Prostaglandin D2 (PGD2) is a lipid signaling molecule belonging to the prostaglandin family. It originates from arachidonic acid, a fatty acid found in cell membranes, and acts as a local mediator in numerous biological processes. PGD2 exerts diverse effects throughout the body, influencing various cellular activities and tissue functions.
What Prostaglandin D2 Does in the Body
PGD2 is synthesized through a specific pathway involving enzymes like prostaglandin D synthase, which converts prostaglandin H2 (PGH2) into PGD2. This conversion is a step in the arachidonic acid cascade, a series of reactions that produce various lipid mediators. PGD2 is found in many tissues, including the central nervous system and peripheral tissues like immune cells, endothelial cells, and cardiomyocytes.
This molecule influences smooth muscle activity, leading to either contraction or relaxation depending on the tissue and receptor type. For example, it can cause bronchoconstriction in airways and affect blood vessel diameter. PGD2 also participates in the body’s inflammatory response, modulating the activity of various immune cells.
Prostaglandin D2 and Allergic Reactions
PGD2 plays a role in allergic and inflammatory conditions, particularly those involving mast cells. During an allergic response, mast cells release PGD2, acting as a mediator. This release contributes to symptoms of allergic asthma, such as airway narrowing (bronchoconstriction) and increased mucus production. In allergic rhinitis, elevated PGD2 levels contribute to nasal congestion and sneezing.
PGD2 interacts with specific receptors on immune cells, namely D prostanoid 1 (DP1) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2 or DP2). These interactions help to recruit immune cells like Th2 cells, eosinophils, and basophils, intensifying the allergic symptoms.
Prostaglandin D2 and Hair Growth
Research has identified a link between elevated levels of PGD2 in the scalp and androgenetic alopecia, commonly known as male and female pattern baldness. In individuals experiencing this type of hair loss, hair follicles undergo miniaturization, a process where they shrink and produce progressively finer, shorter hairs until they cease production altogether. PGD2 contributes to this miniaturization by inhibiting hair growth. It achieves this effect by interacting with specific receptors on hair follicle stem cells, disrupting the normal hair growth cycle. Increased PGD2 in the scalp suppresses the regenerative capacity of these follicles, leading to hair thinning and loss.
Prostaglandin D2 and Sleep
Beyond its roles in inflammation and hair biology, PGD2 also functions as an endogenous sleep-promoting substance within the brain. During periods of wakefulness, PGD2 levels gradually increase in the brain. This accumulation signals the body to transition into sleep, specifically promoting non-REM (rapid eye movement) sleep. PGD2 exerts its sleep-inducing effects by acting on specific brain regions, such as the preoptic area, which is involved in sleep regulation. It interacts with its receptors in these areas to initiate and maintain the sleep state.