PDGF-AA (Platelet-Derived Growth Factor AA) is a widely expressed protein that forms disulfide linked homodimers or heterodimers with PDGF-B. PDGF-AA is expressed by monocytes, macrophages, fibroblasts, vascular smooth muscle cells, and vascular endothelial cells. It acts principally as a chemoattractant and inducer of protein synthesis in multiple cell types. PDGF-AA binds and signals through homodimers of the receptor tyrosine kinase PDGF R alpha which itself associates with FGF R1 and Neuropilin-1. PDGF-AA additionally signals through heterodimers of PDGF R alpha and PDGF R beta.