Metabolic and regulatory responses involved in cold acclimation in Atlantic killifish, Fundulus heteroclitus

Ectotherms often respond to prolonged cold exposure by increasing mitochondrial capacity via elevated mitochondrial volume density [ V V (mit,f)]. In fish, higher V V (mit,f) is typically associated with increased expression of nuclear respiratory factor 1 (Nrf1), a transcription factor that induces...

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Published in:	Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 187; no. 3; pp. 463 - 475
Main Authors:	Healy, Timothy M., Chung, Dillon J., Crowther, Kyle G., Schulte, Patricia M.
Format:	Journal Article
Language:	English
Published:	Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2017 Springer Nature B.V
Subjects:	Acclimatization Acclimatization - physiology Animal Physiology Animals Biochemistry Biomedical and Life Sciences Biomedicine Biosynthesis Citrate (si)-Synthase - metabolism Cold Temperature Cytochrome Fish Proteins - genetics Fish Proteins - metabolism Freshwater Fundulidae - physiology Fundulus heteroclitus Gene Expression Human Physiology Life Sciences Low temperature Marine Metabolism Mitochondria, Muscle - metabolism Muscles - metabolism Nuclear Respiratory Factor 1 - genetics Original Paper Oxygen Consumption Temperature Zoology Canada United States > US New Jersey Fish Oxygen consumption Temperature Mitochondria Mitochondrial biogenesis Gene expression
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Summary:	Ectotherms often respond to prolonged cold exposure by increasing mitochondrial capacity via elevated mitochondrial volume density [ V V (mit,f)]. In fish, higher V V (mit,f) is typically associated with increased expression of nuclear respiratory factor 1 (Nrf1), a transcription factor that induces expression of nuclear-encoded respiratory genes. To examine if nrf1 expression or the expression of other genes that regulate mitochondrial biogenesis contribute to changes in whole-organism metabolic rate during cold acclimation, we examined the time course of changes in the expression of these genes and in metabolic rate in Atlantic killifish, Fundulus heteroclitus . Cold acclimation rapidly decreased metabolic rate, but increased the expression of nrf1 more gradually, with a time course that depended on how rapidly the fish were transitioned to low temperature. Cold-induced nrf1 expression was not associated with increases in biochemical indicators of mitochondrial respiratory capacity, suggesting that cold-induced mitochondrial biogenesis may occur without increases in oxidative capacity in this species. These observations imply that changes in nrf1 expression and metabolic rate due to cold acclimation occur through different physiological mechanisms, and that increases in V V (mit,f) are likely not directly related to changes in metabolic rate with cold acclimation in this species. However, nrf1 expression differed between northern and southern killifish subspecies regardless of acclimation temperature, consistent with observed differences in metabolic rate and V V (mit,f) at 5 °C between these subspecies. Taken together, these results reveal substantial complexity in the regulation of V V (mit,f) and mitochondrial capacity with temperature in fish and the relationship of these parameters to metabolic rate.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0174-1578 1432-136X
DOI:	10.1007/s00360-016-1042-9