Low temperature directly activates the initial glycerol antifreeze response in isolated rainbow smelt (Osmerus mordax) liver cells

Abstract

Rainbow smelt (Osmerus mordax) accumulate high levels of glycerol in winter that serve as an antifreeze. Liver glycogen is a source of glycerol during the early stages of glycerol accumulation, whereas dietary glucose and amino acids are essential to maintain rates of glycerol synthesis. We presently report rates of glycerol and glucose production by isolated hepatocytes. Cells from fish held at 0.4 to -1.5 degrees C and incubated at 0.4 degrees C were metabolically quiescent with negligible rates of glycerol or glucose production. Hepatocytes isolated from fish maintained at 8 degrees C and incubated at 8 degrees C produced glucose but not glycerol. Glycerol production was activated in cells isolated from 8 degrees C fish and incubated at 0.4 degrees C without substrate or when glucose, aspartate, or pyruvate was available in the medium. Incubation at 0.4 degrees C without substrate resulted in similar molar rates of glucose and glycerol production in concert with glycogen mobilization. Glycogenolysis and glycerol production were associated with increases in total in vitro activities of glycogen phosphorylase and glycerol-3-phosphate dehydrogenase. Maximal in vitro activities of hexokinase and glucokinase were not influenced by temperature, but high activities of a low-K(m) hexokinase may serve to redirect glycogen-derived glucose to glycolysis as opposed to releasing it from the cells. Rates of glycerol production were not enhanced in cells from fish held at 8 degrees C and incubated at 0.4 degrees C with adrenergic or glucocorticoid stimulation. As such, low temperature alone is sufficient to activate the glycerol production mechanism and results in a shift from glucose to a mix of glucose and glycerol production.

Cold tolerance and seasonal gene expression in Dendroctonus ponderosae.

“…This conclusion is similar to the findings of numerous other studies investigating the overwintering accumulation of glycerol, such as: metabolite assays observing glycogen depletion (Storey et al, 1981a;Storey and Storey, 1986;Pullin and Bale, 1989;Churchill and Storey, 1989;Han and Bauce, 1998;Li et al, 2002), increased glycogenolytic enzyme activities Joanisse and Storey, 1994a;Joanisse and Storey, 1995;Clow et al, 2008) and increased glycogenolytic gene transcript accumulation (Richards et al, 2010).…”

Seasonal shifts in accumulation of glycerol biosynthetic gene transcripts in mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), larvae

“…The opposing trends observed between GP transcript accumulation and temperature in both the fall (Figure 2A) and the following spring ( Figure 3A) support the hypothesis that glycerol production is the result of the metabolism of glycogen in the mountain pine beetle. This conclusion is similar to the findings of numerous other studies of glycerol accumulation in overwintering insects, including: metabolite assays observing glycogen depletion (Storey et al, 1981a;Storey and Storey, 1986;Pullin and Bale, 1989;Churchill and Storey, 1989;Han and Bauce, 1998;Li et al, 2002); increased glycogenolytic enzyme activities (Storey and Storey, 1981b;Joanisse and Storey, 1994a;Joanisse and Storey, 1995;Clow et al, 2008); and increased glycogenolytic gene transcript accumulation (Richards et al, 2010). Transcript accumulation data reported for GP herein was found to be consistent with the proteomic findings of Bonnett et al (2012).…”

“…The FBP seasonal transcript accumulation profile produced for mountain pine beetle larvae suggests that, in addition to glycerol production, gluconeogenesis may produce additional glucose as well. In a similar way, in addition to producing glycerol, cold treatment of rainbow smelt hepatocypes also produced glucose (Clow et al, 2008).…”

Glycerol loss to water exceeds glycerol catabolism via glycerol kinase in freeze-resistant rainbow smelt (Osmerus mordax)

“…A drop of temperature was determined as the trigger of glycerol accumulation, while a change in the photoperiod is more likely the trigger for the decrease in plasma glycerol reported from late January/late February (3,7). Liver is the major site of production for the entire animal (reviewed in Ref.…”