Role of redox signaling in the autonomous proliferative response of endothelial cells to hypoxia.

Endothelial cells exhibit an autonomous proliferative response to hypoxia, independent of paracrine effectors. In cultured endothelial cells of porcine aorta, we analyzed the signaling of this response, with a focus on the roles of redox signaling and the MEK/ERK pathway. Transient hypoxia (1 hour) stimulated proliferation by 61+/-4% (n=16; P<0.05 versus control), quantified after 24 hours normoxic postincubation. Hypoxia induced an activation of ERK2 and of NAD(P)H oxidase and a burst of reactive oxygen species (ROS), determined by DCF fluorescence. To inhibit the MEK/ERK pathway, we used PD 98059 (PD, 20 micromol/L); to downregulate NAD(P)H oxidase, we applied p22phox antisense oligonucleotides; and to inhibit mitochondrial ROS generation, we used the ubiquinone derivate mitoQ (MQ, 10 micromol/L). All three inhibitions suppressed the proliferative response: PD inhibited NAD(P)H oxidase activation; p22phox antisense transfection did not inhibit ERK2 activation, but suppressed ROS production; and MQ inhibited ERK2 activation and ROS production. The autonomous proliferative response depends on the MEK/ERK pathway and redox signaling steps upstream and downstream of ERK. Located upstream is ROS generation by mitochondria, downstream is NAD(P)H oxidase.

Signaling of hypoxia-induced autonomous proliferation of endothelial cells.

Endothelial cells exhibit an autonomous proliferative response to hypoxia, independent of paracrine effectors. In cultured endothelial cells of porcine aorta, we analyzed the signaling and compared hypoxia with mitochondrial inhibition by rotenone. Particularly, roles of the mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway and cytosolic Ca2+ were studied. Hypoxia resulted in increased proliferation by 65+/-2%. Hypoxia induced transient activation of p42 MAPK (phosphorylation rose from 11+/-5 to 51+/-7%), followed by translocation of p42 MAPK into the nucleus. The proliferative response was diminished after inhibition of the MEK/MAPK pathway by PD 98059 (20 microM) or UO 126 (10 microM) but not sensitive to 8-phenyl-theophillin (10 microM), an adenosine receptor blocker, nor to a neutralizing antibody for vascular endothelial growth factor (VEGF). Inhibition of intracellular Ca2+ release, capacitive Ca2+ influx, or removal of extracellular Ca2+ prevented hypoxic Ca2+ overload and the proliferative response. Suppression of cytosolic Ca2+ rise did not interfere with activation of p42 MAPK but abolished its nuclear translocation. Effects of hypoxia were mimicked by rotenone (10 microM. Transient hypoxic inhibition of mitochondria induces a proliferative endothelial response mediated through Ca2+-independent activation and Ca2+-dependent nuclear translocation of p42 MAPK. This proliferative response is independent of adenosine or VEGF.

[Factor XIII and endothelial barrier function]. / Faktor XIII und endotheliale Barrierenfunktion.

Activated factor XIII (FXIIIa) crosslinks fibrin monomers to a stable clot. Due to this function, FXIIIa plays a major role in hemostasis and fibrinolysis. Additionally, it is well known that FXIIIa has a special meaning in cell adhesion and migration, in generation of extracellular matrix, in tissue repair and wound healing. New experimental studies revealed a FXIIIa stabilizing endothelial barrier function. In this function, FXIIIa reduces endothelial permeability for macromolecules in cultured endothelial monolayers and prevents impending barrier failure in coronary arteries of isolated hearts. This effect is due to the cross-linking of several proteins within the extracellular matrix, especially in the interendothelial clefts.

[Factor XIII and wound healing]. / Faktor XIII und Wundheilung.

In addition to those wounds with increasing fragility of capillaries during impaired healing, there are especially long lasting diabetic wounds or calf ulcerations due to chronic venous insufficiency or postthrombotic syndrome that show a failure of endothelial barrier function with an increased permeability as an important part of its pathophysiological situation. The possibility of controlling this increased permeability is of great therapeutical interest and may give distinct benefit for wound healing. In the close past, clinical as well as experimental studies revealed the plasma transglutaminase (factor XIIIa) as potential new strategy in treatment of increased vascular permeability.