A19 INTERLEUKIN-6 AND INTERLEUKIN-22 MEDIATE DISTICT REGULATION OF MITOCHONDRIAL DYNAMICS IN PATHOBIONT INFECTED GUT EPITHELIA

TL;DR

This study shows that IL-6 and IL-22 have different effects on mitochondrial function in gut cells infected with a harmful E. coli strain, with IL-6 helping to restore mitochondrial health.

Contribution

The paper reveals distinct regulatory roles of IL-6 and IL-22 on mitochondrial dynamics in pathobiont-infected gut epithelia.

Findings

IL-6 reduces mitochondrial fragmentation and restores membrane potential during E. coli-LF82 infection.

IL-22 does not prevent mitochondrial damage caused by E. coli-LF82.

IL-6, but not IL-22, reduces intracellular bacterial viability and increases autophagy markers.

Abstract

The IBD-associated pathobiont attaching-invading Escherichia coli (AIEC) strain LF82 induces mitochondrial fragmentation and depolarization in epithelial cells, resulting in impaired ATP production and reduced barrier function. Interleukin (IL)-6 and IL-22 are omnipresent in the inflamed gut, can directly affect epithelial function and both mobilize STAT-3, the serine727 phosphorylated form of which can translocate to mitochondria. Thus, we posed the question, will IL-6 or IL-22 rescue or exaggerate the mitochondrial damage evoked by exposure to E. coli-LF82?

1. To determine if IL-6 and IL-22 modulate mitochondrial function during E. coli-LF82 infection

2. To assess the mechanisms by which IL-6 and IL-22 affect mitochondrial function in model gut epithelia

Human colon-derived T84 epithelial cells were infected with E. coli-LF82 (108 CFU/mL, 4h) ± a 18h pre-treatment and then co-treatment with IL-6 or IL-22 (both 10 ng/mL). Bacterial internalization was evaluated, and mitochondrial network morphology visualized with MitoTracker Red and confocal microscopy. Mitochondrial membrane potential was evaluated using TMRE staining and flow cytometry, and ATP measured by a luminescence assay. STAT3 phosphorylation (S727 and Y705) in whole-cell extracts was determined via western blot in response to IL-6 or IL-22 during E. coli-LF82 infection.

IL-6 inhibited E. coli-LF82 evoked mitochondrial fragmentation, with significantly more cells showing a fused tubular pattern: mitochondrial membrane potential was restored by ~50% and ATP depletion was less severe (n=5). IL-6 elicited increased pS727-STAT3. In contrast, IL-22 failed to prevent any of the mitochondrial changes caused by E. coli-LF82, did not cause increased pS727-STAT3 but bioactivity was confirmed by increased pY705-STAT3. IL-6, but not IL-22, reduced the number of viable intracellular bacteria without affecting bacterial growth and increased markers of autophagy activation.

We have uncovered divergent effects of the STAT3 activators, IL-6 and IL-22, in the control of epithelial mitochondrial dynamics and function when challenged with a bacterial pathobiont. We speculate that IL-6 limits the effects of E. coli-LF82 via mitochondrially-directed pS727-STAT3 signaling and upregulation of autophagy. Understanding the precise role of STAT3- activating cytokines signaling in mitochondrial regulation could reveal new target to enhance epithelial barrier function.

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