Myeloid Specific HO-1-SIRT1-p53 Nexus Protects Against Iron Induced Chronic Liver Injury in Sickle Cell Disease

Sickle cell disease (SCD) is an autosomal-recessive-genetic disorder that affects ~100,000 Americans and millions of people worldwide. People with SCD experience multiple complications, including acute pain episodes, stroke, and organ damage, with a median life expectancy of 42-47 years in the United States. Red blood cell transfusions are an important therapeutic intervention in SCD, however, chronically transfused SCD patients develop severe iron overload in the liver, heart, spleen, and endocrine organs with increased expression of inflammatory markers. In addition, there is evidence of abnormal iron metabolism in SCD with prior studies showing a low urinary hepcidin level in children with SCD and highly variable levels in adults. Thus, hepatic iron homeostasis in SCD both at baseline and upon repeated blood transfusion remains incompletely understood.

In this study we evaluated iron homeostasis in Townes sickle cell mice at baseline and upon iron overload by iron dextran administration. We also evaluated the potential contribution of hepatic macrophages in hepatic iron homeostasis. Townes mice exhibited significant iron accumulation in the liver at baseline. We found significant reduction of hepcidin and increase in ferroportin and ferritin levels in the liver of sickle mice at baseline. However, upon hepatic iron overload (which was generated by intraperitoneal injections of iron dextran (1 g/kg) once a week for upto 10 weeks) the hepcidin ferroportin homeostasis was impaired and we found reduction of ferroportin and ferritin and increase in hepcidin in the sickle mouse liver. Immunohistochemically we could see a significant enrichment of iron loaded macrophages in the liver of SCD mice at baseline. Clodronate liposome mediated depletion of hepatic kupffer cells caused significant liver injury, hepatocyte death, systemic and hepatic iron accumulation and mortality in the mouse liver at baseline suggesting a protective role of hepatic kupffer cells in iron homeostasis. Mechanistic analysis further revealed protective mechanism through myeloid specific heme oxygenase 1 (HO-1)-sirtuin -1 (SIRT1)-p53 signaling that can potentially alleviate iron induced chronic liver injury in the SCD mice. At baseline, HO1 generated by kupffer cells stimulated SIRT1 activation in SCD mouse hepatocytes. Furthermore, HO-1 and SIRT1 prevented iron-induced senescence and hepatocyte cell death via regulating P53 signaling. Clodronate liposome-mediated kupffer cell loss drastically lowered HO-1 expression, which in turn reduced SIRT1 in SCD liver and accelerated senescence and cell death. In line with this finding, we also detected elevated levels of SIRT-1 in SCD patients’ blood serum. Work is currently underway to understand how modulation of HO-1-SIRT1-p53 signaling pathway can be used as a therapeutic option to combat iron induced chronic liver injury.

Sundd:CSL Behring Inc: Research Funding; Bayer Hemophilia Award Program: Research Funding; Novartis corporation: Research Funding; IHP Therapeutics: Research Funding.