The renin-angiotensin system and atherosclerosis

HMGB1 promotes Ox-LDL-induced endothelial cell damage by inhibiting PI3K/Akt signaling pathway

BACKGROUND

Atherosclerosis is the pathological basis of cardio-cerebrovascular diseases. Oxidized low-density lipoprotein (ox-LDL) is an important risk factor for atherosclerosis. Ox-LDL leads to endothelial cell (EC) damage and dysfunction through various processes and promotes the occurrence and deterioration of atherosclerosis. High mobility group box-1 (HMGB1) is a protein associated with cellular damage. In the present study, the effect of HMGB1 on ox-LDL-induced EC damage was determined and the underlying mechanism explored.

MATERIALS AND METHODS

Human umbilical vein ECs (HUVECs) were exposed to ox-LDL to induce endothelial damage and changes in HMGB1 expression level were detected using western blotting analysis and reverse transcription-quantitative PCR. To observe the effect of HMGB1 on ox-LDL-induced damage, the HMGB1 expression was downregulated with siRNA, and cell viability, cytotoxicity, and apoptosis rate were assessed. HUVECs were pretreated with LY294002, an inhibitor of the PI3K/Akt pathway, to determine whether the effect of HMGB1 on damage is via the PI3K-Akt pathway.

RESULTS

The results showed that ox-LDL can upregulate HMGB1 expression in HUVECs and downregulation of HMGB1 expression can prevent ox-LDL-induced damage in HUVECs. Furthermore, the effect of HMGB1 on ox-LDL-induced damage could be promoted by inhibiting the PI3K/Akt signaling pathway.

CONCLUSION

The results indicate HMGB1 may be a promising research target to alleviate ox-LDL-induced EC damage.

A Mixture of Algae and Extra Virgin Olive Oils Attenuates the Cardiometabolic Alterations Associated with Aging in Male Wistar Rats

Aging is one of the major risk factors for suffering cardiovascular and metabolic diseases. Due to the increase in life expectancy, there is a strong interest in the search for anti-aging strategies to treat and prevent these aging-induced disorders. Both omega 3 polyunsaturated fatty acids (ω-3 PUFA) and extra virgin olive oil (EVOO) exert numerous metabolic and cardiovascular benefits in the elderly. In addition, EVOO constitutes an interesting ingredient to stabilize ω-3 PUFA and decrease their oxidation process due to its high content in antioxidant compounds. ω-3 PUFA are commonly obtained from fish. However, more ecological and sustainable sources, such as algae oil (AO) can also be used. In this study, we aimed to study the possible beneficial effect of an oil mixture composed by EVOO (75%) and AO (25%) rich in ω-3 PUFA (35% docosahexaenoic acid (DHA) and 20% eicosapentaenoic acid (EPA)) on the cardiometabolic alterations associated with aging. For this purpose; young (three months old) and old (24 months old) male Wistar rats were treated with vehicle or with the oil mixture (2.5 mL/kg) for 21 days. Treatment with the oil mixture prevented the aging-induced increase in the serum levels of saturated fatty acids (SFA) and the aging-induced decrease in the serum concentrations of mono-unsaturated fatty acids (MUFA). Old treated rats showed increased serum concentrations of EPA and DHA and decreased HOMA-IR index and circulating levels of total cholesterol, insulin and IL-6. Treatment with the oil mixture increased the mRNA levels of antioxidant and insulin sensitivity-related enzymes, as well as reduced the gene expression of pro-inflammatory markers in the liver and in cardiac and aortic tissues. In addition, the treatment also prevented the aging-induced endothelial dysfunction and vascular insulin resistance through activation of the PI3K/Akt pathway. Moreover, aortic rings from old rats treated with the oil mixture showed a decreased response to the vasoconstrictor AngII. In conclusion, treatment with a mixture of EVOO and AO improves the lipid profile, insulin sensitivity and vascular function in aged rats and decreases aging-induced inflammation and oxidative stress in the liver, and in the cardiovascular system. Thus, it could be an interesting strategy to deal with cardiometabolic alterations associated with aging.

Pathobiological Interactions of Local Bone Marrow Renin-Angiotensin System and Central Nervous System in Systemic Arterial Hypertension

Circulating renin-angiotensin system (RAS) and local paracrin-autocrin-intracrin tissue-based RAS participate in numerous pathobiological events. Pro-inflammatory, pro-fibrotic, and pro-thrombotic consequences associated with local RAS activation have been detected at cellular and molecular level. Regenerative progenitor cell therapy in response to RAS modulating pharmacotherapy has emerged as an adjunct in the context of endothelial cell injury and regeneration to improve regeneration of the vascular endothelium. Local hematopoietic bone marrow (BM) RAS symbolizes the place of cross-interaction between vascular biology and cellular events from embryogenesis to definitive hematopoiesis underlying vascular atherosclerosis. The BM microenvironment also contains Mas receptors, which control the proliferative role of Ang 1-7 on hematopoietic stem cells. Ang 1-7 is produced from Ang-II or Ang-I with the help of ACE2. Various tissues and organs also have an effect on the RAS system. The leukocytes contain and synthesize immunoreactive angiotensinogen species capable of producing angiotensin in the basal state or after incubation with renin. The significance of RAS employment in atherosclerosis and hypertension was indicated by novel bidirectional Central Nervous System (CNS) RAS-BM RAS communications. Myeloid cells generated within the context of hematopoietic BM RAS are considered as the initiators and decision shapers in atherosclerosis. Macrophages in the atherosclerotic lesions contain angiotensin peptides by which RAS blockers inhibit monocyte activation and adherence. Furthermore, vascular biology in relation to inflammation and neoplasia is also affected by local tissue RAS. The purpose of this article is to outline interactions of circulating and local angiotensin systems, especially local bone marrow RAS, in the vascular pathobiological microenvironment of CNS.

Angiotensinogen and Megalin Interactions Contribute to Atherosclerosis-Brief Report

Objective- AGT (Angiotensinogen) is the unique precursor of the renin-angiotensin system that is sequentially cleaved by renin and ACE (angiotensin-converting enzyme) to produce Ang II (angiotensin II). In this study, we determined how these renin-angiotensin components interact with megalin in kidney to promote atherosclerosis. Approach and Results- AGT, renin, ACE, and megalin were present in the renal proximal convoluted tubules of wild-type mice. Hepatocyte-specific AGT deficiency abolished AGT protein accumulation in proximal tubules and diminished Ang II concentrations in kidney, while renin was increased. Megalin was most abundant in kidney and exclusively present on the apical side of proximal tubules. Inhibition of megalin by antisense oligonucleotides (ASOs) led to ablation of AGT and renin proteins in proximal tubules, while leading to striking increases of urine AGT and renin concentrations, and 70% reduction of renal Ang II concentrations. However, plasma Ang II concentrations were unaffected. To determine whether AGT and megalin interaction contributes to atherosclerosis, we used both male and female low-density lipoprotein receptor^-/- mice fed a saturated fat-enriched diet and administered vehicles (PBS or control ASO) or megalin ASO. Inhibition of megalin did not affect plasma cholesterol concentrations, but profoundly reduced atherosclerotic lesion size in both male and female mice. Conclusions- These results reveal a regulatory role of megalin in the intrarenal renin-angiotensin homeostasis and atherogenesis, positing renal Ang II to be an important contributor to atherosclerosis that is mediated through AGT and megalin interactions.

The roles of FGF21 in atherosclerosis pathogenesis

FGF21 is a peptide hormone that regulates homeostasis of lipid and glucose as well as energy metabolism. It is mainly expressed and secreted in liver and adipose tissues, and it is expressed in lower amounts in the aorta. Recent clinical and preclinical studies indicate increased serum FGF21 levels in atherosclerosis patients. Also, FGF21 therapy has been reported to reduce the initiation and progression of atherosclerosis in animal models and in vitro studies. Moreover, growing evidence indicates that administration of exogenous FGF21 induces anti-atherosclerotic effects, because of its ability to reduce lipid profile, alleviation of oxidative stress, inflammation, and apoptosis. Therefore, FGF21 can not only be considered as a biomarker for predicting atherosclerosis, but also induce protective effects against atherosclerosis. Besides, serum levels of FGF21 increase in various diseases including in diabetes mellitus, hypertension, and obesity, which may be related to initiating and exacerbating atherosclerosis. On the other hand, FGF21 therapy significantly improves lipid profiles, and reduces vascular inflammation and oxidative stress in atherosclerosis related diseases. Therefore, further prospective studies are needed to clarify whether FGF21 can be used as a prognostic biomarker to identify individuals at future risk of atherosclerosis in these atherosclerosis-associated diseases. In this review, we will discuss the possible mechanism by which FGF21 protects against atherosclerosis.

The relationship between plasma renin activity and serum lipid profiles in patients with primary arterial hypertension

Introduction:

The aim of the study was to evaluate clinical and biochemical differences between patients with low-renin and high-renin primary arterial hypertension (AH), mainly in reference to serum lipids, and to identify factors determining lipid concentrations.

Materials and methods:

In untreated patients with AH stage 1 we measured plasma renin activity (PRA) and subdivided the group into low-renin (PRA < 0.65 ng/mL/h) and high-renin (PRA ⩾ 0.65 ng/mL/h) AH. We compared office and 24-h ambulatory blood pressure, serum aldosterone, lipids and selected biochemical parameters between subgroups. Factors determining lipid concentration in both subgroups were assessed in regression analysis.

Results:

Patients with high-renin hypertension (N = 58) were characterized by higher heart rate (p = 0.04), lower serum sodium (p < 0.01) and aldosterone-to-renin ratio (p < 0.01), and significantly higher serum aldosterone (p = 0.03), albumin (p < 0.01), total protein (p < 0.01), total cholesterol (p = 0.01) and low-density lipoprotein cholesterol (LDL-C) (p = 0.04) than low-renin subjects (N = 39). In univariate linear regression, only PRA in the low-renin group was in a positive relationship with LDL-C (R² = 0.15, β = 1.53 and p = 0.013); this association remained significant after adjustment for age, sex, and serum albumin and aldosterone concentrations.

Conclusions:

Higher serum levels of total and LDL-C characterized high-renin subjects, but the association between LDL-C level and PRA existed only in low-renin primary AH.

Angiotensin-(1-7) and Alamandine on Experimental Models of Hypertension and Atherosclerosis

PURPOSE OF REVIEW

The purpose of this review was to summarize the current knowledge on the role of angiotensin-(1-7) [Ang-(1-7)] and alamandine in experimental hypertension and atherosclerosis.

RECENT FINDINGS

The renin-angiotensin system (RAS) is a very complex system, composed of a cascade of enzymes, peptides, and receptors, known to be involved in the pathogenesis of hypertension and atherosclerosis. Ang-(1-7), identified and characterized in 1987, and alamandine, discovered 16 years after, are the newest two main effector molecules from the RAS, protecting the vascular system against hypertension and atherosclerosis. While the beneficial effects of Ang-(1-7) have been widely studied in several experimental models of hypertension, much less studies were performed in experimental models of atherosclerosis. Alamandine has shown similar vascular effects to Ang-(1-7), namely, endothelial-dependent vasorelaxation mediated by nitric oxide and hypotensive effects in experimental hypertension. There are few studies on the effects of alamandine on atherosclerosis.

Dyrk1A-ASF-CaMKIIδ Signaling Is Involved in Valsartan Inhibition of Cardiac Hypertrophy in Renovascular Hypertensive Rats

OBJECTIVES

It is known that the expression, activity and alternative splicing of Ca2+/calmodulin-dependent protein kinase IIδ (CaMKIIδ) are dysregulated in the cardiac remodeling process. Recently, we found a further signaling pathway, by which dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) regulates the alternative splicing of CaMKIIδ via the alternative splicing factor (ASF), i.e., Dyrk1A-ASF-CaMKIIδ. In this study, we aimed to investigate whether Dyrk1A-ASF-CaMKIIδ signaling was involved in valsartan inhibition of cardiac hypertrophy in renovascular hypertensive rats.

METHODS

Rats were subjected to two kidney-one clip (2K1C) surgery and then treated with valsartan (30 mg/kg/day) for 8 weeks. Hypertrophic parameter analysis was then performed. Western blot analysis was used to determine the protein expression of Dyrk1A and ASF and RT-PCR was used to analyze the alternative splicing of CaMKIIδ in the left ventricular (LV) sample.

RESULTS

Valsartan attenuated cardiac hypertrophy in 2K1C rats but without impairment of cardiac systolic function. Increased protein expression of Dyrk1A and decreased protein expression of ASF were observed in the LV sample of 2K1C rats. Treatment of 2K1C rats with valsartan reversed the changes in Dyrk1A and ASF expression in the LV sample. Valsartan adjusted the 2K1C-induced imbalance in alternative splicing of CaMKIIδ by upregulating the mRNA expression of CaMKIIδC and downregulating the mRNA expression of CaMKIIδA and CaMKIIδB.

CONCLUSIONS

Valsartan inhibition of cardiac hypertrophy in renovascular hypertensive rats was mediated, at least partly, by Dyrk1A-ASF-CaMKIIδ signaling.

The renin-angiotensin system and its involvement in vascular disease

The renin-angiotensin system (RAS) plays a critical role in the pathogenesis of many types of cardiovascular diseases including cardiomyopathy, valvular heart disease, aneurysms, stroke, coronary artery disease and vascular injury. Besides the classical regulatory effects on blood pressure and sodium homoeostasis, the RAS is involved in the regulation of contractility and remodelling of the vessel wall. Numerous studies have shown beneficial effect of inhibition of this system in the pathogenesis of cardiovascular diseases. However, dysregulation and overexpression of the RAS, through different molecular mechanisms, also induces, the initiation of vascular damage. The key effector peptide of the RAS, angiotensin II (Ang II) promotes cell proliferation, apoptosis, fibrosis, oxidative stress and inflammation, processes known to contribute to remodelling of the vasculature. In this review, we focus on the components that are under the influence of the RAS and contribute to the development and progression of vascular disease; extracellular matrix defects, atherosclerosis and ageing. Furthermore, the beneficial therapeutic effects of inhibition of the RAS on the vasculature are discussed, as well as the need for additive effects on top of RAS inhibition.

Angiotensin II upregulates endothelial lipase expression via the NF-kappa B and MAPK signaling pathways

BACKGROUND

Angiotensin II (AngII) participates in endothelial damage and inflammation, and accelerates atherosclerosis. Endothelial lipase (EL) is involved in the metabolism and clearance of high density lipoproteins (HDL), the serum levels of which correlate negatively with the onset of cardiovascular diseases including atherosclerosis. However, the relationship between AngII and EL is not yet fully understood. In this study, we investigated the effects of AngII on the expression of EL and the signaling pathways that mediate its effects in human umbilical vein endothelial cells (HUVECs).

METHODS AND FINDINGS

HUVECs were cultured in vitro with different treatments as follows: 1) The control group without any treatment; 2) AngII treatment for 0 h, 4 h, 8 h, 12 h and 24 h; 3) NF-κB activation inhibitor pyrrolidine dithiocarbamate (PDTC) pretreatment for 1 h before AngII treatment; and 4) mitogen-activated protein kinase (MAPK) p38 inhibitor (SB203580) pretreatment for 1 h before AngII treatment. EL levels in each group were detected by immunocytochemical staining and western blotting. HUVECs proliferation was detected by MTT and proliferating cell nuclear antigen (PCNA) immunofluorescence staining. NF-kappa B (NF-κB) p65, MAPK p38, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and phosphorylated extracellular signal-regulated kinase (p-ERK) expression levels were assayed by western blotting. The results showed that the protein levels of EL, NF-κB p65, MAPK p38, JNK, and p-ERK protein levels, in addition to the proliferation of HUVECs, were increased by AngII. Both the NF-kB inhibitor (PDTC) and the MAPK p38 inhibitor (SB203580) partially inhibited the effects of AngII on EL expression.

CONCLUSION

AngII may upregulate EL protein expression via the NF-κB and MAPK signaling pathways.

Cathepsin G deficiency decreases complexity of atherosclerotic lesions in apolipoprotein E-deficient mice

Cathepsin G is a serine protease with a broad range of catalytic activities, including production of angiotensin II, degradation of extracellular matrix and cell-cell junctions, modulation of chemotactic responses, and induction of apoptosis. Cathepsin G mRNA expression is increased in human coronary atheroma vs. the normal vessel. To assess whether cathepsin G modulates atherosclerosis, cathepsin G knockout (Cstg(-/-)) mice were bred with apolipoprotein E knockout (Apoe(-/-)) mice to obtain Ctsg(+/-)Apoe(-/-) and Ctsg(+/+)Apoe(-/-) mice. Heterozygous cathepsin G deficiency led to a 70% decrease in cathepsin G activity in bone marrow cells, but this reduced activity did not impair generation of angiotensin II in bone marrow-derived macrophages (BMDM). Atherosclerotic lesions were compared in male Cstg(+/-)Apoe(-/-) and Cstg(+/+)Apoe(-/-) mice after 8 wk on a high-fat diet. Plasma cholesterol levels and cholesterol distribution within serum lipoprotein fractions did not differ between genotypes nor did the atherosclerotic lesion areas in either the aortic root or aortic arch. Cstg(+/-)Apoe(-/-) mice, however, showed a lower percentage of complex lesions within the aortic root and a smaller number of apoptotic cells compared with Cstg(+/+)Apoe(-/-) littermates. Furthermore, apoptotic Cstg(-/-) BMDM were more efficiently engulfed by phagocytic BMDM than were apoptotic Ctsg(+/+) BMDM. Thus cathepsin G activity may impair efferocytosis, which could lead to an accumulation of lesion-associated apoptotic cells and the accelerated progression of early atherosclerotic lesions to more complex lesions in Apoe(-/-) mice.

Angiotensin converting enzyme 2 and atherosclerosis

Angiotensin converting enzyme 2 (ACE2) is a homolog of angiotensin converting enzyme (ACE) which generates angiotensin II from angiotensin I. ACE, its product angiotensin II and the downstream angiotensin type I receptor are important components of the renin-angiotensin system (RAS). Angiotensin II, the most important component of the RAS, promotes the development of atherosclerosis. The identification of ACE2 in 2000 opened a new chapter of research on the regulation of the RAS. ACE2 degrades pro-atherosclerotic angiotensin II and generates anti-atherosclerotic angiotensin 1-7. In this review, we explored the importance of ACE2 in protecting experimental animals from developing atherosclerosis and its involvement in human atherosclerosis. We also examined the published evidence assessing the importance of ACE2 in different cell types relevant to atherosclerosis and putative underlying cellular and molecular mechanisms linking ACE2 with protection from atherosclerosis. ACE2 shifts the balance from angiotensin II to angiotensin 1-7 inhibiting the progression of atherosclerosis in animal models.

Multilocus analysis in candidate genes ACE, AGT, and AGTR1 and predisposition to peripheral arterial disease: role of ACE D/-240T haplotype

OBJECTIVE

Peripheral arterial disease (PAD) is a common manifestation of systemic atherosclerosis. Apart from traditional cardiovascular risk factors, several novel biologic mediators and genetic predisposing factors appear relevant in determining the atherogenetic process leading to PAD. Genes encoding for renin angiotensin system (RAS) components have been proposed as candidate in atherosclerosis. This study investigated four polymorphisms in angiotensinogen (AGT), angiotensin converting enzyme (ACE), and angiotensin II receptor type 1 (AGTR1), genes of RAS, in both predicting PAD and modulating the severity of the disease.

METHODS

The ACE I/D and -240A>T, AGT M235T, and AGTR1 1166A>C polymorphisms were analyzed in 281 PAD patients and in 485 controls comparable for age and sex.

RESULTS

The ACE D and -240T alleles both significantly influenced the predisposition to PAD. The ACE D, but not -240 T, allele remained associated with PAD after Bonferroni correction (P = .004) and adjustment for cardiovascular risk factors (P = .03). The ACE D allele influenced PAD predisposition with a dose-dependent effect (odds ratio for ACE ID vs II genotype, 1.77; P = .006; ACE DD vs II genotype, 2.15; P = .001). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T haplotype significantly and independently influenced the predisposition to PAD (P = .02). In 190 PAD patients with no additional atherosclerotic localizations (isolated PAD), a significant association between ACE D and -240T alleles and PAD was observed. Only the ACE D allele remained associated with isolated PAD after Bonferroni correction (P = .02) and after adjustment for cardiovascular risk factors (P = .02). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T, but not the D/-240A haplotype significantly influenced the predisposition to PAD (P = .0003). No influence of the polymorphisms analyzed on the severity of the disease, according to Rutherford categories, was found.

CONCLUSIONS

The present study contributes data to highlight the role of the ACED/-240T haplotype in predisposing to PAD, also in the absence of other atherosclerotic comorbidities.

Angiotensin type 2 receptor is expressed in human atherosclerotic lesions

Objective. Expression of the angiotensin type 2 receptor (AT2-receptor) occurs in many animal models of atherosclerosis. However, its expression in human plaques and its functional role remains undetermined.This study examined AT2-receptor expression in human atherosclerotic plaque and also explored its potentially important functional role in atherosclerosis.

Material and methods. We analysed carotid atherosclerotic plaques obtained from 14 Caucasian patients who had previously carotid artery stenosis. Half of all subjects undergone endarterectomy for symptomatic carotid artery stenosis. Half of all subjects received treatment with an angiotensin receptor blocker (ARB) (n=7); the remaining subjects received no intervention in the renin-angiotensin system (n=7). Immunohistochemistry measured tissue expression of smooth muscle cells (α-actin), macrophages (CD68 antibody), collagen (picro-sirius), and AT2-receptor (AT2-receptor antibody).

Results. AT2-receptor expression occurred consistently in all specimens. Although cellular localisation varied, AT2-receptor expression levels correlated with macrophage levels (p<0.01). Compared to conventional treatment, ongoing ARB treatment affected neither AT2-receptor levels nor plaque composition.

Conclusions. AT2-receptor is expressed in human atherosclerotic plaque. Furthermore, we detected no functionally important role of AT2-receptor expression and found no evidence that ARB treatment regulates AT2-receptor expression.

Endogenous angiotensin II enhances atherogenesis in apoprotein E-deficient mice with renovascular hypertension through activation of vascular smooth muscle cells

Renovascular hypertension is one of the most important risk factors in the development of atherosclerosis. However, very little is known about the role of angiotensin II (AII), a key regulator of blood pressure homeostasis, on renovascular hypertension-associated atherogenesis. To study a possible role of AII on atherogenesis, we generated apoE-deficient hypertensive mice with either normal or increased AII production by applying 1-kidney, 1-clip (1K1C) or 2-kidney, 1-clip (2K1C) operation, respectively. Hypertension was successfully achieved in both mice groups, and was persistent for 8 weeks. Atherosclerosis quantification showed a marked increase in lesion area in aortic sinus of 2K1C mice as compared with 1K1C mice, suggesting a potential role of endogenous AII on atherogenesis. In the immunohistochemical analysis, induction of renovascular hypertension with 2K1C for 8 weeks led to an enhanced accumulation of macrophages in the aortic sinus, which was accompanied by a parallel increase in scavenger receptor A (SRA) expression on the macrophages. In in vitro experiments, although treatment of cells with increasing concentrations of AII (0.1 to 10 microM) affects neither SRA expression nor oxLDL uptake by macrophages, conditioned media (CM) derived from AII-stimulated vascular smooth muscle cells (VSMC) increased macrophage uptake of oxLDL in association with an enhanced expression of SRA on the macrophages. These findings suggest that the increased generation of AII in renovascular hypertension may initiate and promote atherosclerosis by activation of VSMC.