Digital Theses Archive


Tesi etd-03222022-182733

Type of thesis
Region-specific lipid markers of plaque vulnerability investigated by MALDI mass spectrometry imaging of human carotid atherosclerotic lesions
Scientific disciplinary sector
Istituto di Scienze della Vita - TRANSLATIONAL MEDICINE 2018
  • human carotid plaque
  • lipids
  • MALDI mass spectrometry imaging
  • Plaque vulnerability
Exam session start date
Atherosclerosis is a systemic disease characterized by a lipid-rich plaque in arterial walls. Atherosclerotic plaques are heterogeneous and composed of different cell populations, proteins and debris. The worst outcome of atherosclerosis is plaque rupture, luminal thrombosis and clogging of smaller vessels, which cause potentially lethal or disabling events. The biological mechanisms leading to plaque rupture are still largely unknown. <br>The goal of the study is the identification of region-specific lipid markers of plaque vulnerability to gain a better insight of the molecular background underlying plaque rupture. <br>Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) enables the spatially resolved molecular analysis of tissue sections. Here it was used to investigate the lipid composition of carotid plaques from symptomatic (vulnerable plaque) and asymptomatic patients. The cellular and molecular composition of the plaques were demarcated using histological staining and immunofluorescence microscopy, and used to define specific regions-of-interest. The analysis focused on macrophage-rich regions, vascular smooth muscle cells (VSMCs) of the inner plaque layer, VSMCs of the outer plaque layer, the lipid-necrotic core, and collagen-rich regions. Hierarchical cluster analysis was performed to compare and contrast the lipid profiles of plaque regions, and between symptomatic and asymptomatic patients. Partial least squares regression was used to select features that distinguished symptomatic and asymptomatic lesions.<br>The comparison of the lipid profiles of different regions revealed that the lipid profile of VSMCs of the fibrous cap is closer in composition to the macrophage-region than VSMCs of the outer plaque layer, suggesting that VSMC migration to the vessel lumen is accompanied by a change in lipid composition. Macrophage-rich regions and inner VSMCs of symptomatic plaques were found to be enriched in phosphatidylcholines; in asymptomatic plaques the same regions were characterized by cholesteryl esters and triglycerides, the main constituents of lipid droplets, suggesting better cholesterol management of cells of asymptomatic lesions. Lysophosphatidylcholines were found to be increased in VSMCs of the inner layer of asymptomatic plaques. Lysophosphatidylcholines stimulate VSMC proliferation and migration, crucial to the build-up of the fibrous cap and thus a stable plaque.<br>MALDI MSI of carotid atherosclerosis lesions successfully identified lipid markers of plaque vulnerability. The effect of lipids on plaque rupture, previously observed only in in-vitro and animal models, was verified here by applying for the first time MALDI MSI to the analysis of plaques from asymptomatic and symptomatic patients. A better understanding of the biological mechanisms of plaque vulnerability is critical for the development of plaque stabilizing drugs and better patient management.<br>