Our studies address a critical problem in hemoglobin (Hb) biology: how inherently unstable globin protein subunits are folded and maintained during normal and pathological erythropoiesis. We discovered alpha hemoglobin stabilizing protein (AHSP), an erythroid protein that specifically binds free alpha globin subunit, stabilizes its structure and limits its pro-oxidant activities. Our preliminary studies suggest two distinct functions for AHSP. First, to detoxify excess alpha globin that accumulates during normal erythropoiesis and in various anemias, particularly beta thalassemia. Second, to fold and stabilize newly formed alpha globin subunits en route to HbA (alpha beta) synthesis. Of potential importance to both functions, we discovered that degradation of AHSP mRNA is accelerated by iron, an essential component of HbA and determinant of nascent globin protein stability. Our overall view is that AHSP facilitates normal HbA synthesis and also buffers against imbalances that arise from genetic or environmental stresses, such as thalassemias and iron deficiency. Now we seek to better understand AHSP activities and their relevance to human health.
Aim 1 uses mouse genetics to investigate AHSP functions in vivo. We will examine the consequences of manipulated AHSP expression in thalassemias and create Ahsp gene missense mutations in mice to probe mechanisms of AHSP protein function.
Aim 2 studies the biochemical properties of AHSP. We will test in vitro if AHSP promotes reconstitution of HbA from its purified apo-globin and heme components and search for new erythroid proteins that interact with alpha globin-AHSP complexes.
Aim 3 examines the mechanisms by which iron regulates AHSP expression and the physiological implications of this pathway during altered iron homeostasis. If successful, our work will establish new basic principles of Hb biology and erythropoiesis. In addition, there are potential practical long-term benefits. For example, understanding how AHSP detoxifies excess alpha Hb should illustrate novel therapeutic approaches for human beta thalassemias. Elucidating the role of AHSP in HbA synthesis may provide tools to optimize the manufacture of recombinant Hb-based blood substitutes. Finally, defining functional interactions between iron and AHSP could provide insights into the pathophysiology and management of iron overload and deficiency states.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Erythrocyte and Leukocyte Biology Study Section (ELB)
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Bishop, Terry Rogers
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Children's Hospital of Philadelphia
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Traxler, Elizabeth A; Thom, Christopher S; Yao, Yu et al. (2018) Nonspecific inhibition of erythropoiesis by short hairpin RNAs. Blood 131:2733-2736
Sankaran, Vijay G; Weiss, Mitchell J (2015) Anemia: progress in molecular mechanisms and therapies. Nat Med 21:221-30
Thom, Christopher S; Traxler, Elizabeth A; Khandros, Eugene et al. (2014) Trim58 degrades Dynein and regulates terminal erythropoiesis. Dev Cell 30:688-700
Strader, Michael Brad; Hicks, Wayne A; Kassa, Tigist et al. (2014) Post-translational transformation of methionine to aspartate is catalyzed by heme iron and driven by peroxide: a novel subunit-specific mechanism in hemoglobin. J Biol Chem 289:22342-57
Thom, Christopher S; Dickson, Claire F; Gell, David A et al. (2013) Hemoglobin variants: biochemical properties and clinical correlates. Cold Spring Harb Perspect Med 3:a011858
Mollan, Todd L; Banerjee, Sambuddha; Wu, Gang et al. (2013) ?-Hemoglobin stabilizing protein (AHSP) markedly decreases the redox potential and reactivity of ?-subunits of human HbA with hydrogen peroxide. J Biol Chem 288:4288-98
Khandros, Eugene; Thom, Christopher S; D'Souza, Janine et al. (2012) Integrated protein quality-control pathways regulate free ?-globin in murine ?-thalassemia. Blood 119:5265-75
Mollan, Todd L; Khandros, Eugene; Weiss, Mitchell J et al. (2012) Kinetics of ?-globin binding to ?-hemoglobin stabilizing protein (AHSP) indicate preferential stabilization of hemichrome folding intermediate. J Biol Chem 287:11338-50
Raess, Philipp W; Paessler, Michelle E; Bagg, Adam et al. (2012) ?-Hemoglobin-stabilizing protein is a sensitive and specific marker of erythroid precursors. Am J Surg Pathol 36:1538-47
Khandros, Eugene; Mollan, Todd L; Yu, Xiang et al. (2012) Insights into hemoglobin assembly through in vivo mutagenesis of ?-hemoglobin stabilizing protein. J Biol Chem 287:11325-37

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