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1 Genetics, North Carolina State University, Raleigh, NC, USA
2 Pediatrics, Washington University School of Medicine, St. Louis, MO, USA
3 Biology, Francis Marion University, Florence, SC, USA
4 Biology, University of Minnesota Duluth, Duluth, MN, USA
* To whom correspondence should be addressed. E-mail: mandrews{at}d.umn.edu.
Thirteen-lined ground squirrels (Spermophilus tridecemlineatus) exploit the low-temperature activity of pancreatic triacylglycerol lipase (PTL) during hibernation. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTLs expressed in yeast. Both the human and ground squirrel enzymes displayed high activity at temperatures as low as 0°C and showed Q10 values of 1.2-1.5 over a range of 37 to 7°C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state. Western blots show elevated levels of PTL protein during hibernation in both heart and white adipose tissue (WAT). Significant increases in PTL gene expression are seen in heart, WAT and testis; but not in pancreas where PTL mRNA levels are highest. Surprisingly, up-regulation of PTL in testis is also accompanied by expression of the PTL-specific cofactor, colipase. The multi-tissue expression of PTL during hibernation supports its role as a key enzyme that shows high activity at low temperatures.
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