From the Cradle to the Grave: The Role of Macrophages in Erythropoiesis and Erythrophagocytosis

Tissue Iron Distribution in Anemic Patients with End-Stage Kidney Disease: Results of a Pilot Study

Background/Objectives: Anemia is a frequent multifactorial co-morbidity in end-stage kidney disease (ESKD) associated with morbidity and poor QoL. Apart from insufficient erythropoietin formation, iron deficiency (ID) contributes to anemia development. Identifying patients in need of iron supplementation with current ID definitions is difficult since no good biomarker is available to detect actual iron needs. Therefore, new diagnostic tools to guide therapy are needed. Methods: We performed a prospective cohort study analyzing tissue iron content with MRI-based R2*-relaxometry in 20 anemic ESKD patients and linked it with iron biomarkers in comparison to 20 otherwise healthy individuals. Results: ESKD patients had significantly higher liver (90.1 s-1 vs. 36.1 s-1, p < 0.001) and spleen R2* values (119.8 s-1 vs. 19.3 s-1, p < 0.001) compared to otherwise healthy individuals, while their pancreas and heart R2* values did not significantly differ. Out of the 20 ESKD patients, 17 had elevated spleen and 12 had elevated liver R2* values. KDIGO guidelines (focusing on serum iron parameters) would recommend iron supplementation in seven patients with elevated spleen and four patients with elevated liver R2* values. Conclusions: These findings highlight that liver and especially spleen iron concentrations are significantly higher in ESKD patients compared to controls. Tissue iron overload diverged from classical iron parameters suggesting need of iron supplementation. Measurement of MRI-guided tissue iron distribution might help guide treatment of anemic ESKD patients.

Diffuse tumors: Molecular determinants shared by different cancer types

Most cancer types have both diffuse and non-diffuse subtypes, which have rather distinct morphologies, namely scattered tiny tumors vs. one solid tumor, and different levels of aggressiveness. However, the causes for forming such distinct subtypes remain largely unknown. Using the diffuse and non-diffuse gastric cancers (GCs) as the illustrative example, we present a computational study based on the transcriptomic data from the TCGA and GEO databases, to address the following questions: (i) What are the key molecular determinants that give rise to the distinct morphologies between diffuse and non-diffuse cancers? (ii) What are the main reasons for diffuse cancers to be generally more aggressive than non-diffuse ones of the same cancer type? (iii) What are the reasons for their distinct immunoactivities? And (iv) why do diffuse cancers on average tend to take place in younger patients? The study is conducted using the framework we have previously developed for elucidation of general drivers cancer formation and development. Our main discoveries are: (a) the level of (poly-) sialic acids deployed on the surface of cancer cells is a significant factor contributing to questions (i) and (ii); (b) poly-sialic acids synthesized by ST8SIA4 are the key to question (iii); and (c) the circulating growth factors specifically needed by the diffuse subtype dictate the answer to question (iv). All these predictions are substantiated by published experimental studies. Our further analyses on breast, prostate, lung, liver, and thyroid cancers reveal that these discoveries generally apply to the diffuse subtypes of these cancer types, hence indicating the generality of our discoveries.

Comprehensive analysis of prohibited substances and methods in sports: Unveiling trends, pharmacokinetics, and WADA evolution

This review systematically compiles sports-related drugs, substances, and methodologies based on the most frequently detected findings from prohibited lists published annually by the World Anti-Doping Agency (WADA) between 2003 and 2021. Aligned with structure of the 2023 prohibited list, it covers all proscribed items and details the pharmacokinetics and pharmacodynamics of five representatives from each section. Notably, it explores significant metabolites and metabolic pathways associated with these substances. Adverse analytical findings are summarized in tables for clarity, and the prevalence is visually represented through charts. The review includes a concise historical overview of doping and WADA's role, examining modifications in the prohibited list for an understanding of evolving anti-doping measures.

Impaired hemoglobin clearance by sinusoidal endothelium promotes vaso-occlusion and liver injury in sickle cell disease

Sickle cell disease (SCD) is a monogenic disorder that affects 100,000 African-Americans and millions of people worldwide. Intra-erythrocytic polymerization of sickle hemoglobin (HbS) promotes erythrocyte sickling, impaired rheology, ischemia and hemolysis, leading to the development of progressive liver injury in SCD. Liver-resident macrophages and monocytes are known to enable the clearance of HbS; however, the role of liver sinusoidal endothelial cells (LSEC) in HbS clearance and liver injury in SCD remains unknown. Using real-time intravital (in vivo) imaging in mice liver as well as flow cytometric analysis and confocal imaging of primary human LSEC, we show for the first time that liver injury in SCD is associated with accumulation of HbS and iron in the LSEC, leading to senescence of these cells. Hemoglobin uptake by LSEC was mediated by micropinocytosis. Hepatic monocytes were observed to attenuate LSEC senescence by accelerating HbS clearance in the liver of SCD mice; however, this protection was impaired in P-selectin-deficient SCD mice secondary to reduced monocyte recruitment in the liver. These findings are the first to suggest that LSEC contribute to HbS clearance and HbS-induced LSEC senescence promotes progressive liver injury in SCD mice. Our results provide a novel insight into the pathogenesis of hemolysis-induced chronic liver injury in SCD caused by LSEC senescence. Identifying the regulators of LSEC-mediated HbS clearance may lead to new therapies to prevent the progression of liver injury in SCD.

Heme metabolism in nonerythroid cells

Heme is an iron-containing prosthetic group necessary for the function of several proteins termed "hemoproteins." Erythrocytes contain most of the body's heme in the form of hemoglobin and contain high concentrations of free heme. In nonerythroid cells, where cytosolic heme concentrations are 2 to 3 orders of magnitude lower, heme plays an essential and often overlooked role in a variety of cellular processes. Indeed, hemoproteins are found in almost every subcellular compartment and are integral in cellular operations such as oxidative phosphorylation, amino acid metabolism, xenobiotic metabolism, and transcriptional regulation. Growing evidence reveals the participation of heme in dynamic processes such as circadian rhythms, NO signaling, and the modulation of enzyme activity. This dynamic view of heme biology uncovers exciting possibilities as to how hemoproteins may participate in a range of physiologic systems. Here, we discuss how heme is regulated at the level of its synthesis, availability, redox state, transport, and degradation and highlight the implications for cellular function and whole organism physiology.

Alcohol-Associated Liver Disease Outcomes: Critical Mechanisms of Liver Injury Progression

Alcohol-associated liver disease (ALD) is a substantial cause of morbidity and mortality worldwide and represents a spectrum of liver injury beginning with hepatic steatosis (fatty liver) progressing to inflammation and culminating in cirrhosis. Multiple factors contribute to ALD progression and disease severity. Here, we overview several crucial mechanisms related to ALD end-stage outcome development, such as epigenetic changes, cell death, hemolysis, hepatic stellate cells activation, and hepatic fatty acid binding protein 4. Additionally, in this review, we also present two clinically relevant models using human precision-cut liver slices and hepatic organoids to examine ALD pathogenesis and progression.

Bufalin reprograms erythrocyte lifespan through p38 MAPK and Rac1 GTPase

Ample evidence indicates that bufalin (BFN), a cardiotonic steroid in Bufo toad toxin, possesses a potent anticancer activity mainly by stimulating apoptosis in cancer cells. Human red blood cells (RBCs) undergo eryptosis which contributes to a plethora of pathological conditions. No reports, however, have examined the potential toxicity of BFN to RBCs. This study aims to characterize the biochemical mechanisms governing the influence of BFN on the physiology and lifespan of RBCs. Isolated RBCs from healthy volunteers were exposed to anticancer concentrations of commercially available BFN from the skin of Bufo gargarizans (10-200 μM) for 24 h at 37 °C. Photometric assays were used to estimate hemolysis and hemolytic markers, and flow cytometry was used to detect eryptotic markers. Phosphatidylserine externalization was captured by fluorescein isothiocyante-labeled annexin V, cellular dimensions by light scatter patterns, and intracellular Ca2+ and reactive oxygen species (ROS) by fluorogenic dyes Fluo4/AM and 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA), respectively. BFN caused Ca2+-independent hemolysis and release of LDH, AST, CK, and K+, and increased annexin V-bound cells, cytosolic Ca2+, cell shrinkage, and ROS levels. BFN also disrupted Na+ and Mg2+ trafficking, and was sensitive to PEG 8000, sucrose, SB203580, and NSC 23766. In whole blood, BFN depleted hemoglobin stores, increased fragmented RBCs, and was selectively toxic to reticulocytes, lymphocytes, and platelets. In conclusion, BFN elicits premature RBC death, subject to regulation by p38 MAPK and Rac1 GTPase, and is detrimental to other peripheral blood cells. Altogether, these novel findings prompt cautious consideration of the toxin in anticancer therapy.

Platelets mediate the clearance of senescent red blood cells by forming prophagocytic platelet-cell complexes

ABSTRACT

In humans, ∼0.1% to 0.3% of circulating red blood cells (RBCs) are present as platelet-RBC (P-RBC) complexes, and it is 1% to 2% in mice. Excessive P-RBC complexes are found in diseases that compromise RBC health (eg, sickle cell disease and malaria) and contribute to pathogenesis. However, the physiological role of P-RBC complexes in healthy blood is unknown. As a result of damage accumulated over their lifetime, RBCs nearing senescence exhibit physiological and molecular changes akin to those in platelet-binding RBCs in sickle cell disease and malaria. Therefore, we hypothesized that RBCs nearing senescence are targets for platelet binding and P-RBC formation. Confirming this hypothesis, pulse-chase labeling studies in mice revealed an approximately tenfold increase in P-RBC complexes in the most chronologically aged RBC population compared with younger cells. When reintroduced into mice, these complexes were selectively cleared from the bloodstream (in preference to platelet-free RBC) through the reticuloendothelial system and erythrophagocytes in the spleen. As a corollary, patients without a spleen had higher levels of complexes in their bloodstream. When the platelet supply was artificially reduced in mice, fewer RBC complexes were formed, fewer erythrophagocytes were generated, and more senescent RBCs remained in circulation. Similar imbalances in complex levels and senescent RBC burden were observed in humans with immune thrombocytopenia (ITP). These findings indicate that platelets are important for binding and clearing senescent RBCs, and disruptions in platelet count or complex formation and clearance may negatively affect RBC homeostasis and may contribute to the known risk of thrombosis in ITP and after splenectomy.

Cell death by phagocytosis

Cells can die as a consequence of being phagocytosed by other cells - a form of cell death that has been called phagotrophy, cell cannibalism, programmed cell removal and primary phagocytosis. However, these are all different manifestations of cell death by phagocytosis (termed 'phagoptosis' for short). The engulfed cells die as a result of cytotoxic oxidants, peptides and degradative enzymes within acidic phagolysosomes. Cell death by phagocytosis was discovered by Metchnikov in the 1880s, but was neglected until recently. It is now known to contribute to developmental cell death in nematodes, Drosophila and mammals, and is central to innate and adaptive immunity against pathogens. Cell death by phagocytosis mediates physiological turnover of erythrocytes and other leucocytes, making it the most abundant form of cell death in the mammalian body. Immunity against cancer is also partly mediated by macrophage phagocytosis of cancer cells, but cancer cells can also phagocytose host cells and other cancer cells in order to survive. Recent evidence indicates neurodegeneration and other neuropathologies can be mediated by microglial phagocytosis of stressed neurons. Thus, despite cell death by phagocytosis being poorly recognized, it is one of the oldest, commonest and most important forms of cell death.

Signaling-biophysical modeling unravels mechanistic control of red blood cell phagocytosis by macrophages in sickle cell disease

Red blood cell (RBC) aging manifests through progressive changes in cell morphology, rigidity, and expression of membrane proteins. To maintain the quality of circulating blood, splenic macrophages detect the biochemical signals and biophysical changes of RBCs and selectively clear them through erythrophagocytosis. In sickle cell disease (SCD), RBCs display alterations affecting their interaction with macrophages, leading to aberrant phagocytosis that may cause life-threatening spleen sequestration crises. To illuminate the mechanistic control of RBC engulfment by macrophages in SCD, we integrate a system biology model of RBC-macrophage signaling interactions with a biophysical model of macrophage engulfment, as well as in vitro phagocytosis experiments using the spleen-on-a-chip technology. Our modeling framework accurately predicts the phagocytosis dynamics of RBCs under different disease conditions, reveals patterns distinguishing normal and sickle RBCs, and identifies molecular targets including Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP1) and cluster of differentiation 47 (CD47)/signal regulatory protein α (SIRPα) as therapeutic targets to facilitate the controlled clearance of sickle RBCs in the spleen.

A secretory protein neudesin regulates splenic red pulp macrophages in erythrophagocytosis and iron recycling

Neudesin, originally identified as a neurotrophic factor, has primarily been studied for its neural functions despite its widespread expression. Using 8-week-old neudesin knockout mice, we elucidated the role of neudesin in the spleen. The absence of neudesin caused mild splenomegaly, shortened lifespan of circulating erythrocytes, and abnormal recovery from phenylhydrazine-induced acute anemia. Blood cross-transfusion and splenectomy experiments revealed that the shortened lifespan of erythrocytes was attributable to splenic impairment. Further analysis revealed increased erythrophagocytosis and decreased iron stores in the splenic red pulp, which was linked to the upregulation of Fcγ receptors and iron-recycling genes in neudesin-deficient macrophages. In vitro analysis confirmed that neudesin suppressed erythrophagocytosis and expression of Fcγ receptors through ERK1/2 activation in heme-stimulated macrophages. Finally, we observed that 24-week-old neudesin knockout mice exhibited severe symptoms of anemia. Collectively, our results suggest that neudesin regulates the function of red pulp macrophages and contributes to erythrocyte and iron homeostasis.

Organogermanium, Ge-132, promotes the clearance of senescent red blood cells via macrophage-mediated phagocyte activation

Red blood cells (RBCs) are renewed in a cyclic manner. Aging RBCs are captured and degraded by phagocytic cells, and heme metabolic pigments are subsequently excreted in feces. We evaluated the effect of an organogermanium compound on RBC metabolism and found that the phagocytosis of RAW264.7 macrophage-like cells was increased by treatment with 3-(trihydroxygermyl)propanoic acid (THGP). Additionally, consumption of Ge-132 (a dehydrate polymer of THGP) changed the fecal color to bright yellow and increased the erythrocyte metabolic pigment levels and antioxidant activity in feces. These data suggest that Ge-132 may activate macrophages in the body and promote the degradation of aged RBCs. Furthermore, Ge-132 intake promoted not only increases in RBC degradation but also the induction of erythroblast differentiation in bone marrow cells. The normal hematocrit levels were maintained due to the maintenance of homeostasis, even though Ge-132 ingestion increased erythrocyte degradation. Therefore, Ge-132 enhances the degradation of senescent RBCs by macrophages. In turn, RBC production is increased to compensate for the amount of degradation, and RBC metabolism is increased.

Intravenous Senescent Erythrocyte Vaccination Modulates Adaptive Immunity and Splenic Complement Production

Targeted delivery of vaccines to the spleen remains a challenge. Inspired by the erythrophagocytotic process in the spleen, we herein report that intravenous administration of senescent erythrocyte-based vaccines profoundly alters their tropism toward splenic antigen-presenting cells (APCs) for imprinting adaptive immune responses. Compared with subcutaneous inoculation, intravenous vaccination significantly upregulated splenic complement expression in vivo and demonstrated synergistic antibody killing in vitro. Consequently, intravenous senescent erythrocyte vaccination produces potent SARS-CoV-2 antibody-neutralizing effects, with potential protective immune responses. Moreover, the proposed senescent erythrocyte can deliver antigens from resected tumors and adjuvants to splenic APCs, thereby inducing a personalized immune reaction against tumor recurrence after surgery. Hence, our findings suggest that senescent erythrocyte-based vaccines can specifically target splenic APCs and evoke adaptive immunity and complement production, broadening the tools for modulating immunity, helping to understand adaptive response mechanisms to senescent erythrocytes better, and developing improved vaccines against cancer and infectious diseases.

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.

Defining solute carrier transporter signatures of murine immune cell subsets

Solute carrier (SLC) transporters are membrane-bound proteins that facilitate nutrient transport, and the movement across cellular membranes of various substrates ranging from ions to amino acids, metabolites and drugs. Recently, SLCs have gained increased attention due to their functional linkage to innate immunological processes such as the clearance of dead cells and anti-microbial defense. Further, the druggable nature of these transporters provides unique opportunities for improving outcomes in different immunological diseases. Although the SLCs represent the largest group of transporters and are often identified as significant hits in omics data sets, their role in immunology has been insufficiently explored. This is partly due to the absence of tools that allow identification of SLC expression in particular immune cell types and enable their comparison before embarking on functional studies. In this study, we used publicly available RNA-Seq data sets to analyze the transcriptome in adaptive and innate immune cells, focusing on differentially and highly expressed SLCs. This revealed several new insights: first, we identify differentially expressed SLC transcripts in phagocytes (macrophages, dendritic cells, and neutrophils) compared to adaptive immune cells; second, we identify new potential immune cell markers based on SLC expression; and third, we provide user-friendly online tools for researchers to explore SLC genes of interest (and the rest of the genes as well), in three-way comparative dot plots among immune cells. We expect this work to facilitate SLC research and comparative transcriptomic studies across different immune cells.

SARS-CoV-2 Impact on Red Blood Cell Morphology

Severe COVID-19 alters the biochemical and morphological characteristics of blood cells in a wide variety of ways. To date, however, the vast majority of research has been devoted to the study of leukocytes, while erythrocyte morphological changes have received significantly less attention. The aim of this research was to identify erythrocyte morphology abnormalities that occur in COVID-19, compare the number of different poikilocyte types, and measure erythrocyte sizes to provide data on size dispersion. Red blood cells obtained from 6 control donors (800-2200 cells per donor) and 5 COVID-19 patients (800-1900 cells per patient) were examined using low-voltage scanning electron microscopy. We did not discover any forms of erythrocyte morphology abnormalities that would be specific to COVID-19. Among COVID-19 patients, we observed an increase in the number of acanthocytes (p = 0.01) and a decrease in the number of spherocytes (p = 0.03). In addition, our research demonstrates that COVID-19 causes an increase in the median (p = 0.004) and interquartile range (p = 0.009) when assessing erythrocyte size. The limitation of our study is a small number of participants.

Macrophage deficiency in CSF1R-knockout rat embryos does not compromise placental or embryo development

Macrophages are an abundant cell population in the placenta and developing embryo and appear to be involved in processes of vascularization, morphogenesis, organogenesis, and hematopoiesis. The proliferation, differentiation, and survival are dependent on signals from the macrophage colony-stimulating factor receptor, CSF1R. Aside from the role in macrophages, Csf1r mRNA is highly expressed in placental trophoblasts. To explore the function of macrophages and Csf1r in placental and embryonic development, we analyzed the impact of homozygous Csf1r null mutation (Csf1rko) in the rat. In late gestation, IBA1+ macrophages were abundant in control embryos in all tissues, including the placenta, and greatly reduced in the Csf1rko. CSF1R was also detected in stellate macrophage-like cells and in neurons using anti-CSF1R antibody but was undetectable in trophoblasts. However, the neuronal signal was not abolished in the Csf1rko. CD163 was most abundant in cells forming the center of erythroblastic islands in the liver and was also CSF1R dependent. Despite the substantial reduction in macrophage numbers, we detected no effect of the Csf1rko on development of the placenta or any organs, the relative abundance of vascular elements (CD31 staining), or cell proliferation (Ki67 staining). The loss of CD163+ erythroblastic island macrophages in the liver was not associated with anemia or any reduction in the proliferative activity in the liver, but there was a premature expansion of CD206+ cells, presumptive precursors of liver sinusoidal endothelial cells. We suggest that many functions of macrophages in development of the placenta and embryo can be provided by other cell types in their absence.

The hematopoietic microenvironment: a network of niches for the development of all blood cell lineages

Blood cell formation (hematopoiesis) takes place mainly in the bone marrow, within the hematopoietic microenvironment, composed of a number of different cell types and their molecular products that together shape spatially organized and highly specialized microstructures called hematopoietic niches. From the earliest developmental stages and throughout the myeloid and lymphoid lineage differentiation pathways, hematopoietic niches play a crucial role in the preservation of cellular integrity and the regulation of proliferation and differentiation rates. Current evidence suggests that each blood cell lineage develops under specific, discrete niches that support committed progenitor and precursor cells and potentially cooperate with transcriptional programs determining the gradual lineage commitment and specification. This review aims to discuss recent advances on the cellular identity and structural organization of lymphoid, granulocytic, monocytic, megakaryocytic, and erythroid niches throughout the hematopoietic microenvironment and the mechanisms by which they interconnect and regulate viability, maintenance, maturation, and function of the developing blood cells.

Changes in Hematological and Hemorheological Parameters Following Mild COVID-19: A 4-Month Follow-Up Study

BACKGROUND

Coronavirus Disease 2019 (COVID-19) was described to affect red blood cells (RBC) in both severe and mild disease courses. The aim of this study was to investigate whether hematological and hemorheological changes that were previously described for COVID-19 patients after the acute infection state are still prominent after another 4 months to assess potential long-term effects.

METHODS

Hematological and RBC rheological parameters, including deformability and aggregation, were measured 41 days after infection in COVID-19 patients and non-COVID control (T0) and 4 months later in COVID-19 patients (T1).

RESULTS

The data confirm alterations in hematological parameters, mainly related to cell volume and hemoglobin concentration, but also reduced deformability and increased aggregation at T0 compared to control. While RBC deformability seems to have recovered, hemoglobin-related parameters and RBC aggregation were still impaired at T1. The changes were thus more pronounced in male COVID-19 patients.

CONCLUSION

COVID-19-related changes of the RBC partly consist of several months and might be related to persistent symptoms reported by many COVID-19 patients.

Dysfunction of CD169+ macrophages and blockage of erythrocyte maturation as a mechanism of anemia in Plasmodium yoelii infection

Plasmodium parasites cause malaria with disease outcomes ranging from mild illness to deadly complications such as severe malarial anemia (SMA), pulmonary edema, acute renal failure, and cerebral malaria. In young children, SMA often requires blood transfusion and is a major cause of hospitalization. Malaria parasite infection leads to the destruction of infected and noninfected erythrocytes as well as dyserythropoiesis; however, the mechanism of dyserythropoiesis accompanied by splenomegaly is not completely understood. Using Plasmodium yoelii yoelii 17XNL as a model, we show that both a defect in erythroblastic island (EBI) macrophages in supporting red blood cell (RBC) maturation and the destruction of reticulocytes/RBCs by the parasites contribute to SMA and splenomegaly. After malaria parasite infection, the destruction of both infected and noninfected RBCs stimulates extramedullary erythropoiesis in mice. The continuous decline of RBCs stimulates active erythropoiesis and drives the expansion of EBIs in the spleen, contributing to splenomegaly. Phagocytosis of malaria parasites by macrophages in the bone marrow and spleen may alter their functional properties and abilities to support erythropoiesis, including reduced expression of the adherence molecule CD169 and inability to support erythroblast differentiation, particularly RBC maturation in vitro and in vivo. Therefore, macrophage dysfunction is a key mechanism contributing to SMA. Mitigating and/or alleviating the inhibition of RBC maturation may provide a treatment strategy for SMA.

Hemolysis dictates monocyte differentiation via two distinct pathways in sickle cell disease vaso-occlusion

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by painful vaso-occlusive crises (VOC) and chronic hemolysis. The mononuclear phagocyte system is pivotal to SCD pathophysiology, but the mechanisms governing monocyte/macrophage differentiation remain unknown. This study examined the influence of hemolysis on circulating monocyte trajectories in SCD. We discovered that hemolysis stimulated CSF-1 production, partly by endothelial cells via Nrf2, promoting classical monocyte (CMo) differentiation into blood patrolling monocytes (PMo) in SCD mice. However, hemolysis also upregulated CCL-2 through IFN-I, inducing CMo transmigration and differentiation into tissue monocyte-derived macrophages. Blocking CMo transmigration by anti-P selectin antibody in SCD mice increased circulating PMo, corroborating that CMo-to-tissue macrophage differentiation occurs at the expense of CMo-to-blood PMo differentiation. We observed a positive correlation between plasma CSF-1/CCL-2 ratios and blood PMo levels in patients with SCD, underscoring the clinical significance of these two opposing factors in monocyte differentiation. Combined treatment with CSF-1 and anti-P selectin antibody more effectively increased PMo numbers and reduced stasis compared with single-agent therapies in SCD mice. Altogether, these data indicate that monocyte fates are regulated by the balance between two heme pathways, Nrf2/CSF-1 and IFN-I/CCL-2, and suggest that the CSF-1/CCL-2 ratio may present a diagnostic and therapeutic target in SCD.

Splenectomy improves erythrocyte functionality in spherocytosis based on septin abundance, but not maturation defects

Splenectomy improves the clinical parameters of patients with hereditary spherocytosis, but its potential benefit to red blood cell (RBC) functionality and the mechanism behind this benefit remain largely overlooked. Here, we compared 7 nonsplenectomized and 13 splenectomized patients with mutations in the β-spectrin or the ankyrin gene. We showed that hematological parameters, spherocyte abundance, osmotic fragility, intracellular calcium, and extracellular vesicle release were largely but not completely restored by splenectomy, whereas cryohemolysis was not. Affected RBCs exhibited decreases in β-spectrin and/or ankyrin contents and slight alterations in spectrin membrane distribution, depending on the mutation. These modifications were found in both splenectomized and nonsplenectomized patients and poorly correlated with RBC functionality alteration, suggesting additional impairments. Accordingly, we found an increased abundance of septins, small guanosine triphosphate-binding cytoskeletal proteins. Septins-2, -7, and -8 but not -11 were less abundant upon splenectomy and correlated with the disease severity. Septin-2 membrane association was confirmed by immunolabeling. Except for cryohemolysis, all parameters of RBC morphology and functionality correlated with septin abundance. The increased septin content might result from RBC maturation defects, as evidenced by (1) the decreased protein 4.2 and Rh-associated glycoprotein content in all patient RBCs, (2) increased endoplasmic reticulum remnants and endocytosis proteins in nonsplenectomized patients, and (3) increased lysosomal and mitochondrial remnants in splenectomized patients. Our study paves the way for a better understanding of the involvement of septins in RBC membrane biophysical properties. In addition, the lack of restoration of septin-independent cryohemolysis by splenectomy may call into question its recommendation in specific cases.

The Role of the Spleen and the Place of Splenectomy in Autoimmune Hemolytic Anemia-A Review of Current Knowledge

Autoimmune hemolytic anemia (AIHA) is a rare, very heterogeneous, and sometimes life-threatening acquired hematologic disease characterized by increased red blood cell (RBC) destruction by autoantibodies (autoAbs), either with or without complement involvement. Recent studies have shown that the involvement of T- and B-cell dysregulation and an imbalance of T-helper 2 (Th2) and Th17 phenotypes play major roles in the pathogenesis of AIHA. AIHA can be primary (idiopathic) but is more often secondary, triggered by infections or drug use or as a part of other diseases. As the location of origin of autoAbs and the location of autoAb-mediated RBC clearance, as well as the location of extramedullary hematopoiesis, the spleen is crucially involved in all the steps of AIHA pathobiology. Splenectomy, which was the established second-line therapeutic option in corticosteroid-resistant AIHA patients for decades, has become less common due to increasing knowledge of immunopathogenesis and the introduction of targeted therapy. This article provides a comprehensive overview of current knowledge regarding the place of the spleen in the immunological background of AIHA and the rapidly growing spectrum of novel therapeutic approaches. Furthermore, this review emphasizes the still-existing expediency of laparoscopic splenectomy with appropriate perioperative thromboprophylaxis and the prevention of infection as a safe and reliable therapeutic option in the context of the limited availability of rituximab and other novel therapies.

Measurement of red blood cell deformability during morphological changes using rotating-glass-plate-based scanning optical tweezers

It is important to measure the deformability of red blood cells (RBCs) before transfusion, which is a key factor in the gas transport ability of RBCs and changes during storage of RBCs in vitro. Moreover, the morphology of RBCs also changes during storage. It is proposed that the change in morphology is related to the change in deformability. However, the efficiency of typical methods that use particles as handles is low, especially in the deformability measurement of echinocyte and spherocytes. Therefore, the deformability of RBCs with different morphologies is hard to be measured and compared in the same experiment. In this study, we developed a cost-effective and efficient rotating-glass-plate-based scanning optical tweezers device for the measurement of deformability of RBCs. The performance of this device was evaluated, and the deformability of three types of RBCs was measured using this device. Our results clearly show that the change of erythrocyte morphology from discocyte to echinocyte and spherocyte during storage in vitro is accompanied by a decrease in deformability.

An unconventional mechanism of IL-1β secretion that requires Type I IFN in lupus monocytes

Systemic Lupus Erythematosus (SLE) is characterized by autoreactive B cell activation, upregulation of Type I Interferon (IFN) and widespread inflammation. Mitochondrial nucleic acids (NAs) are increasingly recognized as triggers of IFN 1 . Thus, defective removal of mitochondria from mature red blood cells (Mito + RBCs), a feature of SLE, contributes to IFN production by myeloid cells 2 . Here we identify blood monocytes (Mo) that have internalized RBCs and co-express IFN-stimulated genes (ISGs) and interleukin-1β (IL-1β) in SLE patients with active disease. We show that ISG expression requires the interaction between Mito + RBC-derived mitochondrial DNA (mtDNA) and cGAS, while IL-1β production entails Mito + RBC-derived mitochondrial RNA (mtRNA) triggering of RIG-I-like receptors (RLRs). This leads to the cytosolic release of Mo-derived mtDNA that activates the NLRP3 inflammasome. Importantly, IL-1β release depends on the IFN-inducible myxovirus resistant protein 1 (MxA), which enables the translocation of this cytokine into a trans-Golgi network (TGN)-mediated unconventional secretory pathway. Our study highlights a novel and synergistic pathway involving IFN and the NLRP3 inflammasome in SLE.

Calcium, Phosphate, and Vitamin D Status in Patients with Sarcoidosis-Associations with Disease Activity and Symptoms

Sarcoidosis is a systemic granulomatous disease with a variety of presentations. One of the known symptoms are altered vitamin D metabolism and hypercalcemia. In our study, we aimed to assess associations between disease activity, inflammatory parameters, and vitamin D and calcium status. The secondary aim was to find any dependencies between calcium and vitamin D metabolism and fatigue and quality of life in patients with sarcoidosis. We enrolled 58 patients with sarcoidosis (47 classified as active disease, 11 classified as non-active) and compared them with 25 healthy volunteers. Calcium concentration was significantly higher in the study group than in healthy controls. It correlated with some inflammatory markers but not with vitamin D status. Not calcium nor vitamin D, but phosphate concentration correlated with life quality was assessed with the use of the Sarcoidosis Health Questionnaire. An association between phosphate concentration and fatigue was also noted, but it did not reach statistical significance. Calcium concentration was higher in patients with sarcoidosis, but it was not an indicator of the disease activity, while phosphate concentration was significantly lower in patients with active sarcoidosis.

Macrophages Provide Essential Support for Erythropoiesis, and Extracellular ATP Contributes to a Erythropoiesis-Supportive Microenvironment during Repeated Psychological Stress

Psychological stress is a significant contributor to various chronic diseases and affects multiple physiological processes including erythropoiesis. This study aimed to examine the tissue-specific contributions of macrophages and extracellular ATP, as a signal of disturbed tissue homeostasis, to erythropoiesis under conditions of repeated psychological stress. Adult male BALB/c mice were subjected to 2 h daily restraint stress for seven consecutive days. Clodronate-liposomes were used to deplete resident macrophages from the bone marrow and spleen two days prior to the first restraint procedure, as well as newly recruited macrophages, every third day for the duration of the experiment. Repeated stress induced a considerable increase in the number of erythroid progenitor cells as well as in the percentage of CD71+/Ter119+ and CD71-/Ter119+ cells in the bone marrow and spleen. Macrophage depletion completely abolished the stimulative effect of repeated stress on immature erythroid cells, and prevented stress-induced increases in ATP levels, P2X7 receptor (P2X7R) expression, and ectonucleotidase CD39 activity and expression in the bone marrow and spleen. The obtained results demonstrate the stimulative effects of repeated stress on erythroid cells, extracellular ATP levels, P2X7R expression, CD39 activity and expression within the bone marrow and spleen, as well as the essential role of macrophages in stress-induced changes.

Red Blood Cell Metabolism In Vivo and In Vitro

Red blood cells (RBC) are the most abundant cell in the human body, with a central role in oxygen transport and its delivery to tissues. However, omics technologies recently revealed the unanticipated complexity of the RBC proteome and metabolome, paving the way for a reinterpretation of the mechanisms by which RBC metabolism regulates systems biology beyond oxygen transport. The new data and analytical tools also informed the dissection of the changes that RBCs undergo during refrigerated storage under blood bank conditions, a logistic necessity that makes >100 million units available for life-saving transfusions every year worldwide. In this narrative review, we summarize the last decade of advances in the field of RBC metabolism in vivo and in the blood bank in vitro, a narrative largely influenced by the authors' own journeys in this field. We hope that this review will stimulate further research in this interesting and medically important area or, at least, serve as a testament to our fascination with this simple, yet complex, cell.

Loss of Dnmt3a impairs hematopoietic homeostasis and myeloid cell skewing via the PI3Kinase pathway

Loss-of-function mutations in the DNA methyltransferase 3A (DNMT3A) are seen in a large number of patients with acute myeloid leukemia (AML) with normal cytogenetics and are frequently associated with poor prognosis. DNMT3A mutations are an early preleukemic event, which - when combined with other genetic lesions - result in full-blown leukemia. Here, we show that loss of Dnmt3a in hematopoietic stem and progenitor cells (HSC/Ps) results in myeloproliferation, which is associated with hyperactivation of the phosphatidylinositol 3-kinase (PI3K) pathway. PI3Kα/β or the PI3Kα/δ inhibitor treatment partially corrects myeloproliferation, although the partial rescue is more efficient in response to the PI3Kα/β inhibitor treatment. In vivo RNA-Seq analysis on drug-treated Dnmt3a-/- HSC/Ps showed a reduction in the expression of genes associated with chemokines, inflammation, cell attachment, and extracellular matrix compared with controls. Remarkably, drug-treated leukemic mice showed a reversal in the enhanced fetal liver HSC-like gene signature observed in vehicle-treated Dnmt3a-/- LSK cells as well as a reduction in the expression of genes involved in regulating actin cytoskeleton-based functions, including the RHO/RAC GTPases. In a human PDX model bearing DNMT3A mutant AML, PI3Kα/β inhibitor treatment prolonged their survival and rescued the leukemic burden. Our results identify a potentially new target for treating DNMT3A mutation-driven myeloid malignancies.

Blocking the CD47-SIRPα interaction reverses the disease phenotype in a polycythemia vera mouse model

Polycythemia vera (PV) is a hematopoietic stem cell neoplasm driven by somatic mutations in JAK2, leading to increased red blood cell (RBC) production uncoupled from mechanisms that regulate physiological erythropoiesis. At steady-state, bone marrow macrophages promote erythroid maturation, whereas splenic macrophages phagocytose aged or damaged RBCs. The binding of the anti-phagocytic ("don't eat me") CD47 ligand expressed on RBCs to the SIRPα receptor on macrophages inhibits phagocytic activity protecting RBCs from phagocytosis. In this study, we explore the role of the CD47-SIRPα interaction on the PV RBC life cycle. Our results show that blocking CD47-SIRPα in a PV mouse model due to either anti-CD47 treatment or loss of the inhibitory SIRPα-signal corrects the polycythemia phenotype. Anti-CD47 treatment marginally impacted PV RBC production while not influencing erythroid maturation. However, upon anti-CD47 treatment, high-parametric single-cell cytometry identified an increase of MerTK+ splenic monocyte-derived effector cells, which differentiate from Ly6C^hi monocytes during inflammatory conditions, acquire an inflammatory phagocytic state. Furthermore, in vitro, functional assays showed that splenic JAK2 mutant macrophages were more "pro-phagocytic," suggesting that PV RBCs exploit the CD47-SIRPα interaction to escape innate immune attacks by clonal JAK2 mutant macrophages.

Heme oxygenase 1 in erythropoiesis: an important regulator beyond catalyzing heme catabolism

Heme oxygenase 1 (HO-1), encoded by the HMOX-1 gene, is the main heme oxygenase that catalyzes the degradation of heme into iron, carbon monoxide, and biliverdin. HMOX-1 gene expression is stimulated by oxidative stress and regulated at transcriptional and post-transcriptional levels. After translation, subcellular location and protein stability of HO-1 are also altered by different extracellular and intracellular stimuli. HO-1 plays a key role in regulating iron homeostasis and cell protection and has become a new target for disease treatment. Erythropoiesis is a tightly controlled, iron-dependent process that begins with hematopoietic stem cells and maturates to red blood cells. HO-1 is expressed in hematopoietic stem/progenitor cells, hematopoietic niche cells, erythroblasts, and especially erythroblastic island and phagocytic macrophages. HO-1 functions importantly in the entire erythroid development process by influencing hematopoietic stem cell proliferation, erythroid lineage engagement, terminal erythroid differentiation, and even senescent RBC erythrophagocytosis. HO-1 is also related to stress erythropoiesis and certain red blood cell diseases. Elucidation of HO-1 regulation and function in erythropoiesis will be of great significance for the treatment of related diseases.

Recent updates of stem cell-based erythropoiesis

Blood transfusions are now an essential part of modern medicine. Transfusable red blood cells (RBCs) are employed in various therapeutic strategies; however, the processes of blood donation, collection, and administration still involve many limitations. Notably, a lack of donors, the risk of transfusion-transmitted disease, and recent pandemics such as COVID-19 have prompted us to search for alternative therapeutics to replace this resource. Originally, RBC production was attempted via the ex vivo differentiation of stem cells. However, a more approachable and effective cell source is now required for broader applications. As a viable alternative, pluripotent stem cells have been actively used in recent research. In this review, we discuss the basic concepts related to erythropoiesis, as well as early research using hematopoietic stem cells ex vivo, and discuss the current trend of in vitro erythropoiesis using human-induced pluripotent stem cells.

Type-1 interferon-dependent and -independent mechanisms in cyclic GMP-AMP synthase-stimulator of interferon genes-driven auto-inflammation

The cyclic cyclic gaunosine monophosphate adenosine monophosphate (GMP-AMP) synthase-stimulator of interferon genes (cGAS-STING) pathway senses cytosolic dsDNA and initiates immune responses against pathogens. It is also implicated in several auto-inflammatory diseases known as monogenic interferonopathies, specifically Three prime repair exonuclease 1 (Trex1) loss-of-function (LOF), Dnase2 LOF, and stimulator of interferon genes-associated-vasculopathy-with-onset-in-infancy (SAVI). Although monogenic interferonopathies have diverse clinical presentations, they are distinguished by the elevation of type-1 interferons (T1IFNs). However, animal models have demonstrated that T1IFNs contribute to only some disease outcomes and that cGAS-STING activation also promotes T1IFN-independent pathology. For example, while T1IFNs drive the immunopathology associated with Trex1 LOF, disease in Dnase2 LOF is partially independent of T1IFNs, while disease in SAVI appears to occur entirely independent of T1IFNs. Additionally, while the cGAS-STING pathway is well characterized in hematopoietic cells, these animal models point to important roles for STING activity in nonhematopoietic cells in disease. Together, these models illustrate the complex role that cGAS-STING-driven responses play in the pathogenesis of inflammatory diseases across tissues.

Effects of urban particulate matter on the quality of erythrocytes

With the acceleration of industrialisation and urbanisation, air pollution has become a serious global concern as a hazard to human health, with urban particulate matter (UPM) accounting for the largest share. UPM can rapidly pass into and persist within systemic circulation. However, few studies exist on whether UPM may have any impact on blood components. In this study, UPM standards (SRM1648a) were used to assess the influence of UPM on erythrocyte quality in terms of oxidative and metabolic damage as well as phagocytosis by macrophages in vitro and clearance in vivo. Our results showed that UPM had weak haemolytic properties. It can oxidise haemoglobin and influence the oxygen-carrying function, redox balance, and metabolism of erythrocytes. UPM increases the content of reactive oxygen species (ROS) and decreases antioxidant function according to the data of malonaldehyde (MDA), glutathione (GSH), and glucose 6 phosphate dehydrogenase (G6PDH). UPM can adhere to or be internalised by erythrocytes at higher concentrations, which can alter their morphology. Superoxide radicals produced in the co-incubation system further disrupted the structure of red blood cell membranes, thereby lowering the resistance to the hypotonic solution, as reflected by the osmotic fragility test. Moreover, UPM leads to an increase in phosphatidylserine exposure in erythrocytes and subsequent clearance by the mononuclear phagocytic system in vivo. Altogether, this study suggests that the primary function of erythrocytes may be affected by UPM, providing a warning for erythrocyte quality in severely polluted areas. For critically ill patients, transfusion of erythrocytes with lesions in morphology and function will have serious clinical consequences, suggesting that potential risks should be considered during blood donation screening. The current work expands the scope of blood safety studies.

Impaired iron recycling from erythrocytes is an early hallmark of aging

Aging affects iron homeostasis, as evidenced by tissue iron loading and anemia in the elderly. Iron needs in mammals are met primarily by iron recycling from senescent red blood cells (RBCs), a task chiefly accomplished by splenic red pulp macrophages (RPMs) via erythrophagocytosis. Given that RPMs continuously process iron, their cellular functions might be susceptible to age-dependent decline, a possibility that has been unexplored to date. Here, we found that 10- to 11-month-old female mice exhibit iron loading in RPMs, largely attributable to a drop in iron exporter ferroportin, which diminishes their erythrophagocytosis capacity and lysosomal activity. Furthermore, we identified a loss of RPMs during aging, underlain by the combination of proteotoxic stress and iron-dependent cell death resembling ferroptosis. These impairments lead to the retention of senescent hemolytic RBCs in the spleen, and the formation of undegradable iron- and heme-rich extracellular protein aggregates, likely derived from ferroptotic RPMs. We further found that feeding mice an iron-reduced diet alleviates iron accumulation in RPMs, enhances their ability to clear erythrocytes, and reduces damage. Consequently, this diet ameliorates hemolysis of splenic RBCs and reduces the burden of protein aggregates, mildly increasing serum iron availability in aging mice. Taken together, we identified RPM collapse as an early hallmark of aging and demonstrated that dietary iron reduction improves iron turnover efficacy.

Oxidants and Antioxidants in the Redox Biochemistry of Human Red Blood Cells

Red blood cells (RBCs) are exposed to both external and internal sources of oxidants that challenge their integrity and compromise their physiological function and supply of oxygen to tissues. Autoxidation of oxyhemoglobin is the main source of endogenous RBC oxidant production, yielding superoxide radical and then hydrogen peroxide. In addition, potent oxidants from other blood cells and the surrounding endothelium can reach the RBCs. Abundant and efficient enzymatic systems and low molecular weight antioxidants prevent most of the damage to the RBCs and also position the RBCs as a sink of vascular oxidants that allow the body to maintain a healthy circulatory system. Among the antioxidant enzymes, the thiol-dependent peroxidase peroxiredoxin 2, highly abundant in RBCs, is essential to keep the redox balance. A great part of the RBC antioxidant activity is supported by an active glucose metabolism that provides reducing power in the form of NADPH via the pentose phosphate pathway. There are several RBC defects and situations that generate oxidative stress conditions where the defense mechanisms are overwhelmed, and these include glucose-6-phosphate dehydrogenase deficiencies (favism), hemoglobinopathies like sickle cell disease and thalassemia, as well as packed RBCs for transfusion that suffer from storage lesions. These oxidative stress-associated pathologies of the RBCs underline the relevance of redox balance in these anucleated cells that lack a mechanism of DNA-inducible antioxidant response and rely on a complex and robust network of antioxidant systems.

Metabolic regulation of stress erythropoiesis, outstanding questions, and possible paradigms

Steady state erythropoiesis produces new erythrocytes at a constant rate to replace the senescent cells that are removed by macrophages in the liver and spleen. However, infection and tissue damage disrupt the production of erythrocytes by steady state erythropoiesis. During these times, stress erythropoiesis is induced to compensate for the loss of erythroid output. The strategy of stress erythropoiesis is different than steady state erythropoiesis. Stress erythropoiesis generates a wave of new erythrocytes to maintain homeostasis until steady state conditions are resumed. Stress erythropoiesis relies on the rapid proliferation of immature progenitor cells that do not differentiate until the increase in serum Erythropoietin (Epo) promotes the transition to committed progenitors that enables their synchronous differentiation. Emerging evidence has revealed a central role for cell metabolism in regulating the proliferation and differentiation of stress erythroid progenitors. During the initial expansion stage, the immature progenitors are supported by extensive metabolic changes which are designed to direct the use of glucose and glutamine to increase the biosynthesis of macromolecules necessary for cell growth and division. At the same time, these metabolic changes act to suppress the expression of genes involved in erythroid differentiation. In the subsequent transition stage, changes in niche signals alter progenitor metabolism which in turn removes the inhibition of erythroid differentiation generating a bolus of new erythrocytes to alleviate anemia. This review summarizes what is known about the metabolic regulation of stress erythropoiesis and discusses potential mechanisms for metabolic regulation of proliferation and differentiation.

TLR7 modulates extramedullary splenic erythropoiesis in P. yoelii NSM-infected mice through the regulation of iron metabolism of macrophages with IFN-γ

Splenomegaly is a prominent clinical manifestation of malaria and the causes remain incompletely clear. Anemia is induced in malaria and extramedullary splenic erythropoiesis is compensation for the loss of erythrocytes. However, the regulation of extramedullary splenic erythropoiesis in malaria is unknown. An inflammatory response could facilitate extramedullary splenic erythropoiesis in the settings of infection and inflammation. Here, when mice were infected with rodent parasites, Plasmodium yoelii NSM, TLR7 expression in splenocytes was increased. To explore the roles of TLR7 in splenic erythropoiesis, we infected wild-type and TLR7 ^-/- C57BL/6 mice with P. yoelii NSM and found that the development of splenic erythroid progenitor cells was impeded in TLR7 ^-/- mice. Contrarily, the treatment of the TLR7 agonist, R848, promoted extramedullary splenic erythropoiesis in wild-type infected mice, which highlights the implication of TLR7 on splenic erythropoiesis. Then, we found that TLR7 promoted the production of IFN-γ that could enhance phagocytosis of infected erythrocytes by RAW264.7. After phagocytosis of infected erythrocytes, the iron metabolism of RAW264.7 was upregulated, evidenced by higher iron content and expression of Hmox1 and Slc40a1. Additionally, the neutralization of IFN-γ impeded the extramedullary splenic erythropoiesis modestly and reduced the iron accumulation in the spleen of infected mice. In conclusion, TLR7 promoted extramedullary splenic erythropoiesis in P. yoelii NSM-infected mice. TLR7 enhanced the production of IFN-γ, and IFN-γ promoted phagocytosis of infected erythrocytes and the iron metabolism of macrophages in vitro, which may be related to the regulation of extramedullary splenic erythropoiesis by TLR7.

Defining newly formed and tissue-resident bone marrow-derived macrophages in adult mice based on lysozyme expression

Tissue-resident macrophages are derived from different precursor cells and display different phenotypes. Reconstitution of the tissue-resident macrophages of inflamed or damaged tissues in adults can be achieved by bone marrow-derived monocytes/macrophages. Using lysozyme (Lysm)-GFP-reporter mice, we found that alveolar macrophages (AMs), Kupffer cells, red pulp macrophages (RpMacs), and kidney-resident macrophages were Lysm-GFP-, whereas all monocytes in the fetal liver, adult bone marrow, and blood were Lysm-GFP+. Donor-derived Lysm-GFP+ resident macrophages gradually became Lysm-GFP- in recipients and developed gene expression profiles characteristic of tissue-resident macrophages. Thus, Lysm may be used to distinguish newly formed and long-term surviving tissue-resident macrophages that were derived from bone marrow precursor cells in adult mice under pathological conditions. Furthermore, we found that Irf4 might be essential for resident macrophage differentiation in all tissues, while cytokine and receptor pathways, mTOR signaling pathways, and fatty acid metabolic processes predominantly regulated the differentiation of RpMacs, Kupffer cells, and kidney macrophages, respectively. Deficiencies in ST2, mechanistic target of rapamycin (mTOR) and fatty acid-binding protein 5 (FABP5) differentially impaired the differentiation of tissue-resident macrophages from bone marrow-derived monocytes/macrophages in the lungs, liver, and kidneys. These results indicate that a combination of shared and unique signaling pathways coordinately shape tissue-resident macrophage differentiation in various tissues.

Hemolysis, free hemoglobin toxicity, and scavenger protein therapeutics

During hemolysis, erythrophagocytes dispose damaged red blood cells. This prevents the extracellular release of hemoglobin, detoxifies heme, and recycles iron in a linked metabolic pathway. Complementary to this process, haptoglobin and hemopexin scavenge and shuttle the red blood cell toxins hemoglobin and heme to cellular clearance. Pathological hemolysis outpaces macrophage capacity and scavenger synthesis across a diversity of diseases. This imbalance leads to hemoglobin-driven disease progression. To meet a void in treatment options, scavenger protein-based therapeutics are in clinical development.

Hematologic cytopenia post CAR T cell therapy: Etiology, potential mechanisms and perspective

Chimeric Antigen-Receptor (CAR) T-cell therapies have shown dramatic efficacy in treating relapsed and refractory cancers, especially B cell malignancies. However, these innovative therapies cause adverse toxicities that limit the broad application in clinical settings. Hematologic cytopenias, one frequently reported adverse event following CAR T cell treatment, are manifested as a disorder of hematopoiesis with decreased number of mature blood cells and subdivided into anemia, thrombocytopenia, leukopenia, and neutropenia, which increase the risk of infections, fatigue, bleeding, fever, and even fatality. Herein, we initially summarized the symptoms, etiology, risk factors and management of cytopenias. Further, we elaborated the cellular and molecular mechanisms underlying the initiation and progression of cytopenias following CAR T cell therapy based on previous studies about acquired cytopenias. Overall, this review will facilitate our understanding of the etiology of cytopenias and shed lights into developing new therapies against CAR T cell-induced cytopenias.

Erythrophagocytes in hemolytic anemia, wound healing, and cancer

Hemolysis is a ubiquitous pathology defined as premature red blood cell destruction within the circulation or local tissues. One of the most archetypal functions of macrophages is phagocytosis of damaged or extravasated red blood cells, preventing the extracellular release of toxic hemoglobin and heme. Upon erythrophagocytosis, spiking intracellular heme concentrations drive macrophage transformation into erythrophagocytes, leveraging antioxidative and iron recycling capacities to defend against hemolytic stress. This unique phenotype transformation is coordinated by a regulatory network comprising the transcription factors BACH1, SPI-C, NRF2, and ATF1. Erythrophagocytes negatively regulate inflammation and immunity and may modulate disease-specific outcomes in hemolytic anemia, wound healing, atherosclerosis, and cancer. In this opinion article, we outline the known and presumed functions of erythrophagocytes and their implications for therapeutic innovation and research.

Methodologies and tools to shed light on erythrophagocytosis

Red blood cells (RBC) are the most abundant circulating cell of the human body. RBC are constantly exposed to multiple stresses in the circulation, leading to molecular and structural impairments and death. The physiological process of RBC senescence or ageing is referred to as eryptosis. At the end of their lifespan, aged RBC are recognized and removed from the blood by professional phagocytes via a phenomenon called erythrophagocytosis (EP); the phagocytosis of RBC. Some genetic and acquired diseases can influence eryptosis, thereby affecting RBC lifespan and leading to hemolytic anemia. In some diseases, such as diabetes and atherosclerosis, eryptosis and EP can participate in disease progression with both professional and non-professional phagocytes. Therefore, investigating the process of EP in vivo and in vitro, as well as in different cell types, will not only contribute to the understanding of the physiological steps of EP, but also to the deciphering of the specific mechanisms involving RBC and EP that underlie certain pathologies. In this review, the process of EP is introduced and the different methods for studying EP are discussed together with examples of the experimental procedures and materials required.

Unraveling the interplay between iron homeostasis, ferroptosis and extramedullary hematopoiesis

Iron participates in myriad processes necessary to sustain life. During the past decades, great efforts have been made to understand iron regulation and function in health and disease. Indeed, iron is associated with both physiological (e.g., immune cell biology and function and hematopoiesis) and pathological (e.g., inflammatory and infectious diseases, ferroptosis and ferritinophagy) processes, yet few studies have addressed the potential functional link between iron, the aforementioned processes and extramedullary hematopoiesis, despite the obvious benefits that this could bring to clinical practice. Further investigation in this direction will shape the future development of individualized treatments for iron-linked diseases and chronic inflammatory disorders, including extramedullary hematopoiesis, metabolic syndrome, cardiovascular diseases and cancer.

Macrophages: key players in erythrocyte turnover

The development of red blood cells (RBCs), or erythropoiesis, occurs in specialized niches in the bone marrow, called erythroblastic islands, composed of a central macrophage surrounded by erythroblasts at different stages of differentiation. Upon anemia or hypoxemia, erythropoiesis extends to extramedullary sites, mainly spleen and liver, a process known as stress erythropoiesis, leading to the expansion of erythroid progenitors, iron recruitment and increased production of reticulocytes and mature RBCs. Macrophages are key cells in both homeostatic and stress erythropoiesis, providing conditions for erythroid cells to survive, proliferate and differentiate. During RBCs aging and injury, macrophages play a fundamental role again, performing the clearance of these cells and recycling iron for new erythroblasts in development. Thus, macrophages are crucial components of the RBCs turnover and in this review, we aimed to cover the main known mechanisms involved in the process of birth and death of RBCs, highlighting the importance of macrophage functions in the whole RBC lifecycle.

Novel insights into alcoholic liver disease: Iron overload, iron sensing and hemolysis

The liver is the major target organ of continued alcohol consumption at risk and resulting alcoholic liver disease (ALD) is the most common liver disease worldwide. The underlying molecular mechanisms are still poorly understood despite decades of scientific effort limiting our abilities to identify those individuals who are at risk to develop the disease, to develop appropriate screening strategies and, in addition, to develop targeted therapeutic approaches. ALD is predestined for the newly evolving translational medicine, as conventional clinical and health care structures seem to be constrained to fully appreciate this disease. This concept paper aims at summarizing the 15 years translational experience at the Center of Alcohol Research in Heidelberg, namely based on the long-term prospective and detailed characterization of heavy drinkers with mortality data. In addition, novel experimental findings will be presented. A special focus will be the long-known hepatic iron accumulation, the somewhat overlooked role of the hematopoietic system and novel insights into iron sensing and the role of hepcidin. Our preliminary work indicates that enhanced red blood cell (RBC) turnover is critical for survival in ALD patients. RBC turnover is not primarily due to vitamin deficiency but rather to ethanol toxicity directly targeted to erythrocytes but also to the bone marrow stem cell compartment. These novel insights also help to explain long-known aspects of ALD such as mean corpuscular volume of erythrocytes (MCV) and elevated aspartate transaminase (GOT/AST) levels. This work also aims at identifying future projects, naming unresolved observations, and presenting novel hypothetical concepts still requiring future validation.

Dysregulation of Iron Homeostasis in the Central Nervous System and the Role of Ferroptosis in Neurodegenerative Disorders

Significance: Iron accumulation occurs in the central nervous system (CNS) in a variety of neurological conditions as diverse as spinal cord injury, stroke, multiple sclerosis, Parkinson's disease, and others. Iron is a redox-active metal that gives rise to damaging free radicals if its intracellular levels are not controlled or if it is not properly sequestered within cells. The accumulation of iron occurs due to dysregulation of mechanisms that control cellular iron homeostasis. Recent Advances: The molecular mechanisms that regulate cellular iron homeostasis have been revealed in much detail in the past three decades, and new advances continue to be made. Understanding which aspects of iron homeostasis are dysregulated in different conditions will provide insights into the causes of iron accumulation and iron-mediated tissue damage. Recent advances in iron-dependent lipid peroxidation leading to cell death, called ferroptosis, has provided useful insights that are highly relevant for the lipid-rich environment of the CNS. Critical Issues: This review examines the mechanisms that control normal cellular iron homeostasis, the dysregulation of these mechanisms in neurological disorders, and more recent work on how iron can induce tissue damage via ferroptosis. Future Directions: Quick and reliable tests are needed to determine if and when ferroptosis contributes to the pathogenesis of neurological disorders. In addition, there is need to develop better druggable agents to scavenge lipid radicals and reduce CNS damage for neurological conditions for which there are currently few effective treatments. Antioxid. Redox Signal. 37, 150-170.

The Endless Wars: Severe Fever With Thrombocytopenia Syndrome Virus, Host Immune and Genetic Factors

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging arboviral infectious disease with a high rate of lethality in susceptible humans and caused by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV). Currently, neither vaccine nor specific antiviral drugs are available. In recent years, given the fact that both the number of SFTS cases and epidemic regions are increasing year by year, SFTS has become a public health problem. SFTSV can be internalized into host cells through the interaction between SFTSV glycoproteins and cell receptors and can activate the host immune system to trigger antiviral immune response. However, SFTSV has evolved multiple strategies to manipulate host factors to create an optimal environment for itself. Not to be discounted, host genetic factors may be operative also in the never-ending winning or losing wars. Therefore, the identifications of SFTSV, host immune and genetic factors, and their interactions are critical for understanding the pathogenic mechanisms of SFTSV infection. This review summarizes the updated pathogenesis of SFTS with regard to virus, host immune response, and host genetic factors to provide some novel perspectives of the prevention, treatment, as well as drug and vaccine developments.

Mechanisms of 8-aminoquinoline induced haemolytic toxicity in a G6PDd humanized mouse model

Primaquine (PQ) and Tafenoquine (TQ) are clinically important 8‐aminoquinolines (8‐AQ) used for radical cure treatment of P. vivax infection, known to target hepatic hypnozoites. 8‐AQs can trigger haemolytic anaemia in individuals with glucose‐6‐phosphate dehydrogenase deficiency (G6PDd), yet the mechanisms of haemolytic toxicity remain unknown. To address this issue, we used a humanized mouse model known to predict haemolytic toxicity responses in G6PDd human red blood cells (huRBCs). To evaluate the markers of eryptosis, huRBCs were isolated from mice 24–48 h post‐treatment and analysed for effects on phosphatidylserine (PS), intracellular reactive oxygen species (ROS) and autofluorescence. Urinalysis was performed to evaluate the occurrence of intravascular and extravascular haemolysis. Spleen and liver tissue harvested at 24 h and 5–7 days post‐treatment were stained for the presence of CD169+ macrophages, F4/80+ macrophages, Ter119+ mouse RBCs, glycophorin A+ huRBCs and murine reticulocytes (muRetics). G6PDd‐huRBCs from PQ/TQ treated mice showed increased markers for eryptosis as early as 24 h post‐treatment. This coincided with an early rise in levels of muRetics. Urinalysis revealed concurrent intravascular and extravascular haemolysis in response to PQ/TQ. Splenic CD169+ macrophages, present in all groups at day 1 post‐dosing were eliminated by days 5–7 in PQ/TQ treated mice only, while liver F4/80 macrophages and iron deposits increased. Collectively, our data suggest 8‐AQ treated G6PDd‐huRBCs have early physiological responses to treatment, including increased markers for eryptosis indicative of oxidative stress, resulting in extramedullary haematopoiesis and loss of splenic CD169+ macrophages, prompting the liver to act as the primary site of clearance.

Arsenic retention in erythrocytes and excessive erythrophagocytosis is related to low selenium status by impaired redox homeostasis

Arsenic (As) contamination in drinking water is a global public health problem. Epidemiological studies have shown that selenium (Se) deficiency is associated with an increasing risk of arsenism. However, the association between Se status and As retention in erythrocytes and mechanisms underlying this association have not been fully investigated. In the present study, a total of 165 eligible subjects were recruited and As was found to accumulate in blood mainly by retention in erythrocytes. Retention of As in erythrocytes was negatively correlated with Se status, antioxidant parameters related to Se and As methylation capacity, but positively correlated with the protein-binding capacity of As. Additionally, erythrocytes isolated from subjects with low Se status exhibited cellular damage along with lower protein levels of CD47, which could be aggravated by hydrogen peroxide treatment. Consistent with the human study, the erythrocytes from mice with sub-chronic As exposure exhibited similar cellular damage and shown to be phagocytosed by splenic macrophages, and these effects were mitigated by dietary Se supplementation. Furthermore, hydrogen peroxide treatment induced excessive phagocytosis of erythrocytes with As exposure by splenic macrophages, while co-treating erythrocytes with the reducing agent, N-Acetyl-l-cysteine, mitigated this excessive erythrophagocytosis. Hyperactivation of the NFκB pathway was also detected in splenic macrophages after excessive erythrophagocytosis. In conclusion, this study found that low Se status involving impaired redox homeostasis increased As retention in erythrocytes, which were subsequently phagocytosed by splenic macrophages and led to an increased inflammatory status of splenic macrophages. These findings provide insight into physiological features of arsenism related to Se status and redox homeostasis.