ABSTRACT
Uterine artery endothelium undergoes a form of functional adaptation during pregnancy because of an increase in Cx43 communication, resulting in increased Ca2+/IP3 exchange and more synchronous and sustained vasodilator production. We have shown previously that acute exposure to growth factors and TNF can block this adaptation through ERK and/or Src-mediated Cx43 phosphorylation. In preeclampsia such adapted function is already missing, but while elevated TNF is associated with this condition, particularly after 28 weeks (late PE), elevated circulating VEGF165 is not. Given PE is a long term condition emerging in the second half of pregnancy, and is often associated with added edema, we now compare the chronic effects of these two factors on the cell monolayer in order to establish if the breakdown of junctional adherens and tight junctional assemblies in which Cx43 resides could also explain loss of vasodilatory function. We report that while TNF can degrade monolayer integrity even in the 0.1-1 ng/ml physiologic range, VEGF up to 10 ng/ml does not. In addition, the progressive action of TNF is mediated through Src and ERK signaling to promote internalization and destruction of VE-Cadherin (VE-Cad) and ZO-1, as well as the expression and secretion of a variety of proteases. At least one protein degraded from the extracellular space is VE-Cad, resulting in release of a shed VE-Cad protein product, and consistent with monolayer breakdown being sensitive to both Src and MEK/ERK kinase inhibitors and the general protease inhibitor GM6001. We conclude that the greater association of TNF with 'late' PE is as much due to its longer term destabilizing effects on junctional assemblies as it is to acute closure of Cx43 channels themselves. New therapies aimed at stabilizing these junctional assemblies may help treat this hypertensive condition.
