Recent progress in understanding and manipulating haemoglobin switching for the haemoglobinopathies

The Discovery of Selective Protein Arginine Methyltransferase 5 Inhibitors in the Management of β-Thalassemia through Computational Methods

β-Thalassemia is an inherited genetic disorder associated with β-globin chain synthesis, which ultimately becomes anemia. Adenosine-2,3-dialdehyde, by inhibiting arginine methyl transferase 5 (PRMT5), can induce fetal hemoglobin (HbF) levels. Hence, the materialization of PRMT5 inhibitors is considered a promising therapy in the management of β-thalassemia. This study conducted a virtual screening of certain compounds similar to 5'-deoxy-5'methyladenosine (3XV) using the PubChem database. The top 10 compounds were chosen based on the best docking scores, while their interactions with the PRMT5 active site were analyzed. Further, the top two compounds demonstrating the lowest binding energy were subjected to drug-likeness analysis and pharmacokinetic property predictions, followed by molecular dynamics simulation studies. Based on the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) score and molecular interactions, (3R,4S)-2-(6-aminopurin-9-yl)-5-[(4-ethylcyclohexyl)sulfanylmethyl]oxolane-3,4-diol (TOP1) and 2-(6-Aminopurin-9-yl)-5-[(6-aminopurin-9-yl)methylsulfanylmethyl]oxolane-3,4-diol (TOP2) were identified as potential hit compounds, while TOP1 exhibited higher binding affinity and stabler binding capabilities than TOP2 during molecular dynamics simulation (MDS) analysis. Taken together, the outcomes of our study could aid researchers in identifying promising PRMT5 inhibitors. Moreover, further investigations through in vivo and in vitro experiments would unquestionably confirm that this compound could be employed as a therapeutic drug in the management of β-thalassemia.

Targeting HIF-1α in sickle cell disease and cancer: unraveling therapeutic opportunities and risks

INTRODUCTION

HIF-1α, a key player in medical science, holds immense significance in therapeutic approaches. This review delves into its complex dynamics, emphasizing the delicate balance required for its modulation. HIF-1α stands as a cornerstone in medical research, its role extending to therapeutic strategies. This review explores the intricate interplay surrounding HIF-1α, highlighting its critical involvement and the necessity for cautious modulation.

AREAS COVERED

In sickle cell disease (SCD), HIF-1α's potential to augment fetal hemoglobin (HbF) production and mitigate symptoms is underscored. Furthermore, its role in cancer is examined, particularly its influence on survival in hypoxic tumor microenvironments, angiogenesis, and metastasis. The discussion extends to the intricate relationship between HIF-1α modulation and cancer risks in SCD patients, emphasizing the importance of balancing therapeutic benefits and potential hazards.

EXPERT OPINION

Managing HIF-1α modulation in SCD patients requires a nuanced approach, considering therapeutic potential alongside associated risks, especially in exacerbating cancer risks. An evolutionary perspective adds depth, highlighting adaptations in populations adapted to low-oxygen environments and aligning cancer cell metabolism with primitive cells. The role of HIF-1α as a therapeutic target is discussed within the context of complex cancer biology and metabolism, acknowledging varied responses across diverse cancers influenced by intricate evolutionary adaptations.

Unraveling the Complexity of Vaso-Occlusive Crises in Sickle Cell Disease: Insights from a Resource-Limited Setting

Background/Objectives: This study investigated vaso-occlusive crises (VOCs) in sickle cell disease in Lubumbashi, Democratic Republic of Congo, aiming to understand the disease complexities amidst limited resources. With sickle cell hemoglobinopathies on the rise in sub-Saharan Africa, this nine-year study explored factors associated with VOCs and hematological components. Methods: This study comprised 838 patients, analyzing VOCs and hematological changes over time. Demographic characteristics and blood composition changes were carefully categorized. A total of 2910 crises were observed and managed, with analyses conducted on severity, localization, and age groups using statistical methods. Results: The majority of crises were mild or moderate, primarily affecting osteoarticular regions. Statistical analysis revealed significant disparities in crisis intensity based on location and age. The association between blood samples and the number of comorbidities was investigated. Significant positive associations were found for all parameters, except monocytes, indicating a potential link between blood variables and complication burden. Survival analysis using Cox regression was performed to predict the probability of experiencing a second crisis. No significant effects of medication or localization were observed. However, intensity (p < 0.001), age (p < 0.001), and gender (p < 0.001) showed significant effects. Adjusted Hazard Ratios indicated increased risk with age and male gender and reduced risk with mild or severe crisis intensity compared to light. Conclusions: This research sheds light on the complexities of VOCs in resource-limited settings where sickle cell disease is prevalent. The intricate interplay between clinical, laboratory, and treatment factors is highlighted, offering insights for improved patient care. It aims to raise awareness of patient challenges and provide valuable information for targeted interventions to alleviate their burden.

Prognostic Value of Pretreatment Fetal Hemoglobin Levels in Patients with Myelodysplastic Syndromes and Acute Myeloid Leukemia Treated with Azacitidine: A Single-center Retrospective Study

Objective Azacitidine (AZA) has been the standard of care for elderly patients with high-risk myelodysplastic syndromes (MDS). However, reliable clinical predictors of outcome have yet to be identified. The prognostic value of fetal hemoglobin (HbF) levels has been reported for decitabine therapy. We evaluated pretreatment HbF levels in AZA monotherapy as a prognostic marker in MDS/acute myeloid leukemia (AML). Methods This study included chemotherapy-naïve patients who had received seven-day treatment schedules of AZA and whose HbF levels were measured at the onset of treatment between March 2011 and July 2020. Patients were grouped into HbF-normal (<1.0%) or HbF-elevated (≥1.0%) groups. Responses were classified according to the International Working Group 2006 criteria. Patients Twenty-nine patients were included and classified as having either MDS (n=21), chronic myelomonocytic leukemia (n=5), myelodysplastic/myeloproliferative neoplasm unclassifiable (n=1), or AML with <30% marrow blasts (n=2) based on the World Health Organization 2016 diagnostic criteria. According to the revised International Prognostic Scoring System classification, 20/29 patients were at intermediate, high, or very high risk. Pretreatment HbF levels were elevated in 13/29 patients. Results The median follow-up duration was 13.0 (range 1.5-93.5) months. The HbF-elevated group was associated with a significantly higher hematologic improvement rate (76.9% vs. 25%, p=0.009) and better overall survival (median, 21.0 vs. 13.0 months, p=0.048) than the HbF-normal group. Conclusion These results suggest that elevated pretreatment HbF levels can predict better outcomes in patients with MDS/AML treated with AZA.

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

Ex vivo cellular system that accurately replicates sickle cell disease and β-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 β-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.

A Population-Oriented Genetic Scoring System to Predict Phenotype: A Pathway to Personalized Medicine in Iraqis With β-Thalassemia

To assess the roles of genetic modifiers in Iraqi β-thalassemia patients, and determine whether a genotype-based scoring system could be used to predict phenotype, a total of 224 Iraqi patients with molecularly characterized homozygous or compound heterozygous β-thalassemia were further investigated for α-thalassemia deletions as well as five polymorphisms namely: rs7482144 C > T at HBG2, rs1427407 G > T and rs10189857 A > G at BCL11A, and rs28384513 A > C and rs9399137 T > C at HMIP. The enrolled patients had a median age of 14 years, with 96 males and 128 females. They included 144 thalassemia major, and 80 thalassemia intermedia patients. Multivariate logistic regression analysis revealed that a model including sex and four of these genetic modifiers, namely: β+ alleles, HBG2 rs7482144, α-thalassemia deletions, and BCL11A rs1427407 could significantly predict phenotype (major versus intermedia) with an overall accuracy of 83.9%. Furthermore, a log odds genetic score based on these significant predictors had a highly significant area under curve of 0.917 (95% CI 0.882-0.953). This study underscores the notion that genetic scoring systems should be tailored to populations in question, since genetic modifiers (and/or their relative weight) vary between populations. The population-oriented genetic scoring system created by the current study to predict β-thalassemia phenotype among Iraqis may pave the way to personalized medicine in this patient's group.

miR-365-3p mediates BCL11A and SOX6 erythroid-specific coregulation: A new player in HbF activation

Hemoglobin switching is a complex biological process not yet fully elucidated. The mechanism regulating the suppression of fetal hemoglobin (HbF) expression is of particular interest because of the positive impact of HbF on the course of diseases such as β-thalassemia and sickle cell disease, hereditary hemoglobin disorders that affect the health of countless individuals worldwide. Several transcription factors have been implicated in the control of HbF, of which BCL11A has emerged as a major player in HbF silencing. SOX6 has also been implicated in silencing HbF and is critical to the silencing of the mouse embryonic hemoglobins. BCL11A and SOX6 are co-expressed and physically interact in the erythroid compartment during differentiation. In this study, we observe that BCL11A knockout leads to post-transcriptional downregulation of SOX6 through activation of microRNA (miR)-365-3p. Downregulating SOX6 by transient ectopic expression of miR-365-3p or gene editing activates embryonic and fetal β-like globin gene expression in erythroid cells. The synchronized expression of BCL11A and SOX6 is crucial for hemoglobin switching. In this study, we identified a BCL11A/miR-365-3p/SOX6 evolutionarily conserved pathway, providing insights into the regulation of the embryonic and fetal globin genes suggesting new targets for treating β-hemoglobinopathies.

Biology of Anemia: A Public Health Perspective

Our goal is to present recent progress in understanding the biological mechanisms underlying anemia from a public health perspective. We describe important advances in understanding common causes of anemia and their interactions, including iron deficiency (ID), lack of other micronutrients, infection, inflammation, and genetic conditions. ID develops if the iron circulating in the blood cannot provide the amounts required for red blood cell production and tissue needs. ID anemia develops as iron-limited red blood cell production fails to maintain the hemoglobin concentration above the threshold used to define anemia. Globally, absolute ID (absent or reduced body iron stores that do not meet the need for iron of an individual but may respond to iron supplementation) contributes to only a limited proportion of anemia. Functional ID (adequate or increased iron stores that cannot meet the need for iron because of the effects of infection or inflammation and does not respond to iron supplementation) is frequently responsible for anemia in low- and middle-income countries. Absolute and functional ID may coexist. We highlight continued improvement in understanding the roles of infections and inflammation in causing a large proportion of anemia. Deficiencies of nutrients other than iron are less common but important in some settings. The importance of genetic conditions as causes of anemia depends upon the specific inherited red blood cell abnormalities and their prevalence in the settings examined. From a public health perspective, each setting has a distinctive composition of components underlying the common causes of anemia. We emphasize the coincidence between regions with a high prevalence of anemia attributed to ID (both absolute and functional), those with endemic infections, and those with widespread genetic conditions affecting red blood cells, especially in sub-Saharan Africa and regions in Asia and Oceania.

Human cellular model systems of β-thalassemia enable in-depth analysis of disease phenotype

β-thalassemia is a prevalent genetic disorder causing severe anemia due to defective erythropoiesis, with few treatment options. Studying the underlying molecular defects is impeded by paucity of suitable patient material. In this study we create human disease cellular model systems for β-thalassemia by gene editing the erythroid line BEL-A, which accurately recapitulate the phenotype of patient erythroid cells. We also develop a high throughput compatible fluorometric-based assay for evaluating severity of disease phenotype and utilize the assay to demonstrate that the lines respond appropriately to verified reagents. We next use the lines to perform extensive analysis of the altered molecular mechanisms in β-thalassemia erythroid cells, revealing upregulation of a wide range of biological pathways and processes along with potential novel targets for therapeutic investigation. Overall, the lines provide a sustainable supply of disease cells as research tools for identifying therapeutic targets and as screening platforms for new drugs and reagents.

Erythroid lineage chromatin accessibility maps facilitate identification and validation of NFIX as a fetal hemoglobin repressor

Human genetics has validated de-repression of fetal gamma globin (HBG) in adult erythroblasts as a powerful therapeutic paradigm in diseases involving defective adult beta globin (HBB)¹. To identify factors involved in the switch from HBG to HBB expression, we performed Assay for Transposase Accessible Chromatin with high-throughput sequencing (ATAC-seq)² on sorted erythroid lineage cells derived from bone marrow (BM) or cord blood (CB), representing adult and fetal states, respectively. BM to CB cell ATAC-seq profile comparisons revealed genome-wide enrichment of NFI DNA binding motifs and increased NFIX promoter chromatin accessibility, suggesting that NFIX may repress HBG. NFIX knockdown in BM cells increased HBG mRNA and fetal hemoglobin (HbF) protein levels, coincident with increased chromatin accessibility and decreased DNA methylation at the HBG promoter. Conversely, overexpression of NFIX in CB cells reduced HbF levels. Identification and validation of NFIX as a new target for HbF activation has implications in the development of therapeutics for hemoglobinopathies.

Editing the core region in HPFH deletions alters fetal and adult globin expression for treatment of β-hemoglobinopathies

Reactivation of fetal hemoglobin (HbF) is a commonly adapted strategy to ameliorate β-hemoglobinopathies. However, the continued production of defective adult hemoglobin (HbA) limits HbF tetramer production affecting the therapeutic benefits. Here, we evaluated deletional hereditary persistence of fetal hemoglobin (HPFH) mutations and identified an 11-kb sequence, encompassing putative repressor region (PRR) to β-globin exon-1 (βE1), as the core deletion that ablates HbA and exhibits superior HbF production compared with HPFH or other well-established targets. PRR-βE1-edited hematopoietic stem and progenitor cells (HSPCs) retained their genome integrity and their engraftment potential to repopulate for long-term hematopoiesis in immunocompromised mice producing HbF positive cells in vivo. Furthermore, PRR-βE1 gene editing is feasible without ex vivo HSPC culture. Importantly, the editing induced therapeutically significant levels of HbF to reverse the phenotypes of both sickle cell disease and β-thalassemia major. These findings imply that PRR-βE1 gene editing of patient HSPCs could lead to improved therapeutic outcomes for β-hemoglobinopathy gene therapy.

Fetal Hemoglobin Regulation in Beta-Thalassemia

β-thalassemia is caused by mutations that reduce β-globin production, causing globin chain imbalance, ineffective erythropoiesis, and consequent anemia. Increased fetal hemoglobin (HbF) levels can ameliorate the severity of β-thalassemia by compensating for the globin chain imbalance. Careful clinical observations paired with population studies and advances in human genetics have enabled the discovery of major regulators of HbF switching (i.e. BCL11A, ZBTB7A) and led to pharmacological and genetic therapies for treating β-thalassemia patients. Recent functional screens using genome editing and other emerging tools have identified many new HbF regulators, which may improve therapeutic HbF induction in the future.

Gene Therapy and Gene Editing for β-Thalassemia

After many years of intensive research, emerging data from clinical trials indicate that gene therapy for transfusion-dependent β-thalassemia is now possible. Strategies for therapeutic manipulation of patient hematopoietic stem cells include lentiviral transduction of a functional erythroid-expressed β-globin gene and genome editing to activate fetal hemoglobin production in patient red blood cells. Gene therapy for β-thalassemia and other blood disorders will invariably improve as experience accumulates over time. The best overall approaches are not known and perhaps not yet established. Gene therapy comes at a high cost, and collaboration between multiple stakeholders is required to ensure that these new medicines are administered equitably.

Molecular Basis and Genetic Modifiers of Thalassemia

Thalassemia syndromes are common monogenic disorders and represent a significant health issue worldwide. In this review, the authors elaborate on fundamental genetic knowledge about thalassemias, including the structure and location of globin genes, the production of hemoglobin during development, the molecular lesions causing α-, β-, and other thalassemia syndromes, the genotype-phenotype correlation, and the genetic modifiers of these conditions. In addition, they briefly discuss the molecular techniques applied for diagnosis and innovative cell and gene therapy strategies to cure these conditions.

Allogeneic hematopoietic stem cell transplantation to cure sickle cell disease: A review

Sickle cell disease (SCD) had first been mentioned in the literature a century ago. Advancement in the molecular basis of the pathophysiology of the disease opens the door for various therapeutic options. Though life-extending treatments are available for treating patients with SCD, allogeneic hematopoietic stem cell transplantation (HSCT) is the only option as of yet. A major obstacle before HSCT to cure patients with SCD is the availability of donors. Matched sibling donors are available only for a small percentage of patients. To expand the donor pool, different contrasting approaches of allogeneic HSCT like T-cell replete and deplete have been tested. None of those tested approaches have been without the risk of GvHD and graft rejection. Other limitations such as transplantation-related infections and organ dysfunction caused by the harsh conditioning regimen need to be addressed on a priority basis. In this review, we will discuss available allogeneic HSCT approaches to cure SCD, as well as recent advancements to make the approach safer. The center of interest is using megadose T-cell-depleted bone marrow in conjugation with donor-derived CD8 veto T cells to achieve engraftment and tolerance across MHC barriers, under reduced intensity conditioning (RIC). This approach is in phase I/II clinical trial at the MD Anderson Cancer Centre and is open to patients with hemoglobinopathies.

PUM1 mediates the posttranscriptional regulation of human fetal hemoglobin

The fetal-to-adult hemoglobin switching at about the time of birth involves a shift in expression from γ-globin to β-globin in erythroid cells. Effective re-expression of fetal γ-globin can ameliorate sickle cell anemia and β-thalassemia. Despite the physiological and clinical relevance of this switch, its posttranscriptional regulation is poorly understood. Here, we identify Pumilo 1 (PUM1), an RNA-binding protein with no previously reported functions in erythropoiesis, as a direct posttranscriptional regulator of β-globin switching. PUM1, whose expression is regulated by the erythroid master transcription factor erythroid Krüppel-like factor (EKLF/KLF1), peaks during erythroid differentiation, binds γ-globin messenger RNA (mRNA), and reduces γ-globin (HBG1) mRNA stability and translational efficiency, which culminates in reduced γ-globin protein levels. Knockdown of PUM1 leads to a robust increase in fetal hemoglobin (∼22% HbF) without affecting β-globin levels in human erythroid cells. Importantly, targeting PUM1 does not limit the progression of erythropoiesis, which provides a potentially safe and effective treatment strategy for sickle cell anemia and β-thalassemia. In support of this idea, we report elevated levels of HbF in the absence of anemia in an individual with a novel heterozygous PUM1 mutation in the RNA-binding domain (p.(His1090Profs∗16); c.3267_3270delTCAC), which suggests that PUM1-mediated posttranscriptional regulation is a critical player during human hemoglobin switching.

Effective therapies for sickle cell disease: are we there yet?

Sickle cell disease (SCD) is a common genetic blood disorder associated with acute and chronic pain, progressive multiorgan damage, and early mortality. Recent advances in technologies to manipulate the human genome, a century of research and the development of techniques enabling the isolation, efficient genetic modification, and reimplantation of autologous patient hematopoietic stem cells (HSCs), mean that curing most patients with SCD could soon be a reality in wealthy countries. In parallel, ongoing research is pursuing more facile treatments, such as in-vivo-delivered genetic therapies and new drugs that can eventually be administered in low- and middle-income countries where most SCD patients reside.

Activation of γ-globin expression by hypoxia-inducible factor 1α

Around birth, globin expression in human red blood cells (RBCs) shifts from γ-globin to β-globin, which results in fetal haemoglobin (HbF, α2γ2) being gradually replaced by adult haemoglobin (HbA, α2β2)1. This process has motivated the development of innovative approaches to treat sickle cell disease and β-thalassaemia by increasing HbF levels in postnatal RBCs2. Here we provide therapeutically relevant insights into globin gene switching obtained through a CRISPR-Cas9 screen for ubiquitin-proteasome components that regulate HbF expression. In RBC precursors, depletion of the von Hippel-Lindau (VHL) E3 ubiquitin ligase stabilized its ubiquitination target, hypoxia-inducible factor 1α (HIF1α)3,4, to induce γ-globin gene transcription. Mechanistically, HIF1α-HIF1β heterodimers bound cognate DNA elements in BGLT3, a long noncoding RNA gene located 2.7 kb downstream of the tandem γ-globin genes HBG1 and HBG2. This was followed by the recruitment of transcriptional activators, chromatin opening and increased long-range interactions between the γ-globin genes and their upstream enhancer. Similar induction of HbF occurred with hypoxia or with inhibition of prolyl hydroxylase domain enzymes that target HIF1α for ubiquitination by the VHL E3 ubiquitin ligase. Our findings link globin gene regulation with canonical hypoxia adaptation, provide a mechanism for HbF induction during stress erythropoiesis and suggest a new therapeutic approach for β-haemoglobinopathies.

Transmembrane Protein ANTXR1 Regulates γ-Globin Expression by Targeting the Wnt/β-Catenin Signaling Pathway

Reactivation of fetal hemoglobin (HbF, α2γ2) alleviates clinical symptoms in patients with β-thalassemia and sickle cell disease, although the regulatory mechanisms of γ-globin expression have not yet been fully elucidated. Recent studies found that interfering with the expression of the membrane protein ANTXR1 gene upregulated γ-globin levels. However, the exact mechanism by which ANTXR1 regulates γ-globin levels remains unclear. Our study showed that overexpression and knockdown of ANTXR1 in K562, cord blood CD34⁺, and HUDEP-2 cells decreased and increased γ-globin expression, respectively. ANTXR1 regulates the reactivation of fetal hemoglobin (HbF, α2γ2) in K562, cord blood CD34⁺, and adult peripheral blood CD34⁺ cells through interaction with LRP6 to promote the nuclear entry of β-catenin and activate the Wnt/β-catenin signaling pathway. The overexpression or knockdown of ANTXR1 on γ-globin and Wnt/β-catenin signaling in K562 cells was reversed by the inhibitor XAV939 and the activator LiCl, respectively, where XAV939 inhibits the transcription of β-catenin in the Wnt pathway, but LiCl inhibits GSK3-β. We also showed that the binding ability of the rank4 site in the transcriptional regulatory region of the SOX6 gene to c-Jun was significantly increased after overexpression of ANTXR1 in K562 cells. SOX6 protein expression was increased significantly after overexpression of the c-Jun gene, indicating that the transcription factor c-Jun initiated the transcription of SOX6, thereby silencing γ-globin. Our findings may provide a new intervention target for the treatment of β-hemoglobinopathies.

Down-regulation of the transcriptional repressor ZNF802 (JAZF1) reactivates fetal hemoglobin in β0-thalassemia/HbE

Reactivating of fetal hemoglobin (HbF; α2γ2) can ameliorate the severity of β-thalassemia disease by compensating for adult hemoglobin deficiency in patients. Previously, microarray analysis revealed that zinc finger protein (ZNF)802 (also known as Juxta-posed with another zinc finger gene-1 (JAZF1)) was upregulated in human erythroblasts derived from adult peripheral blood compared with fetal liver-derived cells, implying a potential role as a HbF repressor. However, deficiency in ZNF802 induced by lentiviral shRNA in β⁰-thalassemia/hemoglobinE erythroblasts had no effect on erythroblast proliferation and differentiation. Remarkably, the induction of HBG expression was observed at the transcriptional and translational levels resulting in an increase of HbF to 35.0 ± 3.5%. Interestingly, the embryonic globin transcripts were also upregulated but the translation of embryonic globin was not detected. These results suggest ZNF802 might be a transcriptional repressor of the γ-globin gene in adult erythroid cells.

Comparison of transcriptome profiles of nucleated red blood cells in cord blood between preterm and full-term neonates

BACKGROUND

The reactivation of fetal γ-globin expression is an effective strategy for ameliorating the clinical symptoms of β-hemoglobinopathies. However, the mechanism of globin switching, especially the roles of long non-coding RNAs (lncRNAs) in this process, remains elusive.

METHODS

We compared the in vivo transcriptome profiles of nucleated red blood cells (NRBCs) isolated from the umbilical cord blood of preterm and full-term newborns. We collected 75 umbilical cord blood samples and performed qPCR of the candidate genes.

RESULTS

In this study, we identified 7,166 differentially expressed protein-coding genes, 3,243 differentially expressed lncRNAs, and 79 differentially expressed microRNAs. Our data show that the Fanconi anemia pathway and the H19/let-7/LIN28B axis may be involved in γ- to β-globin gene switching. Moreover, we constructed the hub gene network of the differentially expressed transcription factors. Based on qPCR, we found that BCL11A was differentially expressed based on biological sex. We also confirmed that H19 is differentially expressed and established the H19-related network to reveal the potential regulatory mechanisms.

CONCLUSION

We present the profiles of the in vivo transcriptome differences of NRBCs between preterm and full-term neonates for the first time, and provide novel research targets for β-hemoglobinopathies.

Essay the (unusual) heuristic value of Hox gene clusters; a matter of time?

Ever since their first report in 1984, Antennapedia-type homeobox (Hox) genes have been involved in such a series of interesting observations, in particular due to their conserved clustered organization between vertebrates and arthropods, that one may legitimately wonder about the origin of this heuristic value. In this essay, I first consider different examples where Hox gene clusters have been instrumental in providing conceptual advances, taken from various fields of research and mostly involving vertebrate embryos. These examples touch upon our understanding of genomic evolution, the revisiting of 19th century views on the relationships between development and evolution and the building of a new framework to understand long-range and pleiotropic gene regulation during development. I then discuss whether the high value of the Hox gene family, when considered as an epistemic object, is related to its clustered structure (and the absence thereof in some animal species) and, if so, what is it in such particular genetic oddities that made them so generous in providing the scientific community with interesting information.

Multiplex CRISPR/Cas9 genome editing in hematopoietic stem cells for fetal hemoglobin reinduction generates chromosomal translocations

Sickle cell disease and β-thalassemia are common monogenic disorders that cause significant morbidity and mortality globally. The only curative treatment currently is allogeneic hematopoietic stem cell transplantation, which is unavailable to many patients due to a lack of matched donors and carries risks including graft-versus-host disease. Genome editing therapies targeting either the BCL11A erythroid enhancer or the HBG promoter are already demonstrating success in reinducing fetal hemoglobin. However, where a single locus is targeted, reliably achieving levels high enough to deliver an effective cure remains a challenge. We investigated the application of a CRISPR/Cas9 multiplex genome editing approach, in which both the BCL11A erythroid enhancer and HBG promoter are disrupted within human hematopoietic stem cells. We demonstrate superior fetal hemoglobin reinduction with this dual-editing approach without compromising engraftment or lineage differentiation potential of edited cells post-xenotransplantation. However, multiplex editing consistently resulted in the generation of chromosomal rearrangement events that persisted in vivo following transplantation into immunodeficient mice. The risk of oncogenic events resulting from such translocations therefore currently prohibits its clinical translation, but it is anticipated that, in the future, alternative editing platforms will help alleviate this risk.

The Alberta Newborn Screening Approach for Sickle Cell Disease: The Advantages of Molecular Testing

Sickle cell disease (SCD), a group of inherited red blood cell (RBC) disorders caused by pathogenic variants in the beta-globin gene (HBB), can cause lifelong disabilities and/or early mortality. If diagnosed early, preventative measures significantly reduce adverse outcomes related to SCD. In Alberta, Canada, SCD was added to the newborn screening (NBS) panel in April 2019. The primary conditions screened for are sickle cell anemia (HbS/S), HbS/C disease, and HbS/β thalassemia. In this study, we retrospectively analyzed the first 19 months of SCD screening performance, as well as described our approach for screening of infants that have received a red blood cell transfusion prior to collection of NBS specimen. Hemoglobins eluted from dried blood spots were analyzed using the Bio-Rad™ VARIANT nbs analyzer (Bio-Rad Laboratories, Inc., Hercules, CA, USA). Targeted sequencing of HBB was performed concurrently in samples from all transfused infants. During the period of this study, 43 of 80,314 screened infants received a positive NBS result for SCD, and of these, 34 were confirmed by diagnostic testing, suggesting a local SCD incidence of 1:2400 births. There were 608 infants with sickle cell trait, resulting in a carrier frequency of 1:130. Over 98% of non-transfused infants received their NBS results within 10 days of age. Most of the 188 transfused infants and 2 infants who received intrauterine transfusions received their final SCD screen results within 21 ± 10 d of birth. Our SCD screening algorithm enables detection of affected newborns on the initial NBS specimen, independent of the reported blood transfusion status.

Recent Approaches for Manipulating Globin Gene Expression in Treating Hemoglobinopathies

Tissue oxygenation throughout life depends on the activity of hemoglobin (Hb) one of the hemeproteins that binds oxygen in the lungs and secures its delivery throughout the body. Hb is composed of four monomers encoded by eight different genes the expression of which is tightly regulated during development, resulting in the formation of distinct hemoglobin tetramers in each developmental stage. Mutations that alter hemoglobin structure or its regulated expression result in a large group of diseases typically referred to as hemoglobinopathies that are amongst the most common genetic defects worldwide. Unprecedented efforts in the last decades have partially unraveled the complex mechanisms that control globin gene expression throughout development. In addition, genome wide association studies have revealed protective genetic traits capable of ameliorating the clinical manifestations of severe hemoglobinopathies. This knowledge has fueled the exploration of innovative therapeutic approaches aimed at modifying the genome or the epigenome of the affected cells to either restore hemoglobin function or to mimic the effect of protective traits. Here we describe the key steps that control the switch in gene expression that concerns the different globin genes during development and highlight the latest efforts in altering globin regulation for therapeutic purposes.

Thalassemias: From gene to therapy

Thalassemias (α, β, γ, δ, δβ, and εγδβ) are the most common genetic disorders worldwide and constitute a heterogeneous group of hereditary diseases characterized by the deficient synthesis of one or more hemoglobin (Hb) chain(s). This leads to the accumulation of unstable non-thalassemic Hb chains, which precipitate and cause intramedullary destruction of erythroid precursors and premature lysis of red blood cells (RBC) in the peripheral blood. Non-thalassemic Hbs display high oxygen affinity and no cooperativity. Thalassemias result from many different genetic and molecular defects leading to either severe or clinically silent hematologic phenotypes. Thalassemias α and β are particularly diffused in the regions spanning from the Mediterranean basin through the Middle East, Indian subcontinent, Burma, Southeast Asia, Melanesia, and the Pacific Islands, whereas δβ-thalassemia is prevalent in some Mediterranean regions including Italy, Greece, and Turkey. Although in the world thalassemia and malaria areas overlap apparently, the RBC protection against malaria parasites is openly debated. Here, we provide an overview of the historical, geographic, genetic, structural, and molecular pathophysiological aspects of thalassemias. Moreover, attention has been paid to molecular and epigenetic pathways regulating globin gene expression and globin switching. Challenges of conventional standard treatments, including RBC transfusions and iron chelation therapy, splenectomy and hematopoietic stem cell transplantation from normal donors are reported. Finally, the progress made by rapidly evolving fields of gene therapy and gene editing strategies, already in pre-clinical and clinical evaluation, and future challenges as novel curative treatments for thalassemia are discussed.

TEA domain transcription factor 4 modulates repression of fetal haemoglobin by direct binding to the γ-globin gene promoters

Re-activation of fetal haemoglobin (HbF) has been proved to be an effective strategy for the treatment of β-haemoglobinopathies. In this study, we identified TEA domain transcription factor 4 (TEAD4) as a new potential regulator of HbF by integrating public data sets with quantitative polymerase chain reaction analysis in β-thalassaemia patients. Significant negative correlation was observed between the expression of TEAD4 and HbF levels in β-thalassaemia patients. Functional validations of TEAD4 inhibition in both β-thalassaemia CD34⁺ cells and HUDEP-2 cells indicated that depletion of TEAD4 led to a significant increase of HbF. Finally, we identified a binding motif of TEAD4 on γ-globin gene promoters; its disruption consistently led to de-repression of HbF. Taken together, these results demonstrate that TEAD4 could act as a transcriptional inhibitor of the γ-globin gene through direct binding on its promoter. Our findings demonstrate a novel role of TEAD4 on the regulation of HbF, which may benefit patients with β-haemoglobinopathies.

Reproducible immortalization of erythroblasts from multiple stem cell sources provides approach for sustainable RBC therapeutics

Developing robust methodology for the sustainable production of red blood cells in vitro is essential for providing an alternative source of clinical-quality blood, particularly for individuals with rare blood group phenotypes. Immortalized erythroid progenitor cell lines are the most promising emergent technology for achieving this goal. We previously created the erythroid cell line BEL-A from bone marrow CD34⁺ cells that had improved differentiation and enucleation potential compared to other lines reported. In this study we show that our immortalization approach is reproducible for erythroid cells differentiated from bone marrow and also from far more accessible peripheral and cord blood CD34⁺ cells, consistently generating lines with similar improved erythroid performance. Extensive characterization of the lines shows them to accurately recapitulate their primary cell equivalents and provides a molecular signature for immortalization. In addition, we show that only cells at a specific stage of erythropoiesis, predominantly proerythroblasts, are amenable to immortalization. Our methodology provides a step forward in the drive for a sustainable supply of red cells for clinical use and for the generation of model cellular systems for the study of erythropoiesis in health and disease, with the added benefit of an indefinite expansion window for manipulation of molecular targets.

A natural DNMT1 mutation elevates the fetal hemoglobin level via epigenetic derepression of the γ-globin gene in β-thalassemia

DNA methyltransferase 1 (DNMT1) is a major epigenetic regulator of the formation of large macromolecular complexes that repress human γ-globin expression by maintaining DNA methylation. However, very little is known about the association of DNMT1 variants with β-thalassemia phenotypes. We systematically investigated associations between variants in DNMT1 and phenotypes in 1142 β-thalassemia subjects and identified a novel missense mutation (c.2633G>A, S878F) in the DNMT1 bromo-adjacent homology-1 (BAH1) domain. We functionally characterized this mutation in CD34+ cells from patients and engineered HuDEP-2 mutant cells. Our results demonstrate that DNMT1 phosphorylation is abrogated by substituting serine with phenylalanine at position 878, resulting in lower stability and catalytic activity loss. S878F mutation also attenuated DNMT1 interactions with BCL11A, GATA1, and HDAC1/2, and reduced recruitment of DNMT1 to the γ-globin (HBG) promoters, leading to epigenetic derepression of γ-globin expression. By analyzing the F-cell pattern, we demonstrated that the effect of DNMT1 mutation on increased fetal hemoglobin (HbF) is heterocellular. Furthermore, introduction of S878F mutation into erythroid cells by clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) recapitulated γ-globin reactivation. Thus, the natural S878F DNMT1 mutation is a novel modulator of HbF synthesis and represents a potential new therapeutic target for β-hemoglobinopathies.

Reactivation of a developmentally silenced embryonic globin gene

The α- and β-globin loci harbor developmentally expressed genes, which are silenced throughout post-natal life. Reactivation of these genes may offer therapeutic approaches for the hemoglobinopathies, the most common single gene disorders. Here, we address mechanisms regulating the embryonically expressed α-like globin, termed ζ-globin. We show that in embryonic erythroid cells, the ζ-gene lies within a ~65 kb sub-TAD (topologically associating domain) of open, acetylated chromatin and interacts with the α-globin super-enhancer. By contrast, in adult erythroid cells, the ζ-gene is packaged within a small (~10 kb) sub-domain of hypoacetylated, facultative heterochromatin within the acetylated sub-TAD and that it no longer interacts with its enhancers. The ζ-gene can be partially re-activated by acetylation and inhibition of histone de-acetylases. In addition to suggesting therapies for severe α-thalassemia, these findings illustrate the general principles by which reactivation of developmental genes may rescue abnormalities arising from mutations in their adult paralogues.

Genome-based therapeutic interventions for β-type hemoglobinopathies

For decades, various strategies have been proposed to solve the enigma of hemoglobinopathies, especially severe cases. However, most of them seem to be lagging in terms of effectiveness and safety. So far, the most prevalent and promising treatment options for patients with β-types hemoglobinopathies, among others, predominantly include drug treatment and gene therapy. Despite the significant improvements of such interventions to the patient's quality of life, a variable response has been demonstrated among different groups of patients and populations. This is essentially due to the complexity of the disease and other genetic factors. In recent years, a more in-depth understanding of the molecular basis of the β-type hemoglobinopathies has led to significant upgrades to the current technologies, as well as the addition of new ones attempting to elucidate these barriers. Therefore, the purpose of this article is to shed light on pharmacogenomics, gene addition, and genome editing technologies, and consequently, their potential use as direct and indirect genome-based interventions, in different strategies, referring to drug and gene therapy. Furthermore, all the latest progress, updates, and scientific achievements for patients with β-type hemoglobinopathies will be described in detail.

Single-nucleotide-level mapping of DNA regulatory elements that control fetal hemoglobin expression

Pinpointing functional noncoding DNA sequences and defining their contributions to health-related traits is a major challenge for modern genetics. We developed a high-throughput framework to map noncoding DNA functions with single-nucleotide resolution in four loci that control erythroid fetal hemoglobin (HbF) expression, a genetically determined trait that modifies sickle cell disease (SCD) phenotypes. Specifically, we used the adenine base editor ABEmax to introduce 10,156 separate A•T to G•C conversions in 307 predicted regulatory elements and quantified the effects on erythroid HbF expression. We identified numerous regulatory elements, defined their epigenomic structures and linked them to low-frequency variants associated with HbF expression in an SCD cohort. Targeting a newly discovered γ-globin gene repressor element in SCD donor CD34+ hematopoietic progenitors raised HbF levels in the erythroid progeny, inhibiting hypoxia-induced sickling. Our findings reveal previously unappreciated genetic complexities of HbF regulation and provide potentially therapeutic insights into SCD.

Research in Sickle Cell Disease: From Bedside to Bench to Bedside

Sickle cell disease (SCD) is an exemplar of bidirectional translational research, starting with a remarkable astute observation of the abnormally shaped red blood cells that motivated decades of bench research that have now translated into new drugs and genetic therapies. Introduction of hydroxyurea (HU) therapy, the only SCD-modifying treatment for >30 years and now standard care, was initiated through another clinical observation by a pediatrician. While the clinical efficacy of HU is primarily due to its fetal hemoglobin (HbF) induction, the exact mechanism of how it increases HbF remains not fully understood. Unraveling of the molecular mechanism of how HU increases HbF has provided insights on the development of new HbF-reactivating agents in the pipeline. HU has other salutary effects, reduction of cellular adhesion to the vascular endothelium and inflammation, and dissecting these mechanisms has informed bench-both cellular and animal-research for development of the 3 recently approved agents: endari, voxelotor, and crizanlizumab; truly, a bidirectional bench to bedside translation. Decades of research to understand the mechanisms of fetal to adult hemoglobin have also culminated in promising anti-sickling genetic therapies and the first-in-human studies of reactivating an endogenous (γ-globin) gene HBG utilizing innovative genomic approaches.

ZNF410 represses fetal globin by singular control of CHD4

Known fetal hemoglobin (HbF) silencers have potential on-target liabilities for rational β-hemoglobinopathy therapeutic inhibition. Here, through transcription factor (TF) CRISPR screening, we identify zinc-finger protein (ZNF) 410 as an HbF repressor. ZNF410 does not bind directly to the genes encoding γ-globins, but rather its chromatin occupancy is concentrated solely at CHD4, encoding the NuRD nucleosome remodeler, which is itself required for HbF repression. CHD4 has two ZNF410-bound regulatory elements with 27 combined ZNF410 binding motifs constituting unparalleled genomic clusters. These elements completely account for the effects of ZNF410 on fetal globin repression. Knockout of ZNF410 or its mouse homolog Zfp410 reduces CHD4 levels by 60%, enough to substantially de-repress HbF while eluding cellular or organismal toxicity. These studies suggest a potential target for HbF induction for β-hemoglobin disorders with a wide therapeutic index. More broadly, ZNF410 represents a special class of gene regulator, a conserved TF with singular devotion to regulation of a chromatin subcomplex.

Epigenetic inactivation of ERF reactivates γ-globin expression in β-thalassemia

The fetal-to-adult hemoglobin switch is regulated in a developmental stage-specific manner and reactivation of fetal hemoglobin (HbF) has therapeutic implications for treatment of β-thalassemia and sickle cell anemia, two major global health problems. Although significant progress has been made in our understanding of the molecular mechanism of the fetal-to-adult hemoglobin switch, the mechanism of epigenetic regulation of HbF silencing remains to be fully defined. Here, we performed whole-genome bisulfite sequencing and RNA sequencing analysis of the bone marrow-derived GYPA⁺ erythroid cells from β-thalassemia-affected individuals with widely varying levels of HbF groups (HbF ≥ 95th percentile or HbF ≤ 5th percentile) to screen epigenetic modulators of HbF and phenotypic diversity of β-thalassemia. We identified an ETS2 repressor factor encoded by ERF, whose promoter hypermethylation and mRNA downregulation are associated with high HbF levels in β-thalassemia. We further observed that hypermethylation of the ERF promoter mediated by enrichment of DNMT3A leads to demethylation of γ-globin genes and attenuation of binding of ERF on the HBG promoter and eventually re-activation of HbF in β-thalassemia. We demonstrated that ERF depletion markedly increased HbF production in human CD34⁺ erythroid progenitor cells, HUDEP-2 cell lines, and transplanted NCG-Kit-V831M mice. ERF represses γ-globin expression by directly binding to two consensus motifs regulating γ-globin gene expression. Importantly, ERF depletion did not affect maturation of erythroid cells. Identification of alterations in DNA methylation of ERF as a modulator of HbF synthesis opens up therapeutic targets for β-hemoglobinopathies.

Distinct miRNA Signatures and Networks Discern Fetal from Adult Erythroid Differentiation and Primary from Immortalized Erythroid Cells

MicroRNAs (miRNAs) are small non-coding RNAs crucial for post-transcriptional and translational regulation of cellular and developmental pathways. The study of miRNAs in erythropoiesis elucidates underlying regulatory mechanisms and facilitates related diagnostic and therapy development. Here, we used DNA Nanoball (DNB) small RNA sequencing to comprehensively characterize miRNAs in human erythroid cell cultures. Based on primary human peripheral-blood-derived CD34+ (hCD34+) cells and two influential erythroid cell lines with adult and fetal hemoglobin expression patterns, HUDEP-2 and HUDEP-1, respectively, our study links differential miRNA expression to erythroid differentiation, cell type, and hemoglobin expression profile. Sequencing results validated by reverse-transcription quantitative PCR (RT-qPCR) of selected miRNAs indicate shared differentiation signatures in primary and immortalized cells, characterized by reduced overall miRNA expression and reciprocal expression increases for individual lineage-specific miRNAs in late-stage erythropoiesis. Despite the high similarity of same-stage hCD34+ and HUDEP-2 cells, differential expression of several miRNAs highlighted informative discrepancies between both cell types. Moreover, a comparison between HUDEP-2 and HUDEP-1 cells displayed changes in miRNAs, transcription factors (TFs), target genes, and pathways associated with globin switching. In resulting TF-miRNA co-regulatory networks, major therapeutically relevant regulators of globin expression were targeted by many co-expressed miRNAs, outlining intricate combinatorial miRNA regulation of globin expression in erythroid cells.

Extracellular laminin regulates hematopoietic potential of pluripotent stem cells through integrin β1-ILK-β-catenin-JUN axis

Recombinant matrices have enabled feeder cell-free maintenance cultures of human pluripotent stem cells (hPSCs), with laminin 511-E8 fragment (LM511-E8) being widely used. However, we herein report that hPSCs maintained on LM511-E8 resist differentiating to multipotent hematopoietic progenitor cells (HPCs), unlike hPSCs maintained on LM421-E8 or LM121-E8. The latter two LM-E8s bound weakly to hPSCs compared with LM511-E8 and activated the canonical Wnt/β-catenin signaling pathway. Moreover, the extracellular LM-E8-dependent preferential hematopoiesis was associated with a higher expression of integrin β1 (ITGB1) and downstream integrin-linked protein kinase (ILK), β-catenin and phosphorylated JUN. Accordingly, the lower coating concentration of LM511-E8 or addition of a Wnt/β-catenin signaling activator, CHIR99021, facilitated higher HPC yield. In contrast, the inhibition of ILK, Wnt or JNK by inhibitors or mRNA knockdown suppressed the HPC yield. These findings suggest that extracellular laminin scaffolds modulate the hematopoietic differentiation potential of hPSCs by activating the ITGB1-ILK-β-catenin-JUN axis at the undifferentiated stage. Finally, the combination of low-concentrated LM511-E8 and a revised hPSC-sac method, which adds bFGF, SB431542 and heparin to the conventional method, enabled a higher yield of HPCs and higher rate for definitive hematopoiesis, suggesting a useful protocol for obtaining differentiated hematopoietic cells from hPSCs in general.

Gene Therapy for Inherited Bleeding Disorders

Decades of preclinical and clinical studies developing gene therapy for hemophilia are poised to bear fruit with current promising pivotal studies likely to lead to regulatory approval. However, this recent success should not obscure the multiple challenges that were overcome to reach this destination. Gene therapy for hemophilia A and B benefited from advancements in the general gene therapy field, such as the development of adeno-associated viral vectors, as well as disease-specific breakthroughs, like the identification of B-domain deleted factor VIII and hyperactive factor IX Padua. The gene therapy field has also benefited from hemophilia B clinical studies, which revealed for the first time critical safety concerns related to immune responses to the vector capsid not anticipated in preclinical models. Preclinical studies have also investigated gene transfer approaches for other rare inherited bleeding disorders, including factor VII deficiency, von Willebrand disease, and Glanzmann thrombasthenia. Here we review the successful gene therapy journey for hemophilia and pose some unanswered questions. We then discuss the current state of gene therapy for these other rare inherited bleeding disorders and how the lessons of hemophilia gene therapy may guide clinical development.

A Small Key for a Heavy Door: Genetic Therapies for the Treatment of Hemoglobinopathies

Throughout the past decades, the search for a treatment for severe hemoglobinopathies has gained increased interest within the scientific community. The discovery that ɤ-globin expression from intact HBG alleles complements defective HBB alleles underlying β-thalassemia and sickle cell disease, has provided a promising opening for research directed at relieving ɤ-globin repression mechanisms and, thereby, improve clinical outcomes for patients. Various gene editing strategies aim to reverse the fetal-to-adult hemoglobin switch to up-regulate ɤ-globin expression through disabling either HBG repressor genes or repressor binding sites in the HBG promoter regions. In addition to these HBB mutation-independent strategies involving fetal hemoglobin (HbF) synthesis de-repression, the expanding genome editing toolkit is providing increased accuracy to HBB mutation-specific strategies encompassing adult hemoglobin (HbA) restoration for a personalized treatment of hemoglobinopathies. Moreover, besides genome editing, more conventional gene addition strategies continue under investigation to restore HbA expression. Together, this research makes hemoglobinopathies a fertile ground for testing various innovative genetic therapies with high translational potential. Indeed, the progressive understanding of the molecular clockwork underlying the hemoglobin switch together with the ongoing optimization of genome editing tools heightens the prospect for the development of effective and safe treatments for hemoglobinopathies. In this context, clinical genetics plays an equally crucial role by shedding light on the complexity of the disease and the role of ameliorating genetic modifiers. Here, we cover the most recent insights on the molecular mechanisms underlying hemoglobin biology and hemoglobinopathies while providing an overview of state-of-the-art gene editing platforms. Additionally, current genetic therapies under development, are equally discussed.

Therapeutic gene editing strategies using CRISPR-Cas9 for the β-hemoglobinopathies

With advancements in gene editing technologies, our ability to make precise and efficient modifications to the genome is increasing at a remarkable rate, paving the way for scientists and clinicians to uniquely treat a multitude of previously irremediable diseases. CRISPR-Cas9, short for clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9, is a gene editing platform with the ability to alter the nucleotide sequence of the genome in living cells. This technology is increasing the number and pace at which new gene editing treatments for genetic disorders are moving toward the clinic. The β-hemoglobinopathies are a group of monogenic diseases, which despite their high prevalence and chronic debilitating nature, continue to have few therapeutic options available. In this review, we will discuss our existing comprehension of the genetics and current state of treatment for β-hemoglobinopathies, consider potential genome editing therapeutic strategies, and provide an overview of the current state of clinical trials using CRISPR-Cas9 gene editing.

Epigenetic regulation of hemoglobin switching in non-human primates

Human hemoglobin switching describes the highly regulated, sequential expression of the 5 β-like globin genes (HBE, HBG2, HBG1, HBD and HBB) of the human β-globin gene complex. The sequential activation of these β or β-like globin genes during human development from early embryonic through late fetal ('adult') stages, and during erythroid maturation, occurs in an order corresponding to their 5' to 3' location on chromosome 11. The β-hemoglobinopathies are the most common inherited diseases in humanity, and are diseases of mutated HBB or its altered regulation. Since the other β-like globin genes can potentially substitute for defective HBB, much translational research is directed toward understanding and manipulating sequential activation at the human β-globin gene complex to treat β-hemoglobinopathies. Non-human primates provide a vital contribution to such efforts because of their recapitulation of the developmental/maturational switch in hemoglobin production as observed in humans (mice do not model this switch). Valuable insights into druggable epigenetic forces that mediate the switch have been thereby gained. We review important lessons learned in non-human primates, complemented by other studies, and suggest rational next steps.

Targeted Protein Degradation as a Promising Tool for Epigenetic Upregulation of Fetal Hemoglobin

The level of fetal hemoglobin (HbF) is an important disease modifier for β-thalassemia and sickle cell disease patients. Indeed, genetic tinkering with the HbF repression machinery has demonstrated great potential for disease mitigation. Such genetic treatments are costly and the high incidence of β-hemoglobinopathies in low-income countries, therefore, calls for the development of affordable, off-the-shelf, oral treatments. The use of PROTAC (PRoteolysis TArgeting Chimeras) technology to influence the epigenetic mechanisms involved in HbF suppression may provide a solution. In this minireview, we briefly explain the HbF repression network highlighting the epigenetic factors that could be targeted for degradation by PROTACs. We hope that this review will inspire clinicians, molecular and chemical biologists to collaborate and contribute to this fascinating field, which should ultimately deliver drugs that reactivate HbF expression with high specificity and low toxicity.

PLGA-Nanoparticles for Intracellular Delivery of the CRISPR-Complex to Elevate Fetal Globin Expression in Erythroid Cells

Ex vivo gene editing of CD34⁺ hematopoietic stem and progenitor cells (HSPCs) offers great opportunities to develop new treatments for a number of malignant and non-malignant diseases. Efficient gene-editing in HSPCs has been achieved using electroporation and/or viral transduction to deliver the CRISPR-complex, but cellular toxicity is a drawback of currently used methods. Nanoparticle (NP)-based gene-editing strategies can further enhance the gene-editing potential of HSPCs and provide a delivery system for in vivo application. Here, we developed CRISPR/Cas9-PLGA-NPs efficiently encapsulating Cas9 protein, single gRNA and a fluorescent probe. The initial 'burst' of Cas9 and gRNA release was followed by a sustained release pattern. CRISPR/Cas9-PLGA-NPs were taken up and processed by human HSPCs, without inducing cellular cytotoxicity. Upon escape from the lysosomal compartment, CRISPR/Cas9-PLGA-NPs-mediated gene editing of the γ-globin gene locus resulted in elevated expression of fetal hemoglobin (HbF) in primary erythroid cells. The development of CRISPR/Cas9-PLGA-NPs provides an attractive tool for the delivery of the CRISPR components to target HSPCs, and could provide the basis for in vivo treatment of hemoglobinopathies and other genetic diseases.

Fetal Hemoglobin in Sickle Hemoglobinopathies: High HbF Genotypes and Phenotypes

Fetal hemoglobin (HbF) usually consists of 4 to 10% of total hemoglobin in adults of African descent with sickle cell anemia. Rarely, their HbF levels reach more than 30%. High HbF levels are sometimes a result of β-globin gene deletions or point mutations in the promoters of the HbF genes. Collectively, the phenotype caused by these mutations is called hereditary persistence of fetal hemoglobin, or HPFH. The pancellularity of HbF associated with these mutations inhibits sickle hemoglobin polymerization in most sickle erythrocytes so that these patients usually have inconsequential hemolysis and few, if any, vasoocclusive complications. Unusually high HbF can also be associated with variants of the major repressors of the HbF genes, BCL11A and MYB. Perhaps most often, we lack an explanation for very high HbF levels in sickle cell anemia.