BMP signaling in the C. elegans immune response to bacterial pathogen regulates anti-microbial peptide expression through cell non-autonomous activity

Abstract

Host response to pathogens recruits multiple tissues in part through conserved cell signaling pathways. In C. elegans, the bone morphogenetic protein (BMP) like DBL-1 signaling pathway has a role in the response to infection in addition to other roles in development and post-developmental functions. In the regulation of body size, the DBL-1 pathway acts through cell autonomous signal activation in the epidermis (hypodermis). We have now elucidated the tissues that respond to DBL-1 signaling upon exposure to two bacterial pathogens. The receptors and Smad signal transducers for DBL-1 are expressed in pharyngeal muscle, intestine, and epidermis. We demonstrate that expression of receptor-regulated Smad (R-Smad) gene sma-3 in the pharynx is sufficient to improve the impaired survival phenotype of sma-3 mutants and that expression of sma-3 in the intestine has no effect when exposing worms to bacterial infection of the intestine. We also show that two antimicrobial peptide genes - abf-2 and cnc-2 - are regulated by DBL-1 signaling through R-Smad SMA-3 activity in the pharynx. Finally, we show that pharyngeal pumping activity is reduced in sma-3 mutants and that other pharynx-defective mutants also have reduced survival on a bacterial pathogen. Our results identify the pharynx as a tissue that responds to BMP signaling to coordinate a systemic response to bacterial pathogens. Significance StatementO_LIInnate immunity is the first line of defense against pathogens. Conserved cell signaling pathways are known to be involved in host-pathogen response, but how they coordinate a systemic response is less well understood. C_LIO_LIIn the nematode C. elegans, bone morphogenetic protein (BMP) signaling is required for survival on pathogenic bacteria. Using transgenic strains, the authors identify a major role for a specific organ, the pharynx, in BMP-dependent survival. C_LIO_LIThese findings demonstrate that an organ can serve as a pathogen sensor to trigger multiple modes of response to bacterial pathogens, include a barrier response and regulation of anti-microbial peptide expression. C_LI