The role of apoptosis in the regulation of hematopoietic stem cells: Overexpression of Bcl-2 increases both their number and repopulation potential

The bone marrow niche and hematopoietic system are distinctly remodeled by CD45-targeted astatine-211 radioimmunotherapy

Radioimmunotherapy (RIT) is used to treat patients with hematological malignancies known to infiltrate the bone marrow (BM) microenvironment. RIT uses target-specific monoclonal antibodies stably conjugated to radionuclides to deliver cytotoxic radiation to cells of interest. While RIT is effective at delivering radiation to cancer cells, normal tissue is also exposed to radiation upon RIT, the consequences of which are largely unknown. Here, we studied the cellular and molecular effects of CD45-targeted astatine-211 ( 211 At) RIT, IgG non-targeted 211 At RIT, and Cesium-137 total-body irradiation (TBI) on hematopoietic cells and their BM niche in wild-type immunocompetent mice. Relative to non-targeted RIT or TBI, CD45-targeted RIT significantly delayed hematopoietic regeneration overall in the peripheral blood and BM and reduced hematopoietic stem/progenitor cell recovery and colony-forming ability. While BM endothelial cells (ECs) do not express the CD45 antigen, CD45-targeted RIT significantly depleted BM ECs compared to non-targeted RIT or TBI. RNA sequence analysis revealed significantly different transcriptomic profiles of BM ECs from CD45-RIT-treated mice compared to non- targeted RIT or TBI. ECs from CD45-RIT-treated mice, but not TBI or IgG-RIT-treated mice, were transcriptionally enriched for TGFβ, NOTCH, and IFNα signaling pathways compared to untreated mice. Collectively, our study indicates that CD45-targeted RIT severely impacts hematopoietic and EC niche recovery compared to non- targeted approaches. Future studies are required to determine the long-term consequences of such RIT-driven effects on BM niche physiology and how BM niche reprogramming by RIT affects cancer cells.

KEY POINTS

CD45-targeted radioimmunotherapy more effectively suppresses the hematopoietic system than non- targeted radiation delivery.The bone marrow vascular niche is differentially reprogrammed by CD45-targeted radioimmunotherapy compared to non-targeted radiation delivery.

The Potential of Human Pulmonary Mesenchymal Stem Cells as Vectors for Radiosensitizing Metallic Nanoparticles: An In Vitro Study

BACKGROUND/OBJECTIVES

Metallic nanoparticles (NPs) exhibit interesting radiosensitizing effects, and finding a way to accurately deliver them appears to be crucial. Due to their tumor tropism, mesenchymal stem cells (MSCs) represent a strategic approach. Therefore, we aimed to evaluate the impact of core-shell Fe3O4@Au NPs on the functionality of human pulmonary MSCs (HPMSCs).

METHODS/RESULTS

The results showed that 100 µg/mL Fe3O4@Au NPs, accumulated in HPMSCs (revealed by Prussian blue staining), did not alter cell viability as assessed by cell counting, MTT, and LDH assays. However, caspase 9 and Bcl2 gene expression, evaluated by RT-qPCR, was regulated 72 h after exposure to the NPs. Moreover, the NPs also decreased proinflammatory cytokine/chemokine secretions, except for CXCL8 (ELISA). These modulations were associated with the downregulation of AMPK gene expression at 24 h. In contrast, the NPs did not modulate VEGF, PI3K, or PDGF gene expression. Nevertheless, a decrease in VEGF secretion was observed after 24 h of exposure to the NPs. Interestingly, the Fe3O4@Au NPs did not modulate Nrf2 gene expression, but they did regulate the expression of the genes encoding Nox4 and HMOX-1. Additionally, the NPs increased ROS production, suggesting a redox imbalance.

CONCLUSIONS

Finally, the Fe3O4@Au NPs did not affect the HPMSCs' viability or proangiogenic/tumorigenic markers. These findings are encouraging for investigating the effects of Fe3O4@Au NPs delivered by HPMSCs to tumor sites in combination with radiation.

Lethal and sublethal effects of programmed cell death pathways on hematopoietic stem cells

Programmed cell death is an evolutionally conserved cellular process in multicellular organisms that eliminates unnecessary or rogue cells during development, infection, and carcinogenesis. Hematopoietic stem cells (HSCs) are a rare, self-renewing, and multipotent cell population necessary for the establishment and regeneration of the hematopoietic system. Counterintuitively, key components necessary for programmed cell death induction are abundantly expressed in long-lived HSCs, which often survive myeloablative stress by engaging a prosurvival response that counteracts cell death-inducing stimuli. Although HSCs are well known for their apoptosis resistance, recent studies have revealed their unique vulnerability to certain types of programmed necrosis, such as necroptosis and ferroptosis. Moreover, emerging evidence has shown that programmed cell death pathways can be sublethally activated to cause nonlethal consequences such as innate immune response, organelle dysfunction, and mutagenesis. In this review, we summarized recent findings on how divergent cell death programs are molecularly regulated in HSCs. We then discussed potential side effects caused by sublethal activation of programmed cell death pathways on the functionality of surviving HSCs.

Ex vivo expansion potential of murine hematopoietic stem cells is a rare property only partially predicted by phenotype

The scarcity of hematopoietic stem cells (HSCs) restricts their use in both clinical settings and experimental research. Here, we examined a recently developed method for expanding rigorously purified murine HSCs ex vivo. After 3 weeks of culture, only 0.1% of cells exhibited the input HSC phenotype, but these accounted for almost all functional long-term HSC activity. Input HSCs displayed varying potential for ex vivo self-renewal, with alternative outcomes revealed by single-cell multimodal RNA and ATAC sequencing profiling. While most HSC progeny offered only transient in vivo reconstitution, these cells efficiently rescued mice from lethal myeloablation. The amplification of functional HSC activity allowed for long-term multilineage engraftment in unconditioned hosts that associated with a return of HSCs to quiescence. Thereby, our findings identify several key considerations for ex vivo HSC expansion, with major implications also for assessment of normal HSC activity.

Identification of a Musashi2 translocation as a novel oncogene in myeloid leukemia

Myeloid leukemias, diseases marked by aggressiveness and poor outcomes, are frequently triggered by oncogenic translocations. In the case of chronic myelogenous leukemia (CML) the BCR-ABL fusion initiates chronic phase disease with second hits allowing progression to blast crisis. Although Gleevec has been transformative for CML, blast crisis CML remains relatively drug resistant. Here we show that MSI2-HOXA9, a translocation with an unknown role in cancer, can serve as a second hit in driving bcCML. Compared to BCR-ABL, BCR-ABL/MSI2-HOXA9 led to a more aggressive disease in vivo with decreased latency, increased lethality and a differentiation blockade that is a hallmark of blast crisis. Domain mapping revealed that the MSI2 RNA binding domain RRM1 had a preferential impact on growth and lethality of bcCML relative to RRM2 or the HOXA9 domain. Mechanistically, MSI2-HOXA9 triggered global downstream changes with a preferential upregulation of mitochondrial components. Consistent with this, BCR-ABL/MSI2-HOXA9 cells exhibited a significant increase in mitochondrial respiration. These data suggest that MSI2-HOXA9 acts, at least in part, by increasing expression of the mitochondrial polymerase Polrmt and augmenting mitochondrial function and basal respiration in blast crisis. Collectively, our findings demonstrate for the first time that translocations involving the stem and developmental signal MSI2 can be oncogenic, and suggest that MSI, which we found to be a frequent partner for an array of translocations, could also be a driver mutation across solid cancers.

Hematopoietic stem cells through the ages: A lifetime of adaptation to organismal demands

Hematopoietic stem cells (HSCs), which govern the production of all blood lineages, transition through a series of functional states characterized by expansion during fetal development, functional quiescence in adulthood, and decline upon aging. We describe central features of HSC regulation during ontogeny to contextualize how adaptive responses over the life of the organism ultimately form the basis for HSC functional degradation with age. We particularly focus on the role of cell cycle regulation, inflammatory response pathways, epigenetic changes, and metabolic regulation. We then explore how the knowledge of age-related changes in HSC regulation can inform strategies for the rejuvenation of old HSCs.

The critical role of apoptosis in mesenchymal stromal cell therapeutics and implications in homeostasis and normal tissue repair

Mesenchymal stromal cells (MSCs) have been extensively tested for the treatment of numerous clinical conditions and have demonstrated good safety but mixed efficacy. Although this outcome can be attributed in part to the heterogeneity of cell preparations, the lack of mechanistic understanding and tools to establish cell pharmacokinetics and pharmacodynamics, as well as the poorly defined criteria for patient stratification, have hampered the design of informative clinical trials. We and others have demonstrated that MSCs can rapidly undergo apoptosis after their infusion. Apoptotic MSCs are phagocytosed by monocytes/macrophages that are then reprogrammed to become anti-inflammatory cells. MSC apoptosis occurs when the cells are injected into patients who harbor activated cytotoxic T or NK cells. Therefore, the activation state of cytotoxic T or NK cells can be used as a biomarker to predict clinical responses to MSC treatment. Building on a large body of preexisting data, an alternative view on the mechanism of MSCs is that an inflammation-dependent MSC secretome is largely responsible for their immunomodulatory activity. We will discuss how these different mechanisms can coexist and are instructed by two different types of MSC "licensing": one that is cell-contact dependent and the second that is mediated by inflammatory cytokines. The varied and complex mechanisms by which MSCs can orchestrate inflammatory responses and how this function is specifically driven by inflammation support a physiological role for tissue stroma in tissue homeostasis, and it acts as a sensor of damage and initiator of tissue repair by reprogramming the inflammatory environment.

Stem cell architecture drives myelodysplastic syndrome progression and predicts response to venetoclax-based therapy

Myelodysplastic syndromes (MDS) are heterogeneous neoplastic disorders of hematopoietic stem cells (HSCs). The current standard of care for patients with MDS is hypomethylating agent (HMA)-based therapy; however, almost 50% of MDS patients fail HMA therapy and progress to acute myeloid leukemia, facing a dismal prognosis due to lack of approved second-line treatment options. As cancer stem cells are the seeds of disease progression, we investigated the biological properties of the MDS HSCs that drive disease evolution, seeking to uncover vulnerabilities that could be therapeutically exploited. Through integrative molecular profiling of HSCs and progenitor cells in large patient cohorts, we found that MDS HSCs in two distinct differentiation states are maintained throughout the clinical course of the disease, and expand at progression, depending on recurrent activation of the anti-apoptotic regulator BCL-2 or nuclear factor-kappa B-mediated survival pathways. Pharmacologically inhibiting these pathways depleted MDS HSCs and reduced tumor burden in experimental systems. Further, patients with MDS who progressed after failure to frontline HMA therapy and whose HSCs upregulated BCL-2 achieved improved clinical responses to venetoclax-based therapy in the clinical setting. Overall, our study uncovers that HSC architectures in MDS are potential predictive biomarkers to guide second-line treatments after HMA failure. These findings warrant further investigation of HSC-specific survival pathways to identify new therapeutic targets of clinical potential in MDS.

Mitochondrial calcium homeostasis in hematopoietic stem cell: Molecular regulation of quiescence, function, and differentiation

Hematopoiesis is based on the existence of hematopoietic stem cells (HSC) with the capacity to self-proliferate and self-renew or to differentiate into specialized cells. The hematopoietic niche is the essential microenvironment where stem cells reside and integrate various stimuli to determine their fate. Recent studies have identified niche containing high level of calcium (Ca²⁺) suggesting that HSCs are sensitive to Ca²⁺. This is a highly versatile and ubiquitous second messenger that regulates a wide variety of cellular functions. Advanced methods for measuring its concentrations, genetic experiments, cell fate tracing data, single-cell imaging, and transcriptomics studies provide information into its specific roles to integrate signaling into an array of mechanisms that determine HSC identity, lineage potential, maintenance, and self-renewal. Accumulating and contrasting evidence, are revealing Ca²⁺ as a previously unacknowledged feature of HSC, involved in functional maintenance, by regulating multiple actors including transcription and epigenetic factors, Ca²⁺-dependent kinases and mitochondrial physiology. Mitochondria are significant participants in HSC functions and their responsiveness to cellular demands is controlled to a significant extent via Ca²⁺ signals. Recent reports indicate that mitochondrial Ca²⁺ uptake also controls HSC fate. These observations reveal a physiological feature of hematopoietic stem cells that can be harnessed to improve HSC-related disease. In this review, we discuss the current knowledge Ca²⁺ in hematopoietic stem cell focusing on its potential involvement in proliferation, self-renewal and maintenance of HSC and discuss future research directions.

The Effect of Dietary Intervention With High-Oleocanthal and Oleacein Olive Oil in Patients With Early-Stage Chronic Lymphocytic Leukemia: A Pilot Randomized Trial

AIM

Oleocanthal and oleacein (OC/OL) have important in vitro and in vivo antitumor properties; however, there is no data about their anticancer activity in humans. The aim of this pilot study was to test if patients at early stage of chronic lymphocytic leukemia (CLL) could adhere to and tolerate an intervention with high OC/OL extra virgin olive oil (EVOO) and if this intervention could lead to any changes in markers related to the disease.

METHODS

A pilot dietary intervention (DI) was made in patients with CLL in Rai stages 0-II who did not follow any treatment (NCT04215367). In the first intervention (DI1), 20 CLL patients were included in a blind randomized study and were separated into two groups. One group (A) of 10 patients consumed 40 ml/day of high OC/OL-EVOO (416 mg/Kg OC and 284 mg/kg OL) for 3 months. A second group (B) of 10 patients consumed 40 ml/day of low OC/OL (82 mg/kg OC and 33 mg/kg OL) for 3 months. After a washout period of 9-12 months, a second intervention (DI2) only with High OC/OL-EVOO for 6 months was performed with 22 randomly selected patients (16 from the DI1 (8 from each group) and 6 new). Hematological, biochemical, and apoptotic markers were analyzed in the serum of the patients. In addition, cellular proliferation and apoptosis markers were studied in isolated proteins from peripheral blood mononuclear cells.

RESULTS

The results of the DI1 showed beneficial effects on hematological and apoptotic markers only with High OC/OL-EVOO. During the DI2, a decrease in the white blood cell and lymphocyte count was observed (p ≤0.05), comparing 3 months before the intervention and 6 months after it. After 3 and 6 months of DI2, an increase (p ≤0.05) was observed in the apoptotic markers ccK18 and Apo1-Fas, and also in the cell cycle negative regulator p21, and also a decrease in the antiapoptotic protein Survivin, and in the cellular proliferation marker Cyclin D.

CONCLUSIONS

This is the first clinical trial with High OC/OL-EVOO that indicates that it could be a promising dietary feature for the improvement of CLL inducing the apoptosis of their cancer cells and improving the metabolism of the patients.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT04215367, identifier: NCT04215367.

Multistage hematopoietic stem cell regulation in the mouse: A combined biological and mathematical approach

We have reconciled steady-state and stress hematopoiesis in a single mathematical model based on murine in vivo experiments and with a focus on hematopoietic stem and progenitor cells. A phenylhydrazine stress was first applied to mice. A reduced cell number in each progenitor compartment was evidenced during the next 7 days through a drastic level of differentiation without proliferation, followed by a huge proliferative response in all compartments including long-term hematopoietic stem cells, before a return to normal levels. Data analysis led to the addition to the 6-compartment model, of time-dependent regulation that depended indirectly on the compartment sizes. The resulting model was finely calibrated using a stochastic optimization algorithm and could reproduce biological data in silico when applied to different stress conditions (bleeding, chemotherapy, HSC depletion). In conclusion, our multi-step and time-dependent model of immature hematopoiesis provides new avenues to a better understanding of both normal and pathological hematopoiesis.

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We describe a new 6-compartment time-dependent regulated model of hematopoiesis

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Biological data under steady state and stress and cell dynamics were used

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Modeling is able to recapitulate effects from chemotherapy, bleeding, or HSC depletion

The telomere complex and the origin of the cancer stem cell

Exquisite regulation of telomere length is essential for the preservation of the lifetime function and self-renewal of stem cells. However, multiple oncogenic pathways converge on induction of telomere attrition or telomerase overexpression and these events can by themselves trigger malignant transformation. Activation of NFκB, the outcome of telomere complex damage, is present in leukemia stem cells but absent in normal stem cells and can activate DOT1L which has been linked to MLL-fusion leukemias. Tumors that arise from cells of early and late developmental stages appear to follow two different oncogenic routes in which the role of telomere and telomerase signaling might be differentially involved. In contrast, direct malignant transformation of stem cells appears to be extremely rare. This suggests an inherent resistance of stem cells to cancer transformation which could be linked to a stem cell’specific mechanism of telomere maintenance. However, tumor protection of normal stem cells could also be conferred by cell extrinsic mechanisms.

High glucose macrophage exosomes enhance atherosclerosis by driving cellular proliferation & hematopoiesis

We investigated whether extracellular vesicles (EVs) produced under hyperglycemic conditions could communicate signaling to drive atherosclerosis. We did so by treating Apoe-/- mice with exosomes produced by bone marrow-derived macrophages (BMDM) exposed to high glucose (BMDM-HG-exo) or control. Infusions of BMDM-HG-exo increased hematopoiesis, circulating myeloid cell numbers, and atherosclerotic lesions with an accumulation of macrophage foam and apoptotic cells. Transcriptome-wide analysis of cultured macrophages treated with BMDM-HG-exo or plasma EVs isolated from subjects with type II diabetes revealed a reduced inflammatory state and increased metabolic activity. Furthermore, BMDM-HG-exo induced cell proliferation and reprogrammed energy metabolism by increasing glycolytic activity. Lastly, profiling microRNA in BMDM-HG-exo and plasma EVs from diabetic subjects with advanced atherosclerosis converged on miR-486-5p as commonly enriched and recognized in dysregulated hematopoiesis and Abca1 control. Together, our findings show that EVs serve to communicate detrimental properties of hyperglycemia to accelerate atherosclerosis in diabetes.

Suppression Of Aberrant Activation Of NF-κB Pathway In Drug-resistant Leukemia Stem Cells Contributes To Parthenolide-potentiated Reversal Of Drug Resistance In Leukemia

Although many drugs that targeted the specific features of leukemia stem cells (LSCs) have substantial application in the clinical treatment of leukemia, the LSCs relapsed and caused drug-resistant leukemia. Therefore, it is necessary to identify the unique features of LSCs in relapsing and drug-resistant leukemia and also to explore the drugs that directed at these features. Our clinical data have indicated that relapsed patients with acute myeloid leukemia have more abundant proportion of LSCs with enhanced breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) expression when compared to the untreated patients. The results showed that compared with LSCs derived from sensitive K562 cells, LSCs from drug-resistant K562/ADM cells have much higher chemotherapeutic resistance, and so we termed these cells as “drug-resistant LSCs”. Subsequently, aberrant activation of NF-κB pathway in drug-resistant LSCs was further using gene chip analysis. Also, parthenolide (PTL), which is a specific NF-κB inhibitor, effectively eliminated drug-resistant LSCs and enhanced the sensitivity of K562/ADM cells to doxorubicin-induced apoptosis by down-regulating NF-κB pathway-mediated P-gp expression. These findings make the research area of LSCs more abundant and provide a potential therapeutic strategy for the treatment of refractory and relapsed leukemia.

Emerging role of nutritional short-chain fatty acids (SCFAs) against cancer via modulation of hematopoiesis

The understanding of gut microbiota has emerged as a significant frontier in development of strategies to maintain normal human body's homeostasis and preventing the disease development over the last decade. The composition of the gut microbiota influences the clinical benefit of immune checkpoints in patients with advanced cancer, but the mechanisms underlying this relationship are unclear. Cancer is among the leading causes of mortality worldwide. So far, there is no universal treatment for cancer and despite significant advances, a lot of improvement on cancer therapy is required. Owing to its role in preserving the host's health and maintaining cellular integrity, the human gut microbiome has recently drawn a lot of interest as a target for cancer treatment. Dietary fiber is fermented by the gut microbiota to generate short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, which are physiologically active metabolites. SCFAs can modulate the pathophysiology of the tumor environment through various critical signaling pathways. In addition, SCFAs can bind to carcinogens and other toxic chemicals, thus facilitating their biotransformation and elimination through different excretory mechanisms. This review discusses the mechanisms of action of short-chain fatty acids in modulating hematopoiesis of various immune system cells and the resultant beneficial anti-cancer effects. It also provides future perspectives on cancer therapy.

Large fluctuations in multi-scale modeling for rest hematopoiesis

Hematopoiesis is a biological phenomenon (process) of production of mature blood cells by cellular differentiation. It is based on amplification steps due to an interplay between renewal and differentiation in the successive cell types from stem cells to mature blood cells. We will study this mechanism with a stochastic point of view to explain unexpected fluctuations on the mature blood cell number, as surprisingly observed by biologists and medical doctors in a rest hematopoiesis. We consider three cell types: stem cells, progenitors and mature blood cells. Each cell type is characterized by its own dynamics parameters, the division rate and the renewal and differentiation probabilities at each division event. We model the global population dynamics by a three-dimensional stochastic decomposable branching process. We show that the amplification mechanism is given by the inverse of the small difference between the differentiation and renewal probabilities. Introducing a parameter K which scales simultaneously the size of the first component, the differentiation and renewal probabilities and the mature blood cell death rate, we describe the asymptotic behavior of the process for large K. We show that each cell type has its own size and time scales. Focusing on the third component, we prove that the mature blood cell population size, conveniently renormalized (in time and size), is expanded in an unusual way inducing large fluctuations. The proofs are based on a fine study of the different scales involved in the model and on the use of different convergence and average techniques in the proofs.

GSDME maintains hematopoietic stem cells by balancing pyroptosis and apoptosis

GSDME contains a pore-forming domain at its N-terminal region to execute pyroptosis. Our previous study has reported that forced expression of Gsdme impairs the reconstitution capacity of hematopoietic stem cells (HSCs). While, how GSDME-mediated pyroptosis regulates HSCs remains unknown. Here, we show that hematopoietic stem and progenitor cells are capable to undergo pyroptosis in response to cisplatin treatment and GSDME is one of the genes mediating such process. Gsdme -/- mice revealed no difference in the steady state of blood system while Gsdme -/- HSCs exhibited compromised reconstitution capacity due to increased apoptosis. Briefly, this study reveals that GSDME modulates HSC function by coordinating pyroptosis and apoptosis.

Regulation of Decay Accelerating Factor Primes Human Germinal Center B Cells for Phagocytosis

Germinal centers (GC) are sites for extensive B cell proliferation and homeostasis is maintained by programmed cell death. The complement regulatory protein Decay Accelerating Factor (DAF) blocks complement deposition on host cells and therefore also phagocytosis of cells. Here, we show that B cells downregulate DAF upon BCR engagement and that T cell-dependent stimuli preferentially led to activation of DAF^lo B cells. Consistent with this, a majority of light and dark zone GC B cells were DAF^lo and susceptible to complement-dependent phagocytosis, as compared with DAF^hi GC B cells. We could also show that the DAF^hi GC B cell subset had increased expression of the plasma cell marker Blimp-1. DAF expression was also modulated during B cell hematopoiesis in the human bone marrow. Collectively, our results reveal a novel role of DAF to pre-prime activated human B cells for phagocytosis prior to apoptosis.

Understanding the "SMART" features of hematopoietic stem cells and beyond

Since the huge success of bone marrow transplantation technology in clinical practice, hematopoietic stem cells (HSCs) have become the gold standard for defining the properties of adult stem cells (ASCs). Here, we describe the "self-renewal, multi-lineage differentiation, apoptosis, rest, and trafficking" or "SMART" model, which has been developed based on data derived from studies of HSCs as the most well-characterized stem cell type. Given the potential therapeutic applications of ASCs, we delineate the key characteristics of HSCs using this model and speculate on the physiological relevance of stem cells identified in other tissues. Great strides are being made in understanding the biology of ASCs, and efforts are now underway to develop safe and effective ASC-based therapies in this emerging area.

Multiple Genes Surrounding Bcl-xL, a Common Retroviral Insertion Site, Can Influence Hematopoiesis Individually or in Concert

Retroviral insertional mutagenesis (RIM) is both a relevant risk in gene therapy and a powerful tool for identifying genes that enhance the competitiveness of repopulating hematopoietic stem and progenitor cells (HSPCs). However, focusing only on the gene closest to the retroviral vector insertion site (RVIS) may underestimate the effects of RIM, as dysregulation of distal and/or multiple genes by a single insertion event was reported in several studies. As a proof of concept, we examined the common insertion site (CIS) Bcl-x_L, which revealed seven genes located within ±150 kb from the RVIS for our study. We confirmed that Bcl-x_L enhanced the competitiveness of HSPCs, whereas the Bcl-x_L neighbor Id1 hindered HSPC long-term repopulation. This negative influence of Id1 could be counteracted by co-expressing Bcl-x_L. Interestingly, >90% of early reconstituted myeloid cells were found to originate from transduced HSPCs upon simultaneous overexpression of Bcl-x_L and Id1, which implies that Bcl-x_L and Id1 can collaborate to rapidly replenish the myeloid compartment under stress conditions. To directly compare the competitiveness of HSPCs conveyed by multiple transgenes, we developed a multiple competitor competitive repopulation (MCCR) assay to simultaneously screen effects on HSPC repopulating capacity in a single mouse. The MCCR assay revealed that multiple genes within a CIS can have positive or negative impact on hematopoiesis. Furthermore, these data highlight the importance of studying multiple genes located within the proximity of an insertion site to understand complex biological effects, especially as the number of gene therapy patients increases.

A stem cell reporter based platform to identify and target drug resistant stem cells in myeloid leukemia

Intratumoral heterogeneity is a common feature of many myeloid leukemias and a significant reason for treatment failure and relapse. Thus, identifying the cells responsible for residual disease and leukemia re-growth is critical to better understanding how they are regulated. Here, we show that a knock-in reporter mouse for the stem cell gene Musashi 2 (Msi2) allows identification of leukemia stem cells in aggressive myeloid malignancies, and provides a strategy for defining their core dependencies. Specifically, we carry out a high throughput screen using Msi2-reporter blast crisis chronic myeloid leukemia (bcCML) and identify several adhesion molecules that are preferentially expressed in therapy resistant bcCML cells and play a key role in bcCML. In particular, we focus on syndecan-1, whose deletion triggers defects in bcCML growth and propagation and markedly improves survival of transplanted mice. Further, live imaging reveals that the spatiotemporal dynamics of leukemia cells are critically dependent on syndecan signaling, as loss of this signal impairs their localization, migration and dissemination to distant sites. Finally, at a molecular level, syndecan loss directly impairs integrin β7 function, suggesting that syndecan exerts its influence, at least in part, by coordinating integrin activity in bcCML. These data present a platform for delineating the biological underpinnings of leukemia stem cell function, and highlight the Sdc1-Itgβ7 signaling axis as a key regulatory control point for bcCML growth and dissemination.

B-cell lymphoma-2 inhibition and resistance in acute myeloid leukemia

Spurred by better understanding of disease biology, improvements in molecular diagnostics, and the development of targeted therapies, the treatment of acute myeloid leukemia (AML) has undergone significant evolution in recent years. Arguably, the most exciting shift has come from the success of treatment with the B-cell lymphoma-2 inhibitor venetoclax. When given in combination with a hypomethylating agent or low dose cytarabine, venetoclax demonstrates high response rates, some of which are durable. In spite of this, relapses after venetoclax treatment are common, and much interest exists in elucidating the mechanisms of resistance to the drug. Alterations in leukemic stem cell metabolism have been identified as a possible escape route, and clinical trials focusing on targeting metabolism in AML are ongoing. This review article highlights current research regarding venetoclax treatment and resistance in AML with a focus on cellular metabolism.

The ubiquitin-editing enzyme A20 controls NK cell homeostasis through regulation of mTOR activity and TNF

The study of Vetters et al. identifies the ubiquitin-modifying enzyme A20 as a critical regulator of mTOR. Loss of A20 unleashes mTOR activity and induces NK cell death, underscoring the need for a tightly controlled mTOR pathway for proper NK cell homeostasis.

The ubiquitin-editing enzyme A20 is a well-known regulator of immune cell function and homeostasis. In addition, A20 protects cells from death in an ill-defined manner. While most studies focus on its role in the TNF-receptor complex, we here identify a novel component in the A20-mediated decision between life and death. Loss of A20 in NK cells led to spontaneous NK cell death and severe NK cell lymphopenia. The few remaining NK cells showed an immature, hyperactivated phenotype, hallmarked by the basal release of cytokines and cytotoxic molecules. NK-A20^−/− cells were hypersensitive to TNF-induced cell death and could be rescued, at least partially, by a combined deficiency with TNF. Unexpectedly, rapamycin, a well-established inhibitor of mTOR, also strongly protected NK-A20^−/− cells from death, and further studies revealed that A20 restricts mTOR activation in NK cells. This study therefore maps A20 as a crucial regulator of mTOR signaling and underscores the need for a tightly balanced mTOR pathway in NK cell homeostasis.

Connexin 43 hemichannels protect bone loss during estrogen deficiency

Estrogen deficiency in postmenopausal women is a major cause of bone loss, resulting in osteopenia, osteoporosis, and a high risk for bone fracture. Connexin 43 (Cx43) hemichannels (HCs) in osteocytes play an important role in osteocyte viability, bone formation, and remodeling. We showed here that estrogen deficiency reduced Cx43 expression and HC function. To determine if functional HCs protect osteocytes and bone loss during estrogen deficiency, we adopted an ovariectomy model in wild-type (WT) and two transgenic Cx43 mice: R76W (dominant-negative mutant inhibiting only gap junction channels) and Cx43 Δ130–136 (dominant-negative mutant compromising both gap junction channels and HCs). The bone mineral density (BMD), bone structure, and histomorphometric changes of cortical and trabecular bones after ovariectomy were investigated. Our results showed that the Δ130–136 transgenic cohort had greatly decreased vertebral trabecular bone mass compared to WT and R76W mice, associated with a significant increase in the number of apoptotic osteocyte and empty lacunae. Moreover, osteoclast surfaces in trabecular and cortical bones were increased after ovariectomy in the R76W and WT mice, respectively, but not in ∆130–136 mice. These data demonstrate that impairment of Cx43 HCs in osteocytes accelerates vertebral trabecular bone loss and increase in osteocyte apoptosis, and further suggest that Cx43 HCs in osteocytes protect trabecular bone against catabolic effects due to estrogen deficiency.

Channels that form between cells and their extracellular environment help protect bone tissue from the damage wrought by low estrogen levels, a major cause of bone loss in post-menopausal women. Jean Jiang from the UT Health San Antonio and colleagues showed that depleting the estrogen hormone in mouse bone cells reduced levels of connexin 43 and impaired the protein’s ability to forms pores known as ‘hemichannels’. The researchers surgically removed the ovaries of various mouse strains to induce estrogen deficiencies. They found that transgenic mice without working hemichannels had reduced bone mass compared to normal mice or mice that could make hemichannels but lacked the ability for those channels to come together to form complete passageways. The findings highlight the importance of connexin 43 hemichannels in protecting bone tissue against osteoporosis.

The autophagy Protein Atg5 Plays a Crucial Role in the Maintenance and Reconstitution Ability of Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) in bone marrow are pluripotent cells that can constitute the hematopoiesis system through self-renewal and differentiation into immune cells and red blood cells. To ensure a competent hematopoietic system for life, the maintenance of HSCs is tightly regulated. Although autophagy, a self-degradation pathway for cell homeostasis, is essential for hematopoiesis, the role of autophagy key protein Atg5 in HSCs has not been thoroughly investigated. In this study, we found that Atg5 deficiency in hematopoietic cells causes survival defects, resulting in severe lymphopenia and anemia in mice. In addition, the absolute numbers of HSCs and multiple-lineage progenitor cells were significantly decreased, and abnormal erythroid development resulted in reduced erythrocytes in blood of Vav_Atg5^−/− mice. The proliferation of Lin⁻Sca-1⁺c-Kit⁺ HSCs was aberrant in bone marrow of Vav_Atg5^−/− mice, and mature progenitors and terminally differentiated cells were also significantly altered. Furthermore, the reconstitution ability of HSCs in bone marrow chimeric mice was significantly decreased in the presence of Atg5 deficiency in HSCs. Mechanistically, impairment of autophagy-mediated clearance of damaged mitochondria was the underlying cause of the HSC functional defects. Taken together, these results define the crucial role of Atg5 in the maintenance and the reconstitution ability of HSCs.

Enhanced expressions of FHL2 and iASPP predict poor prognosis in acute myeloid leukemia

iASPP is a negative regulator of the apoptotic function of p53, and it can enhance the ability of hematopoietic stem cells to self-renew and resist chemo- and radiation therapy. Recent study showed that iASPP could impact the proliferation and apoptosis of leukemia cells by interacting with FHL2. However, whether they have prognostic significance in acute myeloid leukemia (AML) is unknown. Eighty-four AML patients with FHL2 and iASPP expression data from The Cancer Genome Atlas database were enrolled in the study. Patients with high expressions of FHL2 and iASPP had significantly shorter event-free survival (EFS) and overall survival (OS) than patients with low expressions (P = 0.005, P = 0.003, respectively). Univariate analysis indicated that high expressions of FHL2 or iASPP were unfavorable for EFS and OS (all P < 0.05), while multivariate analysis confirmed that high FHL2 expression was an independent risk factor for EFS and OS (all P < 0.05). In patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), however, EFS and OS were not significantly different between FHL2 or iASPP high- and low-expression groups. Our results suggested that high expressions of FHL2 and iASPP were poor prognostic factors for AML, but the prognostic effect might be overcome by allo-HSCT.

Stem cell homeostasis by integral feedback through the niche

Hematopoiesis is a paradigm for tissue development and renewal from stem cells. Experiments show that the maintenance of hematopoietic stem cells (HSCs) relies on signals from niche cells. However, it is not known how the size of the HSC compartment is set. Competition by HSCs for niche access has been suggested, yet niche cells in the bone marrow outnumber HSCs. Here we propose a cooperative model of HSC homeostasis in which stem and niche cells mutually interact such that niche cells function as negative feedback regulators of HSC proliferation. This model explains puzzling experimental findings, including homeostatic recovery of the HSC compartment after irradiation versus apparent lack of recovery after HSC ablation. We show that bidirectional niche-stem cell regulation has properties of a proportional-integral feedback controller. Moreover, we predict that the outflux of differentiated cells from HSCs can be regulated by the affinity of HSCs for niche cells. Much effort has been devoted to elucidating niche cell signaling to stem cells; our theoretical insights indicate that studying the effect of stem cells on the niche may be equally important for understanding stem cell homeostasis.

Proteinase 3 Limits the Number of Hematopoietic Stem and Progenitor Cells in Murine Bone Marrow

Hematopoietic stem and progenitor cells (HSPCs) undergo self-renewal and differentiation to guarantee a constant supply of short-lived blood cells. Both intrinsic and extrinsic factors determine HSPC fate, but the underlying mechanisms remain elusive. Here, we report that Proteinase 3 (PR3), a serine protease mainly confined to granulocytes, is also expressed in HSPCs. PR3 deficiency intrinsically suppressed cleavage and activation of caspase-3, leading to expansion of the bone marrow (BM) HSPC population due to decreased apoptosis. PR3-deficient HSPCs outcompete the long-term reconstitution potential of wild-type counterparts. Collectively, our results establish PR3 as a physiological regulator of HSPC numbers. PR3 inhibition is a potential therapeutic target to accelerate and increase the efficiency of BM reconstitution during transplantation.

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Proteinase 3 (PR3) is expressed in hematopoietic stem and progenitor cells (HSPCs)

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Deficiency of PR3 leads to expansion of HSPCs in murine bone marrow

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PR3 regulates spontaneous HSPC apoptosis by cleaving and activating caspase-3

Signaling Pathways Regulating Hematopoietic Stem Cell and Progenitor Aging

Purpose of Review

Functional decline of hematopoiesis that occurs in the elderly, or in patients who receive therapies that trigger cellular senescence effects, results in a progressive reduction in the immune response and an increased incidence of myeloid malignancy. Intracellular signals in hematopoietic stem cells and progenitors (HSC/P) mediate systemic, microenvironment, and cell-intrinsic effector aging signals that induce their decline. This review intends to summarize and critically review our advances in the understanding of the intracellular signaling pathways responsible for HSC decline during aging and opportunities for intervention.

Recent Findings

For a long time, aging of HSC has been thought to be an irreversible process imprinted in stem cells due to the cell intrinsic nature of aging. However, recent murine models and human correlative studies provide evidence that aging is associated with molecular signaling pathways, including oxidative stress, metabolic dysfunction, loss of polarity and an altered epigenome. These signaling pathways provide potential targets for prevention or reversal of age-related changes.

Summary

Here we review our current understanding of the signalling pathways that are differentially activated or repressed during HSC/P aging, focusing on the oxidative, metabolic, biochemical and structural consequences downstream, and cell-intrinsic, systemic, and environmental influences.

In vivo selection with lentiviral expression of Bcl2T69A/S70A/S87A mutant in hematopoietic stem cell-transplanted mice

Current in vivo selections for hematopoietic stem cell (HSC)-based gene therapy are drug dependent and not without risk of cytotoxicity or tumorigenesis. We developed a new in vivo selection system with the non-phosphorylatable Bcl2 mutant Bcl2^{T69A/S70A/S87A} (Bcl2^AAA), which makes in vivo selection drug independent and without risk of cytotoxicity or tumorigenesis. We demonstrated in HSC-transplanted mice that Bcl2^AAA facilitated efficient in vivo selection in the absence of any exogenously applied drugs under both myeloablative and non-myeloablative conditioning. In mice transplanted with retrovirally transduced sca-1-positive bone marrow cells, the marked cell level increased from 26.38% of input transduced cells to 92.61 ± 0.95% of peripheral blood cells for myeloablative transplantation or to 37.82 ± 6.35% for non-myeloablative transplantation 6 months after transplantation. Bcl2^AAA did not induce tumorigenesis and does not influence hematopoiesis and the function of the reconstituted blood system. However, the high-level constitutive expression of Bcl2^AAA mediated by retroviral vector induced exhaustion of the marked cells after tertiary transplantation. Fortunately, low-level constitutive expression of Bcl2^AAA driven by an internal promoter in lentiviral vector could both maintain the marked cell level (24.13 ± 5.27%, 27.17 ± 5.51%, 24.33 ± 5.08%, and 22.07 ± 4.44% for primary, secondary, tertiary, and quaternary recipients) and avoid the exhaustion of the marked cells even in quaternary recipients. Importantly, the low-level constitutive expression of Bcl2^AAA did not induce tumorigenesis. Thus, the in vivo selection employing the low-level constitutive expression of Bcl2^AAA provides a general platform which is relevant for widespread applications of gene therapy.

MicroRNA-30 inhibits antiapoptotic factor Mcl-1 in mouse and human hematopoietic cells after radiation exposure

We previously reported that microRNA-30 (miR-30) expression was initiated by radiation-induced proinflammatory factor IL-1β and NFkB activation in mouse and human hematopoietic cells. However, the downstream effectors of miR-30 and its specific role in radiation-induced cell death are not well understood. In the present study, we evaluated effects of radiation on miR-30 expression and activation of intrinsic apoptotic pathway Bcl-2 family factors in in vivo mouse and in vitro human hematopoietic cells. CD2F1 mice and human CD34+ cells were exposed to different doses of gamma-radiation. In addition to survival studies, mouse blood, bone marrow (BM) and spleen cells and human CD34+ cells were collected at 4 h, and 1, 3 and 4 days after irradiation to determine apoptotic and stress response signals. Our results showed that mouse serum miR-30, DNA damage marker γ-H2AX in BM, and Bim, Bax and Bak expression, cytochrome c release, and caspase-3 and -7 activation in BM and/or spleen cells were upregulated in a radiation dose-dependent manner. Antiapoptotic factor Mcl-1 was significantly downregulated, whereas Bcl-2 was less changed or unaltered in the irradiated mouse cells and human CD34+ cells. Furthermore, a putative miR-30 binding site was found in the 3′ UTR of Mcl-1 mRNA. miR-30 directly inhibits the expression of Mcl-1 through binding to its target sequence, which was demonstrated by a luciferase reporter assay, and the finding that Mcl-1 was uninhibited by irradiation in miR-30 knockdown CD34+ cells. Bcl-2 expression was not affected by miR-30. Our data suggest miR-30 plays a key role in radiation-induced apoptosis through directly targeting Mcl-1in hematopoietic cells.

β-Arrestin2 mediates progression of murine primary myelofibrosis

Primary myelofibrosis is a myeloproliferative neoplasm associated with significant morbidity and mortality, for which effective therapies are lacking. β-Arrestins are multifunctional adaptor proteins involved in developmental signaling pathways. One isoform, β-arrestin2 (βarr2), has been implicated in initiation and progression of chronic myeloid leukemia, another myeloproliferative neoplasm closely related to primary myelofibrosis. Accordingly, we investigated the relationship between βarr2 and primary myelofibrosis. In a murine model of MPLW515L-mutant primary myelofibrosis, mice transplanted with donor βarr2-knockout (βarr2-/-) hematopoietic stem cells infected with MPL-mutant retrovirus did not develop myelofibrosis, whereas controls uniformly succumbed to disease. Although transplanted βarr2-/- cells homed properly to marrow, they did not repopulate long-term due to increased apoptosis and decreased self-renewal of βarr2-/- cells. In order to assess the effect of acute loss of βarr2 in established primary myelofibrosis in vivo, we utilized a tamoxifen-induced Cre-conditional βarr2-knockout mouse. Mice that received Cre (+) donor cells and developed myelofibrosis had significantly improved survival compared with controls. These data indicate that lack of antiapoptotic βarr2 mediates marrow failure of murine hematopoietic stem cells overexpressing MPLW515L. They also indicate that βarr2 is necessary for progression of primary myelofibrosis, suggesting that it may serve as a novel therapeutic target in this disease.

Anti-apoptotic BCL-2 family members in development

Almost 30 years ago it was first appreciated that anti-apoptotic B-cell lymphoma-2 (BCL-2) prevents the induction of apoptosis not only in malignant cells, but also in normal cellular lineages. This critical observation has rapidly evolved from merely identifying new BCL-2 family members to understanding how their biochemical interactions trigger the cell death process, and, more recently, to pharmacological inhibition of anti-apoptotic BCL-2 function in disease. Indeed, the proper regulation of apoptosis is important in many aspects of life including development, homeostasis, and disease biology. To better understand these processes, scientists have used many tools to assess the contribution of individual anti-apoptotic BCL-2 family members. This review will focus on the prominent roles for BCL-2 and other pro-survival family members in promoting the development of mammals during early embryogenesis, neurogenesis, and hematopoiesis.

How One Thing Led to Another

I started research in high school, experimenting on immunological tolerance to transplantation antigens. This led to studies of the thymus as the site of maturation of T cells, which led to the discovery, isolation, and clinical transplantation of purified hematopoietic stem cells (HSCs). The induction of immune tolerance with HSCs has led to isolation of other tissue-specific stem cells for regenerative medicine. Our studies of circulating competing germline stem cells in colonial protochordates led us to document competing HSCs. In human acute myelogenous leukemia we showed that all preleukemic mutations occur in HSCs, and determined their order; the final mutations occur in a multipotent progenitor derived from the preleukemic HSC clone. With these, we discovered that CD47 is an upregulated gene in all human cancers and is a "don't eat me" signal; blocking it with antibodies leads to cancer cell phagocytosis. CD47 is the first known gene common to all cancers and is a target for cancer immunotherapy.

Necdin modulates leukemia-initiating cell quiescence and chemotherapy response

Acute myeloid leukemia (AML) is a devastating illness which carries a very poor prognosis, with most patients living less than 18 months. Leukemia relapse may occur because current therapies eliminate proliferating leukemia cells but fail to eradicate quiescent leukemia-initiating cells (LICs) that can reinitiate the disease after a period of latency. While we demonstrated that p53 target gene Necdin maintains hematopoietic stem cell (HSC) quiescence, its roles in LIC quiescence and response to chemotherapy are unclear. In this study, we utilized two well-established murine models of human AML induced by MLL-AF9 or AML1-ETO9a to determine the role of Necdin in leukemogenesis. We found that loss of Necdin decreased the number of functional LICs and enhanced myeloid differentiation in vivo, leading to delayed development of leukemia induced by MLL-AF9. Importantly, Necdin null LICs expressing MLL-AF9 were less quiescent than wild-type LICs. Further, loss of Necdin enhanced the response of MLL-AF9⁺ leukemia cells to chemotherapy treatment, manifested by decreased viability and enhanced apoptosis. We observed decreased expression of Bcl2 and increased expression of p53 and its target gene Bax in Necdin null leukemia cells following chemotherapy treatment, indicating that p53-dependent apoptotic pathways may be activated in the absence of Necdin. In addition, we found that loss of Necdin decreased the engraftment of AML1-ETO9a⁺ hematopoietic stem and progenitor cells in transplantation assays. However, Necdin-deficiency did not affect the response of AML1-ETO9a⁺ hematopoietic cells to chemotherapy treatment. Thus, Necdin regulates leukemia-initiating cell quiescence and chemotherapy response in a context-dependent manner. Our findings suggest that pharmacological inhibition of Necdin may hold potential as a novel therapy for leukemia patients with MLL translocations.

The Implications and Future Perspectives of Nanomedicine for Cancer Stem Cell Targeted Therapies

Cancer stem cells (CSCs) are believed to exhibit distinctive self-renewal, proliferation, and differentiation capabilities, and thus play a significant role in various aspects of cancer. CSCs have significant impacts on the progression of tumors, drug resistance, recurrence and metastasis in different types of malignancies. Due to their primary role, most researchers have focused on developing anti-CSC therapeutic strategies, and tremendous efforts have been put to explore methods for selective eradication of these therapeutically resistant CSCs. In recent years, many reports have shown the use of CSCs-specific approaches such as ATP-binding cassette (ABC) transporters, blockade of self-renewal and survival of CSCs, CSCs surface markers targeted drugs delivery and eradication of the tumor microenvironment. Also, various therapeutic agents such as small molecule drugs, nucleic acids, and antibodies are said to destroy CSCs selectively. Targeted drug delivery holds the key to the success of most of the anti-CSCs based drugs/therapies. The convention CSCs-specific therapeutic agents, suffer from various problems. For instance, limited water solubility, small circulation time and inconsistent stability of conventional therapeutic agents have significantly limited their efficacy. Recent advancement in the drug delivery technology has demonstrated that specially designed nanocarrier-based drug delivery approaches (nanomedicine) can be useful in delivering sufficient amount of drug molecules even in the most interiors of CSCs niches and thus can overcome the limitations associated with the conventional free drug delivery methods. The nanomedicine has also been promising in designing effective therapeutic regime against pump-mediated drug resistance (ATP-driven) and reduces detrimental effects on normal stem cells. Here we focus on the biological processes regulating CSCs' drug resistance and various strategies developed so far to deal with them. We also review the various nanomedicine approaches developed so far to overcome these CSCs related issues and their future perspectives.

Cancer progression by reprogrammed BCAA metabolism in myeloid leukaemia

Reprogrammed cellular metabolism is a common characteristic observed in various cancers. However, whether metabolic changes directly regulate cancer development and progression remains poorly understood. Here we show that BCAT1, a cytosolic aminotransferase for branched-chain amino acids (BCAAs), is aberrantly activated and functionally required for chronic myeloid leukaemia (CML) in humans and in mouse models of CML. BCAT1 is upregulated during progression of CML and promotes BCAA production in leukaemia cells by aminating the branched-chain keto acids. Blocking BCAT1 gene expression or enzymatic activity induces cellular differentiation and impairs the propagation of blast crisis CML both in vitro and in vivo. Stable-isotope tracer experiments combined with nuclear magnetic resonance-based metabolic analysis demonstrate the intracellular production of BCAAs by BCAT1. Direct supplementation with BCAAs ameliorates the defects caused by BCAT1 knockdown, indicating that BCAT1 exerts its oncogenic function through BCAA production in blast crisis CML cells. Importantly, BCAT1 expression not only is activated in human blast crisis CML and de novo acute myeloid leukaemia, but also predicts disease outcome in patients. As an upstream regulator of BCAT1 expression, we identified Musashi2 (MSI2), an oncogenic RNA binding protein that is required for blast crisis CML. MSI2 is physically associated with the BCAT1 transcript and positively regulates its protein expression in leukaemia. Taken together, this work reveals that altered BCAA metabolism activated through the MSI2-BCAT1 axis drives cancer progression in myeloid leukaemia.

T11TS repress gliomagenic apoptosis of bone marrow hematopoietic stem cells

Combating gliomagenic global immunosuppression is one of the emerging key for improving prognosis in malignant glioma. Apoptosis plays a pivotal role within the adult hematopoietic system particularly in regulating the cells of immune system. Gliomagenic regulation of apoptotic mediators within bone marrow milieu has not been elucidated. We previously demonstrated that administration of membrane glycopeptides T11 target structure (T11TS) not only rejuvenate bone marrow hematopoietic stem cells (BMHSCs) from glioma mediated hibernation by inhibiting gliomagenic overexpression of Ang-1/Tie-2 but also stimulate glioma mediated diminution of expression CD34, c-kit, and Sca-1 markers. In the present study, we investigated the impact of glioma on apoptotic signaling cascades of BMHSCs and consequences following T11TS therapy. Bone marrow smear and Annexin V staining confirm gliomagenic acceleration of apoptotic fate of BMHSCs whereas T11TS treatment in glioma-bearing rats disrupted apoptosis of BMHSCs. Flowcytometry, immunoblotting, and immunofluorescence imagining results revealed multi potent T11TS not only significantly downregulates gliomagenic overexpression of Fas, Fas L, Bid, and caspase-8, the pro-apoptotic extrinsic mediators but also strongly inhibits cytosolic release of cytochrome-c, Apf-1, and Bax to deactivate gliomagenic caspase-9, 3 the key intrinsic apoptotic mediators followed by up modulation of anti-apoptotic Bcl-2 in glioma associated HSCs. T11TS is also able to diminish the perforin-granzyme B mediated apoptotic verdict of BMHSCs during gliomagenesis. The anti-apoptotic action of T11TS on glioma associated BMHSCs provide a crucial insight into how T11TS exerts its immunomodulatory action against glioma mediated immune devastation.

The early secreted antigenic target of 6 kD of Mycobacterium tuberculosis inhibits the proliferation and differentiation of human peripheral blood CD34+ cells

Abnormalities in hematopoiesis are common in tuberculosis patients and highly prevalent in AIDS patients with tuberculosis coinfection. To explore the potential role of the early secreted antigenic target of 6-kD (ESAT-6) of Mycobacterium tuberculosis (Mtb) in abnormal hematopoiesis in tuberculosis, we studied the effect of ESAT-6 on proliferation and differentiation of in vitro-expanded CD34⁺ cells isolated from the peripheral blood of the healthy donors. ESAT-6 but not control protein antigen 85A (Ag85A) of Mtb inhibited the proliferation of CD34⁺ cell derived peripheral blood stem/progenitor cells (PBSPC) in a dose dependent manner when determined by MTT-assay. ESAT-6 but not Ag85A reduced the number of colony forming cells (CFC) of PBSPC by 60-90% as determined by CFC assay by incubation of CD34⁺ cells in a semi-solid cellulose media in the presence of cytokine cocktail for two weeks. ESAT-6 but not Ag85A increased the percentages of the Annexin-V positive cells and enhanced the cleavage of caspase-3 in PBSPC in a time and dose dependent manner as determined by flow cytometry and Western blot analysis, respectively. ESAT-6 also inhibited murine bone marrow derived non-adherent cell proliferation in response to granulocyte-macrophage colony stimulating factor treatment. We conclude that ESAT-6, an essential virulence factor of Mtb, may contribute to the abnormal hematopoiesis of tuberculosis patients by inhibiting the proliferation and differentiation of hematopoietic cells via apoptosis.

Large-Scale Exome-wide Association Analysis Identifies Loci for White Blood Cell Traits and Pleiotropy with Immune-Mediated Diseases

White blood cells play diverse roles in innate and adaptive immunity. Genetic association analyses of phenotypic variation in circulating white blood cell (WBC) counts from large samples of otherwise healthy individuals can provide insights into genes and biologic pathways involved in production, differentiation, or clearance of particular WBC lineages (myeloid, lymphoid) and also potentially inform the genetic basis of autoimmune, allergic, and blood diseases. We performed an exome array-based meta-analysis of total WBC and subtype counts (neutrophils, monocytes, lymphocytes, basophils, and eosinophils) in a multi-ancestry discovery and replication sample of ∼157,622 individuals from 25 studies. We identified 16 common variants (8 of which were coding variants) associated with one or more WBC traits, the majority of which are pleiotropically associated with autoimmune diseases. Based on functional annotation, these loci included genes encoding surface markers of myeloid, lymphoid, or hematopoietic stem cell differentiation (CD69, CD33, CD87), transcription factors regulating lineage specification during hematopoiesis (ASXL1, IRF8, IKZF1, JMJD1C, ETS2-PSMG1), and molecules involved in neutrophil clearance/apoptosis (C10orf54, LTA), adhesion (TNXB), or centrosome and microtubule structure/function (KIF9, TUBD1). Together with recent reports of somatic ASXL1 mutations among individuals with idiopathic cytopenias or clonal hematopoiesis of undetermined significance, the identification of a common regulatory 3' UTR variant of ASXL1 suggests that both germline and somatic ASXL1 mutations contribute to lower blood counts in otherwise asymptomatic individuals. These association results shed light on genetic mechanisms that regulate circulating WBC counts and suggest a prominent shared genetic architecture with inflammatory and autoimmune diseases.

Image-based detection and targeting of therapy resistance in pancreatic adenocarcinoma

Pancreatic intraepithelial neoplasia (PanIN) is a premalignant lesion that can progress to pancreatic ductal adenocarcinoma, a highly lethal malignancy marked by its late stage at clinical presentation and profound drug resistance¹. The genomic alterations that commonly occur in pancreatic cancer include activation of KRAS2 and inactivation of p53, and SMAD4^2-4. To date, however, it has been challenging to target these pathways therapeutically; thus the search for other key mediators of pancreatic cancer growth remains an important endeavor. Here we show that the stem cell determinant Musashi (Msi) is a critical element of pancreatic cancer progression in both genetic models and patient derived xenografts. Specifically, we developed Msi reporter mice that allowed image based tracking of stem cell signals within cancers, revealing that Msi expression rises as PanIN progresses to adenocarcinoma, and that Msi-expressing cells are key drivers of pancreatic cancer: they preferentially harbor the capacity to propagate adenocarcinoma, are enriched in circulating tumor cells, and are markedly drug resistant. This population could be effectively targeted by deletion of either Msi1 or Msi2, which led to a striking defect in PanIN progression to adenocarcinoma and an improvement in overall survival. Msi inhibition also blocked the growth of primary patient-derived tumors, suggesting that this signal is required for human disease. To define the translational potential of this work we developed antisense oligonucleotides against Msi; these showed reliable tumor penetration, uptake and target inhibition, and effectively blocked pancreatic cancer growth. Collectively, these studies highlight Msi reporters as a unique tool to identify therapy resistance, and define Msi signaling as a central regulator of pancreatic cancer.

Mesenchymal Wnt/β-Catenin Signaling Controls Epithelial Stem Cell Homeostasis in Teeth by Inhibiting the Antiapoptotic Effect of Fgf10

Continuous growth of rodent incisors relies on epithelial stem cells (SCs) located in the SC niche called labial cervical loop (LaCL). Here, we found a population of apoptotic cells residing in a specific location of the LaCL in mouse incisor. Activated Caspase 3 and Caspase 9, expressed in this location colocalized in part with Lgr5 in putative SCs. The addition of Caspase inhibitors to incisors ex vivo resulted in concentration dependent thickening of LaCL. To examine the role of Wnt signaling in regulation of apoptosis, we exposed the LaCL of postnatal day 2 (P2) mouse incisor ex vivo to BIO, a known activator of Wnt/β-catenin signaling. This resulted in marked thinning of LaCL as well as enhanced apoptosis. We found that Wnt/β-catenin signaling was intensely induced by BIO in the mesenchyme surrounding the LaCL, but, unexpectedly, no β-catenin activity was detected in the LaCL epithelium either before or after BIO treatment. We discovered that the expression of Fgf10, an essential growth factor for incisor epithelial SCs, was dramatically downregulated in the mesenchyme around BIO-treated LaCL, and that exogenous Fgf10 could rescue the thinning of the LaCL caused by BIO. We conclude that the homeostasis of the epithelial SC population in the mouse incisor depends on a proper rate of apoptosis and that this apoptosis is controlled by signals from the mesenchyme surrounding the LaCL. Fgf10 is a key mesenchymal signal limiting apoptosis of incisor epithelial SCs and its expression is negatively regulated by Wnt/β-catenin. Stem Cells 2015;33:1670-1681.