Apolipoprotein is the protein part of plasma lipoprotein that can bind and transport blood fat to various tissues of the body for metabolism and utilization. A large number of studies have found that the mutation of apolipoprotein gene can form polymorphisms of different alleles and further form apolipoprotein with different phenotypes, which can affect the metabolism and utilization of blood fat, thus affecting the occurrence and development of hyperlipidemia, atherosclerosis and cardiovascular and cerebrovascular diseases. Apolipoprotein is the protein component of plasma lipoprotein, which can be divided into five categories: A, B, C, D and E. Its basic function is to transport adipose and stabilize the structure of lipoprotein. Some apolipoprotein also has functions of activating lipoprotein metabolic enzymes and recognizing receptors. APO is mainly synthesized in the liver (partly in the small intestine) and is named according to the ABC system. Each class can be subdivided into several subclasses, represented by Roman numerals.

Apolipoprotein is an important component of plasma lipoprotein, endows lipids with soluble form, and plays an important role in plasma lipoprotein metabolism:1. Promoting lipid transport;2. Regulating enzyme activity;3. Guiding the binding of plasma lipoprotein to cell surface receptors. It is an extremely active group of plasma proteins. Here are some typical apolipoproteins:

APOA1
APOA1 is the most common component of APOA group, and is the main apolipoprotein in HDL. The physiological functions of APOA1 include: 1. Make up lipoprotein and maintain its structural stability and integrity. Experiments showed that APOA1 could spontaneously bind to lipids in aqueous solution. 2.APOA1 can activate the activity of lecithin cholesterol acyl transferase (LCAT) transfer. It has been confirmed that APOA1 catalyzes cholesterol esterification by activating LCAT. APOA1 peptides Ⅲ (peptides 116-151) is the center of activation; 3. Some scholars reported that APOA1 can act as a ligand of HDL receptor; APOA1 can form macromolecular complexes with transferrin and copper-blue proteins to transport iron and copper ions.

APOA4
APOA4 is an apolipoprotein with polymorphism and a biological half-life of 10h, which was first found in rats DHL and CM. Its physiological function is unknown now, but it is presumed to play an important role in the reverse transport of HDL.

APOC2
APOC2 is involved in the regulation of lipoprotein metabolism, especially plays an important role in the regulation of plasma rich TG lipoprotein catabolism. High concentration of 1 will inhibit the hydrolysis of rich TG lipoprotein, or affect the liver receptor's uptake of rich TG lipoprotein, causing the increase of plasma TG level and the formation of hypertriglyceridemia. It can also inhibit the activity of lecithin cholesterol acyltransferase. The main manifestations of APOC2 are:

Increased: Ⅰ, Ⅱ high lipoprotein hematic disease, primary biliary cirrhosis, nephrotic syndrome, etc.

Decreased: coronary heart disease, liver cirrhosis, APOC Ⅱ deficiency, etc.

APOE4
APOE4 is a polymorphic protein involved in the transformation and metabolism of lipoproteins. Its genes can regulate many biological functions and are related to the incidence of many eye diseases. The study of APOE4 and its gene polymorphism is one of the hot spots in medical research at present. To explore their internal relationship has important clinical application value for the prevention, diagnosis and treatment of eye diseases. APOE4 has the following physiological functions: 1. It is a ligand of LDL receptor and CM residue receptor of liver cells, which is closely related to lipoprotein metabolism; 2. APOE4 has polymorphism, which is closely related to the occurrence and development of atherosclerosis.3. Participate in the activation of lipolytic enzymes, the immune regulation and the regeneration of nerve tissue.

Since the early 1980s, with the development and application of molecular biology technology, the cDNA and genes of APO A1, A2, A4, (a), B, C1, C2, C3, C4, D, E, F, H and J have been isolated and identified. The chromosomal localization of these apolipoprotein genes has also been completed. The identification of apolipoprotein cDNA and genes and the chromosomal localization provide a new tool for the in-depth study of the structure and function of apolipoprotein, the expression and regulation of apolipoprotein genes, and the relationship between genetic variation of apolipoprotein genes and atherosclerosis. Polymorphisms of various apolipoprotein genes have been reported in a large number of literatures. The in-depth study of apolipoprotein is of great significance for the diagnosis and treatment of abnormal lipoprotein metabolism and early atherosclerosis.