Interleukin-22 suppresses major histocompatibility complex II in mucosal epithelial cells

Major histocompatibility complex (MHC) II is dynamically expressed on mucosal epithelial cells and is induced in response to inflammation and parasitic infections, upon exposure to microbiota, and is increased in chronic inflammatory diseases. However, the regulation of epithelial cell-specific MHC II during homeostasis is yet to be explored. We discovered a novel role for IL-22 in suppressing epithelial cell MHC II partially via the regulation of endoplasmic reticulum (ER) stress, using animals lacking the interleukin-22-receptor (IL-22RA1), primary human and murine intestinal and respiratory organoids, and murine models of respiratory virus infection or with intestinal epithelial cell defects. IL-22 directly downregulated interferon-γ-induced MHC II on primary epithelial cells by modulating the expression of MHC II antigen A α (H2-Aα) and Class II transactivator (Ciita), a master regulator of MHC II gene expression. IL-22RA1-knockouts have significantly higher MHC II expression on mucosal epithelial cells. Thus, while IL-22-based therapeutics improve pathology in chronic disease, their use may increase susceptibility to viral infections.

Pancreatic Interleukin-22 Receptor Signaling is Critical in Maintaining Beta-Cell Insulin Production and is Hepatoprotective

We discovered that the cytokine interleukin-22 (IL-22) is an efficient natural inhibitor of cellular stress and exogenous IL-22 improved insulin quality in pancreatic β-cells in preclinical models of Type 2 diabetes. Importantly, IL-22 completely restored glucose tolerance, suppressed fasting hyperinsulinemia/hyperproinsulinemia, and restored insulin sensitivity in obese animals. Moreover, metabolic improvements were accompanied by significant improvements in circulating triglycerides, liver function (AST:ALT ratio) and a reduction in hepatic lipid accumulation. Whilst the IL-22 receptor, IL-22RA1 is highly expressed in the pancreas and liver, its endogenous role in these tissues remains elusive. To explore this, we generated tissue specific IL-22ra1 knockout mice lacking the receptor in pancreatic β-cells (Il-22ra1fl/fl x Ins2Cre: IL-22ra1β-cell−/−) and hepatocytes (Il-22ra1fl/fl x AlbCre: IL-22ra1Hep−/−). We assessed their metabolic phenotype including glycemic control, hepatic lipid accumulation, and hepatic markers of cellular stress, lipid, and glucose metabolism with age or with obesity. We discovered that IL-22ra1β-cell−/− animals developed hyperglycemia with age and had defective insulin secretion, which was exacerbated when on a high fat diet. Interestingly, they also had a significant increase in markers of hepatic inflammation and cellular stress. In conclusion we demonstrate, for the first time, that local endogenous IL-22 secretion in pancreatic β-cells maintains insulin biosynthesis. Moreover, our work highlights the importance of the pancreatic-β-cell-liver axis as the absence of pancreatic IL-22ra1 signaling leads to a marked increase in liver inflammation and cellular stress.

Gut microbiota shape the inflammatory response in mice with an epithelial defect

Intestinal epithelial cell endoplasmic reticulum (ER) stress has been implicated in intestinal inflammation. It remains unclear whether ER stress is an initiator of or a response to inflammation. Winnie mice, carrying a Muc2 gene mutation resulting in intestinal goblet cell ER stress, develop spontaneous colitis with a depleted mucus barrier and increased bacterial translocation. This study aims to determine whether the microbiota was required for the development of Winnie colitis, and whether protein misfolding itself can initiate inflammation directly in absence of the microbiota. To assess the role of microbiota in driving Winnie colitis, WT and Winnie mice on the same background were rederived into the germ-free facility and housed in the Trexler-type soft-sided isolators. The colitis phenotype of these mice was assessed and compared to WT and Winnie mice housed within a specific pathogen-free facility. We found that Winnie colitis was substantially reduced but not abolished under germ-free conditions. Expression of inflammatory cytokine genes was reduced but several chemokines remained elevated in absence of microbiota. Concomitantly, ER stress was also diminished, although mucin misfolding persisted. RNA-Seq revealed that Winnie differentiated colon organoids have decreased expression of the negative regulators of the inflammatory response compared to WT. This data along with the increase in Mip2a chemokine expression, suggests that the epithelial cells in the Winnie mice are more responsive to stimuli. Moreover, the data demonstrate that intestinal epithelial intrinsic protein misfolding can prime an inflammatory response without initiating the unfolded protein response in the absence of the microbiota. However, the microbiota is necessary for the amplification of colitis in Winnie mice. Genetic predisposition to mucin misfolding in secretory cells initiates mild inflammatory signals. However, the inflammatory signal sets a forward-feeding cycle establishing progressive inflammation in the presence of microbiota.Abbreviations: Endoplasmic Reticulum: ER; Mucin-2: Muc-2; GF: Germ-Free; Inflammatory Bowel Disease: IBD.