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.