Oxidative stress promotes myocardial fibrosis by upregulating KCa3.1 channel expression in AGT-REN double transgenic hypertensive mice.

The intermediate-conductance Ca2+-activated K+ (KCa3.1) channels play a pivotal role in the cardiac fibroblast proliferation and inflammatory reaction during the progression of myocardial fibrosis. However, the relationship between KCa3.1 expression and oxidative stress, the important factor of promoting fibrosis, has not been clearly established. This study was designed to investigate whether the role of oxidative stress in promoting myocardial fibrosis is related to KCa3.1 channel by using biochemical approaches. It was found that mean blood pressure, plasma Ang II level, and myocardium malondialdehyde (MDA) content of angiotensinogen-renin (AGT-REN) double transgenic hypertension (dTH) mice were higher than those in wild-type (WT) mice of the same age (4, 8 and 12 months) and were significantly increased with age. However, plasma Ang (1-7) level and myocardium superoxide dismutase (SOD) activity showed a downward trend and were lower than those of the same-aged WT mice (4, 8 and 12 months). In addition, protein expression of myocardium KCa3.1 channel in 4-, 8-, and 12-month-old dTH mice were significantly higher than that of the same-aged WT mice and gradually increased with age. TRAM-34, a blocker of KCa3.1 channel, and losartan mitigated the myocardial structural and functional damage by inhibiting collagen deposition and decreasing the expression of β-MHC. After intervention of ROS scavenger N-acetyl cysteine (NAC) and NADPH inhibitor apocynin (Apo) in 6-month-old dTH mice for 4 weeks, myocardial oxidative stress level was reduced and KCa3.1 channel protein expression was decreased. Meanwhile, Apo inhibited the myocardium p-ERK1/2/T-ERK protein expression in dTH mice, and after blockage of ERK1/2 pathway with PD98059, the KCa3.1 protein expression was reduced. These results demonstrate for the first time that KCa3.1 channel is likely to be a critical target on the oxidative stress for its promoting role in myocardial fibrosis, and the ERK1/2 pathway may be involved in the regulation of oxidative stress to KCa3.1.