Paradoxical increase in LDL oxidation by endothelial cells from an atherosclerosis-resistant mouse strain

Inflammation and enhanced atherogenesis in the carotid artery with altered blood flow in an atherosclerosis-resistant mouse strain

Ligation of the common carotid artery near its bifurcation in apolipoprotein E-deficient (Apoe^-/- ) mice leads to rapid atherosclerosis development, which is affected by genetic backgrounds. BALB/cJ (BALB) mice are resistant to atherosclerosis, developing much smaller aortic lesions than C57BL/6 (B6) mice. In this study, we examined cellular events leading to lesion formation in carotid arteries with or without blood flow restriction of B6 and BALB Apoe^-/- mice. Blood flow was obstructed by ligating the left common carotid artery near its bifurcation in one group of mice, and other group received no surgical intervention. Without blood flow interruption, BALB-Apoe^-/- mice formed much smaller atherosclerotic lesions than B6-Apoe^-/- mice after 12 weeks of Western diet (3,325 ± 1,086 vs. 81,549 ± 9,983 µm² /section; p = 2.1E-7). Lesions occurred at arterial bifurcations in both strains. When blood flow was obstructed, ligated carotid artery of both strains showed notable lipid deposition, inflammatory cell infiltration, and rapid plaque formation. Neutrophils and macrophages were observed in the arterial wall of BALB mice 3 days after ligation and 1 week after ligation in B6 mice. CD4 T cells were observed in intimal lesions of BALB but not B6 mice. By 4 weeks, both strains developed similar sizes of advanced lesions containing foam cells, smooth muscle cells, and neovessels. Atherosclerosis also occurred in straight regions of the contralateral common carotid artery where MCP-1 was abundantly expressed in the intima of BALB mice. These findings indicate that the disturbed blood flow is more prominent than high fat diet in promoting inflammation and atherosclerosis in hyperlipidemic BALB mice.

MicroRNA-148a-3p promotes survival and migration of endothelial cells isolated from Apoe deficient mice through restricting circular RNA 0003575

The incidence of atherosclerosis is greatly increased, which becomes the leading cause for the death and disability worldwide. Endothelial cells dysfunction plays a substantial role in the pathogenesis of atherosclerosis. MicroRNA-148a-3p (miR-148a-3p) and circular RNA 0003575 (circ_0003575) modulated lipid metabolism and proliferative function of endothelial cells, respectively. However, the role of them in modulation of endothelial cell function and progression of atherosclerosis remains unknown. Endothelial cells were isolated from the aorta of Apoe^-/- mice. miR-148a-3p in atherosclerosis patients and healthy controls were measured by qRT-PCR. Overexpression and knockdown of miR-148a-3p in endothelial cells were established. The proliferation, migration and apoptosis of endothelial cells were measured by MTT, Transwell, and fluorescence microscope, respectively. Online software (miRWalk 2.0 and RegRNA2.0) and databases (miRWalk, miRanda, RNA22, and Targetscan) were used to predict potential target genes of miR-148a-3p and circ_0003575. The expression of target genes was detected through western blotting. The expression of miR-148a-3p was significantly upregulated in patients with atherosclerosis as relative to healthy people. Overexpression of miR-148a-3p exhibited stimulatory effects on endothelial cell proliferation and migration and inhibited programmed cell death. Six intersection target genes, c-MAF, FOXO4, FOXO3, MITF, ETV7, and CRX, were predicted between miR-148a-3p and circ_0003575. The opposite effects of circ_0003575 and miR-148a-3p on the expression of FOXO4 and FOXO3, which are essential for lipid metabolism. We demonstrate that miR-148a-3p suppresses FOXO4 and FOXO3 expression via interruption of circ_0003575 function, which in turn impairs the proliferative and migratory function of endothelial cells, eventually exacerbating the atherosclerosis.

Cilostazol Attenuates Angiotensin II-Induced Abdominal Aortic Aneurysms but Not Atherosclerosis in Apolipoprotein E-Deficient Mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a permanent dilation of the abdominal aorta associated with rupture, which frequently results in fatal consequences. AAA tissue is commonly characterized by localized structural deterioration accompanied with inflammation and profound accumulation of leukocytes, although the specific function of these cells is unknown. Cilostazol, a phosphodiesterase III inhibitor, is commonly used for patients with peripheral vascular disease or stroke because of its anti-platelet aggregation effect and anti-inflammatory effect, which is vasoprotective effect. In this study, we evaluated the effects of cilostazol on angiotensin II-induced AAA formation.

APPROACH AND RESULTS

Male apolipoprotein E-deficient mice were fed either normal diet or a diet containing cilostazol (0.1% wt/wt). After 1 week of diet consumption, mice were infused with angiotensin II (1000 ng/kg per minute) for 4 weeks. Angiotensin II infusion increased maximal diameters of abdominal aortas, whereas cilostazol administration significantly attenuated dilatation of abdominal aortas, thereby, reducing AAA incidence. Cilostazol also reduced macrophage accumulation, matrix metalloproteinases activation, and inflammatory gene expression in the aortic media. In cultured vascular endothelial cells, cilostazol reduced expression of inflammatory cytokines and adhesive molecules through activation of the cAMP-PKA (protein kinase A) pathway.

CONCLUSIONS

Cilostazol attenuated angiotensin II-induced AAA formation by its anti-inflammatory effect through phosphodiesterase III inhibition in the aortic wall. Cilostazol may be a promising new therapeutic option for AAAs.

Celery Seed Extract Blocks Peroxide Injury in Macrophages via Notch1/NF-κB Pathway

Oxidized low-density lipoprotein (ox-LDL)-induced macrophage foam cell formation and injury is one of the major atherogenic factors. This study is aimed to investigate the protective effect of celery seed extract (CSE) on ox-LDL-induced injury of macrophages and the underlying signaling pathway. RAW264.7 macrophages were pre-incubated with CSE for 24 h, followed by stimulation with ox-LDL. Oil red O staining and enzymatic colorimetry indicated CSE significantly lessened lipid droplets and total cholesterol (TC) content in ox-LDL-injured macrophages. ELISA revealed that CSE decreased the secretion of inflammatory cytokine TNF-α and IL-6 by 12–27% and 5–15% respectively. MTT assay showed CSE promoted cell viability by 16–40%. Cell apoptosis was also analyzed by flow cytometry and laser scanning confocal microscope and the data indicated CSE inhibited ox-LDL-induced apoptosis of macrophages. Meanwhile, western blot analysis showed CSE suppressed NF-κBp65 and notch1 protein expressions stimulated by ox-LDL in macrophages. These results suggest that CSE inhibits ox-LDL-induced macrophages injury via notch1/NF-κB pathway.

Minimally modified low-density lipoprotein induces macrophage endoplasmic reticulum stress via toll-like receptor 4

Minimally modified low-density lipoprotein (mm-LDL) induces intimal foam cell formation, which is promoted by endoplasmic reticulum stress (ERS), a cross-point to link cellular processes with multiple risk factors that exist in all stages of atherosclerosis. However, it remains unclear whether mm-LDL-induced lipid accumulation in macrophages involves ERS and its underlying mechanisms. We showed that mm-LDL induced the accumulation of lipid droplets in RAW264.7 macrophages with increased free cholesterol in the endoplasmic reticulum, which was markedly attenuated by pretreatment with an antibody against toll-like receptor 4 (TLR4). Additionally, mm-LDL stimulated the transport of Cy3-labeled activating transcription factor 6 (ATF6), a key sensor to the unfolded protein response (UPR), from cytoplasm into nucleus. The expression of phosphorylated inositol-requiring enzyme 1 (p-IRE1), another sensor to the UPR, and its two downstream molecules, X box binding protein 1 and glucose-regulated protein 78 (GRP78), were significantly upregulated by mm-LDL. The alterations induced by mm-LDL were all significantly inhibited by antibodies against TLR4 or CD36. In addition, the upregulation of p-IRE1 and GRP78 and the nuclear translocation of ATF6 induced by mm-LDL were significantly attenuated by TLR4 siRNA. These results suggest that mm-LDL may induce free cholesterol accumulation in the endoplasmic reticulum and subsequently stimulate ERS and activate the UPR signaling pathway mediated by ATF6 and IRE1 in macrophages, a process that is potentially mediated by TLR4.

Genetic susceptibility of the arterial wall is an important determinant of atherosclerosis in C57BL/6 and FVB/N mouse strains

OBJECTIVE

How genetic variations among inbred mouse strains translate into differences in atherosclerosis susceptibility is of significant interest for the development of new therapeutic strategies. The objective of the present study was to examine whether genetically controlled arterial wall properties influence atherosclerosis susceptibility in FVB/N (FVB) and C57BL/6 (B6) apolipoprotein E knockout (apoE(-/-)) mouse strains.

METHODS AND RESULTS

Common carotid artery segments from B6 apoE(-/-), F1 apoE(-/-), and FVB apoE(-/-) mice were transplanted to hybrid F1 apoE(-/-) mice, which can accept grafts from both parental strains without adaptive immune responses. The mice were fed a high-fat diet, and atherosclerosis was induced in the transplanted artery segments by placement of a perivascular constrictive collar. Artery segments from B6 apoE(-/-) mice developed much larger atherosclerotic lesions than artery segments from FVB or F1 apoE(-/-) mice. No differences in aortic arch atherosclerosis of the recipient mice were observed between groups.

CONCLUSIONS

Genetically controlled factors acting at the level of the arterial wall are important determinants of atherosclerosis susceptibility in FVB apoE(-/-) and B6 apoE(-/-) mice.

Depressive behavior and vascular dysfunction: a link between clinical depression and vascular disease?

As chronic stress and depression have become recognized as significant risk factors for peripheral vascular disease in patients with no prior history of vasculopathy, we interrogated this relationship utilizing an established mouse model of chronic stress/depressive symptoms from behavioral research. Male mice were exposed to 8 wk of unpredictable chronic mild stress (UCMS; e.g., wet bedding, predator sound/smell, random disruption of light/dark cycle), with indexes of depressive behavior (coat status, grooming, and mobility) becoming exacerbated vs. controls. In vascular rings, constrictor (phenylephrine) and endothelium-independent dilator (sodium nitroprusside) responses were not different between groups, although endothelium-dependent dilation (methacholine) was attenuated with UCMS. Nitric oxide synthase (NOS) inhibition was without effect in UCMS but nearly abolished reactivity in controls, while cyclooxygenase inhibition blunted dilation in both. Combined blockade abolished reactivity in controls, although a significant dilation remained in UCMS that was abolished by catalase. Arterial NO production was attenuated by UCMS, although H2O2 production was increased. UCMS mice demonstrated an increased, although variable, insulin resistance and inflammation. However, while UCMS-induced vascular impairments were consistent, the predictive power of aggregate plasma levels of insulin, TNF-alpha, IL-1beta, and C-reactive peptide were limited. However, when separated into tertiles with regard to vascular outcomes, insulin resistance and hypertension were predictive of the most severe vascular impairments. Taken together, these data suggest that aggregate insulin resistance, inflammation, and hypertension in UCMS mice are not robust predictors of vascular dysfunction, suggesting that unidentified mechanisms may be superior predictors of poor vascular outcomes in this model.

siRNA silencing reveals role of vascular cell adhesion molecule-1 in vascular smooth muscle cell migration

Vascular cell adhesion molecule-1 (VCAM-1) is an adhesion molecule expressed by endothelial cells for recruitment of leukocytes during inflammation. It is also abundantly expressed by smooth muscle cells in atherosclerotic lesions and in injured arteries. In this study, we examined the role of VCAM-1 in smooth muscle cell migration. Smooth muscle cells were isolated from the aorta of C57BL/6 mice and transfected with short interfering RNAs (siRNAs) targeting VCAM-1. Inhibition on VCAM-1 expression by siRNAs was assessed by Western blot analysis, RT-PCR and by measuring soluble VCAM-1 concentrations in the incubation medium. One siRNA that showed greater suppression on VCAM-1 expression was used for migration assay. A single scratch wound was made on 70% confluent cells and cells migrated from wounded monolayer were counted 24 and 48h after injury. Treatment with VCAM-1 siRNA resulted in a significant reduction in the number of migrated cells. This siRNA also exhibited a minor effect on smooth muscle cell proliferation. Thus, our findings indicate that VCAM-1 is necessary for the migration of smooth muscle cells and interfering VCAM-1 expression could be an effective approach to prevention and treatment of atherosclerosis and restenosis.

Complicated atheromatous plaque as integral atherogenesis

Genesis of plaque lesion as atherosclerosis is based on the involvement of endothelium and smooth muscle cells