Gamma-aminobutyric acid (GABA) suppresses hemocyte phagocytosis by binding to GABA receptors and modulating corresponding downstream pathways in blood clam, Tegillarca granosa

Yihan Yu; Dandan Tian; Sanghyok Ri; Tongchol Kim; Kwangjin Ju; Jiongming Zhang; Shuangshuang Teng; Weixia Zhang; Wei Shi; Guangxu Liu

doi:10.1016/j.fsi.2023.108608

Gamma-aminobutyric acid (GABA) suppresses hemocyte phagocytosis by binding to GABA receptors and modulating corresponding downstream pathways in blood clam, Tegillarca granosa

Fish Shellfish Immunol. 2023 Mar:134:108608. doi: 10.1016/j.fsi.2023.108608. Epub 2023 Feb 8.

Authors

Affiliations

¹ College of Animal Sciences, Zhejiang University, Hangzhou, 310058, PR China.
² College of Animal Sciences, Zhejiang University, Hangzhou, 310058, PR China; College of Life Science, Kim Hyong Jik University of Education, Pyongyang, 99903, North Korea.
³ College of Animal Sciences, Zhejiang University, Hangzhou, 310058, PR China; College of Aquaculture, Wonsan Fisheries University, Wonsan, 999093, North Korea.
⁴ Zhejiang Mariculture Research Institute, Wenzhou, 325005, PR China.
⁵ College of Animal Sciences, Zhejiang University, Hangzhou, 310058, PR China. Electronic address: guangxu_liu@zju.edu.cn.

PMID: 36764632
DOI: 10.1016/j.fsi.2023.108608

Abstract

Although accumulating data demonstrated that gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, plays an important regulatory role in immunity of vertebrates, its immunomodulatory function and mechanisms of action remain poorly understood in invertebrates such as bivalve mollusks. In this study, the effect of GABA on phagocytic activity of hemocytes was evaluated in a commercial bivalve species, Tegillarca granosa. Furthermore, the potential regulatory mechanism underpinning was investigated by assessing potential downstream targets. Data obtained demonstrated that in vitro GABA incubation significantly constrained the phagocytic activity of hemocytes. In addition, the GABA-induced suppression of phagocytosis was markedly relieved by blocking of GABA_A and GABA_B receptors using corresponding antagonists. Hemocytes incubated with lipopolysaccharides (LPS) and GABA had significant higher K⁺-Cl^- cotransporter 2 (KCC2) content compared to the control. In addition, GABA treatment led to an elevation in intracellular Cl^-, which was shown to be leveled down to normal by blocking the ionotropic GABA_A receptor. Treatment with GABA_A receptor antagonist also rescued the suppression of GABA_A receptor-associated protein (GABARAP), KCC, TNF receptor associated factor 6 (TRAF6), inhibitor of nuclear factor kappa-B kinase subunit alpha (IKKα), and nuclear factor kappa B subunit 1 (NFκB) caused by GABA incubation. Furthermore, incubation of hemocytes with GABA resulted in a decrease in cAMP content, an increase in intracellular Ca²⁺, and downregulation of cAMP-dependent protein kinase (PKA), calmodulin kinase II (CAMK2), calmodulin (CaM), calcineurin (CaN), TRAF6, IKKα, and NFκB. All these above-mentioned changes were found to be evidently relieved by blocking the metabotropic G-protein-coupled GABA_B receptor. Our results suggest GABA may play an inhibitory role on phagocytosis through binding to both GABA_A and GABA_B receptors, and subsequently regulating corresponding downstream pathways in bivalve invertebrates.

Keywords: Ca(2+) signaling pathway; GABA receptor; Gamma-aminobutyric acid (GABA); NFκB signaling pathway; Phagocytosis; Tegillarca granosa.

MeSH terms

Animals
Hemocytes / metabolism
I-kappa B Kinase / metabolism
Phagocytosis
Receptors, GABA* / metabolism
Receptors, GABA-A* / metabolism
TNF Receptor-Associated Factor 6 / metabolism
gamma-Aminobutyric Acid / pharmacology

Substances

Receptors, GABA
Receptors, GABA-A
I-kappa B Kinase
TNF Receptor-Associated Factor 6
gamma-Aminobutyric Acid