Lysophosphatidic acid (LPA) is a simple phospholipid composed of a phosphate group, a glycerol moiety, and a single hydrocarbon chain. Despite its simple structure, LPA functions as a bioactive signaling molecule through its six specific G protein-coupled receptors, LPA1–LPA6.
Apolipoprotein(a) [Apo(a)] is the primary component of lipoprotein(a) [Lp(a)]. It exhibits serine proteinase activity and undergoes autoproteolysis. Apo(a) inhibits tissue-type plasminogen activator (t-PA). Lp(a) may serve as a ligand for megalin/Gp330. Proteolytic cleavage of Apo(a) results in the formation of mini-Lp(a). Apo(a) fragments accumulate in atherosclerotic lesions, potentially promoting thrombogenesis. O-glycosylation may limit proteolytic fragmentation. The homology of Apo(a) with plasminogen kringles IV and V is believed to contribute to its atherogenicity, as these fragments compete with plasminogen for fibrin(ogen) binding.