Impairment of Hepcidin Upregulation by Lipopolysaccharide in the Interleukin-6 Knockout Mouse Brain

Abstract

To find out whether the Interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) signaling pathway is involved in the expression of hepcidin in the mouse brain in vivo, we investigated the phosphorylation of STAT3, as well as the expression of hepcidin mRNA, ferroportin 1 (Fpn1) and ferritin light chain (Ft-L) proteins in the cortex and hippocampus of LPS-treated wild type (IL-6+/+) and IL-6 knockout (IL-6-/-) mice. We demonstrated that IL-6 knockout could significantly reduce the response of hepcidin mRNA, phospho-STAT3, Fpn1 and Ft-L protein expression to LPS treatment, in both the cortex and hippocampus of mice. Also, Stattic, an inhibitor of STAT3, significantly reduced the expression of phospho-STAT3 and hepcidin mRNA in the cortex and hippocampus of the LPS-treated wild type mice. These findings provide in vivo evidence for the involvement of the IL-6/STAT3 signaling pathway in the expression of hepcidin.

The Dual Role of Hepcidin in Brain Iron Load and Inflammation

“…In physiological conditions hepcidin expression in brain structures and cells (neurons, glial cells, endothelial cells, epithelial cells of choroid plexus) has been consistently observed by in vivo studies in humans and rodents, albeit in low levels ( Krause et al, 2000 ; Pigeon et al, 2001 ; Zechel et al, 2006 ; Wang et al, 2008 , 2010 ; Hänninen et al, 2009 ; Raha et al, 2013 ; Wei et al, 2014 ; Farajdokht et al, 2015 ; Raha-Chowdhury et al, 2015 ; Graf et al, 2016 ; Li Y. et al, 2016 ; Pan et al, 2016 ; Tan et al, 2016 ; Lu et al, 2017 ; You et al, 2017 ; Zhang et al, 2017 ). Data from human and animal studies suggest that local hepcidin is more robustly expressed in pathophysiological states ( Sun et al, 2012 ; Urrutia et al, 2013 ; Tan et al, 2016 ; Xiong et al, 2016 ; You et al, 2017 ; Zhang et al, 2017 ). Similar to other cells, hepcidin main target protein in brain cells is FPN, but also iron import proteins ( Sun et al, 2012 ; Urrutia et al, 2013 ; Tan et al, 2016 ; Xiong et al, 2016 ; You et al, 2017 ; Zhang et al, 2017 ).…”

“…Data from human and animal studies suggest that local hepcidin is more robustly expressed in pathophysiological states ( Sun et al, 2012 ; Urrutia et al, 2013 ; Tan et al, 2016 ; Xiong et al, 2016 ; You et al, 2017 ; Zhang et al, 2017 ). Similar to other cells, hepcidin main target protein in brain cells is FPN, but also iron import proteins ( Sun et al, 2012 ; Urrutia et al, 2013 ; Tan et al, 2016 ; Xiong et al, 2016 ; You et al, 2017 ; Zhang et al, 2017 ).…”

Hepcidin and its therapeutic potential in neurodegenerative disorders

“…The fact that LPS and E. coli infection upregulates the levels of hepcidin mRNA and/or protein in the brain shows that HAMP gene expression can also be upregulated by inflammation, as was found outside of the brain. The finding that pretreatment with hepcidin reduces Aβ treatment‐induced IL‐6 expression and secretion in astrocytes and microglia and reduces neurotoxicity and oxidative damage triggered by conditioned media obtained from Aβ‐treated astrocytes and microglia imply that hepcidin can downregulate inflammatory and prooxidant processes .…”

“…The finding that pretreatment with hepcidin reduces Aβ treatment‐induced IL‐6 expression and secretion in astrocytes and microglia and reduces neurotoxicity and oxidative damage triggered by conditioned media obtained from Aβ‐treated astrocytes and microglia imply that hepcidin can downregulate inflammatory and prooxidant processes . Recent studies have also demonstrated that intracerebroventricular injection of LPS can upregulate hepcidin expression and also downregulate Fpn1 levels in the cortex and substantia nigra of the rat brain. LPS was able to increase neuronal hepcidin expression only when neurons were cocultured with BV‐2 microglia, and this upregulation was suppressed by IL‐6 neutralizing antibody in vitro.…”

“…Today, it has been well‐confirmed that the 25‐amino acid peptide (Figure ) is a principal regulator of systemic iron homeostasis, in addition to playing an important role in host defense in inflammation as well as functioning as a major component of innate immunity . Hepcidin binds to its membrane receptor ferroportin 1 (Fpn1/IREG1/Slc40a1/MTP1), currently the only identified cellular iron exporter independently discovered by three groups, which induces the internalization and degradation of the hepcidin/Fpn1 complex, suppressing the export of iron from the enterocytes where dietary iron is absorbed, the macrophages that recycle hemoglobin iron and the hepatocytes which are major iron storage cells, inducing a systemic reduction of iron availability . Also, disrupted hepcidin production has emerged as a causative factor in many iron‐related disorders, including iron overload‐associated hereditary hemochromatosis and iron‐loading anemia (hepcidin deficiency), iron insufficiency‐induced iron‐restricted anemia (hepcidin excess), autoimmune disease, various types of cancers, and also chronic kidney disease …”