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Leducq Transatlantic Network on Transcription Factor KLF2 and Cardiovascular Disease:

Leducq - Transatlantic Networks of Excellence draws together the efforts of 3 United States and 3 European Union research teams. This project started in 2019 and runs for a period of 5 years with the support of a $6,000,000 grant from Fondation Leducq.

What is the Leducq transcription factor Klf2 and cardiovascular disease project about?

The Leducq project is built around the long-standing observation that atherosclerotic lesions occur preferentially in regions of arteries that, due to branching or sharp curvature, are subject to lower flow magnitude and disturbances in flow profiles, that is, flow that reverses or shows complicated changes in direction with each heartbeat. By contrast, regions of arteries with high, unidirectional flow are protected from disease, even in the presence of risk factors such as high cholesterol, hypertension, smoking and so on.

Studies from several labs identified a protein named kruppel-like factor 2 (KLF2) that is elevated in the endothelial cells in atherosclerosis-resistant regions of arteries under high flow and decreased in atherosclerosis-prone regions under disturbed flow. KLF2 is a transcription factor, that is, a protein that binds DNA and regulates the production of other proteins. In arterial endothelial cells, it was found to induce expression of a whole set of protective genes that inhibit inflammation, blood clotting and oxidative stress. In culture, applying fluid flow to endothelial cells induced KLF2 by about 20-fold. Interestingly, statins, the widely used drugs for lowering cholesterol, also induce KLF2, in this case by about 4- or 5-fold, which is thought to make an important contribution to their efficacy in preventing heart attacks.

Studies on how KLF2 is induced found that flow activates a protein kinase (a protein that regulates other proteins by attaching a phosphate group at specific locations) called Erk5, and activated Erk5 triggers KLF2 expression. But how flow activates Erk5 has remained an open question for nearly 15 years. We decided to answer this question using a recently invented technique to determine which proteins affect flow induction of KLF2. This technique is called CRISPR-Cas9 and allowed us to test all of the genes in the mammalian genome. This experiment revealed that nearly 1000 genes have some effect, about 2/3 reducing and 1/3 increasing KLF2 levels.

This list provides the basis for the Leducq grant. Our goal is first to understand the molecular mechanism by which flow activates Erk5 and induces KLF2. Perhaps even more important, the list of genes whose deletion/mutation increases KLF2 levels represents proteins that if inhibited could increase KLF2 and inhibit atherosclerosis. These genes are therefore possible drug targets.

In parallel, the Kahn lab implicated KLF2 in a vascular disease called cerebral cavernous malformations or CCM. This is primarily a disease in which mutation of any member of a group of genes (CCM1, CCM2 and CCM3) gives rise to malformations in the brain of the affected people. These lesions are fragile and prone to rupture, causing strokes, often with devastating if not lethal consequences. Many cases are inherited and lead to multiple lesions and strokes in young people. Kahn and colleagues found that KLF2 was highly increased in the mutated endothelial cells. Using mouse models with mutation of CCM genes, they found that instead of promoting vessel stability, KLF2 promoted enlargement of these lesions, worsening the disease. Thus, in this setting, KLF2 must induce a distinct set of genes. This behavior, inducing different genes in different contexts, is common among transcription factors.