In insects the fat body plays a fundamental role in energy metabolism. It is the principal site for storage of both glycogen and triacylglycerol (TG). Physiological mechanisms must operate to accumulate energy stores, either as glycogen or TG, during times of excess energy intake, e.g., during larval development, or to mobilize energy stores during times of need, e.g., flight or starvation. Clearly an understanding of these mechanisms is of fundamental importance in insect biochemistry/physiology, and may provide information useful for the development of insect-specific control strategies. The long-range goal of this project is to characterize the signal transduction systems involved in glycogen and TG mobilization in insect fat body. In the initial stages of the project the experimental insect will be larvae and adults of M. sexta which exhibit predominately a glycogenolytic effect of AKH in the larval stage and a predominately lipolytic effect of AKH in adults. This means we can study either glycogenolysis or lipolysis depending on which life stage of the insecxt is selected. In the long-range we plan to use the reagents and insights developed from studies on M. sexta to investigate regulation of energy metabolism in the fat body of the mosquito, Aedes aegypti.
The specific aims of this proposal re: To characterize the fat body hormone sensitive lipase, and, in particular, to determine the mechanism of it phosphorylation and to test the hypothesis that phosphorylation of the enzyme activates lipolysis because phosphorylation of the enzyme leads to translocation from the cytoplasm to the fat droplet; To determine the pathway for diacylglycerol synthesis in fat body which is activated by lipolysis of the triacylglycerol stores, and to characterize regulation of the pathway; To determine if trehalose synthesis is regulated during glycogenolysis, and, in particular, to test the hypothesis that fructose- 2,6-bisphophate plays an important regulatory role by inhibiting glycolysis and thereby shunting glucose-1-phosphate into trehalose synthesis; To determine the role of the cAMP-dependent protein kinase in regulating glycogenolysis and lipolysis; To determine the relative importance of calcium ion and protein phosphorylation in activating phosphorylase kinase, which is the key enzyme in activating glycogen phosphorylase and, hence, glycogenolysis.
