To identify ISC niche-derived signals that are required for gut homeostasis and/or infection-induced regeneration, we selected all secreted peptides (app 800) and receptors (app 600) expressed in the adult gut, performed adult-specific knockdown of these in different gut resident cell populations using RNAis, and screened for increased sensitivity to oral infection with the mildly pathogenic bacteria Ecc15. Among the candidate genes identified in the primary screen, we conducted a secondary screen on the top 46 (secreted peptides) and 69 (receptor) hits, which were selected based on reproducibility and conservation in higher organisms. For this screen, we evaluated the effects of knocking down candidate genes on tissue turnover in homeostatic conditions (WPG I + III) and the proliferative response triggered by intestinal infection (II-III). Among our top candidate hits, we identified the two Drosophila activin ligands, Activin- (Act) and Dawdle (Daw) as key regulators of adult gut homeostasis. In short, we found that Act and Daw control distinct steps of intestinal stem cell (ISC)-to-enterocyte (EC) maturation and couple different environmental cues with the appropriate adaptive responses. While Act is highly upregulated in EBs in response to infection and required for the accelerated tissue turnover associated with regenerative growth, Daw responds to nutritional cues and plays an essential role in the adaptation of organ size to nutrient intake. This work was presented at several internal conferences (as selected talk) and published in Nature Communication in January 2024 (Christensen et al 2024).
Our screens also identified the highly conserved PDGF-VEGF-related ligand, Pvf1, and its receptor, PDGF-VEGF-related receptor, Pvr, as critical regulators ISC migration during gut regeneration. (WPGI-III). This work was presented as talks at multiple international conferences and will be submitted for publication within the next few months.
Finally, we could show that the highly conserved Drosophila TNFR, Wengen (Wgn), is required in the enterocytes (ECs) of the adult gut to restrict lipid catabolism, suppress immune activity, and maintain tissue homeostasis. Wgn limits autophagy-dependent lipolysis by restricting cytoplasmic levels of the TNFR effector, TNFR-associated factor 3 (dTRAF3), while it suppresses immune processes through inhibition of the dTAK1/TAK1-Relish/NF-κB pathway in a dTRAF2-dependent manner. This suggests that Wgn/TNFR functions as an intersection between metabolism and immunity allowing pathogen-induced metabolic reprogramming to fuel the energetically costly task of combatting an infection. Our work highlights the important protective and metabolic functions TNFRs might serve in the gut of healthy individuals and raises the question as to how the widespread use of anti-TNF therapies in the treatment of chronic inflammatory diseases, such as inflammatory bowels disease might affect these. This work was presented at several international conferences (as selected talk) and published in Science Advances last year (Loudhaief et al 2023).
