Antimicrobial peptides do not directly contribute to aging in Drosophila, but improve lifespan by preventing dysbiosis.

Antimicrobial peptides (AMPs) are innate immune effectors first studied for their role in host defense. Recent studies have implicated these peptides in the clearance of aberrant cells and in neurodegenerative syndromes. In Drosophila, many AMPs are produced downstream of Toll and Imd NF-κB pathways upon infection. Upon aging, AMPs are upregulated, drawing attention to these molecules as possible causes of age-associated inflammatory diseases. However, functional studies overexpressing or silencing these genes have been inconclusive. Using an isogenic set of AMP gene deletions, we investigated the net impact of AMPs on aging. Overall, we found no major effect of individual AMPs on lifespan, with the possible exception of Defensin. However, ΔAMP14 flies lacking seven AMP gene families display reduced lifespan. Increased bacterial load in the food of aged ΔAMP14 flies suggests their lifespan reduction is due to microbiome dysbiosis, consistent with a previous study. Moreover, germ-free conditions extends the lifespan of ΔAMP14 flies. Overall, our results do not point to an overt role of individual AMPs in lifespan. Instead, we find that AMPs collectively impact lifespan by preventing dysbiosis during aging.