Regulation of heme uptake in intestinal epithelial cells

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DESCRIPTION (provided by applicant): Project Summary: In this proposal, Dr. Aliye Uc is seeking a RO3 award to expand on her studies of intestinal heme uptake and transport mechanisms initiated under her KO8 grant, DK-63135. With the support of her KO8 funding, Dr. Uc started to examine heme-intestinal epithelial cell interactions through course work and laboratory investigations. Heme provides the majority of body's iron, but little is known about its intestinal absorption. Dr. Uc's observations so far suggest that enterocytes actively control heme uptake and transport, a phenomeon that can have an important role in the regulation of body iron stores. In the current R03 application, Dr. Uc proposes to begin investigating vesicular transport mechanisms involved in heme absorption and metabolism. Based on her preliminary data, Dr. Uc hypothesizes that heme is acquired by intestinal epithelial cells via an active and tightly regulated process that involves vesicular transport. Basolateral membrane heme uptake occurs via clathrin-dependent endocytosis; apical (lumen) heme is acquired via a membrane protein-dependent, cholesterol-sensitive, caveolar/lipid raft endocytosis. The specific aims are to: 1) Determine the vesicular transport mechanisms involved in intestinal heme uptake by using electron microscopy and cell fractionation techniques and colocalization with proteins that are trasported via clathrin or caveolae/lipid raft dependent pathways; 2) Determine the regulatory mechanisms involved in intestinal heme uptake by studying the role of a membrane heme binding protein and heme oxygenase-1. The current RO3 application, if approved will give Dr. Uc the opportunity to expand on her KO8-related goals and objectives as she approaches a full transition to an independent investigator status. The supportive environment at the University of Iowa will provide a perfect medium for Dr. Uc to accomplish her goal to become a fully independent clinician scientist. Relevance: Heme, found in red meat provides the majority of body's iron, but it can also cause injury by producing toxic free radicals. Because of its dual effects, intestinal heme absorption should be carefully regulated. However, it is not clear how intestinal epithelial cells take up heme from the diet or if they regulate its absorption. Defining intestinal heme uptake pathways will have a great impact in understanding disorders associated with iron overload (hereditary hemochromatosis, iron overload secondary to blood transfusions) and nutritional iron deficiency