Copper Regulates the Susceptibility of Zebrafish Larvae to Inflammatory Stimuli by Controlling Neutrophil/Macrophage Survival.

Mingyue Chen,Jiangping Xu,Ming-Xian Chang,Jing-Xia Liu,Yi Luo

doi:10.3389/fimmu.2019.02599

Abstract

Copper has been revealed to negatively affect the hematopoietic system, which has an important function in immune pathogen defense, but little is known about the potential mechanism. In this study, copper-stressed larvae exhibited significantly increased mortality as well as reduced percentages of GFP-labeled macrophages and neutrophils after Aeromonas hydrophila (A. hydrophila) infection. However, those copper-stressed GFP-labeled macrophages and neutrophils showed more rapid responses to A. hydrophila infection. The transcriptional profiles in copper-stressed macrophages or neutrophils were unveiled by RNA-Sequencing, and KEGG pathway analysis revealed enrichment of differentially expressed genes (DEGs) in lysosome, apoptosis, oxidative phosphorylation, phagosome, etc. The copper-stressed macrophages or neutrophils were revealed to have an increase in reactive oxygen species (ROS) and mitochondria ROS (mROS)-mediated apoptosis, and a reduction in phagocytosis. Furthermore, the A. hydrophila-infected copper-stressed macrophages or neutrophils were found to be unable to maintain a consistently increased expression in immune responsive genes. This study demonstrated for the first time that copper might induce the susceptibility of fish larvae to inflammatory stimuli via triggering macrophage or neutrophil apoptosis, leading to reduced phagocytic activities and non-sustainable immune responses in immune macrophages or neutrophils.

Highlights

During zebrafish embryogenesis, primitive macrophages are initiated and specified at 12–16 hpf and primitive neutrophils at 16 hpf [1, 2] from rostral blood island (RBI) [3, 4]
The responses of copper-stressed larvae and their macrophages and neutrophils to A. hydrophila infection were further investigated, and the reactive oxygen species (ROS)mediated apoptosis and the down-regulated phagocytic activities of neutrophils and macrophages were found to be associated with the sensitivity of copper-stressed fish larvae to A. hydrophila infection in this study
A. hydrophila is a gram-negative opportunistic pathogen found in aquatic environment, but the potential molecular mechanisms of how it functions as an opportunistic pathogen in inducing fish mortality are still scare

Summary

Introduction

Primitive macrophages are initiated and specified at 12–16 hpf (hours post fertilization) and primitive neutrophils at 16 hpf [1, 2] from rostral blood island (RBI) [3, 4]. Zebrafish rely exclusively on innate immune system before they form functional adaptive immunity at around 28 dpf (days post fertilization) [6]. Copper Regulates the Susceptibility of Zebrafish to Inflammation vertebrate models for studying host–microbe interactions due to their advantages in in vivo imaging and genetic analysis [7, 8]. To date, studies on host–microbe interaction in fish under a stressed environment are scarce, and little is known about the cellular biology and transcriptional responses of leukocyte cells to microbe infection in stressed fish

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Conclusion