Regulation Of Hematopoiesis Research Articles

Study of phenotypic and cytotoxic properties of erythroid cells of the spleen under hematopoiesis-stimulating effects

In recent years, research has revealed a wide variety of erythroid cell functions, including modulation of innate and adaptive immune responses. Anemic or hypoxic stress stimulates a physiological response in the form of stress erythropoiesis, aimed at increasing oxygen delivery to tissues. Stress erythropoiesis activates progenitor cells and uses mechanisms that differ from stationary bone marrow erythropoiesis. To consider the role of erythroid cells in the regulation of hematopoiesis, hematopoiesis-activating states were modeled: chemically induced hemolytic anemia, acute blood loss, hypoxia. A series of experiments was carried out on first-generation hybrid mice CBA C57Bl6. Isolation of erythroid cells was performed using magnetic separation for the CD71 marker. The stages of differentiation of erythroid cells were determined by the combination of expression of TER-119 and CD71 markers and direct light scattering parameters in the population of both CD45-positive and CD45-negative spleen cells. To study the immunoregulatory activity of erythroid cells, we investigated the mediated cytotoxicity of splenocytes against tumor cells of the mouse melanoma B78 line after cultivation with conditioned spleen media after various hematopoiesis-stimulating effects. With various hemopoiesis-stimulating effects, the quantitative and qualitative composition of the spleen cells is reorganized depending on the compensatory mechanism for restoring homeostasis. An analysis of the cellular composition of the spleen showed that under hematopoiesis-stimulating effects, a redistribution of populations with the CD45 marker occurs: during hypoxia, the number of CD45-negative cells sharply decreases and the number of CD45-positive cells increases. The population of basophilic erythroblasts is the least susceptible to quantitative changes under all hematopoiesis-stimulating effects. During hypoxia, the most noticeable change in the cellular composition of the spleen is observed due to the increased accumulation of CD45-positive erythroid cells in the spleen. Mediators of erythroid cells of the spleen of mice after hypoxia do not lead to an increase in the cytotoxic proapoptotic effect of splenocytes on tumor cells, in contrast to the erythroid cells of the normal spleen, spleen with anemia and blood loss. Thus, it is tissue hypoxia that is the process that not only stimulates erythropoiesis, but also leads to the maximum change in the suppressive properties of surrounding cells. We assume that the implementation of compensatory mechanisms under the studied hematopoiesis-stimulating effects is aimed at activating the mechanisms of innate immunity and local immunosuppression to prevent local inflammation, accumulate nutrients, and attract cellular elements to the focus of hematopoiesis to restore homeostatic functions.

Adenosine signaling inhibits erythropoiesis and promotes myeloid differentiation.

Intracellular uptake of adenosine is essential for optimal erythroid commitment and differentiation of hematopoietic progenitor cells. The role of adenosine signaling is well documented in the regulation of blood flow, cell proliferation, apoptosis, and stem cell regeneration. However, the role of adenosine signaling in hematopoiesis remains unclear. In this study, we show that adenosine signaling inhibits the proliferation of erythroid precursors by activating the p53 pathway and hampers the terminal erythroid maturation. Furthermore, we demonstrate that the activation of specific adenosine receptors promotes myelopoiesis. Overall, our findings indicate that extracellular adenosine could be a new player in the regulation of hematopoiesis.

Understanding the Wnt Signaling Pathway in Acute Myeloid Leukemia Stem Cells: A Feasible Key against Relapses.

Wnt signaling is a highly conserved pathway in evolution which controls important processes such as cell proliferation, differentiation and migration, both in the embryo and in the adult. Dysregulation of this pathway can favor the development of different types of cancer, such as acute myeloid leukemia and other hematological malignancies. Overactivation of this pathway may promote the transformation of pre-leukemic stem cells into acute myeloid leukemia stem cells, as well as the maintenance of their quiescent state, which confers them with self-renewal and chemoresistance capacity, favoring relapse of the disease. Although this pathway participates in the regulation of normal hematopoiesis, its requirements seem to be greater in the leukemic stem cell population. In this review, we explore the possible therapeutic targeting of Wnt to eradicate the LSCs of AML.

The Profile of microRNA Expression in Diffuse Large B-Cell Lymphoma

Non-Hodgkin’s lymphoma (NHL) is a heterogeneous group of cancers characterized by different pathogenesis and prognosis. The main methods for treating NHL are chemotherapy, immunochemotherapy, and radiation therapy; however, most of these cancers are known to be chemoresistant or return rapidly after the short chemotherapy-induced remission. Therefore, searching for alternative cytoreductive therapy options is quite relevant today. Aberrant microRNA (miRNA) expression is one of the mechanisms responsible for the emergence and progression of lymphoid malignancies. This study was aimed at identifying the miRNA expression profile in diagnostic biopsy specimens harvested from the lymph nodes affected by diffuse large B-cell lymphoma (DLBCL) and identifying miRNA markers, which can potentially be used to design a novel type of ta-rgeted anticancer drugs that would allow one to achieve maximum therapy personalization and increase its efficacy. The key study objects were histological specimens harvested from the lymph nodes by excisional d-iagnostic biopsy and treated using the conventional histomorphological formalin fixation methods. The study group consisted of patients with DLBCL (n = 52). The biopsy specimens harvested from patients with reactive lymphadenopathy (RL) (n = 40) constituted the control group. The miR-150 expression level was reduced over 12-fold (p = 3.6 × 10‒15) compared to that in the tissues of non-cancerous nodular masses. B-ioinformatic analysis revealed that miR-150 is involved in regulation of hematopoiesis and lymphopoiesis. The findings obtained in this study allow considering miR-150 a promising therapeutic target having a great potential for clinical applications.

Long term in vivo Dlk1 gene transfer protects against myocardial fibrosis-induced cardiac dysfunction

Introduction: Cardiac fibrosis can independently contribute to the impairment of cardiac function and development of heart failure. Early activation of pro-fibrotic genetic pathways has been suggested to occur well before adverse ventricular remodeling occurs in fibrosis as it progresses to heart failure. Delta-like homolog 1 (Dlk1), a paternally imprinted gene that encodes a transmembrane protein that contains multiple epidermal growth factor repeats, has been shown to play a critical role as a regulator of cell differentiation, neuronal differentiation, bone differentiation, and hematopoiesis. We hypothesize that Dlk-1 could regulate myocardial fibrosis via inhibition of fibroblast-myofibroblast conversion and therefore restrain cardiac fibrosis progression. Methods: Wildtype (WT) and Dlk1 knockout (Dlk1-/-) mice were subjected to myocardial infarction (MI) by permanent ligation of the left anterior descending artery to induce heart failure. A recombinant adeno-associated virus 9 (AAV9) was used to deliver Dlk1 into the myocardium in vivo. Cardiac function and hemodynamic changes were measured by echocardiography and left ventricular catheterization. Immunohistochemistry and confocal microscopy were used to determine the expression of pro-fibrotic markers. Total RNA was prepared from left ventricular (LV) tissue or cardiomyocytes and fibroblasts from Dlk1-/- and WT hearts. Masson trichrome staining was used to determine abnormal collagen deposition in the heart. Result: Myocardial fibrosis was demonstrated by increased expression of alpha-smooth muscle actin (αSMA), collagen, fibronectin, connective tissue growth factor, along with a substantial increase in the deposition of collagen as evident from Masson's trichrome staining. We observed downregulated Dlk-1 mRNA and protein expression in ischemic tissues from human patients and infarcted pigs’ hearts. The reduced levels of Dlk1 were associated with increased mRNA expression of pro-fibrotic molecules, collagen1a, LOX and αSMA in the scar area. Echocardiographic analysis revealed substantial LV chamber dilatation and reduced fractional shortening (FS %) in Dlk1 null mice as compared to WT, whereas the mice treated with AAV9-Dlk1 for 8-10 weeks showed a significant improvement in cardiac function. Consistently, Dlk1-deficient mice exhibited impairment in heart function, cardiac fibrosis and myocyte hypertrophy and increased expression of atrial natriuretic peptide, and B-type natriuretic peptide, while AAV9-Dlk1-treated mice significantly reduced cardiac remodeling and myocardial fibrosis. Conclusion: Restoration of Dlk1 in the heart following MI-induced heart failure improved cardiac function and attenuated myocardial fibrosis. The findings from the current study suggest a critical role for Dlk1 in myocardial fibrosis-induced cardiac remodeling, indicating that Dlk1 gene therapy may be a viable therapeutic approach for heart failure. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A mechanosensitive vascular niche for Drosophila hematopoiesis

Hematopoietic stem and progenitor cells maintain blood cell homeostasis by integrating various cues provided by specialized microenvironments or niches. Biomechanical forces are emerging as key regulators of hematopoiesis. Here, we report that mechanical stimuli provided by blood flow in the vascular niche control Drosophila hematopoiesis. In vascular niche cells, the mechanosensitive channel Piezo transduces mechanical forces through intracellular calcium upregulation, leading to Notch activation and repression of FGF ligand transcription, known to regulate hematopoietic progenitor maintenance. Our results provide insight into how the vascular niche integrates mechanical stimuli to regulate hematopoiesis.

The cytokine receptor CRLF3 is a human neuroprotective EV-3 (Epo) receptor.

The evolutionary conserved orphan cytokine receptor-like factor 3 (CRLF3) has been implicated in human disease, vertebrate hematopoiesis and insect neuroprotection. While its specific functions are elusive, experimental evidence points toward a general role in cell homeostasis. Erythropoietin (Epo) is a major regulator of vertebrate hematopoiesis and a general cytoprotective cytokine. Erythropoietic functions mediated by classical Epo receptor are understood in great detail whereas Epo-mediated cytoprotective mechanisms are more complex due to involvement of additional Epo receptors and a non-erythropoietic splice variant with selectivity for certain receptors. In the present study, we show that the human CRLF3 mediates neuroprotection upon activation with the natural Epo splice variant EV-3. We generated CRLF3 knock-out iPSC lines and differentiated them toward the neuronal lineage. While apoptotic death of rotenone-challenged wild type iPSC-derived neurons was prevented by EV-3, EV-3-mediated neuroprotection was absent in CRLF3 knock-out neurons. Rotenone-induced apoptosis and EV-3-mediated neuroprotection were associated with differential expression of pro-and anti-apoptotic genes. Our data characterize human CRLF3 as a receptor involved in Epo-mediated neuroprotection and identify CRLF3 as the first known receptor for EV-3.

A decision support system based on artificial intelligence and systems biology for the simulation of pancreatic cancer patient status.

Oncology treatments require continuous individual adjustment based on the measurement of multiple clinical parameters. Prediction tools exploiting the patterns present in the clinical data could be used to assist decision making and ease the burden associated to the interpretation of all these parameters. The goal of this study was to predict the evolution of patients with pancreatic cancer at their next visit using information routinely recorded in health records, providing a decision-support system for clinicians. We selected hematological variables as the visit's clinical outcomes, under the assumption that they can be predictive of the evolution of the patient. Multivariate models based on regression trees were generated to predict next-visit values for each of the clinical outcomes selected, based on the longitudinal clinical data as well as on molecular data sets streaming from in silico simulations of individual patient status at each visit. The models predict, with a mean prediction score (balanced accuracy) of 0.79, the evolution trends of eosinophils, leukocytes, monocytes, and platelets. Time span between visits and neutropenia were among the most common factors contributing to the predicted evolution. The inclusion of molecular variables from the systems-biology in silico simulations provided a molecular background for the observed variations in the selected outcome variables, mostly in relation to the regulation of hematopoiesis. In spite of its limitations, this study serves as a proof of concept for the application of next-visit prediction tools in real-world settings, even when available data sets are small.

Bone Marrow Adipose Tissue: Regulation of Osteoblastic Niche, Hematopoiesis and Hematological Malignancies.

Bone marrow adipose tissue (BMAT) creates a specific microniche within multifunctional bone marrow (BM) ecosystem which imposes changes in surrounding cells and at systemic level. Moreover, BMAT contributes to spatial and temporal separation and metabolic compartmentalization of BM, thus regulating BM homeostasis and diseases. Recent findings have identified novel progenitor subsets of bone marrow adipocytes (BMAd)s recruited during the BM adipogenesis within different skeletal and hematopoietic stem cell niches. Potential of certain mesenchymal BM cells to differentiate into both osteogenic and adipogenic lineages, contributes to the complex interplay of BMAT with endosteal (osteoblastic) niche compartments as an important cellular player in bone tissue homeostasis. Targeting and ablation of BMAT cells at certain states might be an optional and promising strategy for improvement of bone health. Additionally, recent findings demonstrated spatial distribution of BMAds related to hematopoietic cells and pointed out important functional roles in the vital processes such as long-term hematopoiesis. BM adipogenesis appears to be an emergency phenomenon that follows the production of hematopoietic stem and progenitor cell niche factors, thus regulating physiological, stressed, and malignant hematopoiesis. Lipolytic and secretory activity of BMAds can influence survival and proliferation of hematopoietic cells at different maturation stages. Due to their different lipid status, constitutive and regulated BMAds are important determinants of normal and malignant hematopoietic cells. Further elucidation of cellular and molecular players involved in BMAT expansion and crosstalk with malignant cells is of paramount importance for conceiving the new therapies for improvement of BM health.

Manganese-Based Tumor Immunotherapy.

As an essential micronutrient, manganese (Mn) participates in various physiological processes and plays important roles in host immune system, hematopoiesis, endocrine function, and oxidative stress regulation. Mn-based nanoparticles are considered to be biocompatible and show versatile applications in nanomedicine, in particular utilized in tumor immunotherapy in the following ways: 1) acting as a biocompatible nanocarrier to deliver immunotherapeutic agents for tumor immunotherapy; 2) serving as an adjuvant to regulate tumor immune microenvironment and enhance immunotherapy; 3) activating host's immune system through the cGAS-STING pathway to trigger tumor immunotherapy; 4) real-time monitoring tumor immunotherapy effect by magnetic resonance imaging (MRI) since Mn2+ ions are ideal MRI contrast agent which can significantly enhance the T1 -weighted MRI signal after binding to proteins. This comprehensive review focuses on the most recent progress of Mn-based nanoplatforms in tumor immunotherapy. The characteristics of Mn are first discussed to guide the design of Mn-based multifunctional nanoplatforms. Then the biomedical applications of Mn-based nanoplatforms, including immunotherapy alone, immunotherapy-involved multimodal synergistic therapy, and imaging-guided immunotherapy are discussed in detail. Finally, the challenges and future developments of Mn-based tumor immunotherapy are highlighted.

Impact of the Aryl Hydrocarbon Receptor on Aurora A Kinase and the G2/M Phase Pathway in Hematopoietic Stem and Progenitor Cells

Recent evidence suggests that the environment-sensing transcription factor aryl hydrocarbon receptor (AHR) is an important regulator of hematopoiesis. Yet, the mechanisms and extent of AHR-mediated regulation within the most primitive hematopoietic cells, hematopoietic stem and progenitor cells (HSPCs), are poorly understood. Through a combination of transcriptomic and flow cytometric approaches, this study provides new insight into how the AHR influences hematopoietic stem and progenitor cells. Comparative analysis of intraphenotypic transcriptomes of hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells from AHR knockout (AHR KO) and wild type mice revealed significant differences in gene expression patterns. Notable among these were differences in expression of cell cycle regulators, specifically an enrichment of G2/M checkpoint genes when Ahr was absent. This included the regulator Aurora A kinase (Aurka, AurA). Analysis of AurA protein levels in HSPC subsets using flow cytometry, in combination with inducible AHR KO or in vivo AHR antagonism, showed that attenuation of AHR increased levels of AurA in HSCs and lineage-biased MPP cells. Overall, these data highlight a potential novel mechanism by which AHR controls HSC homeostasis and HSPC differentiation. These findings advance the understanding of how AHR influences and regulates primitive hematopoiesis.

BATF sustains homeostasis and functionality of bone marrow Treg cells to preserve homeostatic regulation of hematopoiesis and development of B cells.

Bone marrow Treg cells (BM Tregs) orchestrate stem cell niches crucial for hematopoiesis. Yet little is known about the molecular mechanisms governing BM Treg homeostasis and function. Here we report that the transcription factor BATF maintains homeostasis and functionality of BM Tregs to facilitate homeostatic regulation of hematopoiesis and B cell development. Treg-specific ablation of BATF profoundly compromised proportions of BM Tregs associated with reduced expression of Treg effector molecules, including CD44, ICOS, KLRG1, and TIGIT. Moreover, BATF deficiency in Tregs led to increased numbers of hematopoietic stem cells (HSCs), multipotent progenitors (MPPs), and granulocyte-macrophage progenitors (GMPs), while reducing the functionality of myeloid progenitors and the generation of common lymphoid progenitors. Furthermore, Tregs lacking BATF failed to support the development of B cells in the BM. Mechanistically, BATF mediated IL-7 signaling to promote expression of effector molecules on BM Tregs and their homeostasis. Our studies reveal a previously unappreciated role for BATF in sustaining BM Treg homeostasis and function to ensure hematopoiesis.

Disruption of stem cell niche-confined R-spondin 3 expression leads to impaired hematopoiesis.

Self-renewal and differentiation of stem and progenitor cells are tightly regulated to ensure tissue homeostasis. This regulation is enabled both remotely by systemic circulating cues, such as cytokines and hormones, and locally by various niche-confined factors. R-spondin 3(RSPO3) is one of the most potent enhancers of Wnt signaling, and its expression is usually restricted to the stem cell niche where it provides localized enhancement of Wnt signaling to regulate stem cell expansion and differentiation. Disruption of this niche-confined expression can disturb proper tissue organization and lead to cancers. Here, we investigate the consequences of disrupting the niche-restricted expression of RSPO3 in various tissues, including the hematopoietic system. We show that normal Rspo3 expression is confined to theperivascular niche in the bone marrow. Induction of increased systemic levels of circulating RSPO3 outside of the niche results in prominent loss of early B-cell progenitors and anemia but surprisingly has no effect on hematopoietic stem cells. Using molecular, pharmacologic, and genetic approaches, we show that these RSPO3-induced hematopoietic phenotypes are Wnt and RSPO3 dependent and mediated through noncanonical Wnt signaling. Our study highlights a distinct role for a Wnt/RSPO3 signaling axis in the regulation of hematopoiesis, as well as possible challenges related to therapeutic use of RSPOs for regenerative medicine.

MicroRNA Expression Profiling of Diffuse Large B-Cell Lymphoma

Non-Hodgkin lymphoma (NHL) is a heterogeneous group of cancers that differ in pathogenesis and prognosis. The main methods of treating NHL include chemotherapy, immunochemotherapy, and radiation therapy. However, a significant proportion of these tumors are chemoresistant or rapidly recur after a short chemotherapy-induced remission. In this regard, the search for alternative cytoreductive therapeutic methods is relevant. Aberrant expression of microRNA (miRNA) is one of the mechanisms responsible for the emergence and progression of malignant lymphoid neoplasms. We analyzed the profile of miRNA expression in the biopsy material from lymph nodes affected by diffuse large B-cell lymphoma (DLBCL). The key material of the study was histological preparations of lymph nodes obtained by excisional diagnostic biopsy and treated using conventional histomorphological formalin fixation methods. The study group consisted of patients with DLBCL (n = 52); the control group consisted of patients with reactive lymphadenopathy (RL) (n = 40). It was shown that the miR-150 expression level in DLBCL was reduced by more than 12 times (</>p = 3.6 x 10^(-15)) compared with RL. Bioinformatics analysis revealed the involvement of miR-150 in the regulation of hematopoiesis and lymphopoiesis. The data we obtained allow us to consider miR-150 as a promising therapeutic target with great potential in clinical practice.

Fli1 and Tissue Fibrosis in Various Diseases.

Being initially described as a factor of virally-induced leukemias, Fli1 (Friend leukemia integration 1) has attracted considerable interest lately due to its role in both healthy physiology and a variety of pathological conditions. Over the past few years, Fli1 has been found to be one of the crucial regulators of normal hematopoiesis, vasculogenesis, and immune response. However, abnormal expression of Fli1 due to genetic predisposition, epigenetic reprogramming (modifications), or environmental factors is associated with a few diseases of different etiology. Fli1 hyperexpression leads to malignant transformation of cells and progression of cancers such as Ewing's sarcoma. Deficiency in Fli1 is implicated in the development of systemic sclerosis and hypertensive disorders, which are often accompanied by pronounced fibrosis in different organs. This review summarizes the initial findings and the most recent advances in defining the role of Fli1 in diseases of different origin with emphasis on its pro-fibrotic potential.

A Prognostic Model of Pseudogenes in Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is a hematologic malignancy characterized by the abnormal proliferation of myeloid hematopoietic cells and it is urgently needed to develop new molecular biomarkers to predict clinical outcomes and improve therapeutic effects. The differentially expressed genes were identified by comparing TCGA with GETx data. Univariate LASSO and multivariate cox regression analysis were performed to identify prognosis-associated pseudogenes. Based on the overall survival of related pseudogenes, we used them to construct a prognostic model for AML patients. Moreover, we built the pseudogenes-miRNA-mRNA ceRNA networks and explored their involved biological functions and pathways via GO and KEGG enrichment analysis. Seven prognosis-associated pseudogenes were identified, including CCDC150P1, DPY19L1P1, FTH1P8, GTF2IP4, HLA-K, NAPSB, and PDCD6IPP2. The risk model based on these 7 pseudogenes could accurately predict the 1-year, 3-year, and 5-year survival rates. The GO and KEGG enrichment analyses demonstrated that these prognosis-associated pseudogenes were significantly enriched in cell cycle, myeloid leukocyte differentiation, regulation of hemopoiesis, and other critical cancer-related biological functions and pathways. We systematically and comprehensively analyzed the prognostic role of pseudogenes in AML. The prognostic model of pseudogenes we identified is an independent predictor of overall survival in AML and could be used as biomarker for AML treatment.

Expression of MicroRNA-155 in Patients with Non-Hodgkin Lymphoma, Coronavirus Disease 2019, or Both: A Cross-Sectional Study.

Non-Hodgkin lymphoma (NHL) is the eleventh leading cause of cancer-related death in the world. Diffuse large B-cell lymphoma (DLBCL) is the most common type of NHL. Up to winter 2021-2022, the death toll caused by the coronavirus disease 2019 (COVID-19) has exceeded 5.6 million worldwide. Possible molecular mechanisms involved in the systemic inflammation, and cytokine storm in COVID-19 patients are still not fully understood. MicroRNA-155 (miR-155) plays a role in the post-transcriptional gene regulation of hematopoiesis, oncogenesis, and inflammation. The present study aimed to evaluate the expression of miR-155 in patients with DLBCL and/or COVID-19. A cross-sectional study was conducted from July to December 2020 in Tehran (Iran) to evaluate the expression of miR-155 in adult patients diagnosed with DLBCL and/or COVID-19. The real-time polymerase chain reaction technique was used to evaluate the expression of miR-155 in the sera of 92 adults who were either healthy or suffering from DLBCL and/or COVID-19. Relative quantification of gene expression was calculated in terms of cycle threshold (Ct) value. Data were analyzed using SPSS software, and P<0.05 was considered statistically significant. The expression of miR-155 was not associated with the sex or age of the participants. In comparison with healthy individuals (-ΔCt -1.92±0.25), the expression of miR-155 increased in patients with COVID-19 (1.95±0.14), DLBCL (2.25±0.16), or both (4.33±0.65). The expression of miR-155 increased in patients with DLBCL and/or COVID-19.

Usp22 is an intracellular regulator of systemic emergency hematopoiesis

Emergency hematopoiesis is a concerted response aimed toward enhanced protection from infection, involving multiple cell types and developmental stages across the immune system. Despite its importance, the underlying molecular regulation remains poorly understood. The deubiquitinase USP22 regulates the levels of monoubiquitinated histone H2B (H2Bub1), which is associated with activation of interferon responses upon viral infection. Here, we show that in the absence of infection or inflammation, mice lacking Usp22 in all hematopoietic cells display profound systemic emergency hematopoiesis, evident by increased hematopoietic stem cell proliferation, myeloid bias, and extramedullary hematopoiesis. Functionally, loss of Usp22 results in elevated phagocytosis by neutrophilic granulocytes and enhanced innate protection against Listeria monocytogenes infection. At the molecular level, we found this state of emergency hematopoiesis associated with transcriptional signatures of myeloid priming, enhanced mitochondrial respiration, and innate and adaptive immunity and inflammation. Augmented expression of many inflammatory genes was linked to elevated locus-specific H2Bub1 levels. Collectively, these results demonstrate the existence of a tunable epigenetic state that promotes systemic emergency hematopoiesis in a cell-autonomous manner to enhance innate protection, identifying potential paths toward immune enhancement.

PEAR1 is a potential regulator of early hematopoiesis of human pluripotent stem cells.

Hemogenic endothelial (HE) cells are specialized endothelial cells to give rise to hematopoietic stem/progenitor cellsduring hematopoietic development. The underlying mechanisms that regulate endothelial-to-hematopoietic transition (EHT) of human HE cells are not fully understand. Here, we identified platelet endothelial aggregation receptor-1 (PEAR1) as a novel regulator of early hematopoietic development in human pluripotent stem cells (hPSCs). We found that the expression of PEAP1 was elevated during hematopoietic development. A subpopulation of PEAR1+ cells overlapped with CD34+ CD144+ CD184+ CD73- arterial-type HE cells. Transcriptome analysis by RNA sequencing indicated that TAL1/SCL, GATA2, MYB, RUNX1 and other key transcription factors for hematopoietic development were mainly expressed in PEAR1+ cells, whereas the genes encoding for niche-related signals, such as fibronectin, vitronectin, bone morphogenetic proteinsand jagged1, were highly expressed in PEAR1- cells. The isolated PEAR1+ cells exhibited significantly greater EHT capacity on endothelial niche, compared with the PEAR1- cells. Colony-forming unit (CFU) assays demonstrated the multilineage hematopoietic potential of PEAR1+ -derived hematopoietic cells. Furthermore, PEAR1 knockout in hPSCs by CRISPR/Cas9 technology revealed that the hematopoietic differentiation was impaired, resulting in decreased EHT capacity, decreased expression of hematopoietic-related transcription factors, and increased expression of niche-related signals. In summary, this study revealed a novel role of PEAR1 in balancing intrinsic and extrinsic signals for early hematopoietic fate decision.

Novel Evidence That Intracellular Complement Network (complosome) Is Expressed in Hematopoietic Stem Cells (HSPCs) and Regulates Their Trafficking, Metabolism, and Proliferation in an Intracrine-Dependent Manner By Engaging Pattern Recognition Receptor Nlrp3 Inflammasome

Background. Complement cascade (ComC) proteins, including C3 and C5 components, are synthesized in the liver; however, recent reports indicate their expression in lymphocytes as well (Immunity 2020;52(3):513-527). Accordingly, intracellular ComC proteins have been reported to be cleaved to active C3a and C5a mediators that interact with corresponding receptors in an intracrine-depended manner. This novel regulatory loop operating in lymphocytes has been named ''complosome''. Aim of the study.Because hematopoiesis and lymphopoiesis have a common stem cell origin and similar mechanisms are involved in regulating the biology of both lineages, we asked if complosome is also expressed and functional in normal murine hematopoietic stem progenitor cells (HSPCs). We also address a challenging question if intracellular ComC mediators could activate pattern recognition receptor Nlrp3 inflammasome that, as we reported, regulates trafficking, proliferation and metabolism of HSPCs (Leukemia 2022;36(1):23-32;Stem Cell Rev Rep. 2020 16(5):954-967). Materials and Methods. First, we phenotyped purified murine and human HSPCs for expression of major complement elements, including C3, C5, C3aR, C5aR, and cathepsin L that cleaves intracellular C3 to C3a. Next, we focused on a crucial distal executive part of ComC, protein C5, and evaluated in C5-KO and C5aR-KO mice the number of HSPCs and their clonogeneic potential. We also studied hematopoietic recovery of these animals after sublethal irradiation (650 cGy). Activation of Nlrp3 inflammasome in C5a-KO and C5aR-KO in response to hematopoietic growth factors and cytokines was evaluated by immunofluorescence Glow assay. We also studied homing and engraftment of C5-KO and C5aR-KO mice-derived HSPCs transplanted into normal WT recipients. Finally, we performed a metabolomic analysis of C5-KO, C5aR-KO, and control WT mice in steady-state conditions and after stimulation with selected hematopoietic growth factors and cytokines. Results. We show for the first time that purified murine and human HSPCs express complosome elements, including C3, C5, C3aR, C5aR, and cathepsin L. Next, C5-KO and C5aR-KO mice also have a lower number of HSPCs and clonogenic progenitors in bone marrow (BM), and display defect of hematopoietic recovery from sublethal irradiation. Furthermore, BM cells isolated from these animals had impaired homing and engraftment in normal WT recipients, supported by the observation that HSPCs from complosome deficient mice had a defect in migration to stromal-derived factor-1 (SDF-1), which correlated with decreased activation of Nlrp3 inflammasome. This defect could be alleviated by direct activation of Nlrp3 inflammasome by nigericin. Finally, our metabolic studies revealed a defect in glucose, amino acids, and lipid metabolism in C5-KO and C5aR-KO mice which correlates with complosome deficiency and Nlrp3 inflammasome activation. Conclusions. We provide for the first time evidence that complosome is expressed and functional in normal HSPCs and by engaging Nlrp3 inflammasome regulates metabolism, proliferation, and migration of HSPCs. Thus, our data sheds new intriguing light on innate immunity as a regulator of hematopoiesis that involves intracellular activation of Nlrp3 inflammasome. We currently focus on Nlrp3 inflammasome-released alarmins released from the cells in response to complosome-Nlrp3 inflammasome activation that accounts for observed phenomena. These studies are essential to develop more efficient ex vivo expansion strategies of HSPCs and to understand better intrinsic mechanisms that regulate metabolism of these cells.