In addition, phosphorylation of p38 was induced by stretch stimuli in SMCs (12). These findings led us to assume that apoptosis of SMCs in AAD tissue may be related to JNK and p38 phosphorylation. Angiotensin II has been shown to induce cellular hypertrophy in vascular SMCs by GSK2118436 mouse acting through the G protein-coupled AT1 receptor, which results in various cardiovascular diseases and activates ERK1/2, JNK, and p38 (14) and (15). In recent years, much focus has been placed on the role of G protein-coupled receptors, including the angiotensin II receptor, because they can be activated without agonist
stimulation (16). The angiotensin II receptor also causes initiation of an intra-cellular signaling cascade in response to mechanical stretch without agonist stimulation. A specific type of angiotensin II receptor blocker (ARB) inhibits both agonist-induced and stretch-induced activation (17). Olmesartan
is known as a potent ARB and works as an inverse agonist (18). We previously reported that olmesartan inhibits SMC migration through the inhibition of JNK activation (4). Therefore, we hypothesized that olmesartan may inhibit stretch-induced SMC death through the inhibition of the JNK- or p38-mediated intracellular signaling cascades. In this study, we investigated cultured rat aortic smooth muscle cell (RASMC) Target Selective Inhibitor Library concentration death induced by cyclic mechanical stretch, which mimics an acute increase in blood pressure, and examined the effect of olmesartan on this event. We also investigated the changes in stretch-induced intracellular signaling including JNK and p38 and examined the effect of olmesartan on these changes. The study design was approved by the animal care and use committee of Nara Medical University based on the Guidelines for the Use of Laboratory Animals of Nara Medical University (No. 11011) and this study was conducted in because accordance with the Guide for the Care and Use of Laboratory Animals as adopted and promulgated by the United States National Institutes of Health. RASMCs were isolated from male Sprague-Dawley rats weighing 250–300 g according to previously published methods
(19). The cells were grown in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS, HyClone, Logan, UT) and antibiotics (100 units/ml penicillin, 100 μg/ml streptomycin). The culture was maintained in a humidified atmosphere containing 5% CO2 at 37 °C. RASMCs from passage three to eight were grown to 70%–80% confluence in collagen I-coated (70 μg/cm2) silicon chambers (STREX Inc., Osaka, Japan) and then growth-arrested by incubation in serum-free DMEM for 24 h prior to use. The cells were then subjected to mechanical stretch (60 cycles/min, 20% elongation) for a given time period by using the computer-controlled mechanical Strain Unit (STREX Inc, Osaka, Japan) according to previously published methods (20). After cyclic stretch, the medium was replaced with DMEM-containing 0.1% FBS.