Proliferation Of Hematopoietic Stem Cells Research Articles

Oncogenic role of RARG rearrangements in acute myeloid leukemia resembling acute promyelocytic leukemia

Acute myeloid leukemia (AML) featuring retinoic acid receptor-gamma (RARG) rearrangements exhibits morphological features resembling those of acute promyelocytic leukemia but is associated with drug resistance and poor clinical outcomes. However, the mechanisms underlying the role of RARG fusions in leukemogenesis remain elusive. Here, we show that RARG fusions disrupt myeloid differentiation and promote proliferation and self-renewal of hematopoietic stem and progenitor cells (HSPCs) by upregulating BCL2 and ATF3. RARG fusions overexpression leads to preleukemic phenotypes but fails to induce oncogenic transformation. However, the co-occurrence of RARG fusions and heterozygous Wt1 loss induce fully penetrant AML by activating MYC and HOXA9/MEIS1 targets. Leveraging Connectivity Map resources and high-throughput screening, we identify venetoclax, homoharringtonine, and daunorubicin as potential therapeutic options for RARG-AML. Overall, our findings provide pivotal insights into the molecular mechanisms governed by RARG fusions and enhanced by WT1 loss in AML development and propose a rational therapeutic strategy for RARG-AML.

Donkey-Hide Gelatin-Derived Carbon Dots Activate Erythropoiesis and Eliminate Oxidative Stress for Aplastic Anemia Treatment.

Aplastic anemia (AA) is a life-threatening hematologic disease with limited therapeutic options. Stalled erythropoiesis and oxidative stress-induced hemocyte apoptosis are the main pathological features of AA, yet therapeutic agents that address these issues remain elusive. In this study, we report distinctive donkey-hide gelatin-derived carbon dots (G-CDs) that enable erythropoiesis activation and oxidative stress elimination to tackle refractory AA. We demonstrate that G-CDs can promote the proliferation and erythroid differentiation of hematopoietic stem cells as well as erythrocyte maturation, activating the whole process of erythropoiesis. Moreover, G-CDs display multienzyme-like activities and dramatically alleviate the oxidative stress of bone marrow and peripheral blood via catalytic scavenging of multiple reactive oxygen species, reconstructing the hematopoietic microenvironment. Intravenously or orally administered to AA mice induced by chemotherapy drugs, G-CDs significantly boost the level of red blood cells and hemoglobin and lead to the complete recovery of hematopoietic function, showing better therapeutic performance than clinically approved erythropoietin (EPO) without adverse effects. By collaboratively addressing the issues of stalled erythropoiesis and oxidative stress, the G-CDs-based intervention strategy may offer a powerful paradigm for clinical AA management.

Pregnane X receptor activation promotes hematopoiesis during liver regeneration by inducing proliferation of hematopoietic stem and progenitor cells in mice

Liver regeneration is a complex process that involves the recruitment of bone marrow (BM)-derived hematopoietic stem and progenitor cells (HSPCs). Pregnane X receptor (PXR), also known as NR1I2, is an important regulator for liver enlargement and regeneration. However, the role of PXR activation in hematopoiesis during liver regeneration remains unclear. This study investigates the effects of PXR activation on HSPCs and hematopoiesis during liver regeneration, as well as the underlying mechanisms involved. Using a 70% partial hepatectomy (PHx) on C57BL/6 wild-type (WT) and Pxr-null mice, we observed a significant correlation between the changes in HSPCs numbers in BM and the process of liver regeneration. PXR activation significantly increased the population of Lineage- Sca-1+ c-Kit+ (LSK) cells in the BM, which are key HSPCs involved in hematopoiesis. Additionally, PXR activation increased serum levels of thrombopoietin (TPO) and erythropoietin (EPO), factors known to support HSPCs proliferation and hematopoiesis in the process of liver regeneration. PXR activation does not affect the hematopoietic function of normal mice. Furthermore, mice subjected to irradiation or busulfan-induced hematopoietic dysfunction exhibited impaired liver regeneration, which was alleviated by PXR activation. Importantly, in Pxr-null mice, the promotive effects of PXR activation on liver regeneration and increase of HSPCs were markedly diminished. Moreover, liver-specific Pxr silencing using AAV-Pxr shRNA attenuated the PXR activation-mediated liver regeneration and increase in BM LSK cells, confirming the critical role of hepatic PXR in hematopoiesis during liver regeneration. Collectively, these findings reveal that PXR activation promotes HSPCs proliferation and hematopoiesis during liver regeneration, providing new insights into the molecular mechanisms underlying the role of PXR in liver regeneration and hematopoiesis.

Polycomb group protein Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of self-renewal and proliferation genes.

Polycomb group (PcG) proteins play important roles in hematopoietic stem cell (HSC) self-renewal. Mel18 and Bmi1 are homologs of the PCGF subunit within the Polycomb repressive complex 1 (PRC1). Bmi1 (PCGF4) enhances HSC self-renewal and promotes terminal differentiation. However, the role of Mel18 (PCGF2) in hematopoiesis is not fully understood and how Mel18 regulates gene transcription in HSCs remains elusive. We found that acute deletion of Mel18 in the hematopoietic compartment significantly increased the frequency of functional HSCs in the bone marrow. Furthermore, we demonstrate that Mel18 inhibits HSC self-renewal and proliferation. RNA-seq studies revealed that HSC self-renewal and proliferation gene signatures are enriched in Mel18-/- hematopoietic stem and progenitors (HSPCs) compared to Mel18+/+ HSPCs. Notably, ATAC-seq revealed increased chromatin accessibility at genes important for HSC self-renewal, whereas CUT&RUN showed decreased enrichment of H2AK119ub1 at genes important for proliferation, leading to increased expression of both Hoxb4 and Cdk4 in Mel18-/- HSPCs. Thus, we demonstrate that Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of genes important for HSC self-renewal and proliferation.

Stress memory of heart failure in hematopoietic niche promotes recurrence via adipocytic skewing of mesenchymal stromal cells

Abstract Background Heart failure (HF) is marked by recurrent acute decompensations, which poses significant treatment challenges in advanced stages. Our preceding work demonstrated that hematopoietic stem cells (HSCs) from HF-experienced mice induce cardiac fibrosis and dysfunction when transplanted, as a result of epigenetic alterations favoring myeloid hematopoiesis and impeding the differentiation of monocytes into cardiac mature macrophages. These findings hint at epigenetic modifications in HSCs as potential drivers of HF recurrence, suggesting their manipulation as a novel therapeutic strategy. However, the exact mechanisms by which HF-associated stress leads to these epigenetic changes remain unclear. Given the crucial role of bone marrow mesenchymal stromal cells (MSCs) in maintaining HSC stemness, this study explores the impact of cardiac stress on MSC function and its subsequent effect on HSCs. Purpose This study aims to elucidate the mechanisms behind the phenotypic changes in HSCs and to identify novel therapeutic targets to mitigate HF recurrence by investigating the role of MSCs in the hematopoietic niche under cardiac stress. Methods & Results Initially, we examined MSC phenotypic changes during HF using bulk and single-cell RNA sequencing. Results from transverse aortic constriction (TAC) model mice revealed a shift towards adipocyte differentiation under cardiac stress. Histological analyses confirmed an increase in adipocytes in TAC mice compared to controls, suggesting a stress-induced predisposition of MSCs towards adipocytic lineage commitment. This trend was further supported by ex vivo models using MSCs isolated from TAC mice. Notably, the proportion of adipocyte lineage-specific MSCs correlated with cardiac dysfunction severity. Subsequently, we assessed the impact of HF-conditioned MSCs on HF development by transplanting healthy HSCs with MSCs from control or TAC mice. Mice receiving HF-conditioned MSCs developed HF, evidenced by reduced ejection fraction and cardiac fibrosis. In these mice, a notable increase in HSC proliferation and a relative increase of myeloid cells within the peripheral blood were observed, along with an increase in proinflammatory cardiac macrophages. These findings suggest HF induces a "stress memory" in bone marrow MSCs. To test the potential of inhibiting adipocyte differentiation of MSCs in erasing this stress memory, we administered MSC phenotype-modulating agents to TAC mice, resulting in improved cardiac function and the disappearance of adipocytes from the bone marrow. Conclusions This study sheds light on how cardiac stress affects the bone marrow niche, leading to adipocytic skewing of MSCs and subsequent alterations in HSCs, thereby exacerbating cardiac dysfunction. The potential of targeting bone marrow niche components in HF treatment is highlighted.

The E3 Ubiquitin Ligase Trip12 attenuates Wnt9a/Fzd9b signaling during hematopoietic stem cell development.

Wnt signaling is essential for both the development and homeostasis of diverse cellular lineages, including hematopoietic stem cells. Organism-wide, Wnt signals are tightly regulated, as overactivation of the pathway can lead to tumorigenesis. Although numerous Wnt ligands and Frizzled (Fzd) receptors exist, how particular Wnt/Fzd pairings are established and how their signals are regulated is poorly understood. We have previously identified the requirements of the cognate pairing of Wnt9a and Fzd9b for early hematopoietic stem cell proliferation. However, the specific signals governing activation, but equally important, the molecular mechanisms required to turn the signal 'off,' are unknown. Here, we show that the E3 ubiquitin ligase Trip12 (thyroid hormone receptor interactor 12) is specifically required to ubiquitinate the third intracellular loop of Fzd9b at K437, targeting it for lysosomal degradation. In contrast to other ubiquitin ligases described to regulate the cell surface availability of multiple Fzds broadly, our data indicate that Trip12 is selective for Fzd9b. We further demonstrate that this occurs through ubiquitination at K437 of Fzd9b in the third intracellular loop, ultimately leading to a decrease in Fzd9b receptor availability and in Wnt9a/Fzd9b signaling that impacts hematopoietic stem cell proliferation in zebrafish. Our results point to specific mechanisms driving the availability of different Fzd receptors. Determining how particular Fzd abundance is regulated at the membrane will be critical to developing specific therapies for human intervention.

Genome sequencing in the management of myelodysplastic syndromes and related disorders.

Myeloid neoplasms originate from the clonal proliferation of hematopoietic stem cells, which is driven by the acquisition of somatic genetic mutations. Within these disorders, myelodysplastic syndromes (MDS) are specifically characterized by morphologic abnormalities (dysplasia) and impaired maturation of myeloid precursors (ineffective hematopoiesis), resulting in peripheral blood cytopenia. Several studies have advanced the field of MDS, with a few landmark papers leading to a paradigm shift, opening new avenues of research and enabling a molecular revolution. These seminal papers include the first description of the 5q- syndrome, the identification of somatic mutations of TET2 in myeloid neoplasms, the detection of common pathway mutations in the splicing machinery, and the discovery of clonal hematopoiesis. The somatic genomic landscape of MDS is now well-defined. Genes that are recurrently mutated include epigenetic regulators, as well as genes of RNA splicing machinery, transcription regulation, DNA repair control, cohesin complex, and signal transduction. Furthermore, several disorders with a germline genetic predisposition to MDS have been identified, collectively accounting for up to 15% of all MDS cases. Genomic profiling can significantly improve the diagnostic approach to MDS, allowing the identification of distinct nosologic entities such as SF3B1-mutant or TP53-mutant MDS. The Molecular International Prognostic Scoring System for MDS (IPSS-M) has already proven to be a valuable tool for individualized risk assessment and treatment decisions. In addition, the recently developed molecular taxonomy of MDS will likely facilitate the implementation of precision medicine approaches for these disorders. This will necessitate the establishment of specialized infrastructures within public health systems, involving close collaboration between healthcare institutions, academia, and the life sciences industry.

Single-cell RNA-seq analysis revealed the stemness of a specific cluster of B cells in acute lymphoblastic leukemia progression.

Childhood acute lymphoblastic leukemia (ALL) is a common pediatric cancer. The heterogeneous characterization of B cells in ALL progression poses new challenges to researchers. We used single-cell sequencing to explore the critical role of B cells in regulating the ALL immune microenvironment. We collected the single cell (sc) RNA-seq data of ALL and health sample from the gene expression omnibus (GEO) database, the "Seurat" and "harmony" R package was used for quality control and scRNA-seq analysis, in which the CellMarker2.0 database was used for cell type annotation. Subsequently, the FindAllMarkers function was used to identify the differentially expressed genes (DEGs) among various cell types and the DAVID database was applied for the biological process of DEGs. Then, the "inferCNV" package was used for copy number variation, regulons and cell communication were performed by SCENIC tool and CellChat package. The role of the target gene in regulating ALL progression was assessed using RT-qPCR, Transwell and scratch healing assays. We identified nine mainly cell clusters after scRNA-seq analysis, in which the B cells had higher infiltration proportion in the ALL samples and were sub-clustered into five cell sub-groups. The B cells 1 is closely associated with cell proliferation and stemness (TNFAIP3 and KDM5B), and the significant CNV of amplification occurred on chr6 and chr21 that supported stemness of B cells1. RXRB is a key transcription factor mediated the proliferation of B cells 1, which in turn suppressed hematopoietic stem cells (HSCs) proliferation and promoted cytotoxic NK/T cells activation through diverse cell communication ways. One of the key regulators of B cells is MYC, which promotes the migration and invasive ability of cell line leukemia cell lines. This study reveals the stemness characteristics of B cells and their critical role in ALL progression, a finding that provides new potential directions for the development of targeted therapies against ALL.

DNA methylation drives hematopoietic stem cell aging phenotypes after proliferative stress.

Aging of hematopoietic stem cells (HSCs) is implicated in various aging phenotypes, including immune dysfunction, anemia, and malignancies. The role of HSC proliferation in driving these aging phenotypes, particularly under stress conditions, remains unclear. Therefore, we induced forced replications of HSCs in vivo by a cyclical treatment with low-dose fluorouracil (5FU) and examined the impact on HSC aging. Our findings show that proliferative stress induces several aging phenotypes, including altered leukocyte counts, decreased lymphoid progenitors, accumulation of HSCs with high expression of Slamf1, and reduced reconstitution potential, without affecting stem cell self-renewal capacity. The divisional history of HSCs was imprinted in the DNA methylome, consistent with functional decline. Specifically, DNA methylation changes included global hypermethylation in non-coding regions and similar frequencies of hypo- and hyper-methylation at promoter regions, particularly affecting genes targeted by the PRC2 complex. Importantly, initial forced replication promoted DNA damage repair accumulated with age, but continuous proliferative stress led to the accumulation of double-strand breaks, independent of functional decline. Overall, our results suggest that HSC proliferation can drive some aging phenotypes primarily through epigenetic mechanisms, including DNA methylation changes.

Maintenance of hematopoietic stem cells by tyrosine-unphosphorylated STAT5 and JAK inhibition

AbstractAdult hematopoietic stem cells (HSCs) are responsible for the lifelong production of blood and immune cells, a process regulated by extracellular cues, including cytokines. Many cytokines signal through the conserved Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in which tyrosine-phosphorylated STATs (pSTATs) function as transcription factors. STAT5 is a pivotal downstream mediator of several cytokines known to regulate hematopoiesis, but its function in the HSC compartment remains poorly understood. In this study, we show that STAT5-deficient HSCs exhibit an unusual phenotype, including reduced multilineage repopulation and self-renewal, combined with reduced exit from quiescence and increased differentiation. This was driven not only by the loss of canonical pSTAT5 signaling, but also by the loss of distinct transcriptional functions mediated by STAT5 that lack canonical tyrosine phosphorylation (uSTAT5). Consistent with this concept, expression of an unphosphorylatable STAT5 mutant constrained wild-type HSC differentiation, promoted their maintenance, and upregulated transcriptional programs associated with quiescence and stemness. The JAK1/2 inhibitor, ruxolitinib, which increased the uSTAT5:pSTAT5 ratio, had similar effects on murine HSC function; it constrained HSC differentiation and proliferation, promoted HSC maintenance, and upregulated transcriptional programs associated with stemness. Ruxolitinib also enhanced serial replating of normal human hematopoietic stem and progenitor cells (HSPCs), calreticulin-mutant murine HSCs, and HSPCs obtained from patients with myelofibrosis. Our results therefore reveal a previously unrecognized interplay between pSTAT5 and uSTAT5 in the control of HSC function and highlight JAK inhibition as a potential strategy for enhancing HSC function during ex vivo culture. Increased levels of uSTAT5 may also contribute to the failure of JAK inhibitors to eradicate myeloproliferative neoplasms.

The Role of SIRT1 in Leukemia.

Leukemia is a type of hematological malignancy (HM) caused by uncontrolled proliferation, apoptosis, and differentiation of hematopoietic stem cells (HSCs). Leukemia cells proliferate greatly in the bone marrow (BM), infiltrate other tissues and organs, and affect the normal hematopoietic function. Although the emergence of new targeted agents and immune agents has improved the prognosis of patients, due to the complex pathogenic factors and heterogeneity of leukemia, there are still some patients with poor prognosis. Recent studies have shown that silent information regulator 1 (SIRT1) is involved in the proliferation, apoptosis, metabolism, and senescence of leukemia cells. As a double-edged sword in leukemia cells, SIRT1 can both promote and inhibit the growth of leukemia cells. Since its mechanism of action has not been elucidated, it is urgent to explore the regulatory mechanism of SIRT1 in leukemia. In this review, we discussed the mechanisms of SIRT1 in different aspects of leukemia, providing a theoretical basis for the treatment of patients with leukemia.

Cytokines and Myeloproliferative Neoplasms: Current Research Status from Mechanism to Clinic--Review

Myeloproliferative neoplasms (MPN) are a group of malignant myeloid tumors caused by hematopoietic stem cell proliferation. The discovery of gene mutations has elucidated the pathogenesis of MPN and provided molecular diagnostic criteria for MPN. Recent studies have shown that there are cytokine disorders in MPN patients, and the changes in the microenvironment caused by these cytokine disorders may have great significance for the pathophysiology and pathogenesis of MPN, which may lead to corresponding clinical symptoms and different prognosis in patients. In this review, the latest research progress on the role and status of cytokines in MPN will be summarized.

Relationship between adipocytes and hematological tumors in the bone marrow microenvironment: a literature review.

The bone marrow microenvironment is closely related to normal hematopoiesis and hematologic tumors. Adipocytes are an important part of the bone marrow microenvironment, in which they can release free fatty acids (FFAs) through lipolysis and secrete adipocytokines, etc., and participate in normal hematopoiesis, which is closely related to the occurrence and treatment of hematological tumors. In this review, we aim to discuss how bone marrow adipocytes (BMAs) can influence the proliferation, apoptosis, and chemotherapy resistance of cancer cells by reprogramming lipid metabolism and the secretion of various adipocytokines. Studies from 2000 to July 2024 were reviewed from PubMed, Springer Link, and the Web of Science using the keywords bone marrow microenvironment, adipocytes, lipid metabolism, adipocytokines, hematological tumor, cancer, and their combinations. Unreliable articles such as those that are old and have a low impact factor are excluded, and there is no restriction on language. Adipocytes can regulate the proliferation and differentiation of hematopoietic stem cells (HSCs) by secreting inflammatory factors and adipocytokines to maintain hematopoietic homeostasis. Adipocytes can also stimulate and accelerate the occurrence and progression of hematological tumors by secreting adipocytokines and mediating the reprogramming of lipid metabolism. Moreover, abundant adipocytes in bone marrow can protect tumor cells by physically blocking and/or secreting cytokines, leading to chemotherapy resistance. Therefore, the targeted inhibition of related lipid metabolism pathways and adipocytokines might be a potential therapeutic target for hematological tumors, which would be helpful to inhibit tumor growth and correct chemotherapy resistance.

JAK2V617F-dependent down regulation of SHP-1 expression participates in the selection of myeloproliferative neoplasm cells in the presence of TGF-β.

Myeloproliferative neoplasms (MPNs) are characterized by an increased production of blood cells due to the acquisition of mutations such as JAK2V617F. TGF-β, whose secretion is increased in MPN patients, is known to negatively regulate haematopoietic stem cell (HSC) proliferation. Using an isogenic JAK2V617F or JAK2 wild-type UT-7 cell line we observed that JAK2V617F cells resist to TGF-β antiproliferative activity. Although TGF-β receptors and SMAD2/3 expressions are similar in both cell types, TGF-β-induced phosphorylation of SMAD2/3 is reduced in UT-7 JAK2V617F cells compared with JAK2 WT cells. We confirmed that JAK2V617F mutated cells are resistant to the antiproliferative effect of TGF-β in a competitive assay as we observed a positive selection of JAK2V617F cells when exposed to TGF-β. Using cell lines, CD34-positive cells from MPN patients and bone marrow cells from JAK2V617F knock-in mice we identified a down regulation of the SHP-1 phosphatase, which is required for the regulation of HSC quiescence by TGF-β. The transduction of SHP-1 cDNA (but not a phosphatase inactive cDNA) restores the antiproliferative effect of TGF-β in JAK2V617F mutated cells. Finally, SC-1, a known agonist of SHP-1, antagonized the selection of JAK2V617F mutated cells in the presence of TGF-β. In conclusion, we show a JAK2-dependent down regulation of SHP-1 in MPN patients' cells which is related to their resistance to the antiproliferative effect of TGF-β. This may participate in the clonal selection of cancer cells in MPNs.

Next-Generation Sequencing-based Genetic Landscape and its Clinical Implications for Egyptian Patients with Acute Myeloid Leukemia and Myelodysplastic Syndrome

Abstract Background Myeloid malignancies are a heterogeneous group of clonal disorders characterized by disturbed hematopoietic stem cells self-renewal, proliferation, and differentiation capacity as a result of genetic and epigenetic changes. The molecular landscape of these diseases is complex involving many molecular alterations. Several techniques have been used to identify these genetic alterations including; FISH, RT-PCR (real time-PCR) and recently next generation sequencing (NGS) that is capable of detecting copy number variations (CNV) or translocations by a fast less expensive technique making it more practical in clinical practice. Objectives Designing a genetic map for Egyptian population with myeloid and detecting the prognostic impact of these genetic alterations. Patients and Methods Myeloid NGS Oncomine 79-gene panel was applied on 42 patients diagnosed with myeloid neoplasms (Mainly AML & MDS) recruited from the hematology unit, and their follow up till 12 months. Results Among the different studied groups, the highest NGS variants were found in AML compared to other myeloid neoplasms, while the percentage of patients with no NGS variants is higher in MDS (77.8%). The most frequently mutated genes detected in myeloid neoplasms were NPM1 mutation in 8 patients (19%), followed by NRAS mutation in 7 patients (16.7%). BCR-ABL1 and CALR mutations were significantly more common in the MPN group (P- value =0.000). TET2 was significantly more common in MDS/MPN patients (P-value =0.027). TP53 mutation was detected in all myeloid neoplasms (Mainly in MDS) except AML (P-value =0.027). NPM1 was significantly more frequent in AML group (P-value =0.042). There was a significant correlation between the presence of NGS variants and the clinical outcome, as the presence of one or more NGS variants is associated with poor clinical outcome & lower survival rate (p value =0.038). Conclusion Assessment of clinically important genetic alterations by NGS is essential for the diagnosis, prognosis, monitor measurable residual disease and detect predictive mutational markers/therapeutic targets in myeloid neoplasms. However, it cannot identify structural abnormalities, so simultaneous cytogenetic analysis to have a complete picture of the genomic profile is essential.

Transcripts of repetitive DNA elements signal to block phagocytosis of hematopoietic stem cells.

Macrophages maintain hematopoietic stem cell (HSC) quality by assessing cell surface Calreticulin (Calr), an "eat-me" signal induced by reactive oxygen species (ROS). Using zebrafish genetics, we identified Beta-2-microglobulin (B2m) as a crucial "don't eat-me" signal on blood stem cells. A chemical screen revealed inducers of surface Calr that promoted HSC proliferation without triggering ROS or macrophage clearance. Whole-genome CRISPR-Cas9 screening showed that Toll-like receptor 3 (Tlr3) signaling regulated b2m expression. Targeting b2m or tlr3 reduced the HSC clonality. Elevated B2m levels correlated with high expression of repetitive element (RE) transcripts. Overall, our data suggest that RE-associated double-stranded RNA could interact with TLR3 to stimulate surface expression of B2m on hematopoietic stem and progenitor cells. These findings suggest that the balance of Calr and B2m regulates macrophage-HSC interactions and defines hematopoietic clonality.

USP4 regulates ribosome biogenesis and protein synthesis for hematopoietic stem cell regeneration and leukemia progression.

Enhanced ribosome biogenesis and protein synthesis are required for cell proliferation. During hematopoietic regeneration, hematopoietic stem cells (HSCs) proliferate rapidly to replenish the hematopoietic system. How HSCs respond and regulate ribosome biogenesis and protein synthesis during regeneration remains unclear. Here, we analyzed the expression of a series of ubiquitin-specific-proteases (USPs) during HSC regeneration. We found USP4 expression is significantly increased in proliferating HSCs. Further functional and mechanistic investigations revealed a crucial regulatory function of USP4 in HSC regeneration and leukemia progression by modulating ribosome biogenesis and protein synthesis. USP4 deubiquitinates and stabilizes PES1 to facilitate ribosome biogenesis and protein synthesis in proliferative HSCs and leukemic cells. Usp4 deletion significantly decreases protein synthesis, proliferation and reconstitution capacity of HSCs. Usp4 inhibition suppresses ribosome biogenesis and proliferation of leukemic cells, and prolongs the survival of AML (Acute myeloid leukemia) mice. These findings provide a new insight into the response mechanism of ribosome biogenesis and protein synthesis in HSCs, and their contribution to leukemia progression.

Developments of Fms-like Tyrosine Kinase 3 Inhibitors as Anticancer Agents for AML Treatment.

FMS-like tyrosine kinase 3 (FLT3) is a commonly mutated gene in acute myeloid leukemia. As a receptor tyrosine kinase (RTK), FLT3 plays a role in the proliferation and differentiation of hematopoietic stem cells. As the most frequent molecular alteration in AML, FLT3 has drawn the attention of many researchers, and a lot of small molecule inhibitors targeting FLT3 have been intensively investigated as potential drugs for AML therapy. In this paper, PubMed and SciFinder® were used as a tool; the publications about "FLT3 inhibitor" and "Acute myeloid leukemia" were surveyed from 2014 to the present with an exclusion of those published as patents. In this study, the structural characterization and biological activities of representative FLT3 inhibitors were summarized. The major challenges and future directions for further research are discussed. Recently, numerous FLT3 inhibitors have been discovered and employed in FLT3-mutated AML treatment. In order to overcome the drug resistance caused by FLT3 mutations, screening multitargets FLT3 inhibitors has become the main research direction. In addition, the emergence of irreversible FLT3 inhibitors also provides new ideas for discovering new FLT3 inhibitors.

Lysosomal membrane protein TMEM106B modulates hematopoietic stem and progenitor cell proliferation and differentiation by regulating LAMP2A stability.

Hematopoietic stem and progenitor cells (HSPCs) are successfully employed for hematological transplantations, and impaired HSPC function causes hematological diseases and aging. HSPCs maintain the lifelong homeostasis of blood and immune cells through continuous self-renewal and maintenance of the multilineage differentiation potential. TMEM106B is a transmembrane protein localized on lysosomal membranes and associated with neurodegenerative and cardiovascular diseases; however, its roles in HSPCs and hematopoiesis are unknown. Here, we established tmem106bb-/- knockout (KO) zebrafish and showed that tmem106bb KO reduced the proliferation of HSPCs during definitive hematopoiesis. The differentiation potential of HSPCs to lymphoid lineage was reduced, whereas the myeloid and erythroid differentiation potentials of HPSCs were increased in tmem106bb-/- zebrafish. Similar results were obtained with morpholino knockdown of tmem106bb. Mechanistically, TMEM106B interacted with LAMP2A, the lysosomal associated membrane protein 2A, impaired LAMP2A-Cathepsin A interaction, and enhanced LAMP2A stability; tmem106bb KO or TMEM106B knockdown caused LAMP2A degradation and impairment of chaperone-mediated autophagy (CMA). Knockdown of lamp2a caused similar phenotypes to that in tmem106bb-/- zebrafish, and overexpression of lamp2a rescued the impaired phenotypes of HSPCs in tmem106bb-/- embryos. These results uncover a novel molecular mechanism for the maintenance of HSPC proliferation and differentiation through stabilizing LAMP2A via TMEM106B-LAMP2A interaction.

Effects of PM2.5 exposure on hematopoiesis and coupled immune disorder in adult male mice

Fine particulate matter, namely PM2.5, increases the risk of morbidity and mortality in various systems, including the hematopoietic and immune systems. However, there is limited experimental evidence supporting the association between PM2.5 exposure and hematopoietic outcomes as most studies focus on epidemiological data. In this study, adult male mice were exposed to PM2.5 for a long time to investigate hematopoietic toxicity. There were significant increases in red blood cells (RBC), hemoglobin (HGB), and white blood cells (WBC) in peripheral blood after 5-month real-environmental PM2.5 exposure, indicating elevated circulatory inflammation and potential hematopoietic abnormality. Moreover, we observed abnormal proliferation and differentiation of hematopoietic stem and progenitor cells (HSPCs), along with altered mRNA levels of hematopoietic genes and increased proinflammatory factors in the bone marrow (BM). Transcriptomic analysis of BM cells suggested that PM2.5 exposure activated immune responses associated with lymphocytes. Then, PM2.5 exposure via intratracheal instillation was performed for 8 weeks to verify the toxic effect. The results of the complete blood count were similar to those of real-environmental exposure, with drastic changes in the number and function of HSPCs, as well as mRNA levels of the hematopoietic genes and increased inflammatory factors in the BM being detected. Furthermore, lymphocyte subsets changed significantly in the BM and spleen, confirming immune disorder following PM2.5 exposure. In conclusion, PM2.5 interfered with the process of BM hematopoiesis by triggering inflammation and leading to immune disorder. Our study provided experimental evidence for the hematopoietic toxicity of PM2.5 and highlighted the significance of reducing air pollution.