We are working toward a new perspective in understanding and manipulating the pathophysiology of beta thalassemia, a common and debilitating inherited anemia. A hallmark of this disorder is excessive free ? hemoglobin (Hb), an unstable protein that generates reactive oxygen species (ROS) and forms cytotoxic precipitates. We identified alpha hemoglobin stabilizing protein (AHSP), an abundant erythroid protein that enhances the solubility of free alphaHb and limits its biochemical reactivity. Ahsp-/- mice exhibit hemolytic anemia with Hb precipitates and excessive ROS. Moreover, loss of AHSP exacerbates beta thalassemia in mice, raising the possibility that altered AHSP function or expression could modulate beta thalassemia phenotypes in humans. Preliminary data support both mechanisms. First, we discovered a naturally occurring missense mutation, AHSP N75I, which impairs protein function and is associated with unexpectedly severe beta thalassemia in two pedigrees. Second, AHSP appears to be a quantitative trait locus (QTL) whose expression varies considerably between different individuals. Moreover, reduced AHSP expression associates with more severe clinical disease in several independent studies of small beta thalassemia cohorts and pedigrees. Together, these findings lead to the hypothesis that AHSP is a genetic modifier of beta thalassemia. We will test this by analyzing thalassemic populations for AHSP gene mutations, including N75I, and determining their effects on gene expression and/or protein function. In addition, we will study how variations in erythroid AHSP expression affect nascent alpha-Hb pools, oxidative stress and clinical severity in beta thalassemic patients. Our findings should provide new insights into the mechanisms of normal erythropoiesis and the pathophysiology of beta thalassemia. Ultimately, this information could provide a basis for developing novel therapeutic approaches to mitigate the toxicities of free alpha-Hb in beta thalassemia.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL087427-04
Application #
7756618
Study Section
Erythrocyte and Leukocyte Biology Study Section (ELB)
Program Officer
Goldsmith, Jonathan C
Project Start
2007-01-19
Project End
2010-12-31
Budget Start
2010-01-01
Budget End
2010-12-31
Support Year
4
Fiscal Year
2010
Total Cost
$411,250
Indirect Cost
Name
Children's Hospital of Philadelphia
Department
Type
DUNS #
073757627
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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
Crowley, Moira A; Mollan, Todd L; Abdulmalik, Osheisa Y et al. (2011) A hemoglobin variant associated with neonatal cyanosis and anemia. N Engl J Med 364:1837-43
Nasimuzzaman, Md; Khandros, Eugene; Wang, Xiaomei et al. (2010) Analysis of alpha hemoglobin stabilizing protein overexpression in murine ?-thalassemia. Am J Hematol 85:820-2
Khandros, Eugene; Weiss, Mitchell J (2010) Protein quality control during erythropoiesis and hemoglobin synthesis. Hematol Oncol Clin North Am 24:1071-88
Gell, David A; Feng, Liang; Zhou, Suiping et al. (2009) A cis-proline in alpha-hemoglobin stabilizing protein directs the structural reorganization of alpha-hemoglobin. J Biol Chem 284:29462-9

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