Where do growth factors come from?

Growth factors are produced and secreted by all cell types in the epidermis and dermis such as keratinocytes, melanocytes, and fibroblasts. These secreted growth factors can act in a paracrine or autocrine manner, influencing adjacent cells or cells that produced them. It has also been shown that growth factors originate from platelets, plasma, from the bone matrix, osteocytes, osteoblasts, and from bone marrow. Platelets contain various growth factors (e.g. PDGF, TGF-B) which are released at the site of injury to promote regeneration and tissue repair. In the laboratory, growth factors can be derived from different human cells such as bone marrow and fat stem cells. Stem cells in the bone marrow and other tissues produce growth factors which support tissue growth and maintenance. For example, mesenchymal stem cells are known to secrete factors and promote tissue repair. Osteocytes are involved in the regulation of bone remodeling. Growth factors such as IGF-1 play a crucial role in regulating the balance between bone resorption and formation (coupling bone remodeling). IGF-1 is one of the most abundant growth factors deposited in the bone matrix, is secreted locally, and has a direct relationship with bone mineral density.