Redox regulation in Atlantic cod (Gadus morhua) embryos developing under normal and heat-stressed conditions

Kaja H. Skjærven, Samuel Penglase, Pål A. Olsvik, Kristin Hamre
2013 Free Radical Biology & Medicine  
With regard to predicted oceanic warming, we studied the effects of heat stress on the redox system during embryonic development of Atlantic cod (Gadus morhua), with emphasis on the glutathione balance, activities of key antioxidant enzymes, and their mRNA levels. The embryos were incubated at optimal temperature for development (6 1C) or slightly above the threshold temperature (10 1C). The regulation of all the redox-related parameters measured at optimum development was highly dynamic and
more » ... ghly dynamic and complex, indicating the importance of both maternal and zygotic contributions to maintaining redox equilibrium. Development at 10 1C caused a significantly higher mortality at the blastula and early gastrula stages, indicating severe stress. Measures of the glutathione redox couple showed a significantly more reduced state in embryos at 10 1C compared to 6 1C at the post-gastrula stages. Mean normalized expression of nrf2, trxred, g6pd, gclc, nox1, CuZnsod, and mt in embryos kept at 10 1C revealed stage-specific significantly reduced mRNA levels. Activities of antioxidant enzymes changed both during ontogenesis and in response to temperature, but did not correlate with mRNA levels. As the embryos need a tightly regulated redox environment to coordinate between growth and differentiation, these findings suggest that the altered redox balance might participate in inducing phenotypic changes caused by elevated temperature. & 2012 Elsevier Inc. A challenge during embryonic development is the activation and coordination of catabolic and anabolic pathways, while simultaneously managing reactive metabolic by-products, such as reactive oxygen species (ROS) and reactive nitrogen species. ROS are generated mainly through the mitochondrial electrontransport chain, in the endoplasmic reticulum, and through the activity of several enzymes. These oxidants are balanced by reductants, also called antioxidants. Overproduction of ROS and/ or lack of antioxidant capacity can shift the delicate cellular and extracellular redox equilibria, leading to irreversible oxidative modifications at the molecular, cellular, and organ levels and consequently the development of pathologies [1] . Changes in temperature have a more profound effect during early life and embryos tend to be more stenothermal than juveniles and adults [2, 3] . The embryonic stages are the "thermal bottlenecks" for the Atlantic cod distribution, with optimum development occurring at temperatures around 6 1C, whereas embryos developing at or above threshold temperature (10 1C) are severely stressed [4, 5] . As the routine metabolic rate increases with increasing temperature [3], we hypothesized that an increase in seawater temperatures, such as those predicted for the North Atlantic Ocean (UK Climate Projections Briefing Report-UKCIP09 [6]), will affect the redox system in the sensitive cod embryos. The redox system can be viewed by assuming a redox balance [7-9]. The redox potential of cells is under strict control through regulation of the concentrations and ratios of several redox couples, the most important being the glutathione couple (reduced glutathione (GSH)/oxidized glutathione (GSSG)). GSH/ GSSG is present in all cells in millimolar concentrations and usually at ratios higher than 100:1 [9] . Evidence suggests that the concentration and ratio of GSH and GSSG control inter-and intramolecular oxidation states of protein thiols and thereby the amount of S-S bonding, glutathionylation, and phosphorylation of proteins. Changes in the three-dimensional conformation along with the addition of side chains to proteins change their activity, and the regulation of the redox potential (E) can therefore modulate signaling pathways and hence change cell fate. This is in accordance with the finding that differentiating cells have a higher E than proliferating cells [7, 10] and treating cells to inhibit growth and induce differentiation increases E, whereas treating them to promote growth reduces E [8]. Furthermore, different cell compartments have different E. The mitochondria are more reduced than the cytosol. The cytosol of cells is in turn more reduced than the extracellular plasma [8] . Other redox couples,
doi:10.1016/j.freeradbiomed.2012.11.022 pmid:23246569 fatcat:fw2nvbxixncnvimgkln6uf7ipm