# mTOR signaling regulates demand-adapted hematopoiesis and metabolic reprogramming required for an effective cellular immune response in Drosophila melanogaster larvae

## TL;DR

This study shows that the mTOR pathway in fruit fly larvae controls immune cell development and metabolism during infection.

## Contribution

The study reveals that mTOR signaling regulates immune cell fate and metabolic changes in Drosophila hemocytes during stress.

## Key findings

- mTOR signaling induces lamellocyte differentiation in Drosophila hemocytes.
- mTOR activity is suppressed in mature lamellocytes despite being necessary for their formation.
- Hemocyte activation involves metabolic shifts like aerobic glycolysis and glutaminolysis.

## Abstract

The evolutionarily conserved mechanistic Target of Rapamycin (mTOR) pathway connects energy and nutrient availability to growth, proliferation, differentiation, immunity and survival. Here, we investigated the role of the mTOR pathway in Drosophila hematopoiesis and immunity using genetic and transcriptomic analyses of peripheral larval blood cells (hemocytes). We show that blood cell-directed mTor expression induced lamellocyte differentiation as seen after parasitoid wasp infection. Genetic epistasis revealed that lamellocyte hematopoiesis downstream of mTor is mediated by the JNK and p38 pathways. Transcriptomic profiling showed largely similar changes in gene expression patterns of wasp infected and mTor overexpressing hemocytes. While mTOR signaling is necessary for proper lamellocyte differentiation, mTOR Complex 1 (mTORC1) activity is suppressed in mature lamellocytes. Our transcriptome data indicated that hemocyte activation is accompanied by a shift in metabolism towards aerobic glycolysis for energy production, the oxidative pentose phosphate pathway for NADPH recycling, ROS production and detoxification as well as glutaminolysis for glutathione production. Our data highlight the key role of mTOR in controlling blood cell fate in Drosophila.

The immune system relies on specialized blood cells that can rapidly develop in response to infection or injury. However, the signals that guide blood cells to adopt specific immune functions are not fully understood. In this study, we used the fruit fly (Drosophila melanogaster), a widely used model organism that shares many conserved biological pathways with humans, to investigate how immune blood cells form during stress or infection. We focused on the mechanistic Target of Rapamycin (mTOR) pathway, which is known to regulate cell growth and metabolism. We found that overexpressing mTor in circulating blood cells causes them to develop into lamellocytes, a specialized immune cell type normally produced during parasitic wasp infection. This response requires additional stress-related signaling pathways, suggesting that mTOR works together with immune signaling networks to control blood cell fate. Interestingly, while mTOR activity is necessary to initiate lamellocyte formation, its activity decreases once these cells mature. These findings identify mTOR as a key regulator of immune blood cell development in Drosophila.