Pathogen threat proximity shapes host extracellular vesicle production in pre-infection response

Abstract

Extracellular vesicles (EVs) play a crucial role in immune responses, yet it remains unclear whether pathogen metabolites alone can stimulate EV production prior to infection. Using Caenorhabditis elegans, we investigate this question through the lens of exophers - large, evolutionarily conserved EVs known to enhance proteostasis, extend lifespan, and improve reproductive fitness. Our study uncovers distinct regulatory mechanisms driving EV production in response to pathogen-derived volatile metabolites and non-volatile secretome, providing insights into host-pathogen signaling before physical interaction. We reveal a sophisticated network that adjusts EV production based on pathogen proximity: non-volatile secretome (including tripeptide Ile-Pro-Pro), signaling an immediate threat, activate immune-dependent EV pathways, while volatile metabolites, forewarning potential danger, initiate immunity-independent exopher production. Both responses rely on sensory neurons, with ASK, ADL, and AWC neurons playing central roles in each, and additional input from ASI, AWB, and ASH neurons specifically enhancing non-volatile secretome-induced EV production. Downstream signal integration is mediated by a circuit involving the RMG hub and AIB/AIA interneurons, with the AIB-specific NPR-9 receptor playing a critical role. Molecularly, we identified multiple GPCRs, including SRI-19, SRI-36/39, and SRR-6, as crucial for the non-volatile response, and revealed that SRR-6 functions in the intestine to regulate muscle exopher production, demonstrating a novel gut-muscle signaling axis. Notably, exposure to volatile pathogen metabolites significantly boosts offspring fitness during infection in SRI-19-dependent manner, albeit at the cost of maternal survival when conditions are being harsher. Thus, our study shows that C. elegans distinguishes pathogen proximity through compound types, activating EV-dependent physiological responses tailored to either immediate or anticipated threats to optimize survival across generations.