Short-term mechanisms activated by NGF to induce pulmonary arterial hyperreactivity

Abstract

We have previously shown a pathophysiological role for NGF in pulmonary hypertension, particularly in pulmonary arterial (PA) hyperreactivity. Our experiments have suggested different mechanisms activated by NGF depending on a short‑ or a long-term PA treatment. The aim of the present study was to determine the mechanisms activated after a NGF short‑term PA treatment (1h). Contractions of rat PA were induced ex vivo by endothelin-1 (ET-1, 10-12-10-6M) in the absence or presence of NGF (100ng/ml, 1h), with or without K252a (TrkA kinase inhibitor, 300nM) or Y‑27632 (ROCK inhibitor, 10µM). NGF‑induced phosphorylation of myosin phosphatase target subunit 1 (MYPT1) was evaluated in vitro by Western blotting in primary human PA smooth muscle cells (hPASMC). Basal and ET-1-induced (10-7M) calcium responses were evaluated in vitro in primary rat PASMC (rPASMC) using calcium imaging (Fura2, Fluo-4), in the absence or presence of NGF (100ng/ml, 1h). Calcium sources involved in NGF-increased calcium concentration were determined using Thapsigargin (1µM), Cyclopiazonic Acid (10µM), or an extracellular medium without Ca²+. Ex vivo, our results show that NGF (1h) induces rat PA hyperreactivity to ET-1 in a TrkA and ROCK dependent-manner. In vitro, NGF (1h) induces MYPT1 phosphorylation in hPASMC and enhances both basal and ET-1-increased intracellular calcium concentrations in rPASMC, with endoplasmic reticulum being the main calcium source contributing to these effects. In conclusion, our results show that NGF induces PA hyperreactivity through activation of its TrkA receptor, leading to both modulation of calcium intracellular concentrations and sensitization mechanisms involving the ROCK pathway.