Focal adhesion kinase mediates microvascular leakage and endothelial barrier dysfunction in ischemia-reperfusion injury.

Intestinal ischemia-reperfusion (I/R) injury occurs under various surgical or disease conditions, where tissue hypoxia followed by reoxygenation results in the production of oxygen radicals and inflammatory mediators. These substances can target the endothelial barrier, leading to microvascular leakage. In this study, we induced intestinal I/R injury in mice by occluding the superior mesenteric artery, followed by removing the clamp to resume blood circulation. We assessed microvascular permeability to plasma proteins in vivo using intravital microscopy, measuring the time-dependent tracer distribution in the intravascular versus extravascular space in the mouse mesentery. Additionally, we examined endothelial cell-cell adhesive barrier resistance and junction morphology in cultured endothelial cell monolayers. At the molecular level, FAK inhibition similarly inhibited endothelial junction opening and barrier dysfunction in response to hydrogen peroxide-induced oxidative stress. To further investigate FAK's role with tissue/cell specificity, we developed an endothelial-specific inducible FAK knockout mouse model by crossbreeding FAK-floxed (FAK) mice with Tie-2-CreER transgenic mice. Compared to their wild-type controls, endothelial-specific FAK-deficient mice showed a blunted microvascular hyperpermeability response following I/R injury in the gut. Overall, our study demonstrates that FAK plays a significant signaling role in mediating endothelial barrier dysfunction and microvascular leakage during ischemia-reperfusion injury.