Expression of a chimeric retroviral-lipase mRNA confers enhanced lipolysisin a hibernating mammal

Hibernating mammals can survive several months without feeding by limiting their carbohydrate catabolism and using triacylglycerols stored in white ad ipose tissue (WAT) as their primary source of fuel. Here we show that a lip olytic enzyme normally found in the gut, pancreatic triacylglycerol lipase (PTL), is expressed in WAT of hibernating 13-lined ground squirrels (Spermo philus tridecemlineatus). PTL expressed in WAT is encoded by an unusual chi meric retroviral-PTL mRNA similar to 500 bases longer than the predominant PTL message found in other ground squirrel tissues. Seasonal measurements d etect the chimeric mRNA and PTL enzymatic activity in WAT before and during hibernation, with both showing their lowest observed levels 1 wk after hib ernation concludes in mid-March. PTL is expressed in addition to hormone-se nsitive lipase, the enzyme typically responsible for hydrolysis of triacylg lycerols in WAT. Because of the distinct catalytic and regulatory propertie s of both enzymes, this dual-triacylglycerol lipase system provides a means by which the fuel requirements of hibernating 13-lined ground squirrels ca n be met without interruption.