Ca2+/Calmodulin-NOS/NO-TNFs Pathway Hallmarks the Inflammation Response of Oyster During Aerial Exposure

Hao Chen,Lingling Wang,Rui Liu,Huan Zhang,Linsheng Song,Lusheng Xin,Hao Wang,Xue Qiao,Lin Wang

doi:10.3389/fmars.2020.603825

Abstract

Aerial exposure (emersion) due to the periodical ebb and flow of tides is a major stressor for intertidal organisms and a key environmental factor in shaping their local communities. Oysters are among the most emersion-tolerant mollusk species and can survive for several days under aerial exposure. Noticeably, overwhelming inflammation responses could occur during the emersion stress. However, mechanisms beneath the activation and modulation of emersion-induced inflammation response have remained largely unknown. Ca2+ is an important intracellular second messenger that plays indispensable roles in inflammation response by cooperation with calmodulin (CaM) genes. Here, we showed that intracellular Ca2+ accumulates rapidly in oyster hemocytes during emersion stress along with the changes in the protein levels of three CaM genes, which function as intracellular sensors of Ca2+. As downstream effector of Ca2+/CaM complex, nitric oxide synthase (NOS) activity in hemocytes was enhanced during the emersion stress, facilitating a greater production of nitrite oxide (NO). Augmentation of NO concentration was associated with the increased mRNA expression levels of two oyster cytokines (CgTNFs) during aerial exposure. The robust accumulation of cytokines and severe injury of tissues in oysters have been regarded as potential cause and marker of their death in prolonged emersion stress. Here, both the expression levels of CgTNFs and the tissue injuries of oysters were attenuated when Ca2+/CaM complex or NOS activity were repressed in vivo during the emersion stress. These findings indicate that Ca2+/CaM-NOS/NO-CgTNFs pathway is critically involved in the emersion-induced inflammation response in oysters and plays a role in the resistance against long-term aerial exposure.

Highlights

The intertidal region is characterized by drastic fluctuations of physical parameters, such as tidal level and temperature, which makes the intertidal zone one of the most physiologically challenging environments for life
The activity of nitric oxide synthase (NOS) in oyster hemocytes increased significantly starting from the first day of emersion (1.30-fold of basal level at the first day, 1.39-fold at the second day, p < 0.05) and declined moderately on the third day of stress (1.18-fold of basal level, Figure 1C)
The oysters are a dominant mollusk in most intertidal region and known as an emersion-tolerant invertebrate as it could survive for several days under aerial exposure (Dong et al, 2017)

Summary

Introduction

The intertidal region is characterized by drastic fluctuations of physical parameters, such as tidal level and temperature, which makes the intertidal zone one of the most physiologically challenging environments for life. Aerial exposure or emersion due to periodical ebb and flow of tides is a major stressor for intertidal organisms associated with water loss, osmotic stress, hypoxia, and food deprivation (Strachan et al, 2015; Zhang et al, 2015). Notwithstanding, some intertidal organisms, especially algae and sessile mollusks, are well adapted to the periodical emersion morphologically, behaviorally, or physiologically (Diederich et al, 2015; Strachan et al, 2015; Duan et al, 2016). There is limited empirical evidence demonstrating the mechanism underlying the responses to emersion, especially with regard to the biological processes during early resistance and final succumbing to stress in intertidal invertebrates

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Conclusion