VPP 211: General Veterinary Pathology (1+1)

GROWTH FACTORS

Growth factors (GF) act by autocrine, paracrine, endocrine or signalling pathways. GFs play a role in the movement of inflammatory cells, in contractility of cells, differentiation and in wound healing. These are polypeptides found in the serum and/or elaborated by cells.

The main growth factors are:

• Epidermal growth factor (EGF): It is a polypeptide of 6-kDa, a progression factor which acts by combining with EGF receptors in the cell membrane. Transforming growth factor-alpha (TGF-α) is homologous to this factor. Both are mitogenic for epithelial cells and fibroblasts.
• Platelet derived growth factor (PDGF): It is stored in platelets and of 30-kDa size. PDGF may be released upon activation of platelets, macrophages, endothelium and tumour cells. It is a complement factor and requires a progression factor for its activation. PDGF is responsible for migration and proliferation of fibroblasts, macrophages and smooth muscle cells. Therefore, PGDF is important in angiogenesis.
• Fibroblast growth factor (FGF): It includes acidic and basic FGFs. These are involved in angiogenesis, cell migration and proliferation of endothelial cells. Besides, they are involved in wound repair, development and haematopoesis. Basic FGFs are found in many organs and released by activated macrophages. Acidic FGF is usually found in neural tissue.
• Transforming growth factor-beta (TGF-β): It is derived from platelets, endothelium, T cells and macrophages.It induces fibrosis by stimulating fibroblast chemotaxis, collagen and fibronectin synthesis and inhibition of collagen degradation. It is also inhibitory to most epithelial cells’ growth.
• Vascular endothelial growth factor (VEGF): It promotes formation of blood vessels (Angiogenesis), also plays a role in angiogenesis of chronic inflammation and healing of wounds. Specifically, lymphatic endothelial cell proliferation induced by VEGF.
• Tumour necrosis factor-alpha (TNF-α) and Interleukin-1 (IL-1) : These cytokines play a role in fibroplasia by attracting fibroblasts and increasing collagen synthesis. TNF-α is also angiogenic in nature.