Growth factors are signalling proteins that stimulate cell growth, differentiation, survival, inflammation, proliferation and tissue repair and regeneration. Growth factors are important for regulating a variety of cellular processes and are typically secreted at the site of repair by many cell types including platelets, stem cells, and fibroblasts. Normal cells require growth factors to maintain viability and they can exert their effects though endocrine, paracrine or autocrine mechanisms. Growth factors act as signalling molecules between cells and due to their slow diffusion in intercellular spaces they usually act locally.
Individual growth factor proteins often occur within families of proteins, including angiopoietins, bone morphogenetic proteins, ephrins, erythropoietin, the glial cell line-derived neurotrophic factor (GDNF) family, interleukins, neuregulins, neurotrophins, ephrins, the insulin family, thrombopoietin, the vascular endothelial growth factor family (VEGR), the epidermal growth factor family (EGF), the platelet-derived growth factor family (PDGF) and the fibroblast growth factor family (FGF). PDGF is the major protein growth factor in human serum. Growth factors are very important in disease states, with VEGR, FGFR, EGFR and PDGR having major roles in cancer progression and FGF, EGF, and nerve growth factor (NGF) playing key roles in brain or spinal cord injury and acute organ injuries.