Glossary
Neurotrophin
The neurotrophins (NGF, BDNF, NT-3, NT-4/5) are four growth factors that signal via Trk receptors and p75NTR. Their structure, receptors and research context.
The neurotrophins form a small family of secreted growth factors: NGF, BDNF, NT-3 and NT-4/5. Each of the four adopts a cystine-knot fold, assembles into non-covalent homodimers and is made as a pro-form that furin or proconvertases cleave. Together they control whether neurons survive, how axons grow, how strong synapses are and, in sensory neurons, how sensitised nociceptors become.
How the receptors decide the outcome
Two receptor systems work side by side. The Trk receptor tyrosine kinases provide selectivity: TrkA favours NGF, TrkB favours BDNF and NT-4/5, and TrkC favours NT-3, which also shows some TrkA/TrkB cross-reactivity. The p75 neurotrophin receptor, part of the TNF-receptor superfamily, binds all four with comparable affinity and, together with sortilin, prefers the unprocessed pro-forms — in which case it signals apoptosis and growth-cone collapse. Whether a neurotrophin keeps a neuron alive or removes it thus depends on its processing state and on the receptors that cell displays.
A catalogue note: the neurotrophins themselves are recombinant proteins rather than synthetic peptides. Small peptides sold in the cognitive category are investigated as modulators of neurotrophin expression or as Trk-targeted mimetics, and that difference should be kept clear in any experimental report.
Related terms and material
nootropic · recombinant · in vitro. Reference material: neurotrophin research family, nootropic peptides. Further reading: brain research hub.