VEGF-A is a dimeric glycoprotein synthesized by cross-linking two identical subunits (Mr. 23000) with disulfide bonds, with a molecular weight of 40-45KD. Its gene is located on chromosome 6p21.3, with a total length of 14kb and consists of 8 exons and 7 introns. Due to the different splicing methods of its mRNA, it forms seven existing forms, namely VEGF121, VEGF145, VEGF148, VEGF183, VEGF165, VEGF189, and VEGF206, each containing 121 to 206 amino acids, which are linked to a homologous dimer by disulfide bonds. VEGF165 has 44 amino acids encoded by exon 7 and has a high affinity for heparin. VEGF121, VEGF145, and VEGF165 can all induce endothelial cell proliferation and angiogenesis in vivo. Most VEGF-A expressing cells can simultaneously produce several VEGF-A variants, with VEGF121 and VEGF165 being the most common, followed by VEGF189.