Endothelial cells (EC) are the innermost lining cells of all blood vessels. EC represent the barrier between blood flowing in the blood vessel, and the wall of the blood vessel.
EC normally function to keep blood vessels healthy. For example, EC in the pulmonary arteries:
- Produce chemical substances (also known as mediators) that relax the pulmonary arteries, keeping the blood pressure very low in the pulmonary arteries in normal humans. These important vasodilator chemicals include nitric oxide (NO) and prostacyclin.
- Produce chemical substances that act on other cells in the wall of the blood vessels (such as smooth muscle cells and fibroblasts), and prevent these cells from growing or multiplying. These chemicals include nitric oxide (NO) and prostacyclin.
- Produce chemical substances that prevent blood clots (also known as thrombosis) from forming. These anti-thrombotic chemicals include thrombomodulin and TPA (tissue plasminogen activator).
There is much scientific evidence that endothelial cells (EC) are abnormal in the pulmonary arteries of patients with PH. EC could be abnormal for several reasons:
- EC can be affected by the presence of defective genes (also known as mutant genes), such as the genes that cause FPAH.
- EC can be damaged by the high blood pressure in the pulmonary arteries in PH (also known as high PAP).
- EC can be damaged by high blood flow through the pulmonary arteries in birth defects of the heart (also known as congenital heart disease = CHD), such as ASD (atrial septal defect) and VSD (ventricular septal defect).
- EC can be damaged by blood clots forming in the pulmonary arteries in PH.
- EC can be damaged by some infections, such as infection with the HIV virus.
Abnormal EC in the pulmonary arteries lead to more damage to the pulmonary arteries and worsening of PH. Abnormal EC lead to:
- Higher pulmonary artery pressure (PAP) due to production of less vasodilator chemicals such as NO and prostacyclin, and production of more vasoconstrictor chemicals such as endothelin-1 (ET-1), and serotonin.
- Increased growth of EC in the pulmonary arteries.
- Increased multiplication (also known as proliferation) of EC in the pulmonary arteries.
- Narrowing and closing of pulmonary arteries due to increased growth and numbers of other cells in the walls of pulmonary arteries, such as smooth muscle cells and fibroblasts.
- Narrowing and closing of pulmonary arteries due to scarring of the blood vessel walls.
Increased formation of blood clots in the pulmonary arteries (also known as thrombosis).