Background: Recent studies link endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) to inflammatory bowel disease. Altered eIF2α phosphorylation (eIF2α-P), a regulatory hub of the UPR, was observed in mucosal tissue of patients with inflammatory bowel disease. In this study, we examined the mechanistic role of eIF2α-P in intestinal epithelial cell (IEC) function and intestinal homeostasis in mice.
Methods: We generated mice with villin-Cre-mediated conditional expression of nonphosphorylatable Ser51Ala mutant eIF2α in IECs (AAIEC mice). We analyzed AAIEC mice under normal conditions and on challenge with oral infection of Salmonella Typhimurium or dextran sulfate sodium-induced colitis.
Results: Loss of eIF2α-P did not affect the normal proliferation or differentiation of IECs. However, AAIEC mice expressed decreased secretory proteins including lysozyme, suggesting eIF2α-P is required for Paneth cell function. The ultrastructure of AA Paneth cells exhibited a reduced number of secretory granules, a fragmented ER, and distended mitochondria under normal conditions. UPR gene expression was defective in AA IECs. Translation of Paneth cell specific messenger RNAs encoding lysozyme and cryptidins was significantly defective leading to the observed granule-deficient phenotype, which was associated with reduced ribosomal recruitment of these messenger RNAs to the ER membrane. Consequently, AAIEC mice were more susceptible to oral Salmonella infection and dextran sulfate sodium-induced colitis.
Conclusions: We conclude eIF2α phosphorylation is required for the normal function of intestinal Paneth cells and mucosal homeostasis by activating UPR signaling and promoting messenger RNA recruitment to the ER membrane for translation.
Article first Published online 26 February 2014
*Del E. Webb Neuroscience, Aging and Stem Cell Research Center, Sanford Burnham Medical Research Institute, La Jolla, California;
†Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, Michigan; and
‡Department of Medicine, University of California San Diego, La Jolla, California. Dr. Cao is now with Columbia University College of Physicians and Surgeons, New York, New York. Dr. Harrington is now with Medical University of the Americas, Charlestown, Nevis, West Indies.
Reprints: Randal J. Kaufman, PhD, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, Sanford Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037-1062 (e-mail: firstname.lastname@example.org).
Supported by NIH Grants HL057346, DK042394, DK088227, HL052173 and a CCFA Senior Research Award 3800 (R.J.K.), DK035108 and DK080506 (L.E.), and a Rackham Graduate Student Research Grant (S.S.C.).
The authors have no conflicts of interest to disclose.
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Received November 26, 2013
Accepted January 24, 2014