Background: Many insect species have evolved the ability to survive extracellular freezing. The search for the underlying principles of their natural freeze tolerance remains hampered by our poor understanding of the mechanistic nature of freezing damage itself. Objectives: Here, in search of potential primary cellular targets of freezing damage, we compared mitochondrial responses (changes in morphology and physical integrity, respiratory chain protein functionality, and mitochondrial inner membrane (IMM) permeability) in freeze-sensitive vs. freeze-tolerant phenotypes of the larvae of the drosophilid fly, Chymomyza costata. Methods: Larvae were exposed to freezing stress at -30°C for 1 h, which is invariably lethal for the freeze-sensitive phenotype but readily survived by the freeze-tolerant phenotype. Immediately after melting, the metabolic activity of muscle cells was assessed by the Alamar Blue assay, the morphology of muscle mitochondria was examined by transmission electron microscopy, and the functionality of the oxidative phosphorylation system was measured by Oxygraph-2K microrespirometry. Results: The muscle mitochondria of freeze-tolerant phenotype larvae remained morphologically and functionally intact after freezing stress. In contrast, most mitochondria of the freeze-sensitive phenotype were swollen, their matrix was diluted and enlarged in volume, and the structure of the IMM cristae was lost. Despite this morphological damage, the electron transfer chain proteins remained partially functional in lethally frozen larvae, still exhibiting strong responses to specific respiratory substrates and transferring electrons to oxygen. However, the coupling of electron transfer to ATP synthesis was severely impaired. Based on these results, we formulated a hypothesis linking the observed mitochondrial swelling to a sudden loss of barrier function of the IMM.

• Klíčová slova
• freeze tolerance, insects, mitochondrial swelling, oxidative phosphorylation, permeability transition, respiration,
• Publikační typ
• časopisecké články MeSH

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.

• Klíčová slova
• Drosophila, ImpL2, insulin resistance, lipoproteins, macrophage polarization,
• MeSH
• antagonisté inzulinu metabolismus   farmakologie   MeSH
• bakteriální infekce * metabolismus   MeSH
• Drosophila metabolismus   MeSH
• inzulin metabolismus   MeSH
• inzulinová rezistence * MeSH
• makrofágy metabolismus   MeSH
• proteiny Drosophily * metabolismus   MeSH
• proteiny vázající IGF metabolismus   MeSH
• savci MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• antagonisté inzulinu MeSH
• ImpL2 protein, Drosophila MeSH Prohlížeč
• inzulin MeSH
• proteiny Drosophily * MeSH
• proteiny vázající IGF MeSH