Trehalose as a source for privileged immunity in Drosophila

Project Information

IMMUNETREH

Grant agreement ID: 867430

DOI

10.3030/867430

Project closed

EC signature date 25 November 2019

Start date 1 January 2020

End date 12 February 2023

Funded under

• SPREADING EXCELLENCE AND WIDENING PARTICIPATION

Total cost

€ 156 980,64

EU contribution

€ 156 980,64

Coordinated by

JIHOCESKA UNIVERZITA V CESKYCH BUDEJOVICICH
Czechia

Periodic Reporting for period 1 - IMMUNETREH (Trehalose as a source for privileged immunity in Drosophila)

Reporting period: 2020-01-01 to 2021-12-31

Summary of the context and overall objectives of the project

This project focuses on studying the effect of trehalose, the main sugar in insects, on the immune response of fruit flies. When the immune system is activated, it requires large amounts of energy to function effectively. It therefore gets preferential access to energy from the rest of the body to ensure its survival - that's why we call it the privileged immune system. The concept of privileged immunity has broad implications, including human physiology. However, we do not fully understand how this energy distribution is controlled. This is where fruit flies, which are simple organisms with useful genetic tools, come in handy for research.

Particularly, we addressed the following questions:
- Is trehalose an important source for insect immune cells?
- Is the conversion of trehalose to glucose inside immune cells crucial for their metabolism and for an effective immune response?
- Is the utilization of trehalose by immune cells dependent on the regulation of sugar metabolism at the whole organism level, or are immune cells privileged in this sense?

To address these questions, we use the infection of fruit fly larvae by parasitoid wasps that inject their eggs into the larvae. If the infected larva does not destroy the egg by an effective immune response, the parasitoid consumes the developing fly in the pupa. Using this model of immune response stimulation, we found that systemic trehalose metabolism is important for an effective immune response in fruit flies. We also found that immune cells metabolize trehalose and use it to respond to oxidative stress. The immune system uses oxygen radicals to kill the parasitoid egg, but the oxidative stress response is important to protect the host itself from these radicals so that it is not killed by its own immune reaction. The metabolism of trehalose in immune cells is independent of regulation at the whole organism level, demonstrating that the immune system is privileged. To obtain these results, we introduced an approach, still unique in Drosophila research, to measure metabolism specifically in immune cells of living fruit fly larvae.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To investigate the role of trehalose metabolism in the immune response, we used infection of Drosophila larvae with parasitoid wasps. To analyze metabolism, we introduced a unique immune cell-specific metabolomics as well as 13C stable isotope tracing in vivo and combined these techniques with cell-specific genetic manipulation in vivo.
We found that the glucose transporter GluT1 is not important in immune cells and that the trehalose transporter TreT1-1 can transport both glucose and trehalose as well as MFS3, and that three other putative carbohydrate transporters are strongly expressed. The strong expression of multiple carbohydrate transporters that can compensate for each other is what makes immune cells privileged during the immune response. Moreover, sugar uptake and metabolism is insulin-independent, i.e. independent of systemic regulation. We generated a transgenic line with a reporter specific for cytoplasmic trehalase expression and showed that lamellocytes, specialized immune cells that arise during infection to encapsulate the parasitoid, specifically regulate cytoplasmic trehalase expression and metabolize trehalose. We described complex metabolic changes in the activated immune cells and found that resting immune cells use glucose as a source, whereas lamellocytes metabolize trehalose. They utilize trehalose during elevated glycolysis to produce ATP and lactate, a common observation for activated immune cells. They also metabolize trehalose/glucose in the so-called cyclic pentose phosphate pathway, in which glucose is repeatedly oxidized to produce more NADPH, a relatively new and unexplored phenomenon in immunometabolism. We have verified that this cyclic pentose phosphate pathway is crucial for an effective immune response. However, this metabolism specifically in lamellocytes is important for the response to oxidative stress and thus for protecting the host from its own toxic immune reaction. When trehalose metabolism was reduced, host immunity was increased but ultimately its fitness as a surviving adult was reduced.
Posters:
DOI: https://doi.org/10.6084/m9.figshare.12141153.v1
DOI: https://doi.org/10.6084/m9.figshare.12144831.v1

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Progress beyond the state of the art: we introduced a unique, cell-specific metabolomics and 13C stable isotope tracing in vivo in a Drosophila model. We can now combine these techniques with cell-specific genetic manipulation in vivo, making Drosophila a very powerful model for studying the genetic basis of metabolism at a tissue-specific level.
Expected results: we are currently completing a manuscript that we plan to publish in the open access journal – Title: “Carbohydrate metabolism of Drosophila hemocytes during the immune response to parasitoid wasps”. Authors: Kazek, Chodáková, Moos, Nedbalová, Bajgar, McMullen, Lehr, Strych, Šimek, Doležal
Potential impacts: we have described complex metabolic changes in activated immune cells of Drosophila larvae. There have been many reports of metabolic changes in Drosophila immune cells, but all are based on changes in gene expression, not direct measurements of metabolites - our work thus represents an important step towards the apparent hot topic of Drosophila immunometabolism. Scientists can now use our established methodology in their studies, and our work can serve as a reference of metabolic changes for future studies. Immunometabolism has recently become a hot topic in human health, but there are still many unexplored fundamental biological issues related to immunometabolism, and therefore simple model organisms can make important contributions to the field. We expect that the demonstration of the importance of the cyclic pentose phosphate pathway in activated immune cells, a so far understudied immunometabolic phenomenon, will stimulate further research in the biomedical field as well. Our research has provided an example of a molecular mechanism important for host protection during the immune response, opening a new avenue to study this important aspect of immunity beyond the field of Drosophila research.
Socio-economic impacts - although the results have been achieved in purely basic research, we can envision possible future impacts in at least two areas: (1) agriculture and (2) human health. Our results provide a better understanding of insect physiology and metabolism and could therefore be applied, for example, to better pest control of crops, which is also safer for non-pests, environment as well as human consumers. For example, parasitoid wasps are used in the protection of vineyards from insect pests. Since the changes in immunometabolism that we studied in this project are universal to both insect and human immune cells, the new insights gained in the fruit fly model can be directly applied to biomedical problems with the potential to treat various pathologies associated with human immunity. Our project also brings a hitherto very rare support for the concept of privileged immunity - wider promotion of this concept among the general public has the potential to promote healthier living. When people understand why the immune system needs more energy during an immune response, they can better adapt their behavior during illness to return to health sooner.

Cytoplasmic trehalase expression marked by GFP in lamellocytes encapsulating parasitoid wasp egg