What Are Pericytes Their Function In Blood Vessels?

Pericytes are cells that wrap around the tiny blood vessels in your body, including capillaries, venules, and arterioles. They are embedded in the basement membrane of the vessel wall and play a vital role in regulating blood flow, maintaining the blood-brain barrier, and supporting the growth and repair of blood vessels. Think of them as the support staff of your circulatory system—they are not blood cells themselves, but they are essential for keeping your smallest blood vessels stable and functional.

Where Are Pericytes Found in the Body?

Pericytes are found throughout the body wherever there are small blood vessels. They are most dense in the central nervous system, where they cover a large portion of the capillary surface. In the brain, pericytes are a critical part of the neurovascular unit, which includes neurons, other support cells, and the blood vessels themselves.

Outside the brain, pericytes are present in the heart, lungs, skin, skeletal muscle, and kidneys. Their density varies by tissue. In the brain and retina, pericyte coverage is especially high because these organs have strict control over what enters their tissue. In skeletal muscle, coverage is lower, which allows for more rapid changes in blood flow during exercise.

What Are Pericytes Their Function In Blood Vessels?

The primary function of pericytes in blood vessels is to provide structural support and regulate blood flow. Capillaries are only one cell layer thick, and without pericytes, they would be fragile and prone to leaking. Pericytes wrap around the outside of these vessels, sending out long projections that grip the endothelial cells—the cells that line the inside of the vessel.

Pericytes also contain contractile proteins, similar to muscle cells. When they contract, they narrow the blood vessel and reduce blood flow. When they relax, blood flow increases. This is especially important in the brain, where blood flow must match the metabolic needs of active neurons. Some research suggests that pericytes help direct blood to active brain regions, though the exact degree of their influence compared to other mechanisms is still being studied.

Beyond physical support and blood flow control, pericytes release signaling molecules that help endothelial cells survive. Without pericytes, blood vessels become unstable, leaky, and prone to abnormal growth. This is why pericyte loss is linked to several diseases.

How Do Pericytes Maintain the Blood-Brain Barrier?

The blood-brain barrier is a selective filter that protects the brain from toxins, pathogens, and substances in the blood that could harm neurons. Pericytes are a key part of this barrier. They sit between the endothelial cells and the surrounding brain tissue, helping to maintain the tight junctions that seal the vessel wall.

Studies in animals have shown that when pericytes are absent or dysfunctional, the blood-brain barrier becomes leaky. Molecules that should stay in the blood can enter the brain tissue, causing inflammation and damage. Pericytes also perform a cleanup role, clearing debris from the basement membrane and helping to maintain the health of the vessel wall.

In conditions like stroke or traumatic brain injury, pericyte loss is an early event. This contributes to the breakdown of the blood-brain barrier and the swelling that follows. Protecting pericytes is now considered a potential therapeutic target for these conditions, though no clinical treatments have been developed yet.

What Happens When Pericytes Are Damaged or Lost?

Pericyte dysfunction is linked to several serious conditions. One of the most studied is diabetic retinopathy, a leading cause of blindness in working-age adults. In this condition, high blood sugar damages the small blood vessels in the retina. Pericytes are among the first cells to die, and their loss causes the capillaries to weaken and form microaneurysms—tiny bulges that leak fluid and blood.

Pericyte loss is also seen in Alzheimer’s disease. Post-mortem brain tissue from people with Alzheimer’s shows reduced pericyte coverage. Some researchers believe that pericyte degeneration contributes to the vascular problems seen in the disease, including reduced blood flow and a leaky blood-brain barrier. However, it is not yet clear whether pericyte loss is a cause of Alzheimer’s or a consequence of the disease process.

In the heart, pericyte loss after a heart attack can impair the formation of new blood vessels in damaged tissue. This slows recovery and may contribute to heart failure. In the kidneys, pericyte dysfunction is associated with fibrosis—the buildup of scar tissue that impairs kidney function over time.

Can Pericytes Repair Blood Vessels?

Pericytes do have some capacity for repair. In response to injury, they can detach from the vessel wall, multiply, and migrate to the site of damage. Once there, they can help stabilize newly formed blood vessels during the process of angiogenesis—the growth of new capillaries.

Some research has suggested that pericytes can act as stem cells, differentiating into other cell types such as smooth muscle cells, fat cells, and even cartilage cells. This has generated interest in using pericytes for regenerative medicine. However, the extent to which pericytes function as true stem cells in the adult human body is still debated. Most of the evidence comes from laboratory studies, and the behavior of pericytes in living tissue may be more limited.

What is clear is that pericytes are essential for the maturation of new blood vessels. When a new capillary forms, pericytes are recruited to the vessel wall to provide stability. Without them, the new vessel is fragile and likely to regress. This is why pericyte function is a focus of research in wound healing and tissue regeneration.

How Do Pericytes Differ From Other Vascular Cells?

Pericytes are often confused with smooth muscle cells, but they are distinct. Smooth muscle cells wrap around larger vessels, like arteries and veins, in multiple layers. Pericytes wrap around smaller vessels in a single layer and have a different shape—they are branched and irregular. Pericytes also lack some of the protein markers found in smooth muscle cells.

Endothelial cells line the inside of all blood vessels and are the primary barrier between blood and tissue. Pericytes sit on the outside of the vessel, embedded in the basement membrane. The two cell types communicate extensively, exchanging signals that keep the vessel healthy.

Another difference is location. Endothelial cells are present in every blood vessel in the body. Pericytes are only found on microvessels—capillaries, venules, and small arterioles. Larger vessels rely on smooth muscle cells instead of pericytes for support and contraction.

Are Pericytes a Target for Future Treatments?

Given their role in so many diseases, pericytes are being investigated as a therapeutic target. In cancer, pericytes are part of the tumor microenvironment. Tumors recruit pericytes to stabilize the abnormal blood vessels they need to grow. Some experimental cancer treatments aim to disrupt pericyte function to starve tumors of blood supply. However, this approach is complex, because disrupting pericytes can also make vessels leakier, which may help tumors spread.

In neurological diseases, preserving pericyte function is a more promising direction. Researchers are exploring drugs that prevent pericyte death after stroke or that promote pericyte repair in chronic conditions like diabetic retinopathy. Some of these are in early clinical trials, but none are approved for use yet.

The evidence is strongest for the role of pericytes in diabetic retinopathy. Anti-VEGF injections, which are already used to treat this condition, work partly by reducing abnormal blood vessel growth. Preserving pericytes is a complementary strategy that could prevent the vessel damage from occurring in the first place. But again, no pericyte-specific treatment has reached clinical use.