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

• 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
• DOI: 10.1007/s00360-016-1042-9
• EISSN: 1432-136X
• ISSN: 0174-1578

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.