Biology subjects

Philpott, D. J.

Publications and source records attributed to Philpott, D. J..

3 recordsLinked to original sources

bioRxiv2019

Nod-like receptors are critical for gut-brain axis signaling

Gut-brain axis signaling is critical for maintaining health and homeostasis. Stressful life events can impact gut-brain signaling, leading to altered mood, cognition and intestinal dysfunction. Here we identify nucleotide binding oligomerization domain (Nod)-like receptors (NLR), Nod1 and Nod2, as novel regulators for gut-brain signaling. NLR are innate immune pattern recognition receptors expressed in the gut and brain, important in the regulation of gastrointestinal (GI) physiology. We found that mice deficient in both Nod1 and Nod2 (NodDKO) demonstrate signs of stress-induced anxiety, cognitive impairment and depression in the context of a hyperactive hypothalamic-pituitary-adrenal axis. These deficits were coupled with impairments in the serotonergic pathway in the brain, decreased hippocampal neurogenesis, and reduced neural activation. In addition, NodDKO mice had increased GI permeability and altered serotonin signaling in the gut following exposure to acute stress. Administration of the selective serotonin reuptake inhibitor, fluoxetine, abrogated behavioral impairments and restored serotonin signaling. We also identified that intestinal epithelial cell-specific deletion of Nod1 (VilCre+Nod1f/f), but not Nod2, increased susceptibility to stress-induced anxiety-like behavior and cognitive impairment following exposure to stress. Together these data suggest that intestinal epithelial NLR are novel modulators of gut-brain communication and may serve as potential novel therapeutic targets for the treatment of gut-brain disorders.

physiology↗

bioRxiv2019

NOD1 mediates non-canonical inflammasome processing of interleukin-18 in epithelial cells to Helicobacter pylori infection.

The interleukin-1 family members, IL-1{beta} and IL-18, are processed into their biologically active forms by multi-protein complexes, known as inflammasomes. Although the inflammasome pathways that mediate IL-1{beta} processing in myeloid cells have been extensively studied, those involved in IL-18 processing, particularly in non-myeloid cells, are still poorly understood. Here, we have identified the cytosolic sensor NOD1 as a key regulator of IL-18 processing in epithelial cells responding to Helicobacter pylori infection. Importantly, NOD1 processing of IL-18 occurs independently of the canonical inflammasome proteins, NLRP3 and ASC. Instead, NOD1 interacts directly with caspase-1 via homotypic binding of caspase-activation recruitment domains. We show that IL-18 is important in maintaining tissue homeostasis and protecting against pre-neoplastic changes due to gastric H. pylori infection. These findings reveal an unanticipated role for NOD1 in a new type of inflammasome that regulates epithelial cell production of bioactive IL-18 with tissue protective functions.

immunology↗

bioRxiv2019

Trace levels of peptidoglycan in serum underlie the NOD-dependent cytokine response to endoplasmic reticulum stress

NOD1 and NOD2 are intracellular sensors of bacterial peptidoglycan that belong to the Nod-like receptor (NLR) family of innate immune proteins. In addition to their role as direct bacterial sensors, it was recently proposed that NOD proteins could detect endoplasmic reticulum (ER) stress induced by thapsigargin, an inhibitor of the sarcoplasmic or endoplasmic reticulum calcium ATPase family (SERCA) that pumps Ca2+ into the ER, resulting in pro-inflammatory signalling. Here, we confirm that thapsigargin induces pro-inflammatory signalling in epithelial cells in a NOD-dependent manner. However, the effect was specific to thapsigargin, as tunicamycin and the subtilase cytotoxin SubAB from Shiga toxigenic Escherichia coli, which induce ER stress by other mechanisms, did not induce cytokine expression. The calcium ionophore A23187 also induced NOD-dependent signalling, and the calcium chelator BAPTA-AM blunted thapsigargin-dependent pro-inflammatory signalling, showing NOD proteins responded to a rise in intracellular Ca2+. Since intracellular Ca2+ directly affects vesicular trafficking, we tested if thapsigargin-induced NOD activation required endocytosis. Our results demonstrate that both endocytosis and the addition of serum to the cell culture medium were required for thapsigargin-mediated NOD activation. Finally, we analyzed cell culture grade fetal calf serum as well as serum from laboratory mice by high-pressure liquid chromatography and mass spectrometry, and identified the presence of various peptidoglycan fragments. We propose that cellular perturbations that affect intracellular Ca2+ can trigger internalization of peptidoglycan trace contaminants found in culture serum, thereby stimulating pro-inflammatory signalling. The presence of peptidoglycan in animal serum suggests that a homeostatic function of NOD signalling may have been previously overlooked.

immunology↗