Increased Ferroportin-1 Expression and Rapid Splenic Iron Loss Occur with Anemia Caused by Salmonella enterica Serovar Typhimurium Infection in Mice

Abstract

e The Gram-negative intracellular bacterium Salmonella enterica serovar Typhimurium causes persistent systemic inflammatory disease in immunocompetent mice. Following oral inoculation with S. Typhimurium, mice develop a hematopathological syndrome akin to typhoid fever with splenomegaly, microcytic anemia, extramedullary erythropoiesis, and increased hemophagocytic macrophages in the bone marrow, liver, and spleen. Additionally, there is marked loss of iron from the spleen, an unanticipated result, given the iron sequestration reported in anemia of inflammatory disease. To establish why tissue iron does not accumulate, we evaluated multiple measures of pathology for 4 weeks following oral infection in mice. We demonstrate a quantitative decrease in splenic iron following infection despite increased numbers of splenic phagocytes. Infected mice have increased duodenal expression of the iron exporter ferroportin-1, consistent with increased uptake of dietary iron. Liver and splenic macrophages also express high levels of ferroportin-1. These observations indicate that splenic and hepatic macrophages export iron during S. Typhimurium infection, in contrast to macrophage iron sequestration observed in anemia of inflammatory disease. Tissue macrophage export of iron occurs concurrent with high serum concentrations of interferon gamma (IFN-␥) and interleukin 12 (IL-12). In individual mice, high concentrations of both proinflammatory (tumor necrosis factor alpha [TNF-␣])and anti-inflammatory (IL-10) cytokines in serum correlate with increased tissue bacterial loads throughout 4 weeks of infection. These in vivo observations are consistent with previous cell culture studies and suggest that the relocation of iron from tissue macrophages during infection may contribute to anemia and also to host survival of acute S. Typhimurium infection.T yphoid fever is acquired upon oral ingestion of food or water contaminated with Salmonella enterica serovar Typhi or Paratyphi and remains a serious threat to public health, especially in developing countries (1). Human typhoid fever causes a broad range of clinical signs, including splenomegaly, neuropathy, and hematopathology, such as cytopenias (2), that have been modeled in laboratory mice infected with Salmonella enterica serovar Typhimurium (3). Inbred mouse strains with differing genetic backgrounds are characterized as either sensitive or resistant to S. Typhimurium. Sensitivity to the intracellular bacterial infection is caused by genetic deficiencies in the innate or adaptive immune system (4, 5). For instance, mice lacking the cation transporter Nramp1 (Slc11a1), a regulator of cellular iron metabolism, are extremely sensitive to infection. Nramp1 ϩ mice are considered resistant to S. Typhimurium, because infection is generally nonfatal (6-8). Resistant mice infected by natural oral inoculation develop systemic infection with an acute hematopathological syndrome similar to that of humans with typhoid fever, including fever, anemia, inflammatory disease characterized by periph...

Hepcidin-(In)dependent Mechanisms of Iron Metabolism Regulation during Infection by Listeria and Salmonella

“…This alteration per se may explain the liver iron retention and the decrease in serum iron levels observed in infected mice. Our data are in apparent contrast with previously reported observations of an increase in ferroportin expression associated with Salmonella infection (32,33). These discrepancies may be explained by two main reasons.…”

Ironing out Ferroportin

“…However, countervailing effects may predominate during chronic infection: mechanisms that increase ferroportin transcription appear as a part of a natural and protective iron-modulating innate immune response to Salmonella infection of macrophages, and this response can be enhanced by interferon-gamma (Nairz et al, 2008). This increased expression of ferroportin in macrophages is also observed in vivo following infection of mice, where it results in loss of spleen iron (Brown et al, 2015). The upregulation of ferroportin in Salmonella -infected macrophages is at least in part driven by nitric-oxide-mediated Nrf2 activation, which in turn increases transcription of the ferroportin gene (Nairz et al, 2013).…”

Hepcidin regulation in the anemia of inflammation

“…Previous studies in this model also revealed local mechanisms in macrophages that limit iron availability, including induction of ferroportin transcription by interferon γ, nitric oxide and nuclear factor erythroid 2-related factor 2 (NRF2) [40]. This may help explain the reduced spleen iron levels seen in more chronic Salmonella typhimurium infection [41]. More work is needed to better understand the diverse roles of hepcidin and iron in infection and immunity, and the reader is referred to recent reviews for more in depth discussions [7;40].…”