PECAM, also known as CD31, is a protein that helps cells stick together. It is a fundamental part of how cells interact, particularly those involved in blood and blood vessel function. Understanding PECAM’s role provides insight into various health conditions.
Defining PECAM and Its Location
PECAM, or Platelet Endothelial Cell Adhesion Molecule, is a transmembrane glycoprotein. It spans across the cell’s outer membrane and has sugar molecules attached. The protein weighs approximately 130 kilodaltons (kDa). Its structure includes six immunoglobulin-like domains on its outer part, which are involved in cell interactions.
This protein is found on the surface of several cell types within the vascular system. It is present on endothelial cells, which form the inner lining of blood vessels, and is concentrated at the junctions where these cells meet. PECAM also appears on platelets, involved in clotting, and on certain white blood cells, including monocytes, neutrophils, and some T cells.
PECAM’s Functions in the Body
PECAM plays a multifaceted role in mediating how cells interact, especially within the circulatory system. One of its primary functions involves cell-to-cell adhesion, where it helps cells bind to each other. This adhesive property is important in maintaining the integrity of blood vessel walls and facilitating interactions between endothelial cells and other blood cells.
A significant role for PECAM is in leukocyte transmigration, also known as diapedesis. This is the process where white blood cells, such as monocytes and neutrophils, move from inside blood vessels through the vessel walls into surrounding tissues. PECAM facilitates this migration by forming a “homophilic interaction,” meaning PECAM on the leukocyte surface binds to PECAM on the endothelial cell surface, guiding the white blood cell across the barrier. This step is a necessary part of the body’s immune response and inflammatory processes, allowing immune cells to reach sites of infection or injury.
PECAM also contributes to maintaining vascular integrity, which refers to the strength and stability of blood vessel walls. It helps in forming and maintaining the tight junctions between endothelial cells, which are like seals that prevent leakage from blood vessels. This function is important for controlling vascular permeability and ensuring that blood components remain within the vessels. Furthermore, PECAM has a role in the initial stages of angiogenesis, the process of forming new blood vessels. It can influence the formation of new endothelial cell tubes, which are the foundational structures of new blood vessels.
PECAM’s Impact on Health and Disease
Dysregulation or altered expression of PECAM can contribute to various health conditions. In inflammation, abnormal PECAM activity can alter or worsen the inflammatory response. For example, if leukocyte transmigration is not properly regulated by PECAM, too many or too few immune cells might reach a site of inflammation, leading to prolonged or ineffective responses.
PECAM is also implicated in the development and progression of atherosclerosis, a condition where plaque builds up inside arteries. Its involvement in cell adhesion and inflammatory processes within blood vessels can contribute to the formation and growth of these plaques. The protein’s role in endothelial cell interactions and leukocyte movement makes it a factor in the complex events that lead to arterial hardening.
In cancer, PECAM can influence both tumor angiogenesis and metastasis. Tumor angiogenesis refers to the formation of new blood vessels that supply nutrients to growing tumors, allowing them to expand. PECAM’s involvement in this process means it can promote the growth of these blood vessels. PECAM may also play a part in metastasis, the spread of cancer cells from the primary tumor to other parts of the body.
PECAM’s involvement also extends to autoimmune disorders, where the immune system mistakenly attacks the body’s own tissues. PECAM-1 can act as an inhibitory receptor in circulating platelets and leukocytes. Its ability to regulate immune cell activation and migration suggests a potential role in these conditions. For example, studies in mice lacking PECAM-1 have shown increased numbers of certain B cells and the development of autoantibodies, indicating its influence on immune system balance.