The cellular stress response in fish exposed to salinity fluctuations

• Published in: Journal of experimental zoology. Part A, Ecological and integrative physiology Ecological and integrative physiology, 2020-07, Vol.333 (6), p.421-435
• Main Authors: Evans, Tyler G., Kültz, Dietmar
• Format: Article
• Language: English
• Subjects: Animals; cell cycle; compatible osmolytes; DNA damage; energy metabolism; Fishes - physiology; programmed cell death; protein unfolding; Salinity; Sodium Chloride - chemistry; Sodium Chloride - pharmacology; Stress, Physiological - drug effects; Water - chemistry
• ISSN: 2471-5638; 2471-5646
• DOI: 10.1002/jez.2350

Salinity stress occurs when salt concentration in the environment changes rapidly, for example because of tidal water flow, rainstorms, drought, or evaporation from small bodies of water. However, gradual changes in salt concentration can also cause osmotic stress in aquatic habitats if levels breach thresholds that reduce the fitness of resident organisms. The latter scenario is exemplified by climate change driven salinization of estuaries and by dilution of ocean surface salinity through changes in the water cycle. In this review, we discuss how fish employ the evolutionarily conserved cellular stress response (CSR) to cope with these different forms of salinity stress. Macromolecular damage is identified as the cause of impaired physiological performance during salinity stress and serves as the signal for inducing a CSR. Basic aspects of the CSR have been observed in fish exposed to salinity stress, including repair and protection of cellular macromolecules, reallocation of energy, cell cycle arrest, and in severe cases, programmed cell death. Osmosensing and signal transduction events that regulate these aspects of the CSR provide a link between environmental salinity and adaptive physiological change required for survival. The CSR has evolved to broaden the range of salinities tolerated by certain euryhaline fish species, but is constrained in stenohaline species that are sensitive to changes in environmental salinity. Knowledge of how the CSR diverges between euryhaline and stenohaline fish enables understanding of physiological mechanisms that underlie salt tolerance and facilitates predictions as to the relative vulnerabilities of different fish species to a rapidly changing hydrosphere. Changes in intra‐ or extracellular osmolality (such as an increase in sodium ion concentration) can disrupt the structure of cellular macromolecules such as proteins, lipids, and DNA. Macromolecular damage serves as the trigger for the cellular stress response that acts to repair this damage through synthesis of molecular chaperones, programmed cell death (apoptosis), and changes in metabolism. Research Highlights This review summarizes current knowledge of cellular stress response (CSR) mechanisms used by fish to mitigate the effects of salinity stress. Osmosensing and signal transduction events that connect salinity change with the CSR are described.