KLF1-null neonates display hydrops fetalis and a deranged erythroid transcriptome

Mutations in linker-2 of KLF1 impair expression of membrane transporters and cytoskeletal proteins causing hemolysis

The SP/KLF family of transcription factors harbour three C-terminal C2H2 zinc fingers interspersed by two linkers which confers DNA-binding to a 9-10 bp motif. Mutations in KLF1, the founding member of the family, are common. Missense mutations in linker two result in a mild phenotype. However, when co-inherited with loss-of-function mutations, they result in severe non-spherocytic hemolytic anemia. We generate a mouse model of this disease by crossing Klf1+/- mice with Klf1H350R/+ mice that harbour a missense mutation in linker-2. Klf1H350R/- mice exhibit severe hemolysis without thalassemia. RNA-seq demonstrate loss of expression of genes encoding transmembrane and cytoskeletal proteins, but not globins. ChIP-seq show no change in DNA-binding specificity, but a global reduction in affinity, which is confirmed using recombinant proteins and in vitro binding assays. This study provides new insights into how linker mutations in zinc finger transcription factors result in different phenotypes to those caused by loss-of-function mutations.

Epigenetic dissection of human blood group genes reveals regulatory elements and detailed characteristics of KEL and four other loci

BACKGROUND

Blood typing is essential for safe transfusions and is performed serologically or genetically. Genotyping predominantly focuses on coding regions, but non-coding variants may affect gene regulation, as demonstrated in the ABO, FY and XG systems. To uncover regulatory loci, we expanded a recently developed bioinformatics pipeline for discovery of non-coding variants by including additional epigenetic datasets.

METHODS

Multiple datasets including ChIP-seq with erythroid transcription factors (TFs), histone modifications (H3K27ac, H3K4me1), and chromatin accessibility (ATAC-seq) were analyzed. Candidate regulatory regions were investigated for activity (luciferase assays) and TF binding (electrophoretic mobility shift assay, EMSA, and mass spectrometry, MS).

RESULTS

In total, 814 potential regulatory sites in 47 blood-group-related genes were identified where one or more erythroid TFs bound. Enhancer candidates in CR1, EMP3, ABCB6, and ABCC4 indicated by ATAC-seq, histone markers, and co-occupancy of 4 TFs (GATA1/KLF1/RUNX1/NFE2) were investigated but only CR1 and ABCC4 showed increased transcription. Co-occupancy of GATA1 and KLF1 was observed in the KEL promoter, previously reported to contain GATA1 and Sp1 sites. TF binding energy scores decreased when three naturally occurring variants were introduced into GATA1 and KLF1 motifs. Two of three GATA1 sites and the KLF1 site were confirmed functionally. EMSA and MS demonstrated increased GATA1 and KLF1 binding to the wild-type compared to variant motifs.

DISCUSSION

This combined bioinformatics and experimental approach revealed multiple candidate regulatory regions and predicted TF co-occupancy sites. The KEL promoter was characterized in detail, indicating that two adjacent GATA1 and KLF1 motifs are most crucial for transcription.

The GWAS SNP rs80207740 modulates erythrocyte traits via allele-specific binding of IKZF1 and targeting XPO7 gene

Genome-wide association studies have identified many single nucleotide polymorphisms (SNPs) associated with erythrocyte traits. However, the functional variants and their working mechanisms remain largely unknown. Here, we reported that the SNP of rs80207740, which was associated with red blood cell (RBC) volume and hemoglobin content across populations, conferred enhancer activity to XPO7 gene via allele-differentially binding to Ikaros family zinc finger 1 (IKZF1). We showed that the region around rs80207740 was an erythroid-specific enhancer using reporter assays, and that the G-allele further enhanced activity. 3D genome evidence showed that the enhancer interacted with the XPO7 promoter, and eQTL analysis suggested that the G-allele upregulated expression of XPO7. We further showed that the rs80207740-G allele facilitated the binding of transcription factor IKZF1 in EMSA and ChIP analyses. Knockdown of IKZF1 and GATA1 resulted in decreased expression of Xpo7 in both human and mouse erythroid cells. Finally, we constructed Xpo7 knockout mouse by CRISPR/Cas9 and observed anemic phenotype with reduced volume and hemoglobin content of RBC, consistent to the effect of rs80207740 on erythrocyte traits. Overall, our study demonstrated that rs80207740 modulated erythroid indices by regulating IKZF1 binding and Xpo7 expression.

Saracatinib prompts hemin-induced K562 erythroid differentiation but suppresses erythropoiesis of hematopoietic stem cells

Human myeloid leukemia cells (such as K562) could be used for the study of erythropoiesis, and mature erythroid markers and globins could be induced during leukemia cell differentiation; however, the pathways involved are different compared with those of hematopoietic stem cells (HSCs).We identified the differentially expressed genes (DEGs) of K562 cells and HSCs associated with stem cells and erythroid differentiation. Furthermore, we showed that hemin-induced differentiation of K562 cells could be induced by serum starvation or treatment with the tyrosine kinase inhibitor saracatinib. However, erythroid differentiation of HSCs was inhibited by the deprivation of the important serum component erythropoietin (EPO) or treatment with saracatinib. Finally, we found that the mRNA expression of K562 cells and HSCs was different during saracatinib-treated erythroid differentiation, and the DEGs of K562 cells and HSCs associated with tyrosine-protein kinase were identified.These findings elucidated the cellular phenomenon of saracatinib induction during erythroid differentiation of K562 cells and HSCs, and the potential mechanism is the different mRNA expression profile of tyrosine-protein kinase in K562 cells and HSCs.

Impact of transcription factors KLF1 and GATA1 on red blood cell antigen expression: a review

KLF transcription factor 1 (KLF1) and GATA binding protein 1 (GATA1) are transcription factors (TFs) that initiate and regulate transcription of the genes involved in erythropoiesis. These TFs possess DNA-binding domains that recognize specific nucleotide sequences in genes, to which they bind and regulate transcription. Variants in the genes that encode either KLF1 or GATA1 can result in a range of hematologic phenotypes-from benign to severe forms of thrombocytopenia and anemia; they can also weaken the expression of blood group antigens. The Lutheran (LU) blood group system is susceptible to TF gene variations, particularly KLF1 variants. Individuals heterozygous for KLF1 gene variants show reduced Lutheran antigens on red blood cells that are not usually detected by routine hemagglutination methods. This reduced antigen expression is referred to as the In(Lu) phenotype. For accurate blood typing, it is important to distinguish between the In(Lu) phenotype, which has very weak antigen expression, and the true Lunull phenotype, which has no antigen expression. The International Society of Blood Transfusion blood group allele database registers KLF1 and GATA1 variants associated with modified Lutheran expression. Here, we review KLF1 and recent novel gene variants defined through investigating blood group phenotype and genotype discrepancies or, for one report, investigating cases with unexplained chronic anemia. In addition, we include a review of the GATA1 TF, including a case report describing the second GATA1 variant associated with a serologic Lu(a-b-) phenotype. Finally, we review both past and recent reports on variations in the DNA sequence motifs on the blood group genes that disrupt the binding of the GATA1 TF and either remove or reduce erythroid antigen expression. This review highlights the diversity and complexity of the transcription process itself and the need to consider these factors as an added component for accurate blood group phenotyping.

Erythroid Krüppel-Like Factor (KLF1): A Surprisingly Versatile Regulator of Erythroid Differentiation

Erythroid Krüppel-like factor (KLF1), first discovered in 1992, is an erythroid-restricted transcription factor (TF) that is essential for terminal differentiation of erythroid progenitors. At face value, KLF1 is a rather inconspicuous member of the 26-strong SP/KLF TF family. However, 30 years of research have revealed that KLF1 is a jack of all trades in the molecular control of erythropoiesis. Initially described as a one-trick pony required for high-level transcription of the adult HBB gene, we now know that it orchestrates the entire erythroid differentiation program. It does so not only as an activator but also as a repressor. In addition, KLF1 was the first TF shown to be directly involved in enhancer/promoter loop formation. KLF1 variants underlie a wide range of erythroid phenotypes in the human population, varying from very mild conditions such as hereditary persistence of fetal hemoglobin and the In(Lu) blood type in the case of haploinsufficiency, to much more serious non-spherocytic hemolytic anemias in the case of compound heterozygosity, to dominant congenital dyserythropoietic anemia type IV invariably caused by a de novo variant in a highly conserved amino acid in the KLF1 DNA-binding domain. In this chapter, we present an overview of the past and present of KLF1 research and discuss the significance of human KLF1 variants.

Molecular and haematological characterisation of haemolytic anaemia associated with biallelic KLF1 mutations: a case series

AIMS

Krüppel-like factor 1 (KLF1) is an erythroid-specific transcription factor playing an important role in erythropoiesis and haemoglobin (Hb) switching. Biallelic KLF1 mutations can cause haemolytic anaemia with thalassaemia-like syndromes but are rarely reported. We explore the KLF1 mutations in Thai subjects with unexplainable haemolytic anaemia.

METHODS

The study was done on 57 subjects presented with haemolytic anaemia and elevated Hb F without β-thalassaemia diseases. Hb analysis was performed using capillary electrophoresis. Analyses of α-thalassaemia, β-thalassaemia and KLF1 genes were performed using PCR-based methods and DNA sequencing.

RESULTS

Thirteen subjects with compound heterozygous for a known and five new genetic KLF1 interactions were identified, including KLF1:c.519_525dupCGGCGCC/c.892G>C with class 3/2 (n=8), and each subject with new genetic interaction, including KLF1:c.-154C>T;643C>T/c.983G>A with class 3/2, KLF1:c.-154C>T;643C>T/c.809C>G with class 3/2, KLF1:c892G>C/c.983G>A with class 2/2, KLF1:c.892G>C/c.1001C>G with class 2/2 and KLF1:c.1001C>G/c.1003G>A with class 2/2. Most of them had anaemia with Hb levels ranging from 45 to 110 g/L, hypochromic microcytosis, aniso-poikilocytosis, increased Hb F levels (17.9%-47.4%), small amounts of Hb Bart's, regular blood transfusion, hyperbilirubinaemia, increased serum ferritin and nucleated red blood cell.

CONCLUSIONS

Biallelic KLF1 mutations associated with anaemia may not be uncommon in Thailand. Characteristics of haemolytic anaemia, abnormal red cell morphology with nucleated red blood cells and elevated Hb F, and presenting small amounts of Hb Bart's without thalassaemia diseases are useful markers to further investigation of the KLF1 gene.

A novel human cellular model of CDA IV enables comprehensive analysis revealing the molecular basis of the disease phenotype

Red blood cell disorders can result in severe anemia. One such disease congenital dyserythropoietic anemia IV (CDA IV) is caused by the heterozygous mutation E325K in the transcription factor KLF1. However, studying the molecular basis of CDA IV is severely impeded by the paucity of suitable and adequate quantities of material from patients with anemia and the rarity of the disease. We, therefore, took a novel approach, creating a human cellular disease model system for CDA IV that accurately recapitulates the disease phenotype. Next, using comparative proteomics, we reveal extensive distortion of the proteome and a wide range of disordered biological processes in CDA IV erythroid cells. These include downregulated pathways the governing cell cycle, chromatin separation, DNA repair, cytokinesis, membrane trafficking, and global transcription, and upregulated networks governing mitochondrial biogenesis. The diversity of such pathways elucidates the spectrum of phenotypic abnormalities that occur with CDA IV and impairment to erythroid cell development and survival, collectively explaining the CDA IV disease phenotype. The data also reveal far more extensive involvement of KLF1 in previously assigned biological processes, along with novel roles in the regulation of intracellular processes not previously attributed to this transcription factor. Overall, the data demonstrate the power of such a model cellular system to unravel the molecular basis of disease and how studying the effects of a rare mutation can reveal fundamental biology.

Identification of a genomic DNA sequence that quantitatively modulates KLF1 transcription factor expression in differentiating human hematopoietic cells

The onset of erythropoiesis is under strict developmental control, with direct and indirect inputs influencing its derivation from the hematopoietic stem cell. A major regulator of this transition is KLF1/EKLF, a zinc finger transcription factor that plays a global role in all aspects of erythropoiesis. Here, we have identified a short, conserved enhancer element in KLF1 intron 1 that is important for establishing optimal levels of KLF1 in mouse and human cells. Chromatin accessibility of this site exhibits cell-type specificity and is under developmental control during the differentiation of human CD34+ cells towards the erythroid lineage. This site binds GATA1, SMAD1, TAL1, and ETV6. In vivo editing of this region in cell lines and primary cells reduces KLF1 expression quantitatively. However, we find that, similar to observations seen in pedigrees of families with KLF1 mutations, downstream effects are variable, suggesting that the global architecture of the site is buffered towards keeping the KLF1 genetic region in an active state. We propose that modification of intron 1 in both alleles is not equivalent to complete loss of function of one allele.

Congenital dyserythropoietic anemia type IV in the genetic era: A rare neonatal case report of rapid identification with a review of the literature

Congenital dyserythropoietic anemia type IV (CDAIV) is a rare inherited hematological disorder, presenting with severe anemia due to altered erythropoiesis and hemolysis, with variable needs for recurrent transfusions. We present a case of a transfusion-dependent male newborn who presented at birth with severe hemolytic anemia, and required an intrauterine transfusion. Genetic testing rapidly identified a Kruppel-like factor 1 (KLF1) pathogenic variant (c.973G>A, p.E325K), known to be causative for CDAIV. This case highlights the advantages of next-generation sequencing testing for congenital hemolytic anemia: diagnostic speed, guidance on natural history, and optimized clinical management and anticipatory guidance for parents and clinicians. Additionally, we reviewed the literature for all CDAIV cases.

In Vitro Human Haematopoietic Stem Cell Expansion and Differentiation

The haematopoietic system plays an essential role in our health and survival. It is comprised of a range of mature blood and immune cell types, including oxygen-carrying erythrocytes, platelet-producing megakaryocytes and infection-fighting myeloid and lymphoid cells. Self-renewing multipotent haematopoietic stem cells (HSCs) and a range of intermediate haematopoietic progenitor cell types differentiate into these mature cell types to continuously support haematopoietic system homeostasis throughout life. This process of haematopoiesis is tightly regulated in vivo and primarily takes place in the bone marrow. Over the years, a range of in vitro culture systems have been developed, either to expand haematopoietic stem and progenitor cells or to differentiate them into the various haematopoietic lineages, based on the use of recombinant cytokines, co-culture systems and/or small molecules. These approaches provide important tractable models to study human haematopoiesis in vitro. Additionally, haematopoietic cell culture systems are being developed and clinical tested as a source of cell products for transplantation and transfusion medicine. This review discusses the in vitro culture protocols for human HSC expansion and differentiation, and summarises the key factors involved in these biological processes.

A Review of CRISPR Cas9 for SCA: Treatment Strategies and Could Target β-globin Gene and BCL11A Gene using CRISPR Cas9 Prevent the Patient from Sickle Cell Anemia?

BACKGROUND: Sickle cell anemia is a hereditary globin chain condition that leads to hemolysis and persistent organ damage. Chronic hemolytic anemia, severe acute and chronic pain, and end-organ destruction occur throughout the lifespan of sickle cell anemia. SCD is associated with a higher risk of mortality. Genome editing with CRISPR-associated regularly interspersed short palindromic repeats (CRISPR/Cas9) have therapeutic potential for sickle cell anemia thala. AIM: This research aimed to see if using CRISPR/Cas9 to target β-globin gene is an effective therapeutic and if it has a long-term effect on Sickle Cell Anemia. METHODS: The method used in this study summarizes the article by looking for keywords that have been determined in the title and abstract. The authors used official guidelines from Science Direct, PubMed, Google Scholar, and Journal Molecular Biology to select full-text articles published within the last decade, prioritizing searches within the past 10 years. RESULTS: CRISPR/Cas9-mediated genome editing in clinical trials contributes to α-globin gene deletion correcting β-thalassemia through balanced α- and β-globin ratios and inhibiting disease progression. CONCLUSION: HBB and BCL11A targeting by CRISPR/Cas9 deletion effectively inactivate BCL11A, a repressor of fetal hemoglobin production. However, further research is needed to determine its side effects and safety.

Krüppel-Like Factor 1: A Pivotal Gene Regulator in Erythropoiesis

Krüppel-like factor 1 (KLF1) plays a crucial role in erythropoiesis. In-depth studies conducted on mice and humans have highlighted its importance in erythroid lineage commitment, terminal erythropoiesis progression and the switching of globin genes from γ to β. The role of KLF1 in haemoglobin switching is exerted by the direct activation of β-globin gene and by the silencing of γ-globin through activation of BCL11A, an important γ-globin gene repressor. The link between KLF1 and γ-globin silencing identifies this transcription factor as a possible therapeutic target for β-hemoglobinopathies. Moreover, several mutations have been identified in the human genes that are responsible for various benign phenotypes and erythroid disorders. The study of the phenotype associated with each mutation has greatly contributed to the current understanding of the complex role of KLF1 in erythropoiesis. This review will focus on some of the principal functions of KLF1 on erythroid cell commitment and differentiation, spanning from primitive to definitive erythropoiesis. The fundamental role of KLF1 in haemoglobin switching will be also highlighted. Finally, an overview of the principal human mutations and relative phenotypes and disorders will be described.

Regulation of Heme Synthesis by Mitochondrial Homeostasis Proteins

Heme plays a central role in diverse, life-essential processes that range from ubiquitous, housekeeping pathways such as respiration, to highly cell-specific ones such as oxygen transport by hemoglobin. The regulation of heme synthesis and its utilization is highly regulated and cell-specific. In this review, we have attempted to describe how the heme synthesis machinery is regulated by mitochondrial homeostasis as a means of coupling heme synthesis to its utilization and to the metabolic requirements of the cell. We have focused on discussing the regulation of mitochondrial heme synthesis enzymes by housekeeping proteins, transport of heme intermediates, and regulation of heme synthesis by macromolecular complex formation and mitochondrial metabolism. Recently discovered mechanisms are discussed in the context of the model organisms in which they were identified, while more established work is discussed in light of technological advancements.

Molecular and cellular mechanisms that regulate human erythropoiesis

To enable effective oxygen transport, ∼200 billion red blood cells (RBCs) need to be produced every day in the bone marrow through the fine-tuned process of erythropoiesis. Erythropoiesis is regulated at multiple levels to ensure that defective RBC maturation or overproduction can be avoided. Here, we provide an overview of different layers of this control, ranging from cytokine signaling mechanisms that enable extrinsic regulation of RBC production to intrinsic transcriptional pathways necessary for effective erythropoiesis. Recent studies have also elucidated the importance of posttranscriptional regulation and highlighted additional gatekeeping mechanisms necessary for effective erythropoiesis. We additionally discuss the insights gained by studying human genetic variation affecting erythropoiesis and highlight the discovery of BCL11A as a regulator of hemoglobin switching through genetic studies. Finally, we provide an outlook of how our ability to measure multiple facets of this process at single-cell resolution, while accounting for the impact of human variation, will continue to refine our knowledge of erythropoiesis and how this process is perturbed in disease. As we learn more about this intricate and important process, additional opportunities to modulate erythropoiesis for therapeutic purposes will undoubtedly emerge.

Epigenetic and Transcriptional Control of Erythropoiesis

Erythropoiesis is a process of enormous magnitude, with the average person generating two to three million red cells every second. Erythroid progenitors start as large cells with large nuclei, and over the course of three to four cell divisions they undergo a dramatic decrease in cell size accompanied by profound nuclear condensation, which culminates in enucleation. As maturing erythroblasts are undergoing these dramatic phenotypic changes, they accumulate hemoglobin and express high levels of other erythroid-specific genes, while silencing much of the non-erythroid transcriptome. These phenotypic and gene expression changes are associated with distinct changes in the chromatin landscape, and require close coordination between transcription factors and epigenetic regulators, as well as precise regulation of RNA polymerase II activity. Disruption of these processes are associated with inherited anemias and myelodysplastic syndromes. Here, we review the epigenetic mechanisms that govern terminal erythroid maturation, and their role in human disease.

Zkscan3 affects erythroblast development by regulating the transcriptional activity of GATA1 and KLF1 in mice

ZKSCAN3 encodes a zinc-finger transcription factor that regulates the expression of important genes and plays a significant role in tumor development, pathogenesis, and metastasis. However, its biological functions under normal physiological conditions remain largely unknown. In our previous studies, using flow cytometry, we found that the deletion of Zkscan3 may cause abnormal erythropoiesis. In this study, we found that, in a Zkscan3 knockout mice model, the number of splenic early-stage (basophilic-erythroblasts) and late-stage (chromatophilic-erythroblasts to polychromatophilic-erythroblasts through orthochromatophilic-erythroblasts) erythroblasts increased, whereas the number of late erythroblasts in the bone marrow decreased. Moreover, the phenotype was exacerbated after treating mice with phenylhydrazine (PHZ), which causes severe hemolytic anemia. In the knockout mice treated with PHZ, the percentage of reticulocyte in the peripheral blood conspicuously increased, whereas MCHC and red blood cells decreased. Then, we performed RNA-seq and quantitative-polymerase chain reaction assay and found that the expression of GATA1 and Tiam1 in erythroblasts were upregulated, whereas KLF1 was downregulated. Luciferase assays showed that Zkscan3 inhibited the transcription of GATA1 and Tiam1 and promoted the expression of KLF1. Additionally, ChIP and CO-IP results confirmed that Zkscan3 directly interacts with GATA1 and inhibits its transcriptional activity in MEL cells. Our results demonstrate, for the first time, the significant role of Zkscan3 in physiological erythropoiesis through the interaction with GATA1, both at the DNA and protein level, and with Tiam1 and KLF1 at the DNA level.

Regulatory association of long noncoding RNAs and chromatin accessibility facilitates erythroid differentiation

Erythroid differentiation is a dynamic process regulated by multiple factors, whereas the interaction between long noncoding RNAs (lncRNAs) and chromatin accessibility and its influence on erythroid differentiation remains unclear. To elucidate this interaction, we used hematopoietic stem cells, multipotent progenitor cells, common myeloid progenitor cells, megakaryocyte-erythroid progenitor cells, and erythroblasts from human cord blood as an erythroid differentiation model to explore the coordinated regulatory functions of lncRNAs and chromatin accessibility by integrating RNA-seq and ATAC-seq data. We revealed that the integrated network of chromatin accessibility and lncRNAs exhibits stage-specific changes throughout the erythroid differentiation process and that the changes at the erythroblast stage of maturation are dramatic. We identified a subset of stage-specific lncRNAs and transcription factors (TFs) that associate with chromatin accessibility during erythroid differentiation, in which lncRNAs are key regulators of terminal erythroid differentiation via an lncRNA-TF-gene network. LncRNA PCED1B-AS1 was revealed to regulate terminal erythroid differentiation by coordinating GATA1 dynamically binding to the chromatin and interacting with the cytoskeleton network during erythroid differentiation. DANCR, another lncRNA that is highly expressed at the megakaryocyte-erythroid progenitor cell stage, was verified to promote erythroid differentiation by compromising megakaryocyte differentiation and coordinating with chromatin accessibility and TFs, such as RUNX1. Overall, our results identify the associated network of lncRNAs and chromatin accessibility in erythropoiesis and provide novel insights into erythroid differentiation and abundant resources for further study.

Novel variants in Krueppel like factor 1 that cause persistence of fetal hemoglobin in In(Lu) individuals

Beta-hemoglobinopathies become prominent after birth due to a switch from γ-globin to the mutated β-globin. Haploinsufficiency for the erythroid specific indispensable transcription factor Krueppel-like factor 1 (KLF1) is associated with high persistence of fetal hemoglobin (HPFH). The In(Lu) phenotype, characterized by low to undetectable Lutheran blood group expression is caused by mutations within KLF1 gene. Here we screened a blood donor cohort of 55 Lutheran weak or negative donors for KLF1 variants and evaluated their effect on KLF1 target gene expression. To discriminate between weak and negative Lutheran expression, a flow cytometry (FCM) assay was developed to detect Lu antigen expression. The Lu(a-b-) (negative) donor group, showing a significant decreased CD44 (Indian blood group) expression, also showed increased HbF and HbA2 levels, with one individual expressing HbF as high as 5%. KLF1 exons and promoter sequencing revealed variants in 80% of the Lutheran negative donors. Thirteen different variants plus one high frequency SNP (c.304 T > C) were identified of which 6 were novel. In primary erythroblasts, knockdown of endogenous KLF1 resulted in decreased CD44, Lu and increased HbF expression, while KLF1 over-expressing cells were comparable to wild type (WT). In line with the pleiotropic effects of KLF1 during erythropoiesis, distinct KLF1 mutants expressed in erythroblasts display different abilities to rescue CD44 and Lu expression and/or to affect fetal (HbF) or adult (HbA) hemoglobin expression. With this study we identified novel KLF1 variants to be include into blood group typing analysis. In addition, we provide further insights into the regulation of genes by KLF1.

Downregulation of KLF4 activates embryonic and fetal globin mRNA expression in human erythroid progenitor cells

The Krüppel-like factor (KLF) family dominates highly conserved three zinc finger DNA binding domains at the C-terminus and variable transactivation domains at the N-terminus. Humans possess 18 KLF genes that are differentially expressed in various tissues. Several KLFs recognize a specific CACCC DNA motif that is commonly found within hematopoietic-specific promoters. To investigate those KLFs that are involved in human hemoglobin (Hb) switching, the present study analyzed a previous microarray data set from fetal and adult erythroid cells and validated the mRNA expression levels of 18 KLFs by reverse transcription-quantitative PCR (RT-qPCR). KLF with a decreased expression level in the fetuses was selected for a functional study in human erythroid progenitor cells using lentiviral-based short hairpin RNA knockdown. The fetuses demonstrated a lower level of KLF4 mRNA expression when compared with the adults. Downregulation of KLF4 in erythroid progenitor cells from healthy individuals and individuals with β⁰-thalassemia/HbE evidenced the increasing embryonic and fetal globin mRNA expression with neither significant cytotoxicity nor gene expression alteration of the examined globin regulators, KLF1, B-cell lymphoma/leukemia 11A and lymphoma/leukemia-related factor. These findings demonstrate that the downregulation of KLF4 is associated with increased embryonic and fetal globin gene expression in human erythroid progenitor cells. Moreover, identifying putative compounds or molecular approaches that effectively downregulate KLF4 and further induce embryonic globin expression may provide an alternative therapeutic strategy for α-globin substitution in severe α-thalassemia.

Multiple functions of autophagy in vascular calcification

Background

Vascular calcification is a closely linked to cardiovascular diseases, such as atherosclerosis, chronic kidney disease, diabetes, hypertension and aging. The extent of vascular calcification is closely correlate with adverse clinical events and cardiovascular all-cause mortality. The role of autophagy in vascular calcification is complex with many mechanistic unknowns.

Methods

In this review, we analyze the current known mechanisms of autophagy in vascular calcification and discuss the theoretical advantages of targeting autophagy as an intervention against vascular calcification.

Results

Here we summarize the functional link between vascular calcification and autophagy in both animal models of and human cardiovascular disease. Firstly, autophagy can reduce calcification by inhibiting the osteogenic differentiation of VSMCs related to ANCR, ERα, β-catenin, HIF-1a/PDK4, p62, miR-30b, BECN1, mTOR, SOX9, GHSR/ERK, and AMPK signaling. Conversely, autophagy can induce osteoblast differentiation and calcification as mediated by CREB, degradation of elastin, and lncRNA H19 and DUSP5 mediated ERK signaling. Secondly, autophagy also links apoptosis and vascular calcification through AMPK/mTOR/ULK1, Wnt/β-catenin and GAS6/AXL synthesis, as apoptotic cells become the nidus for calcium-phosphate crystal deposition. The failure of mitophagy can activate Drp1, BNIP3, and NR4A1/DNA‑PKcs/p53 mediated intrinsic apoptotic pathways, which have been closely linked to the formation of vascular calcification. Additionally, autophagy also plays a role in osteogenesis by regulating vascular calcification, which in turn regulates expression of proteins related to bone development, such as osteocalcin, osteonectin, etc. and regulated by mTOR, EphrinB2 and RhoA. Furthermore, autophagy also promotes vitamin K2-induced MC3T3 E1 osteoblast differentiation and FGFR4/FGF18- and JNK/complex VPS34–beclin-1-related bone mineralization via vascular calcification.

Conclusion

The interaction between autophagy and vascular calcification are complicated, with their interaction affected by the disease process, anatomical location, and the surrounding microenvironment. Autophagy activation in existent cellular damage is considered protective, while defective autophagy in normal cells result in apoptotic activation. Identifying and maintaining cells at the delicate line between these two states may hold the key to reducing vascular calcification, in which autophagy associated clinical strategy could be developed.

Severe neonatal haemolytic anaemia caused by compound heterozygous KLF1 mutations: report of four families and literature review

Mutations in the KLF1 gene, which encodes a transcription factor playing a role in erythropoiesis, have recently been demonstrated to be a rare cause of hereditary haemolytic anaemia. We described the genotypic and phenotypic spectra of four unrelated families with compound heterozygous class 2/class 3 KLF1 mutations. All patients had p.G176RfsX179 on one allele and either p.A298P, p.R301H or p.G335R on the other allele. All presented on the first day of life with severe haemolytic anaemia with abnormal red blood cell morphology, markedly increased nucleated red blood cells and hyperbilirubinaemia. Three patients later became transfusion-dependent. All parents with heterozygous KLF1 mutation without co-inherited thalassaemia had normal to borderline mean corpuscular volume (MCV) and normal to slightly elevated Hb F. Fifteen previously reported cases of biallelic KLF1 mutations were identified from a literature review. All except one presented with severe haemolytic anaemia in the neonatal period. Our finding substantiates that compound heterozygous KLF1 mutations are associated with severe neonatal haemolytic anaemia and expands the haematologic phenotypic spectrum. In carriers, the previously suggested findings of low MCV, high Hb A₂ and high Hb F are inconsistent; thus this necessitates molecular studies for the identification of carriers.

Compound Heterozygosity for KLF1 Mutations Causing Hemolytic Anemia in Children: A Case Report and Literature Review

Background

Anemia is one of the most common diseases affecting children worldwide. Hereditary forms of anemia due to gene mutations are difficult to diagnose because they only rely on clinical manifestations. In regions with high prevalence of thalassemia such as southern China, pediatric patients with a hereditary hemolytic anemia (HHA) phenotype are often diagnosed with β-thalassemia. However, HHA can be caused by other gene defects. Here, a case previously diagnosed with thalassemia in a local hospital was sent to our laboratory for further genetic diagnosis. Preliminary molecular testing did not identify any mutations in globin genes.

Methods

All blood samples were collected after informed consent had been obtain from the proband’s parents. Both clinical and genetic analyses were conducted for the patient and her family members, including clinical data collection and sequencing of the KLF1 gene. Relevant literature was reviewed, including genetically confirmed cases with well-documented clinical summaries.

Results

Based on the detailed clinical data for this case, we diagnosed the patient with severe HHA. Sanger sequencing confirmed that there was a mutation on each KLF1 allele in the proband, which is missense mutation c.892G > C (p.Ala298Pro) inherited from father and frameshift mutation c.525_526insCGGCGCC (p.Gly176Argfs^∗179) from the mother, respectively. A summary of the KLF1 mutation spectrum and a clarification of genotype–phenotype correlation were performed through a combined analysis of the case and literature studies.

Conclusion

This study corrected the misdiagnosis and identified the etiology in a Chinese patient with HHA. Identification of the disease-causing gene is important for the treatment and care of the patient and prevention of another affected childbirth in her family. In addition, this study provided insight to better distinguish HHA patients with β-thalassemia mutations from those with KLF1 mutations.

Identification of potential chemical compounds enhancing generation of enucleated cells from immortalized human erythroid cell lines

Immortalized erythroid cell lines are expected to be a promising source of ex vivo manufactured red blood cells (RBCs), however the induction of enucleation in these cell lines is inefficient at present. We utilized an imaging-based high-throughput system to identify chemical compounds that trigger enucleation of human erythroid cell lines. Among >3,300 compounds, we identified multiple histone deacetylase inhibitors (HDACi) inducing enucleated cells from the cell line, although an increase in membrane fragility of enucleated cells was observed. Gene expression profiling revealed that HDACi treatment increased the expression of cytoskeletal genes, while an erythroid-specific cell membrane protein, SPTA1, was significantly down-regulated. Restoration of SPTA1 expression using CRISPR-activation partially rescued the fragility of cells and thereby improved the enucleation efficiency. Our observations provide a potential solution for the generation of mature cells from erythroid cell lines, contributing to the future realization of the use of immortalized cell lines for transfusion therapies.

In an imaging-based screen of >3,300 compounds compounds, Soboleva et al identify HDAC inhibitors as mediators of erythroid cell enucleation. They further show that the erythroid-specific cell membrane protein, SPTA1, is downregulated in HDAC inhibited cells and that restoration of SPTA1 expression using CRISPR-activation partially rescues the fragility of cells, improving enucleation efficiency.

CRISPR/Cas9-mediated β-globin gene knockout in rabbits recapitulates human β-thalassemia

β-thalassemia, an autosomal recessive blood disorder that reduces the production of hemoglobin, is majorly caused by the point mutation of the HBB gene resulting in reduced or absent β-globin chains of the hemoglobin tetramer. Animal models recapitulating both the phenotype and genotype of human disease are valuable in the exploration of pathophysiology and for in vivo evaluation of novel therapeutic treatments. The docile temperament, short vital cycles, and low cost of rabbits make them an attractive animal model. However, β-thalassemia rabbit models are currently unavailable. Here, using CRISPR/Cas9-mediated genome editing, we point mutated the rabbit β-globin gene HBB2 with high efficiency and generated a β-thalassemia rabbit model. Hematological and histological analyses demonstrated that the genotypic mosaic F0 displayed a mild phenotype of anemia, and the heterozygous F1 exhibited typical characteristics of β-thalassemia. Whole-blood transcriptome analysis revealed that the gene expression was altered in HBB2-targeted when compared with WT rabbits. And the highly expressed genes in HBB2-targeted rabbits were enriched in lipid and iron metabolism, innate immunity, and hematopoietic processes. In conclusion, using CRISPR-mediated HBB2 knockout, we have created a β-thalassemia rabbit model that accurately recapitulates the human disease phenotype. We believe this tool will be valuable in advancing the investigation of pathogenesis and novel therapeutic targets of β-thalassemia and associated complications.

Hemoglobin switching in mice carrying the Klf1Nan variant

Haploinsufficiency for transcription factor KLF1 causes a variety of human erythroid phenotypes, such as the In(Lu) blood type, increased HbA2 levels, and hereditary persistence of fetal hemoglobin. Severe dominant congenital dyserythropoietic anemia IV (OMIM 613673) is associated with the KLF1 p.E325K variant. CDA-IV patients display ineffective erythropoiesis and hemolysis resulting in anemia, accompanied by persistent high levels of embryonic and fetal hemoglobin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1Nan causes dominant hemolytic anemia with many similarities to CDA-IV. Here we investigated the impact of Klf1Nan on the developmental expression patterns of the endogenous beta-like and alpha-like globins, and the human beta-like globins carried on a HBB locus transgene. We observe that the switch from primitive, yolk sac-derived, erythropoiesis to definitive, fetal liver-derived, erythropoiesis is delayed in Klf1wt/Nan embryos. This is reflected in globin expression patterns measured between E12.5 and E14.5. Cultured Klf1wt/Nan E12.5 fetal liver cells display growth- and differentiation defects. These defects likely contribute to the delayed appearance of definitive erythrocytes in the circulation of Klf1wt/Nan embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1wt/Nan animals, silencing of the embryonic/fetal globin genes is impeded, but only minute amounts are expressed. Thus, in contrast to human KLF1 p.E325K, mouse KLF1 p.E339D does not lead to persistent high levels of embryonic/fetal globins. Our results support the notion that KLF1 affects gene expression in a variant-specific manner, highlighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.

Inhibition of Embryonic HSP 90 Function Promotes Variation of Cold Tolerance in Zebrafish

Accumulating evidence indicates that heat shock protein 90 (HSP90) plays essential roles in modulation of phenotypic plasticity in vertebrate development, however, the roles of HSP90 in modulation of cold tolerance capacity in fish are still unclear. In the present study, we showed that transient inhibition of embryonic HSP90 function by a chemical inhibitor or low conductivity stress promoted variation of cold tolerance capacity in adult zebrafish. Further work showed that embryonic HSP90 inhibition enhanced cold tolerance in adult zebrafish could be transmitted to their offspring. RNA-seq data showed that embryonic HSP90 inhibition enhanced cold tolerance involves variation of gene expression related to proteasome, lysosome, autophagy, and ribosome. Experiments with zebrafish ZF4 cells showed that two differentially expressed genes atg9b and psmd12 were up-regulated by radicicol treatment and provided protective roles for cells under cold stress, indicating that up-regulation of autophagy and proteasome function contributes to enhanced cold tolerance. The present work sheds a light on the roles of HSP90 in regulation of phenotypic plasticity associated with thermal adaptation in fish.

Severe anemia caused by dominant mutations in Krüppel-like factor 1 (KLF1)

The etiology and severity of anemia, a common blood disorder, are diverse. Dominant mutations in Krüppel-like factor 1 (KLF1/EKLF) underlie the molecular basis for some of them. KLF1 is a zinc finger transcription factor that plays an essential role in red blood cell proliferation and differentiation. Mutations have been identified in the KLF1 gene that cause hematologic diseases. Two of these alter one allele but generate an extreme phenotype: the mouse Nan mutation (E339D) leads to hemolytic neonatal anemia with hereditary spherocytosis, and the human CDA mutation (E325K) causes congenital dyserythropoietic anemia (CDA) type IV. These modify functionally important amino acids in the zinc finger DNA-binding domain at positions involved in direct interactions with regulatory elements of KLF1's target genes. Although the two dominant mutations alter the same evolutionarily conserved glutamic acid residue, the substitutions are not equivalent and lead to divergent consequences for the molecular mechanisms underlying activity of these mutants, particularly in recognition and interaction with their unique binding sites. Consequently, the properties of the protein are transformed such that it acquires novel dominant characteristics whose effects may not be limited to the erythroid compartment. KLF1 mutants cause loss-of-function/haploinsufficiency effects on some KLF1 wild-type target genes, while at the same time gain-of-function effects activate ectopic sites and neomorphic gene expression. Such anomalies not only lead to intrinsic red cell problems, but also to expression of non-erythroid genes that systemically disturb organ development. This review highlights recent molecular, biochemical, and genetic studies of KLF1 mutants, particularly the dramatic consequences that come from just a single amino acid change. The study of these variants provides an important contribution to the overall understanding of the DNA-protein interface of the zinc finger subtype of transcription factors, and the potential clinical consequences of what might appear to be a minor change in sequence.

Glucose Phosphate Isomerase Deficiency: High Prevalence of p.Arg347His Mutation in Indian Population Associated with Severe Hereditary Non-Spherocytic Hemolytic Anemia Coupled with Neurological Dysfunction

OBJECTIVES

Glucose-6-phosphate isomerase (GPI) deficiency is an autosomal recessive genetic disorder causing hereditary non-spherocytic hemolytic anemia (HNSHA) coupled with a neurological disorder. The aim of this study was to identify GPI genetic defects in a cohort of Indian patients with HNSHA coupled with neurological dysfunction.

METHODS

Thirty-five patients were screened for GPI deficiency in the HNSHA patient group; some were having neurological dysfunction. Enzyme activity was measured by spectrophotometric method. The genetic study was done by single-stranded conformation polymorphism (SSCP) analysis, restriction fragment length polymorphism (RFLP) analysis by the restriction enzyme AciI for p.Arg347His (p.R347H) and confirmation by Sanger's sequencing.

RESULTS

Out of 35 patients, 15 showed 35% to 70% loss of GPI activity, leading to neurological problems with HNSHA. Genetic analysis of PCR products of exon 12 of the GPI gene showed altered mobility on SSCP gel. Sanger's sequencing revealed a homozygous c1040G > A mutation predicting a p.Arg347His replacement which abolishes AciI restriction site. The molecular modeling analysis suggests p.Arg347 is involved in dimerization of the enzyme. Also, this mutation generates a more labile enzyme which alters its three-dimensional structure and function.

CONCLUSIONS

This report describes the high prevalence of p.Arg347His pathogenic variant identified in Indian GPI deficient patients with hemolytic anemia and neuromuscular impairment. It suggests that neuromuscular impairment with hemolytic anemia cases could be investigated for p.Arg347His pathogenic variant causing GPI deficiency because of neuroleukin activity present in the GPI monomer which has neuroleukin action at the same active site and generates neuromuscular problems as well as hemolytic anemia.

Increased autophagy in EphrinB2-deficient osteocytes is associated with elevated secondary mineralization and brittle bone

Mineralized bone forms when collagen-containing osteoid accrues mineral crystals. This is initiated rapidly (primary mineralization), and continues slowly (secondary mineralization) until bone is remodeled. The interconnected osteocyte network within the bone matrix differentiates from bone-forming osteoblasts; although osteoblast differentiation requires EphrinB2, osteocytes retain its expression. Here we report brittle bones in mice with osteocyte-targeted EphrinB2 deletion. This is not caused by low bone mass, but by defective bone material. While osteoid mineralization is initiated at normal rate, mineral accrual is accelerated, indicating that EphrinB2 in osteocytes limits mineral accumulation. No known regulators of mineralization are modified in the brittle cortical bone but a cluster of autophagy-associated genes are dysregulated. EphrinB2-deficient osteocytes displayed more autophagosomes in vivo and in vitro, and EphrinB2-Fc treatment suppresses autophagy in a RhoA-ROCK dependent manner. We conclude that secondary mineralization involves EphrinB2-RhoA-limited autophagy in osteocytes, and disruption leads to a bone fragility independent of bone mass.

Osteoblasts mediate bone formation, and their differentiation requires expression of EphrinB2. Here, the authors show that EphrinB2 is also expressed by osteocytes, and that its genetic ablation in mice is associated with altered autophagy, elevated mineralization and brittle bone.

Gene expression in blood from an individual with β-thalassemia: An RNA sequence analysis

BACKGROUND

Transcriptome profiling in individuals affected with β-thalassemia, especially in individuals who carry novel mutations in the HBB, may improve our understanding of the heterogeneity and molecular mechanisms of the disease.

METHODS

Members of a family with a daughter affected with thalassemia intermedia, although her mother was not clinically affected, were examined. We also characterized genome-wide gene expression in the family using real-time quantitative polymerase chain reaction and high-throughput RNA-sequencing mRNA expression profiling of blood.

RESULTS

We described the downregulation of the β-globin gene in β-thalassemia by RNA-sequencing analysis using a sample from an affected individual and her mother, who have a novel mutation in the HBB that creates a cryptic donor splice site. The daughter has a typical β-thalassemia allele as well, and an unexpectedly severe phenotype. The differentially expressed genes are enriched in pathways that are directly or indirectly related to β-thalassemia such as hemopoiesis, heme biosynthesis, response to oxidative stress, inflammatory responses, immune responses, control of circadian rhythm, apoptosis, and other cellular activities.

CONCLUSION

We compare our findings with published results of RNA-sequencing analysis of sickle cell disease and erythroblasts from a KLF1-null neonate with hydrops fetalis, and recognize similarities and differences in their transcriptional expression patterns.

An update on the Scianna blood group system

This update of the Scianna blood group system (Brunker PA, Flegel WA. Scianna: the lucky 13th blood group system. Immunohematology 2011;27:41-57) provides the recent work on the genetic variation of ERMAP across more world populations, the elucidation of the molecular basis of an historical serologic case, new cases of antibodies in the system, the development of new serologic reagents, and new discoveries in the biology of the erythroid membrane associated protein (ERMAP). Although genetic variation in ERMAP has been extensively cataloged, nonsynonymous variants associated with alloantigens have remained limited, and no new antigens have been identified. The first case of a severe hemolytic transfusion reaction to anti-Sc2 has recently been reported, highlighting the importance of pursuing the possibility of antibodies to low-prevalence antigens via indirect antiglobulin testing as a routine component of all transfusion reaction investigations. The expanding use of molecular testing in blood centers and transfusion services has uncovered a wider population distribution of Scianna antigens and heightened the awareness of this blood group system. The International Society of Blood Transfusion recognizes seven antigens in the Scianna blood group system 13.

Corrupted DNA-binding specificity and ectopic transcription underpin dominant neomorphic mutations in KLF/SP transcription factors

Background

Mutations in the transcription factor, KLF1, are common within certain populations of the world. Heterozygous missense mutations in KLF1 mostly lead to benign phenotypes, but a heterozygous mutation in a DNA-binding residue (E325K in human) results in severe Congenital Dyserythropoietic Anemia type IV (CDA IV); i.e. an autosomal-dominant disorder characterized by neonatal hemolysis.

Results

To investigate the biochemical and genetic mechanism of CDA IV, we generated murine erythroid cell lines that harbor tamoxifen-inducible (ER™) versions of wild type and mutant KLF1 on a Klf1^−/− genetic background. Nuclear translocation of wild type KLF1 results in terminal erythroid differentiation, whereas mutant KLF1 results in hemolysis without differentiation. The E to K variant binds poorly to the canonical 9 bp recognition motif (NGG-GYG-KGG) genome-wide but binds at high affinity to a corrupted motif (NGG-GRG-KGG). We confirmed altered DNA-binding specificity by quantitative in vitro binding assays of recombinant zinc-finger domains. Our results are consistent with previously reported structural data of KLF-DNA interactions. We employed 4sU-RNA-seq to show that a corrupted transcriptome is a direct consequence of aberrant DNA binding.

Conclusions

Since all KLF/SP family proteins bind DNA in an identical fashion, these results are likely to be generally applicable to mutations in all family members. Importantly, they explain how certain mutations in the DNA-binding domain of transcription factors can generate neomorphic functions that result in autosomal dominant disease.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5805-z) contains supplementary material, which is available to authorized users.

Genetic disarray follows mutant KLF1-E325K expression in a congenital dyserythropoietic anemia patient

Congenital dyserythropoietic anemia type IV is caused by a heterozygous mutation, Glu325Lys (E325K), in the KLF1 transcription factor. Molecular characteristics of this disease have not been clarified, partly due to its rarity. We expanded erythroid cells from a patient's peripheral blood and analyzed its global expression pattern. We find that a large number of erythroid pathways are disrupted, particularly those related to membrane transport, globin regulation, and iron utilization. The altered genetics lead to significant deficits in differentiation. Glu325 is within the KLF1 zinc finger domain at an amino acid critical for site specific DNA binding. The change to Lys is predicted to significantly alter the target site recognition sequence, both by subverting normal recognition and by enabling interaction with novel sites. Consistent with this, we find high level ectopic expression of genes not normally present in the red cell. These altered properties explain patients' clinical and phenotypic features, and elucidate the dominant character of the mutation.

KLF1 mutation E325K induces cell cycle arrest in erythroid cells differentiated from congenital dyserythropoietic anemia patient-specific induced pluripotent stem cells

Krüppel-like factor 1 (KLF1), a transcription factor controlling definitive erythropoiesis, is involved in sequential control of terminal cell division and enucleation via fine regulation of key cell cycle regulator gene expression in erythroid lineage cells. Type IV congenital dyserythropoietic anemia (CDA) is caused by a monoallelic mutation at the second zinc finger of KLF1 (c.973G>A, p.E325K). We recently diagnosed a female patient with type IV CDA with the identical missense mutation. To understand the mechanism underlying the dyserythropoiesis caused by the mutation, we generated induced pluripotent stem cells (iPSCs) from the CDA patient (CDA-iPSCs). The erythroid cells that differentiated from CDA-iPSCs (CDA-erythroid cells) displayed multinucleated morphology, absence of CD44, and dysregulation of the KLF1 target gene expression. In addition, uptake of bromodeoxyuridine by CDA-erythroid cells was significantly decreased at the CD235a⁺/CD71⁺ stage, and microarray analysis revealed that cell cycle regulator genes were dysregulated, with increased expression of negative regulators such as CDKN2C and CDKN2A. Furthermore, inducible expression of the KLF1 E325K, but not the wild-type KLF1, caused a cell cycle arrest at the G1 phase in CDA-erythroid cells. Microarray analysis of CDA-erythroid cells and real-time polymerase chain reaction analysis of the KLF1 E325K inducible expression system also revealed altered expression of several KLF1 target genes including erythrocyte membrane protein band 4.1 (EPB41), EPB42, glutathione disulfide reductase (GSR), glucose phosphate isomerase (GPI), and ATPase phospholipid transporting 8A1 (ATP8A1). Our data indicate that the E325K mutation in KLF1 is associated with disruption of transcriptional control of cell cycle regulators in association with erythroid membrane or enzyme abnormalities, leading to dyserythropoiesis.

The Pleiotropic Effects of GATA1 and KLF1 in Physiological Erythropoiesis and in Dyserythropoietic Disorders

In the last few years, the advent of new technological approaches has led to a better knowledge of the ontogeny of erythropoiesis during development and of the journey leading from hematopoietic stem cells (HSCs) to mature red blood cells (RBCs). Our view of a well-defined hierarchical model of hematopoiesis with a near-homogeneous HSC population residing at the apex has been progressively challenged in favor of a landscape where HSCs themselves are highly heterogeneous and lineages separate earlier than previously thought. The coordination of these events is orchestrated by transcription factors (TFs) that work in a combinatorial manner to activate and/or repress their target genes. The development of next generation sequencing (NGS) has facilitated the identification of pathological mutations involving TFs underlying hematological defects. The examples of GATA1 and KLF1 presented in this review suggest that in the next few years the number of TF mutations associated with dyserythropoietic disorders will further increase.

Differential role of Kruppel like factor 1 (KLF1) gene in red blood cell disorders

The master erythroid regulator KLF1,plays a pivotal role during erythroid lineage development by regulating the expression of many erythroid genes. Variations in the KLF1 gene are found to be associated with varied erythroid phenotypes. With the aim of determining the role of KLF1 gene variations in HbF induction and their genotype phenotype relationship, in this study, we screened 370 individuals with different hemoglobinopathy condition. Hematological analysis was carried out using automated blood cell counter and Variant II HPLC (Biorad). KLF1 gene mutations were screened using automated DNA sequencing. Expression analysis was carried out using q-RT PCR of KLF1, BCL11A and γ-globin after selective enrichment and culturing of CD 34 +ve cells into an erythroid lineage. Over all 14 KLF1 gene variations were identified, of which six variants were novel. The incidence of KLF1 gene mutations was found to be 8.1%. It was seen that KLF1 mutations contributed in borderline HbA₂ levels as 7.6% of our borderline HbA₂ cases showed presence of KLF1 variations. It also contributed in induction of HbF levels under stress erythropoietic conditions. Gene expression studies revealed inverse correlation of KLF1, BCL11A (reduced) with γ-globin gene expression (increased) in patients showing KLF1 gene mutations, thus indicating the role of KLF1 gene in regulating the γ-globin gene expression. The identification of genomic variants of the KLF1 may help in determining the functionally active domain of this protein and will facilitate in understanding the wide spectrum of phenotypes generated by these variants.

Research advances in erythrocyte regeneration sources and methods in vitro

Erythrocytes (red blood cells, RBCs) facilitate gas exchange in the lungs and transport oxygen to the tissues. The human body must maintain erythrocyte regeneration to support metabolically active cells and tissues. In many hematological diseases, erythrocyte regeneration is impaired. Researchers have studied erythrocyte regeneration for many years both in vivo and in vitro. In this review, we summarize the sources and main culture methods for generating mature and functional red blood cells in vitro. Hematopoietic stem cells (HSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are classic sources for erythrocyte regeneration. In addition, alternative sources such as immortalized adult human erythroid cell lines and transformed fibroblasts have also been generated and have produced functional red blood cells. The culture systems for erythrocytes differ among laboratories. Researchers hope that improvements in culture techniques may contribute to improved RBC outcomes for blood transfusions, drug delivery and the treatment of hematological diseases.

Molecular diagnosis of unexplained haemolytic anaemia using targeted next-generation sequencing panel revealed (p.Ala337Thr) novel mutation in GPI gene in two Indian patients

Glucose-6-phosphate isomerase (GPI) deficiency is an autosomal recessive genetic disorder causing congenital haemolytic anaemia (CHA). Diagnosis of GPI deficiency by the biochemical method is unpredicted. Molecular diagnosis by identifying genetic mutation is the gold standard method for confirmation of disease, but causative genes involved in CHA are numerous, and identifying a gene-by-gene approach using Sanger sequencing is also cumbersome, expensive and labour intensive. Recently, next-generation targeted sequencing is more useful in the diagnosis of unexplained haemolytic anaemia. We used targeted next-generation sequencing (NGS) clinical panel for diagnosis of unexplained haemolytic anaemia in two Indian patients which were pending for a long time. All possible causes of haemolytic anaemia were found within normal limit. NGS by clinical exome panel revealed homozygous novel missense mutation in exon 12, c.1009G>A (p.Ala337Thr) in both patients. We further confirm by measuring red blood cell GPI activity in the patients and showed deficiency whereas parents were having intermediate activity. c.1009G>A mutation was also confirmed by Sanger sequencing of exon 12 of GPI gene. The structural-functional analysis by bioinformatics software like Swiss PDB, PolyPhen-2 and PyMol suggested that this pathogenic variant has a direct impact on the structural rearrangement at the region near the active site of the enzyme. This rapid and high-performance targeted NGS assay can be configured to detect specific CHA mutations unique to an individual defect, making it a potentially valuable method for diagnosis of unexplained haemolytic anaemia.

Investigation of the variable In(Lu) phenotype caused by KLF1 variants

INTRODUCTION

KLF1 is an essential transcriptional activator that drives erythropoiesis. KLF1 variants can result in the Inhibitor of Lutheran, or In(Lu), phenotype where red blood cells (RBCs) have reduced BCAM (LU) and CD44 (IN). Other RBC surface molecules also have changed expression; however, there is controversy in the literature regarding which are truly impacted. We aimed to investigate KLF1 variants in the Australian population.

STUDY DESIGN AND METHODS

In(Lu) samples were sourced through screening and through the RBC reference laboratory. Blood donor samples (8036) were screened to identify weakened/absent Lu^b antigen. Samples were genotyped by massively parallel sequencing, while surface carbohydrates and blood group molecules were assessed by flow cytometry. Hemoglobin (Hb) types were analyzed by high-performance liquid chromatography.

RESULTS

Four of 8036 donors were identified to be In(Lu), and two previously identified In(Lu) samples were provided from the RBC reference laboratory. Five different KLF1 variants were identified; two were novel: c.954G>C/p.Trp318Cys and c.421C>T/p.Arg141*. BCAM and CD44 were reduced in all samples, consistent with previous reports. As a group, In(Lu) RBCs had reduced CD35 (KN), ICAM4 (LW), and CD147 (OK), and demonstrated increased binding of lectins ECA and SNAI. One In(Lu) sample had elevated HbF and another elevated HbA2.

CONCLUSION

Different KLF1 variants may potentially produce variable phenotypes. A framework for investigating KLF1 variants and their phenotypic impact has been provided. In the future, given available international databases, further testing algorithms (as advocated here) will allow for correlation of phenotype with genotype and therefore accurately document this variability between KLF1 variants.

KFL1 Gene Variants in α-Thalassemia Individuals with Increased Fetal Hemoglobin in a Chinese Population

Krüppel-like factor 1 (KLF1) is a pleiotropic erythroid transcription factor that is a regulator of definitive erythropoiesis. The aim of this study was to detect KLF1 gene variants in α-thalassemia (α-thal) carriers with an increased Hb F level in a Chinese population, and determine the changes of hematological parameters as a result of interactions between KLF1 gene mutations and α-thal. Subjects with α-thal and Hb F levels of ≥1.0% were selected for further investigation. Direct sequencing was used to detect KLF1 gene mutations. Hematological parameters of subjects with α-thal and concomitant KLF1 gene mutations and those with α-thal alone were compared. The KLF1 gene variants were detected in 46 of 275 (16.7%) individuals with α-thal and Hb F levels of ≥1.0%. The detection rate of KLF1 gene mutations rose correspondingly when the Hb F level increased. For α⁰-thal carriers, significantly lower mean corpuscular volume (MCV) and mean corpuscular hemoglobin (Hb) (MCH) values were observed in KLF1 gene mutation-positive carriers than that in KLF1 gene mutation-free carriers; conversely, significantly higher Hb A₂ and Hb F levels were observed in the former condition rather than in the latter condition. The results of this study indicate that KLF1 gene variants are common in Chinese subjects with α-thal and increased Hb F levels, and KLF1 gene mutations decreased the red blood cell (RBC) indices in α-thal carriers as that in normal adults.

KLF1 E325K-associated Congenital Dyserythropoietic Anemia Type IV: Insights Into the Variable Clinical Severity

We identified a child with KLF1-E325K congenital dyserythropoietic anemia type IV who experienced a severe clinical course, fetal anemia, hydrops fetalis, and postnatal transfusion dependence only partially responsive to splenectomy. The child also had complete sex reversal, the cause which remains undetermined. To gain insights into our patient's severe hematologic phenotype, detailed analyses were performed. Erythrocytes from the patient and parents demonstrated functional abnormalities of the erythrocyte membrane, attributed to variants in the α-spectrin gene. Hypomorphic alleles in SEC23B and YARS2 were also identified. We hypothesize that coinheritance of variants in relevant erythrocyte genes contribute to the clinical course in our patient and other E325K-linked congenital dyserythropoietic anemia IV patients with severe clinical phenotypes.

The Shape Shifting Story of Reticulocyte Maturation

The final steps of erythropoiesis involve unique cellular processes including enucleation and reorganization of membrane proteins and the cytoskeleton to produce biconcave erythrocytes. Surprisingly this process is still poorly understood. In vitro erythropoiesis protocols currently produce reticulocytes rather than biconcave erythrocytes. In addition, immortalized lines and iPSC-derived erythroid cell suffer from low enucleation and suboptimal final maturation potential. In light of the increasing prospect to use in vitro produced erythrocytes as (personalized) transfusion products or as therapeutic delivery agents, the mechanisms driving this last step of erythropoiesis are in dire need of resolving. Here we review the elusive last steps of reticulocyte maturation with an emphasis on protein sorting during the defining steps of reticulocyte formation during enucleation and maturation.

Genetic therapies for sickle cell disease

After decades with few novel therapeutic options for sickle cell disease (SCD), autologous hematopoietic stem cell (HSC) based genetic therapies including lentiviral gene therapy (GT), and genome editing (GE) now appear imminent. Lentiviral GT has advanced considerably in the past decade with promising clinical trial results in multiple disorders. For β-hemoglobinopathies, GT strategies of gene addition and fetal hemoglobin induction through BCL11A regulation are both being evaluated in open clinical trials. GE techniques offer the possibility of a nonviral curative approach, either through sickle hemoglobin mutation repair or fetal hemoglobin elevation. Although GE currently remains at the preclinical stage, multiple clinical trials will likely open soon. In addition to reviewing current strategies for GT and GE, this review highlights important next steps toward optimization of these therapies. All autologous cell-based genetic therapies rely on safely obtaining an adequate yield of autologous HSCs for genetic modification and transplantation. HSC collection is uniquely challenging in SCD. Peripheral mobilization with plerixafor has recently emerged as a promising approach. The acute and long-term toxicities associated with myeloablative conditioning are risks that may not be acceptable to a significant number of SCD patients, highlighting the need for novel conditioning regimens. Finally, increasing availability of autologous genetic therapies will require comprehensive and collaborative discussions regarding cost and access for SCD patients, at individual centers and worldwide.