Iron overload is the main cause of mortality and morbidity in patients with hereditary hemochromatosis and beta-thalassemia. There is a need for new approaches to prevent and treat these diseases. Intestinal hyperabsorption of iron is a critical mechanism leading to tissue iron overload, and inhibiting intestinal iron absorption presents a potential target. Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors consisting of an alpha-subunit (HIF1-alpha or HIF2-alpha) and beta-subunit (aryl hydrocarbon nuclear translocator (ARNT). Using genetic mouse models and cell lines of HIF signaling, we have shown that intestinal HIF2-alpha is a critical regulator of iron absorption. More recently we demonstrate that HIF2-alpha (but not HIF1-alpha) is the central transcription factor required for regulating intestinal iron absorptive genes and is robustly increased in mouse models of hereditary hemochromatosis and beta-thalassemia. Moreover, intestine-specific HIF-alpha overexpressing mice develop spontaneous iron overload. Based on these observations, we hypothesize that intestinal HIF2-alpha-induced iron absorption is critical in the pathogenesis of iron overload and hematological disorders and presents a novel target for therapy. The long-term objectives of the proposed studies are to elucidate precise mechanisms of how HIF2-alpha regulates intestinal iron absorption as an impetus to the development of therapeutic regimens that can be used to treat hemochromatosis and beta-thalassemia. We will pursue our objectives through four interconnected Specific Aims.
Aim 1 will determine mechanisms by which intestinal HIF2-alpha is activated during iron overload and hematological disorders. This will be examined in intestinal-derived cell lines and Hfe-/-, Hbbth3/+, and Hbbth3/th3 models of hereditary hemochromatosis, beta-thalassemia intermedia, and Cooley's anemia (beta-thalassemia major), respectively.
Aim 2 will assess the molecular mechanisms of iron absorptive gene activation by HIF2-alpha. This will be examined by promoter analysis with a focus on HIF2-alpha iron absorptive target genes.
This Aim will also identify novel target genes of HIF2-alpha using genome-wide promoter binding studies in duodenal tissues from mouse models of hereditary hemochromatosis and beta-thalassemia.
Aims 3 and 4 will determine the requirement for HIF2-alpha in the progression of tissue iron overload in mouse models of hemochromatosis and beta-thalassemia. This will be examined in Hfe-/-, Hbbth3/+, and Hbbth3/th3 mouse models that contain a conditional disruption of HIF2-alpha in the intestine. Successful completion of these studies will increase our understanding of how intestinal iron absorption is regulated, and lays the foundation for pursuing new therapeutic strategies in patients with iron overload and hematological disorders.
Hemochromatosis and beta-thalassemia represent a significant public health problem and new therapies are needed for clinical management of these diseases. Tissue iron overload associated with these diseases present life-threatening complications. The goal of this work is to determine if intestinal HIF2-alpha represents a novel target to restrict iron loading in patients with hemochromatosis and beta-thalassemia.
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