Loss of α-hemoglobin–stabilizing protein impairs erythropoiesis and exacerbates β-thalassemia
Yi Kong, … , Andrew J. Gow, Mitchell J. Weiss
Yi Kong, … , Andrew J. Gow, Mitchell J. Weiss
Published November 15, 2004
Citation Information: J Clin Invest. 2004;114(10):1457-1466. https://doi.org/10.1172/JCI21982.
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Loss of α-hemoglobin–stabilizing protein impairs erythropoiesis and exacerbates β-thalassemia

Abstract

Hemoglobin (Hb) A production during red blood cell development is coordinated to minimize the deleterious effects of free α- and β-Hb subunits, which are unstable and cytotoxic. The α-Hb–stabilizing protein (AHSP) is an erythroid protein that specifically binds α-Hb and prevents its precipitation in vitro, which suggests that it may function to limit free α-Hb toxicities in vivo. We investigated this possibility through gene ablation and biochemical studies. AHSP–/– erythrocytes contained hemoglobin precipitates and were short-lived. In hematopoietic tissues, erythroid precursors were elevated in number but exhibited increased apoptosis. Consistent with unstable α-Hb, AHSP–/– erythrocytes contained increased ROS and evidence of oxidative damage. Moreover, purified recombinant AHSP inhibited ROS production by α-Hb in solution. Finally, loss of AHSP worsened the phenotype of β-thalassemia, a common inherited anemia characterized by excess free α-Hb. Together, the data support a model in which AHSP binds α-Hb transiently to stabilize its conformation and render it biochemically inert prior to Hb A assembly. This function is essential for normal erythropoiesis and, to a greater extent, in β-thalassemia. Our findings raise the possibility that altered AHSP expression levels could modulate the severity of β-thalassemia in humans.

Authors

Yi Kong, Suiping Zhou, Anthony J. Kihm, Anne M. Katein, Xiang Yu, David A. Gell, Joel P. Mackay, Kazuhiko Adachi, Linda Foster-Brown, Calvert S. Louden, Andrew J. Gow, Mitchell J. Weiss

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Figure 7

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Intercrosses of β-globin+/th-3AHSP+/– double-heterozygous mice. The th-3...
Intercrosses of β-globin+/th-3AHSP+/– double-heterozygous mice. The th-3 mutant β-globin allele represents a targeted deletion of the b1 and b2 adult globin genes; heterozygous animals exhibit β-thalassemia intermedia, while the homozygous state is lethal in utero. (A) Mating strategy. The β-globin and AHSP genes are physically linked on mouse chromosome 7. Double-heterozygous mice used were the F1 progeny of intercrosses of simple AHSP+/– heterozygotes and β-globin+/th-3 heterozygotes, ensuring that the two mutant alleles were on separate chromosomes (trans configuration). The genotype frequencies of live-born offspring resulting from F1 intercrosses are described in Table 2. +, wild-type allele; –, deleted allele. (B) Hematocrits of β-globin–AHSP compound mutant embryos, with genotypes shown below the x axis. For comparison, embryos are grouped according to the presence or absence of thalassemia (β-globin+/th-3 genotype); thalassemic embryos are subdivided into AHSP-null versus AHSP–wild-type or -heterozygous states. Asterisk denotes either + or – alleles for AHSP. Each symbol represents one embryo analyzed: triangles, β-globin+/+ embryos; circles, β-globin+/th-3 with at least one wild-type AHSP allele; diamonds, β-globin+/th-3AHSP–/–. Color coding is used to specify the AHSP genotype within each group: black, +/+; white, +/–; red, –/–. (C) Blood smears of β-globin+/th-3 embryos with +/+ or –/– AHSP genotypes. Most of the erythrocytes are anucleate definitive (fetal liver derived). Nucleated cells: EP, primitive (yolk sac derived); ED, definitive. Among thalassemic embryos, those lacking AHSP exhibited more prominent eosinophilic erythrocyte inclusions (examples marked by double asterisks) and increased circulating ED cells. Original magnification, ×100.