Pregnancy

Angiotensin II Elevates Nitric Oxide Synthase 3 Expression and Nitric Oxide Production via a Mitogen-Activated Protein Kinase Cascade in Ovine Fetoplacental Artery Endothelial Cells

Abstract
Normal pregnancy is associated with high angiotensin II (ANG II) concentrations in the maternal and fetal circulation. These high levels of ANG II may promote production vasodilators such as nitric oxide (NO). ANG II receptors are expressed in ovine fetoplacental artery endothelial (OFPAE) cells and mediate ANG II-stimulated OFPAE cell proliferation. Herein, we tested whether ANG II stimulates NO synthase 3 (NOS3, also known as eNOS) expression and total NO (NO_x) production via activation of mitogen-activated protein kinase 3/1 (MAPK3/1, also known as ERK1/2) in OFPAE cells. ANG II elevated (p <0.05) eNOS protein, but not mRNA levels with a maximum effect at 10 nM. ANG II also dose-dependently increased (p< 0.05) NO_x production with a maximal effect at doses of 1 to 100 nM. Activation of ERK1/2 by ANG II was determined by immunocytochemistry and Western blot analysis. ANG II rapidly induced positive staining for phosphorylated ERK1/2, appearing in cytosol after 1-5 min of ANG II treatment, accumulating in nuclei after 10 min, and disappearing at 15 min. ANG II increased (p < 0.05) phosphorylated ERK1/2 protein levels. Activation of ERK1/2 was confirmed by an immunocomplex kinase assay using ELK1 as a substrate. PD98059 significantly inhibited ANG II-induced ERK1/2 activation, and the ANG II-elevated eNOS protein levels, but only partially reduced ANG II-increased NO_x production. Thus, in OFPAE cells the ANG II increased NO_x production is associated with elevated eNOS protein expression, which is mediated at least via activation of the mitogen-activated protein kinase kinases 1 and 2 (MAP2K1 and 2, also known as MEK1/2)/ERK1/2 cascade. Together with our previous observation that ANG II stimulates OFPAE cell proliferation, these data suggest that ANG II is a key regulator for both vasodilation and angiogenesis in the ovine fetoplacenta.

Key words: Growth factors • Kinases • Nitric oxide • Placenta • Signal transduction

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