Tumor Necrosis Factor α Inhibits Expression of the Iron Regulating Hormone Hepcidin in Murine Models of Innate Colitis

Nanda Kumar N Shanmugam,Wendy S Garrett,Shiri Ellenbogen,Adam Lacy-Hulbert,Carey Ann Gallini,Estela Trebicka,Subhankar Mukhopadhyay,Bobby J Cherayil,Lijian Wang

doi:10.1371/journal.pone.0038136

Abstract

BackgroundAbnormal expression of the liver peptide hormone hepcidin, a key regulator of iron homeostasis, contributes to the pathogenesis of anemia in conditions such as inflammatory bowel disease (IBD). Since little is known about the mechanisms that control hepcidin expression during states of intestinal inflammation, we sought to shed light on this issue using mouse models.Methodology/Principal FindingsHepcidin expression was evaluated in two types of intestinal inflammation caused by innate immune activation—dextran sulfate sodium (DSS)-induced colitis in wild-type mice and the spontaneous colitis occurring in T-bet/Rag2-deficient (TRUC) mice. The role of tumor necrosis factor (TNF) α was investigated by in vivo neutralization, and by treatment of a hepatocyte cell line, as well as mice, with the recombinant cytokine. Expression and activation of Smad1, a positive regulator of hepcidin transcription, were assessed during colitis and following administration or neutralization of TNFα. Hepcidin expression progressively decreased with time during DSS colitis, correlating with changes in systemic iron distribution. TNFα inhibited hepcidin expression in cultured hepatocytes and non-colitic mice, while TNFα neutralization during DSS colitis increased it. Similar results were obtained in TRUC mice. These effects involved a TNFα-dependent decrease in Smad1 protein but not mRNA.Conclusions/SignificanceTNFα inhibits hepcidin expression in two distinct types of innate colitis, with down-regulation of Smad1 protein playing an important role in this process. This inhibitory effect of TNFα may be superseded by other factors in the context of T cell-mediated colitis given that in the latter form of intestinal inflammation hepcidin is usually up-regulated.

Highlights

Inflammatory conditions are often accompanied by a debilitating anemia known as the anemia of inflammation (AI) [1]
When we extended the time of DSS treatment, we were surprised to find that hepcidin expression was significantly reduced by 7 days (Figure 1A) and remained at a persistently low level for as long as 2 weeks
Our findings suggest that the inhibitory effect of TNFa on hepcidin expression during DSS colitis is mediated by down-regulation of Smad1 protein and consequent interference with bone morphogenetic proteins (BMPs)-activated signals

Summary

Introduction

Inflammatory conditions are often accompanied by a debilitating anemia known as the anemia of inflammation (AI) [1]. The pathogenesis of AI is related to abnormally elevated levels of the liver peptide hormone hepcidin, a key regulator of systemic iron metabolism [2]. With the discovery of the role played by hepcidin in AI, recent investigations have attempted to determine whether this hormone is involved in the anemia of IBD. Urinary hepcidin was found to be significantly elevated in a study of children with active Crohn’s disease, correlating with decreased iron absorption from the gut [5]. An investigation of adults with IBD demonstrated elevated serum hepcidin levels in the patients that correlated positively with disease activity and negatively with hemoglobin [6]. Abnormal expression of the liver peptide hormone hepcidin, a key regulator of iron homeostasis, contributes to the pathogenesis of anemia in conditions such as inflammatory bowel disease (IBD). Since little is known about the mechanisms that control hepcidin expression during states of intestinal inflammation, we sought to shed light on this issue using mouse models

Methods

Results

Conclusion