AMP-activated protein kinase α1 phosphorylates PHD2 to maintain systemic iron homeostasis

Background: Iron is essential for all mammalian life, and either a deficiency or excess of iron can cause diseases. AMP-activated protein kinase (AMPK) is a critical regulator of metabolic homeostasis; however, it has not been established whether AMPK regulates iron metabolism. Methods: Iron, hepcidin and ferroportin levels were examined in mice with global and hepatocyte-specific knockout of AMPK alpha 1 and AMPK alpha 2. Primary AMPK alpha 1 or AMPK alpha 2 deleted hepatocytes were isolated and cultured in hypoxia condition to explore PHD2, HIF and hydroxylated HIF1 alpha levels. We performed immunoprecipitation, in vitro AMPK kinase assay and site-direct mutant assay to detect phosphorylation sites of PHD2. We also obtained liver tissues from patients with anaemia of chronic disease undergoing surgery, AMPK alpha 1 and hydroxylated HIF1 alpha levels were measured by immunohistochemical analysis. Results: We found that mice with global deficiency of AMPK alpha 1, but not AMPK alpha 2, exhibited hypoferraemia as well as iron sequestration in the spleen and liver. Hepatocyte-specific, but not myeloid-specific, ablation of AMPK alpha 1 also reduced serum iron levels in association with increased hepcidin and decreased ferroportin protein levels. Mechanistically, AMPK alpha 1 directly phosphorylated prolyl hydroxylase domain-containing (PHD)2 at serines 61 and 136, which suppressed PHD2-dependent hydroxylation of hypoxia-inducible factor (HIF)1 alpha and subsequent regulation of hepatic hepcidin-related iron signalling. Inhibition of PHD2 hydroxylation ameliorated abnormal iron metabolism in hepatic AMPK alpha 1-deficient mice. Furthermore, we found hepatic AMPK alpha/PHD2/HIF alpha/hepcidin axes were highly clinically relevant to anaemia of chronic disease. Conclusion: In conclusion, these observations suggest that hepatic AM PK alpha 1 has an essential role in maintaining iron homeostasis by PHD2-dependent regulation of hepcidin, thus providing a potentially promising approach for the treatment of iron disturbances in chronic diseases.

Automated summary

This study found that hepatic AMPK alpha 1 plays an essential role in maintaining iron homeostasis by regulating hepcidin through its interaction with PHD2. This discovery provides a new potential approach for treating iron disturbances in chronic diseases.