[Show abstract][Hide abstract] ABSTRACT: Excess free alpha-globin is cytotoxic and contributes to the pathophysiology of b-thalassemia. Alpha hemoglobin stabilizing protein (AHSP) is a molecular chaperone that binds free alpha-globin to promote its folding and inhibit its ability to produce damaging reactive oxygen species. Reduced AHSP levels correlate with increased severity of b-thalassemia in some human cohorts, but causal mechanistic relationships are not established for these associations. We used transgenic and lentiviral gene transfer methods to investigate whether supraphysiologic AHSP levels could mitigate the severity of b-thalassemia intermedia by providing an increased sink for the excess pool of alpha-globin chains. We tested wild-type AHSP and two mutant versions with amino acid substitutions that confer 3- or 13-fold higher affinity for alpha-globin. Erythroid overexpression of these AHSP proteins up to 11-fold beyond endogenous levels had no major effects on hematologic parameters in b-thalassemic animals. Our results demonstrate that endogenous AHSP is not limiting for a-globin detoxification in a murine model of b-thalassemia.
Preview · Article · Oct 2010 · American Journal of Hematology
[Show abstract][Hide abstract] ABSTRACT: Alpha-hemoglobin stabilizing protein (AHSP) is a potential modifier of beta-thalassemia by virtue of its ability to detoxify excess free alpha-globin. However, examination of patients with beta-thalassemia from a few geographic regions failed to identify obvious AHSP mutations. We extended these studies by analyzing AHSP gene sequences in 366 anonymous individuals from five different areas of the world. We detected numerous polymorphisms comprising 18 different haplotypes and two rare missense mutations. Two sequence variations produce functional effects in laboratory assays. First, a rare missense mutation in a Brazilian/Mediterranean cohort converts asparagine to isoleucine at position 75 of AHSP protein and impairs its ability to inhibit reactive oxygen species production by alpha-hemoglobin. Second, a high-frequency polymorphism in intron 1 of the AHSP gene (12391 G>A) alters an Oct-1 transcription factor binding site previously shown to be important for optimal gene expression. The 12391A polymorphism impairs Oct-1 binding and inhibits the ability of AHSP regulatory sequences to activate expression of a linked luciferase reporter. Although structural mutations predicted to alter AHSP protein function or ablate its activity are rare, the 12391 G>A SNP is common and represents a potential mechanism through which genetically determined variations in AHSP expression could influence beta-thalassemia.
Full-text · Article · Feb 2008 · American Journal of Hematology