Neurotrophic tyrosine kinase receptor B/neurotrophin 4 signaling axis is perturbed in clinical and experimental pulmonary fibrosis.

The neurotrophins (NTs) are emerging as exciting new participants in normal lung physiology, as well as in several pathological processes in diseased lungs. In this study, the increased expression of NT4/5 and of its cognate receptor, the neurotrophic tyrosine kinase receptor Type 2 (TrkB), was observed in human lungs explanted from patients with idiopathic pulmonary fibrosis (IPF), and in lungs from mice with bleomycin-induced pulmonary fibrosis. The expression of NT4/5 and TrkB localized to hyperplastic alveolar Type II cells (ATII) and fibroblastic foci in affected lungs.