Proinflammatory Role of Leukocyte-Derived Egr-1 in the Development of Murine Postoperative Ileus

Background & Aims: Early growth response gene-1 (Egr-1) is an important inflammatory transcription factor. We hypothesize that leukocyte-derived Egr-1 plays a key inflammatory role in causing postoperative ileus. Methods: Wild-type, Egr-1 knockout, and chimera mice (constructed by irradiation followed by injection with Egr-1^+/+ or Egr-1^−/− bone marrow) were subjected to surgical manipulation of the gastrointestinal tract to induce ileus. Reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry quantified and localized Egr-1. Lumenal transit of nonabsorbable fluorescein isothiocyanate-labeled dextran and in vitro organ bath techniques measured functional gastrointestinal motility. Inflammatory mediator expressions were measured by Griess reaction, enzyme-linked immunosorbent assay, and multiplex Luminex assay. Results: Intestinal manipulation rapidly and significantly induced Egr-1 messenger RNA and protein within the inflamed muscularis externa. Egr-1 was colocalized early to smooth muscle and enteric neurons and later in extravasated monocytes after surgery when postoperative ileus was functionally prominent. The functional severity of postoperative ileus was significantly ameliorated in mice deficient in Egr-1^−/− and chimera wild-type mice transplanted with Egr-1^−/− bone marrow, whereas knockout mice with Egr-1^+/+ bone marrow again displayed significant ileus. Motility was mechanistically associated in Egr-1^−/− gene deficiency with a down-regulation in the release of nitric oxide, prostanoids, monocyte chemoattractant protein-1, macrophage inflammatory protein-1α, interleukin-6, interleukin-1, and granulocyte colony-stimulating factor, as well as a decrease in the recruitment of leukocytes into the manipulated muscle wall of the intestine compared with wild-type mice. Conclusions: Leukocyte-derived Egr-1 plays an early critical inflammatory role in the initiation of the postoperative inflammatory response, which leads to a prolonged decreased in gastrointestinal motility after intestinal surgery.

Abbreviations used in this paper: Egr-1, early growth response gene-1, COX, cyclooxygenase-1, iNOS, inducible nitric oxide synthase