“…Apart from VEGF, other key molecules involved in neovascularization in DR include platelet-derived growth factor (PDGF), placental growth factor (PlGF) and others. Platelet-derived growth factors are secreted by platelets, endothelial cells, activated macrophages and smooth muscle cells and are vital players of DR ( 49 – 51 ); PDGF has 4 polypeptide chains(PDGF-A, PDGF-B, PDGF-C, and PDGF-D) and becomes active by homodimer isoform formation such as PDGF-AA, PDGF-BB, PDGF-CC and PDGF-DD or heterodimeric form PDGF-AB. PDGF ligands will bind to transmembrane tyrosine kinase PDGF receptors, which contain homodimeric and heterodimeric isoforms such as PDGFR-αα, PDGFR-ββ and PDGFR-αβ ( 50 ).…”