The role of lipogenic enzymes in the vascular smooth muscle cell to foam cell transition. Restricted; Files Only
Bogan, Bethany (Spring 2024)
Published
Abstract
Atherosclerosis is a frequent, severe, and progressive disease that represents the leading cause of death worldwide. During the progression of atherosclerosis, the tunica intima of the affected vessel accumulates a specialized type of macrophages called foam cells. These cells ingest circulating low-density lipoproteins and become laden with lipids. Vascular smooth muscle cells (VSMCs) comprise the majority of the vasculature and thus are essential to vascular function. A significant portion of VSMCs undergo phenotypic modulation during the development of atherosclerosis.
Vascular smooth muscle cells (VSMCs), in their contractile and differentiated state, are fundamental for maintaining vascular function. Upon exposure to cholesterol (CHO), VSMCs undergo dedifferentiation, adopting characteristics of foam cells– lipid-laden, macrophage-like cells pivotal in atherosclerotic plaque formation. CHO uptake by VSMCs leads to two primary pathways: ABCA1-mediated efflux or storage in lipid droplets as cholesterol esters (CEs). CE formation, involving the condensation of free CHO and fatty acids, is catalyzed by sterol O-acyltransferase 1 (SOAT1). The necessary fatty acids are synthesized by the lipogenic pathway.
The aim of this work was to investigate the role of the main lipogenic enzymes Acetyl CoA carboxylase 1 (ACACA), ATP-Citrate Lyase (ACLY), and fatty acid synthase (FASN) in VSMC to foam cell transition. While ACACA or ACLY genes were not changed in human atherosclerosis, we found that FASN is significantly upregulated in atherosclerotic human coronary arteries. This observation led us to hypothesize that FASN-mediated fatty acid biosynthesis is crucial in the transformation of VSMCs into foam cells. Our study reveals that CHO treatment upregulates FASN in human aortic SMCs, concurrent with increased expression of CD68 and upregulation of KLF4, markers associated with the foam cell transition. Crucially, downregulation of FASN inhibits the CHO-induced upregulation of CD68 and KLF4 in VSMCs. Additionally, FASN-deficient VSMCs exhibit hindered lipid accumulation and an impaired transition to the foam cell phenotype following CHO exposure, while the addition of the fatty acid palmitate, the main FASN product, exacerbates this transition. FASN-deficient cells also show decreased SOAT1 expression and elevated ABCA1. Notably, similar effects are observed in KLF4-deficient cells. Our findings demonstrate that FASN plays an essential role in the CHO-induced upregulation of KLF4 and the VSMC to foam cell transition and suggest that targeting FASN could be a novel therapeutic strategy to regulate VSMC phenotypic modulation.
Table of Contents
TABLE OF CONTENTS 7
INDEX OF FIGURES 11
LIST OF ABBREVIATIONS 13
Chapter 1:
Introduction
1. Atherosclerosis 15
1.1.2. Pathologies associated with atherosclerosis. 22
1.1.2.1. Peripheral Artery Disease (PAD). 22
1.1.2.2. Coronary Artery, Disease (CAD). 23
1.1.2.3. Stroke. 26
1.2. Smooth Muscle Cells. 28
1.2.2. Transcriptional Programs leading to Smooth muscle differentiation. 30
1.2.3. Smooth muscle cells Plasticity and Phenotypic Modulation. 33
1.3. Mechanism of VSMC-derived Foam cell formation. 36
1.4. Cholesterol Esterification and Cholesterol Efflux. 38
1.5. de novo Lipogenesis. 42
1.6. Dissertation Objectives. 46
Chapter 2:
The role of fatty acid synthase in the modulation of vascular smooth muscle cells into a foam cell phenotype.
2.1. Introduction. 47
2.2. Materials and Methods. 49
2.2.1. Human coronary arteries.
2.2.2. RNA-seq in Cholesterol-treated HASMCs.
2.2.3. Cell Culture and Cholesterol treatment.
2.2.4. Cell Transfection.
2.2.5. Preparation of Bovine Serum Albumin (BSA)-Palmitate Conjugate and cell treatment.
2.2.6. Intracellular neutral lipids staining.
2.2.7. Western Blots.
2.2.8. Statistical Analysis.
2.3. Results. 53
2.3.1. Cholesterol induced phenotypic switching is accompanied by the upregulation of the fatty acid synthase (FASN) in VSMC in vivo and in vitro.
2.3.2. FASN deficiency inhibits cholesterol-induced VSMC-derived foam cell formation.
2.3.3. FASN regulates proteins from the cholesterol efflux pathway.
2.3.4. KLF4 is the downstream effector of FASN.
2.4. Discussion. 68
Chapter 3:
FASN participates in PKA activation and ABCA1 phosphorylation at Ser-2054
3.1. Introduction. 72
3.2. Materials and Methods. 73
3.2.1. Cell Culture and Cholesterol treatment.
3.2.2. Cell Transfection.
3.2.3. Western Blots.
3.2.4. Statistical Analysis.
3.3. Results. 74
3.3.1. Downregulation of FASN expression causes an increase in the expression of Phospho-PKA substrate in the presence of cholesterol.
3.3.2. FASN deficiency and cholesterol treatment increases the protein expression of Phospho-ABCA1.
3.3.3. Proposed mechanism of the downstream mechanism of FASN mediating activation of ABCA1 expression
3.4. Discussion 78
Chapter 4:
The role of the enzymes acetyl CoA carboxylase (ACACA) and ATP citrate lyase (ACLY) in the formation of vascular smooth muscle cell derived- foam cells.
4.1. Introduction. 81
4.2. Materials and Methods. 81
4.1.1. Cell Culture and Cholesterol treatment.
4.2.2. Cell Transfection.
4.2.3. Intracellular neutral lipids staining.
4.2.4. Western Blots.
4.2.5. Statistical Analysis.
4.3. Results. 83
4.3.1. Lipogenic enzymes ACACA and ACLY are increased during VSMC phenotypic modulation.
4.3.2. ACACA deficiency does not affect cholesterol-induced expression of CD68.
4.3.3. ACACA deficiency does not affect cholesterol-induced lipid accumulation.
4.3.4. ACLY deficiency does not affect cholesterol-induced lipid accumulation.
4.4. Discussion. 92
Chapter 5:
5.1. Discussion 94
5.1.1. VSMC plasticity and diseases.
5.1.2. VSMCs in mechanisms of metabolism.
5.1.3. Foam cells in lipid metabolism.
5.1.4. Foam cells and Disease.
5.1.5. Fatty Acid Synthase in VSMC foam cell formation
5.2. Conclusions and Future Directions
About this Dissertation
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