Jiuli Zhang

Restriction of dietary food without malnutrition robustly extends lifespan in more than
twenty species. It was also reported that fruit flies (Drosophila melanogaster) deficient in
olfactory function live longer and that the longevity induced by food restriction is partially
due to decreased olfaction. These observations suggest food assimilation through the gastrointestinal
tract and food smell detected by olfactory neurons influence lifespan. The
insulin growth factor signaling pathway is regulated by nutrient levels and has been shown
to mediate the lifespan extension conferred by food restriction and defective gustatory neurons
in the nematode Caenorhabditis elegans. However, the mechanism remains unclear.
Autophagy is a lysosomal degradation pathway and is sensitive to nutrient availability. We
found autophagy activity in the intestine and food sensory neurons acts in parallel to mediate
food restriction and insulin signaling regulated lifespan extension in Caenorhabditis elegans.
Moreover, intestinal and neuronal autophagy converge on unidentified neurons to
control the secretion of neuropeptides that regulate lifespan. These data suggest autophagy is an essential component in a neuroendocrine pathway that coordinates how environmental
food cues detected by sensory neurons and food nutrients assimilated by the intestine
influence lifespan. These findings may contribute to understanding the aging process in
mammals.

In the last decade, C. elegans has emerged as an invertebrate organism to study interactions between hosts and pathogens, including the host defense against gram-negative bacterium Salmonella typhimurium. Salmonella establishes persistent infection in the intestine of C. elegans and results in early death of infected animals. A number of immunity mechanisms have been identified in C. elegans to defend against Salmonella infections. Autophagy, an evolutionarily conserved lysosomal degradation pathway, has been shown to limit the Salmonella replication in C.
elegans and in mammals. Here, a protocol is described to infect C. elegans with Salmonella typhimurium, in which the worms are exposed to Salmonella for a limited time, similar to Salmonella infection in humans. Salmonella infection significantly shortens the lifespan of C. elegans. Using the essential autophagy gene bec-1 as an example, we combined this infection method with C. elegans RNAi feeding approach and showed this protocol can be used to examine the function of C. elegans host genes in defense against Salmonella infection. Since C. elegans whole genome RNAi libraries are available, this protocol makes it possible to comprehensively screen for C. elegans genes that protect against
Salmonella and other intestinal pathogens using genome-wide RNAi libraries.

Salmonella typhimurium infects both intestinal epithelial cells and macrophages. Autophagy is a lysosomal
degradation pathway that is present in all eukaryotes. Autophagy has been reported to limit the
Salmonella replication in Caenorhabditis elegans and in mammals. However, it is unknown whether intestinal
autophagy activity plays a role in host defense against Salmonella infection in C. elegans. In this
study, we inhibited the autophagy gene bec-1 in different C. elegans tissues and examined the survival
of these animals following Salmonella infection. Here we show that inhibition of the bec-1 gene in the
intestine but not in other tissues confers susceptibility to Salmonella infection, which is consistent with
recent studies in mice showing that autophagy is involved in clearance of Salmonella in the intestinal epithelial
cells. Therefore, the intestinal autophagy activity is essential for host defense against Salmonella
infection from C. elegans to mice, perhaps also in humans.