Nramp1‐functionality increases iNOS expression via repression of IL‐10 formation

Abstract

In mice, resistance to certain intracellular microbes depends on the expression of a late phagosomal protein termed natural‐resistance associated macrophage protein 1 (Nramp1, Slc11a1). Nramp1‐functionality is associated with alterations of cellular iron homeostasis and a sustained pro‐inflammatory immune response, including the formation of the antimicrobial effector molecule NO. To investigate the underlying mechanism we used RAW‐264.7 murine macrophage cells stably transfected with a functional Nramp1 allele (RAW‐37) or Nramp1 non‐functional controls (RAW‐21). We found that the production of and signalling by the anti‐inflammatory cytokine IL‐10 was significantly enhanced in macrophages lacking functional Nramp1. Upon infection of macrophages with Salmonella typhimurium pathogen survival was significantly better in RAW‐21 than in RAW‐37, which inversely correlated to NO and TNF‐α formation. Addition of a neutralising anti‐IL‐10 antibody to RAW‐21 cells led to a significantly reduced survival of S. typhimurium within these cells and enhanced formation of NO and TNF‐α reaching levels comparable to that observed in cells bearing functional Nramp1. Oppositely, supplementation of iron to RAW‐21 cells further increased IL‐10 formation. Thus, Nramp1 mediates effective host defence in part via suppression of excessive IL‐10 production which may relate to Nramp1‐mediated reduction of cellular iron pools, thus strengthening antimicrobial effector mechanisms.

Macrophages and Iron Metabolism

“…Namely, lowering intracellular heme-iron in macrophages promotes the induction of NOS2, TNF, IL-6, IL-12 and histocompatibility (MHC) class II expression in response to IFNγ, an effect mediated in part by NRAMP1 (Fritsche et al, 2008) and involving the transcription factors HIF1α, nuclear factor for IL-6 (NF-IL6) and STAT family of transcription factors (Soares and Weiss, 2015). …”

Animal Models for Salmonellosis: Applications in Vaccine Research

“…The Nramp1 transporter is an intracellular protein that is recruited to the endosome, where it functions as a transporter for divalent cations, including Fe 2ϩ and Mn 2ϩ (39). There are several ways this transporter is thought to impact Salmonella survival, including denying the bacterium access to iron and activating inflammatory responses such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) (40)(41)(42). For susceptible (Nramp1 S ) mice, infection via the orogastric route leads to a systemic infection and is ultimately lethal in several days or up to 2 weeks (depending on the dose).…”

High Levels of Tumor Necrosis Factor-α Downregulate Antimicrobial Iron Transport Protein, Nramp1, in Chronic Hemodialysis Patients: A Key Factor for Infection Risk

“…Using the murine macrophage cell line RAW264.7, it was observed that Nramp1 expression in macrophages can be further upregulated by exposure of these cells to both bacterial lipopolysaccharide and interferon-γ (IFN-γ), as well as to other inflammatory stimuli [22,23]. In addition, a macrophage cell line stably transfected with functional Nramp1 infected with Salmonella typhimurium produced more TNF-α than those with non-functional Nramp1, which accelerated the activity of antimicrobial effector mechanisms [23,24,25]. These differences between the present and previous studies, however, are not easily explained.…”