Endogenous hepcidin synthesis protects the distal nephron against hemin and hemoglobin mediated necroptosis

Abstract

Hemoglobinuria is associated with kidney injury in various hemolytic pathologies. Currently, there is no treatment available and its pathophysiology is not completely understood. Here we studied the potential detrimental effects of hemoglobin (Hb) exposure to the distal nephron (DN). Involvement of the DN in Hb kidney injury was suggested by the induction of renal hepcidin synthesis (p < 0.001) in mice repeatedly injected with intravenous Hb. Moreover, the hepcidin induction was associated with a decline in urinary kidney injury markers 24p3/NGAL and KIM1, suggesting a role for hepcidin in protection against Hb kidney injury. We demonstrated that uptake of Hb in the mouse cortical collecting duct cells (mCCDcl1) is mediated by multi-protein ligand receptor 24p3R, as indicated by a significant 90% reduction in Hb uptake (p < 0.001) after 24p3R silencing. Moreover, incubation of mCCDcl1 cells with Hb or hemin for 4 or 24 h resulted in hepcidin synthesis and increased mRNA expression of markers for oxidative, inflammatory and ER stress, but no cell death as indicated by apoptosis staining. A protective role for cellular hepcidin against Hb-induced injury was demonstrated by aggravation of oxidative, inflammatory and ER stress after 4 h Hb or hemin incubation in hepcidin silenced mCCDcl1 cells. Hepcidin silencing potentiated hemin-mediated cell death that could be diminished by co-incubation of Nec-1, suggesting that endogenous hepcidin prevents necroptosis. Combined, these results demonstrate that renal hepcidin synthesis protects the DN against hemin and hemoglobin-mediated injury.

Systemic and local hepcidin as emerging and important peptides in renal homeostasis and pathology

“…The increased renal hepcidin production with decreased renal ferritin during acute renal iron load observed by Refaat et al seems to be in line with the previous studies . Still, the molecular pathways that induce hepcidin upregulation during hem‐induced injury are to be resolved . It is interesting to notice that distal tubule shows no signs of FPN expression compared to proximal tubule in physiological conditions .…”

“…Studies in mice models suggest that hemoglobin degradation in distal tubule increases local hepcidin expression. The increased local hepcidin production protects tubular cells from oxidative stress and apoptosis, which is confirmed by silencing the renal hepcidin production in collecting duct cell culture models [21,37] (Fig. 2).…”

“…Veuthey et al have suggested that prohepcidin is produced by proximal tubule, though it has to be mentioned that authors of this study did not measure mRNA expression, but rather immunohistochemical expression of this peptide, which could mean that the presence of the peptide inside proximal tubular cells is due to absorption from the blood filtrate which contains the systemic form of the peptide [36]. van Swelm et al have shown that renal hepcidin is secreted in distal tubule, and one of the causes of increased local hepcidin expression occurs via hemoglobin-induced kidney injury [21,37] (Table 1). But, hepcidin expression is not confined to tubular cells, because there is evidence of hepcidin expression in the leukocytes of renal interstitium during inflammation [38].…”

“…Local hepcidin could affect renal iron homeostasis by regulating the expression of DMT1 and/or TFR1, which are known renal iron carriers [40,43,44]. Interestingly, local hepcidin does not seem to affect FPN expression in all the portions of the nephron, which is the classical mode of action of hepcidin in other organs [21,37,40]. In addition, renal FPN seems to be affected by cellular iron load not by increasing its expression, but by being distributed to the surface of the basolateral membrane [45].…”

“…In addition, renal FPN seems to be affected by cellular iron load not by increasing its expression, but by being distributed to the surface of the basolateral membrane [45]. Finally, studies show that hepcidin might affect renal iron metabolism independently from FPN [21,37,42]. On the other hand, similarly to liver hepcidin, renal hepcidin could be induced through BMP6/SMAD pathway [35].…”