Gillis, T. E. | bioRxiv Science

bioRxiv2021

Mitogen-activated protein kinases contribute to temperature induced cardiac remodelling in rainbow trout (Oncorhynchus mykiss) heart

Rainbow trout (Oncorhynchus mykiss) live in temperate environments and experience seasonal changes in temperature that range between 4{degrees}C and 20{degrees}C. Laboratory studies demonstrate that cold and warm acclimation of male trout can have oppositional effects on cardiac hypertrophy and the collagen content of the heart. The cellular mechanisms behind temperature induced cardiac remodelling are unclear, as is why this response differs between male and female fish. Recent work utilizing cultured trout cardiac fibroblasts suggests that collagen deposition is regulated, at least in part, by mitogen-activated protein kinase (MAPK) cell signalling pathways. We therefore hypothesized that temperature-dependent cardiac remodelling is regulated by these same cell signalling pathways. To test this, male and female trout were acclimated to 18{degrees}C (warm) in the summer and to 4{degrees}C (cold) in the winter and the activation of MAPK pathways in the hearts were characterized and compared to that of control fish maintained at 12{degrees}C. Animals, maintained under a natural photoperiod matched to time of year, were sampled throughout each acclimation. p38 MAPK phosphorylation increased in the hearts of female fish during the cold acclimation protocol and the phosphorylation of extracellular signal-regulated kinase (ERK) increased in the hearts of male fish with warm acclimation. These results indicate that thermal acclimation has transient and sex-specific effects on the phosphorylation of MAPKs.

zoology↗

bioRxiv2021

Cold-acclimation induces life stage-specific responses in the cardiac proteome of Western painted turtles (Chrysemys picta bellii): implications for anoxia tolerance

Western painted turtles (Chrysemys picta bellii) are the most anoxia-tolerant tetrapod. Survival time improves at low temperature and during ontogeny, such that adults acclimated to 3{degrees}C survive far longer without oxygen than either warm-acclimated adults or cold-acclimated hatchlings. Since protein synthesis is rapidly suppressed to save energy at the onset of anoxia exposure, this study tested the hypothesis that cold-acclimation would evoke preparatory changes in protein expression that would support enhanced anoxia survival in adult but not hatchling turtles. To test this, adult and hatchling turtles were acclimated to either 20{degrees}C (warm) or 3{degrees}C (cold) for 5 weeks, and then the heart ventricles were collected for quantitative proteomic analysis using labeled isobaric tags and mass spectrometry. The relative abundances of 1316 identified proteins were compared between temperatures and developmental stages. The effect of cold-acclimation on the cardiac proteome was most evident when life stage was included as a covariable, suggesting that ontogenic differences in anoxia tolerance may be predicated on successful maturation of the heart from its hatchling to adult form and, only after this maturation occurs, will cold-acclimation induce protein expression changes appropriate for supporting heart function during prolonged anoxia. The main differences between the hatchling and adult cardiac proteomes reflect an increase in metabolic scope that included more myoglobin and increased investment in both aerobic and anaerobic energy pathways. Mitochondrial structure and function were key targets of life stage- and temperature-induced changes to the cardiac proteome, including reduced complex II proteins in cold-acclimated adults that may help down-regulate the electron transport system and avoid succinate accumulation during anoxia. Therefore, targeted cold-induced changes to the cardiac proteome may be a contributing mechanism for stagespecific anoxia tolerance in turtles.

physiology↗