Cholinergic activation of HLH-30/TFEB promotes C. elegans infection resilience

Innate host defense depends on transcriptional programs, which support survival through two strategies that can vary independently. Resistance lowers pathogen burden, while resilience limits the damage a given burden causes. In Caenorhabditis elegans infected with Staphylococcus aureus , the highly conserved transcription factor HLH-30/TFEB drives most of the host response, which mediates infection resilience. We previously showed that EGL-30/Gαq, PLC-1/PLCε, and DKF-1/PRKD activate HLH-30/TFEB during infection. The same phospholipase C and protein kinase D step activates TFEB in mouse macrophages infected with Salmonella or S. aureus . However, the input that drives the EGL-30/Gαq, PLC-1/PLCε, and DKF-1/PRKD module to activate HLH-30/TFEB during infection remained unknown. Here we report that acetylcholine, acting on muscarinic receptors, is one such input. Atropine and scopolamine, two muscarinic antagonists in clinical use, as well as muscarinic receptor gene silencing blunted HLH-30/TFEB activation by infection. Moreover, a mutation of unc-17/SLC18A3 that lowers acetylcholine release from neurons impaired HLH-30/TFEB activation and induction of its target genes, while pathogen burden remained high. In uninfected animals, muscarinic agonist arecoline was sufficient to activate HLH-30/TFEB, in a muscarinic receptor-dependent manner. Nicotine, in contrast, had no effect. The agonist also lengthened survival of infection without lowering pathogen burden, in an HLH-30/TFEB-dependent manner. Silencing egl-30/GNAQ , plc-1/PLCE1 , or dkf-1/PRKD1-3 cut activation by the agonist just as it cut activation by infection, showing that both stimuli require the same module. In mammals the link documented so far between acetylcholine and TFEB runs through nicotinic receptors, so whether the muscarinic route is conserved remains open. Thus, we favor a model in which infection drives neurons to release acetylcholine onto the intestinal epithelium, where muscarinic receptors acting through EGL-30/Gαq, PLC-1/PLCε, and DKF-1/PRKD activate HLH-30/TFEB and strengthen infection resilience.

Animals survive an infection in two ways, often at once. They can kill the microbe, and they can limit the harm it does while it is still there. We study the second mechanism in the roundworm Caenorhabditis elegans , which fights bacteria with many of the same genes people do. A protein called HLH-30, known as TFEB in humans, switches on most of the genes this animal needs to withstand infection by Staphylococcus aureus . Which signals switch HLH-30 on during an infection has been unclear. We found that one of the signals comes from the nervous system. During infection, neurons release acetylcholine, a common neurotransmitter. Acetylcholine reaches the gut lining, where receptors pass the message inward and switch HLH-30 on. Drugs used in the clinic to block those receptors keep HLH-30 off, and so does removing the receptors themselves. A drug that stimulates the same receptors switches HLH-30 on even with no infection, and it helps animals survive infection without killing any more bacteria. The same receptors and the same protein are present in people. Whether this signal can be tuned to help a patient tolerate an infection is an important question to research in the future.