A therosclerosis is characterized with plaque formation in large and medium-sized blood vessels. The stiffened and narrowed blood vessels limit blood circulation and increase plaque thrombogenicity, which threatens the functionality of vital organs such as the heart and brain. [1][2][3] The development of atherosclerosis is a chronic pathological process. Vascular remodeling and inflammation, endothelial dysfunction, smooth muscle cell (SMC) proliferation and migration, and accumulation of cholesterol-rich lipoproteins in blood vessel walls are early events of atherogenesis, resulting in the recruitment of circulating monocytes, their adhesion to endothelium via adhesion molecules, and their differentiation into macrophages. 4 The subendothelial accumulation of cholesterol-laden macrophages is morphologically recognized as foam cells. In humans, these fatty streaks can progress to more advanced lesions characterized by a lipid-rich necrotic core and a fibrous cap consisting of SMCs and collagen.Lesion rupture can result from the decreased viability of SMCs that is necessary for collagen production and for the structural integrity of the fibrous cap following the release of matrix metalloproteinases from apoptotic macrophages. 4-8 Editorial see p 2472 Clinical Perspective on p 2534Hydrogen sulfide (H 2 S), a member of the gasotransmitter family, plays a number of important physiological roles within the body, including protection against cardiovascular disease.9-11 Cystathionine γ-lyase (CSE) endogenously produces H 2 S in the cardiovascular system, 12,13 and the deficiency of CSE in mice leads to decreased endogenous H 2 S level, age-dependent increase in blood pressure, impaired endothelium-dependent vasorelaxation, and accumulation of homocysteine in the blood.14 Administration of NaHS (a H 2 S donor) protects rat aortic SMCs from the cytotoxicity caused Background-Cystathionine γ-lyase (CSE) produces hydrogen sulfide (H 2 S) in the cardiovascular system. The deficiency of CSE in mice leads to a decreased endogenous H 2 S level, an age-dependent increase in blood pressure, and impaired endothelium-dependent vasorelaxation. To date, there is no direct evidence for a causative role of altered metabolism of endogenous H 2 S in atherosclerosis development. Methods and Results-Six-week-old CSE gene knockout and wild-type mice were fed with either a control chow or atherogenic paigen-type diet for 12 weeks. Plasma lipid profile and homocysteine levels, blood pressure, oxidative stress, atherosclerotic lesion size in the aortic roots, cell proliferation, and adhesion molecule expression were then analyzed. CSE-knockout mice fed with atherogenic diet developed early fatty streak lesions in the aortic root, elevated plasma levels of cholesterol and low-density lipoprotein cholesterol, hyperhomocysteinemia, increased lesional oxidative stress and adhesion molecule expression, and enhanced aortic intimal proliferation. Treatment of CSE-knockout mice with NaHS, but not N-acetylcysteine or ezetimibe, inhibited the acceler...

Background-Apoptotic cell death contributes to atherosclerotic lesion instability, rupture, and thrombogenicity. Recent findings suggest that free cholesterol (FC) accumulation in macrophages induces endoplasmic reticulum (ER) stress/unfolded protein response (UPR) and apoptotic cell death; however, it is not known at what stage of lesion development the UPR is induced in macrophages or whether a correlation exists between UPR activation, FC accumulation, and apoptotic cell death. Methods and Results-Aortic root sections from apolipoprotein E-deficient (apoE Ϫ/Ϫ ) mice at 9 weeks of age (early-lesion group) or 23 weeks of age (advanced-lesion group) fed a standard chow diet were examined for markers of UPR activation (GRP78, phospho-PERK, CHOP, and TDAG51), apoptotic cell death (TUNEL and cleaved caspase-3), and lipid accumulation (filipin and oil red O). UPR markers were dramatically increased in very early intimal macrophages and in macrophage foam cells from fatty streaks and advanced atherosclerotic lesions. Although accumulation of FC was observed in early-lesion-resident macrophage foam cells, no evidence of apoptotic cell death was observed; however, UPR activation, FC accumulation, and apoptotic cell death were observed in a small percentage of advanced-lesionresident macrophage foam cells. Conclusions-UPR activation occurs at all stages of atherosclerotic lesion development. The additional finding that macrophage apoptosis did not correlate with UPR activation and FC accumulation in early-lesion-resident macrophages suggests that activation of other cellular mediators and/or pathways are required for apoptotic cell death. (Circulation.

Despite widespread use of statins to reduce low-density lipoprotein cholesterol (LDL-C) and associated atherosclerotic cardiovascular risk, many patients do not achieve sufficient LDL-C lowering due to muscle-related side effects, indicating novel treatment strategies are required. Bempedoic acid (ETC-1002) is a small molecule intended to lower LDL-C in hypercholesterolemic patients, and has been previously shown to modulate both ATP-citrate lyase (ACL) and AMP-activated protein kinase (AMPK) activity in rodents. However, its mechanism for LDL-C lowering, efficacy in models of atherosclerosis and relevance in humans are unknown. Here we show that ETC-1002 is a prodrug that requires activation by very long-chain acyl-CoA synthetase-1 (ACSVL1) to modulate both targets, and that inhibition of ACL leads to LDL receptor upregulation, decreased LDL-C and attenuation of atherosclerosis, independently of AMPK. Furthermore, we demonstrate that the absence of ACSVL1 in skeletal muscle provides a mechanistic basis for ETC-1002 to potentially avoid the myotoxicity associated with statin therapy.

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Untreated cystathionine beta-synthase (CBS) deficiency in humans is characterized by extremely elevated plasma total homocysteine (tHcy>200 microM), with thrombosis as the major cause of morbidity. Treatment with vitamins and diet leads to a dramatic reduction in thrombotic events, even though patients often still have severe elevations in tHcy (>80 microM). To understand the difference between extreme and severe hyperhomocysteinemia, we have examined two mouse models of CBS deficiency: Tg-hCBS Cbs(-/-) mice, with a mean serum tHcy of 169 microM, and Tg-I278T Cbs(-/-) mice, with a mean tHcy of 296 microM. Only Tg-I278T Cbs(-/-) animals exhibited strong biological phenotypes, including facial alopecia, osteoporosis, endoplasmic reticulum (ER) stress in the liver and kidney, and a 20% reduction in mean survival time. Metabolic profiling of serum and liver reveals that Tg-I278T Cbs(-/-) mice have significantly elevated levels of free oxidized homocysteine but not protein-bound homocysteine in serum and elevation of all forms of homocysteine and S-adenosylhomocysteine in the liver compared to Tg-hCBS Cbs(-/-) mice. RNA profiling of livers indicate that Tg-I278T Cbs(-/-) and Tg-hCBS Cbs(-/-) mice have unique gene signatures, with minimal overlap. Our results indicate that there is a clear pathogenic threshold effect for tHcy and bring into question the idea that mild elevations in tHcy are directly pathogenic.

Background-A causal relation between hyperhomocysteinemia (HHcy) and accelerated atherosclerosis has been established in apolipoprotein E-deficient (apoE Ϫ/Ϫ ) mice. Although several cellular stress mechanisms have been proposed to explain the atherogenic effects of HHcy, including oxidative stress, endoplasmic reticulum (ER) stress, and inflammation, their association with atherogenesis has not been completely elucidated. Methods and Results-ApoEϪ/Ϫ mice were fed a control or a high-methionine (HM) diet for 4 (early lesion group) or 18 (advanced lesion group) weeks to induce HHcy. Total plasma homocysteine levels and atherosclerotic lesion size were significantly increased in early and advanced lesion groups fed the HM diet compared with control groups. Markers of ER stress (GRP78/94, phospho-PERK), oxidative stress (HSP70), and inflammation (phospho-IB-␣) were assessed by immunohistochemical staining of these atherosclerotic lesions. GRP78/94, HSP70, and phospho-IB-␣ immunostaining were significantly increased in the advanced lesion group fed the HM diet compared with the control group. HSP47, an ER-resident molecular chaperone involved in collagen folding and secretion, was also increased in advanced lesions of mice fed the HM diet. GRP78/94 and HSP47 were predominantly localized to the smooth muscle cell-rich fibrous cap, whereas HSP70 and phospho-IB-␣ were observed in the lipid-rich necrotic core. Increased HSP70 and phospho-IB-␣ immunostaining in advanced lesions of mice fed the HM diet are consistent with enhanced carotid artery dihydroethidium staining. Interestingly, GRP78/94 and phospho-PERK were markedly increased in macrophage foam cells from early lesions of mice fed the control or the HM diet.

Objective-Peroxynitrite, a potent oxidant generated by the reaction of NO with superoxide, has been implicated in the promotion of atherosclerosis. We designed this study to determine whether peroxynitrite induces its proatherogenic effects through induction of endoplasmic reticulum (ER) stress. Methods and Results-Human vascular endothelial cells treated with Sin-1, a peroxynitrite generator, induced the expression of the ER chaperones GRP78 and GRP94 and increased eIF2␣ phosphorylation. These effects were inhibited by the peroxynitrite scavenger uric acid. Sin-1 caused the depletion of ER-Ca 2ϩ , an effect known to induce ER stress, resulting in the elevation of cytosolic Ca 2ϩ and programmed cell death (PCD). Sin-1 treatment was also found, via 3-nitrotyrosine and GRP78 colocalization, to act directly on the ER. Adenoviral-mediated overexpression of GRP78 in endothelial cells prevented Sin-1-induced PCD. Consistent with these in vitro findings, 3-nitrotyrosine was observed and colocalized with GRP78 in endothelial cells of early atherosclerotic lesions from apolipoprotein E-deficient mice. Conclusions-Peroxynitrite is an ER stress-inducing agent. Its effects include the depletion of ER-Ca 2ϩ , a known mechanism of ER stress induction. The observation that 3-nitrotyrosine-containing proteins colocalize with markers of ER stress within early atherosclerotic lesions suggests that peroxynitrite contributes to atherogenesis through a mechanism involving ER stress. Key Words: endothelium Ⅲ nitric oxide Ⅲ endoplasmic reticulum Ⅲ atherosclerosis Ⅲ calcium E ndothelial dysfunction/injury represents a key early step in atherogenesis. The majority of risk factors for atherosclerosis, including, hyperlipidemia, hypertension, diabetes, and smoking, are associated with endothelial dysfunction. 1 A major function of the vascular endothelium is the regulation of vascular tone by NO through NO-induced smooth muscle relaxation. 2 Reduced NO bioavailability is a common feature in atherosclerosis and can result from oxidative stress. 3 In the apolipoprotein E-deficient (apoE Ϫ/Ϫ ) mouse model of atherosclerosis, endothelial dysfunction, as shown by decreased NO-mediated vasodilation to acetylcholine, correlates with increased atherosclerotic lesion size. 4 The availability of NO and superoxide (. O 2 -) within the atherosclerotic lesion creates the conditions for peroxynitrite formation because NO and . O 2 -react at physiological pH to form peroxynitrite. 5 A marker of peroxynitrite generation, 3-nitrotyrosine (3-NT) is elevated in human atherosclerotic lesions. 6,7 However, the mechanism by which reduced NO bioavailability and peroxynitrite formation contribute to atherosclerosis remains uncertain. See coverEndoplasmic reticulum (ER) stress, a cellular stress pathway induced by the accumulation of unfolded proteins in the ER, may offer an explanation for the contribution of peroxynitrite to atherosclerosis. ER stress results in an evolutionary conserved cellular response involving the upregulation of a set of genes, including ...

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been associated with fibrotic lung disease, although exactly how they modulate this process remains unclear. Here we investigated the role of GRP78, the main UPR regulator, in an experimental model of lung injury and fibrosis. Grp78(+/-) , Chop(-/-) and wild type C57BL6/J mice were exposed to bleomycin by oropharyngeal intubation and lungs were examined at days 7 and 21. We demonstrate here that Grp78(+/-) mice were strongly protected from bleomycin-induced fibrosis, as shown by immunohistochemical analysis, collagen content and lung function measurements. In the inflammatory phase of this model, a reduced number of lung macrophages associated with an increased number of TUNEL-positive cells were observed in Grp78(+/-) mice. Dual immunohistochemical and in situ hybridization experiments showed that the macrophage population from the protected Grp78(+/-) mice was also strongly positive for cleaved caspase-3 and Chop mRNA, respectively. In contrast, the administration of bleomycin to Chop(-/-) mice resulted in increased quasi-static elastance and extracellular matrix deposition associated with an increased number of parenchymal arginase-1-positive macrophages that were negative for cleaved caspase-3. The data presented indicate that the UPR is activated in fibrotic lung tissue and strongly localized to macrophages. GRP78- and CHOP-mediated macrophage apoptosis was found to protect against bleomycin-induced fibrosis. Overall, we demonstrate here that the fibrotic response to bleomycin is dependent on GRP78-mediated events and provides evidence that macrophage polarization and apoptosis may play a role in this process. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.