IL-4 Protects the Mitochondria Against TNFα and IFNγ Induced Insult During Clearance of Infection with Citrobacter rodentium and Escherichia coli

Abstract

Citrobacter rodentium is a murine pathogen that serves as a model for enteropathogenic Escherichia coli. C. rodentium infection reduced the quantity and activity of mitochondrial respiratory complexes I and IV, as well as phosphorylation capacity, mitochondrial transmembrane potential and ATP generation at day 10, 14 and 19 post infection. Cytokine mRNA quantification showed increased levels of IFNγ, TNFα, IL-4, IL-6, and IL-12 during infection. The effects of adding these cytokines, C. rodentium and E. coli were hence elucidated using an in vitro colonic mucosa. Both infection and TNFα, individually and combined with IFNγ, decreased complex I and IV enzyme levels and mitochondrial function. However, IL-4 reversed these effects, and IL-6 protected against loss of complex IV. Both in vivo and in vitro, the dysfunction appeared caused by nitric oxide-generation, and was alleviated by an antioxidant targeting mitochondria. IFNγ −/− mice, containing a similar pathogen burden but higher IL-4 and IL-6, displayed no loss of any of the four complexes. Thus, the cytokine environment appears to be a more important determinant of mitochondrial function than direct actions of the pathogen. As IFNγ and TNFα levels increase during clearance of infection, the concomitant increase in IL-4 and IL-6 protects mitochondrial function.

Interleukin 4 induces rapid mucin transport, increases mucus thickness and quality and decreases colitis andCitrobacter rodentiumin contact with epithelial cells

“…In response to IFN-γ and TNF-α, the plumpness of the surface goblet cells and the overall morphology was reduced (p < 0.001), whereas IL-4 and IL-13 enhanced these features (p < 0.05, Figure 3(a-f)). Of these four cytokines, IFN-γ, TNF-α and IL-4 were present in WT animals during clearance, whereas IL-13 was only detected in IFN-γ −/mice [1].…”

“…To investigate effects of the pathogen versus the cytokine environment on mucus thickness, we identified that IFNγ −/mice had a similar pathogen burden at 10 dpi ( Figure 2(a)), but increased Il-13, Il-5, Il-4, and Il-6 in IFN-γ −/mice compared to WT mice [1]. IFN-γ −/mice had higher colitis scores (p < 0.001, Figure 2(b) and Supplementary Figure 1).…”

“…during clearance or differential expression in WT versus IFN-γ −/mice at 10 dpi). The cytokines were identified from a dataset of 85 genes involved in Th1/Th2 immune responses from a previous study using samples from the same mice [1]. The mucosal surfaces were treated with cytokines for 96 h to mimic the extended period of elevated cytokine stimulus occurring during C. rodentium infection in vivo [1].…”

“…The cytokines were identified from a dataset of 85 genes involved in Th1/Th2 immune responses from a previous study using samples from the same mice [1]. The mucosal surfaces were treated with cytokines for 96 h to mimic the extended period of elevated cytokine stimulus occurring during C. rodentium infection in vivo [1]. In a first screen for the effects of the cytokines associated with increased mucus thickness on mucin production and goblet cell density, IL-6 and IL-12 did not induce changes; therefore we focused on IFN-γ, TNF-α, IL-4 and IL-13.…”

“…Citrobacter rodentium is a mouse pathogen that uses the same mechanism as EPEC and EHEC to colonize epithelial cells. During the mid-point of infection, the host response to C. rodentium is primarily Th1/Th17 driven, whereas cytokines of "Th2/antiinflammatory" type appear during clearance: interferon gamma (Ifn-γ) and interleukin (IL) Il-12 become upregulated throughout infection whereas Il-4, tumor necrosis factor alpha (Tnf-α) and Il-6 mRNA become upregulated during clearance only [1].…”