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

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 blood cells (hemocytes) from larvae. 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 gene expression 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. Overall design: METHODS: We utilized the GAL4-UAS system to target mTor overexpression to hemocytes. We used the combination of two hemocyte GAL4 lines (He-GAL4 and Hml[delta]-GAL4, HH-GAL4 for short) to drive a wild-type Tor (UAS-TOR.WT) in hemocytes. As a control, we crossed the w1118 line to the HH-GAL4. Both, the HH-GAL4; UAS-TOR.WT and the control larvae were subjected to L. boulardi parasitoid wasps for two hours, and hemocyte samples were collected 48 h after infection start. Hemocytes were also collected from uninfected, age-matched larvae.