Microtubule system in endothelial barrier dysfunction: Disassembly of peripheral microtubules and microtubule reorganization in internal cytoplasm

Endothelial cell barrier dysfunction is associated with dramatic cytoskeletal reorganization, the activation of actomyosin contraction, and, finally, gap formation. Although the role of microtubules in the regulation of endothelial cell barrier function is not fully understood, a number of observations allow for the assumption that the reaction of the microtubule is an extremely important part in the development of endothelial dysfunction. These observations have forced us to examine the role of microtubule reorganization in the regulation of the endothelial cell barrier function. In quiescent endothelial cells, microtubule density is the highest in the centrosome region; however, microtubules are also present near the cell margin. The analysis of microtubule distribution after specific antibody staining using the method of measurement of their fluorescence intensity showed that, in control endothelial cells, the reduction of fluorescence intensity from the cell center to its periphery is described by the equation of exponential regression. The edemagenic agent, thrombin (25 nM), caused the rapid increase of endothelial cell barrier permeability accompanied by a fast decrease in quantity of the peripheral microtubules and reorganization of the microtubule system in the internal cytoplasm of endothelial cells (the decrease of fluorescence intensity is described by the equation of linear regress within as little as 5 min after the beginning of treatment). Both effects are reversible; within 60 min after the beginning of treatment, the microtubule network does not differ from the standard one. Thus, the microtubule system is capable of adapting to the influence of a natural regulator, thrombin. The reorganization of microtubules develops more quickly than the reorganization of the actin filaments system responsible for the subsequent changes of the cell shape during barrier dysfunction. Apparently, the microtubules are the first part in the circuit of the reactions leading to the pulmonary endothelial cell barrier compromise.