mouse NGF 2.5S-ATTO Fluor-647N

The neurotrophins ("neuro" means nerve and "trophe" means nutrient) are a family of soluble, basic protein growth factors which regulate neuronal development, maintenance, survival and death in the CNS and PNS¹.

NGF, the first member of the family to be discovered, was originally purified as a factor supporting and regulating survival, development, function and plasticity of sympathetic and sensory spinal neurons in central and peripheral nervous systems in vivo as well as in vitro^2-4. It is synthesized and secreted by sympathetic and sensory target organs and provides trophic support to neurons as they reach their final target⁵.

Neurotrophin secretion increases in the nervous system following injury. Schwann cells, fibroblasts, and activated mast cells normally synthesize NGF constitutively, however, direct trauma and induction of cytokines combine to increase neurotrophin production in these cells after injury⁶.

NGF is purified in three forms: the 7S, 2.5S and β, in which the biologically active subunit is the β subunit. The structural hallmark of all the neurotrophins is the characteristic arrangement of the disulfide bridges known as the cysteine knot, which has been found in other growth factors such as Platelet-derived growth factor⁷.

Additionally, the involvement of NGF was recently discovered in processes such as asthma⁸, psoriasis⁹ and wound healing¹⁰. The biological effects of NGF are mediated by two receptors: TrkA, which is specific for NGF, and p75^NTR, which binds all the neurotrophins¹¹.

For the past three decades, biotinylated derivatives of NGF have been widely used in the literature as useful probes for the study of the binding and the initial intracellular processing of this growth factor by cells bearing TrkA NGF receptor¹². First studies using ¹²⁵I-NGF have visualized the intracellular location of NGF¹². A biotinylated derivative of NGF that retains biological activity, in conjunction with the appropriate avidin conjugates and fluorescent or confocal microscopic techniques, improve the sensitivity and resolution in many applications. Some examples of applications are: targeting of liposomes containing biotinylated NGF to cells bearing TrkA NGF receptors¹³; elucidating the kinetics and route of ligand-induced internalization of the p75 receptor through signaling endosomes in cycling and differentiated PC12 cells using biotinylated derivative of NGF¹⁴; electrically controlled NGF-Biotin delivery from biotin-doped conductive polymer¹⁵; studying the retrograde axonal transport mechanism of NGF signals from the axon terminal to the cell body^16,17.