IGF1 and intervertebral disk degenerative disorder: During IDD development, several growth promoting factors such as insulin-like growth factor 1 (IGF-I), platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF) exert their beneficial effects (i.e., mitogenic action) via activating ERK by phosphorylation and subsequent DNA synthesis in degenerated disc cells, indicating that MAPKs may be involved in metabolic processes in the IVD 46.