CD36 is a protein found on the surface of many cells throughout the body. Despite its relatively small size, this protein plays a wide range of roles in various biological processes. Its widespread presence and diverse functions impact overall health and bodily function. Understanding CD36 provides insight into how cells interact with their environment and manage various molecular signals.
Understanding CD36 Protein
CD36 is a multi-functional transmembrane glycoprotein. It is part of the “scavenger receptor” family, which means it helps cells take up various molecules from their surroundings. This protein acts as a gatekeeper and sensor for numerous compounds.
CD36 is abundantly present in several key tissues and cell types. These include fat cells (adipocytes), various immune cells like monocytes and macrophages, platelets involved in blood clotting, and endothelial cells that line blood vessels. It is also expressed in skeletal and cardiac muscle cells, liver cells (hepatocytes), and even taste buds. The protein has a large part that extends outside the cell, where it binds to different molecules.
Key Functions of CD36
Fatty Acid Transport
CD36 plays a role in the uptake and metabolism of long-chain fatty acids (LCFAs) by various cells. It is classified as a “fatty acid translocase” because it helps move these fatty acids across the cell membrane into the cell. This function is important for energy production, as LCFAs are a major fuel source for cells, and for fat storage within the body. CD36 is also involved in the transfer of fatty acids into mitochondria, which are the cell’s powerhouses.
Immune Response and Inflammation
CD36 functions as a scavenger receptor, recognizing and binding to a variety of molecules. These include oxidized low-density lipoprotein (oxLDL), which is a modified form of cholesterol, as well as components of pathogens and apoptotic (dying) cells. CD36’s involvement in clearing dead cells, a process called efferocytosis, helps prevent excessive inflammation and supports tissue repair. CD36 on macrophages can also take up lipids, contributing to inflammatory responses.
Sensory Perception
CD36 has a role in sensory perception, particularly in the detection of dietary fats. It is considered a sensor for fatty taste, sometimes referred to as the “sixth taste,” and is expressed on taste receptor cells in the tongue. When long-chain fatty acids interact with CD36 in taste buds, it can lead to signals being sent to the brain and digestive system, influencing food preference and digestive enzyme release. Beyond taste, CD36 has also been implicated in olfaction, the sense of smell.
Platelet Function and Blood Clotting
CD36 is involved in the process of platelet activation and aggregation, which are steps in forming blood clots to stop bleeding. It binds to various ligands, and its interaction with oxidized low-density lipoprotein can make platelets more sensitive to activation. This can lead to platelet aggregation and adhesion, which are important for proper clot formation. CD36 also interacts with certain coagulation factors, contributing to the blood clotting cascade.
CD36’s Role in Health and Disease
Metabolic Disorders
Dysregulation of CD36’s functions can contribute to several metabolic disorders, including obesity, insulin resistance, and type 2 diabetes. Increased CD36 expression in certain tissues, such as adipose tissue and pancreatic beta cells, can lead to increased fatty acid uptake and lipid accumulation, exacerbating these conditions. Higher levels of soluble CD36 in the blood have been linked to obesity and insulin resistance. CD36 overexpression in pancreatic beta cells can impair insulin secretion and reduce insulin release, contributing to type 2 diabetes development in obese individuals.
Cardiovascular Disease
CD36 plays a role in cardiovascular diseases, particularly atherosclerosis, which is the hardening of arteries. On macrophages, CD36 takes up oxidized low-density lipoprotein (oxLDL), leading to the formation of “foam cells” that accumulate in arterial walls and contribute to plaque buildup. Studies suggest CD36’s role in atherosclerosis can be complex. CD36’s involvement in platelet function also links it to conditions like thrombosis (blood clot formation), myocardial infarction (heart attack), and stroke risk.
Cancer
The role of CD36 in cancer progression is an active and complex area of research. CD36 is expressed in various tumor types, with its levels correlating with advanced stages, poorer prognosis, and reduced survival rates. In cancer cells, CD36 can increase fatty acid uptake, which reprograms how tumor cells use lipids for energy and growth. This can favor cancer cell proliferation and promote cancer spread. CD36 expression has also been linked to cancer stem cell markers, with CD36-positive cancer cells showing increased abilities for initiating metastasis.
Infectious Diseases
CD36 is recognized for its role as a receptor for Plasmodium falciparum-infected red blood cells, which is a key mechanism in severe malaria. Plasmodium falciparum parasites, which cause malaria, display proteins on the surface of infected red blood cells that bind to CD36 on the lining of blood vessels. This binding prevents the infected red blood cells from being cleared by the spleen, allowing the parasites to multiply and contributing to the severity of the infection.