Angiogenesis is a fundamental biological process involving the formation of new blood vessels from pre-existing ones. It ensures tissues receive necessary oxygen and nutrients. It is a dynamic, regulated system that expands the body’s vascular network. Understanding angiogenesis provides insight into how our bodies grow, heal, and adapt.
How New Blood Vessels Form
Angiogenesis begins with signals, often triggered by low oxygen in tissues. Cells with low oxygen release growth factors like Vascular Endothelial Growth Factor (VEGF). These growth factors bind to receptors on endothelial cells, which are the specialized cells lining the inside of existing blood vessels, activating them.
Activated endothelial cells initiate coordinated steps. Enzymes called matrix metalloproteinases (MMPs) are released, breaking down the extracellular matrix, a supportive network surrounding the blood vessel. This degradation creates a path for the new vessel to grow into the surrounding tissue.
After matrix breakdown, activated endothelial cells, known as “tip cells,” migrate towards the angiogenic stimulus, leading the new vessel sprout. Other endothelial cells, “stalk cells,” proliferate behind tip cells, adding length to the sprout. These cells form a hollow tube, which becomes the new vessel’s lumen.
As the nascent blood vessel extends, pericytes, which are specialized cells that wrap around existing capillaries, are recruited to the sprout. These pericytes provide structural support and stabilize the new vessel, ensuring its maturation and function. These coordinated actions allow for the formation of a new blood vessel.
Angiogenesis in a Healthy Body
Angiogenesis is a regulated process with various normal physiological functions. During embryonic development, it forms the initial vascular network, supporting organ growth and development.
In adults, angiogenesis continues to be active in specific scenarios. It is involved in wound healing and tissue repair, where new blood vessels are needed to supply oxygen and nutrients to damaged areas, facilitating regeneration. Similarly, the female reproductive cycle relies on angiogenesis for the growth of the uterine lining during menstruation and for the development of the placenta during pregnancy, ensuring adequate blood flow to support fetal development.
Exercise also stimulates angiogenesis, particularly in skeletal muscles and the heart, leading to an increased capillary density that improves oxygen delivery to active tissues. This adaptation allows muscles to work more efficiently and recover more quickly. These examples illustrate how angiogenesis is tightly controlled and beneficial, responding to the body’s changing demands.
When Angiogenesis Goes Awry
While angiogenesis is a beneficial process, its dysregulation can contribute to various diseases. Some conditions involve excessive or uncontrolled blood vessel growth. A prominent example is cancer, where tumors induce angiogenesis to form their own blood supply, providing them with the oxygen and nutrients needed for rapid growth and spread throughout the body.
Wet age-related macular degeneration (AMD), a leading cause of vision loss, is another condition with excessive angiogenesis. In wet AMD, abnormal blood vessels grow underneath the retina, leaking fluid and blood, which can distort vision and lead to blindness. Diabetic retinopathy also involves uncontrolled new vessel growth in the eye, which can cause vision problems.
Conversely, insufficient angiogenesis is also problematic. Chronic wounds may fail to heal due to an inadequate blood supply, preventing nutrient delivery and waste removal. Similarly, in some forms of heart disease, such as after a heart attack, a lack of new blood vessel formation can limit the heart’s ability to repair itself and restore adequate blood flow to damaged areas. Peripheral artery disease, where blood flow to the limbs is restricted, also benefits from increased angiogenesis.
Harnessing Angiogenesis for Health
Understanding angiogenesis has opened avenues for new medical treatments. Scientists and doctors explore ways to either inhibit or promote new blood vessel growth, depending on the disease. For conditions like cancer and wet AMD, anti-angiogenic therapies aim to stop the formation of new blood vessels.
These therapies work by targeting factors that stimulate angiogenesis, such as VEGF, effectively “starving” tumors by cutting off their blood supply and limiting their growth and spread. In wet AMD, anti-angiogenic drugs injected into the eye can reduce the abnormal vessel growth and leakage, preserving vision. Several anti-angiogenic drugs are currently used in cancer treatment.
Pro-angiogenic therapies are being developed to encourage new vessel growth where needed. For example, in chronic wounds that struggle to heal, promoting angiogenesis can deliver more oxygen and nutrients to the site, accelerating the repair process. In heart disease or peripheral artery disease, stimulating new blood vessel formation could help restore blood flow to starved tissues, improving function and reducing symptoms. Research continues to explore manipulating angiogenesis to address medical challenges.