Investigating the Molecular Mechanisms of Renal Hepcidin Induction and Protection upon Hemoglobin-Induced Acute Kidney Injury

Abstract

Hemolysis is known to cause acute kidney injury (AKI). The iron regulatory hormone hepcidin, produced by renal distal tubules, is suggested to exert a renoprotective role during this pathology. We aimed to elucidate the molecular mechanisms of renal hepcidin synthesis and its protection against hemoglobin-induced AKI. In contrast to known hepatic hepcidin induction, incubation of mouse cortical collecting duct (mCCDcl1) cells with IL-6 or LPS did not induce Hamp1 mRNA expression, whereas iron (FeS) and hemin significantly induced hepcidin synthesis (p < 0.05). Moreover, iron/heme-mediated hepcidin induction in mCCDcl1 cells was caused by the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, as indicated by increased nuclear Nrf2 translocation and induced expression of Nrf2 downstream targets GCLM (p < 0.001), NQO1 (p < 0.001), and TXNRD1 (p < 0.005), which could be prevented by the known Nrf2 inhibitor trigonelline. Newly created inducible kidney-specific hepcidin KO mice demonstrated a significant reduction in renal Hamp1 mRNA expression. Phenylhydrazine (PHZ)-induced hemolysis caused renal iron loading and oxidative stress in both wildtype (Wt) and KO mice. PHZ treatment in Wt induced inflammatory markers (IL-6, TNFα) but not Hamp1. However, since PHZ treatment also significantly reduced systemic hepcidin levels in both Wt and KO mice (both p < 0.001), a dissection between the roles of systemic and renal hepcidin could not be made. Combined, the results of our study indicate that there are kidney-specific mechanisms in hepcidin regulation, as indicated by the dominant role of iron and not inflammation as an inducer of renal hepcidin, but also emphasize the complex interplay of various iron regulatory mechanisms during AKI on a local and systemic level.

Functional consequence of myeloid ferritin heavy chain on acute and chronic effects of rhabdomyolysis-induced kidney injury

“…In recent work, we demonstrated that proximal tubular FtH deletion exacerbates AKI and leads to significant mortality during rhabdomyolysis (16). These studies were corroborated by the use of iron chelators and inducers of heme oxygenase expression within the kidney (10,(17)(18)(19)(20).…”

Iron metabolism and chronic inflammation in IgA nephropathy

“…Hepcidin expression increases under iron overload and inflammation and reduces under iron deficiency and hypoxia [ 186 ]. However, many of the current studies on hepcidin and inflammation are in the hepatocytes or AKI [ 187–189 ]. In IgAN, immune damage in the mesangial region promotes IL-6 secretion [ 171 , 190 ], and the tubular damage caused by hematuria also leads to an increase in IL-6 [ 26 , 191 ].…”

Anemia of chronic diseases: current state of the problem and perspectives

“…Другим местом выработки гепсидина являются дистальные собирательные канальцы почек, где индуктором его синтеза в большей мере является повышенный уровень железа/гема, нежели ИЛ-6, что, вероятно, играет важную протективную роль при остром повреждении почек, вызванном гемолизом [14].…”