The Role of Alpha Hemoglobin Stabilizing Protein in Human Beta Thalassemia

Summary

Principal Investigator: Mitchell Weiss
Abstract: 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.
Funding Period: ----------------2007 - ---------------2010-
more information: NIH RePORT

Top Publications

  1. ncbi Population analysis of the alpha hemoglobin stabilizing protein (AHSP) gene identifies sequence variants that alter expression and function
    Camila O Dos Santos
    The Children s Hospital of Philadelphia, Division of Hematology, Philadelphia, Pennsylvania 19104, USA
    Am J Hematol 83:103-8. 2008
  2. pmc α-Hemoglobin-stabilizing protein is a sensitive and specific marker of erythroid precursors
    Philipp W Raess
    Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
    Am J Surg Pathol 36:1538-47. 2012
  3. pmc Hemoglobin variants: biochemical properties and clinical correlates
    Christopher S Thom
    Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
    Cold Spring Harb Perspect Med 3:a011858. 2013
  4. pmc An iron responsive element-like stem-loop regulates alpha-hemoglobin-stabilizing protein mRNA
    Camila O Dos Santos
    Division of Hematology, Children s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA
    J Biol Chem 283:26956-64. 2008
  5. pmc Protein quality control during erythropoiesis and hemoglobin synthesis
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, The Combined Degree Program, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
    Hematol Oncol Clin North Am 24:1071-88. 2010
  6. pmc A hemoglobin variant associated with neonatal cyanosis and anemia
    Moira A Crowley
    Division of Neonatology, Case Western Reserve University, Cleveland, USA
    N Engl J Med 364:1837-43. 2011
  7. pmc Analysis of human alpha globin gene mutations that impair binding to the alpha hemoglobin stabilizing protein
    Xiang Yu
    Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, PA, USA
    Blood 113:5961-9. 2009
  8. pmc Kinetics of α-globin binding to α-hemoglobin stabilizing protein (AHSP) indicate preferential stabilization of hemichrome folding intermediate
    Todd L Mollan
    Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251, USA
    J Biol Chem 287:11338-50. 2012
  9. pmc Integrated protein quality-control pathways regulate free α-globin in murine β-thalassemia
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
    Blood 119:5265-75. 2012
  10. pmc Insights into hemoglobin assembly through in vivo mutagenesis of α-hemoglobin stabilizing protein
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
    J Biol Chem 287:11325-37. 2012

Detail Information

Publications10

  1. ncbi Population analysis of the alpha hemoglobin stabilizing protein (AHSP) gene identifies sequence variants that alter expression and function
    Camila O Dos Santos
    The Children s Hospital of Philadelphia, Division of Hematology, Philadelphia, Pennsylvania 19104, USA
    Am J Hematol 83:103-8. 2008
    ....
  2. pmc α-Hemoglobin-stabilizing protein is a sensitive and specific marker of erythroid precursors
    Philipp W Raess
    Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
    Am J Surg Pathol 36:1538-47. 2012
    ..In contrast, CD235a staining was erythroid-specific but stained non-nucleated red blood cells in all specimens, limiting its utility. We conclude that AHSP is superior to CD71 and CD235a for detecting normal and neoplastic nucleated EPs...
  3. pmc Hemoglobin variants: biochemical properties and clinical correlates
    Christopher S Thom
    Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
    Cold Spring Harb Perspect Med 3:a011858. 2013
    ..Here we review the major classes of hemoglobin variants, emphasizing general concepts and illustrative examples...
  4. pmc An iron responsive element-like stem-loop regulates alpha-hemoglobin-stabilizing protein mRNA
    Camila O Dos Santos
    Division of Hematology, Children s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA
    J Biol Chem 283:26956-64. 2008
    ..In addition, we illustrate a new mechanism through which hemoglobin may be modulated according to iron status...
  5. pmc Protein quality control during erythropoiesis and hemoglobin synthesis
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, The Combined Degree Program, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
    Hematol Oncol Clin North Am 24:1071-88. 2010
    ..Information gained from studies of nonerythroid protein aggregation disorders may be exploited to further understand and perhaps treat β-thalassemia...
  6. pmc A hemoglobin variant associated with neonatal cyanosis and anemia
    Moira A Crowley
    Division of Neonatology, Case Western Reserve University, Cleveland, USA
    N Engl J Med 364:1837-43. 2011
    ..The presence of this polar amino acid in the heme pocket is predicted to enhance hemoglobin denaturation, causing anemia...
  7. pmc Analysis of human alpha globin gene mutations that impair binding to the alpha hemoglobin stabilizing protein
    Xiang Yu
    Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, PA, USA
    Blood 113:5961-9. 2009
    ..Our results better define the biochemical properties of some alpha globin variants and support the hypothesis that AHSP promotes alpha globin chain stability during human erythropoiesis...
  8. pmc Kinetics of α-globin binding to α-hemoglobin stabilizing protein (AHSP) indicate preferential stabilization of hemichrome folding intermediate
    Todd L Mollan
    Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251, USA
    J Biol Chem 287:11338-50. 2012
    ..Reduction of AHSP-bound met-α allows more rapid release to β subunits to form stable fully, reduced hemoglobin dimers and tetramers...
  9. pmc Integrated protein quality-control pathways regulate free α-globin in murine β-thalassemia
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
    Blood 119:5265-75. 2012
    ..Our findings show that multiple interregulated PQC responses degrade excess α-globin. Therefore, β-thalassemia fits into the broader framework of protein-aggregation disorders that use PQC pathways as cell-protective mechanisms...
  10. pmc Insights into hemoglobin assembly through in vivo mutagenesis of α-hemoglobin stabilizing protein
    Eugene Khandros
    Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
    J Biol Chem 287:11325-37. 2012
    ....