Abstract-In vivo, endothelial cells (ECs) are subjected to a complex mechanical environment composed of shear stress, pressure, and circumferential stretch. The aim of this study was to subject bovine aortic ECs to a pulsatile pressure oscillating from 70 to 130 mm Hg (mean of 100 mm Hg) in combination with pulsatile shear stresses from 0.1 to 6 dyne/cm 2 (1 dyne/cm 2 ϭ0.1 N/m 2 ) with or without a cyclic circumferential stretch of 4% for 1, 4, and 24 hours. The effect of highly reversing oscillatory shear stress (range Ϫ3 to ϩ3 dyne/cm 2 , mean of 0.3 dyne/cm 2 ) typical of regions prone to the development of atherosclerotic plaques was also studied at 4 and 24 hours. Endothelin-1 (ET-1) and endothelial constitutive nitric oxide synthase (ecNOS) mRNA expression was time and mechanical force dependent. ET-1 mRNA was maximal at 4 hours and decreased to less than static culture expression at 24 hours, whereas ecNOS mRNA increased over time. Pressure combined with low shear stress upregulated ET-1 and ecNOS mRNA compared with static control. Additional increase in expression for both genes was observed under a combination of higher shear stress and pressure. A cyclic circumferential stretch of 4% did not induce a further increase in ET-1 and ecNOS mRNA at either low or high shear stress. Oscillatory shear stress with pressure induced a higher expression of ET-1 mRNA but lower expression of ecNOS mRNA compared with unidirectional shear stress and pressure. We have shown that the combination of pressure and oscillatory shear stress can downregulate ecNOS levels, as well as upregulate transient expression of ET-1, compared with unidirectional shear stress. These results provide a new insight into the exact role of mechanical forces in endothelial dysfunction in regions prone to the development of atherosclerosis. (Arterioscler Thromb Vasc Biol. 1998;18:686-692.) Key Words: mechanical stress Ⅲ hemodynamics Ⅲ vascular endothelium Ⅲ nitric oxide synthase Ⅲ endothelin T he fluid mechanics of blood are known to transiently regulate vascular tone. In addition to short-term action, fluid mechanics have also been shown to regulate vascular remodeling in the case of long-term changes in pressure (hypertension) and flow rate (pregnancy, arteriovenous shunts, and exercise).1 More importantly, it has been demonstrated that the localization of the atherosclerotic plaque is correlated with regions characterized by oscillatory shear stress environment. 2 This regulation has been demonstrated in part to occur via two molecules secreted by the ECs and which have been identified as ET-1 and NO.ET-1 is a 21-amino acid peptide acting as a powerful vasoconstrictor and an SMC mitogen.3 ET-1 is thought to play an active role in SMC proliferation during remodeling of arteries. ET-1 mRNA expression has been shown to be transiently stimulated at 1 to 4 hours in cultured porcine aortic ECs exposed to a shear stress of 5 dyne/cm 2 (1 dyne/cm 2 ϭ0.1 N/m 2 ) and 30 minutes in BAECs exposed to 15 dyne/cm 2 . 4,5 Longer time exposure to 15 dyne/cm 2...

The interleukin-1 (IL-1) family of cytokines has been implicated in the pathogenesis of atherosclerosis in previous studies. The NLRP3 inflammasome has recently emerged as a pivotal regulator of IL-1β maturation and secretion by macrophages. Little is currently known about a possible role for the NLRP3 inflammasome in atherosclerosis progression in vivo. We generated ApoE−/− Nlrp3−/−, ApoE−/− Asc−/− and ApoE−/− caspase-1−/− double-deficient mice, fed them a high-fat diet for 11 weeks and subsequently assessed atherosclerosis progression and plaque phenotype. No differences in atherosclerosis progression, infiltration of plaques by macrophages, nor plaque stability and phenotype across the genotypes studied were found. Our results demonstrate that the NLRP3 inflammasome is not critically implicated in atherosclerosis progression in the ApoE mouse model.

Abstract-Rupture of vulnerable plaques is the main cause of acute cardiovascular events. However, mechanisms responsible for transforming a stable into a vulnerable plaque remain elusive. Angiotensin II, a key regulator of blood pressure homeostasis, has a potential role in atherosclerosis. To study the contribution of angiotensin II in plaque vulnerability, we generated hypertensive hypercholesterolemic ApoE Ϫ/Ϫ mice with either normal or endogenously increased angiotensin II production (renovascular hypertension models). Hypertensive high angiotensin II ApoE Ϫ/Ϫ mice developed unstable plaques, whereas in hypertensive normal angiotensin II ApoE Ϫ/Ϫ mice plaques showed a stable phenotype. Vulnerable plaques from high angiotensin II ApoE Ϫ/Ϫ mice had thinner fibrous cap (PϽ0.01), larger lipid core (PϽ0.01), and increased macrophage content (PϽ0.01) than even more hypertensive but normal angiotensin II ApoE Ϫ/Ϫ mice. Moreover, in mice with high angiotensin II, a skewed T helper type 1-like phenotype was observed. Splenocytes from high angiotensin II ApoE Ϫ/Ϫ mice produced significantly higher amounts of interferon (IFN)-␥ than those from ApoE Ϫ/Ϫ mice with normal angiotensin II; secretion of IL4 and IL10 was not different. In addition, we provide evidence for a direct stimulating effect of angiotensin II on lymphocyte IFN-␥ production. These findings suggest a new mechanism in plaque vulnerability demonstrating that angiotensin II, within the context of hypertension and hypercholesterolemia, independently from its hemodynamic effect behaves as a local modulator promoting the induction of vulnerable plaques probably via a T helper switch.

Abstract-Hypertension is associated with increased risk of cardiovascular diseases. Antihypertensive treatment, particularly blockade of the renin-angiotensin system, contributes to prevent atherosclerosis-mediated cardiovascular events. Direct comparison of different antihypertensive treatments on atherosclerosis and particularly plaque stabilization is sparse. ApoE Ϫ/Ϫ mice with vulnerable (2-kidney, 1-clip renovascular hypertension model) or stable (1-kidney, 1-clip renovascular hypertension model) atherosclerotic plaques were used. Mice were treated with aliskiren (renin inhibitor), irbesartan (angiotensin-receptor blocker), atenolol (␤-blocker), or amlodipine (calcium channel blocker). Atherosclerosis characteristics were assessed. Hemodynamic and hormonal parameters were measured. Aliskiren and irbesartan significantly prevented atherosclerosis progression in 2-kidney, 1-clip mice. Indeed, compared with untreated animals, plaques showed thinner fibrous cap (PϽ0.05); smaller lipid core (PϽ0.05); decreased media degeneration, layering, and macrophage content (PϽ0.05); and increased smooth muscle cell content (PϽ0.05). Interestingly, aliskiren significantly increased the smooth muscle cell compared with irbesartan. Despite similar blood pressure lowering, only partial plaque stabilization was attained by atenolol and amlodipine. Amlodipine increased plaque smooth muscle cell content (PϽ0.05), whereas atenolol decreased plaque inflammation (PϽ0.05). This divergent effect was also observed in 1-kidney, 1-clip mice. Normalizing blood pressure by irbesartan increased the plasma renin concentration (5932Ϯ1512 ng/mL per hour) more than normalizing it by aliskiren (16085Ϯ5628 ng/mL per hour). Specific renin-angiotensin system blockade prevents atherosclerosis progression. First, evidence is provided that direct renin inhibition mediates atherosclerotic plaque stabilization. In contrast, ␤-blocker and calcium channel blocker treatment only partially stabilize plaques differently influencing atherogenesis. Angiotensin II decisively mediates plaque vulnerability. The plasma renin concentration measurement by an indirect method did not confirm the excessive increase of plasma renin concentration reported in the literature during aliskiren compared with irbesartan or amlodipine treatment. (Hypertension. 2008;51:1306-1311.)