Mechanism of Action
BDNF binds at least two receptors on the surface of cells that are capable of responding to this growth factor, TrkB (pronounced "Track B") and the LNGFR (for low-affinity nerve growth factor receptor, also known as p75). It may also modulate the activity of various neurotransmitter receptors, including the Alpha-7 nicotinic receptor.
TrkB is a receptor tyrosine kinase (meaning it mediates its actions by causing the addition of phosphate molecules on certain tyrosines in the cell, activating cellular signaling). There are other related Trk receptors, TrkA and TrkC. Also, there are other neurotrophic factors structurally related to BDNF: NGF (for Nerve Growth Factor), NT-3 (for Neurotrophin-3) and NT-4 (for Neurotrophin-4). While TrkB is the primary receptor for BDNF and NT-4, TrkA is the receptor for NGF, and TrkC is the primary receptor for NT-3. NT-3 binds to TrkA and TrkB as well, but with less affinity (thus the caveat "primary receptor").
The other BDNF receptor, the p75, plays a somewhat less clear role. Some researchers have shown that the p75NTR binds and serves as a "sink" for neurotrophins. Cells that express both the p75NTR and the Trk receptors might, therefore, have a greater activity, since they have a higher "microconcentration" of the neurotrophin. It has also been shown, however, that the p75NTR may signal a cell to die via apoptosis; so, therefore, cells expressing the p75NTR in the absence of Trk receptors may die rather than live in the presence of a neurotrophin.
Read more about this topic: Brain-derived Neurotrophic Factor
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