Macrophage Metabolism and Pyruvate Kinase M2 in Atherosclerosis

• Applicant: Lukas Tomas, Ph.D.
• Subject Area: Cardiology, Angiology ; Immunology
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450754172

Atherosclerosis is the underlying pathology of myocardial infarction and ischemic stroke, which lead the worldwide mortality statistics. Atherosclerotic plaques develop in response to lipoprotein retention in the arteries and a subsequent chronic inflammation. Macrophages are important innate effector cells and participate in all stages of atherosclerosis development as well as regression. Depending on their specific task, macrophages employ different metabolic pathways to support their effector functions. Previously, we have been able to show that human high-risk atherosclerotic plaques have an altered metabolism when compared with stable plaques. The metabolic profile found in high-risk plaques mirrors the metabolism of inflammatory macrophages and is characterised by an elevated utilization of glycolysis and pathways branching off glycolysis as well as a reduced usage of fatty acid oxidation.A central regulator of the metabolic switch in inflammatory macrophages is the glycolytic enzyme pyruvate kinase (PK) M2. Expression of PKM2 in inflammatory macrophages enables the rewiring of glycolytic flux into pathways branching off glycolysis, such as the pentose-phosphate pathway. In addition to the metabolic regulation, PKM2 can act as a non-metabolic regulator of metabolic reprogramming, by translocating into the nucleus and modulating transcription of e.g. HIF-1α and IL-1β.In preliminary studies I have found a decreased macrophage burden in the aortas of hypercholesterolemic mice that received bone marrow with a deletion of PKM2 in bone marrow-derived macrophages. Herein, I propose to investigate the role of PKM2 expression in macrophages for the development and regression of atherosclerosis in more detail. In aim 1, I will use LDL receptor antisense oligonucleotides to induce hypercholesterolemia and atherosclerosis development in mice with a conditional deletion of PKM2. The use of conditional deletion mice allows me to differentiate between PKM2’s function in yolk sac- and bone marrow-derived macrophages. Aim 2 also applies antisense oligonucleotides in mice with a conditional PKM2 deletion focussing on yolk sac- and bone marrow-derived macrophages. In contrast to aim 1, in these mice the oligonucleotide injection will be discontinued before termination to normalize cholesterol levels and induce atherosclerotic regression. Atherosclerotic plaques and lesional macrophages in atherosclerosis development (aim 1) and regression (aim 2) will be analysed with a range of methods, including multi-parameter flow cytometry, immunohistochemistry and gene expression analysis. In aim 3, I will examine the consequences of PKM2’s metabolic and non-metabolic functions on macrophage features, such as the production of reactive oxygen species and IL-1β as well as inflammasome activation and phagocytosis. This will be done primarily in vitro through the use of immortalized yolk sac- and bone marrow-derived macrophages.

• DFG Programme: WBP Position