Amp-Activated Protein Kinase (AMPK) May Affect Fat Storage by Controlling An Enzyme That Oxidizes Fatty Acids

In mammals, AMP-activated protein kinase (AMPK) is responsible for the control of the body's fuel levels. Essentially, AMPK has multiple metabolic roles, one of which is the regulation of triglyceride metabolism. Because dysregulation of AMPK has been linked to diabetes, obesity, and cardiovascular diseases, it has become a prime target for study. It is important to develop a model species, such as the nematode Caenorhabditis elegans, in which genetic and environmental factors can be controlled. AMPK is conserved in C. elegans, which has two AMPK catalytic subunit orthologs (α1 and α2). Previous research in our lab shows that a null mutation in the α2 subunit, AMPKα2, causes a 90% reduction of the mitochondrial fatty acid oxidative enzyme, ACS-2, due to fasting. The predicted result of this defect would be a reduced ability to metabolize stored lipids during starvation. To test this prediction, Nile red, a lipophilic stain, was used to dye intracellular lipids red in C. elegans. To determine if image analysis is a reasonable way to compare wild-type C. elegans with the AMPKα2 knockout worms, L4 stage worms were stained with Nile red and then starved for 4 and 8 hours. Red fluorescence images were taken of the worms after each time period and fluorescence intensity, above background, was then quantified with software and statistically analyzed. Quantification of fluorescence levels revealed that AMPKα2 knockout worms had significantly higher levels of fat compared to wild-type worms following starvation. Taken together, the available data suggest that one mean by which AMPKα2 regulates fuel homeostasis is by controlling expression of mitochondrial b-oxidative enzymes such as acs-2. Future experiments will examine whether this also occurs in mammals.