Accurate genomic variant detection in single cells with primary template-directed amplification.

Improvements in whole genome amplification (WGA) would enable new types of basic and applied biomedical research, including studies of intratissue genetic diversity that require more accurate single-cell genotyping. Here, we present primary template-directed amplification (PTA), an isothermal WGA method that reproducibly captures >95% of the genomes of single cells in a more uniform and accurate manner than existing approaches, resulting in significantly improved variant calling sensitivity and precision. To illustrate the types of studies that are enabled by PTA, we developed direct measurement of environmental mutagenicity (DMEM), a tool for mapping genome-wide interactions of mutagens with single living human cells at base-pair resolution. In addition, we utilized PTA for genome-wide off-target indel and structural variant detection in cells that had undergone CRISPR-mediated genome editing, establishing the feasibility for performing single-cell evaluations of biopsies from edited tissues. The improved precision and accuracy of variant detection with PTA overcomes the current limitations of accurate WGA, which is the major obstacle to studying genetic diversity and evolution at cellular resolution.

Latent cellular analysis robustly reveals subtle diversity in large-scale single-cell RNA-seq data.

Single-cell RNA sequencing (scRNA-seq) is a powerful tool for characterizing the cell-to-cell variation and cellular dynamics in populations which appear homogeneous otherwise in basic and translational biological research. However, significant challenges arise in the analysis of scRNA-seq data, including the low signal-to-noise ratio with high data sparsity, potential batch effects, scalability problems when hundreds of thousands of cells are to be analyzed among others. The inherent complexities of scRNA-seq data and dynamic nature of cellular processes lead to suboptimal performance of many currently available algorithms, even for basic tasks such as identifying biologically meaningful heterogeneous subpopulations. In this study, we developed the Latent Cellular Analysis (LCA), a machine learning-based analytical pipeline that combines cosine-similarity measurement by latent cellular states with a graph-based clustering algorithm. LCA provides heuristic solutions for population number inference, dimension reduction, feature selection, and control of technical variations without explicit gene filtering. We show that LCA is robust, accurate, and powerful by comparison with multiple state-of-the-art computational methods when applied to large-scale real and simulated scRNA-seq data. Importantly, the ability of LCA to learn from representative subsets of the data provides scalability, thereby addressing a significant challenge posed by growing sample sizes in scRNA-seq data analysis.

Rheb1 loss leads to increased hematopoietic stem cell proliferation and myeloid-biased differentiation in vivo.

Hematopoietic stem cells constitute a unique subpopulation of blood cells that can give rise to all types of mature cells in response to physiological demands. However, the intrinsic molecular machinery that regulates this transformative property remains elusive. In this paper, we demonstrate that small GTPase Rheb1 is a critical regulator of proliferation and differentiation of hematopoietic stem cells in vivo Rheb1 deletion led to increased phenotypic hematopoietic stem cell/hematopoietic progenitor cell proliferation under a steady state condition. Over-proliferating Rheb1-deficient hematopoietic stem cells were severely impaired in functional repopulation assays, and they failed to regenerate the blood system when challenged with hematopoietic ablation by sublethal irradiation. In addition, it was discovered that Rheb1 loss resulted in a lack of maturation of neutrophils / caused neutrophil immaturation by reducing mTORC1 activity, and that activation of the mTORC1 signaling pathway by mTOR activator 3BDO partially restored the maturation of Rheb1-deficient neutrophils. Rheb1 deficiency led to a progressive enlargement of the hematopoietic stem cell population and an eventual excessive myeloproliferation in vivo, including an overproduction of peripheral neutrophils and an excessive expansion of extramedullary hematopoiesis. Moreover, low RHEB expression was correlated with poor survival in acute myeloid leukemia patients with normal karyotype. Our results, therefore, demonstrate a critical and unique role for Rheb1 in maintaining proper hematopoiesis and myeloid differentiation.

Leukemic marrow infiltration reveals a novel role for Egr3 as a potent inhibitor of normal hematopoietic stem cell proliferation.

Cytopenias resulting from the impaired generation of normal blood cells from hematopoietic precursors are important contributors to morbidity and mortality in patients with leukemia. However, the process by which normal hematopoietic cells are overtaken by emerging leukemia cells and how different subsets of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) are distinctly influenced during leukemic cell infiltration is poorly understood. To investigate these important questions, we used a robust nonirradiated mouse model of human MLL-AF9 leukemia to examine the suppression of HSCs and HPCs during leukemia cell expansion in vivo. Among all the hematopoietic subsets, long-term repopulating HSCs were the least reduced, whereas megakaryocytic-erythroid progenitors were the most significantly suppressed. Notably, nearly all of the HSCs were forced into a noncycling state in leukemic marrow at late stages, but their reconstitution potential appeared to be intact upon transplantation into nonleukemic hosts. Gene expression profiling and further functional validation revealed that Egr3 was a strong limiting factor for the proliferative potential of HSCs. Therefore, this study provides not only a molecular basis for the more tightened quiescence of HSCs in leukemia, but also a novel approach for defining functional regulators of HSCs in disease.

ATF4 plays a pivotal role in the development of functional hematopoietic stem cells in mouse fetal liver.

The fetal liver (FL) serves as a predominant site for expansion of functional hematopoietic stem cells (HSCs) during mouse embryogenesis. However, the mechanisms for HSC development in FL remain poorly understood. In this study, we demonstrate that deletion of activating transcription factor 4 (ATF4) significantly impaired hematopoietic development and reduced HSC self-renewal in FL. In contrast, generation of the first HSC population in the aorta-gonad-mesonephros region was not affected. The migration activity of ATF4(-/-) HSCs was moderately reduced. Interestingly, the HSC-supporting ability of both endothelial and stromal cells in FL was significantly compromised in the absence of ATF4. Gene profiling using RNA-seq revealed downregulated expression of a panel of cytokines in ATF4(-/-) stromal cells, including angiopoietin-like protein 3 (Angptl3) and vascular endothelial growth factor A (VEGFA). Addition of Angptl3, but not VEGFA, partially rescued the repopulating defect of ATF4(-/-) HSCs in the culture. Furthermore, chromatin immunoprecipitation assay in conjunction with silencing RNA-mediated silencing and complementary DNA overexpression showed transcriptional control of Angptl3 by ATF4. To summarize, ATF4 plays a pivotal role in functional expansion and repopulating efficiency of HSCs in developing FL, and it acts through upregulating transcription of cytokines such as Angptl3 in the microenvironment.

Excessive proliferation and impaired function of primitive hematopoietic cells in bone marrow due to senescence post chemotherapy in a T cell acute lymphoblastic leukemia model.

BACKGROUND: In clinic settings, rel apsed leukemic patients are found to be more fragile to chemotherapy due to delayed or incomplete hematopoietic recovery, and hematopoiesis of these patients seem to be impaired. METHODS: We established a leukemia therapy model with a non-irradiated T cell acute lymphoblastic leukemia mouse model combined with cytarabine and cyclophosphamide. Dynamic kinetics and functional status of both primitive hematopoietic cells and leukemic cells in a leukemia host under the chemotherapy stress were comprehensively investigated. RESULTS: We successfully established the leukemia therapy model with T lymphoblastic phenotype. After treatment with cytarabine and cyclophosphamide, the frequency of L(-)K(+)S(+) hematopoietic cells tides with the therapy, and stabled when the disease remission, then reduced when relapsed, while leukemic cells showed a delayed but consistent regeneration. Combination of chemotherapy significantly promote an early and transient entrance of L(-)K(+)S(+) hematopoietic cells into active proliferation and induction of apoptosis on L(-)K(+)S(+) cells in vivo. Moreover, in the competitive bone marrow transplantation assays, hematopoietic cells showed gradually diminished regenerative capacity. Testing of senescence-associated beta-galactosidase (SA-ß gal) status showed higher levels in L(-)K(+)S(+) hematopoietic cells post therapy when compared with the control. Gene expression analysis of hematopoietic primitive cells revealed up-regulated p16, p21, and down-regulated egr1 and fos. CONCLUSION: We conclude that primitive hematopoietic cells in bone marrow enter proliferation earlier than leukemic cells after chemotherapy, and gradually lost their regenerative capacity partly by senescence due to accelerated cycling.

Graft-versus-host disease causes broad suppression of hematopoietic primitive cells and blocks megakaryocyte differentiation in a murine model.

Cytopenia and delayed immune reconstitution with acute graft-versus-host disease (aGVHD) indicate a poor prognosis. However, how donor-derived cell hematopoiesis is impaired in aGVHD is not well understood. We addressed this issue by studying the kinetics of hematopoiesis and the functions of hematopoietic stem and progenitor cells in an aGVHD model with haplo-MHC-matched murine bone marrow transplantation. Although hematopoiesis was progressively suppressed during aGVHD, the hematopoietic regenerative potential of donor-derived hematopoietic stem cells remains intact. There was a dramatic reduction in primitive hematopoietic cells and a defect in the ability of these cells to generate common myeloid progenitors (CMPs) and megakaryocyte/erythrocyte progenitors (MEPs). These effects were observed along with a concomitant increase in granulocyte/macrophage progenitors, suggesting that differentiation into MEPs is blocked during aGVHD. Interestingly, cyclosporine A was able to partially reverse the hematopoietic suppression as well as the differentiation blockage of CMPs. These data provide new insights into the pathogenesis of aGVHD and may improve the clinical management of aGVHD.

Single-cell RNA sequencing distinctly characterizes the wide heterogeneity in pediatric mixed phenotype acute leukemia.

BACKGROUND: Mixed phenotype acute leukemia (MPAL), a rare subgroup of leukemia characterized by blast cells with myeloid and lymphoid lineage features, is difficult to diagnose and treat. A better characterization of MPAL is essential to understand the subtype heterogeneity and how it compares with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Therefore, we performed single-cell RNA sequencing (scRNAseq) on pediatric MPAL bone marrow (BM) samples to develop a granular map of the MPAL blasts and microenvironment landscape. METHODS: We analyzed over 40,000 cells from nine pediatric MPAL BM samples to generate a single-cell transcriptomic landscape of B/myeloid (B/My) and T/myeloid (T/My) MPAL. Cells were clustered using unsupervised single-cell methods, and malignant blast and immune clusters were annotated. Differential expression analysis was performed to identify B/My and T/My MPAL blast-specific signatures by comparing transcriptome profiles of MPAL with normal BM, AML, and ALL. Gene set enrichment analysis (GSEA) was performed, and significantly enriched pathways were compared in MPAL subtypes. RESULTS: B/My and T/My MPAL blasts displayed distinct blast signatures. Transcriptomic analysis revealed that B/My MPAL profile overlaps with B-ALL and AML samples. Similarly, T/My MPAL exhibited overlap with T-ALL and AML samples. Genes overexpressed in both MPAL subtypes' blast cells compared to AML, ALL, and healthy BM included MAP2K2 and CD81. Subtype-specific genes included HBEGF for B/My and PTEN for T/My. These marker sets segregated bulk RNA-seq AML, ALL, and MPAL samples based on expression profiles. Analysis comparing T/My MPAL to ETP, near-ETP, and non-ETP T-ALL, showed that T/My MPAL had greater overlap with ETP-ALL cases. Comparisons among MPAL subtypes between adult and pediatric samples showed analogous transcriptomic landscapes of corresponding subtypes. Transcriptomic differences were observed in the MPAL samples based on response to induction chemotherapy, including selective upregulation of the IL-16 pathway in relapsed samples. CONCLUSIONS: We have for the first time described the single-cell transcriptomic landscape of pediatric MPAL and demonstrated that B/My and T/My MPAL have distinct scRNAseq profiles from each other, AML, and ALL. Differences in transcriptomic profiles were seen based on response to therapy, but larger studies will be needed to validate these findings.

Simultaneous monitoring of disease and microbe dynamics through plasma DNA sequencing in pediatric patients with acute lymphoblastic leukemia.

Treatment of acute lymphoblastic leukemia (ALL) necessitates continuous risk assessment of leukemic disease burden and infections that arise in the setting of immunosuppression. This study was performed to assess the feasibility of a hybrid capture next-generation sequencing panel to longitudinally measure molecular leukemic disease clearance and microbial species abundance in 20 pediatric patients with ALL throughout induction chemotherapy. This proof of concept helps establish a technical and conceptual framework that we anticipate will be expanded and applied to additional patients with leukemia, as well as extended to additional cancer types. Molecular monitoring can help accelerate the attainment of insights into the temporal biology of host-microbe-leukemia interactions, including how those changes correlate with and alter anticancer therapy efficacy. We also anticipate that fewer invasive bone marrow examinations will be required, as these methods improve with standardization and are validated for clinical use.

Integrated decoding hematopoiesis and leukemogenesis using single-cell sequencing and its medical implication.

Single-cell RNA sequencing provides exciting opportunities to unbiasedly study hematopoiesis. However, our understanding of leukemogenesis was limited due to the high individual differences. Integrated analyses of hematopoiesis and leukemogenesis potentially provides new insights. Here we analyzed ~200,000 single-cell transcriptomes of bone marrow mononuclear cells (BMMCs) and its subsets from 23 clinical samples. We constructed a comprehensive cell atlas as hematopoietic reference. We developed counterpart composite index (CCI; available at GitHub: https://github.com/pengfeeei/cci) to search for the healthy counterpart of each leukemia cell subpopulation, by integrating multiple statistics to map leukemia cells onto reference hematopoietic cells. Interestingly, we found leukemia cell subpopulations from each patient had different healthy counterparts. Analysis showed the trajectories of leukemia cell subpopulations were similar to that of their healthy counterparts, indicating that developmental termination of leukemia initiating cells at different phases leads to different leukemia cell subpopulations thus explained the origin of leukemia heterogeneity. CCI further predicts leukemia subtypes, cellular heterogeneity, and cellular stemness of each leukemia patient. Analyses of leukemia patient at diagnosis, refractory, remission and relapse vividly presented dynamics of cell population during leukemia treatment. CCI analyses showed the healthy counterparts of relapsed leukemia cells were closer to the root of hematopoietic tree than that of other leukemia cells, although single-cell transcriptomic genetic variants and haplotype tracing analyses showed the relapsed leukemia cell were derived from an early minor leukemia cell population. In summary, this study developed a unified framework for understanding leukemogenesis with hematopoiesis reference, which provided novel biological and medical implication.

[Macrophage inflammatory protein-1α promotes the growth of acute myeloid leukemia cells].

UNLABELLED: BACKGROWND: Macrophage inflammatory protein-1α (MIP-l α/CCL3) belongs to the C-C chemokine family (CCL3), which can be secreted by macrophages, other types of hematopoietic cells and bone marrow stromal cells. Higher levels of MIP-1α were found to be associated with several kinds of hematologic malignancies, including multiple myeloma (MM), chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML). Moreover, MIP-1α has been reported to be an adverse prognostic factor for CLL. However, the impact of MIP-1α on acute myeloid leukemia (AML) has been poorly investigated. OBJECTIVE: To investigate the influence of MIP-1α on proliferction of AML cells. METHODS: Using MLL-AF9 induced AML mouse model, the expression of MIP-1α was measured by real time quantitative RT-PCR. AML cell proliferation was examined by cell counting and colony forming assay (CFC). The influence of blocking the MIP-1α action on the growth and pathogenic ability of AML cells was explored by using the small molecule antagonist for interfering interaction of MIP-1α with its receptor CCR1. RESULTS: The MIP-1α could promote the proliferation and colony formation of AML cells, the blocking MIP-1a could inhibit the growth of AML cells and delay onset of AML. CONCLUSION: The MIP-1a promotes the occurence and progression of AML, therefore blocking the MIP-1α signal pathway may be served as a strategy to inhibit the growth of AML cells, and MIP-1α can be a potential target for treatment of AML.

Notch1-induced T cell leukemia can be potentiated by microenvironmental cues in the spleen.

BACKGROUND: Leukemia is a systemic malignancy originated from hematopoietic cells. The extracellular environment has great impacts on the survival, proliferation and dissemination of leukemia cells. The spleen is an important organ for extramedullary hematopoiesis and a common infiltration site in lymphoid malignancies. Splenomegaly, frequently observed in T cell acute lymphoblastic leukemia (T-ALL), is associated with poor prognosis. However, how the spleen microenvironment distinctly affects T-ALL cells as opposed to bone marrow (BM) microenvironment has not been addressed. METHODS: A Notch1-induced mouse T-ALL model was applied in this study. Flow cytometry and two-photon fluorescence microscopy were used to analyze early distribution of T-ALL cells. MILLIPLEX® MAP Multiplex Immunoassay was performed to measure cytokine/chemokine levels in different microenvironments. Transwell and co-culture experiments were used to test the effects of splenic microenvironment in vitro. Splenectomy was performed to assess the organ specific impact on the survival of T-ALL-bearing mice. RESULTS: More leukemia cells were detected in the spleen than in the BM after injection of T-ALL cells by flow cytometry and two-photon fluorescence microscopy analysis. By screening a panel of cytokines/chemokines, a higher level of MIP-3ß was found in the splenic microenvironment than BM microenvironment. In vitro transwell experiment further confirmed that MIP-3ß recruits T-ALL cells which express a high level of MIP-3ß receptor, CCR7. Furthermore, the splenic microenvironment stimulates T-ALL cells to express a higher level of MIP-3ß, which further recruits T-ALL cells to the spleen. Co-culture experiment found that the splenic microenvironment more potently stimulated the proliferation and migration of T-ALL cells than BM. Moreover, the mice transplanted with T-ALL cells from the spleen had a shorter life span than those transplanted from BM, suggesting increased potency of the T-ALL cells induced by the splenic microenvironment. In addition, splenectomy prolonged the survival of leukemic mice. CONCLUSIONS: Our study demonstrates an organ specific effect on leukemia development. Specifically, T-ALL cells can be potentiated by splenic microenvironment and thus spleen may serve as a target organ for the treatment of some types of leukemia.

[Expression of CD48 as a live marker to distinguish division of hematopoietic stem cells].

Hematopoietic stem cells are capable of self-renewal or differentiation when they divide. Three types of cell divisions exist. A dividing stem cell may generate 2 new stem cells (symmetrical renewal division), or 2 differentiating cells (symmetrical differentiation division), or 1 cell of each type (asymmetrical division). This study was aimed to explore an efficient and stable method to distinguish the way of cell division in hematopoietic stem cells. Previous studies showed that the distribution of Numb in a cell could be used to distinguish the type of cell division in various kinds of cells. Therefore, the distribution of Numb protein was detected by immunofluorescence in mitotic CD48(-)CD150(+)LSK cells of mice exploring the relationship between Numb protein and centrosomes. Since CD48 positive marks the HSC that have lost the ability to reconstitute the blood system in mice, CD48 marker could be used to distinguish cell fate decision between self-renewal and differentiation as a living marker. In this study, the CD48(-)CD150(+)LSK cells were sorted from bone marrow cells of mice and the cells were directly labeled with Alexa Fluor (AF) 488-conjugated anti-CD48 antibody in living cultures. After 3 days, the percentage of AF488(+) cells was evaluated under microscope and by FACS. Then colony forming cell assay (CFC) was performed and the ability of cell proliferation were compared between AF488(+) and AF488(-) cells. The results showed that Numb could be used to distinguish different cell division types of hematopoietic stem cells, which was symmetrically or asymmetrically segregated in mitotic CD48(-)CD150(+)LSK cells. The self-labeled fluorochrome could be detected both by FACS as well as microscope. There were about 40% AF488(+) cells after 3 day-cultures in medium titrated with self-labeled AF 488-conjugated anti-CD48 antibody, and the results were consistent between confocal fluorescence microscopy and flow cytometry analysis. The colony forming ability of AF488(+) cells was significantly higher than that of AF488(-) cells (P < 0.05). The proliferation ability of AF488(-) cells was also significantly higher than AF488(+) cells (P < 0.05). It is concluded that the expression of CD48 can distinguish cell division of hematopoietic stem cells and can be used as a live marker for the loss of stemness. In comparison with the Numb protein staining, this method can be used in living cells, thus provides greater convenience for subsequent cell culture studies and cell transplantation experiments.

[Knockdown of Puma protects cord blood CD34(+) cells against γ- irradiation].

Puma (P53 upregulated modulator of apoptosis) is a BCL-2 homology 3 (BH3)-only BCL-1 family member and a critical mediator of P53-dependent and -independent apoptosis. Puma plays an essential role in the apoptosis of hematopoietic stem cells exposed to irradiation without an increased risk of malignancies. This study was purposed to develop an effective lentiviral vector to target Puma in human hematopoietic cells and to investigate the effect of Puma gene knockdown on the biological function of human cord blood CD34(+) cells. SF-LV-shPuma-EGFP and control vectors were constructed, and packaged with the pSPAX2/pMD2.G packaging plasmids via 293T cells to produce pseudo-type lentiviruses. SF-LV-shPuma-EGFP or control lentiviruses were harvested within 72 hours after transfection and then were used to transduce human cord blood CD34(+) cells. GFP(+) transduced cells were sorted by flow cytometry (FCM) for subsequent studies. Semi-quantitative real time RT PCR, Western blot, FCM with Annexin V-PE/7-AAD double staining, Ki67 staining, colony forming cell assay (CFC), CCK-8 assay and BrdU incorporation were performed to determine the expression of Puma and its effect on the cord blood CD34(+) cells. The results showed that Puma was significantly knocked down in cord blood CD34(+) cells and the low expression of Puma conferred a radio-protective effect on the cord blood CD34(+) cells. This effect was achieved through reduced apoptosis and sustained quiescence after irradiation due to Puma knockdown. It is concluded that knockdown of puma gene in CD34(+) hematopoietic stem cells of human cord blood possesses the radioprotective effect, maintains the cells in silence targeting Puma in human hematopoietic cells may have a similar effect with that on mouse hematopoietic cells as previously shown, and our lentiviral targeting system for Puma provides a valuable tool for future translational studies with human cells.

Identification of functional cooperative mutations of SETD2 in human acute leukemia.

Acute leukemia characterized by chromosomal rearrangements requires additional molecular disruptions to develop into full-blown malignancy, yet the cooperative mechanisms remain elusive. Using whole-genome sequencing of a pair of monozygotic twins discordant for MLL (also called KMT2A) gene-rearranged leukemia, we identified a transforming MLL-NRIP3 fusion gene and biallelic mutations in SETD2 (encoding a histone H3K36 methyltransferase). Moreover, loss-of-function point mutations in SETD2 were recurrent (6.2%) in 241 patients with acute leukemia and were associated with multiple major chromosomal aberrations. We observed a global loss of H3K36 trimethylation (H3K36me3) in leukemic blasts with mutations in SETD2. In the presence of a genetic lesion, downregulation of SETD2 contributed to both initiation and progression during leukemia development by promoting the self-renewal potential of leukemia stem cells. Therefore, our study provides compelling evidence for SETD2 as a new tumor suppressor. Disruption of the SETD2-H3K36me3 pathway is a distinct epigenetic mechanism for leukemia development.

Suppression of cytochrome p450 reductase enhances long-term hematopoietic stem cell repopulation efficiency in mice.

BACKGROUND: Bone marrow microenvironment (niche) plays essential roles in the fate of hematopoietic stem cells (HSCs). Intracellular and extracellular redox metabolic microenvironment is one of the critical factors for the maintenance of the niche. Cytochrome P450 reductase (CPR) is an obligate electron donor to all microsomal cytochrome P450 enzymes (P450 or CYP), and contributes to the redox metabolic process. However, its role in maintaining HSCs is unknown. OBJECTIVE: To examine the effects of low CPR expression on HSCs function using a mouse model of globally suppressed Cpr gene expression (Cpr Low, CL mice). METHODS: Hematopoietic cell subpopulations in bone marrow (BM) and peripheral blood (PB) from WT and CL mice were examined for their repopulation and differentiation ability upon BM competitive transplantation and enriched HSC (LKS(+)) transplantation. Effects of low CPR expression on hematopoiesis were examined by transplanting normal BM cells into CL recipients. Reactive oxygen species (ROS), cell cycle, and apoptosis in CL mice were analyzed by flow cytometry for DCF-DA fluorescence intensity, Ki67 protein, and Annexin-V, respectively. RESULTS: The levels of ROS in BM cells, HPCs and HSCs were comparable between CL and WT mice. In comparison to WT mice, the number of LT-HSCs or ST-HSCs was lower in CL mice while CMPs, GMPs and MEPs in CL mice were higher than that in WT control. Competitive transplantation assay revealed enhanced repopulation capacity of HSCs with low CPR expression, but no difference in differentiation potential upon in vitro experiments. Furthermore, lymphoid differentiation of donor cells decreased while their myeloid differentiation increased under CL microenvironment although the overall level of donor hematopoietic repopulation was not significantly altered. CONCLUSIONS: Our studies demonstrate that suppressing CPR expression enhances the repopulation efficiency of HSCs and a low CPR expression microenvironment favors the differentiation of myeloid over lymphoid lineage cells.

[Knockdown of Larp4b in Lin(-) cells does not affect the colony forming ability of mouse hematopoietic cells].

Larp4b is a member of the LARP family, which can interact with RNA and generally stimulate the translation of mRNA. Abnormal expression of Larp4b can be found in leukemia patients in our previous study. This study was purposed to detect the relative expression of Larp4b mRNA in different subpopulations of mouse hematopoietic cells, to construct lentivirus vector containing shLarp4b targeting mouse gene Larp4b and to explore its effects on mouse Lin(-) cells infected with shLarp4b by lentivirus. SF-LV-shLarP4b-EGFP and control vectors were constructed and two-plasmid lentivirus packing system was used to transfect 293T cells. After 48 h and 72 h, lentivirus SF-LV-shLarp4b-EGFP was harvested and was used to infect Lin(-) cells. After 48 h, EGFP(+) cells was sorted by flow cytometry (FCM). Meanwhile, semi-quantitative real time-PCR, AnnexinV-PE/7-AAD staining, PI staining and colony forming cell assay (CFC) were performed to determine the expression of Larp4b and its effect on the proliferation of hematopoietic progenitor cells. The results showed that Larp4b was highly expressed in myeloid cells. SF-LV-shLarp4b-EGFP was successfully constructed according to the restriction endonuclease digestion assay. RT-PCR confirmed that Larp4b was efficiently knockdown in mouse Lin(-) cells. The low expression of Larp4b did not affect the colony forming number, the apoptosis and cell cycle of Lin(-) cells. It is concluded that knockdown of Larp4b in mouse Lin(-) cells do not contribute to the colony forming ability and the growth of Lin(-) cells in vitro. This useful knockdown system will be used to study in vivo Larp4b in future.

[Differential expression of oxidative reductases in different subsets of mouse hematopoietic cells].

Hematopoietic stem cells (HSC) are the source of all blood cells, which can differentiate into various hematopoietic hierarchy cells. Physiological level of reactive oxygen species (ROS) plays an important role in regulating functions of HSC as excessive ROS is harmful to HSC. Oxidative reductases and antioxidants can eliminate cellular ROS to maintain ROS homeostasis and thus avoid excessive ROS-caused damages. There are several types of oxidative reductases in cells such as catalase, manganese superoxide dismutase (MnSOD), glutathione peroxidase 1 (GPX1), thioredoxin reductase 1 (Txrnd1) and Nqo1 [NAD(P)H dehydrogenase quinone 1]. However, the functional roles of various oxidative reductases in regulating ROS level in hematopoietic cells remain unclear. This study was to investigate the expression patterns of these oxidative reductases in mouse hematopoietic cells that were sorted out via flow cytometry and to find out important oxidative reductases involving in HSC ROS regulation. The expression of various oxidative reductases was detected by semi-quantitative real-time PCR. The results showed that the expression level of catalase in T cell population was 0.14 times that in LT-HSC population (P < 0.05). The expression levels of MnSOD in CLP population and myeloid cells were 0.56 and 0.47 times that in LT-HSC population respectively (P < 0.05). The expression levels of GPX1 in ST-HSC, GMP, Myeloid cells, MEP, T lymphocytes and B lymphocytes were 1.79, 2.96, 2.07, 0.58, 0.10, 0.6 times that in LT-HSC population respectively (P < 0.05). The expression levels of Txrnd1 in ST-HSC, MPP, CMP, GMP, Myeloid cells, T lymphocytes and B lymphocytes were 3.36, 3.18, 4.19, 6.39, 4.27, 0.016, 0.56 time that in LT-HSC population, respectively (P < 0.05). The expression levels of Nqo1 in ST-HSC, MPP, CMP, GMP, CLP and B cell were 0.30, 0.17, 0.25, 0.10, 0.04, 0.01 times that in LT-HSC population, respectively (P < 0.05). It is concluded that the expression levels of oxidative reductases (catalase, MnSOD, GPX1, Txrnd1 and Nqo1) in hematopoietic hierarchy cells are cell-type specific. It suggests that reductases may play divergent roles in various hematopoietic cell populations. More importantly, the expression level of Nqo1 in LT-HSC population significantly increased as compared with other cell populations, thereby suggesting its unique regulatory role in HSC.

Mouse embryonic head as a site for hematopoietic stem cell development.

In the mouse embryo, the aorta-gonad-mesonephros (AGM) region is considered to be the sole location for intraembryonic emergence of hematopoietic stem cells (HSCs). Here we report that, in parallel to the AGM region, the E10.5-E11.5 mouse head harbors bona fide HSCs, as defined by long-term, high-level, multilineage reconstitution and self-renewal capacity in adult recipients, before HSCs enter the circulation. The presence of hemogenesis in the midgestation head is indicated by the appearance of intravascular cluster cells and the blood-forming capacity of a sorted endothelial cell population. In addition, lineage tracing via an inducible VE-cadherin-Cre transgene demonstrates the hemogenic capacity of head endothelium. Most importantly, a spatially restricted lineage labeling system reveals the physiological contribution of cerebrovascular endothelium to postnatal HSCs and multilineage hematopoiesis. We conclude that the mouse embryonic head is a previously unappreciated site for HSC emergence within the developing embryo.