Functional dynamics of macrophage polarization during regeneration in zebrafish – MacrophageDynamics

To study macrophages, we have chosen a simple model, the transparent zebrafish larva that is ideally suited to live observation of immune cells and possesses high homology with human genes and cell types. Injury of the zebrafish caudal fin fold triggers a transient inflammation, followed by a resolution phase contributing to the complete regeneration of the lost tissue; others and we demonstrated that macrophages are required for all steps of this process.
We use this model system to challenge macrophages and we develop genetic tools to study macrophage phenotypes. Combining fluorescent macrophages and high-resolution imaging we dissect the role of candidate genes and signalling pathway involved in macrophage polarization in live vertebrates.

When the body suffers a wound, immune cells move toward the injury site and immediately activate. This activation is thought to be triggered in reaction to danger signals released from the damaged tissues. Previous research identified calcium signalling and Reactive Oxygen Species as conserved early wound signals that emanate from the wound edge and guide leukocytes within tissues. However, little is known about their contribution to macrophage activation during wound healing in vivo. The latest findings of MacrophageDynamics show that calcium is important for macrophage recruitment to a wound and activation towards pro-inflammatory states, while Reactive Oxygen Species are only required for macrophage pro-inflammatory activation. By observing the tiny, transparent fish under a microscope, we observed how individual macrophages are drawn to the wound and how they modify their transcriptional program. We also identified 3 genes, Lyn and Yrk and NfKB, as key regulators of macrophage activation in this system. We thus propose a novel mechanism by which conserved early wound signals drive macrophage activation during wound healing in vivo. The results were particularly relevant for developing new therapeutic strategies to modulate the responses of macrophages during pathological wounds or trauma.

We hope that these studies will allow us to better understand the biology of macrophages in the context of injury and to identify new therapeutic targets to modulate macrophage responses in pathological wounds or trauma in humans.

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At the heart of organisms as complex as the human body lie the macrophages. They are present within all the tissues, either resident or patrolling the organism to deal with any dead cells, injury or infections. While they may share common origins and features, they may have different flavours. Despite an historical wealth of knowledge about macrophage flavours and phenotypes in vitro, they are still poorly understood in vivo. To study macrophages, we have chosen a simple model, the transparent zebrafish larva that is ideally suited to live observation of immune cells and possesses high homology with human genes and cell types. Injury of the zebrafish caudal fin triggers a transient inflammation, followed by a resolution phase contributing to the complete regeneration of the lost tissue; others and we demonstrated that macrophages are required for all steps of this process. Based on solid preliminary results, the MacrophageDynamics proposal aims to 1/ set up original tools to study if and how macrophages switch phenotypes, which so far has proven difficult to observe in vivo, 2/ discover new mechanisms involved in the phenotype switch of macrophages during an inflammatory episode. Leading to potential therapeutic approaches to manipulate macrophage response to boost organ repair, this proposal meets the ANR challenge “life, health and well-being”.