Neonatal immune challenge influences the microbiota and behaviour in a sexually dimorphic manner

There is comorbidity between anxiety disorders and gastrointestinal disorders, with both linked to adverse early life events. The microbiome gut-brain-axis, a bidirectional communication system, is plastic throughout the neonatal period and is a possible mediator of this relationship. Here, we used a well-established neonatal rodent immune activation model to investigate the long-term effect of neonatal lipopolysaccharide (LPS) exposure on adult behaviour and the relationship to microbiome composition. Wistar rats were injected with LPS (0.05 mg/kg) or saline (equivolume) on postnatal days 3 and 5. In adulthood, behavioural tests were performed to assess anxiety-like behaviour, and microbiota sequencing was performed on stool samples. There were distinctly different behavioural phenotypes for LPS-exposed males and females. LPS-exposed males displayed typical anxiety-like behaviours with significantly decreased social interaction (F_(1,22) = 7.576, p = 0.009) and increased defecation relative to saline controls (F_(1,23) = 8.623, p = 0.005). LPS-exposed females displayed a different behavioural phenotype with significantly increased social interaction (F_(1,22) = 6.094, p = 0.018), and exploration (F_(1,24) = 6.359, p = 0.015), compared to saline controls. With respect to microbiota profiling data, Bacteroidota was significantly increased for LPS-exposed females (F_(1,14) = 4.931p = 0.035) and Proteobacteria was decreased for LPS-exposed rats of both sexes versus controls (F_(1,30) = 4.923p = 0.035). Furthermore, alterations in predicted functional pathways for neurotransmitters in faeces were observed with a decrease in the relative abundance of D-glutamine and D-glutamate metabolism in LPS exposed females compared to control females (p < 0.05). This suggests that neonatal immune activation alters both later life behaviour and adult gut microbiota in sex-specific ways. These findings highlight the importance of sex in determining the impact of neonatal immune activation on social behaviour and the gut microbiota.

Regulation of IL-12p40 by HIF controls Th1/Th17 responses to prevent mucosal inflammation

Intestinal inflammatory lesions are inherently hypoxic, due to increased metabolic demands created by cellular infiltration and proliferation, and reduced oxygen supply due to vascular damage. Hypoxia stabilizes the transcription factor hypoxia-inducible factor-1α (HIF) leading to a coordinated induction of endogenously protective pathways. We identified IL12B as a HIF-regulated gene and aimed to define how the HIF-IL-12p40 axis influenced intestinal inflammation. Intestinal lamina propria lymphocytes (LPL) were characterized in wild-type and IL-12p40^-/- murine colitis treated with vehicle or HIF-stabilizing prolyl-hydroxylase inhibitors (PHDi). IL12B promoter analysis was performed to examine hypoxia-responsive elements. Immunoblot analysis of murine and human LPL supernatants was performed to characterize the HIF/IL-12p40 signaling axis. We observed selective induction of IL-12p40 following PHDi-treatment, concurrent with suppression of Th1 and Th17 responses in murine colitis models. In the absence of IL-12p40, PHDi-treatment was ineffective. Analysis of the IL12B promoter identified canonical HIF-binding sites. HIF stabilization in LPLs resulted in production of IL-12p40 homodimer which was protective against colitis. The selective induction of IL-12p40 by HIF-1α leads to a suppression of mucosal Th1 and Th17 responses. This HIF-IL12p40 axis may represent an endogenously protective mechanism to limit the progression of chronic inflammation, shifting from pro-inflammatory IL-12p70 to an antagonistic IL-12p40 homodimer.

A role for guanylate cyclase C in acid-stimulated duodenal mucosal bicarbonate secretion

Luminal acidification provides the strongest physiological stimulus for duodenal HCO3- secretion. Various neurohumoral mechanisms are believed to play a role in acid-stimulated HCO3- secretion. Previous studies in the rat and human duodenum have shown that guanylin and Escherichia coli heat-stable toxin, both ligands of the transmembrane guanylyl cyclase receptor [guanylate cyclase C (GC-C)], are potent stimulators for duodenal HCO3- secretion. We postulated that the GC-C receptor plays an important role in acid-stimulated HCO3- secretion. In vivo perfusion studies performed in wild-type (WT) and GC-C knockout (KO) mice indicated that acid-stimulated duodenal HCO3- secretion was significantly decreased in the GC-C KO animals compared with the WT counterparts. Pretreatment with PD-98059, an MEK inhibitor, resulted in attenuation of duodenal HCO3- secretion in response to acid stimulation in the WT mice with no further effect in the KO mice. In vitro cGMP generation studies demonstrated a significant and comparable increase in cGMP levels on acid exposure in the duodenum of both WT and KO mice. In addition, a rapid, time-dependent phosphorylation of ERK was observed with acid exposure in the duodenum of WT mice, whereas a marked attenuation in ERK phosphorylation was observed in the KO animals despite equivalent levels of ERK in both groups of animals. On the basis of these studies, we conclude that transmembrane GC-C is a key mediator of acid-stimulated duodenal HCO3- secretion. Furthermore, ERK phosphorylation may be an important intracellular mediator of duodenal HCO3- secretion.

Assessment of signs of influenza illness in the ferret model

The ferret model of influenza A infection was evaluated to determine whether physical signs of influenza illness in addition to fever could be adequately followed. Ferrets were evaluated for nasal and systemic signs of influenza infection in a blinded, randomized protocol. Nasal signs were scored depending on the degree of nasal discharge and congestion. Systemic signs were evaluated on the basis of the activity level of ferrets. Nasal and systemic signs in ferrets challenged with influenza began to rise at peak virus shedding. This rise was coincident with the onset of the nasal inflammatory cell response. Nasal and systemic signs were statistically higher in challenged ferrets as compared with controls from 28 to 52 h after infection [P = 0.002 except at 28 h (P = 0.01)]. Despite precautions against influenza transmission, controls shed influenza virus associated with mild increases in nasal and systemic signs late in the course of the study. Our results suggest that severity of influenza illness can be adequately assessed in the ferret model using collective measurements of nasal and systemic signs, temperatures, and nasal cellular infiltration.