A Signaling Pathway to Mediate the Combined Immunomodulation of Acetylcholine and Enkephalin in Oyster Crassostrea gigas.

Zhaoqun Liu,Linsheng Song,Yukun Zhang,Meijia Li,Lingling Wang,Zhi Zhou,Weilin Wang,Yan Zheng,Yanan Zong

doi:10.3389/fimmu.2020.00616

Zhaoqun Liu, Linsheng Song + Show 7 more

Open Access

https://doi.org/10.3389/fimmu.2020.00616

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Abstract

Molluscs have evolved a primitive but complete neuroendocrine-immune (NEI) system with a vast array of neurotransmitters to conduct both humoral and cellular immunomodulation. Previous studies have illustrated the immune functions of several key neurotransmitters. However, the combined effects of multiple neurotransmitters and the signaling pathway to mediate such immunomodulation have not been well-understood. In the present study, iTRAQ and LC-ESI-MS/MS approaches were employed to investigate the combined immunomodulation functions of two crucial neurotransmitters, acetylcholine (ACh), and [Met5]-enkephalin (ENK), in oyster Crassostrea gigas. A total number of 5,379 proteins were identified from hemocytes of oysters after the treatments with Ach and ENK separately or simultaneously, and 1,475 of them were found to be significantly up-regulated, while 1,115 of them were significantly down-regulated. The protein expression patterns in the groups treated by ACh and ENK separately were quite similar, which were dramatically different from that in the group treated by ACh+ENK. One hundred seventy-two proteins were found to be differentially expressed in all the three neurotransmitter treatment groups. Functional validation suggested that ACh and ENK possibly modulate the immune response in oyster hemocytes by enhancing pathogen recognition, cell apoptosis, and the enzyme activities of superoxide dismutase (SOD). Moreover, GO enrichment and co-expression network analyses implied that the combined immunomodulation of ACh and ENK might be mediated by p53, EGF-R–ErbB, and Fc gamma R (FcγR) signaling pathways. These results collectively indicated that multiple neurotransmitters executed a combined and ordered immune regulation through common signaling cascades in molluscs, which was under delicate control to maintain the homeostasis.

Highlights

The hypothesis of neuroendocrine-immune (NEI) regulatory network is proposed on the existence of afferent–efferent pathways between immune and neuroendocrine structures, which refers to a unified feedback network consisting of nervous system, endocrine system, and immune system [1]
The NEI regulatory network consists of nervous system, endocrine system, and immune system, which plays a reciprocal modulatory role in host homeostasis [10]
ITRAQ and LC-ESI-MS/MS approaches were employed to further investigate the signaling pathways mediating the immunomodulation of ACh and ENK, as well as the combined modulatory effects of ACh and ENK

Summary

Introduction

The hypothesis of neuroendocrine-immune (NEI) regulatory network is proposed on the existence of afferent–efferent pathways between immune and neuroendocrine structures, which refers to a unified feedback network consisting of nervous system, endocrine system, and immune system [1]. NEI network carries a reciprocal regulation role among various systems to maintain the homeostasis with the involvement of signaling molecules, such as neurotransmitters, hormones, and cytokines [1]. A primitive but complete NEI system has been characterized in molluscs [5,6,7], which shares structural and molecular similarities with that in vertebrates. As mollusca is the most primitive phyla with a complete NEI system [8], a better understanding of the molecular basis and regulatory pathways of molluscan NEI regulation will undoubtedly contribute to the comparative study of the innate immunity

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