Endothelial Cells: Regulators of Blood Vessel Homeostasis

Endothelial cells line the blood vessels of the body and participate in significant crosstalk with the blood and tissues to maintain blood pressure and vessel homeostasis through regulation of vasodilation and vasoconstriction. In particular, endothelial cells have been implicated in atherosclerosis, a significant health issue and risk factor for heart attackand stroke.

Atherosclerosis is characterized by a buildup of plaques in the arteries, which causes vessel narrowing and subsequent increased blood pressure. During the process of atherosclerosis development, the endothelium may experience damage, causing endothelial cell dysregulation, which can result in an inflammatory environment, which may promote the atherosclerotic process. In addition, endothelial cell regulation of blood flow and coagulation may be disrupted.

Recent Studies Using Lifeline® Endothelial Cells

Thrombotic risk is heavily related to loss of endothelial barrier integrity. In a study from last year, Palekar et al. investigated the efficacy of a nanoparticle-delivered anti-thrombin agent, PPACK, against endothelial cell damage in a mouse model that mimics atherosclerosis. Thrombin is an enzyme that promotes blood clotting through activation of its cell surface receptors (PARs).

To evaluate the effects of PPACK on vessel integrity and thrombotic risk, the authors damaged the carotid artery of mice using photochemical injury and measured the coagulant response. They found that mice treated for one month with nanoparticle PPACK had longer time to vessel occlusion, demonstrating a decreased procoagulent response. Nanoparticle PPACK treatment also improved endothelial cell permeability and decreased plaque accumulation in the aorta.

To further define the molecular mechanisms of PPACK, the authors utilized Lifeline® human aortic endothelial cells treated with PPACK nanoparticles to demonstrate that PPACK inhibits thrombin-induced PAR-1 cleavage, a major effect of thrombin activity. Supporting this, PAR-1 downstream signaling was reduced in mice treated with nanoparticle PPACK. Furthermore, NF-kB activation was decreased in Lifeline® aortic endothelial cells, as well as in aortic plaques of mice treated with PPACK.

Finally, the authors illustrated that PPACK nanoparticle treatment results in decreased thrombin-antithrombin complexes in mouse serum, and decreased soluble vascular cell adhesion molecule 1 (sVCAM-1), demonstrating that PPACK nanoparticle treatment reduces endothelium activation. Together, the results of this study demonstrate that PPACK inhibition of thrombin at atherosclerotic plaques augments endothelial cell integrity and decreases procoagulent activity, and might be a viable therapeutic option for atherosclerosis and prevention of thrombosis.

Increased angiogenesis promotes tumor growth by supporting blood flow to a tumor and anti-angiogenic agents are under investigation as anti-cancer drugs. Peg3 is a tumor suppressor protein that is important for endothelial cell autophagy. In a study from this year, Torres et al. set out to define the mechanism by which Peg3 induces endothelial cell autophagy.

They first established that Peg3 translocates to the nucleus following induction of autophagy. Next, using porcine aortic endothelial cells (PAER2), the authors found that Peg3 directly regulates BECN1 (Beclin 1) transcription, a component of the PI3K and autophagy pathways, to upregulate its protein expression. Using a series of overexpression and knockdown studies, authors confirmed that Peg3 induces autophagy in a Beclin 1-dependent manner.

To determine whether Peg3 affects angiogenesis, the authors overexpressed Peg3 in PAER2 cells and found that Peg3 decreased in vitro wound healing through reduced cell migration in 2D, as well as in a 3D matrix. Interestingly, the authors found that Peg3 overexpression induced changes in secreted factors in the media, suggesting that Peg3 alters the endothelial cell secretome.

Finally, the authors used an in vitro capillary morphogenesis assay with LifeLine® human umbilical vein endothelial cells (HUVECs) to demonstrate that HUVECs grown in conditioned medium from Peg3-overexpressing PAER2 cells did not form capillary tubes due to the abundance of Thrombospondin 1, an antiangiogenic factor in the conditioned medium. Together, the results from this study establish that Peg3 induces endothelial cell autophagy through Beclin 1, and reduces angiogenesis through Thrombospondin 1.

The Lifeline® catalog of endothelial cells includes cells from the following locations, optimized for growth in VascuLife® medium:

• Aorta
• Coronary Artery
• Iliac Artery
• Pulmonary Artery
• Umbilical Vein
• Microvasculature (lung, dermal, cardiac)

Do you have a new method or study to share? Tell us how you are using Lifeline® cells or media to answer your scientific questions and your research could be featured here on our blog!