Abstract P2017: Angiotensin-Induced Constriction via Rho Kinase Activation in Pressure-Overloaded Rat Thoracic Aortas

Abstract

Activation of the angiotensin II (Ang II) receptor increases myosin light chain (MLC) kinase activity and causes inactivation of MLC phosphatase thorough myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation by Rho kinase. This results in MLC phosphorylation and subsequent smooth muscle constriction. However, the detailed mechanism of Rho kinase activation by Ang II is still unknown. The aim of this study was to clarify whether Ang II-induced constriction in pressure-overloaded rat thoracic aortas is mediated by Rho kinase activation through epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase 1 and 2 (Erk1/2), and janus kinase (JAK). Pressure-overload in the rat thoracic aortas was produced by suprarenal abdominal aortic coarctation. After 4 weeks, the thoracic aortas were excised for performing organ chamber experiments. Ang II was cumulatively added to reach a final concentration of a 0.1 – 1 μM. The inhibitors were added to 15 min prior to Ang II, and protein levels were measured by Western blotting. The contractile response to Ang II was significantly enhanced in the pressure-overloaded rats as compared to sham-operated ones [E max (% 40 mM KCl-induced constriction): sham; 44.6 ± 2.4, pressure-overload; 61.6 ± 2.2]. Ang II-induced constriction was attenuated by inhibitors of Rho kinase (E max : sham; 14.2 ± 5.3, pressure-overload; 6.8 ± 0.6), Erk1/2 (E max : sham; 21.2 ± 3.5, pressure-overload; 33.7 ± 3.5), and EGFR (E max : sham; 7.8 ± 2.0, pressure-overload; 26.6 ± 3.0) in both the sham-operated and pressure-overloaded rats. The Ang II-induced constriction was attenuated by JAK inhibitor (E max : sham; 41.9 ± 4.8, pressure-overload; 45.1 ± 4.2) in only pressure-overloaded rats. The protein levels of MYPT1 and JAK exhibited to increase in the pressure-overloaded rat thoracic aortas (MYPT1: sham; 1.0 ± 0.1, pressure-overload; 1.3 ± 0.1, JAK: sham; 1.0 ± 0.1, pressure-overload; 1.2 ± 0.1). These data suggest that Ang II-induced constriction is mediated by Rho kinase activation via EGFR, Erk1/2, and JAK in pressure-overloaded rat thoracic aortas. Moreover, Ang II-induced constriction was enhanced in pressure-overloaded rats probably because the protein levels of MYPT1 and JAK tended to increase in the thoracic aortas.