The role of Nod-like receptors in modulating the microbiota-gut-brain axis following neonatal bacterial infection

Abstract

Objective: Pediatric infection with diarrheal pathogens causes cognitive deficits in adulthood via an unknown mechanism. Neonatal infection with a bacterial enteric pathogen disrupts the development of the microbiota-gut-brain (MGB) axis in adult mice. Given the role of pattern recognition receptors, including Nucleotide Oligomerization Domain 1 (Nod1) in innate immune responses to infection, our objective was to establish their role in disrupted MGB axis communication following neonatal enteropathogenic Escherichia coli (EPEC) infection. Hypothesis: Intestinal epithelial cell (IEC) Nod1 modulates disrupted MGB axis communication following neonatal EPEC infection. Methods: C57BL/6 (male/female) IEC Nod1 conditional knockout mice (IEC cKO; Cre+) and wild type (WT) littermate controls (Cre-) were used. Neonatal mice were infected on postnatal day 7 (P7) with EPEC (10 5 CFU; strain e2348/69; orogastric gavage), or vehicle control (Luria broth). Colonization was assessed at P14 and P21 (MacConkey agar plating) and disease monitored via weight loss and ileal inflammation (qPCR). Behavior and neuroinflammation were assessed in adulthood (6-8 weeks). Behavioral tests included the novel object recognition task (NOR) for cognitive function, the light/dark (L/D) box for anxiety-like behavior, and open field test (OFT) for general and locomotor behavior. Results: Neonatally EPEC-infected Nod1 cKO mice demonstrated blunted ileal inflammation, with similar decreased expression of Il6, Tlr2, Tlr4, and Nod2 in cKO vs WT EPEC-infected mice ( P = NS, n = 4-6 ), with no evidence of inflammation in uninfected controls (WT or cKO). In contrast, evidence of hippocampal neuroinflammation was present in EPEC-infected Nod1 cKO mice, with increased expression of Iba1, Il6, and Il22 ( P < 0.0001, n = 4-6), compared to sham-infected Nod1 cKO mice or uninfected control mice. In addition, EPEC-infected Nod1 cKO mice demonstrated decreased hippocampal expression of the neurogenesis marker Bdnf ( P < 0.0001, n ≥ 4) compared to EPEC-infected WT mice, or uninfected mice. With respect to behavior, EPEC-infected WT mice had a lower exploration ratio (49.5 ± 1.7% vs. 54.6 ± 1.7%, P = 0.0035, n ≥ 8), whereas EPEC-infected Nod1 cKO mice displayed normal exploration of a novel object compared to uninfected Nod1 cKO mice ( P = NS, n = 10-12), without impacting anxiety-like behavior ( P = NS, n = 10-12). Conclusions: IEC Nod1 is important for maintaining MGB axis communication following neonatal EPEC infection. We speculate that decreased ileal inflammation due to absence of Nod1 IEC expression prevents cognitive deficits in adulthood, despite the evidence of neuroinflammation and impaired neurogenesis. Inflammation in the gut and brain will be further characterized by immunofluorescence in ongoing studies. NIH R01AT009365; NIH R21MH108154. Olivia Orahood is an active-duty member of the United States Space Force. The views expressed in this article are those of the author and do not reflect the official policy or position of the United States Space Force, United States Air Force, Department of Defense, or the U.S. Government This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.