Human Apolipoprotein H (APOH) Protein

Background

Apolipoprotein H (APOH), also known as β2-glycoprotein I, is a multifunctional glycoprotein involved in lipid transport, coagulation, and immune regulation. APOH is primarily synthesized in the liver and circulates in the bloodstream, where it binds to phospholipids and lipoproteins, particularly VLDL and chylomicrons. APOH has a significant role in antiphospholipid syndrome (APS), an autoimmune disorder characterized by the presence of antiphospholipid antibodies that interfere with blood clotting. APOH interacts with anionic phospholipids and influences coagulation pathways, contributing to its function as a regulator of hemostasis and thrombosis. It also participates in lipid metabolism, facilitating the clearance of triglyceride-rich lipoproteins by binding to receptors on hepatocytes. Beyond its role in coagulation, APOH has immunological functions, such as modulating inflammatory responses and pathogen recognition, positioning it as a key player in the innate immune system. Elevated APOH levels have been associated with autoimmune diseases, cardiovascular disorders, and infectious diseases, underscoring its role in both homeostasis and disease progression. APOH’s diverse activities, including its interactions with lipids, immune factors, and coagulation pathways, make it an essential protein in physiology and a potential therapeutic target in autoimmune and thrombotic diseases.