The active form of platelet derived growth factor (PDGF) is a dimeric combination of two polypeptide chains: PDGF-A and PDGF-B. The protein can exist as a heterodimer (PDGF-AB) or as one of two homodimers (PDGF-AA, PDGF-BB), resulting in three isoforms. Two types of PDGF receptors also exist: PDGFRα and PDGFRß. The PDGFRß binds only the PDGF-B chain, while PDGFRα can bind both PDGF-A and -B chains. Both of these receptors show specific temporal and spatial expression patterns that are related to cellular responses including mitogenesis, cell migration, chemotaxis, adhesion and differentiation in a variety of cell types.
Spontaneous mutants in which the PDGFRα is absent exhibit fatal defects during fetal development in mice. Some of these malformities include cardiac septal, valve, and outflow tract defects. Similar defects occur when the function of PDGF-A is disrupted by blocking antibodies. Disruption of PDGF-B function, results in ventricular and atrial dilation, hyper-trabeculation and reduction of the ventricular wall to the thickness of a single cell layer.