Mechanisms of Neuroendocrine Stress Response in Drosophila and Its Effect on Carbohydrate and Lipid Metabolism

Response to short-term stress is a fundamental survival mechanism ensuring protection and adaptation in adverse environments. Key components of the neuroendocrine stress reaction in insects are stress-related hormones, including biogenic amines (dopamine and octopamine), juvenile hormone, 20-hydroxyecdysone, adipokinetic hormone and insulin-like peptides. In this review we focus on different aspects of the mechanism of the neuroendocrine stress reaction in insects on the D. melanogaster model, discuss the interaction of components of the insulin/insulin-like growth factors signaling pathway and other stress-related hormones, and suggest a detailed scheme of their possible interaction and effect on carbohydrate and lipid metabolism under short-term heat stress. The effect of short-term heat stress on metabolic behavior and possible regulation of its mechanisms are also discussed here.

The role of insulin signalling in the endocrine stress response in Drosophila melanogaster: A mini-review

The endocrine stress response in Drosophila includes catecholamines, juvenile hormone (JH), 20-hydroxyecdysone (20E) and the insulin/insulin-like growth factor signalling pathway (IIS). Several changes in the IIS and hormonal status that occur under unfavourable conditions are universal and do not depend on the nature of stress exposure. The reviewed studies on the impact of different element of the Drosophila IIS, such as insulin-like receptor, the homologue of its substrate, CHICO, the transcription factor dFOXO and insulin like peptide 6, on the hormonal status suggest that the IIS controls catecholamine metabolism indirectly via JH, and there is a feedback loop in the interaction of JH and IIS. Moreover, at least one of the ways in which the IIS is involved in the control of stress resistance is mediated through JH/dopamine signalling.

The impact of FOXO on dopamine and octopamine metabolism in Drosophila under normal and heat stress conditions

The forkhead boxO transcription factor (FOXO) is a component of the insulin signalling pathway and plays a role in responding to adverse conditions, such as oxidative stress and starvation. In stressful conditions, FOXO moves from the cytosol to the nucleus where it activates gene expression programmes. Here, we show that FOXO in Drosophila melanogaster responds to heat stress as it does to other stressors. The catecholamine signalling pathway is another component of the stress response. In Drosophila, dopamine and octopamine levels rise steeply under heat, nutrition and mechanical stresses, which are followed by a decrease in the activity of synthesis enzymes. We demonstrate that the nearly twofold decline of FOXO expression in foxo^BG01018 mutants results in dramatic changes in the metabolism of dopamine and octopamine and the overall response to stress. The absence of FOXO increases tyrosine decarboxylase activity, the first enzyme in octopamine synthesis, and decreases the enzymatic activity of enzymes in dopamine synthesis, alkaline phosphatase and tyrosine hydroxylase, in young Drosophila females. We identified the juvenile hormone as a mediator of FOXO regulation of catecholamine metabolism. Our findings suggest that FOXO is a possible trigger for endocrinological stress reactions.

Summary: The transcription factor FOXO affects catecholamine metabolism under normal and heat stress conditions in D. melanogaster, and juvenile hormone (JH) is a mediator of this effect.