Nitrate-mediated luminal expansion of Salmonella Typhimurium is dependent on the ER stress protein CHOP

Salmonella Typhimurium is an enteric pathogen that employs a variety of mechanisms to exploit inflammation resulting in expansion in the intestinal tract, but host factors that contribute to or counteract the luminal expansion are not well-defined. Endoplasmic reticulum (ER) stress induces inflammation and plays an important role in the pathogenesis of infectious diseases. However, little is known about the contribution of ER stress-induced inflammation during Salmonella pathogenesis. Here, we demonstrate that the ER stress markers Hspa5 and Xbp1 are induced in the colon of S. Typhimurium infected mice, but the pro-apoptotic transcription factor Ddit3, that encodes for the protein CHOP, is significantly downregulated. S. Typhimurium-infected mice deficient for CHOP displayed a significant decrease in inflammation, colonization, dissemination, and pathology compared to littermate control mice. Preceding the differences in S. Typhimurium colonization, a significant decrease in Nos2 gene and iNOS protein expression was observed. Deletion of Chop decreased the bioavailability of nitrate in the colon leading to reduced fitness advantage of wild type S. Typhimurium over a napA narZ narG mutant strain (deficient in nitrate respiration). CD11b+ myeloid cells, but not intestinal epithelial cells, produced iNOS resulting in nitrate bioavailability for S. Typhimurium to expand in the intestinal tract in a CHOP-dependent manner. Altogether our work demonstrates that the host protein CHOP facilitates iNOS expression in CD11b+ cells thereby contributing to luminal expansion of S. Typhimurium via nitrate respiration.