Protective role of ACE2-Ang-(1-7)-Mas in myocardial fibrosis by downregulating KCa3.1 channel via ERK1/2 pathway

The intermediate-conductance Ca2+-activated K+ (K(Ca)3.1) channel plays a vital role in myocardial fibrosis induced by angiotensin (Ang) II. However, as the antagonists of Ang II, the effect of angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas axis on K(Ca)3.1 channel during myocardial fibrosis remains unknown. This study was designed to explore the function of K(Ca)3.1 channel in the cardioprotective role of ACE2-Ang-(1-7)-Mas. Wild-type (WT) mice, hACE2 transgenicmice (Tg), and ACE2 deficiency mice (ACE2(-/-)) were administrated with Ang II by osmotic mini-pumps. As the activator of ACE2, diminazene aceturate (DIZE) inhibited increase of blood pressure, collagen deposition, and K(Ca)3.1 protein expression in myocardium of WT mice induced by Ang II. In Tg and ACE2(-/-) mice, besides the elevation of blood pressure, Ang II induced transformation of cardiac fibroblast into myofibroblast and resulted in augmentation of hydroxyproline concentration and collagen deposition, as well as K(Ca)3.1 protein expression, but the changes in ACE2(-/-) mice were more obvious than those in Tg mice. Mas antagonist A779 reduced blood pressure, myocardium fibrosis, and myocardium K(Ca)3.1 protein expression by Ang II in Tg mice, but activation of K(Ca)3.1 with SKA-31 in Tg mice promoted the pro-fibrogenic effects of Ang II. Respectively, in ACE2(-/-) mice, TRAM-34, the K(Ca)3.1 blocker, and Ang-(1-7) inhibited increase of blood pressure, collagen deposition, and K(Ca)3.1 protein expression by Ang II. Moreover, DIZE and Ang-(1-7) depressed p-ERK1/2/t-ERK increases by Ang II in WT mice, and after blockage of ERK1/2 pathway with PD98059, the K(Ca)3.1 protein expression was reduced in WT mice. In conclusion, the present study demonstrates that ACE2-Ang-(1-7)-Mas protects the myocardium from hypertension-induced injury, which is related to its inhibiting effect on K(Ca)3.1 channels through ERK1/2 pathway. Our results reveal that K(Ca)3.1 channel is likely to be a critical target on the ACE2-Ang-(1-7)-Mas axis for its protective role in myocardial fibrosis and changes of K(Ca)3.1 induced by homeostasis of ACE-Ang II-AT1 axis and ACE2-Ang-(1-7)-Mas axis may be a new therapeutic target in myocardial fibrosis.