Role of Endothelial Cell CD36 in Atherosclerosis and Fatty Acid Metabolism
Creators: Rekhi, Umar
Publisher: name: University of Alberta Library
Year: 2024

<p>Background and Objective<br>
High-fat Western diets have been linked to the dysregulation of fatty acids (FA) and glucose intake in tissues, resulting in adverse metabolic outcomes such as obesity, insulin resistance, and atherosclerosis. There is a pressing need for new therapeutic approaches to address the challenges posed by this epidemic. This research focuses on the regulation of FA entry into tissues at the endothelial cell (EC) interface, an area that has been understudied but holds potential for identifying novel therapeutic targets. The dysfunctional endothelium, characterized by activation, pro-inflammatory nature, and pro-thrombotic properties, plays a critical role in initiating atherosclerosis and is linked to thrombotic events, myocardial infarction, stroke, and insulin resistance. Dyslipidemia from high-fat diets (HFDs) is a major contributor to endothelial dysfunction. CD36, acting as a receptor for pathological ligands from HFDs and participating in FA uptake, is hypothesized to contribute to EC dysfunction. The primary objective of this study is to investigate the role of EC CD36 in the metabolic changes associated with HFDs. Specifically, the study aims to understand how EC CD36 contributes to fatty acid uptake, systemic metabolism, and the development of atherosclerosis.<br>
Hypothesis<br>
We hypothesize that CD36 is a major EC receptor of FAs and proinflammatory atherogenic ligands, and that loss of EC CD36 will result in a metabolic phenotype and differences in atherosclerosis that correlate with changes in inflammation and FA uptake.</p>

<p>Materials and Methods<br>
We generated EC CD36 knockout (EC CD36 KO) mice using cre-lox technology and a specific cre-promoter (Tie2e cre) that spares CD36 in hematopoietic cells. These mice were fed various diets and crossed with low-density lipoprotein receptor knockout (LDLR KO) mice for evaluating atherosclerosis. EC CD36 KO/LDLR KO and fl/fl CD36/LDLR KO control mice, aged six to eight weeks, were fed a high-fat, high-cholesterol diet for 3, 6, and 16 weeks for atherosclerosis assessments, with separate cohorts of male and female mice examined at each time point. Measurements of fasting glucose and weights were taken before euthanasia; at 3 and 6 weeks. Plasma samples were analyzed for 3-nitrotyrosine (3-NT), triglycerides (TG), total and free cholesterol levels, glucose tolerance test (GTT), and fast protein liquid chromatography (FPLC). At 16 weeks, aorta morphometry was performed on isolated aortas. To investigate the impact of EC CD36 loss on metabolism, four-week-old fl/fl CD36 and EC CD36 KO mice were monitored in metabolic cages after being fed a normal chow (NC) diet. The Comprehensive Laboratory Animal Monitoring System (CLAMS) was employed for indirect calorimetry. After 4 weeks, fasting glucose and weights were measured before euthanasia. Plasma was isolated for untargeted metabolomics by chemical isotope labeling liquid chromatography mass spectrometry, and blood was subjected to flow cytometry. Additionally, we explored the effect of EC CD36 loss in a diabetogenic scenario, with mice fed ingredient-matched diets containing 10% and 45% fat for 12 weeks. GTT was performed at the 8-week time point, and after 12 weeks, mice were sacrificed, and blood was drawn for plasma extraction to conduct TG, cholesterol assays, and FPLC.<br>
Results<br>
The results indicate that EC CD36 KO and EC CD36 KO/LDLR KO mice exhibit metabolic changes, suggesting an uncompensated role for EC CD36 in FA uptake. Notably, the mice lacking EC CD36 expression showed increased glucose clearance across various diets. Male EC CD36 KO mice displayed increased carbohydrate utilization and decreased energy expenditure, as observed through indirect calorimetry. Furthermore, female EC CD36 KO/LDLR KO mice demonstrated reduced atherosclerosis. Metabolomics profiling uncovered altered plasma levels of acetylcarnitine, phenylalanyl-glutamine, threonine, xanthurenic acid and menaquinol in EC CD36 KO mice compared to control mice, providing insights into the intricate metabolic consequences of EC CD36 deficiency.<br>
Conclusion<br>
In conclusion, the data support a significant role for EC CD36 in systemic metabolism and reveal sex-specific impacts on atherosclerosis and energy substrate use. The findings suggest that targeting EC CD36 could be a promising avenue for therapeutic interventions aimed at addressing the metabolic consequences of HFDs. The study offers valuable insights that could enhance our comprehension of how EC CD36 deficiency contributes to endothelial dysfunction, leading to atherosclerosis and metabolic dysregulation induced by HFDs. This research lays the groundwork for future investigations in this crucial domain of cardiovascular health.</p>