Pericytes are vascular cells located on capillaries and other small diameter vessels. They have also been reported to be present in the layers of the arteries called intima, media, and adventitia. Their exact functions are yet to be classified. Pericytes are involved in the development, stabilization, remodeling, and maturation of capillaries and other small vessels. They also regulate blood flow in the capillaries and control angiogenesis. They are also involved in establishing and maintaining the blood-brain-barrier.
An interesting aspect of pericytes is their emerging association with mesenchymal stem cells. Some studies have suggested that mesenchymal stem cells are a subgroup of pericytes. Other studies have shown multipotency of pericytes in many organs such as cartilage, bone, smooth muscle, skeletal muscle, adipose tissue, and the brain. Diseases such as diabetic microangiopathy and even hypertension have been linked to affected pericyte functions. As angiogenesis is also associated with diseases such as cancer, the involvement of pericytes with angiogenesis opens up an avenue to test anti-angiogenesis therapy on pericytes.
The use of cultures of pericytes can allow studies on these interesting cells. Pericytes have been isolated from tissues rich in these cells- the brain and the retina. Other cell sources that have been used are skin, muscle and foetal tissues. Most culturing approaches result in a mixed culture of cells. Techniques such as flow cytometry or magnetic beads can allow the isolation of pure pericyte cell populations. Challenges here are low cell yield along with the complexity and cost involved.
A team led by Tigges published an article in Microvascular research discussing a simple approach to culture pericytes from mice. The protocol involved mincing of the brain tissue and digesting with papain and DNase I in Earl’s Balanced Salt Solution. Post-filtration and centrifugation, the cell pellet was seeded collagen-coated plates with endothelial cell growth medium (ECGM) made of Hams F12, supplemented with 10% FBS, Heparin, ascorbic acid, L-glutamine, penicillin/streptomycin (usually Dulbecco’s Modified Eagle Medium (DMEM) is used but special media too can be used).
As the usual in vivo identification of pericytes involves the close positioning of these cells with endothelial cells, the identification outside such a scenario becomes challenging. In fact, the major contamination of endothelial cell cultures is identified as pericytes! As there is no such single marker that identifies pericytes, the use of several markers can aid in assessing cultures. These include NG2 and PDGFβ-receptor as positive markers. Endothelial cells and pericytes can be distinguished using CD146; the former shows higher expression than the latter. Negative markers include CD11b (Mac-1), GFAP and CD31. The cells in this culture expressed PDGFβ-receptor.
Research constantly explores previously unidentified aspects and phenomena. One such new aspect is culturing pericytes- cells involved in capillary biology and diseases such as hypertension. Culturing cells opens up the avenue of using these systems to assess the functions of pericytes in health and disease.
Tigges, U., Welser-Alves, J. V., Boroujerdi, A., & Milner, R. (2012). A novel and simple method for culturing pericytes from mouse brain. Microvascular research, 84(1), 74–80.