P028. Inflammatory cytokines specifically regulate endoplasmic reticulum stress in colitis
S. Hasnain1, R. Wang1, S. Tauro1, I. Das1, I. Oancea1, P. Jeffery1, T. Florin2, M. McGuckin1, 1Mater Medical Research Institute, Australia, 2University of Queensland and Mater Health Services and MMRI, Australia
The unfolded protein response (UPR) and endoplasmic reticulum (ER) associated protein degradation are highly conserved molecular programs, which are activated by ER stress. They are critical for the quality control of protein synthesis and secretion in secretory cells such as goblet or Paneth cells. Severe ER stress triggers inflammation and is implicated in many chronic inflammatory diseases including IBD. In the Winnie spontaneous colitis mouse model in which Muc2 mucin misfolding leads to ER stress, thiopurine immunomodulation resolves ER stress and restores secretion of mucin but thiopurines do not directly affect ER stress. We hypothesised that inflammatory cytokines modulate ER stress.
We investigated the effect of cytokines on ER stress in Winnie mice with an in vitro screen using a fluorescent protein reporter system which detects the splicing of XBP1 mRNA, itself a direct measure of activity of the UPR endonuclease IRE1 activated by ER stress.
IFNγ, IL-17A/F, IL-23, IL-24 and IL-33, via different mechanisms, drive protein misfolding and ER stress in a variety of secretory cells including mucin-secreting goblet cells. Interestingly, the regulatory cytokines, IL-10 and IL-22, suppressed both cytokine-induced and chemically induced (tunicamycin) ER stress in a STAT1/STAT3-dependent manner, to restore protein secretion. Neutralisation of IL-10R in Winnie mice rapidly exacerbated histological inflammation, increased colonic IFNγ and IL-17A, exacerbated ER stress and increased the accumulation of misfolded Muc2 in ER. Furthermore, Winnie mice haplosufficient for IL-10 or IL-10−/− mice carrying a single Winnie Muc2Win/− allele both developed more severe inflammation; IL-10−/− Muc2Win/Win mice suffered profound colitis and runting. Intraperitoneal recombinant IL-10 or IL-22 aided the production and secretion of Muc2 and ameliorated colitis in Winnie. Administration of tunicamycin to wild-type mice caused intestinal ER stress, which increased when IL-10R1 was blocked.
While cytokine-induced ER stress may have evolved as a mechanism to prevent viral protein synthesis by secretory cells, in chronic non-infectious inflammation such as IBD these pathways will exacerbate inflammation by causing mucus depletion to expose the epithelium to microbes. Strategic antagonism of novel ER-stressor cytokines or augmenting ER-suppressor cytokines is likely to improve secretory protein production and so alleviate pathology in diseases involving protein misfolding, ER stress and inflammation.