Factors governing monocyte-macrophage physiology and function during atherosclerotic cardiovascular disease

Pinos Cabezas, Ivan

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https://hdl.handle.net/2142/117650 Copy

Description

Title

Factors governing monocyte-macrophage physiology and function during atherosclerotic cardiovascular disease

Author(s)

Pinos Cabezas, Ivan

Issue Date

2022-11-23

Director of Research (if dissertation) or Advisor (if thesis)

Amengual Terrasa, Jaume

Doctoral Committee Chair(s)

Erdman , John W

Committee Member(s)

• Nelson, Erik R
• Chen, Hong

Department of Study

Nutritional Sciences

Discipline

Nutritional Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Atherosclerosis
• HIV
• Vitamin A
• Macrophage

Abstract

Cardiovascular diseases (CVDs) are the primary cause of death worldwide, and atherosclerosis is considered the main underlying condition preceding most of the CVDs. Atherosclerosis is characterized by the thickening and stiffening of arteries due to the formation of atheromatous plaques composed by lipids and cellular debris in the arterial wall, a condition that may lead to blood flow occlusion or the rupture of the arterial inner lining. During the initiation of atherosclerosis, high levels of circulating cholesterol-rich lipoparticles and their accumulation in the sub-endothelial space trigger the recruitment of monocyte-derived macrophages that scavenge lipoparticles to become foam cells. Although this process begins early in life and progresses over time with fatal outcomes, preclinical and clinical studies have shown that atherosclerosis is a reversible condition that initiates with the resolution of plaque inflammation to evolve into atherosclerosis regression. The macrophage phenotype is highly dynamic and exhibits tailored responses to several stimuli, playing a central role in the progression and resolution of atherosclerosis. Foam cell formation in atherosclerotic plaques promotes the secretion of pro-inflammatory cytokines that sustain monocyte recruitment, lipoprotein retention, and plaque growth. By contrast, macrophages can also exhibit an anti-inflammatory phenotype that supports lesion stability and tissue healing during atherosclerosis resolution and regression. Therefore, new therapeutic opportunities aim to understand and modulate the factors governing the macrophage phenotype to achieve atherosclerosis regression. The impact of certain inflammatory conditions and dietary components on CVD risk, and to what extent they modulate the macrophage phenotype remains largely unknown. Chronic inflammatory infections, such as the human immunodeficiency virus (HIV) infection, have a particular deleterious effect on CVDs. However, limited mechanistic evidence is available due to the lack of suitable and convenient research animal models. On the other hand, studies support a protective role of β-carotene and vitamin A in atherosclerosis, although the lack of mechanistic insights requires further investigation. The goal of our studies was to investigate the individual impact of two factors affecting immunity, HIV infection and vitamin A, on atherosclerosis development and resolution. Chapter 2 provides a comprehensive review of CVDs, the molecular basis governing atherosclerosis progression and resolution, and the mouse models used in this field. This chapter focuses on HIV infection and vitamin A as pivotal factors modulating the monocyte/macrophage response during atherosclerosis. In Chapter 3, we highlight our efforts in developing a mouse model to study HIV-mediated atherogenesis. To this end, we utilized LDL receptor-deficient (Ldlr-/-) mice infected with an ecotropic HIV virus (EcoHIV). This model mimicked the phenotype observed in HIV-infected individuals, where the infection accelerates the development of atherosclerosis. Our data show that EcoHIV accelerates atherogenesis in Ldlr-/- mice by increasing circulating pro-inflammatory monocyte subsets (Ly6chi), while having no effects on plasma lipid parameters. We also show that EcoHIV preferentially infects Ly6chi monocytes, which are more prone to infiltrate into atherosclerotic lesions. Histological analyses demonstrated increased monocyte transmigration into the arterial wall, higher macrophage content, and greater signs of plaque vulnerability in EcoHIV infected mice compared to uninfected littermates. These effects occurred both male and female mice. In next chapters, we investigated the effect of vitamin A to modulate the macrophage phenotype and play a beneficial role in atherosclerosis. First, to discriminate between effects driven by vitamin A and β-carotene, we used mice deficient in β-carotene oxygenase 1 (BCO1), the enzyme that cleaves β-carotene into retinoids (Chapter 4). Ldlr-/- mice fed β-carotene supplementation showed smaller lesion size and plasma cholesterol levels compared to control-fed littermates, but these effects were abrogated in Ldlr-/-/Bco1-/- mice. Cell culture and in vivo studies showed that retinoic acid, the transcriptionally active vitamin A metabolite, reduced the secretion of hepatic cholesterol and triglycerides in both experimental models. Bone marrow transplant experiments ruled out the effect of myeloid BCO1 expression as responsible for the changes in plaque size observed in our Ldlr-/- model. These results suggest that retinoic acid, and not intact β-carotene, is responsible for the delay in atherosclerosis progression. To examine whether β-carotene and vitamin A affects atherosclerosis resolution, we carried out experiments using several murine experimental models (Chapter 5). We first evaluated the effect β-carotene supplementation during atherosclerosis resolution using two reversible mouse models of atherosclerosis. In our first model, we transiently blocked the LDLR expression using an antisense oligonucleotide, while in our second model, we favored atherosclerosis resolution in Ldlr-/- mice by utilizing a dietary switch. In both models, β-carotene supplementation accelerated atherosclerosis resolution, characterized by lower macrophage and increased collagen content in the lesion, a sign of plaque inflammation and stability, respectively. We demonstrated that the absence of BCO1 abolished these effects, suggesting that β-carotene cleavage into vitamin A is essential to mediate these outcomes. Lastly, we provided mechanistic insights into the effects of vitamin A on atherosclerosis regression by regulating regulatory T cells (Treg) in atherosclerotic lesions. In Chapter 6 we used a cell culture approach in which we combined transcriptomic analyses with functional assays aiming to investigate how retinoic acid, the transcriptionally active form of vitamin A, modulates the macrophage phenotype. Our results showed that under anti-inflammatory stimuli, macrophages increase retinoic acid production, and that exogenous retinoic acid boosted this phenotype, characterized by increased efferocytosis and lysosomal degradation. The overall results from our studies proved valuable insights into the factors affecting macrophage phenotype and their implications in the evolution of atherosclerosis. Future studies should investigate emerging factors that may contribute to atherosclerosis and CVDs, as well as develop new therapeutic approaches to prevent and potentially reverse the progression of this disease.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Ivan Pinos Cabezas

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