Mural cells are a generalized cell population in the microcirculation that comprises vascular smooth muscle cells (vSMCs), and pericytes. Both types are in close contact with the endothelial cells lining the capillaries, and are important for vascular development and stability. The vasculature is a system of small, interconnected tubes that ensure there is proper blood flow to all of the organs.Mural cells are involved in the formation of normal vasculature and are responsive to factors including platelet-derived growth factor B (PDGFB) and vascular endothelial growth factor (VEGF). The weakness and disorganization of tumor vasculature is partly due to the inability of tumors to recruit properly organized mural cells.

Mural cells, like pericytes, are important for how blood vessels work. During the growth of new blood vessels (a process called angiogenesis), pericytes help guide how endothelial cells grow and divide. This process relies on the ability of pericytes to contract. In developing mouse retinas, endothelial cells produce a signal called Pdgfb that attracts pericytes to the area where new blood vessels are forming. Pericytes also help control the amount of a growth factor called Vegfa by using a receptor (Vegfr1) that soaks it up. Without pericytes, there's too much Vegfa, which messes up how the blood vessels grow and branch.

Other research shows that pericytes release a protein called angiopoietin 1, which also helps control new blood vessel growth. Adding extra angiopoietin 1 can fix the blood vessel problems caused by a lack of pericytes. This signaling also helps keep pericytes alive and in place. In fact, removing the receptor for angiopoietin (Tie2) in pericytes can lead to more blood vessel growth in tumors, making them grow faster.

Overall, healthy blood vessel growth depends on teamwork between endothelial cells and pericytes. After the blood vessels have formed, pericytes also help fine-tune the network by causing some vessels to shrink and disappear.

Besides helping with blood vessel growth, mural cells like pericytes also play key roles in shaping blood vessels in specific organs. One important job they have is helping to build and maintain the blood–brain barrier—a protective shield that keeps harmful substances out of the brain.

The blood-brain barrier is made up of endothelial cells, pericytes, and the ends of astrocyte cells, all sitting on a shared support structure called the basement membrane. Pericytes help control how much passes through the blood-brain barrier by managing how endothelial cells move substances across their surface, how astrocyte ends are positioned, and by stopping unwanted proteins from building up in the brain. They also help endothelial cells form tight seals, known as tight junctions, between cells, which are crucial for keeping the barrier strong.

Pericytes can even influence which genes are turned on or off in endothelial cells. Overall, these mural cells work closely with endothelial cells to form and maintain the specialized blood vessels that different organs need—especially in the brain.

Once blood vessels are fully developed, mural cells help manage how blood moves through the brain—a process called neurovascular coupling. This ensures that active areas of the brain get more blood when needed, a response known as functional hyperaemia. Smooth muscle cells (SMCs) are well known for their ability to contract and relax, which allows them to adjust blood vessel width and regulate flow. How strongly these cells contract directly affects how much blood can pass through.