Characterization of Triacylglycerol Dynamics and Lipid Metabolism in the Beetle <i>Tribolium castaneum</i>

Lipids are essential for all organisms, and insects can obtain these macromolecules from their diet or synthesize them from carbohydrates and amino acids. These animals store fatty acids in the form of triacylglycerol in lipid droplets in the fat body and, in times of demand, mobilize these reserves as an energy source or for synthesizing structural lipids. However, details about this metabolism are unknown in most species, such as the beetle Tribolium castaneum. Here, we explored the dynamics of triacylglycerol and lipid metabolism during larval and pupal development, after adult emergence, and under fasting conditions. Larvae accumulated triacylglycerol during development, reaching the highest amounts of lipids in the late stages and the pupa. The expression of fatty acid synthase 1 (TcFAS1) and carnitine palmitoyltransferase 1 (TcCPT-1) was highest early in larval development. Lipase activity was lower in the pupa, similar to that observed for Brummer lipase (TcBmm) gene expression. After adult emergence, triacylglycerol stores decreased, reaching a minimum after 1 week. Gene expression of the de novo fatty acid synthesis pathway increased 4 days after emergence. On the other hand, both TcCPT-1 expression and lipase activity decreased 1 week after emergence. Under starvation, adult beetles survived for a maximum of 6 days. Under these conditions, triacylglycerol stores remained stable while protein levels decreased significantly. In addition, gene expression of TcBmm and acyl-CoA synthetase 5 (TcACSL5) increased. These results are an important step towards using T. castaneum as a model for studying lipid metabolism and metabolic diseases.