Alpha Hemoglobin Stabilizing Protein Gene Research Articles

Alpha-Hemoglobin Stabilizing Protein Gene Polymorphism (rs4499252 A/G) and its Association with Beta-Thalassemia Major in Iraqi Patients.

Beta thalassemia (β-thalassemia) major is a genetic disorder of hemoglobin production that results in a diminished rate of synthesis of one or more of the globin chains causing variable degrees of anemia. Alpha-hemoglobin-stabilizing protein (AHSP) is a specific alpha-globin factor that affects the severity of the disease in patients with β-thalassemia. A recent study was conducted to investigate the polymorphism in the AHSP (rs4499252) gene and its association with β-thalassemia in Iraq. Blood samples were obtained from 90 β-thalassemia patients and 60 healthy individuals as a control group in the Wasit Center for Hereditary Anemia from August 2020 to January 2021. After DNA extraction from the whole blood, to determine the genotype of the AHSP gene, the High-Resolution Melt (HRM) Real-Time PCR was used. The results showed a significant increase (P<0.05) in genotype GG (wild type) of the SNP (rs4499252) in β-thalassemia patients, compared to the control group. On the other hand, genotype AA was significantly higher (P≤0.05) in β-thalassemia patients than in the control group, while the genotype GA showed a non-significant difference (P<0.01) between β-thalassemia patients and the healthy controls. The results also showed that the AHSP expression is a biomarker of hemoglobin H disease severity, and the A allele was more frequent in β-thalassemia patients than the G allele in Iraqi patients.

Stage Specific Expression Pattern of Alpha-Hemoglobin-Stabilizing-Protein (AHSP) Portrayed in Erythroblast Chronology.

During erythropoiesis, the molecular chaperone alpha-hemoglobin-stabilizing protein (AHSP) sequesters free alpha-hemoglobin (αHb) and prevents precipitation of excess αHb. While AHSP is linked to hereditary anemia, the pattern of expression during specific erythroblast stages is poorly understood. We investigated gene and protein expressions of AHSP throughout progressive maturation stages of erythroblasts in biphasic cultures of blood and bone marrow samples from healthy donors. Differentiating erythroblasts were periodically subjected to flow cytometry, Amnis imaging and RT-qPCR analyses. We made parallel in vivo validations from naive murine bone marrow cells. Percentages of AHSP+ erythroblasts, protein expressions and AHSP gene expressions are negligible on culture day 6 (CFU-Es) and progressively increases from culture days 8–12 (peaks on day 12) and declines on day 14. Notably, sub-cellular location of AHSP is both in the cytoplasm and nucleus in the early erythroblasts while in the late stages of maturation AHSP is found predominantly in the nucleus, being expelled with it during enucleation. As both human bone marrow and peripheral blood mononuclear cells (PBMC) derived erythroblasts demonstrated similar expression patterns, sampling of erythroblasts from day 11 cultures could portray erythroblast chronology and provide optimum representative stage specific expression patterns. PBMCs may be suitable for comparison studies of AHSP expression in pathologic erythropoiesi

Alpha-hemoglobin-stabilizing protein (AHSP): a modulatory factor in β-thalassemia.

Hemoglobin (Hb) is an iron-containing metalloprotein that transports oxygen molecules from the lungs to the rest of the human body. Among the different variants of Hb, HbA1 is the most common and is composed of two alpha (αHb) and two beta globin chains (βHb) constructing a heterotetrameric protein complex (α2β2). Due to the higher number of AHSP genes, there is a tendency to produce approximately twice as much of α subunit as β subunit. Therefore, there is a chance of presenting excess α subunit leftover in human blood plasma; excess subunits subsequently bind with each other and aggregates β-thalassemia occurs due to lack of or reduced numbers of βHb subunit. Alpha-hemoglobin-stabilizing protein (AHSP) is a scavenger protein which acts as a molecular chaperon by reversibly binding with free αHb forming a complex (AHSP-αHb) that prevents aggregation and precipitation preventing deleterious effects towards developing serious human diseases including β-thalassemia. Clinical severity worsens if mutations in AHSP gene co-occur in patients with β-thalassemia. Considering the mechanism of action of AHSP and its contribution to ameliorating β-thalassemia severity, it could potentially be used as a modulatory agent in the treatment of β-thalassemia.

Association of alpha hemoglobin-stabilizing protein (AHSP) gene mutation and disease severity among HbE-beta thalassemia patients.

In this study, we aimed to investigate the pattern and association of genetic mutations occurring within the alpha hemoglobin-stabilizing protein (AHSP) gene among HbE beta thalassemia patients with varying phenotypic expressions. Fifty-four diagnosed cases of HbE beta thalassemia (transfusion dependent and independent) were included in the study. Among them, 38 patients with similar genotypes (IVS 1-5, alpha gene deletion and triplication, Xmn polymorphism) were selected for further analysis. AHSP gene sequencing was done for these 38 samples to study associated mutations in AHSP gene. HbE beta thalassemia patients with similar genotypes but different phenotypic expressions were found to have mutations in the AHSP gene. There were five mutations found most prevalent among the samples analyzed for AHSP gene sequencing. Among these, two mutations were from intron 1 region of AHSP and three mutations were found in exon 3. The most prevalent mutation was found at the Oct binding site at intron 1 of AHSP. The mutations in exon 3 were more prevalent among the TDT groups. A mutation in exon 3 changing the amino acid (33rd) from serine to phenylalanine was found to be associated with only TDT group. This study documents that among the HbE beta thalassemia patients with varying severity, an exon mutation in AHSP is significantly prevalent only among the TDT group. Further understanding of the mechanism will shed light upon the impact of AHSP in modifying the disease severity in thalassemia.

Role of Alpha Hemoglobin Stabilizing Protein Expression in Beta Thalassemia Patients

AbstractBackground: Beta (b)-Thalassemia is an autosomal reces-sive inherited disease causing variable degrees of anemia. The molecular defects are owing to point mutations or small deletions leading to diminution or absence of b-globin chain synthesis. The unmatched a-Hb is destructive to itself and other cellular components, resulting in ineffective erythropoi-esis and hemolysis. Alpha-Hemoglobin Stabilizing Protein (AHSP) is a scavenger protein of erythroid that fastly and reversibly attach the a subunit of hemoglobin molecule preventing its precipitation and subsequent hemolysis.Aim of Work: Is to assess AHSP gene expression in thalassemia major and intermedia and its relation to clinical features, laboratory investigations and to determine its role on the severity of thalassemia.Subjects and Methods: This case-control study is consisted of 120 studied subjects categorized into 40 thalassemia major patients, 40 thalassemia intermedia patients and 40 age healthy individuals as a control group. All subjects underwent the following; history, clinical picture, complete blood picture and Hb electrophoresis, serum ferritin and measurement of AHSP, alpha globin and beta globin genes expression by real time PCR.Results: AHSP gene in thal. intermedia group was higher than both thal. major (p<0.001). Beside thal. intermedia group had higher a globin/AHSP ratio versus thal. major group (p=0.011). b globin/AHSP ratio was not significant between both thal. groups. AHSP in thal.major group correlated with a globin and b globin expression and negatively correlated with organomegally, ferritin and no. of blood transfusion. Whereas in thal. intermedia group, was positively correlated with Hb, HCT, MCV, MCH, a globin gene expression, b globin gene expression and b globin/a globin genes ratio.Conclusion: AHSP expression was higher in thalassemia intermedia group than thalassemia major group. Consequently, AHSP can be considered genetic modifier in b thalassemia.

The effect of histone deacetylase inhibitors on AHSP expression.

Alpha-hemoglobin stabilizing protein (AHSP) is a molecular chaperone that can reduce the damage caused by excess free α-globin to erythroid cells in patients with impaired β-globin chain synthesis. We assessed the effect of sodium phenylbutyrate and sodium valproate, two histone deacetylase inhibitors (HDIs) that are being studied for the treatment of hemoglobinopathies, on the expression of AHSP, BCL11A (all isoforms), γ-globin genes (HBG1/2), and some related transcription factors including GATA1, NFE2, EKLF, KLF4, and STAT3. For this purpose, the K562 cell line was cultured for 2, 4, and 6 days in the presence and absence of sodium phenylbutyrate and sodium valproate. Relative real-time qRT-PCR analysis of mRNA levels was performed to determine the effects of the two compounds on gene expression. Expression of all target mRNAs increased significantly (p < 0.05), except for the expression of BCL11A, which was down-regulated (p < 0.05) in the cells treated with both compounds relative to the levels measured for untreated cells. The findings indicated that sodium valproate had a more considerable effect than sodium phenylbutyrate (p < 0.0005) on BCL11A repression and the up-regulation of other studied genes. γ-Globin and AHSP gene expression continuously increased during the culture period in the treated cells, with the highest gene expression observed for 1 mM sodium valproate after 6 days. Both compounds repressed the expression of BCL11A (-XL, -L, -S) and up-regulated GATA1, NFE2, EKLF, KLF4, STAT3, AHSP, and γ-globin genes expression. Moreover, sodium valproate showed a stronger effect on repressing BCL11A and escalating the expression of other target genes. The findings of this in vitro experiment could be considered in selecting drugs for clinical use in patients with β-hemoglobinopathies.

Alpha hemoglobin stabilizing protein: Its causal relationship with the severity of beta thalassemia.

Thalassemia major is characterized by anemia, iron overload and cellular damage. The severity of symptoms correlates with the alpha/non-alpha globin imbalance and is proportional to the magnitude of alpha chain excess. Alpha hemoglobin stabilizing protein (AHSP), the erythroid specific alpha globin chaperone, stabilizes free alpha chains, and prevents the formation of reactive oxygen radicals. Though AHSP expression has been linked to the severity of beta thalassemia, its role as a probable genetic modifier of disease severity, has still not been unequivocally established. In the present study, the level of the chaperone has been seen to vary in regularly transfused beta thalassemia patients, being underexpressed in 64% of cases, upregulated in 16% and comparable to controls in 20% of the cases. This discrepancy may be attributed to the degree of DNA damage, % HbF, and the number of nucleated RBCs in the peripheral blood of these patients. Results reveal that a decrease in the free alpha chain pool, and hence the repertoire of unbound iron, due to elevated HbF and/or the presence of nucleated RBCs in the peripheral blood results in the upregulation of the AHSP gene.

Application of denaturing high performance liquid chromatography for detection of α-hemoglobin-stabilizing protein gene

An assay method for alpha-hemoglobin-stabilizing protein (AHSP) gene was established based on denaturing high performance liquid chromatography (DHPLC). The AHSP gene sequences are divided into six fragments. Because of one or two common single nucleotide polymorphism (SNPs) in the first, second, fourth and sixth fragments, all samples should be analyzed individually when the fragments were detected. The third and fifth fragments were detected by DHPLC technique combined with DNA pooling for no common SNP in the fragments. The six common SNPs in AHSP gene can be genotyped accurately by the established method. After analyzing AHSP gene of 40 samples by DHPLC detection and gene sequencing, it was found that the results of the two methods were completely consistent. After AHSP gene of 365 samples being analyzed by DHPLC, two rare SNPs (11,810 G > A and 12,802 C > T)were found. Two missense mutations (AHSP D29V and AHSP V56G) were also found. AHSP D29V mutation is a novel mutation. AHSP V56G is a rare mutation. It demonstrated that this method is suitable for the detection of alpha-hemoglobin-stabilizing protein gene.

Population analysis of the alpha hemoglobin stabilizing protein (AHSP) gene identifies sequence variants that alter expression and function

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.

Alpha Hemoglobin Stabilizing Protein (AHSP) Optimizes Hemoglobin A Synthesis by Maintaining a Pool of Viable Alpha Globin Subunits.

AHSP binds alpha hemoglobin (Hb) to maintain its structure and limit its prooxidant activities. In addition, AHSP binds and stabilizes apo-alpha globin, which lacks heme. Previously, we demonstrated that Ahsp−/− mice exhibit hemolytic anemia with Hb precipitation in erythroid cells. Through interbreeding of mutant strains, we also showed that loss of AHSP exacerbates beta thalassemia. Together, these studies indicate that AHSP participates in Hb homeostasis and may act to neutralize potentially toxic excess alpha globin that is known to accumulate in normal erythroid precursors, and to a greater extent, in beta thalassemic ones. However, additional functions for AHSP may exist. In particular, AHSP-alpha globin complexes may also promote HbA synthesis. To test this, we depleted the pool of excess alpha globin in Ahsp−/− mice by interbreeding with alpha thalassemic ones. Compared to mice with either mutation alone, compound mutants missing both AHSP and one alpha globin allele (genotype Ahsp−/− //alpha globin*α/αα) exhibited more severe erythroid defects, including worsened anemia, hypochromia, Hb instability and ineffective erythropoiesis. Pulse-labeling of double-mutant reticulocytes showed that alpha to beta globin synthetic ratios were unaffected by loss of AHSP, but precipitation of both alpha and beta nascent chains into cell membranes was strongly enhanced. These data indicate that AHSP is important for erythropoiesis and Hb production even when alpha globin is not produced in excess. In vitro translation studies using wheat germ extracts showed that recombinant AHSP present during the synthesis of alpha globin improved its ability to become incorporated into HbA. Moreover, AHSP conferred protease resistance to nascent alpha globin, suggesting enhanced folding into the native state. Further supporting this interpretation, circular dichroism studies showed that AHSP accelerated refolding of purified denatured alpha Hb. Finally, through pulse labeling of reticulocytes followed by isoelectric focusing of soluble cytosolic fractions, we identified transient pools of free alpha Hb and AHSP-alpha Hb in vivo and showed that Ahsp gene ablation fully depleted both pools. Together, our studies indicate that AHSP acts as a molecular chaperone to promote alpha globin folding and stability prior to its incorporation into HbA. In addition, it is possible that alterations in AHSP gene function or expression could modulate alpha thalassemia severity in patients.

AHSP (Alpha Hemoglobin Stabilizing Protein) Gene Expression during Normal and β-Thalassemic Erythroid Differentiation.

β-thalassemia severity is stricktly related to the amount of free a-chains depending at least in part from different b-thalassemic genotype (β0 /β0, β0/β+, β+ /β+). Recently a new erythroid-specific protein, named AHSP (Alpha Hemoglobin Stabilizing Protein), able to form a stable complex with free α-hemoglobin, has been identified. This protein probably acts as a molecular chaperone to prevent the harmful aggregation and precipitation of α-globin that occurs during normal erythropoiesis and to a greater extent in different β-thalassemias. The aim of this study was to evaluate if the AHSP expression in erythroid cells depends on free α-chains amount. In order to verify this hypothesis, we studied the relative expression of AHSP and globin genes during differentiation of erythroid progenitors derived from peripheral blood of both normal subjects and β-thalassemic patients with different genotypes. Erythroid cultures were set up accordingly to the two phases liquid colture method described by Fibach. Total cytoplasmatic mRNA was extracted by the method of Chomczynsky-Sacchi and quantitative real-time PCR was performed using SYBRGreen to evaluate AHSP, α, β and γ globin genes expression. To quantify gene expression a mathematical model using calibration data (2-ΔΔct) was used and quantification of the house-keeping gene S14 was the internal control. In normal subjects AHSP expression was first detected at proerythroblast stage (on day 3 of culture), peaked at orthocromatic stage (on day 9) and declined to low levels by polychromatophilic-reticulocytes stage (day 13) (a decrease of 65% vs day 9 expression). Globin genes expression reached a steady state (a/non-a ratio value of 0.78 very near to a clinical equilibrium) on day 13. In this situation few free α-globin are detectable explaning the lower need of AHSP expression. In β-thalassemic subjects we observed a persistance of globin gene unbalance with an excess of free α-chains also in the advanced differentiation steps: interestingly the worst was the genotype, the highest was the globin ratio and higher was AHSP expression. In β+/β+ thalassemic patients AHSP expression declined on day 13 (a decrease of 15% vs day 9 expression) and globin gene ratio was 2.4, expression of a persistance of free α-chains excess. In β0 /β+ patients globin gene ratio on day 13 was 2.8 and AHSP expression increased of 2.5 times. Finally in β0/β0 patients globin gene ratio was very high with values up to 9–10; AHSP expression profiles instead were different between different subiects and related not only to globin unbalance but also to ineffective erythropoiesis rate and γ-globin chains persistance. All these findings underline an evident relation between AHSP and globin genes expression, suggesting a probable function of this protein during erythropoiesis.

AHSP Promoter Homopolymer in Beta-Thalassemia Syndromes.

Alpha hemoglobin stabilizing protein (AHSP) is an erythroid protein that binds specifically to the alpha globin chains to form a stable complex, preventing their precipitation before the assembly of the hemoglobin tetramere. Studies have shown thatAHSP is required for normal erythropoiesis,knock-out mice has a phenotype similar to beta thalassemia,loss of AHSP worsens the severity of the disease in thalassemic mice.Therefore, altered AHSP expression or function could account for some of the variability in beta-thalassemia phenotype. At position -160bp upstream of exon 1 of the AHSP gene, two main homopolymers (T18 and T15) have been reported that may influence the AHSP expression and hence the hematological phenotype. In particular the frequence of the shorter T15 homopolymer, which is associated with a lower AHSP expression, was much higher than expected (on the basis of the allele frequency in the healthy population) in a group of 9 patients with thalassemia intermedia, due the compound heterozygosity for beta-thalassemia and the triple alpha globin gene (Mei et al, 2006). We have studied the frequency of T15 and T18 homolpolymers in a group of 20 normal subjects and in patients with different thalassemia syndromes, i.e. beta zero 39 homozygotes with thalassemia major (14 patients) and intermedia (19), compound heterozygotes for beta-thalassemia and triple alpha globin gene (13) and simple carriers for beta thalassemia with thalassemia intermedia phenotype (5). We found the following genotype distribution reported in figure1. There is no difference in the frequency of the genotypes among the groups, except in the severe beta-thalassemia carriers, where the short T15 homopolymer is more common. These findings are consistent with the reduced AHSP expression previously reported in the reticulocytes and in the erythroid cultures of these unusually severe beta thalassemia carriers. (Galanello et al, abs 1881. ASH 2003). Therefore, only in the peculiar group of beta-thalassemia carriers with the clinical features of thalassemia intermedia, the AHSP genotype appears to be a relevant contributory factor in the hematological phenotype. [Display omitted]

Genomic Organization, Chromatin Structure, and Transcriptional Regulation of the Murine Alpha Hemoglobin Stabilizing Protein (AHSP) Gene.

Alpha Hemoglobin Stabilizing Protein (AHSP, Eraf) is an abundant erythroid protein that binds and stabilizes alpha globin and alpha hemoglobin (Hb). In mice, loss of AHSP causes hemolytic anemia, with elevated levels of reactive oxygen species and Hb precipitation in erythrocytes. Loss of AHSP exacerbates beta thalassemia phenotypes in mice, presumably by enhancing the toxicity of excessive free alpha Hb. Based on these findings, AHSP is a candidate modifier gene for beta thalassemia in humans. No mutations in the AHSP coding region have been identified in patients to date. However, several groups reported an inverse correlation between beta thalassemia severity and erythroid AHSP expression levels, raising the possibility that AHSP is a quantitative trait modifier of beta thalassemia. To address this possibility, it is important to define the mechanisms that control expression of the AHSP gene. Transcripts of murine Ahsp are inducible by GATA-1. The goals of the current studies are to investigate the mechanisms of this induction and to define the DNA domain that regulates the locus. Using phylogenetic comparisons, we identified a hotspot for mammalian chromosomal rearrangement just downstream of the Ahsp gene. This hotspot is located at the end of a syntenic block of approximately 350 kb that is conserved in mammals and likely marks the 3′ end of the gene regulatory domain. We focused our initial functional studies on a 7 kb genomic region bounded at the 5′ (centromeric) end of Ahsp by the nearest adjacent gene, an EST expressed in multiple tissues, and at the 3′ (telomeric) end by the rearrangement hotspot. In transient transfection assays, the Ahsp promoter region conferred erythroid-specific expression to a linked reporter gene. In heterologous cells, GATA-1 transactivated the Ahsp promoter in a dose-dependent fashion. To examine GATA-1 binding and its subsequent effects on the Ahsp gene in vivo, we used G1E-ER4 cells, a GATA-1 null erythroblast line that undergoes terminal erythroid maturation after activation of an estradiol-inducible form of GATA-1. We made several findings with regards to the role of GATA-1 in Ahsp gene regulation. First, GATA-1 and its cofactor, Friend of GATA-1 (FOG-1), bind directly to the Ahsp locus at regions that contain conserved GATA consensus motifs and are predicted to be important erythroid regulatory elements by our bioinformatic studies. Second, GATA-1 induces epigenetic changes in chromatin structure that are associated with gene activation, including formation of a DNase I hypersensitive site, hyperacetylation of histones H3 and H4, and methylation of histone H3 lysine-4. Together, these findings begin to establish the DNA region and mechanisms that control Ahsp transcription, allowing for further studies to map the cis elements responsible for population variations in gene expression.

A Natural Variant Sequence in the AHSP Gene May Impact Severity of Beta-Thalassemia.

Alpha-hemoglobin stabilizing protein (AHSP) is an erythroid-specific molecular chaperone that binds the alpha chains of hemoglobin, preventing their precipitation and deleterious effects. Loss of AHSP exacerbates alpha globin precipitation and anemia in a murine model for beta thalassemia. In vitro, recombinant AHSP inhibits the production of reactive oxygen species (ROS) by alpha hemoglobin. To further define the role of AHSP as a modifier of beta-thalassemia, we analyzed AHSP sequences for mutations in a large population of beta-thalassemic and control subjects. A single nucleotide change, from A to T at position 12888 (Genebank accession number AC106.730.2) in the third exon of the AHSP gene was identified, converting asparagine 75 to leucine (N75I). We detected a patient who was heterozygous for both beta-thalassemia (b39/bA) and the AHSP-N75I mutation. She presented with an unusually severe anemia that required regular blood transfusion. The father is hematologically normal, without any thalassemia mutation and heterozygous for AHSP-N751. The mother is heterozygous for the beta 39 mutation with classical mild hypochromic microcytic anemia and no mutation in the AHSP gene. Of 282 unrelated control subjects tested, one (0.35%) contained the N75I mutation. Analysis of red blood cells from this subject revealed normal hemoglobin indices but a small number of Heinz bodies, suggesting hemoglobin precipitation. This finding is similar to what we observed previously in mice that are heterozygous for an AHSP null allele. To investigate how the N75I mutation affects AHSP function, we studied the biochemical properties of the recombinant mutant protein. Surface plasmon resonance showed that the binding affinity of AHSP N75I for alpha hemoglobin is normal. Importantly, compared to wild type AHSP, the N75I mutant protein exhibited significantly reduced capacity to inhibit ROS production by alpha hemoglobin. Hence, AHSP N75I may be less effective at conferring protection from oxidative-mediated damage by free alpha hemoglobin in erythrocytes. These effects, when coupled with beta thalassemia, could result in more severe anemia, implicating AHSP N75I as a potential genetic modifier.

AHSP Is a Quantitative Trait Gene That Modifies the Phenotype of β Thalassemia.

Alpha hemoglobin stabilizing protein (AHSP) was identified in a screen for genes that are activated by the erythroid transcription factor, GATA-1. Studies have shown that:AHSP binds specifically to the α chain of hemoglobin (Hb) but not to β Hb or Hb A;AHSP knock-out mice demonstrated pathological features similar to β thalassemia; andloss of AHSP exacerbates severity of disease in β thalassemia mice.The evidence suggests that AHSP acts as a chaperone for free α Hb and that altered AHSP expression levels could modify the severity of β thalassemia in humans.To assess variation of AHSP expression, mRNA levels were measured in peripheral blood reticulocytes of 103 healthy individuals by quantitative real-time RT-PCR. The sample was approximately 90% (91/103) female with an average age of 52 years (SD=0.14, min=18, max=76). AHSP expression relative to GAPDH, varied up to 3-fold, and did not correlate with age or sex. A systematic survey of the genomic region encompassing the AHSP locus revealed 8 sequence variants of which six were common - five single nucleotide polymorphisms (SNPs), and one homopolymer (Tn) at position 160 bp upstream of exon 1. Four variants (c.-69–237A, c.-69–160 T18, c.-4–27G, and c. 337T) showed strong association with AHSP expression and had nearly equal frequencies. The four variants are in near complete linkage disequilibrium with the minor alleles in coupling. The haplotype consisting of the four minor alleles termed clade B, was associated with relatively lower expression of AHSP. Relative expression of AHSP and AHSP/α globin ratio were both significantly higher (p<0.001) in homozygotes for clade A haplotypes compared to heterozygotes. A potential functional role of one of the variable sites, a T-homopolymer (the T18 variant being part of clade A) in the promoter was investigated in-vitro using luciferase reporter assays in K562 cells. Luciferase activity was 1.30±0.08 times higher in the T18 promoter compared to T14, consistent with genetic studies. We investigated if a shorter homopolymer could have an adverse effect on β thalassemia. Nine patients with thalassemia intermedia and a genotypic combination of heterozygous β thalassemia and 5 α globin genes (aaa/aa) were studied. Based on the allele frequencies in the healthy population, 6–7 of the 9 patients are expected to be homozygous for T18 but only two were observed. In contrast, while 2–3 patients are expected to be heterozygous for the shorter homopolymer, 3 patients were homozygous and 4 heterozygous.In conclusion, AHSP gene expression is variable, with cis control accounting for some of its variance. The subtle altered expression might precipitate a phenotype of thalassemia intermedia in β thalassemia heterozygotes with α globin overload.

A Stem-Loop in the 3′-UTR Mediates Iron-Dependent Regulation of Alpha Hemoglobin Stabilizing Protein mRNA Stability.

Alpha-hemoglobin stabilizing protein (AHSP) acts as a molecular chaperone that binds and stabilizes alpha globin, minimizing the formation of cytotoxic alpha-globin precipitates in red blood cells. It has been proposed that variations in AHSP protein levels could influence disease severity in patients with beta-thalassemia. A number of genomic sequences that could be involved with AHSP transcriptional regulation have been studied. Multiple consensus GATA-1 binding motifs and a single CACCC-binding site have been identified and characterized. In vivo studies demonstrated that AHSP gene transcription is dependent on both EKLF and GATA-1 transcription factors. Here, we identify an IRE (iron response-like element) in the AHSP 3′ untranslated region that is predicted to regulate mRNA stability. IREs are regulatory elements that encode a phylogenetically defined sequence-structure motif that provide a specific recognization site for the IRE-binding proteins (IRE-BP1 or IRE-BP2). Iron starvation of cells induces high affinity binding of cytoplasmic IRE-BP to an IRE, which has at least two distinct known biological consequences. IRE in the 5′-UTR of an mRNA provides for iron-dependent regulation of translation, whereas an IRE in the 3′-UTR confers iron-dependent regulation of mRNA stability. Computer modeling identified a potential IRE stem-loop structure near the 3′-end of murine and human AHSP mRNAs. In vitro binding studies indicate that this structure recognizes an IRE-BP. Moreover, the affinity of this interaction was reduced by mutations that disrupt base pairing within the stem-loop. Iron supplementation, which is predicted to decrease IRE-BP affinity for the IRE, destabilizes AHSP in human and mouse erythroleukemia cells. These results indicate that AHSP expression is regulated by RNA stability in an iron-dependent fashion. Our findings have implications for the control of AHSP expression in beta-thalassemia.

GATA-1 and Oct-1 Are Required for Expression of the Human α-Hemoglobin-stabilizing Protein Gene

Alpha-hemoglobin-stabilizing protein (AHSP) is an erythroid protein that binds and stabilizes alpha-hemoglobin during normal erythropoiesis and in pathological states of alpha-hemoglobin excess. AHSP has been proposed as a candidate gene in some Heinz body hemolytic anemias and as a modifier gene in the beta-thalassemia syndromes. To gain additional insight into the molecular mechanisms controlling the erythroid-specific expression of the AHSP gene and provide the necessary tools for further genetic studies of these disorders, we have initiated identification and characterization of the regulatory elements controlling the human AHSP gene. We mapped the 5'-end of the AHSP erythroid cDNA and cloned the 5'-flanking genomic DNA containing the putative AHSP gene promoter. In vitro studies using transfection of promoter/reporter plasmids in human tissue culture cell lines, DNase I footprinting analyses and gel mobility shift assays, identified an AHSP gene erythroid promoter with functionally important binding sites for GATA-1- and Oct-1-related proteins. In transgenic mice, a reporter gene directed by a minimal human AHSP promoter was expressed in bone marrow, spleen, and reticulocytes, but not in nonerythroid tissues. In vivo studies using chromatin immunoprecipitation assays demonstrated hyperacetylation of the promoter region and occupancy by GATA-1. The AHSP promoter is an excellent candidate region for mutations associated with decreased AHSP gene expression.

Chromatin Remodeling of the Mouse AHSP Gene Requires EKLF.

Alpha-Hemoglobin Stabilizing Protein (AHSP) is an erythroid-specific protein that binds to α-globin, preventing precipitation of α-hemoglobin tetramers. Our interest has focused on how the AHSP gene is specifically expressed in erythroid cells, and we have investigated the roles of cis acting DNA sequences, the transcription factor EKLF and chromatin structure on AHSP gene expression. We have previously shown that the AHSP gene has a single mRNA initiation site followed by a non-coding exon. Putative promoter sequences from −904, −479 or −170 were active in luciferase reporter assays only when the constructs contained the downstream 269 bp containing exon 1 and intron 1. The −904/+269, −479/+269 and −170/+269 constructs gave 53.3+2.0 to 122.1+8.8 -fold increased levels of luciferase expression in K562 cells compared to plasmids without exon 1 and intron 1 (p<0.001; Gallagher et al., BLOOD 102, 267a, 2003). In vitro DNase I footprinting and EMSA assays revealed two regions (−75 to −67 and +153 to +164) that bound GATA-1. Analysis of 5 lines of transgenic mice with between 1 and 11 copies of the −170/+269 promoter fused to the human γ-globin gene demonstrated position independent expression (5/5 lines express) of γ-globin mRNA, at levels that were 4.6% the level of mouse α-globin mRNA per transgene copy. There was no correlation between transgene copy number and the level of γ-globin mRNA and 3/5 lines exhibited variegated expression. We concluded that sequences upstream of −170 or downstream of +269 are required for authentic expression from the AHSP promoter. To examine the role of EKLF in AHSP expression, we used subtractive hybridization, microarray and RNase protection analysis to compare AHSP mRNA levels in fetal liver cells from wild type and EKLF−/− mice. EKLF −/− fetal liver cells had 9 -fold less AHSP mRNA than wild type fetal liver cells, which we propose would exacerbate the moderate β- thalassemia described in EKLF −/− mice. Based on the observation that EKLF associates with an erythroid chromatin remodeling complex (Armstrong et al. Cell 95, 93–104, 1998), we hypothesized that EKLF was involved in chromatin remodeling at the AHSP locus. We assayed for DNase I Hypersensitive sites (HS) in chromatin from 13.5 day wild type and EKLF−/− mouse fetal liver nuclei. We demonstrated a strong DNase I HS between −200 and −400 of the AHSP gene, just upstream of the minimal −170 promoter, that was not present in chromatin from EKLF−/− fetal liver cells. To examine histone acetylation across the 3.5 kb AHSP locus we performed Chromatin Immune Precipitation analysis on wild type and EKLF −/− fetal liver chromatin using 13 different primer pairs (~300 bp intervals). In wild type chromatin there are two regions where histones H3 and H4 were hyperacetylated relative to a control region from the mouse α-globin gene promoter. The 5′ region corresponded to the DNase I HS at −400 to −200, while the second region maps 3′ to the AATAAA signal in the AHSP gene. Histones H3 and H4 were also acetylated in the interval between the hyperacetylated regions, while the chromatin upstream and downstream (~1 kb in each direction) of these regions was hypoacetylated. In contrast, all sites were hypoacetylated in chromatin from EKLF−/− fetal liver cells, correlating with the severe reduction in AHSP gene expression. We conclude that EKLF is required for remodeling the chromatin of the AHSP locus and that EKLF could be a modifier gene for the thalassemia syndromes.

Molecular Analysis of Alpha Hemoglobin Stabilizing Protein (AHSP) in Caucasian Patients with different Beta-Thalassemia Phenotypes.

Beta-thalassemia is a inherited hemoglobin disorder characterized by absent or reduced synthesis of the b globin chains. The pathophysiology and the severity of b-thalassemias reflect the degree of globin chain imbalance and the excess of free a globin chains that precipitate and cause oxidative damage in red cell precursors inducing their premature destruction in the bone marrow (ineffective erythropoiesis). Although the phenotype of b thalassemias can be modified by inherited factors such as different number of a globin genes or increased fetal hemoglobin production, other mechanisms appear to be involved. Recently, a protein, named alpha hemoglobin stabilizing protein (AHSP), that acts as a molecular chaperone specifically for free a globin chains, preventing their precipitation in red cell precursors, has been identified.To establish whether AHSP might have a role in modifying the clinical outcome of b thalassemias, we have analyzed the AHSP gene in 70 Caucasian b thalassaemic subjects: 26 patients with b°/b° genotype (Thalassaemia Major),24 patients with Thalassemia Intermedia (b°/b+ or b+/b+) and 20 patients with a Thalassaemia Intermedia phenotype but with only one mutation in the b globin gene, a normal a globin genotype and no other causes of anemia. In all the subjects, we have performed Denaturing High-Performance Liquid Chromatography (DHPLC) of the three exons and the direct genomic sequencing of coding and noncoding regions (~ 1.5 kb) of AHSP gene. No mutations able to modify the structure or function of AHSP have been found, however we identified eight single nucleotide polymorphisms (SNPs) spanned along the whole gene that segregate in four different aplotypes. To evaluate a possible relationship between a particular aplotype and b thalassemia severity, the allele frequency of each single aplotype in the tree groups has been established and compared to that of 33 Caucasian normal controls: no statistically significant association has been proved. Even though the loss of AHSP aggravates the b thalassaemia phenotype in mice, in Thalassemic Caucasian population the AHSP apparently doesn't make changes in the clinical severity of b thalassemia confirming the results recently found in Thai population.

Multiple Defects in Erythroid Gene Expression in Erythroid Krupple-Like Factor (EKLF) Target Genes in EKLF-Deficient Mice.

EKLF is the founding member of the KLF family of transcription factors. EKLF-deficient (−/−) mice die at d14-15 of gestation of severe anemia, attributed to decreased expression of the β-globin gene. Morphology of fetal-liver derived circulating erythroid cells in EKLF −/− mice does not mimic that seen in thalassemia, and mice expressing high levels of γ-globin bred onto an EKLF −/− background do not correct the anemia or rescue the −/− mice. These data suggest additional red cell defects are present in EKLF −/− mice contributing to the anemia. To address this hypothesis, we performed subtractive hybridization and microarray analyses with RNA isolated from d13.5 fetal livers of wild type (WT,+/+) and EKLF-deficient mice. In subtractive hybridization, WT (1X) was the tester population and EKLF −/− (30X) was the driver. >200 differentially expressed clones were sequenced. 122 clones were β-globin; 21 alpha hemoglobin stabilizing protein (AHSP); and the remainder were RBC membrane proteins including band 3 and β-spectrin. Microarray analyses were performed with Affymetrix GeneChip Mouse Genome 430 2.0 arrays; 3 independent EKLF +/+ and −/− RNA samples were analyzed. AHSP had the most significantly decreased expression in −/− samples, reduced to 5% of WT (p<0.0001). Other significantly down regulated genes, in addition to those identified by subtractive hybridization, included pyruvate kinase and ankyrin. Reduced expression in EKLF −/− RNA was confirmed using ribonuclease protection assay and/or real-time RT-PCR. AHSP mRNA was decreased by 75–90%; band 3 and β-spectrin were decreased by ~40%; ankyrin by 45%, and pyruvate kinase 15%. Flow cytometry of +/+ and −/ − fetal liver cells using TER119 revealed a TER119Hi population of cells absent in −/ − fetal liver cells, suggesting a block in differentiation to more mature erythroid progenitors. To ensure that the potential EKLF target genes were expressed in the TER119Lo population and were not identified because they were present only in the TER119Hi, the expression of each selected gene was analyzed in TER119Lo and TER119Hi cells by real time PCR. Target gene/α-globin ratios indicated the selected genes were expressed at levels >2 fold higher in TER119Lo than TER119Hi cells. Studies of the AHSP locus identified a strong DNaseI hypersensitive site (HS) in WT fetal liver nuclei between 5′ of the AHSP promoter, that was absent in −/ − chromatin. Chromatin immunoprecipitation analysis of WT fetal liver chromatin spanning 3.5kb of the AHSP locus using 13 primer pairs (~300bp intervals from >1kb 5′ and 3′) demonstrated 2 regions of hyperacetylation of histones H3 and H4. The 5′ region corresponded to the DNaseI HS, and the other region maps 3′ of the AHSP polyA signal. Histones H3 and H4 were also acetylated in the interval between these hyperacetylated regions, while the chromatin upstream and downstream of these regions were hypoacetylated. In chromatin from −/ − fetal liver cells, all sites were hypoacetylated, correlating with the severe reduction in AHSP gene expression. These results support the hypothesis that the anemia in EKLF −/ − mice is due to both decreased expression of the β-globin gene and other erythroid genes including those involved in membrane integrity, stabilization of α-globin protein, and glycolysis leading to defects in erythrocyte structure, function, and metabolism. They also suggest that EKLF may act as a transcription factor and a chromatin modulator for genes other than β-globin.