Expression of the AT2 receptor developmentally programs extracellular signal-regulated kinase activity and influences fetal vascular growth

Angiotensin II type 2 (AT2) receptor is abundantly expressed in vascular sm ooth muscle cells (VSMC) of the fetal vasculature during late gestation (em bryonic day 15-20), during which the blood vessels undergo remodeling. To e xamine directly the influence of AT2 receptor expression in the development al biology of VSMC, we studied cultures of VSMC from fetal and postnatal wi ld-type (Agtr2(+)) and AT2 receptor null (Agtr2(-)) mice. Consistent with i n vivo data, AT2 receptor binding in cultured Agtr2(+) VSMC increased by ag e, peaking at embryonic day 20, and decreased dramatically after birth. Ang iotensin II-induced growth in Agtr2(+) VSMC (embryonic day 20) was increase d by the AT2 receptor blocker PD123319, indicating that the AT2 receptors a re functional and exert an antigrowth effect in Agtr2(+) VSMC. Growth of VS MC in response to serum decreased age dependently and was higher in Agtr2(- ) than in Agtr2(+), inversely correlating with AT2 receptor expression. How ever, serum-induced growth in Agtr2(+) and Agtr2- VSMC and the exaggerated Agtr2- VSMC growth was maintained even in the presence of PD 123319 or losa rtan, an AT1 receptor blocker. Moreover, Agtr2- VSMC showed greater growth responses to platelet-derived growth factor and basic fibroblast growth fac tor, indicating that Agtr2(-) cells exhibit a generalized exaggerated growt h phenotype. We studied the mechanism responsible for this phenotype and ob served that extracellular signal-regulated kinase (ERK) activity was higher in Agtr2(-) VSMC at baseline and also in response to serum. ERK kinase inh ibitor PD98059 inhibited both growth and ERK phosphorylation dose-dependent ly, while the regression lines between growth and ERK phosphorylation were identical in Agtr2(+) and Agtr2(-) VSMC, suggesting that increased ERK acti vity in Agtr2(-) VSMC is pivotal in the growth enhancement. Furthermore, th e difference in ERK phosphorylation between Agtr2(+) and Agtr2(-) was aboli shed by vanadate but not by okadaic acid, implicating tyrosine phosphatase in the difference in ERK activity. These results suggest that the AT2 recep tor expression during the fetal vasculogenesis influences the growth phenot ype of VSMC via the modulation of ERK cascade.