The neurotrophin family (Neurotrophins, NTs) is a family of structurally and functionally related peptides which regulates neural survival, development, function, and plasticity. In mammals, NTs consists of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), NT-4/5. Two additional members, NT-6 and NT-7 have been identified only in fish, but mammalian homologs have not yet been identified. NTs mediate their actions by binding to 2 classes of receptors, the tropomyosin receptor kinase (trk) family of receptor tyrosine kinases, and a member of the tumour necrosis factor (TNF)-α family of receptors, p75. NGF binds TrkA, BDNF and NT-4 bind TrkB, and NT-3 binds TrkA, TrkB, and TrkC. In addition, all NTs activate p75 with low affinity, enhancing the activation of Trk receptors. Through these, NTs activate many signaling pathways, including those mediated by ras and members of the cdc-42/ras/rho G protein families, and the MAP kinase, PI-3 kinase, and Jun kinase cascades.
