CAMP‐dependent Rac 1 inactivation is associated with LPS‐induced endothelial barrier breakdown

Abstract

Lipopolysaccharide (LPS)‐induced breakdown of endothelial barrier functions contributes largely to the pathogenesis of sepsis. However, the underlying mechanisms are still unclear. In the present study, incubation of human dermal microvascular endothelial cells with LPS led to a breakdown of endothelial barrier functions within 2–2.5h as revealed by measurements of FITC‐dextran flux and of transendothelial electrical resistance. This was associated with the formation of intercellular gaps, stress fibers and fragmentation of VE‐cadherin immunostaining. Moreover, claudin 5 immunostaining at cell borders was reduced after LPS‐treatment. Activity of small GTPase Rho A, which has been suggested to mediate the LPS‐induced breakdown of the endothelial barrier was not increased after 2h. In contrast, activity of Rac 1, which is known to be important for maintenance of endothelial barrier functions, was significantly reduced to 65 ± 9% after 2h. All LPS‐induced changes of endothelial cells were blocked by a Forskolin/Rolipram‐mediated increase of cAMP. Consistently, LPS led to a significant decrease of intracellular cAMP‐levels to 41 ± 2% after 1h and to 46 ± 8% after 2h. In summary, we suggest that LPS disrupts endothelial barrier functions by decreasing intracellular cAMP‐levels which in turn leads to an inactivation of Rac 1‐activity. Moreover, this mechanism appears to be involved in claudin 5 regulation.