scholarly journals Glycerol production in rainbow smelt (Osmerus mordax) may be triggered by low temperature alone and is associated with the activation of glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase

2006 ◽  
Vol 209 (6) ◽  
pp. 1016-1023 ◽  
Author(s):  
W. R. Driedzic
Keyword(s):  
Low Temperature ◽  
Osmerus Mordax ◽  
Glycerol Production ◽  
Rainbow Smelt ◽  
Glycerol 3 Phosphate Dehydrogenase

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

2008 ◽  
Vol 295 (3) ◽  
pp. R961-R970 ◽  
Author(s):  
Kathy A. Clow ◽  
K. Vanya Ewart ◽  
William R. Driedzic
Keyword(s):  
Low Temperature ◽  
Glucose Production ◽  
Liver Glycogen ◽  
Isolated Hepatocytes ◽  
Osmerus Mordax ◽  
Glycerol Production ◽  
Rainbow Smelt ◽  
Glycerol 3 Phosphate Dehydrogenase ◽  
In Cells

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°C and incubated at 0.4°C were metabolically quiescent with negligible rates of glycerol or glucose production. Hepatocytes isolated from fish maintained at 8°C and incubated at 8°C produced glucose but not glycerol. Glycerol production was activated in cells isolated from 8°C fish and incubated at 0.4°C without substrate or when glucose, aspartate, or pyruvate was available in the medium. Incubation at 0.4°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- Km 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°C and incubated at 0.4°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.

Identification and validation of differentially expressed transcripts in a hepatocyte model of cold-induced glycerol production in rainbow smelt (Osmerus mordax)

2011 ◽  
Vol 301 (4) ◽  
pp. R995-R1010 ◽  
Author(s):  
Jennifer R. Hall ◽  
Kathy A. Clow ◽  
Matthew L. Rise ◽  
William R. Driedzic
Keyword(s):  
Amino Acids ◽  
Low Temperature ◽  
Pyruvate Dehydrogenase ◽  
Cdna Array ◽  
Pyruvate Dehydrogenase Kinase ◽  
Osmerus Mordax ◽  
Type Ii ◽  
Glycerol Production ◽  
Rainbow Smelt ◽  
Transcript Levels

Rainbow smelt ( Osmerus mordax ) avoid freezing by producing antifreeze protein (AFP) and accumulating glycerol. Glyceroneogenesis occurs in liver via a branch in glycolysis and gluconeogenesis and is activated by low temperature. Hepatocytes were isolated from the livers of fish acclimated to 8°C. Cells were incubated at warm (8°C; nonglycerol accumulating) or cold (0.4°C; glycerol accumulating) temperature over a 72-h time course. Reciprocal suppression subtractive hybridization libraries enriched for cold-responsive transcripts were constructed at 72 h. Microarray analyses using a 16K salmonid cDNA array were performed at 24, 48, and 72 h. Expression of type II AFP and 21 carbohydrate, amino acid, or lipid metabolism-related transcripts were validated using quantitative RT-PCR. Type II AFP transcript levels were not directly temperature related. In cold cells, levels of the glucose synthesis transcript were transiently higher. Increased glycerol production was not associated with increased phosphofructokinase or cytosolic glycerol-3-phosphate dehydrogenase transcript levels. Levels of transcripts (phosphoenolpyruvate carboxykinase, mitochondrial malate dehydrogenase, alanine aminotransferase, glutamate dehydrogenase, and aquaglyceroporin 9) associated with mobilization of amino acids to fuel glycerol accumulation were all transiently higher, suggesting a common regulatory mechanism. In cold compared with warm cells, pyruvate dehydrogenase kinase [an inhibitor of pyruvate dehydrogenase (PDH)] transcript levels were 20-fold higher. Potent inhibition of PDH would direct pyruvate and oxaloacetate derived from amino acids to glycerol, as opposed to oxidation via the citric acid cycle. Levels of a transcript potentially encoding glycerol-3-phosphatase, an enzyme not yet characterized in any vertebrate species, were higher following cold incubation. Finally, this study also presents the novel finding of increased glutamine synthetase transcript levels in response to low temperature.

Glycerol-3-phosphatase and not lipid recycling is the primary pathway in the accumulation of high concentrations of glycerol in rainbow smelt (Osmerus mordax)

2013 ◽  
Vol 304 (4) ◽  
pp. R304-R312 ◽  
Author(s):  
Delphine Ditlecadet ◽  
William R. Driedzic
Keyword(s):  
Lipid Metabolism ◽  
Carbon Cycling ◽  
Animal Species ◽  
Strong Support ◽  
Small Fish ◽  
Osmerus Mordax ◽  
Glycerol Production ◽  
Rainbow Smelt ◽  
Hepatic Cells ◽  
High Concentrations

Rainbow smelt is a small fish that accumulates glycerol in winter as a cryoprotectant when the animal is in seawater. Glycerol is synthesized in liver from different substrates that all lead to the formation of glycerol-3-phosphate (G3P). This study assesses whether glycerol is produced by a direct dephosphorylation of G3P by a phosphatase (G3Pase) or by a cycling through the glycerolipid pool followed by lipolysis. Foremost, concentrations of on-board glycerolipids and activity of G3Pase and of enzymes involved in lipid metabolism were measured in smelt liver over the glycerol cycle. Concentrations of on-board glycerolipids did not change over the cycle and were too low to significantly contribute directly to glycerol production but activities of enzymes involved in both potential pathways were up-regulated at the onset of glycerol accumulation. A second experiment conducted with isolated hepatic cells producing glycerol showed 1) that on-board glycerolipids were not sufficient to produce the glycerol released even though phospholipids could account for up to 17% of it, 2) that carbon cycling through the glycerolipid pool was not involved as glycerol was produced at similar rates following inhibition of this pathway, and 3) that G3Pase activity measured was sufficient to allow the synthesis of glycerol at the rate observed. These results are the first to clearly support G3Pase as the metabolic step leading to glycerol production in rainbow smelt and the first to provide strong support for a G3Pase in any animal species.

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