Inflammation induces stress erythropoiesis through heme-dependent activation of SPI-C

Inflammation alters bone marrow hematopoiesis to favor the production of innate immune effector cells at the expense of lymphoid cells and erythrocytes. Furthermore, proinflammatory cytokines inhibit steady-state erythropoiesis, which leads to the development of anemia in diseases with chronic inflammation. Acute anemia or hypoxic stress induces stress erythropoiesis, which generates a wave of new erythrocytes to maintain erythroid homeostasis until steady-state erythropoiesis can resume. Although hypoxia-dependent signaling is a key component of stress erythropoiesis, we found that inflammation also induced stress erythropoiesis in the absence of hypoxia. Using a mouse model of sterile inflammation, we demonstrated that signaling through Toll-like receptors (TLRs) paradoxically increased the phagocytosis of erythrocytes (erythrophagocytosis) by macrophages in the spleen, which enabled expression of the heme-responsive gene encoding the transcription factor SPI-C. Increased amounts of SPI-C coupled with TLR signaling promoted the expression ofGdf15andBmp4, both of which encode ligands that initiate the expansion of stress erythroid progenitors (SEPs) in the spleen. Furthermore, despite their inhibition of steady-state erythropoiesis in the bone marrow, the proinflammatory cytokines TNF-α and IL-1β promoted the expansion and differentiation of SEPs in the spleen. These data suggest that inflammatory signals induce stress erythropoiesis to maintain erythroid homeostasis when inflammation inhibits steady-state erythropoiesis.

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BMP4/Madh5 Dependent Signaling Is Required for the Expansion of a Population of Stress Erythroid Progenitors in the Fetal Liver.

Blood ◽

10.1182/blood.v106.11.4195.4195 ◽

2005 ◽

Vol 106 (11) ◽

pp. 4195-4195

Author(s):

Robert F. Paulson ◽

Prashanth Porayette

Keyword(s):

Bone Marrow ◽

Steady State ◽

Fetal Liver ◽

Erythroid Progenitors ◽

Acute Anemia ◽

Erythroid Response ◽

Stress Erythropoiesis ◽

And Control ◽

Flexed Tail

Abstract Fetal liver hematopoiesis is primarily erythropoiesis, which robustly produces erythrocytes to meet the growing need of the developing embryo. In many ways fetal liver erythropoiesis resembles stress erythropoiesis in the adult, where in response to acute anemia, a unique population of stress erythroid progenitors is rapidly expanded in the spleen. The development of these stress progenitors requires BMP4/Madh5 dependent signals. Spleen stress progenitors exhibit properties that are distinct from bone marrow steady state progenitors in that they are able to rapidly form large BFU-E colonies, which require only Epo stimulation for their generation. Mice mutant at the flexed-tail locus exhibit a defective stress erythroid response because of a mutation in Madh5. In addition to this defect, flexed-tail mice also exhibit a severe fetal-neonatal anemia. We have analyzed fetal liver erythropoiesis in flexed-tail and control embryos. We show that BMP4 is expressed in the fetal liver and its expression correlates with the time of maximum erythropoiesis. In flexed-tail mutant embryos the expression is delayed and this correlates with both a delay and a defect in the expansion of erythroid progenitors. Our analysis also shows that the fetal liver contains two types of erythroid progenitors. One type exhibits the properties of stress BFU-E found in the adult spleen, which are compromised in flexed-tail embryos and a second type that is similar to bone marrow steady state BFU-E. These data demonstrate that BMP4 dependent signaling drives the expansion of erythroid progenitors in the fetal liver in a manner similar to stress erythropoiesis in the adult spleen.

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Ablation of Gata1 in adult mice results in aplastic crisis, revealing its essential role in steady-state and stress erythropoiesis

Blood ◽

10.1182/blood-2007-09-115121 ◽

2008 ◽

Vol 111 (8) ◽

pp. 4375-4385 ◽

Cited By ~ 57

Author(s):

Laura Gutiérrez ◽

Saho Tsukamoto ◽

Mikiko Suzuki ◽

Harumi Yamamoto-Mukai ◽

Masayuki Yamamoto ◽

...

Keyword(s):

Bone Marrow ◽

Steady State ◽

Erythroid Progenitors ◽

Hematopoietic Development ◽

Stress Erythropoiesis ◽

Adult Mice ◽

Aplastic Crisis ◽

Excessive Proliferation ◽

Erythropoietic Response

Abstract The transcription factor Gata1 is expressed in several hematopoietic lineages and plays essential roles in normal hematopoietic development during embryonic stages. The lethality of Gata1-null embryos has precluded determination of its role in adult erythropoiesis. Here we have examined the effects of Gata1 loss in adult erythropoiesis using conditional Gata1 knockout mice expressing either interferon- or tamoxifen-inducible Cre recombinase (Mx-Cre and Tx-Cre, respectively). Mx-Cre–mediated Gata1 recombination, although incomplete, resulted in maturation arrest of Gata1-null erythroid cells at the proerythroblast stage, thrombocytopenia, and excessive proliferation of megakaryocytes in the spleen. Tx-Cre–mediated Gata1 recombination resulted in depletion of the erythroid compartment in bone marrow and spleen. Formation of the early and late erythroid progenitors in bone marrow was significantly reduced in the absence of Gata1. Furthermore, on treatment with a hemolytic agent, these mice failed to activate a stress erythropoietic response, despite the rising erythropoietin levels. These results indicate that, in addition to the requirement of Gata1 in adult megakaryopoiesis, Gata1 is necessary for steady-state erythropoiesis and for erythroid expansion in response to anemia. Thus, ablation of Gata1 in adult mice results in a condition resembling aplastic crisis in human.

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Complete Spatial Mapping of Steady-State and Stress Erythropoiesis

Blood ◽

10.1182/blood-2020-142973 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 7-7

Author(s):

Qingqing Wu ◽

Jizhou Zhang ◽

Courtney Johnson ◽

Anastasiya Slaughter ◽

Margot Lindsay May ◽

...

Keyword(s):

Bone Marrow ◽

Steady State ◽

Single Cells ◽

Differentially Expressed ◽

Published Data ◽

Erythroid Progenitors ◽

Erythroid Progenitor ◽

Clonal Architecture ◽

Stress Erythropoiesis

The anatomy of differentiation in the bone marrow (BM) is poorly understood due to lack of markers to image stepwise HSPC differentiation. We analyzed 250+ cell surface molecules in all hematopoietic progenitors and identified 56 differentially expressed markers in at least one HSPC that can be "mixed and matched" to prospectively image any HSPC of interest in the bone marrow. We used this data to develop a pipeline to map stepwise erythropoiesis in vivo. We found that all erythroid progenitors can be defined as Ly6C-CD27-ESAM-CD117+ cells and then Pre-MegE (earliest erythroid progenitor Cell Stem Cell. 2007 1(4):428-42) are CD150+CD71-. These give rise to CD71+CD150+ Pre-CFU-E that differentiate into CD71+CD150- CFU-E that then generate early erythroblasts. All BFU-E activity was restricted to Pre-MegE and Pre- CFU-E (70 and 30% of all BFU-E) whereas all CFU-E colonies were spread between Pre-MegE (44%), pre-CFU-E (10%) and CFU-E (46%). We also confirmed previously published data showing that CD71 and Ter119 can be used to image stepwise terminal erythropoiesis; CD71+Ter119dim early erythroblasts, CD71+Ter119bright late erythroblasts, CD71dimTer119bright reticulocytes and CD71-Ter119bright erythrocytes. Importantly, all populations were detected at identical frequencies using FACS or confocal imaging indicating that our imaging strategy detects all erythroid cells (Pre-CFU-E: 0.022 vs 0.027 %; CFUE: 0.32 vs 0.30%; Early-Ery: 0.62 vs 0.66%; Late-Ery: 32.05 vs 32.12%; Reticulocyte: 5.98 vs. 3.36%; Erythrocytes: 12.49 vs. 13.47%). We mapped the 3D location of every erythroid lineage cell in mouse sternum and interrogated the spatial relationships between the different maturation steps and with candidate niches. We compared the interactions found in vivo with those found in random simulations. Specifically, we used CD45 and Ter119 to obtain the spatial coordinates of every hematopoietic cell. Then we randomly placed each type of erythroid lineage cell at identical frequencies as those found in vivo to generate random simulations. We found erythroid progenitors show no specific association with HSC, indicating that Pre-Meg-E or more primitive progenitors leave the HSC niche after differentiation. Both Pre-Meg-E and Pre-CFU-E are found as single cells through the central BM space and do not specifically associate with other progenitors, or components of the microenvironment. In contrast almost all CFU-E locate to strings (28 strings per sternum) containing 8 CFU-E that are selectively recruited to sinusoids (mean CFU-E to sinusoid distance=2.2µm). As soon as CFU-E detach from sinusoids they downregulate CD117 and upregulate CD71 giving rise to a cluster of early erythroblasts that buds from the vessel. These progressively upregulate Ter119 to generate large clusters of late erythroblasts that in turn differentiate into clusters of reticulocytes and erythrocytes. To examine the clonal architecture of erythropoiesis we used Ubc-creERT2:confetti mice where a tamoxifen pulse leads to irreversible expression of GFP, CFP, YFP or RFP. Four weeks later we found that the CFU-E strings are oligoclonal with each clone contributing 2-6 CFU-E to the string. The budding erythroblasts clusters are similarly organized. These indicate that different CFU-E are serially recruited to the same sinusoidal spot where they self-renew 1-2 times and then undergo terminal differentiation. We then tracked how this architecture changed in response to stress (hemorrhage). Two days after bleeding we found that Pre-Meg-E and Pre-CFU-E numbers and locations were unaltered. The number of CFU-E strings remained constant (30 CFUE strings/sternum) but all strings contained more CFU-E (2-fold) suggesting increased self-renewal. Unexpectedly, fate mapping showed that the size of CFU-E clones did not increase when compared to steady-state. These results indicate that all CFU-E expand in respond to stress and that this is mediated via increased recruitment and differentiation of upstream progenitors. In summary we have found 56 differentially expressed markers that can be combined to detect most HSPC; validated a 5-color stain to image and fate map all steps of red blood cell maturation in situ; demonstrated that terminal erythropoiesis emerges from strings of sinusoidal CFU-E, and revealed the clonal architecture of normal and stress erythropoiesis. Disclosures No relevant conflicts of interest to declare.

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The MAPK ERK1 is a negative regulator of the adult steady-state splenic erythropoiesis

Blood ◽

10.1182/blood-2009-09-242487 ◽

2010 ◽

Vol 115 (18) ◽

pp. 3686-3694 ◽

Cited By ~ 31

Author(s):

Soizic Guihard ◽

Denis Clay ◽

Laurence Cocault ◽

Nathalie Saulnier ◽

Paule Opolon ◽

...

Keyword(s):

Bone Marrow ◽

Steady State ◽

Bone Marrow Cells ◽

Serum Levels ◽

Negative Regulator ◽

Erythroid Progenitors ◽

Stress Erythropoiesis ◽

Extracellular Signal ◽

Mitogen Activated Protein

Abstract The mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1 (ERK1) and ERK2 are among the main signal transduction molecules, but little is known about their isoform-specific functions in vivo. We have examined the role of ERK1 in adult hematopoiesis with ERK1−/− mice. Loss of ERK1 resulted in an enhanced splenic erythropoiesis, characterized by an accumulation of erythroid progenitors in the spleen, without any effect on the other lineages or on bone marrow erythropoiesis. This result suggests that the ablation of ERK1 induces a splenic stress erythropoiesis phenotype. However, the mice display no anemia. Deletion of ERK1 did not affect erythropoietin (EPO) serum levels or EPO/EPO receptor signaling and was not compensated by ERK2. Splenic stress erythropoiesis response has been shown to require bone morphogenetic protein 4 (BMP4)–dependent signaling in vivo and to rely on the expansion of a resident specialized population of erythroid progenitors, termed stress erythroid burst-forming units (BFU-Es). A great expansion of stress BFU-Es and increased levels of BMP4 mRNA were found in ERK1−/− spleens. The ERK1−/− phenotype can be transferred by bone marrow cells. These findings show that ERK1 controls a BMP4-dependent step, regulating the steady state of splenic erythropoiesis.

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A Shared Signaling Network That Maintains Erythroid Homeostasis By Activating Stress Erythropoiesis Regulates Inflammation: Implications for the Anemia of Chronic Inflammation

Blood ◽

10.1182/blood-2018-99-113448 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 629-629

Author(s):

James Fraser ◽

Adwitia Dey ◽

Shaneice Nettleford ◽

Siyang Hao ◽

Luming Zhao ◽

...

Keyword(s):

Bone Marrow ◽

T Cells ◽

Steady State ◽

Inflammatory Cytokines ◽

Red Cell ◽

Erythroid Progenitors ◽

Stress Erythropoiesis ◽

Inflammatory Signals ◽

Treg Development ◽

Pro Inflammatory Cytokines

Abstract Anemia is a common secondary pathology resulting from inflammatory diseases including cancer or infection. Its exact prevalence is difficult to determine, yet its contributions to the morbidity and mortality of patients and its negative impact on quality of life are clear. Despite the diverse set of factors that can lead to inflammatory anemia, its core pathology of hyperinflammation, iron dysregulation, and lack of red cell production suggests the possibility of a common etiology. Inflammation induces pro-inflammatory cytokines including TNFα, IL-1β and IFNγ that drive myelopoiesis at the expense of steady state bone marrow erythropoiesis. In addition, other cytokines increase the expression of hepcidin, haptoglobin and hemopexin by the liver, leading to the sequestration of iron. While limiting iron can be beneficial in the context of infection, the consequence of this restriction is a further reduction in red cell production in the bone marrow. To compensate for the loss of bone marrow erythropoiesis, inflammation induces stress erythropoiesis in the spleen or liver. Stress erythropoiesis is regulated by different signals which include BMP4 and GDF15 and utilizes stress erythroid progenitors that are distinct from steady state erythroid progenitors. Our work shows that in contrast to steady state erythropoiesis, pro-inflammatory cytokines like TNFα promote the proliferation of stress erythroid progenitors, while anti-inflammatory signals such as PGJ2 and IL-10 promote their differentiation. These studies demonstrate that the expansion and differentiation stages of stress erythropoiesis are coordinated with, and influenced by, signals that initiate and resolve inflammation. In addition, we show that this regulation is reciprocal. Signals that regulate the differentiation of stress erythroid progenitors (GDF15 and BMP4) promote the resolution of inflammation. Mice infected with the model gut pathogen Citrobacter rodentium, exhibit stress erythropoiesis in the spleen, while steady state erythropoiesis in the bone marrow is suppressed until pathogen clearance. We observed that hepcidin expression in the liver increases initially, but then decreases as the expression of erythroferrone by stress erythroid progenitors increased in the spleen, but not the bone marrow. Using mice mutant for GDF15 (GDF15-/-) and for BMP4 signaling (flexed-tail f/f), which exhibit defective stress erythropoiesis, we observed that the expression of hepcidin was dysregulated suggesting that stress erythroid progenitors are responsible for iron regulation at this time. In addition, infection of mutant mice led to increased lethality. During peak infection, we observed morphological differences in the colons of these mice indicative of increased inflammation and systemic infection. These changes were associated with increased expression of pro-inflammatory genes, as well as decreased numbers of FoxP3+ regulatory T-cells (Tregs). Using naïve CD4+ T-cells isolated from uninfected control, f/f or GDF15-/- mice, we observed significantly altered gene expression from mutant T-cells following Treg induction in vitro. However, the addition of BMP4 and GDF15 into these cultures rescued Treg development of mutant naïve T-cells and enhanced Treg development of naïve control T cells. Analysis of the BMP4 and GDF15 signaling pathways in both stress erythroid progenitor differentiation and in Treg development revealed that in both systems these signals converge on the transcription factor HIF1α. Taken together these data support a new model showing that the loss of steady state erythropoiesis due to pro-inflammatory signals is balanced by the activation of stress erythropoiesis by those same factors. Similarly, the differentiation of stress erythroid progenitors appears to regulate iron, and is itself regulated by the same signals that drive the development of Tregs and the expression of anti-inflammatory cytokines during immune resolution. This work supports a novel model where initiation and resolution of inflammatory immune responses are co-regulated with stress erythropoiesis, which allows for a robust immune response while maintaining erythroid homeostasis. Furthermore, this model predicts that alterations to this shared signaling network will underlie the development of chronic inflammatory anemia. Disclosures No relevant conflicts of interest to declare.

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PECULIAR IMMUNOBIOLOGY OF BONE MARROW ALLOGRAFTS

Journal of Experimental Medicine ◽

10.1084/jem.134.1.83 ◽

1971 ◽

Vol 134 (1) ◽

pp. 83-102 ◽

Cited By ~ 207

Author(s):

Gustavo Cudkowicz ◽

Michael Bennett

Keyword(s):

Bone Marrow ◽

Tissue Specificity ◽

Genetic Factors ◽

Bone Marrow Cells ◽

Lymphoid Cells ◽

X Rays ◽

Marrow Graft ◽

Effector Cells ◽

Adult Mice ◽

Regulator Genes

Mice are capable of rejecting H-2-incompatible bone marrow grafts after a single lethal exposure to X-rays. The onset of rejection begins 18–24 hr after transplantation and is completed by 96 hr. Maturation of this type of allograft reactivity does not occur until the 22nd day of life. In adult mice, the resistance to marrow allografts can be weakened by administration of cyclophosphamide or dead cultures of Corynebacterium parvum, but not heterologous anti-thymocyte serum. Sublethal exposures to X-rays 7 or 14 days before transplantation also weaken resistance. There is considerable interstrain variation in the ability of mice to resist allografts, even when H-2 differences between hosts and donor are kept identical. Although H-2 incompatibility is a necessary prerequisite for resistance, additional genetic factors influence the outcome of marrow allografts, presumably by controlling recognition. The regulator genes are determinant specific and the alleles for resistance or responder status appear to be dominant. The responder phenotype is expressed by hemopoietic cells and not by the environment. Accordingly, resistance is conferred to otherwise susceptible mice upon transfer of bone marrow cells but not of serum. The production and differentiation of effector cells for marrow graft rejection are thymus independent. In conclusion, bone marrow allografts elicit a particular transplantation reaction, previously unknown, in irradiated mice. Peculiar features of this reaction are the lack of proliferation of host lymphoid cells, tissue specificity, thymus independence, and regulation by genetic factors which apparently do not affect the fate of other grafts.

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EPO-Dependent Recovery of Late-Stage Erythroid Progenitors in the Marrow Precedes Splenic Expansion: Insights From a Sublethal Radiation Model

Blood ◽

10.1182/blood.v118.21.180.180 ◽

2011 ◽

Vol 118 (21) ◽

pp. 180-180

Author(s):

Scott A Peslak ◽

Jesse Wenger ◽

Amali P Epa ◽

Jeffrey C Bemis ◽

Paul D Kingsley ◽

...

Keyword(s):

Bone Marrow ◽

Steady State ◽

Late Stage ◽

Erythroid Cell ◽

Functional Evaluation ◽

Erythroid Progenitors ◽

Erythroid Progenitor ◽

Irradiation Injury ◽

Radiation Induced ◽

Sublethal Irradiation

Abstract Abstract 180 Erythropoiesis is a robust process of cellular expansion and maturation that occurs in the bone marrow and spleen of mice. Following clastogenic injury such as total body irradiation (TBI), erythroblasts are severely depleted in these organs, resulting in loss of reticulocyte output and the development of a mild anemia (Peslak et al., Exp. Hematol. 2011). However, the mechanistic and microenvironmental factors underlying erythroid recovery following sublethal TBI are poorly understood. To this end, we utilized colony assays to quantify erythroid progenitors, which consist of immature d7 erythroid burst-forming units (BFU-E) and more mature d3 BFU-E and erythroid colony forming units (CFU-E). Imaging flow cytometry was used to quantify erythroblast precursors. We found that d7 BFU-E undergo a slow, incomplete recovery during the first 10 days post-4 Gy TBI of C57Bl/6 mice. In contrast, d3 BFU-E exhibit a robust recovery beginning at 4 days post-TBI that is immediately followed by a rapid increase in CFU-E numbers to over 200 percent of steady-state levels. This initial erythroid progenitor recovery is followed by a wave of erythroid precursor maturation and red cell formation that occurs in close association with macrophages in the bone marrow. These erythroblast islands undergo a rapid synchronous expansion that peaks at 6 days post-TBI, suggesting that the bone marrow microenvironment plays a role in the recovery of the erythron from sublethal TBI. We hypothesized that erythropoietin (EPO), the primary regulator of erythroid survival and proliferation, mediates the rapid, specific expansion of late-stage erythroid progenitors following radiation injury. We found that plasma EPO levels increase 13-fold 4 days after 4 Gy TBI, temporally correlated with expansion of d3 BFU-E. Furthermore, maintenance of steady-state hematocrit levels following TBI prevented EPO induction and blocked expansion of late-stage erythroid progenitors, while exogenous EPO administered at 1 hour post-radiation specifically advanced recovery of late-stage progenitors. These data indicate that EPO is required for expansion of d3 BFU-E and CFU-E following radiation-induced marrow depletion. During times of acute hypoxia, such as the severe anemia induced by bleeding or phenylhydrazine exposure, EPO production is rapidly upregulated and splenic stress erythropoiesis is induced. Surprisingly, splenic erythropoiesis is absent during the rapid initial recovery of erythropoiesis in the bone marrow at 4–6 days post-TBI. However, a massive expansion of CFU-E begins at 7–8 days post-4 Gy TBI in spleen. EPO administration at 4 days following 4 Gy TBI significantly enhances late-stage progenitor recovery exclusively in the marrow, indicating that erythroid progenitors are not present in spleen at the time of rapid bone marrow expansion and that late-stage erythroid progenitor recovery initiates in the marrow and subsequently proceeds to the spleen. Furthermore, we found that erythroid progenitors transiently emerge in the bloodstream at 6–8 days post-TBI, following marrow recovery and prior to initiation of splenic erythropoiesis. These data are consistent with endogenous migration of the erythron from the bone marrow to the spleen during recovery from radiation-induced erythroid injury. Taken together, our data indicate that recovery from sublethal irradiation injury is regulated primarily by the EPO-induced expansion of late-stage erythroid progenitors in the bone marrow. This form of clastogenic injury is critically different from bleeding or hemolysis, which preserve bone marrow and splenic erythroblasts and induce expansion of splenic erythroid stress progenitors. Sublethal irradiation injury thus provides a unique model for the in vivo study of endogenous erythroid recovery. This model may be clinically useful for the functional evaluation of therapeutic factors that regulate or modulate erythroid cell maturation. Disclosures: Bemis: Litron Laboratories: Employment, Patents & Royalties.

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Point mutation in the gene encoding p300 suppresses thrombocytopenia in Mpl−/− mice

Blood ◽

10.1182/blood-2007-10-119677 ◽

2008 ◽

Vol 112 (8) ◽

pp. 3148-3153 ◽

Cited By ~ 24

Author(s):

Maria Kauppi ◽

James M. Murphy ◽

Carolyn A. de Graaf ◽

Craig D. Hyland ◽

Kylie T. Greig ◽

...

Keyword(s):

Bone Marrow ◽

Protein C ◽

Lymphoid Cells ◽

Wild Type ◽

Gene Encoding ◽

Mutagenesis Screen ◽

Transcriptional Regulatory ◽

Regulatory Complex ◽

Transcriptional Coregulator ◽

B Lymphoid

Abstract In an N-nitroso-N-ethylurea (ENU) mutagenesis screen using Mpl−/− mice, we isolated a semidominant suppressor of thrombocytopenia, termed Plt6. The gene mutated in Plt6 mice encodes the transcriptional coregulator p300, and the mutation, a tyrosine to asparagine substitution at amino acid 630 (Y630N), disrupts the interaction between p300 and c-Myb. Mpl−/−p300Plt6/+ mice displayed elevated platelet counts relative to Mpl−/−p300+/+ controls, whereas mice homozygous for the Plt6 mutation produced supraphysiological levels of circulating platelets. On a wild-type genetic background, mice homozygous for the p300Plt6 mutation, or recipients of Mpl+/+p300Plt6/Plt6 bone marrow, also exhibited thrombocytosis as well as deficiencies in B-lymphoid cells. Increased platelet numbers in Plt6 mutant mice were accompanied by significant increases in megakaryocyte progenitor cells within the bone marrow and spleen with concomitantly elevated numbers of megakaryocytes. The expansion of megakaryocytopoiesis and suppression of Mpl−/− thrombocytopenia in Plt6 mutants is highly reminiscent of that observed in mice with mutations affecting the p300 partner protein c-Myb, suggesting an indispensable repressive role for the c-Myb/p300 transcriptional regulatory complex in megakaryocyte develop-ment, the inhibition of which allows substantial thrombopoietin (TPO)–independent platelet production.

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P042 Alteration in immune-effector cells in bone marrow of myelodysplastic syndrome patients

Leukemia Research ◽

10.1016/s0145-2126(07)70112-1 ◽

2007 ◽

Vol 31 ◽

pp. S63-S64

Author(s):

F. Alfinito ◽

L. Luciano ◽

M. Sica ◽

F. Milite ◽

S. Costagliola ◽

...

Keyword(s):

Bone Marrow ◽

Myelodysplastic Syndrome ◽

Immune Effector ◽

Effector Cells ◽

Immune Effector Cells

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Functional Requirements of a Samd14-Capping Protein Interaction in Stress Erythropoiesis

Blood ◽

10.1182/blood-2021-152898 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 288-288

Author(s):

Suhita Ray ◽

Linda Chee ◽

Nicholas T. Woods ◽

Kyle J Hewitt

Keyword(s):

Steady State ◽

Hemolytic Anemia ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Interacting Proteins ◽

Erythroid Progenitors ◽

Erythroid Progenitor ◽

Capping Protein ◽

Sam Domain ◽

Stress Erythropoiesis

Abstract Stress erythropoiesis describes the process of accelerating red blood cell (RBC) production in anemia. Among a number of important mediators of stress erythropoiesis, paracrine signals - involving cooperation between SCF/c-Kit signaling and other signaling inputs - are required for the activation/function of stress erythroid progenitors. Whereas many critical factors required to drive erythropoiesis in normal physiological conditions have been described, whether distinct mechanisms control developmental, steady-state, and stress erythropoiesis in anemia is poorly understood. Our prior work revealed that the Sterile Alpha Motif (SAM) Domain 14 (Samd14) gene is transcriptionally upregulated in a model of acute hemolytic anemia induced by the RBC-lysing chemical phenylhydrazine. Samd14 is regulated by GATA binding transcription factors via an intronic enhancer (Samd14-Enh). In a mouse knockout of Samd14-Enh (Samd14-Enh -/-), we established that the Samd14-Enh is dispensable for steady-state erythropoiesis but is required for recovery from severe hemolytic anemia. Samd14 promotes c-Kit signaling in vivo and ex vivo, and the SAM domain of Samd14 facilitates c-Kit-mediated cellular signaling and stress progenitor activity. In addition, the Samd14 SAM domain is functionally distinct from closely related SAM domains, which demonstrates a unique role for this SAM domain in stress signaling and cell survival. In our working model, Samd14-Enh is part of an ensemble of anemia-responsive enhancers which promote stress erythroid progenitor activity. However, the mechanism underlying Samd14's role in stress erythropoiesis is unknown. To identify potential Samd14-interacting proteins that mediate its function, we performed immunoprecipitation-mass spectrometry on the Samd14 protein. We found that Samd14 interacted with α- and β heterodimers of the F-actin capping protein (CP) complex independent of the SAM domain. CP binds to actin during filament assembly/disassembly and plays a role in cell morphology, migration, and signaling. Deleting a 17 amino acid sequence near the N-terminus of Samd14 disrupted the Samd14-CP interaction. However, mutating the canonical RxR of the CP interaction (CPI) motif, which is required for CP-binding in other proteins, does not abrogate the Samd14-CP interaction. Moreover, replacing this sequence with the canonical CPI domain of CKIP-1 completely disrupts the interaction, indicating that other sequence features are required to maintain the Samd14-CP complex. Ex vivo knockdown of the β-subunit of CP (CPβ), which disrupts the integrity of the CP complex, decreased the percentage of early erythroid precursors (p<0.0001) and decreased (3-fold) progenitor activity as measured by colony formation assays (similar to knockdown of Samd14). Taken together, these data indicate that Samd14 interacts with CP via a unique CP binding (CPB) domain, and that the CP complex coordinates erythroid differentiation in stress erythroid progenitors. To test the function of the Samd14-CP complex, we designed an ex vivo genetic complementation assay to express Samd14 lacking the CPB-domain (Samd14∆CPB) in stress erythroid progenitors isolated from anemic Samd14-Enh -/- mice. Phospho-AKT (Ser473) and phospho-ERK (Thr202/Tyr204) levels in Samd14∆CPB were, respectively, 2.2 fold (p=0.007) and ~7 fold (n=3) lower than wild type Samd14 expressing cells, 5 min post SCF stimulation. Relative to Samd14, Samd14∆CPB expression reduced burst forming unit-erythroid (BFU-E) (2.0 fold) and colony forming unit-erythroid (CFU-E) (1.5 fold). These results revealed that the Samd14-CP interaction is a determinant of BFU-E and CFU-E progenitor cell levels and function. Remarkably, as the requirement of the CPB domain in BFU-E and CFU-E progenitors is distinct from the Samd14-SAM domain (which promotes BFU-E but not CFU-E), the function of Samd14 in these two cell types may differ. Ongoing studies will examine whether the function of Samd14 extends beyond SCF/c-Kit signaling and establish cell type-dependent functions of Samd14 and Samd14-interacting proteins. Given the critical importance of c-Kit signaling in hematopoiesis, the role of Samd14 in mediating pathway activation, and our discovery implicating the capping protein complex in erythropoiesis, it is worth considering the pathological implications of this mechanism in acute/chronic anemia and leukemia. Disclosures No relevant conflicts of interest to declare.

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