Lipidomic data of macrophages isolated from adult fruit flies (Drosophila melanogaster) 24 hours post-infection

The immune response is an energy-demanding process that must be coordinated with systemic metabolic changes redirecting nutrients from stores to the immune system. Although this interplay is fundamental for the function of the immune system, the underlying mechanisms remain elusive. 

Our data show that the pro-inflammatory polarization of Drosophila macrophages is coupled to the production of the insulin antagonist ImpL2 through the activity of the transcription factor HIF1α. ImpL2 production, reflecting nutritional demands of activated macrophages, subsequently impairs insulin signaling in the fat body, thereby triggering FOXO-driven mobilization of lipoproteins. This metabolic adaptation is fundamental for the function of the immune system and an individual’s resistance to infection.

We demonstrated that analogically to Drosophila, mammalian immune-activated macrophages produce ImpL2 homolog IGFBP7 in a HIF1α-dependent manner and that enhanced IGFBP7 production by these cells induces mobilization of lipoproteins from hepatocytes.

Hence, the production of ImpL2/IGFBP7 by macrophages represents an evolutionarily conserved mechanism by which macrophages alleviate insulin signaling in the central metabolic organ to secure nutrients necessary for their function upon bacterial infection.

Methods
Fat bodies from six flies and one hundred thousand isolated macrophages were obtained for each analyzed group. Tissue lipid fraction was extracted by 500 ul of cold chloroform: methanol solution (v/v; 2:1). The samples were then homogenized by a Tissue Lyser II (Qiagen, Prague, Czech Republic) at 50 Hz, -18°C for 5 min and kept further in an ultrasonic bath (0°C, 5 min). Further, the mixture was centrifuged at 10,000 RPM at 4°C for 10 min followed by the removal of the supernatant. The extraction step was repeated under the same conditions. The lower layer of pooled supernatant was evaporated to dryness under a gentle stream of Argon. The dry total lipid extract was re-dissolved in 50 µl of chloroform: methanol solution (v/v; 2:1) and directly measured using previously described methods. Briefly, high-performance liquid chromatography (Accela 600 pump, Accela AS autosampler) combined with mass spectrometry LTQ-XL (all Thermo Fisher Scientific, San Jose, CA, USA) were used. The chromatographic conditions were as follows: Injection volume 5 µl; column Gemini 3 µM C18 HPLC column (150 × 2 mm ID, Phenomenex, Torrance, CA, USA) at 35°C; the mobile phase (A) 5 mM ammonium acetate in methanol with ammonia (0.025%), (B) water and (C) isopropanol: MeOH (8:2); gradient change of A:B:C as follows: 0 min: 92:8:0, 7 min: 97:3:0, 12 min: 100:0:0, 19 min: 93:0:7, 20-29 min: 90:0:10, 40–45 min: 40:0:60, 48 min: 100:0:0, and 50–65 min: 92:8:0 with flow rate 200 µl/min. The mass spectrometry condition: positive (3kV) and negative (-2,5kV) ion detection mode; capillary temperature 200°C. Eluted ions were detected with full scan mode from 200 to 1000 Da with the collisionally induced MS2 fragmentation (NCE 35). Data were acquired and processed by means of XCalibur 4.0 software (Thermo Fisher). The corrected areas under individual analytical peaks were expressed in percentages assuming that the total area of all detected is 100%. Lipidomics data were subsequently analyzed in the online platform LipidSuite (https://suite.lipidr.org/). Data were inputted by the K-Neares Neighbours method (KNN), and normalization was performed by the PQN algorithm. Subsequently, data were explored by PCA and OPLS-DA methods. Differential analysis of lipidomic data was done by univariate analysis and visualized in Volcano plots.