Oncostatin M downregulates the brain endothelial barrier integrity through long-lasting activation of JAK/STAT3 pathway

Oncostatin M (OSM) belongs to the member of interleukin (IL)-6 families. We previously demonstrated that OSM induced the downregulation of blood brain barrier (BBB) function. However, it is not known how the intracellular signaling pathway is involved in OSM-induced BBB impairment and how the other members of IL-6 families including IL-6 and leukemia inhibitory factor (LIF) regulate BBB function. In this study, we demonstrate that OSM among the IL-6 families shows the most powerful property to induce BBB dysfunction via an activation of Janus-activated kinase (JAK)/ signal transducers and activator of transcription (STAT) 3 pathway. We used the in vitro BBB model constructed by rat brain endothelial cells (RBECs) to evaluate the effect of OSM, IL-6 and LIF on BBB function. Two parameters, the permeability of sodium fluorescein (Na-F) and the transendothelial electrical resistance (TEER), were used to detect the barrier integrity of tight junctions (TJs). An exposure of OSM for 24 h produced the increased Na-F permeability and the decreased TEER, but not IL-6 and LIF in the in vitro BBB model. This OSM-induced impairment of the barrier integrity was accompanied with decreased levels of the claudin5 expression in RBECs; these were ameliorated by the inhibition of JAK signaling (an upstream of STAT3 signaling). To determine the reason why OSM among IL-6 families specifically showed the inhibitory effect on BBB function, we examined the time-course of STAT3 phosphorylation in RBECs treated with OSM, IL-6 and LIF (100 ng/mL). OSM up-regulated the phosphorylation levels of STAT3 for 24 h with a peak at 10 min. On the other hand, the exposure of RBECs to IL-6 and LIF for 10 min, but not for more than 60 min, produced the phosphorylated STAT3. These findings suggested that OSM-induced long-lasting increases in the phosphorylation levels of STAT3 largely contributes to the impairment of BBB integrity. Thus, the elevated OSM and the activated JAK/STAT3 pathway has to be considered as a possible mechanism underlying the induction and development of BBB dysfunction under the inflammatory conditions.