Overexpression of Neurotrophin 4 in Skin Enhances Myelinated Sensory Endings but Does Not Influence Sensory Neuron Number

The study investigated the effects of overexpressing neurotrophin 4 (NT4) in the skin of transgenic mice to understand its role in sensory development. It was found that NT4 overexpression increased skin innervation, enhanced hair follicle innervation, and increased the size and density of Meissner corpuscle innervation, similar to the effects of brain-derived neurotrophic factor (BDNF) overexpression. However, unlike BDNF, NT4 did not change the number of Merkel cells in glabrous skin but did increase the number of myelinated axons in nerves projecting to the skin. Despite these changes, there was no increase in the total number of sensory neurons in the dorsal root ganglion or trigeminal ganglion, indicating that NT4 and BDNF have both overlapping and distinct effects on cutaneous sensory innervation.