(A) Immunohistochemical staining of colon of Klf5 in WT mice untreated or treated with DSS for 7 days (brown, Klf5; blue; counterstain). DSS; induction of Klf5 was downstream of mitogen-activated protein kinase signaling. In DSS-induced colitis,Klf5+/mice exhibited greater sensitivity to DSS than WT mice, with significantly higher clinical and histological colitis scores. In recovery experiments,Klf5+/mice showed poor recovery, with continued weight loss and higher mortality than WT mice.Klf5+/mice from the recovery period had reduced epithelial proliferation and cell migration at sites of ulceration compared to WT mice; these reductions correlated with reduced expression of EGFR. == CONCLUSIONS == Epithelial repair is an important aspect of recovery from DSS-induced colitis. The transcription factor KLF5 regulates mucosal healing through its effects on epithelial proliferation and migration. Keywords:inflammatory bowel disease, animal model, inflammatory response, mouse The mammalian gut epithelium forms a dynamic barrier between the organism and various external factors present within the lumen, including diet, microorganisms, and drugs. In the setting of rapid cell turnover and constant changes in luminal content, the intestinal mucosa maintains its integrity through stringent regulation of pathways involving proliferation, migration, differentiation, and cell death. Maintaining tissue homeostasis becomes critical in instances of inflammatory bowel disease (IBD), where dysregulation of these pathways can result in excessive tissue injury, inadequate regeneration and an increased risk of developing cancer. While normal maintenance of the intestinal epithelium by the Wnt signaling pathway has been well characterized1,2, little is known about the molecular events that regulate restoration of tissue homeostasis in response to external stress or injury. Krppel-like factor 5 (KLF5) is a zinc finger-containing transcription factor that belongs to a family of mammalian Krppel-like transcription factors. These factors are often tissue-specific and CP 31398 2HCl serve diverse roles in processes such as cell proliferation, differentiation and embryogenesis3,4. KLF5 is highly expressed in the gut and is enriched in epithelial cells in the proliferative compartment of the CP 31398 2HCl intestinal tract5, indicating a role as a pro-proliferative factor. Indeed, severalin vitrostudies show that ectopic expression of KLF5 enhances proliferation Amotl1 of non-transformed cultured epithelial cells68. KLF5 has also been shown CP 31398 2HCl to mediate the growth and transforming effects of oncogenicKRASin intestinal epithelial cells9. Furthermore, mouse studies reveal that Klf5 promotes proliferation in the settings of bacterial infection and intestinal tumor initiation10,11. The pro-proliferative effects of KLF5 are thought to be mediated through its transcriptional targets, which include the growth factor, platelet-derived growth factor alpha polypeptide (PDGF-A), and cell cycle proteins, cyclin D1, cyclin B1 and Cdc21214. In addition to its role in regulating proliferation, a number of studies indicate that KLF5 may act as a mediator of external stress responses. KLF5 expression is shown to be induced in vascular smooth muscle cells following balloon injury in rat aorta15. This induction is mediated through mitogen-activated protein kinase (MAPK) signaling by the early response gene, early growth response factor 1 (Egr1)15,16. Additional studies in heterozygousKlf5knockout (Klf5+/) mice reveal that KLF5 is a critical factor for tissue remodeling in injured vascular tissues by participating in proliferative and angiogenic responses14. In intestinal epithelial cells (IECs), KLF5 is activated CP 31398 2HCl by the bacterial component, lipopolysaccharide, and enhances inflammatory responses in these cells through its effects on CP 31398 2HCl NF-B signaling17. Furthermore,in vivostudies show that KLF5 is induced by colonization of the mouse colon with the bacterial pathogen,Citrobacter rodentium,and that Klf5 mediates colonic epithelial hyperplasia activated by this infection11. Taken together, these reports indicate a critical role for KLF5 in cellular responses to cardiovascular injury and suggest a similar function for KLF5 in intestinal tissues. In the present study, we utilize the dextran sulfate sodium (DSS)-induced model of colitis to examine the role of Klf5 in promoting restoration of tissue homeostasis. WT andKlf5+/mice were treated with the chemical irritant, DSS, and examined for the response and the ability to recover from DSS-induced injury. Results revealed that reduced levels of Klf5 heightened susceptibility to DSS-induced damage, indicating a protective role for Klf5 in response to chemical-induced injury. Moreover,Klf5+/mice exhibited poor recovery from DSS treatment, indicating that KLF5 is important for restoration of intestinal epithelial homeostasis. == Materials and Methods == == Mice == C57BL/6 mice were purchased from The Jackson Laboratory (Bar Harbor, ME).Klf5+/mice on a C57BL/6 background were generated as described previously11. Mouse strains were bred and.