mechanisms leading to COPD and PVR can provide insight into potential targets for their treatment in aging-related cardiopulmonary diseases.
Lifeline® offers a variety of smooth muscle cells (SMCs) isolated from different tissues as well as primary skeletal muscle satellite cells. Click on the links below for more information on these cell types:
- Prostate SMCs
- Bronchial/Tracheal SMCs
- Lung SMCs
- Aortic SMCs
- Bladder SMCs
- Coronary artery SMCs
- Pulmonary artery SMCs
- Uterine SMCs
- Primary Human Skeletal Muscle Satellite Cells
Recent Research Using Lifeline Pulmonary Artery Smooth Muscle Cells
Previous research in animal models implicates the endogenous sulfur oxide (SO2)/aspartic aminotransferase 1 (AAT1) pathway within pulmonary artery endothelial cells (PAECs) in the pathologies associated with COPD and resulting hypoxic PVR. Based on this, a recent paper by Lui and Colleagues aimed to determine the mechanism by which EC-derived SO2 affects the progression of hypoxic PVR, specifically how SO2 affects PAEC inflammatory response, pulmonary artery smooth muscle cells (PASMC) proliferation, hypertrophy, and collagen production. Both mouse models and in vitro Transwell co-cultures of Lifeline’s human primary PASMCs and PAECs were utilized in the study.
In the initial mouse studies, the level of AAT1 protein and SO2 content in PAECs, as quantified by immunofluorescence and HPLC, was decreased in the lungs of mice exposed to hypoxic conditions compared with mice exposed to normal O2. Transgenic mice (EC-AAT1-Tg) that overexpress AAT1 had increased SO2 levels, which protected against pulmonary hypertension (PH) observed in WT mice when exposed to hypoxic conditions. Furthermore, H&E and Hart’s staining of lung tissue revealed increased thickening of pulmonary artery walls and more muscularized arteries in the hypoxic WT mice not observed in the transgenic mice. This suggested that decreased SO2 levels induced PVR and hypoxic PH. In situ immunofluorescence staining of ICAM-1 and MCP-1 genes, markers of EC inflammation showed that hypoxia dramatically increased their levels in WT but that AAT1 overexpression (EC-AAT1-Tg) successfully inhibited ICAM-1 and MCP-1 increases suggesting that the high levels of SO2 in ECs protects against hypoxic vascular inflammation in an autocrine manner. Staining of Ki-67 (cell division marker), α-SMA (SMC hypertrophy marker) and collagen 1 increased under hypoxic conditions with WT mice but no difference in expression was observed between EC-AAT1-Tg mice with and without hypoxic exposure, which indicates that PASMC proliferation, hypertrophy, and collagen synthesis are influenced in a paracrine manner by EC-induced SO2.
To confirm the role of EC-derived SO2 on human endothelial and pulmonary artery cells, the researchers infected HPAECs using lentivirus with AAT1 shRNA to knockdown SO2 levels and looked at gene expression levels in PAECs and in PASMCs within Transwell co-cultures. Consistent with findings in the mouse studies, reduced SO2 levels directly correlated with hypoxia-induced disease phenotype. Looking specifically at the effect of SO2 on NF-κB (i.e., p50 heterodimers), which has a critical role in cell inflammation, proliferation, and collagen metabolism, showed increased p50 activation and nuclear translocation in HPAECs and HPASMCs in the AAT1 shRNA group compared with the control group, but this effect was reversed by the treatment with SO2 donor suggesting that p50 is the molecular target of SO2. Inhibition of p50 by Andro confirmed this hypothesis since p50 inhibition blocked increases in HPAEC inflammation, HPASMC proliferation, and collagen production caused by the decreased SO2 in AAT1 shRNA ECs.
The researchers clearly demonstrate a novel mechanism of communication between PAEC and PASMC through the SO2/AAT1 pathway and also showed that SO2 acts directly on intracellular p50 where SO2 represses p50 activation and protects against undesirable inflammatory and cell proliferation observed in PVR. SO2 as a potential treatment of hypoxic PVR in aging-related cardiopulmonary diseases like COPD warrants further investigation.
We hope you enjoyed reading this latest installment of the Lifeline blog. If you have used Lifeline cells or media for your research, we would love to hear from you.