Oncostatin M-induced blood-brain barrier impairment is due to prolonged activation of STAT3 signaling in vitro

Oncostatin M (OSM) is a member of the interleukin (IL)-6 family cytokines. We previously demonstrated that OSM induces blood-brain barrier (BBB) impairment. However, functional characterization of IL-6 family cytokines in BBB regulation and the cytokine-related intracellular signaling pathway remain unclear. In this study, we demonstrate that among IL-6 family cytokines, including IL-6 and leukemia inhibitory factor (LIF), OSM is the most potent molecule for inducing BBB dysfunction via prolonged activation of signal transducer and activator of transcription (STAT) 3 following Janus-activated kinase (JAK) activation. OSM but not IL-6 and LIF (100 ng/mL for 24 hours) markedly produced increased sodium fluorescein permeability and decreased transendothelial electrical resistance in rat brain endothelial cell (RBEC) monolayers. This OSM-induced BBB dysfunction was accompanied by decreased levels of claudin-5 expression in RBECs, which were ameliorated by JAK inhibitor. We examined the time-course of STAT3 phosphorylation in RBECs treated with OSM, IL-6, and LIF. OSM upregulated STAT3 phosphorylation levels during a 24 hours period with a peak at 10 minutes. While IL-6 and LIF transiently increased phosphorylated STAT3 at 10 minutes after addition, this phosphorylation decreased during the period from 1 to 24 hours after addition. These findings suggest that OSM-induced sustained increases in STAT3 phosphorylation levels largely contribute to BBB impairment. Thus, elevated OSM levels and activation of brain endothelial JAK/STAT3 signaling pathway under pathological conditions should be considered as a possible hallmark for induction and development of BBB impairment.