Development of pathophysiologically relevant models of sickle cell disease and ß-thalassemia for therapeutic studies.

Ex vivo cellular system that accurately replicates sickle cell disease and ß-thalassemia characteristics is a highly sought-after goal in the field of erythroid biology. In this study, we present the generation of erythroid progenitor lines with sickle cell disease and ß-thalassemia mutation using CRISPR/Cas9. The disease cellular models exhibit similar differentiation profiles, globin expression and proteome dynamics as patient-derived hematopoietic stem/progenitor cells. Additionally, these cellular models recapitulate pathological conditions associated with both the diseases. Hydroxyurea and pomalidomide treatment enhanced fetal hemoglobin levels. Notably, we introduce a therapeutic strategy for the above diseases by recapitulating the HPFH3 genotype, which reactivates fetal hemoglobin levels and rescues the disease phenotypes, thus making these lines a valuable platform for studying and developing new therapeutic strategies. Altogether, we demonstrate our disease cellular systems are physiologically relevant and could prove to be indispensable tools for disease modeling, drug screenings and cell and gene therapy-based applications.

Identification and characterization of CHD4-associated eRNA as a novel modulator of fetal hemoglobin levels in ß-thalassemia.

Fetal-to-adult hemoglobin switching is controlled by programmed silencing of γ-globin while the re-activation of fetal hemoglobin (HbF) is an effective strategy for ameliorating the clinical severity of ß-thalassemia and sickle cell disease. The identification of enhancer RNAs (eRNAs) related to the fetal (α2γ2) to adult hemoglobin (α2ß2) switching remains incomplete. In this study, the transcriptomes of GYPA+ cells from six ß-thalassemia patients with extreme HbF levels were sequenced to identify differences in patterns of noncoding RNA expression. It is interesting that an enhancer upstream of CHD4, an HbF-related core subunit of the NuRD complex, was differentially transcribed. We found a significantly positive correlation of eRNA-CHD4 enhancer-gene interaction using the public database of FANTOM5. Specifically, the eRNA-CHD4 expression was found to be significantly higher in both CD34+ HSPCs and HUDEP-2 than those in K562 cells which commonly expressed high level of HbF, suggesting a correlation between eRNA and HbF expression. Furthermore, prediction of transcription binding sites of cis-eQTLs and the CHD4 genomic region revealed a putative interaction site between rs73264846 and ZNF410, a known transcription factor regulating HbF expression. Moreover, in-vitro validation showed that the inhibition of eRNA could reduce the expression of HBG expression in HUDEP-2 cells. Taken together, the findings of this study demonstrate that a distal enhancer contributes to stage-specific silencing of γ-globin genes through direct modulation of CHD4 expression and provide insights into the epigenetic mechanisms of NuRD-mediated hemoglobin switching.

let-7 miRNAs repress HIC2 to regulate BCL11A transcription and hemoglobin switching.

ABSTRACT: The switch from fetal hemoglobin (γ-globin, HBG) to adult hemoglobin (ß-globin, HBB) gene transcription in erythroid cells serves as a paradigm for a complex and clinically relevant developmental gene regulatory program. We previously identified HIC2 as a regulator of the switch by inhibiting the transcription of BCL11A, a key repressor of HBG production. HIC2 is highly expressed in fetal cells, but the mechanism of its regulation is unclear. Here we report that HIC2 developmental expression is controlled by microRNAs (miRNAs), as loss of global miRNA biogenesis through DICER1 depletion leads to upregulation of HIC2 and HBG messenger RNA. We identified the adult-expressed let-7 miRNA family as a direct posttranscriptional regulator of HIC2. Ectopic expression of let-7 in fetal cells lowered HIC2 levels, whereas inhibition of let-7 in adult erythroblasts increased HIC2 production, culminating in decommissioning of a BCL11A erythroid enhancer and reduced BCL11A transcription. HIC2 depletion in let-7-inhibited cells restored BCL11A-mediated repression of HBG. Together, these data establish that fetal hemoglobin silencing in adult erythroid cells is under the control of a miRNA-mediated inhibitory pathway (let-7 ⊣ HIC2 ⊣ BCL11A ⊣ HBG).

Base editing of key residues in the BCL11A-XL-specific zinc finger domains derepresses fetal globin expression.

BCL11A-XL directly binds and represses the fetal globin (HBG1/2) gene promoters, using 3 zinc-finger domains (ZnF4, ZnF5, and ZnF6), and is a potential target for ß-hemoglobinopathy treatments. Disrupting BCL11A-XL results in derepression of fetal globin and high HbF, but also affects hematopoietic stem and progenitor cell (HSPC) engraftment and erythroid maturation. Intriguingly, neurodevelopmental patients with ZnF domain mutations have elevated HbF with normal hematological parameters. Inspired by this natural phenomenon, we used both CRISPR-Cas9 and base editing at specific ZnF domains and assessed the impacts on HbF production and hematopoietic differentiation. Generating indels in the various ZnF domains by CRISPR-Cas9 prevented the binding of BCL11A-XL to its site in the HBG1/2 promoters and elevated the HbF levels but affected normal hematopoiesis. Far fewer side effects were observed with base editing- for instance, erythroid maturation in vitro was near normal. However, we observed a modest reduction in HSPC engraftment and a complete loss of B cell development in vivo, presumably because current base editing is not capable of precisely recapitulating the mutations found in patients with BCL11A-XL-associated neurodevelopment disorders. Overall, our results reveal that disrupting different ZnF domains has different effects. Disrupting ZnF4 elevated HbF levels significantly while leaving many other erythroid target genes unaffected, and interestingly, disrupting ZnF6 also elevated HbF levels, which was unexpected because this region does not directly interact with the HBG1/2 promoters. This first structure/function analysis of ZnF4-6 provides important insights into the domains of BCL11A-XL that are required to repress fetal globin expression and provide framework for exploring the introduction of natural mutations that may enable the derepression of single gene while leaving other functions unaffected.

Quantitative Model-Based Assessment of Multiple Sickle Cell Disease Therapeutic Approaches Alone and in Combination.

Three sickle cell disease (SCD) treatment strategies, stabilizing oxygenated hemoglobin (oxyHb), lowering 2,3-BPG, and inducing fetal hemoglobin (HbF) expression aim to prevent red blood cell (RBC) sickling by reducing tense-state sickle hemoglobin that contributes to polymer formation. Induction of 30% HbF is seen as the gold standard because 30% endogenous expression is associated with a lack of symptoms. However, the level of intervention required to achieve equivalent polymerization protection by the other strategies is uncertain, and there is little understanding of how these approaches could work in combination. We sought to develop an oxygen saturation model that could assess polymerization protection of all three approaches alone or in combination by extending the Monod-Wymann-Changeux model to include additional mechanisms. Applying the model to monotherapies suggests 51% sickle hemoglobin (HbS) occupancy with an oxyHb stabilizer or lowering RBC 2,3 BPG concentrations to 1.8 mM would produce comparable polymerization protection as 30% HbF. The model predictions are consistent with observed clinical response to the oxyHb stabilizer voxelotor and the 2,3-BPG reducer etavopivat. The model also suggests combination therapy will have added benefit in the case of dose limitations, as is the case for voxelotor, which the model predicts could be combined with 20% HbF or 2,3-BPG reduction to 3.75 mM to reach equivalent protection as 30% HbF. The proposed model represents a unified framework that is useful in supporting decisions in preclinical and early clinical development and capable of evolving with clinical experience to gain new and increasingly confident insights into treatment strategies for SCD.

Do Lower Levels of Fetal Hemoglobin in Preterm Infants Relate to Oxidative Stress?

Fetal hemoglobin (HbF) has a higher affinity to oxygen than adult hemoglobin, allowing for a slower oxygen transfer to peripheral tissue, creating a microenvironment conducive to adequate fetal development in utero. However, most preterm infants receive packed red blood cell transfusions from adult donors leading to a drastic nonphysiological descent of circulating HbF. We hypothesized that this drop could enhance oxygen delivery to peripheral tissues generating a hyperoxic pro-oxidant environment. To investigate this, we assessed differences in oxidative stress biomarkers determined in urine samples in a cohort of 56 preterm infants born <32 weeks' gestation. Median oxidative stress biomarkers were compared between patients with circulating HbF above or below median HbF levels using Wilcoxon rank sum test. Oxidative stress biomarkers were significantly higher in the group of patients with lower levels of HbF. This study provides the initial evidence indicating elevated levels of oxidative stress biomarkers in preterm neonates with lower HbF levels. Based on the results, we hypothesize that HbF may contribute to preventing free radical-associated conditions during the newborn period. Antioxid. Redox Signal. 40, 453-459.

C2H2 Zinc Finger Transcription Factors Associated with Hemoglobinopathies.

In humans, specific aberrations in ß-globin results in sickle cell disease and ß-thalassemia, symptoms of which can be ameliorated by increased expression of fetal globin (HbF). Two recent CRISPR-Cas9 screens, centered on ∼1500 annotated sequence-specific DNA binding proteins and performed in a human erythroid cell line that expresses adult hemoglobin, uncovered four groups of candidate regulators of HbF gene expression. They are (1) members of the nucleosome remodeling and deacetylase (NuRD) complex proteins that are already known for HbF control; (2) seven C2H2 zinc finger (ZF) proteins, including some (ZBTB7A and BCL11A) already known for directly silencing the fetal γ-globin genes in adult human erythroid cells; (3) a few other transcription factors of different structural classes that might indirectly influence HbF gene expression; and (4) DNA methyltransferase 1 (DNMT1) that maintains the DNA methylation marks that attract the MBD2-associated NuRD complex to DNA as well as associated histone H3 lysine 9 methylation. Here we briefly discuss the effects of these regulators, particularly C2H2 ZFs, in inducing HbF expression for treating ß-hemoglobin disorders, together with recent advances in developing safe and effective small-molecule therapeutics for the regulation of this well-conserved hemoglobin switch.

Bach1 inhibitor HPP-D mediates γ-globin gene activation in sickle erythroid progenitors.

Sickle cell disease (SCD) is the most common ß-hemoglobinopathy caused by various mutations in the adult ß-globin gene resulting in sickle hemoglobin production, chronic hemolytic anemia, pain, and progressive organ damage. The best therapeutic strategies to manage the clinical symptoms of SCD is the induction of fetal hemoglobin (HbF) using chemical agents. At present, among the Food and Drug Administration-approved drugs to treat SCD, hydroxyurea is the only one proven to induce HbF protein synthesis, however, it is not effective in all people. Therefore, we evaluated the ability of the novel Bach1 inhibitor, HPP-D to induce HbF in KU812 cells and primary sickle erythroid progenitors. HPP-D increased HbF and decreased Bach1 protein levels in both cell types. Furthermore, chromatin immunoprecipitation assay showed reduced Bach1 and increased NRF2 binding to the γ-globin promoter antioxidant response elements. We also observed increased levels of the active histone marks H3K4Me1 and H3K4Me3 supporting an open chromatin configuration. In primary sickle erythroid progenitors, HPP-D increased γ-globin transcription and HbF positive cells and reduced sickled erythroid progenitors under hypoxia conditions. Collectively, our data demonstrate that HPP-D induces γ-globin gene transcription through Bach1 inhibition and enhanced NRF2 binding in the γ-globin promoter antioxidant response elements.

An α-chain modification rivals the effect of fetal hemoglobin in retarding the rate of sickle cell fiber formation.

Adults with sickle cell disease bear a mutation in the ß-globin gene, leading to the expression of sickle hemoglobin (HbS; α2ßS2). Adults also possess the gene for γ-globin, which is a component of fetal hemoglobin (HbF, α2γ2); however, γ-chain expression normally ceases after birth. As HbF does not form the fibers that cause the disease, pharmacological and gene-modifying interventions have attempted to either reactivate expression of the γ chain or introduce a gene encoding a modified ß chain having γ-like character. Here, we show that a single-site modification on the α chain, αPro114Arg, retards fiber formation as effectively as HbF. Because this addition to the repertoire of anti-sickling approaches acts independently of other modifications, it could be coupled with other therapies to significantly enhance their effectiveness.

Base editing of the HBG promoter induces potent fetal hemoglobin expression with no detectable off-target mutations in human HSCs.

Reactivating silenced γ-globin expression through the disruption of repressive regulatory domains offers a therapeutic strategy for treating ß-hemoglobinopathies. Here, we used transformer base editor (tBE), a recently developed cytosine base editor with no detectable off-target mutations, to disrupt transcription-factor-binding motifs in hematopoietic stem cells. By performing functional screening of six motifs with tBE, we found that directly disrupting the BCL11A-binding motif in HBG1/2 promoters triggered the highest γ-globin expression. Via a side-by-side comparison with other clinical and preclinical strategies using Cas9 nuclease or conventional BEs (ABE8e and hA3A-BE3), we found that tBE-mediated disruption of the BCL11A-binding motif at the HBG1/2 promoters triggered the highest fetal hemoglobin in healthy and ß-thalassemia patient hematopoietic stem/progenitor cells while exhibiting no detectable DNA or RNA off-target mutations. Durable therapeutic editing by tBE persisted in repopulating hematopoietic stem cells, demonstrating that tBE-mediated editing in HBG1/2 promoters is a safe and effective strategy for treating ß-hemoglobinopathies.

Genetic Variation and Sickle Cell Disease Severity: A Systematic Review and Meta-Analysis.

Importance: Sickle cell disease (SCD) is a monogenic disorder, yet clinical outcomes are influenced by additional genetic factors. Despite decades of research, the genetics of SCD remain poorly understood. Objective: To assess all reported genetic modifiers of SCD, evaluate the design of associated studies, and provide guidelines for future analyses according to modern genetic study recommendations. Data Sources: PubMed, Web of Science, and Scopus were searched through May 16, 2023, identifying 5290 publications. Study Selection: At least 2 reviewers identified 571 original, peer-reviewed English-language publications reporting genetic modifiers of human SCD phenotypes, wherein the outcome was not treatment response, and the comparison was not between SCD subtypes or including healthy controls. Data Extraction and Synthesis: Data relevant to all genetic modifiers of SCD were extracted, evaluated, and presented following STREGA and PRISMA guidelines. Weighted z score meta-analyses and pathway analyses were conducted. Main Outcomes and Measures: Outcomes were aggregated into 25 categories, grouped as acute complications, chronic conditions, hematologic parameters or biomarkers, and general or mixed measures of SCD severity. Results: The 571 included studies reported on 29 670 unique individuals (50% ≤ 18 years of age) from 43 countries. Of the 17 757 extracted results (4890 significant) in 1552 genes, 3675 results met the study criteria for meta-analysis: reported phenotype and genotype, association size and direction, variability measure, sample size, and statistical test. Only 173 results for 62 associations could be cross-study combined. The remaining associations could not be aggregated because they were only reported once or methods (eg, study design, reporting practice) and genotype or phenotype definitions were insufficiently harmonized. Gene variants regulating fetal hemoglobin and α-thalassemia (important markers for SCD severity) were frequently identified: 19 single-nucleotide variants in BCL11A, HBS1L-MYB, and HBG2 were significantly associated with fetal hemoglobin (absolute value of Z = 4.00 to 20.66; P = 8.63 × 10-95 to 6.19 × 10-5), and α-thalassemia deletions were significantly associated with increased hemoglobin level and reduced risk of albuminuria, abnormal transcranial Doppler velocity, and stroke (absolute value of Z = 3.43 to 5.16; P = 2.42 × 10-7 to 6.00 × 10-4). However, other associations remain unconfirmed. Pathway analyses of significant genes highlighted the importance of cellular adhesion, inflammation, oxidative and toxic stress, and blood vessel regulation in SCD (23 of the top 25 Gene Ontology pathways involve these processes) and suggested future research areas. Conclusions and Relevance: The findings of this comprehensive systematic review and meta-analysis of all published genetic modifiers of SCD indicated that implementation of standardized phenotypes, statistical methods, and reporting practices should accelerate discovery and validation of genetic modifiers and development of clinically actionable genetic profiles.

Molecular understanding of unusual HbE-ß+-thalassemia with Hb phenotype similar to HbE heterozygote: simple and rapid differentiation using HbE levels.

BACKGROUND: Low HbF expression in HbE-ß+-thalassemia may lead to misdiagnosis of HbE heterozygosity. We aimed to characterize the ß- and α-globin genes and the modifying factors related to HbF expression in patients with an Hb phenotype similar to that of HbE heterozygotes. Furthermore, screening tools for differentiating HbE-ß+-thalassemia from HbE heterozygotes have been investigated. PARTICIPANTS AND METHODS: A total of 2133 participants with HbE and HbA with varying HbF levels were recruited. Polymerase chain reaction-based DNA analysis and sequencing were performed to characterize ß- and α-globin genes. DNA polymorphism at position -158 nt 5' to Gγ-globin was performed by XmnI restriction digestion. Receiver operating characteristic (ROC) curves were constructed using the area under the curve (AUC). Cutoff values of HbA2, HbE, and HbF levels for the differentiation of HbE-ß+-thalassemia from HbE heterozygotes were determined. RESULTS: Five ß+-thalassemia mutations trans to ßE-gene (ß-87(C>A), ß-31(A>G), ß-28(A>G), ß19(A>G), and ß126(T>G)) were identified in 79 patients. Among these, 54 presented with low HbF levels, and 25 presented with high HbF levels. ROC curve analysis revealed an excellent AUC of 1.000 (95% confidence interval:1.000-1.000) for HbE levels, and a cut-off point of ≥35.0% had 100.0% sensitivity, specificity, and Youden's index for differentiating HbE-ß+-thalassemia from HbE heterozygotes. The proportion of α-thalassemia mutations was 46.3 and 8.0% among HbE-ß+-thalassemia patients with low and high HbF levels, respectively. Two rare α-thalassemia mutations (Cap +14(C>G) and initiation codon (ATG>-TG)) of α2-globin genes were identified. The genotype and allele of the polymorphism at -158 nt 5' to Gγ-globin was found to be negatively associated with HbF expression. CONCLUSIONS: HbE-ß+-thalassemia cannot be disregarded until appropriate DNA analysis is performed, and the detection of α-thalassemia mutations should always be performed under these conditions. An HbE level ≥35.0% may indicate screening of samples for DNA analysis for HbE-ß+-thalassemia diagnosis.

HbE-ß⁺-thalassemia displays a wide range of HbF expression, which may lead to the misdiagnosis of HbE heterozygosity in patients whose Hb analysis shows HbE and HbA. α-Thalassemia may be a major factor associated with decreased secondary activation of HbF expression in the disease.HbE may be a potential indicator for effectively differentiating HbE-ß⁺-thalassemia from HbE heterozygotes.The high proportion and heterogeneity of α-thalassemia mutations found in patients with HbE-ß⁺-thalassemia evoke a complex thalassemia syndrome, requiring complete DNA analysis.

Effects of Mithramycin on BCL11A Gene Expression and on the Interaction of the BCL11A Transcriptional Complex to γ-Globin Gene Promoter Sequences.

The anticancer drug mithramycin (MTH), has been proposed for drug repurposing after the finding that it is a potent inducer of fetal hemoglobin (HbF) production in erythroid precursor cells (ErPCs) from ß-thalassemia patients. In this respect, previously published studies indicate that MTH is very active in inducing increased expression of γ-globin genes in erythroid cells. This is clinically relevant, as it is firmly established that HbF induction is a valuable approach for the therapy of ß-thalassemia and for ameliorating the clinical parameters of sickle-cell disease (SCD). Therefore, the identification of MTH biochemical/molecular targets is of great interest. This study is inspired by recent robust evidence indicating that the expression of γ-globin genes is controlled in adult erythroid cells by different transcriptional repressors, including Oct4, MYB, BCL11A, Sp1, KLF3 and others. Among these, BCL11A is very important. In the present paper we report evidence indicating that alterations of BCL11A gene expression and biological functions occur during MTH-mediated erythroid differentiation. Our study demonstrates that one of the mechanisms of action of MTH is a down-regulation of the transcription of the BCL11A gene, while a second mechanism of action is the inhibition of the molecular interactions between the BCL11A complex and specific sequences of the γ-globin gene promoter.

BCL11A-targeted γ-globin gene induction by triterpenoid glycosides of Fagonia indica: A preclinical scientific validation of indigenous herb for the treatment of ß-hemoglobinopathies.

Pharmacological induction of fetal hemoglobin has proven to be a promising therapeutic intervention in ß-hemoglobinopathies by reducing the globin chain imbalance and inhibiting sickle cell polymerization. Fagonia indica has shown therapeutic relevance to ß-thalassemia. Therefore, we study the ethnopharmacological potential of Fagonia indica and its biomarker compounds for their HbF induction ability for the treatment of ß-thalassemia. Here, we identify, compound 8 (triterpenoid glycosides) of F. indica. as a prominent HbF inducer in-vitro and in-vivo. Compound 8 showed potent erythroid differentiation, enhanced cellular proliferation, ample accumulation of total hemoglobin, and a strong notion of γ-globin gene expression in K562 cultures. Compound 8 treatment also revealed strong induction of erythroid differentiation and fetal hemoglobin mRNA and protein in adult erythroid precursor cells. This induction was associated with simultaneous downregulation of BCL11A and SOX6, and overexpression of the GATA-1 gene, suggesting a compound 8-mediated partial mechanism involved in the reactivation of fetal-like globin genes. The in vivo study with compound 8 (10 mg/kg) in ß-YAC mice resulted in significant HbF synthesis demonstrated by the enhanced level of F-cells (84.14 %) and an 8.85-fold increase in the γ-globin gene. Overall, the study identifies compound 8 as a new HbF-inducing entity and provides an early "proof-of-concept" to enable the initiation of preclinical and clinical studies in the development of this HbF-inducing agent for ß-thalassemia.

CRISPR-Cas9 Editing of the HBG1 and HBG2 Promoters to Treat Sickle Cell Disease.

BACKGROUND: Sickle cell disease is caused by a defect in the ß-globin subunit of adult hemoglobin. Sickle hemoglobin polymerizes under hypoxic conditions, producing deformed red cells that hemolyze and cause vaso-occlusion that results in progressive organ damage and early death. Elevated fetal hemoglobin levels in red cells protect against complications of sickle cell disease. OTQ923, a clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9-edited CD34+ hematopoietic stem- and progenitor-cell (HSPC) product, has a targeted disruption of the HBG1 and HBG2 (γ-globin) gene promoters that increases fetal hemoglobin expression in red-cell progeny. METHODS: We performed a tiling CRISPR-Cas9 screen of the HBG1 and HBG2 promoters by electroporating CD34+ cells obtained from healthy donors with Cas9 complexed with one of 72 guide RNAs, and we assessed the fraction of fetal hemoglobin-immunostaining erythroblasts (F cells) in erythroid-differentiated progeny. The gRNA resulting in the highest level of F cells (gRNA-68) was selected for clinical development. We enrolled participants with severe sickle cell disease in a multicenter, phase 1-2 clinical study to assess the safety and adverse-effect profile of OTQ923. RESULTS: In preclinical experiments, CD34+ HSPCs (obtained from healthy donors and persons with sickle cell disease) edited with CRISPR-Cas9 and gRNA-68 had sustained on-target editing with no off-target mutations and produced high levels of fetal hemoglobin after in vitro differentiation or xenotransplantation into immunodeficient mice. In the study, three participants received autologous OTQ923 after myeloablative conditioning and were followed for 6 to 18 months. At the end of the follow-up period, all the participants had engraftment and stable induction of fetal hemoglobin (fetal hemoglobin as a percentage of total hemoglobin, 19.0 to 26.8%), with fetal hemoglobin broadly distributed in red cells (F cells as a percentage of red cells, 69.7 to 87.8%). Manifestations of sickle cell disease decreased during the follow-up period. CONCLUSIONS: CRISPR-Cas9 disruption of the HBG1 and HBG2 gene promoters was an effective strategy for induction of fetal hemoglobin. Infusion of autologous OTQ923 into three participants with severe sickle cell disease resulted in sustained induction of red-cell fetal hemoglobin and clinical improvement in disease severity. (Funded by Novartis Pharmaceuticals; ClinicalTrials.gov number, NCT04443907.).

Effect of hydroxyurea on erythrocyte apoptosis in hemoglobinopathy patients.

BACKGROUND: Hydroxyurea (HU) therapy improves the clinical severity of patients with hemoglobinopathies. Few studies have documented some mechanisms of HU, but the exact mechanism of action is unknown. Phosphatidylserine on erythrocytes is responsible for apoptosis. In this study, we investigate the expression of phosphatidylserine on the erythrocytes surface of hemoglobinopathies before and after HU treatment. RESEARCH DESIGNS AND METHODS: Blood samples from 45 thalassemia intermedia and 40 SCA and 30 HbE-b-thalassemia patients were analyzed before and after 3 and 6 months of HU treatment. The profile of phosphatidylserine was determined by flow-cytometry using the Annexin V-RBC apoptosis kit. RESULTS: Hydroxyurea proved effective in improving clinical severity of hemoglobinopathies. After treatment with hydroxyurea, the percentage of phosphatidylserine-positive cells was significantly reduced in all 3 patient groups (p < 0.0001). Correlation analysis using different hematological parameters as independent variables and % phosphatidylserine  as dependent variable showed a negative relationship with HbF, RBC, and hemoglobin in all 3 patient groups. CONCLUSION: Hydroxyurea reduces the expression of phosphatidylserine on erythrocytes, contributing to the beneficial effects of this therapy. We suggest that the use of such a biological marker in conjunction with HbF levels may provide valuable insights into the biology and consequences of early RBC apoptosis.

The study investigated the role of hydroxyurea in reducing the externalization of phosphatidylserine on the surface of the erythrocyte membrane of patients with hemoglobinopathies. In patients treated with hydroxyurea for 3 and 6 months, the percentage of phosphatidylserine exposure on the erythrocyte surface was reduced compared with baseline. The decreased percentage of phosphatidylserine correlated negatively with hematologic parameters such as red blood cell (RBC), hemoglobin, and fetal hemoglobin (HbF) in patients at baseline and after HU therapy. Treatment with hydroxyurea decreases the percentage of PS exposure on the surface of RBCs, contributing to the beneficial effects of this therapy. We, therefore, suggest that the use of such a biological marker on the erythrocyte cell surface in conjunction with HbF levels may provide valuable insights into the biology and consequences of early erythrocyte apoptosis.

Potent and uniform fetal hemoglobin induction via base editing.

Inducing fetal hemoglobin (HbF) in red blood cells can alleviate ß-thalassemia and sickle cell disease. We compared five strategies in CD34+ hematopoietic stem and progenitor cells, using either Cas9 nuclease or adenine base editors. The most potent modification was adenine base editor generation of γ-globin -175A>G. Homozygous -175A>G edited erythroid colonies expressed 81 ± 7% HbF versus 17 ± 11% in unedited controls, whereas HbF levels were lower and more variable for two Cas9 strategies targeting a BCL11A binding motif in the γ-globin promoter or a BCL11A erythroid enhancer. The -175A>G base edit also induced HbF more potently than a Cas9 approach in red blood cells generated after transplantation of CD34+ hematopoietic stem and progenitor cells into mice. Our data suggest a strategy for potent, uniform induction of HbF and provide insights into γ-globin gene regulation. More generally, we demonstrate that diverse indels generated by Cas9 can cause unexpected phenotypic variation that can be circumvented by base editing.

Proteomics screening uncovers HMGA1 as a promising negative regulator for γ-globin expression in response to decreased ß-globin levels.

Reactivation of fetal hemoglobin (HbF) is a critical goal for the treatment of patients with hemoglobinopathies. ß-globin disorders can trigger stress erythropoiesis in red blood cells (RBCs). Cell-intrinsic erythroid stress signals promote erythroid precursors to express high levels of fetal hemoglobin, which is also known as γ-globin. However, the molecular mechanism underlying γ-globin production during cell-intrinsic erythroid stress remains to be elucidated. Here, we utilized CRISPR-Cas9 to model a stressed state caused by reduced levels of adult ß-globin in HUDEP2 human erythroid progenitor cells. We found that a decrease in ß-globin expression correlates with the upregulation of γ-globin expression. We also identified transcription factor high-mobility group A1 (HMGA1; formerly HMG-I/Y) as a potential γ-globin regulator that responds to reduced ß-globin levels. Upon erythroid stress, there is a downregulation of HMGA1, which normally binds -626 to -610 base pairs upstream from the STAT3 promoter, to downregulate STAT3 expression. STAT3 is a known γ-globin repressor, so the downregulation of HMGA1 ultimately upregulates γ-globin expression. SIGNIFICANCE: This study demonstrated HMGA1 as a potential regulator in the poorly understood phenomenon of stress-induced globin compensation, and after further validation these results might inform new strategies to treat patients with sickle cell disease and ß-thalassemia.

Induction of fetal hemoglobin: Lentiviral shRNA knockdown of HBS1L in ß0-thalassemia/HbE erythroid cells.

Imbalanced globin chain output contributes to thalassemia pathophysiology. Hence, induction of fetal hemoglobin in ß-thalassemia and other ß-hemoglobinopathies are of continuing interest for therapeutic approaches. Genome-wide association studies have identified three common genetic loci: namely ß-globin (HBB), an intergenic region between MYB and HBS1L, and BCL11A underlying quantitative fetal hemoglobin production. Here, we report that knockdown of HBS1L (all known variants) using shRNA in early erythroblast obtained from ß0-thalassemia/HbE patients triggers an upregulation of γ-globin mRNA 1.69 folds. There is modest perturbation of red cell differentiation assessed by flow cytometry and morphology studies. The levels of α- and ß-globin mRNAs are relatively unaltered. Knockdown of HBS1L also increases the percentage of fetal hemoglobin around 16.7 folds when compared to non-targeting shRNA. Targeting HBS1L is attractive because of the potent induction of fetal hemoglobin and the modest effect on cell differentiation.