Endothelial Cells: Regulators of Vessel Homeostasis and Angiogenesis

Endothelial cells line the blood vessels of the circulatory system and play major roles in cardiovascular homeostasis. Through extensive crosstalk with the circulating blood and various cell types contained in the blood, the endothelium is essential for regulating blood flow, vessel repair, and inflammatory responses. Dysregulation of endothelial cells is implicated in various cardiovascular diseases, including atherosclerosis.

In particular, the endothelium regulates angiogenesis, the formation of new blood vessels. Endothelial cells express the receptors for pro-angiogenic growth factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), which induce endothelial cells to proliferate and migrate to form vessels. Angiogenesis is important during development, but is also a significant factor in solid tumor growth. Solid tumors often induce angiogenesis to promote increased blood flow, which supports tumor growth and progression. Therefore, targeted therapies like bevacizumab, which inhibits VEGF, are one approach to target tumor angiogenesis in the hopes of restricting blood flow to tumors.

Lifeline® offers multiple endothelial cell types, which are optimized for growth in VascuLife® medium. The Lifeline® catalog includes:

Aortic endothelial cells
Coronary artery endothelial cells
Microvascular endothelial cells from lung, skin, and heart
Iliac artery endothelial cells
Pulmonary artery endothelial cells
Umbilical vein endothelial cells

Lifeline® HUVECs in Cardiovascular Disease and Mesothelioma Research

Cardiovascular disease is the leading cause of death globally. Exposure to chemicals and toxins is one factor in development of cardiovascular disease, and it is becoming more appreciated that exposure to polychlorinated biphenyls, or PCBs, can cause detrimental health problems like hypertension and vascular inflammation. PCBs are organic chemicals that are presently banned in the US, but were manufactured and utilized for various commercial and industrial uses until 1979. While the proposed mechanism of PCB toxicity has been studied, there is little information about how miRNAs are involved. With this in mind, Wahlang et al. set out to evaluate the effects of PCBs on global miRNA expression.

The authors first treated Lifeline® human umbilical vein endothelial cells (HUVECs; 10-donor pool) with Aroclar 1260, a commercial PCB mixture, for 16 hours, and then performed microarray analysis for miRNA expression changes. They found that a significant number of miRNAs were altered by PCB exposure when compared with vehicle exposure. Among these altered miRNAs, the authors validated that miR-21, miR-31, miR-126, miR-221, and miR-222 expression was upregulated in response to PCB treatment. In particular, these miRNAs are involved in vascular inflammation and atherosclerosis, suggesting they may serve as biomarkers for decreased cardiovascular health induced by PCBs. Together, this study demonstrates that PCBs alter miRNA profiles in endothelial cells and may influence development of cardiovascular disease-related conditions.

Malignant pleural mesothelioma (MPM) is an aggressive tumor that develops in the pleura, which are the membranes that surround and encase the lungs. MPM has a poor prognosis and therefore, development of better therapeutic options is critical. Angiogenesis (described above) is not just induced by VEGF, but can be stimulated by other pro-angiogenic growth factors, including basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and hepatocyte growth factor (HGF). Tumor angiogenesis is also driven by the plasminogen activation system, which includes plasminogen activator inhibitor-1 (PAI-1). In a 2016 study, using in vivo and in vitro models of MPM, Takayama and colleagues investigated whether inhibition of PAI-1 using SK-216 (a PAI-1-specific inhibitor) could have anti-tumor effects, irrespective of the angiogenesis stimulus.

The authors first examined the effects of SK-216 on tumors derived from orthotopically transplanted MPM cell lines (EHMES-10 and MSTO-211H). They determined that EHMES-10 cells highly expressed VEGF, while MSTO-211H cells highly expressed bFGF, making these cell lines good models to study two mechanisms of angiogenesis. The researchers found that SK-216 treatment resulted in reduced tumor weight of both EHMES-10 and MSTO-211H tumors, but had no effect on pleural effusions, which occur when fluid builds up around the lungs.

The authors then compared the effects of SK-216 to those of bevacizumab and found that while bevacizumab decreased tumor weight and pleural effusions of the VEGF-high EHMES-10 tumors as expected, it had no effect on bFGF-MSTO-211H tumors. Using VEGF and FGF receptor inhibitors in combination with SK-216, the authors demonstrated that the anti-tumor effects of SK-216 are through inhibition of VEGF and bFGF in the respective cell lines and therefore, are not limited by the specific pro-angiogenic growth factor stimulus. To confirm that SK-216 was acting by decreasing tumor angiogenesis, the authors examined microvessel density using immunohistochemistry for CD31 and found that SK-216-treated tumors derived from both cell lines had decreased angiogenesis as expected.

Next, the researchers used in vitro proliferation assays to demonstrate that SK-216 does not affect the proliferation of EHMES-10 or MSTO-211H cells alone, but does synergize with cisplatin, a chemotherapy drug that blocks cell proliferation, to reduce tumor weight and prolong survival in vivo. Finally, the group assessed how SK-216 treatment affected Lifeline® HUVEC tube formation in response to different pro-angiogenic growth factors. Interestingly, they found that SK-216 blocked HUVEC migration and tube formation in response to bFGF, PDGF, and HGF, supporting the promiscuous anti-angiogenic effects observed in vivo. Together, the results of this study illustrate that SK-216 negatively affects MPM tumor progression independent of the pro-angiogenic stimulus, and PAI-1 is therefore a good therapeutic target for MPM treatment.

How do you use Lifeline® cells in your research? Share your experiences and model systems with us, and it could be featured on the blog! Check in with us here every other week for a rundown of new research from around the world.