TGF-β Signaling Interferes With the Innate Immune and Metabolic Response to Parasitic Nematode Infection.

The common fruit fly, , is an outstanding model to study the molecular basis of anti-pathogen immunity. The parasitic nematode together with its mutualistic bacteria infects a wide range of insects, including . Recently, we have shown that transforming growth factor-β (TGF-ß) signaling in is regulated in response to parasitic nematode infection. In the current study, we investigated the contribution of two TGF-ß signaling branches, the activin and the bone morphogenetic protein (BMP), to immune function against . We used larvae carrying mutations in the genes coding for the TGF-ß extracellular ligands and . We have demonstrated that the number of circulating hemocytes in uninfected and mutants decreases twofold compared to background controls, yet no significant changes in hemocyte numbers and survival of the TGF-ß mutants are observed upon nematode infection. However, we have shown that nematode-infected mutants express at higher levels and phenoloxidase activity at lower levels compared to their background controls. To elucidate the contribution of TGF-ß signaling in the metabolic response of to parasitic nematodes, we estimated lipid and carbohydrate levels in and mutant larvae infected with . We have found that both nematode-infected mutants contain lipid droplets of larger size, with mutant larvae also containing elevated glycogen levels. Overall, our findings indicate that the regulation of activin and BMP branches of TGF-ß signaling can alter the immune and metabolic processes in during response to parasitic nematode infection. Results from this study shed light on the molecular signaling pathways insects activate to regulate mechanisms for fighting potent nematode parasites, which could lead to the identification of novel management strategies for the control of damaging pests.