Neurotrophin-3

Where it comes from

Made in

Muscle spindles and muscle, the inner ear, gut, and the developing nervous system

Sent out by

During development, and from muscle after nerve injury

Acts on

• Proprioceptive sensory neurons
• Cochlear and vestibular neurons
• Sympathetic and enteric neurons
• Oligodendrocytes

What it does

• Keeps the neurons of position sense alive; mice without it cannot coordinate movement
• Wires the hair cells of the inner ear to the brain
• Supports the enteric nervous system and myelin repair

In medicine

• No medicine. Injected NT-3 was tolerated in small human studies and improved bowel function in a phase 2 trial in functional constipation ²
• In Charcot-Marie-Tooth disease type 1A it was positive in a pilot study of eight patients, four of them treated, which awaits confirmation ¹

Beyond the body’s own use

• The constipation trial is the largest randomised human result: in 107 patients, NT-3 under the skin three times a week increased spontaneous bowel movements and speeded colon transit, while once-weekly dosing did nothing ²
• That programme was not taken further, and the injection-site reactions seen in a third of those treated are part of the reason an injected neurotrophin is a hard medicine to make ²
• The route now taken is gene transfer: an AAV1 vector carrying NT-3 into muscle promoted nerve regeneration in mouse models of Charcot-Marie-Tooth type 1A and has moved into early human trials ³
• Regrowing the nerve supply of the inner ear after noise damage is an animal result, and no human trial of NT-3 for hearing has been run