miR-191 regulates mouse erythroblast enucleation by down-regulating Riok3 and Mxi1

c-Jun targets miR-451a to regulate HQ-induced inhibition of erythroid differentiation via the BATF/SETD5/ARHGEF3 axis

Benzene, a widely used industrial chemical, has been clarified to cause hematotoxicity. Our previous study suggested that miR-451a may play a role in benzene-induced impairment of erythroid differentiation. However, the mechanism underlying remains unclear. In this study, we explored the role of miR-451a and its underlying mechanisms in hydroquinone (HQ)-induced suppression of erythroid differentiation in K562 cells. 0, 1.0, 2.5, 5.0, 10.0, and 50 μM HQ treatment of K562 cells resulted in a dose-dependent inhibition of erythroid differentiation, as well as the expression of miR-451a. Bioinformatics analysis was conducted to predict potential target genes of miR-451a and dual-luciferase reporter assays confirmed that miR-451a can directly bind to the 3'-UTR regions of BATF, SETD5, and ARHGEF3 mRNAs. We further demonstrated that over-expression or down-regulation of miR-451a altered the expression of BATF, SETD5, and ARHGEF3, and also modified erythroid differentiation. In addition, BATF, SETD5, and ARHGEF3 were verified to play a role in HQ-induced inhibition of erythroid differentiation in this study. Knockdown of SETD5 and ARHGEF3 reversed HQ-induced suppression of erythroid differentiation while knockdown of BATF had the opposite effect. On the other hand, we also identified c-Jun as a potential transcriptional regulator of miR-451a. Forced expression of c-Jun increased miR-451a expression and reversed the inhibition of erythroid differentiation induced by HQ, whereas knockdown of c-Jun had the opposite effect. And the binding site of c-Jun and miR-451a was verified by dual-luciferase reporter assay. Collectively, our findings indicate that miR-451a and its downstream targets BATF, SETD5, and ARHGEF3 are involved in HQ-induced erythroid differentiation disorder, and c-Jun regulates miR-451a as a transcriptional regulator in this process.

The miR-144/Hmgn2 regulatory axis orchestrates chromatin organization during erythropoiesis

Differentiation of stem and progenitor cells is a highly regulated process that involves the coordinated action of multiple layers of regulation. Here we show how the post-transcriptional regulatory layer instructs the level of chromatin regulation via miR-144 and its targets to orchestrate chromatin condensation during erythropoiesis. The loss of miR-144 leads to impaired chromatin condensation during erythrocyte maturation. Among the several targets of miR-144 that influence chromatin organization, the miR-144-dependent regulation of Hmgn2 is conserved from fish to humans. Our genetic probing of the miR-144/Hmgn2 regulatory axis establish that intact miR-144 target sites in the Hmgn2 3'UTR are necessary for the proper maturation of erythrocytes in both zebrafish and human iPSC-derived erythroid cells while loss of Hmgn2 rescues in part the miR-144 null phenotype. Altogether, our results uncover miR-144 and its target Hmgn2 as the backbone of the genetic regulatory circuit that controls the terminal differentiation of erythrocytes in vertebrates.

A Review of Key Regulators of Steady-State and Ineffective Erythropoiesis

Erythropoiesis is initiated with the transformation of multipotent hematopoietic stem cells into committed erythroid progenitor cells in the erythroblastic islands of the bone marrow in adults. These cells undergo several stages of differentiation, including erythroblast formation, normoblast formation, and finally, the expulsion of the nucleus to form mature red blood cells. The erythropoietin (EPO) pathway, which is activated by hypoxia, induces stimulation of the erythroid progenitor cells and the promotion of their proliferation and survival as well as maturation and hemoglobin synthesis. The regulation of erythropoiesis is a complex and dynamic interaction of a myriad of factors, such as transcription factors (GATA-1, STAT5), cytokines (IL-3, IL-6, IL-11), iron metabolism and cell cycle regulators. Multiple microRNAs are involved in erythropoiesis, mediating cell growth and development, regulating oxidative stress, erythrocyte maturation and differentiation, hemoglobin synthesis, transferrin function and iron homeostasis. This review aims to explore the physiology of steady-state erythropoiesis and to outline key mechanisms involved in ineffective erythropoiesis linked to anemia, chronic inflammation, stress, and hematological malignancies. Studying aberrations in erythropoiesis in various diseases allows a more in-depth understanding of the heterogeneity within erythroid populations and the development of gene therapies to treat hematological disorders.

The miR-144/Hmgn2 regulatory axis orchestrates chromatin organization during erythropoiesis

Differentiation of stem and progenitor cells is a highly regulated process that involves the coordinated action of multiple layers of regulation. Here we show how the post-transcriptional regulatory layer instructs the level of chromatin regulation via miR-144 and its targets to orchestrate chromatin condensation during erythropoiesis. The loss of miR-144 leads to impaired chromatin condensation during erythrocyte maturation. Among the several targets of miR-144 that influence chromatin organization, the miR-144-dependent regulation of Hmgn2 is conserved from fish to humans. Our genetic probing of the miR-144/Hmgn2 regulatory axis established that intact miR-144 target sites in the Hmgn2 3'UTR are necessary for the proper maturation of erythrocytes in both zebrafish and human iPSC-derived erythroid cells while loss of Hmgn2 rescues in part the miR-144 null phenotype. Altogether, our results uncover miR-144 and its target Hmgn2 as the backbone of the genetic regulatory circuit that controls the terminal differentiation of erythrocytes in vertebrates.

CD41+ extracellular vesicles produced by avian thrombocytes contain microRNAs

Avians have thrombocytes in their blood circulation rather than mammalian platelets. However, many details of thrombocyte characteristics have not been determined. Here, chicken thrombocytes were isolated, and extracellular vesicle (EV) production was investigated. The thrombocyte-specific markers cd41 and cd61 were expressed in the yolk sac at 24 h. According to the embryonic developmental stage, the cd41-expressing tissues changed from the yolk sac to the bone marrow and spleen. Accordingly, the bone marrow and spleen were the main tissues producing thrombocytes in adult chickens. Avian thrombocytes were separated from adult spleen cells through a combination of discontinuous density gradient centrifugation, phagocytic cell removal, and fluorescence-activated cell sorting. Isolated thrombocytes produced CD41+ EVs (CD41+ EVs), and the CD41+ EVs also expressed CD9. Microarray analysis revealed that CD41+ EVs contain many microRNAs. Macrophage lines (RAW264.7) phagocytosed CD41+ EVs, and their phagocytosis and migration activity were suppressed. Microarray analysis also revealed that EVs altered gene expression in macrophages. These data indicated that the CD41+ EV was a carrier of microRNAs produced from thrombocytes and affected the cell characteristics of the received cells. Therefore, the CD41+ EVs of avians worked as a communication tool.

Comprehensive Characterization and Global Transcriptome Analysis of Human Fetal Liver Terminal Erythropoiesis

The fetal liver (FL) is the key erythropoietic organ during fetal development, but knowledge on human FL erythropoiesis is very limited. In this study, we sorted primary erythroblasts from FL cells and performed RNA sequencing (RNA-seq) analyses. We found that temporal gene expression patterns reflected changes in function during primary human FL terminal erythropoiesis. Notably, the expression of genes enriched in proteolysis and autophagy was up-regulated in orthochromatic erythroblasts (OrthoEs), suggesting the involvement of these pathways in enucleation. We also performed RNA-seq of in vitro cultured erythroblasts derived from FL CD34+ cells. Comparison of transcriptomes between the primary and cultured erythroblasts revealed significant differences, indicating impacts of the culture system on gene expression. Notably, the expression of lipid metabolism-related genes was increased in cultured erythroblasts. We further immortalized erythroid cell lines from FL and cord blood (CB) CD34+ cells (FL-iEry and CB-iEry, respectively). FL-iEry and CB-iEry were immortalized at the proerythroblast stage and can be induced to differentiate into OrthoEs, but their enucleation ability was very low. Comparison of the transcriptomes between OrthoEs with and without enucleation capability revealed the down-regulation of pathways involved in chromatin organization and mitophagy in OrthoEs without enucleation capacity, indicating that defects in chromatin organization and mitophagy contribute to the inability of OrthoEs to enucleate. Additionally, the expression of HBE1, HBZ, and HBG2 was up-regulated in FL-iEry compared with CB-iEry, and such up-regulation was accompanied by down-regulated expression of BCL11A and up-regulated expression of LIN28B and IGF2BP1. Our study provides new insights into human FL erythropoiesis and rich resources for future studies.

RIOK3 potentially regulates osteogenesis-related pathways in ankylosing spondylitis and the differentiation of bone marrow mesenchymal stem cells

RNA-binding proteins (RBPs), which are key effectors of gene expression, play critical roles in inflammation and immune regulation. However, the potential biological function of RBPs in ankylosing spondylitis (AS) remains unclear. We identified differentially expressed genes (DEGs) in peripheral blood mononuclear cells (PBMCs) of five patients with AS and three healthy persons by RNA-seq, obtained differentially expressed RBPs by overlapping DEGs and RBPs summary table. RIOK3 was selected as a target RBP and knocked down in mouse bone marrow mesenchymal stem cells (mBMSCs), and transcriptomic studies of siRIOK3 mBMSCs were performed again using RNA-seq. Results showed that RIOK3 knockdown inhibited the expression of genes related to osteogenic differentiation, ribosome function, and β-interferon pathways in mBMSCs. In vitro experiments have shown that RIOK3 knockdown reduced the osteogenic differentiation ability of mBMSCs. Collectively, RIOK3 may affect the differentiation of mBMSCs and participate in the pathogenesis of AS, especially pathological bone formation.

Insight into microRNAs' involvement in hematopoiesis: current standing point of findings

Hematopoiesis is a complex process in which hematopoietic stem cells are differentiated into all mature blood cells (red blood cells, white blood cells, and platelets). Different microRNAs (miRNAs) involve in several steps of this process. Indeed, miRNAs are small single-stranded non-coding RNA molecules, which control gene expression by translational inhibition and mRNA destabilization. Previous studies have revealed that increased or decreased expression of some of these miRNAs by targeting several proto-oncogenes could inhibit or stimulate the myeloid and erythroid lineage commitment, proliferation, and differentiation. During the last decades, the development of molecular and bioinformatics techniques has led to a comprehensive understanding of the role of various miRNAs in hematopoiesis. The critical roles of miRNAs in cell processes such as the cell cycle, apoptosis, and differentiation have been confirmed as well. However, the main contribution of some miRNAs is still unclear. Therefore, it seems undeniable that future studies are required to focus on miRNA activities during various hematopoietic stages and hematological malignancy.

Plasmodium falciparum infection of human erythroblasts induces transcriptional changes associated with dyserythropoiesis

During development down the erythroid lineage, hematopoietic stem cells undergo dramatic changes to cellular morphology and function in response to a complex and tightly regulated program of gene expression. In malaria infection, Plasmodium spp parasites accumulate in the bone marrow parenchyma, and emerging evidence suggests erythroblastic islands are a protective site for parasite development into gametocytes. Although it has been observed that Plasmodium falciparum infection in late-stage erythroblasts can delay terminal erythroid differentiation and enucleation, the mechanism(s) underlying this phenomenon are unknown. Here, we apply RNA sequencing after fluorescence-activated cell sorting of infected erythroblasts to identify transcriptional responses to direct and indirect interaction with P falciparum. Four developmental stages of erythroid cells were analyzed: proerythroblast, basophilic erythroblast, polychromatic erythroblast, and orthochromatic erythroblast. We found extensive transcriptional changes in infected erythroblasts compared with that in uninfected cells in the same culture, including dysregulation of genes involved in erythroid proliferation and developmental processes. Although some indicators of cellular oxidative and proteotoxic stress were common across all stages of erythropoiesis, many responses were specific to cellular processes associated with developmental stage. Together, our results evidence multiple possible avenues by which parasite infection can induce dyserythropoiesis at specific points along the erythroid continuum, advancing our understanding of the molecular determinants of malaria anemia.

CSDE1 promotes miR-451 biogenesis

MicroRNAs are sequentially processed by RNase III enzymes Drosha and Dicer. miR-451 is a highly conserved miRNA in vertebrates which bypasses Dicer processing and instead relies on AGO2 for its maturation. miR-451 is highly expressed in erythrocytes and regulates the differentiation of erythroblasts into mature red blood cells. However, the mechanistic details underlying miR-451 biogenesis in erythrocytes remains obscure. Here, we report that the RNA binding protein CSDE1 which is required for the development of erythroblasts into erythrocytes, controls the expression of miR-451 in erythroleukemia cells. CSDE1 binds miR-451 and regulates AGO2 processing of pre-miR-451 through its N-terminal domains. CSDE1 further interacts with PARN and promotes the trimming of intermediate miR-451 to the mature length. Together, our results demonstrate that CSDE1 promotes biogenesis of miR-451 in erythroid progenitors.

Identification of mammalian transcription factors that bind to inaccessible chromatin

Transcription factors (TFs) are proteins that affect gene expression by binding to regulatory regions of DNA in a sequence specific manner. The binding of TFs to DNA is controlled by many factors, including the DNA sequence, concentration of TF, chromatin accessibility and co-factors. Here, we systematically investigated the binding mechanism of hundreds of TFs by analysing ChIP-seq data with our explainable statistical model, ChIPanalyser. This tool uses as inputs the DNA sequence binding motif; the capacity to distinguish between strong and weak binding sites; the concentration of TF; and chromatin accessibility. We found that approximately one third of TFs are predicted to bind the genome in a DNA accessibility independent fashion, which includes TFs that can open the chromatin, their co-factors and TFs with similar motifs. Our model predicted this to be the case when the TF binds to its strongest binding regions in the genome, and only a small number of TFs have the capacity to bind dense chromatin at their weakest binding regions, such as CTCF, USF2 and CEBPB. Our study demonstrated that the binding of hundreds of human and mouse TFs is predicted by ChIPanalyser with high accuracy and showed that many TFs can bind dense chromatin.

Post-transcriptional regulation of erythropoiesis

Erythropoiesis is a complex, precise, and lifelong process that is essential for maintaining normal body functions. Its strict regulation is necessary to prevent a variety of blood diseases. Normal erythropoiesis is precisely regulated by an intricate network that involves transcription levels, signal transduction, and various epigenetic modifications. In recent years, research on post-transcriptional levels in erythropoiesis has expanded significantly. The dynamic regulation of splicing transitions is responsible for changes in protein isoform expression that add new functions beneficial for erythropoiesis. RNA-binding proteins adapt the translation of transcripts to the protein requirements of the cell, yielding mRNA with dynamic translation efficiency. Noncoding RNAs, such as microRNAs and lncRNAs, are indispensable for changing the translational efficiency and/or stability of targeted mRNAs to maintain the normal expression of genes related to erythropoiesis. N6-methyladenosine-dependent regulation of mRNA translation plays an important role in maintaining the expression programs of erythroid-related genes and promoting erythroid lineage determination. This review aims to describe our current understanding of the role of post-transcriptional regulation in erythropoiesis and erythroid-associated diseases, and to shed light on the physiological and pathological implications of the post-transcriptional regulation machinery in erythropoiesis. These may help to further enrich our understanding of the regulatory network of erythropoiesis and provide new strategies for the diagnosis and treatment of erythroid-related diseases.

Generation of Red Blood Cells from Human Pluripotent Stem Cells-An Update

Red blood cell (RBC) transfusion is a lifesaving medical procedure that can treat patients with anemia and hemoglobin disorders. However, the shortage of blood supply and risks of transfusion-transmitted infection and immune incompatibility present a challenge for transfusion. The in vitro generation of RBCs or erythrocytes holds great promise for transfusion medicine and novel cell-based therapies. While hematopoietic stem cells and progenitors derived from peripheral blood, cord blood, and bone marrow can give rise to erythrocytes, the use of human pluripotent stem cells (hPSCs) has also provided an important opportunity to obtain erythrocytes. These hPSCs include both human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). As hESCs carry ethical and political controversies, hiPSCs can be a more universal source for RBC generation. In this review, we first discuss the key concepts and mechanisms of erythropoiesis. Thereafter, we summarize different methodologies to differentiate hPSCs into erythrocytes with an emphasis on the key features of human definitive erythroid lineage cells. Finally, we address the current limitations and future directions of clinical applications using hiPSC-derived erythrocytes.

Plasmodium falciparum infection of human erythroblasts induces transcriptional changes associated with dyserythropoiesis

During development down the erythroid lineage, hematopoietic stem cells undergo dramatic changes to cellular morphology and function in response to a complex and tightly regulated program of gene expression. In malaria infection, Plasmodium spp . parasites accumulate in the bone marrow parenchyma, and emerging evidence suggests erythroblastic islands are a protective site for parasite development into gametocytes. While it has been observed that Plasmodium falciparum infection of late-stage erythroblasts can delay terminal erythroid differentiation and enucleation, the mechanism(s) underlying this phenomenon are unknown. Here, we apply RNA-seq after fluorescence-activated cell sorting (FACS) of infected erythroblasts to identify transcriptional responses to direct and indirect interaction with Plasmodium falciparum . Four developmental stages of erythroid cells were analyzed: proerythroblast, basophilic erythroblast, polychromatic erythroblast, and orthochromatic erythroblast. We found extensive transcriptional changes in infected erythroblasts compared to uninfected cells in the same culture, including dysregulation of genes involved in erythroid proliferation and developmental processes. Whereas some indicators of cellular oxidative and proteotoxic stress were common across all stages of erythropoiesis, many responses were specific to cellular processes associated with developmental stage. Together, our results evidence multiple possible avenues by which parasite infection can induce dyserythropoiesis at specific points along the erythroid continuum, advancing our understanding of the molecular determinants of malaria anemia.

Key Points

Erythroblasts at different stages of differentiation have distinct responses to infection by Plasmodium falciparum . P. falciparum infection of erythroblasts alters expression of genes related to oxidative and proteotoxic stress and erythroid development.

Occupational exposure to diesel engine exhaust and serum levels of microRNAs in a cross-sectional molecular epidemiology study in China

Diesel engine exhaust (DEE) is an established lung carcinogen, but the biological mechanisms of diesel-induced lung carcinogenesis are not well understood. MicroRNAs (miRNAs) are small noncoding RNAs that play a potentially important role in regulating gene expression related to lung cancer. We conducted a cross-sectional molecular epidemiology study to evaluate whether serum levels of miRNAs are altered in healthy workers occupationally exposed to DEE compared to unexposed controls. We conducted a two-stage study, first measuring 405 miRNAs in a pilot study of six DEE-exposed workers exposed and six controls. In the second stage, 44 selected miRNAs were measured using the Fireplex circulating miRNA assay that profiles miRNAs directly from biofluids of 45 workers exposed to a range of DEE (Elemental Carbon (EC), median, range: 47.7, 6.1-79.7 μg/m³ ) and 46 controls. The relationship between exposure to DEE and EC with miRNA levels was analyzed using linear regression adjusted for potential confounders. Serum levels of four miRNAs were significantly lower (miR-191-5p, miR-93-5p, miR-423-3p, miR-122-5p) and one miRNA was significantly higher (miR-92a-3p) in DEE exposed workers compared to controls. Of these miRNAs, miR-191-5p (p_trend  = .001, FDR = 0.04) and miR-93-5p (p_trend  = .009, FDR = 0.18) showed evidence of an inverse exposure-response with increasing EC levels. Our findings suggest that occupational exposure to DEE may affect circulating miRNAs implicated in biological processes related to carcinogenesis, including immune function.

The accumulation of miR-125b-5p is indispensable for efficient erythroblast enucleation

Erythroblast enucleation is a precisely regulated but not clearly understood process. Polycythemia shows pathological erythroblast enucleation, and we discovered a low miR-125b-5p level in terminal erythroblasts of patients with polycythemia vera (PV) compared to those of healthy controls. Exogenous upregulation of miR-125b-5p levels restored the enucleation rate to normal levels. Direct downregulation of miR-125b-5p in mouse erythroblasts simulated the enucleation issue found in patients with PV, and miR-125b-5p accumulation was found in enucleating erythroblasts, collectively suggesting the importance of miR-125b-5p accumulation for erythroblast enucleation. To elucidate the role of miR-125b-5p in enucleation, gain- and loss-of-function studies were performed. Overexpression of miR-125b-5p improved the enucleation of erythroleukemia cells and primary erythroblasts. Infused erythroblasts with higher levels of miR-125b-5p also exhibited accelerated enucleation. In contrast, miR-125b-5p inhibitors significantly suppressed erythrocyte enucleation. Intracellular imaging revealed that in addition to cytoskeletal assembly and nuclear condensation, miR-125b-5p overexpression resulted in mitochondrial reduction and depolarization. Real-time PCR, western blot analysis, luciferase reporter assays, small molecule inhibitor supplementation and gene rescue assays revealed that Bcl-2, as a direct target of miR-125b-5p, was one of the key mediators of miR-125b-5p during enucleation. Following suppression of Bcl-2, the activation of caspase-3 and subsequent activation of ROCK-1 resulted in cytoskeletal rearrangement and enucleation. In conclusion, this study is the first to reveal the pivotal role of miR-125b-5p in erythroblast enucleation.

An In Vivo Model for Elucidating the Role of an Erythroid-Specific Isoform of Nuclear Export Protein Exportin 7 (Xpo7) in Murine Erythropoiesis

Erythroid nuclear condensation is a complex process in which compaction to one-tenth its original size occurs in an active nucleus simultaneously undergoing transcription and cell division. We previously found that the nuclear exportin Exportin7 (Xpo7), which is erythroid- specific and highly induced during terminal erythropoiesis, facilitates nuclear condensation. We also identified a previously unannotated, erythroid-specific isoform of Xpo7 (Xpo7B) containing a novel first exon Xpo7-1b expressed only in late Ter119+ erythroblasts. To better understand the functional difference between the erythroid Xpo7B isoform and the ubiquitous isoform (Xpo7A) containing the original first exon Xpo7-1a, we created gene-targeted mouse models lacking either exon Xpo7-1a or Xpo7-1b, or both exons 4 and 5, which are completely null for Xpo7 expression. We found that deficiency in Xpo7A does not affect steady-state nor stress erythropoiesis. In contrast, mice lacking the erythroid isoform, Xpo7B, exhibit a mild anemia as well as altered stress erythropoiesis. Complete Xpo7 deficiency resulted in partially penetrant embryonic lethality at the stage when definitive erythropoiesis is prominent in the fetal liver. Inducible complete knockdown of Xpo7 confirms that both steady-state erythropoiesis and stress erythropoiesis are affected. We also observe that Xpo7 deficiency downregulates the expression of important stress response factors, such as Gdf15 and Smad3. We conclude that the erythroid-specific isoform of Xpo7 is important for both steady-state and stress erythropoiesis in mice.

A systematic pan-cancer analysis identifies RIOK3 as an immunological and prognostic biomarker

OBJECTIVES

Despite recent research highlighting the critical function of RIO kinase 3 (RIOK3) in a variety of malignancies, a comprehensive evaluation of RIOK3 in human tumors is absent. Our study helps to clarify the molecular mechanism of RIOK3 in carcinogenesis from multiple perspectives.

METHODS

Our research looked into the potential oncogenic role of RIOK3 in 33 cancers using TCGA (The Cancer Genome Atlas), GTEx (Genotype-Tissue Expression Project), GEO (Gene Expression Omnibus) datasets, and several bioinformatics tools.

RESULTS

RIOK3 expression in tumors is disordered compared to normal tissue, and it is highly linked with the level of MMR (Mismatch repair) gene mutations and DNA methyltransferase expression. According to univariate survival analysis, it could be used as an independent prognostic factor. Further investigation demonstrated that RIOK3 expression was correlated with cancer-associated fibroblast, neutrophil, and endothelial infiltration levels in kidney cancer and was positively correlated with the expression of immune checkpoint markers in different cancers. The functional pathways of RIOK3 also included cell-cell adhesion, protein phosphorylation, and innate immune-related functions.

CONCLUSIONS

These findings suggest that RIOK3 could be used as an immunological and prognostic biomarker in various malignant tumors.

Analyses of erythropoiesis from embryonic stem cell‐CD34 + and cord blood‐CD34 + cells reveal mechanisms for defective expansion and enucleation of embryomic stem cell‐erythroid cells

Red blood cells (RBCs) generated ex vivo have the potential to be used for transfusion. Human embryonic stem cells (ES) and induced pluripotent stem cells (iPS) possess unlimited self‐renewal capacity and are the preferred cell sources to be used for ex vivo RBC generation. However, their applications are hindered by the facts that the expansion of ES/iPS‐derived erythroid cells is limited and the enucleation of ES/iPS‐derived erythroblasts is low compared to that derived from cord blood (CB) or peripheral blood (PB). To address this, we sought to investigate the underlying mechanisms by comparing the in vitro erythropoiesis profiles of CB CD34⁺ and ES CD34⁺ cells. We found that the limited expansion of ES CD34⁺ cell‐derived erythroid cells was associated with defective cell cycle of erythroid progenitors. In exploring the cellular and molecular mechanisms for the impaired enucleation of ES CD34⁺ cell‐derived orthochromatic erythroblasts (ES‐ortho), we found the chromatin of ES‐ortho was less condensed than that of CB CD34⁺ cell‐derived orthochromatic erythroblasts (CB‐ortho). At the molecular level, both RNA‐seq and ATAC‐seq analyses revealed that pathways involved in chromatin modification were down‐regulated in ES‐ortho. Additionally, the expression levels of molecules known to play important role in chromatin condensation or/and enucleation were significantly lower in ES‐ortho compared to that in CB‐ortho. Together, our findings have uncovered mechanisms for the limited expansion and impaired enucleation of ES CD34⁺ cell‐derived erythroid cells and may help to improve ex vivo RBC production from stem cells.

Tra2beta-Dependent Regulation of RIO Kinase 3 Splicing During Rift Valley Fever Virus Infection Underscores the Links Between Alternative Splicing and Innate Antiviral Immunity

Rift Valley fever virus (RVFV) is an emerging pathogen that has potential to cause severe disease in humans and domestic livestock. Propagation of RVFV strain MP-12 is negatively impacted by the actions of RIOK3, a protein involved in the cellular immune response to viral infection. During RVFV infection, RIOK3 mRNA is alternatively spliced to produce an isoform that correlates with the inhibition of interferon β signaling. Here, we identify splicing factor TRA2-β (also known as TRA2beta and hTRA2-β) as a key regulator governing the relative abundance of RIOK3 splicing isoforms. Using RT-PCR and minigenes, we determined that TRA2-β interaction with RIOK3 pre-mRNA was necessary for constitutive splicing of RIOK3 mRNA, and conversely, lack of TRA2-β engagement led to increased alternative splicing. Expression of TRA2-β was found to be necessary for RIOK3's antiviral effect against RVFV. Intriguingly, TRA2-β mRNA is also alternatively spliced during RVFV infection, leading to a decrease in cellular TRA2-β protein levels. These results suggest that splicing modulation serves as an immune evasion strategy by RVFV and/or is a cellular mechanism to prevent excessive immune response. Furthermore, the results suggest that TRA2-β can act as a key regulator of additional steps of the innate immune response to viral infection.

Discrete regulatory modules instruct hematopoietic lineage commitment and differentiation

Lineage commitment and differentiation is driven by the concerted action of master transcriptional regulators at their target chromatin sites. Multiple efforts have characterized the key transcription factors (TFs) that determine the various hematopoietic lineages. However, the temporal interactions between individual TFs and their chromatin targets during differentiation and how these interactions dictate lineage commitment remains poorly understood. Here we perform dense, daily, temporal profiling of chromatin accessibility (DNase I-seq) and gene expression changes (total RNA-seq) along ex vivo human erythropoiesis to comprehensively define developmentally regulated DNase I hypersensitive sites (DHSs) and transcripts. We link both distal DHSs to their target gene promoters and individual TFs to their target DHSs, revealing that the regulatory landscape is organized in distinct sequential regulatory modules that regulate lineage restriction and maturation. Finally, direct comparison of transcriptional dynamics (bulk and single-cell) and lineage potential between erythropoiesis and megakaryopoiesis uncovers differential fate commitment dynamics between the two lineages as they exit the stem and progenitor stage. Collectively, these data provide insights into the temporally regulated synergy of the cis- and the trans-regulatory components underlying hematopoietic lineage commitment and differentiation.

Vesicular formation regulated by ERK/MAPK pathway mediates human erythroblast enucleation

ERK pathway plays a key role in enucleation of human orthochromatic erythroblasts.

ERK regulates human erythroblast enucleation by affecting vesicular formation.

Enucleation is a key event in mammalian erythropoiesis responsible for the generation of enucleated reticulocytes. Although progress is being made in developing mechanistic understanding of enucleation, our understanding of mechanisms for enucleation is still incomplete. The MAPK pathway plays diverse roles in biological processes, but its role in erythropoiesis has yet to be fully defined. Analysis of RNA-sequencing data revealed that the MAPK pathway is significantly upregulated during human terminal erythroid differentiation. The MAPK pathway consists of 3 major signaling cassettes: MEK/ERK, p38, and JNK. In the present study, we show that among these 3 cassettes, only ERK was significantly upregulated in late-stage human erythroblasts. The increased expression of ERK along with its increased phosphorylation suggests a potential role for ERK activation in enucleation. To explore this hypothesis, we treated sorted populations of human orthochromatic erythroblasts with the MEK/ERK inhibitor U0126 and found that U0126 inhibited enucleation. In contrast, inhibitors of either p38 or JNK had no effect on enucleation. Mechanistically, U0126 selectively inhibited formation/accumulation of cytoplasmic vesicles and endocytosis of the transferrin receptor without affecting chromatin condensation, nuclear polarization, or enucleosome formation. Treatment with vacuolin-1 that induces vacuole formation partially rescued the blockage of enucleation by U0126. Moreover, phosphoproteomic analysis revealed that inactivation of the ERK pathway led to downregulation of the endocytic recycling pathway. Collectively, our findings uncovered a novel role of ERK activation in human erythroblast enucleation by modulating vesicle formation and have implications for understanding anemia associated with defective enucleation.

Comprehensive Analysis of microRNAs in Human Adult Erythropoiesis

MicroRNAs (miRNAs) are small non-coding RNAs, which play an important role in various cellular and developmental processes. The study of miRNAs in erythropoiesis is crucial to uncover the cellular pathways that are modulated during the different stages of erythroid differentiation. Using erythroid cells derived from human CD34+ hematopoietic stem and progenitor cells (HSPCs)and small RNA sequencing, our study unravels the various miRNAs involved in critical cellular pathways in erythroid maturation. We analyzed the occupancy of erythroid transcription factors and chromatin accessibility in the promoter and enhancer regions of the differentially expressed miRNAs to integrate miRNAs in the transcriptional circuitry of erythropoiesis. Analysis of the targets of the differentially expressed miRNAs revealed novel pathways in erythroid differentiation. Finally, we described the application of Clustered regularly interspaced short palindromic repeats-Cas9 (CRISPR-Cas9) based editing of miRNAs to study their function in human erythropoiesis.

Blood Pharming – eine realistische Option?

Die Bluttransfusion ist ein wesentlicher und unersetzlicher Teil der modernen Medizin. Jedoch stellt vor allem bei Patienten mit sehr seltenen Blutgruppenkonstellationen der Mangel an Blutprodukten auch heute noch ein wichtiges Gesundheitsproblem weltweit dar. Um diesem Problem entgegenzutreten, versucht man seit einiger Zeit künstlich rote Blutzellen zu generieren. Diese haben potenzielle Vorteile gegenüber Spenderblut, wie z. B. ein verringertes Risiko für die Übertragung von Infektionskrankheiten. Diese Übersicht fasst die aktuellen Entwicklungen über den Prozess der Erythropoese, die Expansionsstrategien der erythrozytären Zellen, der verschiedenen Quellen für ex vivo expandierte Erythrozyten, die Hürden für die klinische Anwendung und die zukünftigen Möglichkeiten der Anwendung zusammen.

Erythrocyte miRNA regulators and malarial pathophysiology

Pathophysiology of Plasmodium falciparum and Plasmodium vivax in malaria vis a vis host and the parasite genome interactions has been deciphered recently to present the biology of cerebral malaria, severe anaemia and placental malaria. Small non-coding RNAs have exhibited their potential to be considered as indicators and regulators of diseases. The malarial pathologies and their associated mechanisms mediated by miRNAs and their role in haematopoiesis and red cell-related disorders are elucidated. Evidence of miRNA carrying exosome-like vesicles released during infection, delivering signals to endothelial cells enhancing gene expression, resulting in parasite sequestration and complications leading to pathologies of cerebral malaria are important breakthroughs. Pregnancy malaria showed Plasmodium surface antigen promoted erythrocyte sequestration in the placental intervillous space, provoking disease development and assorted complications. Syncytiotrophoblast-derived microparticles during pregnancy and fetus development may predict pathophysiological progression on account of their altered miRNA cargoes in malaria.

Riok3 inhibits the antiviral immune response by facilitating TRIM40-mediated RIG-I and MDA5 degradation

The type I interferon (IFN) pathway is a key component of innate immune response upon invasion of foreign pathogens. It is also under precise control to prevent excessive upregulation and undesired inflammation cascade. In the present study, we report that Riok3, an atypical kinase, negatively regulates retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) sensing-induced type I IFN signaling. Riok3 deficiency selectively inhibits RNA viral replication in vitro, resulting from an upregulated type I IFN pathway. Mice with myeloid-specific Riok3 knockout also show a more robust induction of type I IFN upon RNA virus infection and are more resistant to RNA virus-induced pathogenesis. Mechanistically, Riok3 recruits and interacts with the E3 ubiquitin ligase TRIM40, leading to the degradation of RIG-I and melanoma differentiation-associated gene-5 (MDA5) via K48- and K27-linked ubiquitination. Collectively, our data reveal the mechanism that Riok3 employs to be a negative regulator of antiviral innate immunity.

A new role of glutathione peroxidase 4 during human erythroblast enucleation

The selenoprotein glutathione peroxidase 4 (GPX4), the only member of the glutathione peroxidase family able to directly reduce cell membrane-oxidized fatty acids and cholesterol, was recently identified as the central regulator of ferroptosis. GPX4 knockdown in mouse hematopoietic cells leads to hemolytic anemia and to increased spleen erythroid progenitor death. The role of GPX4 during human erythropoiesis is unknown. Using in vitro erythroid differentiation, we show here that GPX4-irreversible inhibition by 1S,3R-RSL3 (RSL3) and its short hairpin RNA-mediated knockdown strongly impaired enucleation in a ferroptosis-independent manner not restored by tocopherol or iron chelators. During enucleation, GPX4 localized with lipid rafts at the cleavage furrows between reticulocytes and pyrenocytes. Its inhibition impacted enucleation after nuclear condensation and polarization and was associated with a defect in lipid raft clustering (cholera toxin staining) and myosin-regulatory light-chain phosphorylation. Because selenoprotein translation and cholesterol synthesis share a common precursor, we investigated whether the enucleation defect could represent a compensatory mechanism favoring GPX4 synthesis at the expense of cholesterol, known to be abundant in lipid rafts. Lipidomics and filipin staining failed to show any quantitative difference in cholesterol content after RSL3 exposure. However, addition of cholesterol increased cholera toxin staining and myosin-regulatory light-chain phosphorylation, and improved enucleation despite GPX4 knockdown. In summary, we identified GPX4 as a new actor of human erythroid enucleation, independent of its function in ferroptosis control. We described its involvement in lipid raft organization required for contractile ring assembly and cytokinesis, leading in fine to nucleus extrusion.

Understanding terminal erythropoiesis: An update on chromatin condensation, enucleation, and reticulocyte maturation

A characteristic feature of terminal erythropoiesis in mammals is extrusion of the highly condensed nucleus out of the cytoplasm. Other vertebrates, including fish, reptiles, amphibians, and birds, undergo nuclear condensation but do not enucleate. Enucleation provides mammals evolutionary advantages by gaining extra space for hemoglobin and being more flexible to migrate through capillaries. Nascent reticulocytes further mature into red blood cells through membrane and proteome remodeling and organelle clearance. Over the past decade, novel molecular mechanisms and signaling pathways have been uncovered that play important roles in chromatin condensation, enucleation, and reticulocyte maturation. These advances not only increase understanding of the physiology of erythropoiesis, but also facilitate efforts in generating in vitro red blood cells for various translational application. In the present review, recent studies in epigenetic modification and release of histones during chromatin condensation are highlighted. New insights in enucleation, including protein sorting, vesicle trafficking, transcriptional regulation, noncoding RNA, cytoskeleton remodeling, erythroblastic islands, and cytokinesis, are summarized. Moreover, organelle clearance and proteolysis mediated by ubiquitin-proteasome degradation during reticulocytes maturation is also examined. Perspectives for future directions in this rapidly evolving research area are also provided.

Erythroid enucleation: a gateway into a "bloody" world

Erythropoiesis is an intricate process starting in hematopoietic stem cells and leading to the daily production of 200 billion red blood cells (RBCs). Enucleation is a greatly complex and rate-limiting step during terminal maturation of mammalian RBC production involving expulsion of the nucleus from the orthochromatic erythroblasts, resulting in the formation of reticulocytes. The dynamic enucleation process involves many factors ranging from cytoskeletal proteins to transcription factors to microRNAs. Lack of optimum terminal erythroid maturation and enucleation has been an impediment to optimum RBC production ex vivo. Major efforts in the past two decades have exposed some of the mechanisms that govern the enucleation process. This review focuses in detail on mechanisms implicated in enucleation and discusses the future perspectives of this fascinating process.

MicroRNAs in β-thalassemia

β-thalassemia is a lethal inherited disease resulting from β-globin gene mutations. Severe β-thalassemia requires regular blood transfusions. Other active interventions, including iron chelating, stem cell transplantation and gene therapy, have remarkably improved the quality of life and prolonged the survival of patients with transfusion-dependent β-thalassemia, but all with significant limitations and complications. MicroRNAs (miRNAs), encoded by a class of endogenous genes, are found to play important roles in regulating globin expression. Among the miRNAs of particular interest related to β-thalassemia, miR-15a/16-1, miR-486-3p, miR-26b, miR-199b-5p, miR-210, miR-34a, miR-138, miR-326, let-7, and miR-17/92 cluster elevate γ-globin expression, while miR-96, miR-146a, miR-223-3p, and miR-144 inhibit γ-globin expression. A couple of miRNAs, miR-144 and miR-150, repress α-globin expression, whereas miR-451 induces α-, β- and γ-globin expression. Single nucleotide polymorphism in miRNA genes or their targeted genes might also contribute to the abnormal expression of hemoglobin. Moreover, changes in the expression of miR-125b, miR-210, miR-451, and miR-609 reflect the severity of anemia and hemolysis in β-thalassemia patients. These results suggest that miRNAs are potential biomarkers for the diagnosis and prognosis of β-thalassemia, and miRNA-based therapeutic strategy might be used as a coordinated approach for effectively treating β-thalassemia.

CAP1, a target of miR-144/451, negatively regulates erythroid differentiation and enucleation

The exact molecular mechanism underlying erythroblast enucleation has been a fundamental biological question for decades. In this study, we found that miR-144/451 critically regulated erythroid differentiation and enucleation. We further identified CAP1, a G-actin-binding protein, as a direct target of miR-144/451 in these processes. During terminal erythropoiesis, CAP1 expression declines along with gradually increased miR-144/451 levels. Enforced CAP1 up-regulation inhibits the formation of contractile actin rings in erythroblasts and prevents their terminal differentiation and enucleation. Our findings reveal a negative regulatory role of CAP1 in miR-144/451-mediated erythropoiesis and thus shed light on how microRNAs fine-tune terminal erythroid development through regulating actin dynamics.

Hypoxia Pathway Proteins are Master Regulators of Erythropoiesis

Erythropoiesis is a complex process driving the production of red blood cells. During homeostasis, adult erythropoiesis takes place in the bone marrow and is tightly controlled by erythropoietin (EPO), a central hormone mainly produced in renal EPO-producing cells. The expression of EPO is strictly regulated by local changes in oxygen partial pressure (pO₂) as under-deprived oxygen (hypoxia); the transcription factor hypoxia-inducible factor-2 induces EPO. However, erythropoiesis regulation extends beyond the well-established hypoxia-inducible factor (HIF)-EPO axis and involves processes modulated by other hypoxia pathway proteins (HPPs), including proteins involved in iron metabolism. The importance of a number of these factors is evident as their altered expression has been associated with various anemia-related disorders, including chronic kidney disease. Eventually, our emerging understanding of HPPs and their regulatory feedback will be instrumental in developing specific therapies for anemic patients and beyond.

Muscarinic acetylcholine receptor regulates self-renewal of early erythroid progenitors

Adult stem and progenitor cells are uniquely capable of self-renewal, and targeting this process represents a potential therapeutic opportunity. The early erythroid progenitor, burst-forming unit erythroid (BFU-E), has substantial self-renewal potential and serves as a key cell type for the treatment of anemias. However, our understanding of mechanisms underlying BFU-E self-renewal is extremely limited. Here, we found that the muscarinic acetylcholine receptor, cholinergic receptor, muscarinic 4 (CHRM4), pathway regulates BFU-E self-renewal and that pharmacological inhibition of CHRM4 corrects anemias of myelodysplastic syndrome (MDS), aging, and hemolysis. Genetic down-regulation of CHRM4 or pharmacologic inhibition of CHRM4 using the selective antagonist PD102807 promoted BFU-E self-renewal, whereas deletion of Chrm4 increased erythroid cell production under stress conditions in vivo. Moreover, muscarinic acetylcholine receptor antagonists corrected anemias in mouse models of MDS, aging, and hemolysis in vivo, extending the survival of mice with MDS relative to that of controls. The effects of muscarinic receptor antagonism on promoting expansion of BFU-Es were mediated by cyclic AMP induction of the transcription factor CREB, whose targets up-regulated key regulators of BFU-E self-renewal. On the basis of these data, we propose a model of hematopoietic progenitor self-renewal through a cholinergic-mediated "hematopoietic reflex" and identify muscarinic acetylcholine receptor antagonists as potential therapies for anemias associated with MDS, aging, and hemolysis.

miR-144/451 inhibits c-Myc to promote erythroid differentiation

Ablation of miR-144/451 disrupts homeostasis of erythropoiesis. Myc, a protooncogenic protein, is essential for erythroblast proliferation but commits rapid downregulation during erythroid maturation. How erythroblasts orchestrate maturation processes through coding and non-coding genes is largely unknown. In this study, we use miR-144/451 knockout mice as in vivo model, G1E, MEL erythroblast lines and erythroblasts from fresh mouse fetal livers as in vitro systems to demonstrate that targeted depletion of miR-144/451 blocks erythroid nuclear condensation and enucleation. This is due, at least in part, to the continued high expression of Myc in erythroblasts when miR-144/451 is absent. Specifically, miR-144/451 directly inhibits Myc in erythroblasts. Loss of miR-144/451 locus derepresses, and thus, increases the expression of Myc. Sustained high levels of Myc in miR-144/451-depleted erythroblasts blocks erythroid differentiation. Moreover, Myc reversely regulates the expression of miR-144/451, forming a positive miR-144/451-Myc feedback to ensure the complete shutoff of Myc during erythropoiesis. Given that erythroid-specific transcription factor GATA1 activates miR-144/451 and inactivates Myc, our findings indicate that GATA1-miR-144/451-Myc network safeguards normal erythroid differentiation. Our findings also demonstrate that disruption of the miR-144/451-Myc crosstalk causes anemia, suggesting that miR-144/451 might be a potential therapeutic target in red cell diseases.

MicroRNA Clustering Assists Processing of Suboptimal MicroRNA Hairpins through the Action of the ERH Protein

Microprocessor initiates the processing of microRNAs (miRNAs) from the hairpin regions of primary transcripts (pri-miRNAs). Pri-miRNAs often contain multiple miRNA hairpins, and this clustered arrangement can assist in the processing of otherwise defective hairpins. We find that miR-451, which derives from a hairpin with a suboptimal terminal loop and a suboptimal stem length, accumulates to 40-fold higher levels when clustered with a helper hairpin. This phenomenon tolerates changes in hairpin order, linker lengths, and the identities of the helper hairpin, the recipient hairpin, the linker-sequence, and the RNA polymerase that transcribes the hairpins. It can act reciprocally and need not occur co-transcriptionally. It requires Microprocessor recognition of the helper hairpin and linkage of the two hairpins, yet predominantly manifests after helper-hairpin processing. It also requires enhancer of rudimentary homolog (ERH), which copurifies with Microprocessor and can dimerize and interact with other proteins that can dimerize, suggesting a model in which one Microprocessor recruits another Microprocessor.

Ago2-Dependent Processing Allows miR-451 to Evade the Global MicroRNA Turnover Elicited during Erythropoiesis

MicroRNAs (miRNAs) are sequentially processed by two RNase III enzymes, Drosha and Dicer. miR-451 is the only known miRNA whose processing bypasses Dicer and instead relies on the slicer activity of Argonaute-2 (Ago2). miR-451 is highly conserved in vertebrates and regulates erythrocyte maturation, where it becomes the most abundant miRNA. However, the basis for the non-canonical biogenesis of miR-451 is unclear. Here, we show that Ago2 is less efficient than Dicer in processing pre-miRNAs, but this deficit is overcome when miR-144 represses Dicer in a negative-feedback loop during erythropoiesis. Loss of miR-144-mediated Dicer repression in zebrafish embryos and human cells leads to increased canonical miRNA production and impaired miR-451 maturation. Overexpression of Ago2 rescues some of the defects of miR-451 processing. Thus, the evolution of Ago2-dependent processing allows miR-451 to circumvent the global repression of canonical miRNAs elicited, in part, by the miR-144 targeting of Dicer during erythropoiesis.

Cellular dynamics of mammalian red blood cell production in the erythroblastic island niche

Red blood cells, or erythrocytes, make up approximately a quarter of all cells in the human body with over 2 billion new erythrocytes made each day in a healthy adult human. This massive cellular production system is coupled with a set of cell biological processes unique to mammals, in particular, the elimination of all organelles, and the expulsion and destruction of the condensed erythroid nucleus. Erythrocytes from birds, reptiles, amphibians and fish possess nuclei, mitochondria and other organelles: erythrocytes from mammals lack all of these intracellular components. This review will focus on the dynamic changes that take place in developing erythroid cells that are interacting with specialized macrophages in multicellular clusters termed erythroblastic islands. Proerythroblasts enter the erythroblastic niche as large cells with active nuclei, mitochondria producing heme and energy, and attach to the central macrophage via a range of adhesion molecules. Proerythroblasts then mature into erythroblasts and, following enucleation, in reticulocytes. When reticulocytes exit the erythroblastic island, they are smaller cells, without nuclei and with few mitochondria, possess some polyribosomes and have a profoundly different surface molecule phenotype. Here, we will review, step-by-step, the biophysical mechanisms that regulate the remarkable process of erythropoiesis with a particular focus on the events taking place in the erythroblastic island niche. This is presented from the biological perspective to offer insight into the elements of red blood cell development in the erythroblastic island niche which could be further explored with biophysical modelling systems.

Altered erythroid-related miRNA levels as a possible novel biomarker for detection of autologous blood transfusion misuse in sport

BACKGROUND

Autologous blood transfusion (ABT) is a performance-enhancing method prohibited in sport; its detection is a key issue in the field of anti-doping. Among novel markers enabling ABT detection, microRNAs (miRNAs) might be considered a promising analytical tool.

STUDY DESIGN AND METHODS

We studied the changes of erythroid-related microRNAs following ABT, to identify novel biomarkers. Fifteen healthy trained males were studied from a population of 24 subjects, enrolled and randomized into a Transfusion (T) and a Control (C) group. Seriated blood samples were obtained in the T group before and after the two ABT procedures (withdrawal, with blood refrigerated or cryopreserved, and reinfusion), and in the C group at the same time points. Traditional hematological parameters were assessed. Samples were tested by microarray analysis of a pre-identified set of erythroid-related miRNAs.

RESULTS

Hematological parameters showed moderate changes only in the T group, particularly following blood withdrawal. Among erythroid-related miRNAs tested, following ABT a pool of 7 miRNAs associated with fetal hemoglobin and regulating transcriptional repressors of gamma-globin gene was found stable in C and differently expressed in three out of six T subjects in the completed phase of ABT, independently from blood conservation. Particularly, two or more erythropoiesis-related miRNAs within the shortlist constituted of miR-126-3p, miR-144-3p, miR-191-3p, miR-197-3p, miR-486-3p, miR-486-5p, and miR-92a-3p were significantly upregulated in T subjects after reinfusion, with a person-to-person variability but with congruent changes.

CONCLUSIONS

This study describes a signature of potential interest for ABT detection in sports, based on the analysis of miRNAs associated with erythroid features.

Regulation of gene expression by miR-144/451 during mouse erythropoiesis

The microRNA (miRNA) locus miR-144/451 is abundantly expressed in erythrocyte precursors, facilitating their terminal maturation and protecting against oxidant stress. However, the full repertoire of erythroid miR-144/451 target messenger RNAs (mRNAs) and associated cellular pathways is unknown. In general, the numbers of mRNAs predicted to be targeted by an miRNA vary greatly from hundreds to thousands, and are dependent on experimental approaches. To comprehensively and accurately identify erythroid miR-144/451 target mRNAs, we compared gene knockout and wild-type fetal liver erythroblasts by RNA sequencing, quantitative proteomics, and RNA immunoprecipitation of Argonaute (Ago), a component of the RNA-induced silencing complex that binds miRNAs complexed to their target mRNAs. Argonaute bound ∼1400 erythroblast mRNAs in a miR-144/451-dependent manner, accounting for one-third of all Ago-bound mRNAs. However, only ∼100 mRNAs were stabilized after miR-144/451 loss. Thus, miR-144 and miR-451 deregulate <10% of mRNAs that they bind, a characteristic that likely applies generally to other miRNAs. Using stringent selection criteria, we identified 53 novel miR-144/451 target mRNAs. One of these, Cox10, facilitates the assembly of mitochondrial electron transport complex IV. Loss of miR-144/451 caused increased Cox10 mRNA and protein, accumulation of complex IV, and increased mitochondrial membrane potential with no change in mitochondrial mass. Thus, miR-144/451 represses mitochondrial respiration during erythropoiesis by inhibiting the production of Cox10.

The mouse KLF1 Nan variant impairs nuclear condensation and erythroid maturation

Krüppel-like factor 1 (KLF1) is an essential transcription factor for erythroid development, as demonstrated by Klf1 knockout mice which die around E14 due to severe anemia. In humans, >140 KLF1 variants, causing different erythroid phenotypes, have been described. The KLF1 Nan variant, a single amino acid substitution (p.E339D) in the DNA binding domain, causes hemolytic anemia and is dominant over wildtype KLF1. Here we describe the effects of the KLF1 Nan variant during fetal development. We show that Nan embryos have defects in erythroid maturation. RNA-sequencing of the KLF1 Nan fetal liver cells revealed that Exportin 7 (Xpo7) was among the 782 deregulated genes. This nuclear exportin is implicated in terminal erythroid differentiation; in particular it is involved in nuclear condensation. Indeed, KLF1 Nan fetal liver cells had larger nuclei and reduced chromatin condensation. Knockdown of XPO7 in wildtype erythroid cells caused a similar phenotype. We propose that reduced expression of XPO7 is partially responsible for the erythroid defects observed in KLF1 Nan erythroid cells.

Transferrin receptor 1 is required for enucleation of mouse erythroblasts during terminal differentiation

Enucleation is the process whereby the nucleus is extruded from the erythroblast during late stage mammalian erythropoiesis. However, the specific signaling pathways involved in this process remain unclear. To better understand the mechanisms underlying erythroblast enucleation, we investigated erythroblast enucleation using both the spleens of adult mice with phenylhydrazine‐induced anemia and mouse fetal livers. Our results indicated that both iron‐bound transferrin (holo‐Tf) and the small‐molecule iron transporter hinokitiol with iron ions (hinokitiol plus iron) promote hemoglobin synthesis and the enucleation of mouse spleen‐derived erythroblasts. Although an antitransferrin receptor 1 (TfR1) monoclonal antibody inhibited both enucleation and hemoglobin synthesis promoted by holo‐Tf, it inhibited only enucleation, but not hemoglobin synthesis, promoted by hinokitiol plus iron. Furthermore, siRNA against mouse TfR1 were found to suppress the enucleation of mouse fetal liver‐derived erythroblasts, and the endocytosis inhibitor MitMAB inhibited enucleation, hemoglobin synthesis, and the internalization of TfR1 promoted by both types of stimuli. Collectively, our results suggest that TfR1, iron ions, and endocytosis play important roles in mouse erythroblast enucleation.

Dual Strategies for Argonaute2-Mediated Biogenesis of Erythroid miRNAs Underlie Conserved Requirements for Slicing in Mammals

While Slicer activity of Argonaute is central to RNAi, conserved roles of slicing in endogenous regulatory biology are less clear, especially in mammals. Biogenesis of erythroid Dicer-independent mir-451 involves Ago2 catalysis, but mir-451-KO mice do not phenocopy Ago2 catalytic-dead (Ago2-CD) mice, suggesting other needs for slicing. Here, we reveal mir-486 as another dominant erythroid miRNA with atypical biogenesis. While it is Dicer dependent, it requires slicing to eliminate its star strand. Thus, in Ago2-CD conditions, miR-486-5p is functionally inactive due to duplex arrest. Genome-wide analyses reveal miR-486 and miR-451 as the major slicing-dependent miRNAs in the hematopoietic system. Moreover, mir-486-KO mice exhibit erythroid defects, and double knockout of mir-486/451 phenocopies the cell-autonomous effects of Ago2-CD in the hematopoietic system. Finally, we observe that Ago2 is the dominant-expressed Argonaute in maturing erythroblasts, reflecting a specialized environment for processing slicing-dependent miRNAs. Overall, the mammalian hematopoietic system has evolved multiple conserved requirements for Slicer-dependent miRNA biogenesis.

Zebrafish miR-462-731 regulates hematopoietic specification and pu.1-dependent primitive myelopoiesis

MicroRNAs (miRNAs) play significant roles in both embryonic hematopoiesis and hematological malignancy. Zebrafish miR-462-731 cluster is orthologous of miR-191-425 in human which regulates proliferation and tumorigenesis. In our previous work, miR-462-731 was found highly and ubiquitously expressed during early embryogenesis. In this study, by loss-of-function analysis (morpholino knockdown combined with CRISRP/Cas9 knockout) and mRNA profiling, we suggest that miR-462-731 is required for normal embryonic development by regulating cell survival. We found that loss of miR-462/miR-731 caused a remarkable decrease in the number of erythroid cells as well as an ectopic myeloid cell expansion at 48 hpf, suggesting a skewing of myeloid-erythroid lineage differentiation. Mechanistically, miR-462-731 provides an instructive input for pu.1-dependent primitive myelopoiesis through regulating etsrp/scl signaling combined with a novel pu.1/miR-462-731 feedback loop. On the other hand, morpholino (MO) knockdown of miR-462/miR-731 resulted in an expansion of posterior blood islands at 24 hpf, which is a mild ventralization phenotype resulted from elevation of BMP signaling. Rescue experiments with both BMP type I receptor inhibitor dorsomorphin and alk8 MO indicate that miR-462-731 acts upstream of alk8 within the BMP/Smad signaling pathway and functions as a novel endogenous BMP antagonist. Besides, an impairment of angiogenesis was observed in miR-462/miR-731 morphants. The specification of arteries and veins was also perturbed, as characterized by the irregular patterning of efnb2a and flt4 expression. Our study unveils a previously unrecognized role of miR-462-731 in BMP/Smad signaling mediated hematopoietic specification of mesodermal progenitors and demonstrates a miR-462-731 mediated regulatory mechanism driving primitive myelopoiesis in the ALPM. We also show a requirement for miR-462-731 in regulating arterial-venous specification and definitive hematopoietic stem cell (HSC) production. The current findings might provide further insights into the molecular mechanistic basis of miRNA regulation of embryonic hematopoiesis and hematological malignancy.

S6K1 phosphorylation-dependent degradation of Mxi1 by β-Trcp ubiquitin ligase promotes Myc activation and radioresistance in lung cancer

Rationale: Mxi1 is regarded as a potential tumor suppressor protein that antagonizes the transcriptional activity of proto-oncogene Myc. However, the clinical significances and underlying mechanisms by which Mxi1 is regulated in lung cancer remain poorly understood.

Methods: Mass spectrometry analysis and immunoprecipitation assay were utilized to detect the protein-protein interaction. The phosphorylation of Mxi1 was evaluated by in vitro kinase assays. Poly-ubiquitination of Mxi1 was examined by in vivo ubiquitination assay. Lung cancer cells stably expressing wild-type Mxi1 or Mxi1-S160A were used for functional analyses. The expression levels of Mxi1 and S6K1 were determined by immunohistochemistry in lung cancer tissues and adjacent normal lung tissues.

Results: We found that Mxi1 is downregulated and correlated with poor prognosis in lung cancer. Using tandem affinity purification technology, we provided evidence that β-Trcp E3 ubiquitin ligase interacts with and promotes the ubiquitination and degradation of Mxi1. Furthermore, we demonstrated that Mxi1 is phosphorylated at S160 site by the protein kinase S6K1 and subsequently degraded via the ubiquitin ligase β-Trcp. Moreover, a phosphorylation mutant form of Mxi1 (Mxi1-S160A), which cannot be degraded by S6K1 and β-Trcp, is much more stable and efficient in suppressing the transcriptional activity of Myc and radioresistance in lung cancer cells. More importantly, a strong inverse correlation between S6K1 and Mxi1 expression was observed in human lung cancer tissues.

Conclusion: Our findings not only establish a crosstalk between the mTOR/S6K1 signaling pathway and Myc activation, but also suggest that targeting S6K1/Mxi1 pathway is a promising therapeutic strategy for the treatment of lung cancer.

Quantitative proteomics reveals that miR-222 inhibits erythroid differentiation by targeting BLVRA and CRKL

miR-222 plays an important role in erythroid differentiation, but the potential targets of miR-222 in the regulation of erythroid differentiation remain to be determined. The target genes of miR-222 were identified by proteomics combined with bioinformatics analysis in this study. Thirteen proteins were upregulated, and 13 were downregulated in K562 cells following transfection with miR-222 inhibitor for 24 and 48 hours. Among these proteins, BLVRA and CRKL were upregulated after transfection of miR-222 inhibitor in K562 cells and human CD34+ HPCs. Moreover, miR-222 mimics reduced and miR-222 inhibitor enhanced the mRNA and protein levels of both BLVRA and CRKL. Luciferase assay showed that miR-222 directly targeted 3'-UTR of BLVRA and CRKL. In addition, overexpression of either BLVRA or CRKL or both increased the erythroid differentiation of K562 cells, while silencing of either BLVRA or CRKL or both by siRNA significantly attenuated hemin-induced erythroid differentiation of K562 cells. Our results indicated that BLVRA and CRKL are targets of miR-222.

Activating and sustaining c-Myc by depletion of miR-144/451 gene locus contributes to B-lymphomagenesis

Hyper activity of protooncogene c-Myc is one of the hallmarks of highly aggressive lymphomas. However, the mechanism of how c-Myc is subjected to activation and amplification is still not well defined. In this study, we use gene knockout strategy to show that targeted depletion of a well-conserved microRNA gene locus miR-144/451 initiates tumorigenesis including B-lymphoma development in aged mice. This is due, at least in part, to the direct activation of the c-Myc gene by loss of miR-144/451 expression in hematopoietic cells. Moreover, oncoprotein c-Myc inversely regulates miR-144/451 expression by directly binding to the miR-144/451 promoter region, forming a miRNA-Myc positive feedback loop to safeguard the high level of c-Myc in B-lymphocytes. We also demonstrate that this miRNA-Myc crosstalk is disrupted in human diffuse large B-cell lymphomas with aberrant c-Myc expression. Therefore, our findings provide strong evidence, for the first time, that deficiency of miR-144/451 expression may play a bona fide role in derepression of silenced c-Myc, which contributes to tumor development including B-lymphomagenesis.

miR-144/451 represses the LKB1/AMPK/mTOR pathway to promote red cell precursor survival during recovery from acute anemia

The microRNAs miR-144 and -451 are encoded by a bicistronic gene that is strongly induced during red blood cell formation (erythropoiesis). Ablation of the miR-144/451 gene in mice causes mild anemia under baseline conditions. Here we show that miR-144/451^−/− erythroblasts exhibit increased apoptosis during recovery from acute anemia. Mechanistically, miR-144/451 depletion increases the expression of the miR-451 target mRNA Cab39, which encodes a co-factor for the serine-threonine kinase LKB1. During erythropoietic stress, miR-144/451^−/− erythroblasts exhibit abnormally increased Cab39 protein, which activates LKB1 and its downstream AMPK/mTOR effector pathway. Suppression of this pathway via drugs or shRNAs enhances survival of the mutant erythroblasts. Thus, miR-144/451 facilitates recovery from acute anemia by repressing Cab39/AMPK/mTOR. Our findings suggest that miR-144/451 is a key protector of erythroblasts during pathological states associated with dramatically increased erythropoietic demand, including acute blood loss and hemolytic anemia.

Dietary miR-451 protects erythroid cells from oxidative stress via increasing the activity of Foxo3 pathway

One fundamental issue in public health is the safety of food products derived from plants and animals. A recent study raised a concern that microRNAs, which widely exist in everyday foods, may alter consumers' functions. However, some studies have strongly questioned the likelihood of dietary uptake of functional microRNAs in mammals. Here we use a microRNA gene knockout animal model to show that miR-144/451 null mice can orally uptake miR-451 from a daily chow diet, and ingestion of wild type blood, that contains abundant miR-451, also enhances the level of miR-451 in the circulating blood of knockout mice. Moreover, reducing miR-451 level in miR-144/451 knockout blood by consuming food lacking miR-451 reduces the anti-oxidant capacity of miR-144/451 null red blood cells by targeting the 14-3-3ζ/Foxo3 pathway, while increasing miR-451 level via gavage-feeding of wild type blood increases the anti-oxidant capacity of miR-144/451 null red blood cells. We conclude that 1) some miRNAs in food can pass through the gastrointestinal tract into the blood to affect consumers' function and 2) microRNA knockout animals such as miR-144/451 null mice can acquire the deleted genetic information from daily foods, which might alter the results and conclusions from the studies using such animals.