Aberrant Activation of p38 MAP Kinase-Dependent Innate Immune Responses Is Toxic to Caenorhabditis elegans

Abstract

Inappropriate activation of innate immune responses in intestinal epithelial cells underlies the pathophysiology of inflammatory disorders of the intestine. Here we examine the physiological effects of immune hyperactivation in the intestine of the nematode Caenorhabditis elegans. We previously identified an immunostimulatory xenobiotic that protects C. elegans from bacterial infection by inducing immune effector expression via the conserved p38 MAP kinase pathway, but was toxic to nematodes developing in the absence of pathogen. To investigate a possible connection between the toxicity and immunostimulatory properties of this xenobiotic, we conducted a forward genetic screen for C. elegans mutants that are resistant to the deleterious effects of the compound, and identified five toxicity suppressors. These strains contained hypomorphic mutations in each of the known components of the p38 MAP kinase cassette (tir-1, nsy-1, sek-1, and pmk-1), demonstrating that hyperstimulation of the p38 MAPK pathway is toxic to animals. To explore mechanisms of immune pathway regulation in C. elegans, we conducted another genetic screen for dominant activators of the p38 MAPK pathway, and identified a single allele that had a gain-of-function (gf) mutation in nsy-1, the MAP kinase kinase kinase that acts upstream of p38 MAPK pmk-1. The nsy-1(gf) allele caused hyperinduction of p38 MAPK PMK-1-dependent immune effectors, had greater levels of phosphorylated p38 MAPK, and was more resistant to killing by the bacterial pathogen Pseudomonas aeruginosa compared to wild-type controls. In addition, the nsy-1(gf) mutation was toxic to developing animals. Together, these data suggest that the activity of the MAPKKK NSY-1 is tightly regulated as part of a physiological mechanism to control p38 MAPK-mediated innate immune hyperactivation, and ensure cellular homeostasis in C. elegans.

Promotion of behavior and neuronal function by reactive oxygen species in C. elegans

“…To do so, it is important to have both gain-of-function and loss-of-function mutant alleles. Two genes in this signaling cascade have both types of alleles available: nsy-1 /MAPKKK and akt-1 /AKT3435. Worms carrying gain-of-function alleles of nsy-1 or akt-1 showed enhanced responses to high osmolarity solution (Supplementary Fig.…”

Coordinated inhibition of C/EBP by Tribbles in multiple tissues is essential for Caenorhabditis elegans development

“…Moreover, innate immune activation with a xenobiotic that provides protection from bacterial infection in the adult has been shown to provoke a growth delay during development [43]. Subsequently, an elegant genetic suppressor screen revealed that mutations in the PMK-1/p38 MAPK pathway suppressed this developmental phenotype [44]. Thus, the NIPI-3/CEBP-1 axis is a key mechanism by which immune effector expression is held in check during nematode development.…”

Next-Generation Sequencing-Based Approaches for Mutation Mapping and Identification in Caenorhabditis elegans

“…As mentioned in the previous section, this can be mitigated to a degree by using an outcross achieving higher mapping accuracy, although not as high as in HA variant mapping. The VDM method has recently been successfully applied to the identification of mutants affecting the innate immune response in C. elegans (Cheesman et al 2016). …”