Autophagy related 16-like 1 (ATG16L1) as a genetic risk factor has exposed the critical role of autophagy in Crohn’s disease (CD)1. Homozygosity for the highly prevalent ATG16L1 risk allele, or murine hypomorphic (HM) activity causes Paneth cell dysfunction2,3. As Atg16l1HM mice do not develop spontaneous intestinal inflammation, the mechanism(s) by which ATG16L1 contributes to disease remains obscure. Deletion of the unfolded protein response (UPR) transcription factor X-box binding protein-1 (Xbp1) in intestinal epithelial cells (IECs), whose human orthologue harbors rare inflammatory bowel disease (IBD) risk variants, results in endoplasmic reticulum (ER) stress, Paneth cell impairment and spontaneous enteritis4. Unresolved ER stress is a common feature of IBD epithelium4,5, and several genetic risk factors of CD affect Paneth cells2,4,6-9. Here we show that impairment in either UPR (Xbp1ΔIEC) or autophagy function (Atg16l1ΔIEC or Atg7ΔIEC) in IECs results in each other’s compensatory engagement, and severe spontaneous CD-like transmural ileitis if both mechanisms are compromised. Xbp1ΔIEC mice exhibit autophagosome formation in hypomorphic Paneth cells, which is linked to ER stress via protein kinase RNA-like endoplasmic reticulum kinase (PERK), elongation initiation factor 2α (eIF2α) and activating transcription factor 4 (ATF4). Ileitis is dependent on commensal microbiota and derives from increased IEC death, inositol requiring enzyme 1α (IRE1α)-regulated NFκB activation and tumor necrosis factor signaling which are synergistically increased when autophagy is deficient. ATG16L1 restrains IRE1α activity and augmentation of autophagy in IECs ameliorates ER stress-induced intestinal inflammation and eases NFκB overactivation and IEC death. ER stress, autophagy induction and spontaneous ileitis emerge from Paneth cell-specific deletion of Xbp1. Genetically and environmentally controlled UPR function within Paneth cells may therefore set the threshold for the development of intestinal inflammation upon hypomorphic ATG16L1 function and implicate ileal CD as a specific disorder of Paneth cells.
The release of endogenous antimicrobial peptides by mammalian epithelial cells contributes to innate mucosal immunity (1, 2). The crypts of Lieberkü hn in the small intestine of most mammals contain Paneth cells that secrete ␣-defensins (cryptdins), lysozyme, secretory phospholipase A 2 , xanthine oxidase, CD95 ligand, CD15, and tumor necrosis factor-␣ as components of apically oriented secretory granules (3-10). Although certain Paneth cell ␣-defensins have been detected in mouse skin and testis (11,12) and in human oropharyngeal and urogenital mucosa (13,14), in the small intestine, ␣-defensins are specific to Paneth cells (9). Exposure of Paneth cells to cholinergic agonists or bacterial stimuli elicits granule discharge into the crypt lumen (15), and carbamylcholine mediates secretion via increased cytosolic Ca 2ϩ (16). Regardless of how mouse Paneth cell secretion is stimulated, cryptdins constitute ϳ70% of the released bactericidal activity, and the concentration of cryptdins is estimated to be 25 mM at the point of secretion in the crypt lumen (15).␣-Defensins are processed from inactive proforms by specific proteolytic cleavage steps. Both neutrophil and Paneth cell ␣-defensins derive from ϳ10-kDa prepropeptides that contain canonical signal sequences, acidic proregions, and an ϳ3.5-kDa mature ␣-defensin peptide in the C-terminal portion of the precursor. For example, maturation of myeloid pro-␣-defensins appears to involve two primary cleavage steps, and most ␣-defensins in mature phagocytic leukocytes are completely processed (17)(18)(19)(20). In a heterologously expressed human neutrophil pro-␣-defensin, deletions in the prosegment adjacent to the proregion-defensin junction impairs post-translational processing in 32DCL3 cells (19).In mouse Paneth cells, matrix metalloproteinase-7 (MMP-7 1 ; matrilysin) mediates the processing and activation of ␣-defensins from 8.4-kDa proforms (21). MMP-7 gene disruption ablates procryptdin processing, resulting in accumulation of cryptdin precursors and the absence of activated mature cryptdin peptides in the small intestine (21). Lacking functional cryptdin peptides, MMP-7-null mice have a defect in clearance of intestinal infections, and they succumb more rapidly and to lower doses of virulent Salmonella typhimurium compared with control mice (21). Thus, the cryptdin deficiency resulting from defective procryptdin activation is associated with a measurable deficit in mucosal immunity and increased risk of systemic disease.In this study, cryptdin biosynthesis was investigated by characterizing details of intracellular procryptdin processing in
Cluster of differentiation 1 (CD1) in humans is a family of major histocompatibility complex (MHC) class I-like molecules expressed on the surface of immature thymocytes, Langerhans cells, and a subpopulation of B cells. The only function identified for human CD1 is as a ligand recognized by a subpopulation of T lymphocytes. In order to study the distribution and function of these molecules in the mouse, a murine CD1 complementary DNA was expressed in mouse fibroblasts and used to produce monoclonal antibodies. These antibodies revealed prominent expression of murine CD1 only on gastrointestinal tract epithelium and in the cytoplasm of hepatocytes. Low levels of expression were also detected on thymocytes and peripheral lymphocytes. The gastrointestinal distribution of murine CD1 suggests that this molecule may be important in epithelial immunity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.