Metalloreductase Steap3 coordinates the regulation of iron homeostasis and inflammatory responses.
BACKGROUND
Iron and its homeostasis are intimately related to inflammatory responses, but the underlying molecular mechanisms are poorly understood. We investigated the role of Steap3 in regulating iron homeostasis in macrophages, and the effects of Steap3 depletion on host inflammatory responses.


METHODS
We analyzed bone marrow-derived macrophages and primary cultured hepatocytes from Steap3(-/-) mouse models to investigate the roles of Steap3 in coordinately regulating iron homeostasis and inflammatory responses. First, we examined iron distribution and iron status in cells deficient in Steap3, as well as the requirement for the Steap3 gene during inflammatory responses. Secondly, we analyzed the regulation of Steap3 expression by inflammatory stimuli and thus, the influence of these stimuli on iron distribution and homeostasis.


RESULTS
We found that Steap3 mRNA was expressed at high levels in macrophages and hepatocytes. Steap3 deficiency led to impaired iron homeostasis, causing abnormal iron distribution and a decreased availability of cytosolic iron in macrophages. Among STEAP family members, Steap3 mRNA was uniquely down-regulated in macrophages stimulated by lipopolysaccharides. To determine whether Steap3 regulated iron homeostasis during inflammatory stress, we treated Steap3(-/-) mice with lipopolysaccharide, which produced greater iron accumulation in the vital tissues of these mice compared to in the tissues of wild-type controls. Furthermore, Steap3 depletion led to impaired induction of interferon-β, monocyte chemoattractant protein-5, and interferon induced protein-10 in macrophages via the TLR4-mediated signaling pathway.


CONCLUSIONS
Steap3 is important in regulating both iron homeostasis and TLR4-mediated inflammatory responses in macrophages. Steap3 deficiency causes abnormal iron status and homeostasis, which leads to impaired TLR4-mediated inflammatory responses in macrophages. Following inflammatory stimuli, Steap3 depletion causes dysregulated iron sequestration and distribution. Our results provide important insights into the function of Steap3 as a coordinate regulator of both iron homeostasis and innate immunity.
Key Laboratory of Nutrition and Metabolism, Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Shanghai, China.
Fan
F
Zhang
Yunlong
Y
Tao
Zhuzhen
Z
Zhang
Xin
X
Guo
Peng
P
An
Yuanyuan
Y
Shen
Qian
Q
Wu
Yu
Y
Yu
Fudi
F
Wang
D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D049109:Cell Proliferation / Q000187:drug effects; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism; D006706:Homeostasis; D007249:Inflammation / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D007501:Iron / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D010088:Oxidoreductases; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D012333:RNA, Messenger; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D007501:Iron; D010088:Oxidoreductases; C473329:TSAP6 protein, mouse