Sickle Cell Disease Promotes Dysregulation of Hepatic Iron Homeostasis By Regulating Hepcidin Expression

Sickle cell disease (SCD) is an autosomal-recessive-genetic disorder that affects millions of people worldwide. Although hepatic crisis affects 10-40% of hospitalized SCD patients and can progress to fatal liver failure, the current treatment is primarily supportive and the molecular pathophysiology remains largely unknown. We found that transgenic, humanized SCD mice developed liver injury with age, manifested by increased inflammation, necrosis and hepatic iron accumulation. The presence of iron particles in SCD liver was confirmed by transmission electron micrograph (TEM) analysis and prussian blue staining which revealed increased iron accumulation in the central and midzonal region of the SCD liver tissue. An increase in aggregates of iron pigment reminiscent of hemosiderin-laden macrophages was also observed in SCD liver tissue. Interestingly, the SCD mice also showed significant enrichment of both hepatic (p=0.02) and serum iron (p=0.04) compared to control AS mice. We determined the expression level of genes commonly involved in iron homeostasis by RT-PCR. Interestingly, a significantly lower expression level of hepcidin transcripts was observed in the liver of SCD mice compared to control mice (AS) (p=0.01).

In order to define the pathways controlling hepcidin transcription in SCD, we performed an RNA-seq analysis in the liver of SCD mice. Remarkably, our data showed significant misexpression of hypoxia signaling pathways. Further analysis revealed a significant increase in hypoxia-inducible factor (HIF)-2α levels in the liver of SCD mice by western blot. Reduced levels of Hepcidin were also confirmed in serum samples from SCD patients compared to controls. Work is currently underway to understand how HIF2α might hypothetically regulate hepcidin expression in the liver. This is particularly relevant because HIF2a translation is known to be regulated by iron through an iron response element at the 5' end of its transcript.

In summary, our results reveal a significant defect in iron homeostasis in the liver of SCD mice, suggesting that impaired iron homeostasis may contribute to hepatobiliary injury in SCD independent of blood transfusions. Our study also highlights the importance of hepcidin as potential therapeutic target in regulation of hepatic injury in SCD.