PI3K/HSCB axis facilitates FOG1 nuclear translocation to promote erythropoiesis and megakaryopoiesis.

Erythropoiesis and megakaryopoiesis are stringently regulated by signaling pathways. However, the precise molecular mechanisms through which signaling pathways regulate key transcription factors controlling erythropoiesis and megakaryopoiesis remain partially understood. Herein, we identified heat shock cognate B (HSCB), which is well known for its iron-sulfur cluster delivery function, as an indispensable protein for friend of GATA 1 (FOG1) nuclear translocation during erythropoiesis of K562 human erythroleukemia cells and cord-blood-derived human CD34+CD90+hematopoietic stem cells (HSCs), as well as during megakaryopoiesis of the CD34+CD90+HSCs. Mechanistically, HSCB could be phosphorylated by phosphoinositol-3-kinase (PI3K) to bind with and mediate the proteasomal degradation of transforming acidic coiled-coil containing protein 3 (TACC3), which otherwise detained FOG1 in the cytoplasm, thereby facilitating FOG1 nuclear translocation. Given that PI3K is activated during both erythropoiesis and megakaryopoiesis, and that FOG1 is a key transcription factor for these processes, our findings elucidate an important, previously unrecognized iron-sulfur cluster delivery independent function of HSCB in erythropoiesis and megakaryopoiesis.

Hookworm infection as a model for deepen knowledge of iron metabolism and erythropoiesis in anemia.

Over the years, there has been progress in understanding the molecular aspects of iron metabolism and erythropoiesis. However, despite research conducted both in laboratories and living organisms, there are still unanswered questions due to the complex nature of these fields. In this study we investigated the effects of hookworm infection on iron metabolism and how the hosts response to anemia is affected using hamsters infected with Ancylostoma ceylanicum as a model. Our data revealed interesting relationships between infection-induced anemia, erythropoiesis, iron metabolism, and immune modulation, such that the elevated production of erythropoietin (EPO) in renal tissue indicated intensified erythropoiesis in response to anemia. Additionally, the increased expression of the erythroferrone (ERFE) gene in the spleen suggested its involvement in iron regulation and erythropoiesis. Gene expression patterns of genes related to iron metabolism varied in different tissues, indicating tissue-specific adaptations to hypoxia. The modulation of pro-inflammatory and anti-inflammatory cytokines highlighted the delicate balance between immune response and erythropoiesis. Data derived from the investigation of changes induced in iron metabolism and stress erythropoiesis following anemia aid in our understanding of mechanisms related to blood spoliation and anemia, which could potentially be extrapolated or compared to other types or causes of anemia. These findings also contribute to our understanding of the pathophysiology of erythropoiesis in the context of blood loss.

Deciphering the regulatory landscape of murine splenic response to anemic stress at single-cell resolution.

ABSTRACT: Stress erythropoiesis can be influenced by multiple mediators through both intrinsic and extrinsic mechanisms in early erythroid precursors. Single-cell RNA sequencing was conducted on spleen tissue isolated from mice subjected to phenylhydrazine and serial bleeding to explore novel molecular mechanisms of stress erythropoiesis. Our results showed prominent emergence of early erythroblast populations under both modes of anemic stress. Analysis of gene expression revealed distinct phases during the development of emerging erythroid cells. Interestingly, we observed the presence of a "hiatus" subpopulation characterized by relatively low level of transcriptional activities that transitions between early stages of emerging erythroid cells, with moderate protein synthesis activities. Moreover, single-cell analysis conducted on macrophage populations revealed distinct transcriptional programs in Vcam1+ macrophages under stress. Notably, a novel marker, CD81, was identified for labeling central macrophages in erythroblastic islands (EBIs), which is functionally required for EBIs to combat anemic stress. These findings offer fresh insights into the intrinsic and extrinsic pathways of early erythroblasts' response to stress, potentially informing the development of innovative therapeutic approaches for addressing anemic-related conditions.

Signaling networks guiding erythropoiesis.

PURPOSE OF REVIEW: Cytokine-mediated signaling pathways, including JAK/STAT, PI3K/AKT, and Ras/MAPK pathways, play an important role in the process of erythropoiesis. These pathways are involved in the survival, proliferation, and differentiation function of erythropoiesis. RECENT FINDINGS: The JAK/STAT pathway controls erythroid progenitor differentiation, proliferation, and survival. The PI3K/AKT signaling cascade facilitates erythroid progenitor survival, proliferation, and final differentiation. During erythroid maturation, MAPK, triggered by EPO, suppresses myeloid genes, while PI3K is essential for differentiation. Pro-inflammatory cytokines activate signaling pathways that can alter erythropoiesis like EPOR-triggered signaling, including survival, differentiation, and proliferation. SUMMARY: A comprehensive understanding of signaling networks is crucial for the formulation of treatment approaches for hematologic disorders. Further investigation is required to fully understand the mechanisms and interactions of these signaling pathways in erythropoiesis.

A comparative study of two routinely used protocols for ex vivo erythroid differentiation.

BACKGROUND: Erythropoiesis is a complex developmental process in which a hematopoietic stem cell undergoes serial divisions and differentiates through well-defined stages to give rise to red blood cells. Over the last decades, several protocols have been developed to perform ex vivo erythroid differentiation, allowing investigation into erythropoiesis and red cell production in health and disease. RESULTS: In the current study, we compared the two commonly used protocols by assessing the differentiation kinetics, synchronisation, and cellular yield, using molecular and cellular approaches. Peripheral blood CD34+ cells were cultured in a two-phase (2P) or a four-phase (4P) liquid culture (LC) and monitored for 20 days. Both protocols could recapitulate all stages of erythropoiesis and generate reticulocytes, although to different extents. Higher proliferation and viability rates were achieved in the 4P-LC, with a higher degree of terminal differentiation and enucleation, associated with higher levels of the erythroid-specific transcription factors GATA-1, KLF-1, and TAL-1. Although the 2P-LC protocol was less efficient regarding terminal erythroid differentiation and maturation, it showed a higher yield of erythroid progenitors in the erythropoietin (EPO)-free expansion phase. CONCLUSIONS: We provide data supporting the use of one protocol or the other to study the biological processes occurring in the early or late stages of erythroid differentiation, depending on the physiological process or pathological defect under investigation in a given study.

Metabolic regulation of erythrocyte development and disorders.

The formation of new red blood cells (RBC) (erythropoiesis) has served as a paradigm for understanding cellular differentiation and developmental control of gene expression. The metabolic regulation of this complex, coordinated process remains poorly understood. Each step of erythropoiesis, including lineage specification of hematopoietic stem cells, proliferation, differentiation, and terminal maturation into highly specialized oxygen-carrying cells, has unique metabolic requirements. Developing erythrocytes in mammals are also characterized by unique metabolic events such as loss of mitochondria with switch to glycolysis, ejection of nucleus and organelles, high-level heme and hemoglobin synthesis, and antioxidant requirement to protect hemoglobin molecules. Genetic defects in metabolic enzymes, including pyruvate kinase and glucose-6-phosphate dehydrogenase, cause common erythrocyte disorders, whereas other inherited disorders such as sickle cell disease and ß-thalassemia display metabolic abnormalities associated with disease pathophysiology. Here we describe recent discoveries on the metabolic control of RBC formation and function, highlight emerging concepts in understanding the erythroid metabolome, and discuss potential therapeutic benefits of targeting metabolism for RBC disorders.

Luspatercept stimulates erythropoiesis, increases iron utilization, and redistributes body iron in transfusion-dependent thalassemia.

Luspatercept, a ligand-trapping fusion protein, binds select TGF-ß superfamily ligands implicated in thalassemic erythropoiesis, promoting late-stage erythroid maturation. Luspatercept reduced transfusion burden in the BELIEVE trial (NCT02604433) of 336 adults with transfusion-dependent thalassemia (TDT). Analysis of biomarkers in BELIEVE offers novel physiological and clinical insights into benefits offered by luspatercept. Transfusion iron loading rates decreased 20% by 1.4 g (~7 blood units; median iron loading rate difference: -0.05 ± 0.07 mg Fe/kg/day, p< .0001) and serum ferritin (s-ferritin) decreased 19.2% by 269.3 ± 963.7 µg/L (p < .0001), indicating reduced macrophage iron. However, liver iron content (LIC) did not decrease but showed statistically nonsignificant increases from 5.3 to 6.7 mg/g dw. Erythropoietin, growth differentiation factor 15, soluble transferrin receptor 1 (sTfR1), and reticulocytes rose by 93%, 59%, 66%, and 112%, respectively; accordingly, erythroferrone increased by 51% and hepcidin decreased by 53% (all p < .0001). Decreased transfusion with luspatercept in patients with TDT was associated with increased erythropoietic markers and decreasing hepcidin. Furthermore, s-ferritin reduction associated with increased erythroid iron incorporation (marked by sTfR1) allowed increased erythrocyte marrow output, consequently reducing transfusion needs and enhancing rerouting of hemolysis (heme) iron and non-transferrin-bound iron to the liver. LIC increased in patients with intact spleens, consistent with iron redistribution given the hepcidin reduction. Thus, erythropoietic and hepcidin changes with luspatercept in TDT lower transfusion dependency and may redistribute iron from macrophages to hepatocytes, necessitating the use of concomitant chelator cover for effective iron management.

Extramedullary hematopoiesis contributes to enhanced erythropoiesis during pregnancy via TGF-ß signaling.

Red blood cells are the predominant cellular component in human body, and their numbers increase significantly during pregnancy due to heightened erythropoiesis. CD71+ erythroid cells (CECs) are immature red blood cells, encompassing erythroblasts and reticulocytes, constitute a rare cell population primarily found in the bone marrow, although they are physiologically enriched in the neonatal mouse spleen and human cord blood. Presently, the mechanisms underlying the CECs expansion during pregnancy remain largely unexplored. Additionally, the mechanisms and roles associated with extramedullary hematopoiesis (EMH) of erythroid cells during pregnancy have yet to be fully elucidated. In this study, our objective was to examine the underlying mechanisms of erythroid-biased hematopoiesis during pregnancy. Our findings revealed heightened erythropoiesis and elevated CECs in both human and mouse pregnancies. The increased presence of transforming growth factor (TGF)-ß during pregnancy facilitated the differentiation of CD34+ hematopoietic stem and progenitor cells (HSPCs) into CECs, without impacting HSPCs proliferation, ultimately leading to enhanced erythropoiesis. The observed increase in CECs during pregnancy was primarily attributed to EMH occurring in the spleen. During mouse pregnancy, splenic stromal cells were found to have a significant impact on splenic erythropoiesis through the activation of TGF-ß signaling. Conversely, splenic macrophages were observed to contribute to extramedullary erythropoiesis in a TGF-ß-independent manner. Our results suggest that splenic stromal cells play a crucial role in promoting extramedullary erythropoiesis and the production of CECs during pregnancy, primarily through TGF-ß-dependent mechanisms.

Phenotypic Alterations in Erythroid Nucleated Cells of Spleen and Bone Marrow in Acute Hypoxia.

Hypoxia leads to metabolic changes at the cellular, tissue, and organismal levels. The molecular mechanisms for controlling physiological changes during hypoxia have not yet been fully studied. Erythroid cells are essential for adjusting the rate of erythropoiesis and can influence the development and differentiation of immune cells under normal and pathological conditions. We simulated high-altitude hypoxia conditions for mice and assessed the content of erythroid nucleated cells in the spleen and bone marrow under the existing microenvironment. For a pure population of CD71+ erythroid cells, we assessed the production of cytokines and the expression of genes that regulate the immune response. Our findings show changes in the cellular composition of the bone marrow and spleen during hypoxia, as well as changes in the composition of the erythroid cell subpopulations during acute hypoxic exposure in the form of a decrease in orthochromatophilic erythroid cells that are ready for rapid enucleation and the accumulation of their precursors. Cytokine production normally differs only between organs; this effect persists during hypoxia. In the bone marrow, during hypoxia, genes of the C-lectin pathway are activated. Thus, hypoxia triggers the activation of various adaptive and compensatory mechanisms in order to limit inflammatory processes and modify metabolism.

E-cadherin/ß-catenin expression is conserved in human and rat erythropoiesis and marks stress erythropoiesis.

E-cadherin is a crucial regulator of epithelial cell-to-cell adhesion and an established tumor suppressor. Aside epithelia, E-cadherin expression marks the erythroid cell lineage during human but not mouse hematopoiesis. However, the role of E-cadherin in human erythropoiesis remains unknown. Because rat erythropoiesis was postulated to reflect human erythropoiesis more closely than mouse erythropoiesis, we investigated E-cadherin expression in rat erythroid progenitors. E-cadherin expression is conserved within the erythroid lineage between rat and human. In response to anemia, erythroblasts in rat bone marrow (BM) upregulate E-cadherin as well as its binding partner ß-catenin. CRISPR/Cas9-mediated knock out of E-cadherin revealed that E-cadherin expression is required to stabilize ß-catenin in human and rat erythroblasts. Suppression of ß-catenin degradation by glycogen synthase kinase 3ß (GSK3ß) inhibitor CHIR99021 also enhances ß-catenin stability in human erythroblasts but hampers erythroblast differentiation and survival. In contrast, direct activation of ß-catenin signaling, using an inducible, stable ß-catenin variant, does not perturb maturation or survival of human erythroblasts but rather enhances their differentiation. Although human erythroblasts do not respond to Wnt ligands and direct GSK3ß inhibition even reduces their survival, we postulate that ß-catenin stability and signaling is mostly controlled by E-cadherin in human and rat erythroblasts. In response to anemia, E-cadherin-driven upregulation and subsequent activation of ß-catenin signaling may stimulate erythroblast differentiation to support stress erythropoiesis in the BM. Overall, we uncover E-cadherin/ß-catenin expression to mark stress erythropoiesis in rat BM. This may provide further understanding of the underlying molecular regulation of stress erythropoiesis in the BM, which is currently poorly understood.

Normal and dysregulated crosstalk between iron metabolism and erythropoiesis.

Erythroblasts possess unique characteristics as they undergo differentiation from hematopoietic stem cells. During terminal erythropoiesis, these cells incorporate large amounts of iron in order to generate hemoglobin and ultimately undergo enucleation to become mature red blood cells, ultimately delivering oxygen in the circulation. Thus, erythropoiesis is a finely tuned, multifaceted process requiring numerous properly timed physiological events to maintain efficient production of 2 million red blood cells per second in steady state. Iron is required for normal functioning in all human cells, the erythropoietic compartment consuming the majority in light of the high iron requirements for hemoglobin synthesis. Recent evidence regarding the crosstalk between erythropoiesis and iron metabolism sheds light on the regulation of iron availability by erythroblasts and the consequences of insufficient as well as excess iron on erythroid lineage proliferation and differentiation. In addition, significant progress has been made in our understanding of dysregulated iron metabolism in various congenital and acquired malignant and non-malignant diseases. Finally, we report several actual as well as theoretical opportunities for translating the recently acquired robust mechanistic understanding of iron metabolism regulation to improve management of patients with disordered erythropoiesis, such as anemia of chronic inflammation, ß-thalassemia, polycythemia vera, and myelodysplastic syndromes.

Normal range and predictors of serum erythroferrone in infants.

BACKGROUND: Erythroferrone (ERFE) has been identified as a hepcidin-regulating hormone synthetized by erythroblasts correlating to the erythropoietic activity and the needs for iron substrate in bone marrow of adults. The present study aimed to assess the ERFE serum concentrations and its predictors in infants. METHODS: ERFE was explored at 4 time points during the first year of life in 45 healthy, breastfed, normal birth weight (NBW) infants, and 136 marginally low birth weight infants (LBW, 2000-2500 g) receiving iron (N = 58) or placebo (N = 78) between 6 weeks and 6 months of age. RESULTS: ERFE concentrations were low at birth, increasing gradually during the first year of life. In NBW infants, reference ranges (5th to 95th percentile) were at 6 weeks <0.005-0.99 ng/mL and at 12 months <0.005-33.7 ng/mL. ERFE was higher in LBW infants at 6 weeks but lower at 12 months compared to NBW and minimally affected by iron supplementation among LBW infants. Correlations of ERFE with erythropoietic and iron status markers were weak and inconsistent. CONCLUSIONS: The role of ERFE in the crosstalk of erythropoiesis and iron homeostasis remains unclear in infants and further studies on ERFE in infants and older children are warranted within the framework of the erythropoietin-ERFE-hepcidin axis. IMPACT: Normal range of erythroferrone in healthy infants is described for the first time. Erythroferrone in infants lacks correlation to iron status and markers of erythropoiesis. The findings indicate differences in infant regulation of iron homeostasis as compared to adults. The findings point to a need to study infant erythropoiesis separately from its adult counterpart. The findings may have clinical impact on management strategies of iron-loading anemia in infancy.

Biomarkers of erythropoiesis response to intravenous iron in a crossover pilot study in unexplained anemia of the elderly.

Anemia is common in older adults, but often unexplained. Previously, we conducted a randomized, controlled trial of intravenous (IV) iron sucrose to study its impact on the 6-minute walk test and hemoglobin in older adults with unexplained anemia and ferritin levels of 20-200 ng/mL. In this report, we present for the first time the response of hemoglobin, as well as the dynamic response of biomarkers of erythropoiesis and iron indices, in a pooled analysis of the initially IV iron-treated group of 9 subjects and the subsequently IV iron treated 10 subjects from the delayed treatment group. We hypothesized that there would be a reproducible hemoglobin response from IV iron, and that iron indices and erythropoietic markers would reflect appropriate iron loading and reduced erythropoietic stress. To investigate the biochemical response of anemia to IV iron, we studied the dynamics of soluble transferrin receptor (STfR), hepcidin, erythropoietin (EPO), and iron indices over 12 weeks after treatment. In total, all 19 treated subjects were evaluable: 9 from initial treatment and 10 after cross-over. Hemoglobin rose from 11.0 to 11.7 g/dL, 12 weeks after initiating IV iron treatment of 1000 mg divided weekly over 5 weeks. We found early changes of iron loading after 1-2 IV iron dose: serum iron increased by 184 mcg/dL from a baseline of 66 mcg/dL, ferritin by 184 ng/mL from 68 ng/mL, and hepcidin by 7.49 ng/mL from 19.2 ng/mL, while STfR and serum EPO declined by 0.55 mg/L and 3.5 mU/mL from 19.2 ng/mL and 14 mU/mL, respectively. The erythroid response and evidence of enhanced iron trafficking are consistent with the hypothesis that IV iron overcomes iron deficient or iron-restricted erythropoiesis. These data provide new insight that iron-restricted erythropoiesis is a potential and targetable mechanism for patients diagnosed with unexplained anemia of the elderly and offers support for larger prospective trials of IV iron among anemic older adults of low to normal ferritin.

Immune Mechanisms in Inflammatory Anemia.

Maintaining the correct number of healthy red blood cells (RBCs) is critical for proper oxygenation of tissues throughout the body. Therefore, RBC homeostasis is a tightly controlled balance between RBC production and RBC clearance, through the processes of erythropoiesis and macrophage hemophagocytosis, respectively. However, during the inflammation associated with infectious, autoimmune, or inflammatory diseases this homeostatic process is often dysregulated, leading to acute or chronic anemia. In each disease setting, multiple mechanisms typically contribute to the development of inflammatory anemia, impinging on both sides of the RBC production and RBC clearance equation. These mechanisms include both direct and indirect effects of inflammatory cytokines and innate sensing. Here, we focus on common innate and adaptive immune mechanisms that contribute to inflammatory anemias using examples from several diseases, including hemophagocytic lymphohistiocytosis/macrophage activation syndrome, severe malarial anemia during Plasmodium infection, and systemic lupus erythematosus, among others.

Multicompartmental trauma alters bone marrow erythroblastic islands.

BACKGROUND: Trauma is associated with widespread inflammation, neuroendocrine activation, and an inadequate bone marrow response to anemia. During late-stage erythropoiesis, erythroid progenitors/erythroblasts form clusters on the surface of specialized bone marrow macrophages where they are supported through terminal differentiation and enucleation. We hypothesized that these erythroblastic islands (EBIs) are adversely impacted by severe trauma. METHODS: Male Sprague-Dawley rats (n = 8/group) were subjected to either multiple injuries (PT) (lung contusion, hemorrhagic shock, cecectomy, and bifemoral pseudofractures), PT plus 2 hours of daily chronic restraint stress (PT/CS), or naive controls. Bone marrow was harvested on days 2 and 7. Nuclear-stained, enriched bone marrow EBIs were fixed and stained for CD71, VCAM-1, and CD163, and confocal images were obtained at 20 times magnification. Numbers of erythroid cells/EBI and ratio of reticulocytes/EBI were counted by a blinded observer. Differences were compared using analysis of variance, with significance defined as p < 0.05. RESULTS: PT and PT/CS had significantly reduced numbers of erythroid cells per EBI on day 2 when compared with naive (PT: 5.9 ± 1.0 cells [ p < 0.05], PT/CS: 6.8 ± 0.8 cells [ p < 0.05] vs. naive: 8.5 ± 0.8 cells). On day 7, the number of erythroid cells/EBI increased following PT (8.3 ± 0.4 cells) but remained reduced following PT/CS (5.9 ± 0.5 cells [ p < 0.05]). This correlated with an increased proportion of reticulocytes/EBI on day 7 following PT, which was not present following PT/CS (PT: 54% [ p < 0.05] vs. PT/CS: 28%). CONCLUSION: Late-stage erythropoiesis was altered following multicompartmental PT early after injury, and these alterations persisted with the addition of daily chronic stress. Alterations in EBI structure and function after severe trauma and critical illness may serve as a promising new area of study to improve mechanistic understanding of persistent anemia after trauma.

Navigating the marrow sea towards erythromyeloblastic islands under normal and inflammatory conditions.

PURPOSE OF REVIEW: Terminal erythroid differentiation occurs in specialized niches called erythroblastic islands. Since their discovery in 1958, these niches have been described as a central macrophage surrounded by differentiating erythroblasts. Here, we review the recent advances made in the characterization of these islands and the role they could play in anaemia of inflammation. RECENT FINDINGS: The utilization of multispectral imaging flow cytometry (flow cytometry with microscopy) has enabled for a more precise characterization of the niche that revealed the presence of maturing granulocytes in close contact with the central macrophage. These erythromyeloblastic islands (EMBIs) can adapt depending on the peripheral needs. Indeed, during inflammation wherein inflammatory cytokines limit erythropoiesis and promote granulopoiesis, EMBIs present altered structures with increased maturing granulocytes and decreased erythroid precursors. SUMMARY: Regulation of the structure and function of the EMBI in the bone marrow emerges as a potential player in the pathophysiology of acute and chronic inflammation and its associated anaemia.

Tipping the balance between erythroid cell differentiation and induction of anemia in response to the inflammatory pathology associated with chronic trypanosome infections.

Infection caused by extracellular single-celled trypanosomes triggers a lethal chronic wasting disease in livestock and game animals. Through screening of 10 Trypanosoma evansi field isolates, exhibiting different levels of virulence in mice, the current study identifies an experimental disease model in which infection can last well over 100 days, mimicking the major features of chronic animal trypanosomosis. In this model, despite the well-controlled parasitemia, infection is hallmarked by severe trypanosomosis-associated pathology. An in-depth scRNA-seq analysis of the latter revealed the complexity of the spleen macrophage activation status, highlighting the crucial role of tissue resident macrophages (TRMs) in regulating splenic extramedullary erythropoiesis. These new data show that in the field of experimental trypanosomosis, macrophage activation profiles have so far been oversimplified into a bi-polar paradigm (M1 vs M2). Interestingly, TRMs exert a double-sided effect on erythroid cells. On one hand, these cells express an erythrophagocytosis associated signature. On another hand, TRMs show high levels of Vcam1 expression, known to support their interaction with hematopoietic stem and progenitor cells (HSPCs). During chronic infection, the latter exhibit upregulated expression of Klf1, E2f8, and Gfi1b genes, involved in erythroid differentiation and extramedullary erythropoiesis. This process gives rise to differentiation of stem cells to BFU-e/CFU-e, Pro E, and Baso E subpopulations. However, infection truncates progressing differentiation at the orthochromatic erythrocytes level, as demonstrated by scRNAseq and flow cytometry. As such, these cells are unable to pass to the reticulocyte stage, resulting in reduced number of mature circulating RBCs and the occurrence of chronic anemia. The physiological consequence of these events is the prolonged poor delivery of oxygen to various tissues, triggering lactic acid acidosis and the catabolic breakdown of muscle tissue, reminiscent of the wasting syndrome that is characteristic for the lethal stage of animal trypanosomosis.

Erythropoiesis and Malaria, a Multifaceted Interplay.

One of the major pathophysiologies of malaria is the development of anemia. Although hemolysis and splenic clearance are well described as causes of malarial anemia, abnormal erythropoiesis has been observed in malaria patients and may contribute significantly to anemia. The interaction between inadequate erythropoiesis and Plasmodium parasite infection, which partly occurs in the bone marrow, has been poorly investigated to date. However, recent findings may provide new insights. This review outlines clinical and experimental studies describing different aspects of ineffective erythropoiesis and dyserythropoiesis observed in malaria patients and in animal or in vitro models. We also highlight the various human and parasite factors leading to erythropoiesis disorders and discuss the impact that Plasmodium parasites may have on the suppression of erythropoiesis.

The role of hypoxia and inflammation in the regulation of iron metabolism and erythropoiesis in COVID-19: The IRONCOVID study.

Coronavirus Disease (COVID-19) can be considered as a human pathological model of inflammation combined with hypoxia. In this setting, both erythropoiesis and iron metabolism appear to be profoundly affected by inflammatory and hypoxic stimuli, which act in the opposite direction on hepcidin regulation. The impact of low blood oxygen levels on erythropoiesis and iron metabolism in the context of human hypoxic disease (e.g., pneumonia) has not been fully elucidated. This multicentric observational study was aimed at investigating the prevalence of anemia, the alterations of iron homeostasis, and the relationship between inflammation, hypoxia, and erythropoietic parameters in a cohort of 481 COVID-19 patients admitted both to medical wards and intensive care units (ICU). Data were collected on admission and after 7 days of hospitalization. On admission, nearly half of the patients were anemic, displaying mild-to-moderate anemia. We found that hepcidin levels were increased during the whole period of observation. The patients with a higher burden of disease (i.e., those who needed intensive care treatment or had a more severe degree of hypoxia) showed lower hepcidin levels, despite having a more marked inflammatory pattern. Erythropoietin (EPO) levels were also lower in the ICU group on admission. After 7 days, EPO levels rose in the ICU group while they remained stable in the non-ICU group, reflecting that the initial hypoxic stimulus was stronger in the first group. These findings strengthen the hypothesis that, at least in the early phases, hypoxia-driven stimuli prevail over inflammation in the regulation of hepcidin and, finally, of erythropoiesis.

Epo-IGF1R cross talk expands stress-specific progenitors in regenerative erythropoiesis and myeloproliferative neoplasm.

We found that in regenerative erythropoiesis, the erythroid progenitor landscape is reshaped, and a previously undescribed progenitor population with colony-forming unit-erythroid (CFU-E) activity (stress CFU-E [sCFU-E]) is expanded markedly to restore the erythron. sCFU-E cells are targets of erythropoietin (Epo), and sCFU-E expansion requires signaling from the Epo receptor (EpoR) cytoplasmic tyrosines. Molecularly, Epo promotes sCFU-E expansion via JAK2- and STAT5-dependent expression of IRS2, thus engaging the progrowth signaling from the IGF1 receptor (IGF1R). Inhibition of IGF1R and IRS2 signaling impairs sCFU-E cell growth, whereas exogenous IRS2 expression rescues cell growth in sCFU-E expressing truncated EpoR-lacking cytoplasmic tyrosines. This sCFU-E pathway is the major pathway involved in erythrocytosis driven by the oncogenic JAK2 mutant JAK2(V617F) in myeloproliferative neoplasm. Inability to expand sCFU-E cells by truncated EpoR protects against JAK2(V617F)-driven erythrocytosis. In samples from patients with myeloproliferative neoplasm, the number of sCFU-E-like cells increases, and inhibition of IGR1R and IRS2 signaling blocks Epo-hypersensitive erythroid cell colony formation. In summary, we identified a new stress-specific erythroid progenitor cell population that links regenerative erythropoiesis to pathogenic erythrocytosis.