Novel roles of copper in adaptive responses to hypoxia

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Copper (Cu) is an essential nutrient that plays vital roles in oxygen transport and utilization. Copper functions directly in the consumption of oxygen via oxidative phosphorylation and is required for the transport of iron which is a vital for oxygen transport within hemoglobin. Despite the importance of copper in oxygen metabolism, little is known regarding the effects of reduced oxygen levels (hypoxia) on copper homeostasis. Hypoxia is a physiological stress that contributes to the pathology of many common diseases, thus the mechanisms by which cells sense and respond to hypoxia is of fundamental importance to human health. Using an innovative CRISPR-based knockout screen for novel regulators of copper homeostasis, mutations in the von Hippel Lindau (VHL) gene were found to stimulate the expression of ATP7B, a copper transporter primarily expressed in hepatocytes. VHL is a master regulator of oxygen sensing and we demonstrate that ATP7B expression is strongly induced by hypoxia in cultured cells and in the liver of mice. ATP7B is essential for inserting copper into the ceruloplasmin, a ferroxidase with known roles in iron export into the plasma. In this proposal, we will test the hypothesis that ATP7B is required for hypoxia-induced erythropoiesis through its ability to facilitate ceruloplasmin-mediated iron export into the plasma. Mutations in the ATP7B gene are known to cause Wilson disease, a lethal disorder of hepatic copper overload. We demonstrate that hypoxia induces hepatic expression of an alternative copper transporter, ATP7A, which is a functional homologue of ATP7B. In this proposal, we will test the hypothesis that hypoxia-induced ATP7A can attenuate hepatic copper overload and liver pathology in the ATP7B-/- mouse model of Wilson disease. To increase the translational potential of our studies, the therapeutic efficacy of a clinically approved hypoxia-mimetic drug Roxadustat will also be tested in ATP7B-/- mice to address its potential for repurposing as a novel treatment for Wilson disease. Finally, based on the demonstrated success of our knockout screen, we will perform an innovative CRISPR- based gene activation screen for novel regulators of copper homeostasis. To test these hypotheses, our proposal will 1) investigate the roles of copper in adaptive responses to hypoxia; 2) test the therapeutic potential of hypoxia in animal models of Wilson disease and 3) identify novel components of mammalian copper homeostasis using an innovative gene activation screen.