The Circulatory System: The Blood Delivery System
The circulatory system delivers the blood and oxygen that all tissues of the body require for normal operation. In particular, the arteries, veins, and capillaries that transport the blood throughout the body are lined by a layer of endothelial cells, which help to maintain blood and vessel homeostasis. They form a barrier between the contents of the blood and the internal environment, as well as help to regulate blood pressure and immune response to inflammation.
At the center of the circulatory system is the heart, which pumps blood throughout the body, and without which we could not survive. The heart itself is composed of a number of cell types, including endothelial cells and fibroblasts that have critical roles in maintaining cardiac function. Additionally, the coordinated activity of cardiac fibroblasts, which produce extracellular matrix proteins, is crucial for tissue recovery and remodeling after an infarction.
Check out the Lifeline® catalog for our cardiac and endothelial cells, which include the following:
- Cardiac microvascular endothelial cells
- Cardiac fibroblasts
- Pulmonary artery endothelial cells
- Aortic endothelial cells
- Coronary artery endothelial cells
- Lung microvascular endothelial cells
- Dermal microvascular endothelial cells (adult and neonatal)
- Iliac artery endothelial cells
- Umbilical cord endothelial cells (HUVECs; primary and 10-donor pool)
Lifeline® HUVECs in Diabetes Research
Diabetes is a metabolic disease in which the body does not produce enough insulin or does not use insulin properly, resulting in high concentrations of glucose in the blood, a condition called hyperglycemia. Diabetes is also associated with a number of complications, including glaucoma, neuropathy, and cardiovascular disease. In particular, vascular complications are a significant cause of diabetes-related deaths, partly due to endothelial cell dysfunction during angiogenesis (the process by which blood vessels are formed). In a 2018 study, Shi and colleagues (opens in new window) set out to determine how the forkhead box protein O1 (FOXO1) transcription factor regulates endothelial cell function in diabetes.
The authors approached this question by defining the effects of loss of FOXO1 function. In this vein, they first examined the effects of FOXO1 inhibition during recovery to ischemia (restriction or loss of blood supply to a tissue) in a mouse model of diabetes, induced using streptozotocin. Following induction of hindlimb ischemia, diabetic mice had reduced blood flow recovery compared with control mice. FOXO1 inhibition in diabetic mice—using AS1842856—resulted in better blood flow recovery and increased numbers of blood vessels in the ischemic limb. Next, the authors assessed wound healing in diabetic mice using a full thickness excision wound model. They found that FOXO1 inhibition in diabetic mice increased wound healing and reduced levels of mitochondrial reactive oxygen species (ROS)—a marker of oxidative stress—compared with untreated mice.
To determine the mechanism by which FOXO1 might affect endothelial cell function, the authors used Lifeline® HUVECs to test tube formation, an in vitro assay used to model angiogenesis. Compared with untreated HUVECs grown in hyperglycemic conditions, which impeded tube formation, HUVECs treated with AS1842856 displayed undisrupted tube formation and had increased levels of pro-angiogenic proteins. Assessment of apoptosis revealed that FOXO1 inhibition also reduced hyperglycemia-induced apoptosis.
FOXO1 inhibition in Lifeline® HUVECs also blocked hyperglycemia-induced disruption of mitochondrial networks, upregulation of Drp1 (a regulator of mitochondrial fission, or division), and Drp1 activation. To determine how Drp1 regulates FOXO1-mediated mitochondrial fission, the authors knocked down Drp1 using siRNA. They found that endothelial cells lacking Drp1 and grown under high glucose conditions maintained their mitochondrial network integrity, produced less mitochondrial ROS, had lower rates of apoptosis, and formed tubule structures. Additionally, they demonstrated that endothelial cell apoptosis and disruption of tubule formation induced by high glucose conditions were largely due to mitochondrial ROS.
Next, the authors investigated whether ROCK1 (a kinase) could mediate the observed hyperglycemia-induced effects on mitochondria in endothelial cells. They found that knockdown of ROCK1 in endothelial cells blocked hyperglycemia-induced loss of mitochondrial networks and lowered Drp1 activation. Lastly, the group demonstrated that ROCK1 protein and transcript expression was downregulated following FOXO1 knockdown or inhibition, and that FOXO1 directly regulates ROCK1 transcription by binding to its promoter.
Together, the results of this study demonstrate that FOXO1 regulates endothelial cell function through Drp1 and ROCK1, and may be a potential therapeutic target for the treatment of vascular dysfunction in diabetes.
How are you using Lifeline® products in your research? Let us know and your study could be featured here on our next blog!