Vascular wall ACE is not required for atherogenesis in ApoE(-/-) mice

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

Angiotensin-Converting Enzyme in Smooth Muscle Cells Promotes Atherosclerosis-Brief Report

OBJECTIVE

Angiotensin-converting enzyme (ACE) is present in many cell types of atherosclerotic lesions. This study determined whether ACE activity in endothelial and smooth muscle cells (SMCs), 2 major resident cell types of the aorta, contributes to hypercholesterolemia-induced atherosclerosis.

APPROACH AND RESULTS

All study mice were in low-density lipoprotein receptor(-/-) background. To determine the contribution of ACE on endothelial cells to atherosclerosis, female ACE floxed mice were bred to male Tie2-Cre transgenic mice. Endothelial cell-specific deletion of ACE significantly decreased serum ACE activity, but had no effect on systolic blood pressure and atherosclerosis. Because ACE protein is present on SMCs, the most abundant cell type of the aorta, we then determined whether ACE on SMCs contributes to atherosclerosis. ACE was depleted from SMCs by breeding female ACE floxed mice with male SM22-Cre transgenic mice. SMC-specific deficiency of ACE did not affect ACE activity in serum, but ablated its presence and activity in the aortic media. Although SMC-specific deficiency of ACE had no effect on systolic blood pressure, it significantly attenuated hypercholesterolemia-induced atherosclerosis in both male and female mice.

CONCLUSIONS

These studies provide direct evidence that ACE derived from endothelial cells does not play a critical role in atherosclerosis. Rather, SMC-derived ACE contributes to atherosclerosis, independent of circulating ACE activity and blood pressure.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Contributions of leukocyte angiotensin-converting enzyme to development of atherosclerosis

OBJECTIVE

This study determined the role of angiotensin-converting enzyme (ACE) on the development of angiotensin I-induced atherosclerosis and the contribution of leukocyte-specific expression of this enzyme.

APPROACH AND RESULTS

To define the contribution of ACE-dependent activity to angiotensin II synthesis in atherosclerotic development, male low-density lipoprotein receptor(-/-) mice were fed a fat-enriched diet and infused with either angiotensin I or angiotensin II. The same infusion rate of these peptides had equivalent effects on atherosclerotic development. Coinfusion of an ACE inhibitor, enalapril, ablated angiotensin I-augmented atherosclerosis but had no effect on angiotensin II-induced lesion development. ACE protein was detected in several cell types in atherosclerotic lesions, with a predominance in macrophages. This cell type secreted angiotensin II, which was ablated by ACE inhibition. To study whether leukocyte ACE contributed to atherosclerosis, irradiated male low-density lipoprotein receptor(-/-) mice were repopulated with bone marrow-derived cells from either ACE(+/+) or ACE(-/-) mice and fed the fat-enriched diet for 12 weeks. Chimeric mice with ACE deficiency in bone marrow-derived cells had modestly reduced atherosclerotic lesions in aortic arches but had no effects in aortic roots.

CONCLUSIONS

ACE mediates angiotensin I-induced atherosclerosis, and ACE expression in leukocytes modestly contributes to atherosclerotic development in hypercholesterolemic mice.

Protective Role of the ACE2/Ang-(1-9) Axis in Cardiovascular Remodeling

Despite reduction in cardiovascular (CV) events and end-organ damage with the current pharmacologic strategies, CV disease remains the primary cause of death in the world. Pharmacological therapies based on the renin angiotensin system (RAS) blockade are used extensively for the treatment of hypertension, heart failure, and CV remodeling but in spite of their success the prevalence of end-organ damage and residual risk remain still high. Novel approaches must be discovered for a more effective treatment of residual CV remodeling and risk. The ACE2/Ang-(1–9) axis is a new and important target to counterbalance the vasoconstrictive/proliferative RAS axis. Ang-(1–9) is hydrolyzed slower than Ang-(1–7) and is able to bind the Ang II type 2 receptor. We review here the current experimental evidence suggesting that activation of the ACE2/Ang-(1–9) axis protects the heart and vessels (and possibly the kidney) from adverse cardiovascular remodeling in hypertension as well as in heart failure.

A new look at the renin-angiotensin system--focusing on the vascular system

The renin-angiotensin system (RAS), critically involved in the control of blood pressure and volume homeostasis, is a dual system comprising a circulating component and a local tissue component. The rate limiting enzyme is renin, which in the circulating RAS derives from the kidney to generate Ang II, which in turn regulates cardiovascular function by binding to AT(1) and AT(2) receptors on cardiac, renal and vascular cells. The tissue RAS can operate independently of the circulating RAS and may be activated even when the circulating RAS is suppressed or normal. A functional tissue RAS has been identified in brain, kidney, heart, adipose tissue, hematopoietic tissue, gastrointestinal tract, liver, endocrine system and blood vessels. Whereas angiotensinsinogen, angiotensin converting enzyme (ACE), Ang I and Ang II are synthesized within these tissues, there is still controversy as to whether renin is produced locally or whether it is taken up from the circulation, possibly by the (pro)renin receptor. This is particularly true in the vascular wall, where expression of renin is very low. The exact function of the vascular RAS remains elusive, but may contribute to fine-tuning of vascular tone and arterial structure and may amplify vascular effects of the circulating RAS, particularly in pathological conditions, such as in hypertension, atherosclerosis and diabetes. New concepts relating to the vascular RAS have recently been elucidated including: (1) the presence of functionally active Ang-(1-7)-Mas axis in the vascular system, (2) the importance of the RAS in perivascular adipose tissue and cross talk with vessels, and (3) the contribution to vascular RAS of Ang II derived from immune and inflammatory cells within the vascular wall. The present review highlights recent progress in the RAS field, focusing on the tissue system and particularly on the vascular RAS.

Angiotensin-converting enzyme 2 deficiency in whole body or bone marrow-derived cells increases atherosclerosis in low-density lipoprotein receptor-/- mice

OBJECTIVE

The renin-angiotensin system contributes to atherosclerotic lesion formation. Angiotensin-converting enzyme 2 (ACE2) catabolizes angiotensin II (Ang II) to angiotensin 1-7 (Ang-(1-7)) to limit effects of the renin-angiotensin system. The purpose of this study was to define the role of ACE2 in atherosclerosis.

METHODS AND RESULTS

Male Ace2(-/y) mice in an low-density lipoprotein receptor-deficient background were fed a high-fat diet for 3 months. ACE2 deficiency increased atherosclerotic area (Ace2(+/y), 17 ± 1; Ace2(-/y), 23 ± 2 mm(2), P < 0.002). This increase was blunted by losartan. To determine whether leukocytic ACE2 influenced atherosclerosis, irradiated low-density lipoprotein receptor-deficient male mice were repopulated with bone marrow-derived cells from Ace2(+/y) or Ace2(-/y) mice and fed a high-fat diet for 3 months. ACE2 deficiency in bone marrow-derived cells increased atherosclerotic area (Ace2(+/y), 1.6 ± 0.3; Ace2(-/y), 2.8 ± 0.3 mm(2); P < 0.05). Macrophages from Ace2(-/y) mice exhibited increased Ang II secretion and elevated expression of inflammatory cytokines. Conditioned media from mouse peritoneal macrophages of Ace2(-/y) mice increased monocyte adhesion to human umbilical vein endothelial cells. Incubation of human umbilical vein endothelial cells with Ang II promoted monocyte adhesion, which was blocked by Ang-(1-7). Coinfusion of Ang-(1-7) with Ang II reduced atherosclerosis.

CONCLUSIONS

These results demonstrate that ACE2 deficiency in bone marrow-derived cells promotes atherosclerosis through regulation of Ang II/Ang-(1-7) peptides.

Genetic variants of the Renin Angiotensin system: effects on atherosclerosis in experimental models and humans

The renin angiotensin system (RAS) has profound effects on atherosclerosis development in animal models, which is partially complimented by evidence in the human disease. Although angiotensin II was considered to be the principal effector of the RAS, a broader array of bioactive angiotensin peptides have been identified that have increased the scope of enzymes and receptors in the RAS. Genetic interruption of the synthesis of these peptides has not been extensively performed in experimental or human studies. A few studies demonstrate that interruption of a component of the angiotensin peptide synthesis pathway reduces experimental lesion formation. The evidence in human studies has not been consistent. Conversely, genetic manipulation of the RAS receptors has demonstrated that AT1a receptors are profoundly involved in experimental atherosclerosis. Few studies have reported links of genetic variants of angiotensin II receptors to human atherosclerotic diseases. Further genetic studies are needed to define the role of RAS in atherosclerosis.