STAT3 and MEK Mediate IL6‐Induced Increase in Endothelial Permeability

Interleukin 6 (IL6) has been shown to induce loss of endothelial barrier function both in vivo and in vitro, but the mechanisms involved are not fully understood. Addition of IL6 together with the soluble form of the gp80 receptor (sIL6r) promoted the activation of multiple pathways, including JAK/STAT3, MEK/Erk and PI3K/Akt in HUVEC. IL6 induced an increase in endothelial permeability and loss of junctional VE‐cadherin and ZO‐1, without a reduction of VE‐cadherin or ZO‐1 protein levels. IL6‐induced STAT3 phosphorylation and loss of barrier function was prevented by treatment with the JAK inhibitor ruxolitinib, suggesting that JAK activity is required for these responses. Furthermore, siRNA‐mediated STAT3 knockdown attenuated the loss of IL6‐induced loss of barrier function. Overexpression of a constitutively active STAT3 however, was not sufficient to induce loss of barrier function by itself, suggesting the requirement of other concurrent signaling pathway(s) downstream of IL6. SFK inhibition by pretreatment with PP2 promoted a short delay, but did not prevent the loss of barrier function. Similarly, the PI3K inhibitor LY‐294002 was unable to prevent the increase in permeability by IL6. In contrast, pretreatment with the MEK inhibitor U0126 attenuated the loss of barrier function in response to IL6, suggesting the involvement of MEK activity in IL6‐induced endothelial hyperpermeability. Collectively, our data suggest that the activity of both STAT3 and MEK, but not SFK or PI3K, are required for the loss of endothelial barrier function through a loss of junctional protein localization but not a reduction of protein levels. Support or Funding Information AHA SDG grant 13SDG17100110