Macrophages undergo a behavioural switch during wound healing in zebrafish

Abstract

In response to wound signals, macrophages are immediately recruited to the injury where they acquire distinct phenotypes and functions, playing crucial roles both in host defense and healing process. Although macrophage phenotypes have been intensively studied during wound healing, mostly using markers and expression profiles, the impact of the wound environment on macrophage shape and behaviour, and the underlying mechanisms deserve more in-depth investigation. Here, we sought to characterize the dynamics of macrophage recruitment and behaviour during aseptic wounding of the caudal fin fold of the zebrafish larva. Using a photo-conversion approach, we demonstrated that macrophages are recruited to the wounded fin fold as a single wave where they switch their phenotype. Intravital imaging of macrophage shape and trajectories revealed that wound-macrophages display a highly stereotypical set of behaviours and change their shape from amoeboid to elongated shape as wound healing proceeds. Using a pharmacological inhibitor of 15-lipoxygenase and protectin D1, a specialized pro-resolving lipid, we investigated the role of polyunsaturated fatty acid metabolism in macrophage behaviour. While inhibition of 15-lipoxygenase using PD146176 or Nordihydroguaiaretic acid (NDGA) decreases the switch from amoeboid to elongated shape, protectin D1 accelerates macrophage reverse migration and favours elongated morphologies. Altogether, our findings suggest that individual macrophages at the wound switch their phenotype leading to important changes in behaviour and shape to adapt to changing environment, and highlight the crucial role of lipid metabolism in the control of macrophage behaviour plasticity during inflammation in vivo.

Keywords: Macrophage; Protectin D1; Specialized pro-resolving mediators; Trafficking; Zebrafish.