WNT signaling modulates the diversification of hematopoietic cells

Deciphering avian hematopoietic stem cells by surface marker screening and gene expression profiling

BACKGROUND

Avian species have played a pivotal role in developmental hematopoiesis research, leading to numerous critical discoveries. Avian influenza, particularly the H5N1 strain, poses a significant threat to poultry and has zoonotic potential for humans. Infections often result in abnormal hematologic profiles, highlighting the complex interplay between avian diseases and hematopoiesis. Many avian diseases can suppress immune cells in the bone marrow (BM), impacting immune responses. Studying hematopoietic stem cells (HSCs) in avian BM is crucial for understanding these processes and developing effective vaccines and protection strategies for both avian and human health.

METHODS

This study adapted methods from mouse studies to isolate avian HSCs as Lineage-negative (Lin-) cells. These isolated cells were further identified as Lin-Sca1+c-Kit+ (LSK) and were found to be more prevalent than in control groups. RT-PCR analyses were conducted, showing that genes like MEIS1 and TSC1 were upregulated, while SIRT1, FOXO1, and AHR were downregulated in these stem cells. Screening for LSK markers revealed ten unique surface antigens in the Sca1+c-Kit+ cell populations, including highly enriched antigens such as CD178, CD227, and CD184. Additionally, studies on quail HSCs demonstrated that similar labeling techniques were effective in quail BM.

RESULTS

The research demonstrated that the identification of avian HSC-specific surface antigens provides valuable insights into the pathogenesis of avian influenza and other diseases, enhancing our understanding of how these diseases suppress HSC function. Notably, the upregulation of MEIS1 and TSC1 genes in LSK cells underscores their critical roles in regulating hematopoietic processes. Conversely, the downregulation of SIRT1, FOXO1, and AHR genes provides important clues about their roles in differentiation and immune response mechanisms.

DISCUSSION

The findings of this study deepen our understanding of the effects of avian diseases on the immune system by identifying surface markers specific to avian HSCs. The suppression of HSC function by pathogens such as influenza highlights the importance of understanding these cells in developing targeted vaccines. These results represent a significant step towards improving global health security by mitigating risks associated with avian pathogens.

Wnt signaling: Modulating tumor-associated macrophages and related immunotherapeutic insights

Wnt signaling pathways are highly conserved cascades that mediate multiple biological processes through canonical or noncanonical pathways, from embryonic development to tissue maintenance, but they also contribute to the pathogenesis of numerous cancers. Recent studies have revealed that Wnt signaling pathways critically control the interplay between cancer cells and tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) and potentially impact the efficacy of cancer immunotherapy. In this review, we summarize the evidence that Wnt signaling pathways boost the maturation and infiltration of macrophages for immune surveillance in the steady state but also polarize TAMs toward immunosuppressive M2-like phenotypes for immune escape in the TME. Both cancer cells and TAMs utilize Wnt signaling to transmit signals, and this interaction is crucial for the carcinogenesis and progression of common solid cancers, such as colorectal, gastric, hepatocellular, breast, thyroid, prostate, kidney, and lung cancers; osteosarcoma; and glioma. Specifically, compared with those in solid cancers, Wnt signaling pathways play a distinct role in the pathogenesis of leukemia. Efforts to develop Wnt-based drugs for cancer treatment are still ongoing, and some indeed enhance the anticancer immune response. We believe that the combination of Wnt signaling-based therapy with conventional or immune therapies is a promising therapeutic approach and can facilitate personalized treatment for most cancers.

Three-Dimensional Avian Hematopoietic Stem Cell Cultures as a Model for Studying Disease Pathogenesis

Three-dimensional (3D) cell culture is attracting increasing attention today because it can mimic tissue environments and provide more realistic results than do conventional cell cultures. On the other hand, very little attention has been given to using 3D cell cultures in the field of avian cell biology. Although mimicking the bone marrow niche is a classic challenge of mammalian stem cell research, experiments have never been conducted in poultry on preparing in vitro the bone marrow niche. It is well known, however, that all diseases cause immunosuppression and target immune cells and their development. Hematopoietic stem cells (HSC) reside in the bone marrow and constitute a source for immune cells of lymphoid and myeloid origins. Disease prevention and control in poultry are facing new challenges, such as greater use of alternative breeding systems and expanding production of eggs and chicken meat in developing countries. Moreover, the COVID-19 pandemic will draw greater attention to the importance of disease management in poultry because poultry constitutes a rich source of zoonotic diseases. For these reasons, and because they will lead to a better understanding of disease pathogenesis, in vivo HSC niches for studying disease pathogenesis can be valuable tools for developing more effective disease prevention, diagnosis, and control. The main goal of this review is to summarize knowledge about avian hematopoietic cells, HSC niches, avian immunosuppressive diseases, and isolation of HSC, and the main part of the review is dedicated to using 3D cell cultures and their possible use for studying disease pathogenesis with practical examples. Therefore, this review can serve as a practical guide to support further preparation of 3D avian HSC niches to study the pathogenesis of avian diseases.

Wnt-5A/B Signaling in Hematopoiesis throughout Life

Wnt signaling is well-known to play major roles in the hematopoietic system, from embryogenesis to aging and disease. In addition to the main β-catenin-dependent pathway, it is now clear that Wnt5a and the structurally related Wnt5b are essential for hematopoiesis, bone marrow colonization and the final steps of hematopoietic stem cell (HSC) maturation via β-catenin-independent signaling. Wnt5a and Wnt5b ligands prevent hematopoietic exhaustion (by maintaining quiescent, long-term HSCs), induce the proliferation of progenitors, and guide myeloid development, in addition to being involved in the development of aging-related alterations. The aim of this review is to summarize the current knowledge on these roles of Wnt5a and Wn5b signaling in the hematopoietic field.

Divergent effects of Wnt5b on IL-3- and GM-CSF-induced myeloid differentiation

The multiple specialized cell types of the hematopoietic system originate from differentiation of hematopoietic stem cells and progenitors (HSPC), which can generate both lymphoid and myeloid lineages. The myeloid lineage is preferentially maintained during ageing, but the mechanisms that contribute to this process are incompletely understood. Here, we studied the roles of Wnt5a and Wnt5b, ligands that have previously been linked to hematopoietic stem cell ageing and that are abundantly expressed by both hematopoietic progenitors and bone-marrow derived niche cells. Whereas Wnt5a had no major effects on primitive cell differentiation, Wnt5b had profound and divergent effects on cytokine-induced myeloid differentiation. Remarkably, while IL-3- mediated myeloid differentiation was largely repressed by Wnt5b, GM-CSF-induced myeloid differentiation was augmented. Furthermore, in the presence of IL-3, Wnt5b enhanced HSPC self-renewal, whereas in the presence ofGM-CSF, Wnt5b accelerated differentiation, leading to progenitor cell exhaustion. Our results highlight discrepancies between IL-3 and GM-CSF, and reveal novel effects of Wnt5b on the hematopoietic system.

Macrophages as a Source and Recipient of Wnt Signals

Macrophages are often viewed through the lens of their core functions, but recent transcriptomic studies reveal them to be largely distinct across tissue types. While these differences appear to be shaped by their local environment, the key signals that drive these transcriptional differences remain unclear. Since Wnt signaling plays established roles in cell fate decisions, and tissue patterning during development and tissue repair after injury, we consider evidence that Wnt signals both target and are affected by macrophage functions. We propose that the Wnt gradients present in developing and adult tissues effectively shape macrophage fates and phenotypes. We also highlight evidence that macrophages, through an ability to dispatch Wnt signals, may couple tissue debridement and matrix remodeling with stem cell activation and tissue repair.

MYCN is a novel oncogenic target in adult B-ALL that activates the Wnt/β-catenin pathway by suppressing DKK3

Dickkopf‐3 (DKK3) is frequently down‐regulated by promoter hypermethylation and is closely associated with a poor prognosis in many cancers. Our previous studies have shown that miR‐708 down‐regulates DKK3 at the post‐transcriptional level in B‐ALL. However, whether transcriptional mechanisms lead to DKK3 silencing remains unclear. Here, we analysed the promoter regions of DKK3 by bioinformatics and found binding sites for MYCN. A dual‐luciferase reporter gene assay and ChIP experiments revealed that MYCN negatively regulates DKK3 at the transcriptional level in B‐ALL cell lines, and using bisulphite sequencing PCR, we affirmed that MYCN has no effect on the methylation of the DKK3 promoter. MYCN silencing in B‐ALL cells resulted in reduced cell proliferation, increased apoptosis and G1 phase arrest. Treatment with MYCN siRNA or 5‐aza‐2′‐deoxycytidine (5‐AdC), a demethylating agent, significantly increased the levels of DKK3 mRNA and protein and decreased the protein levels of p‐GSK3β and nuclear β‐catenin, which indicates inhibition of the Wnt/β‐catenin pathway in vitro. MYCN knockdown significantly decreased the tumorigenic capacity of Nalm6 cells, which restored DKK3 levels and inhibited the Wnt/β‐catenin pathway in vivo. Our study provides an increased understanding of adult B‐ALL pathogenesis, which may be beneficial to the development of effective prognostic markers or therapeutic targets.

Wnt7a induces a unique phenotype of monocyte-derived macrophages with lower phagocytic capacity and differential expression of pro- and anti-inflammatory cytokines

The variation of macrophage functions suggests the involvement of multiple signalling pathways in fine tuning their differentiation. Macrophages that originate from monocytes in the blood migrate to tissue in response to homeostatic or 'danger' signals and undergo substantial morphological and functional modifications to meet the needs of the dominant signals in the microenvironment. Wnts are secreted glycoproteins that play a significant role in organ and cell differentiation, yet their impact on monocyte differentiation is not clear. In this study, we assessed the role of Wnt1 and Wnt7a on the differentiation of monocytes and the subsequent phenotype and function of monocyte-derived macrophages (MDMs). We show that Wnt7a decreased the expression of CD14, CD11b, CD163 and CD206, whereas Wnt1 had no effect. The Wnt7a effect on CD11b was also observed in the brain and spleen of Wnt7a^-/- adult brain mouse tissue and in embryonic Wnt7a^-/- tissue. Wnt7a reduced the phagocytic capacity of M-MDMs, decreased interleukin-10 (IL-10) and IL-12 secretion and increased IL-6 secretion. Collectively, these findings demonstrate that Wnt7a generates an MDM phenotype with both pro-inflammatory and alternative MDM cytokine profiles and reduced phagocytic capacity. As such, Wnt7a can have a significant impact on macrophage responses in health and disease.

Functionally and phenotypically distinct subpopulations of marrow stromal cells are fibroblast in origin and induce different fates in peripheral blood monocytes

Marrow stromal cells constitute a heterogeneous population of cells, typically isolated after expansion in culture. In vivo, stromal cells often exist in close proximity or in direct contact with monocyte-derived macrophages, yet their interaction with monocytes is largely unexplored. In this report, isolated CD146(+) and CD146(-) stromal cells, as well as immortalized cell lines representative of each (designated HS27a and HS5, respectively), were shown by global DNase I hypersensitive site mapping and principal coordinate analysis to have a lineage association with marrow fibroblasts. Gene expression profiles generated for the CD146(+) and CD146(-) cell lines indicate significant differences in their respective transcriptomes, which translates into differences in secreted factors. Consequently, the conditioned media (CM) from these two populations induce different fates in peripheral blood monocytes. Monocytes incubated in CD146(+) CM acquire a tissue macrophage phenotype, whereas monocytes incubated in CM from CD146(-) cells express markers associated with pre-dendritic cells. Importantly, when CD14(+) monocytes are cultured in contact with the CD146(+) cells, the combined cell populations, assayed as a unit, show increased levels of transcripts associated with organismal development and hematopoietic regulation. In contrast, the gene expression profile from cocultures of monocytes and CD146(-) cells does not differ from that obtained when monocytes are cultured with CD146(-) CM. These in vitro results show that the CD146(+) marrow stromal cells together with monocytes increase the expression of genes relevant to hematopoietic regulation. In vivo relevance of these data is suggested by immunohistochemistry of marrow biopsies showing juxtaposed CD146(+) cells and CD68(+) cells associated with these upregulated proteins.

Down-regulation of canonical and up-regulation of non-canonical Wnt signalling in the carcinogenic process of squamous cell lung carcinoma

The majority of lung cancers (LC) belong to the non-small cell lung carcinoma (NSCLC) type. The two main NSCLC sub-types, namely adenocarcinoma (AC) and squamous cell carcinoma (SCC), respond differently to therapy. Whereas the link between cigarette smoke and lung cancer risk is well established, the relevance of non-canonical Wnt pathway up-regulation detected in SCC remains poorly understood. The present study was undertaken to investigate further the molecular events in canonical and non-canonical Wnt signalling during SCC development. A total of 20 SCC and AC samples with matched non-cancerous controls were obtained after surgery. TaqMan array analysis confirmed up-regulation of non-canonical Wnt5a and Wnt11 and identified down-regulation of canonical Wnt signalling in SCC samples. The molecular changes were tested in primary small airway epithelial cells (SAEC) and various lung cancer cell lines (e.g. A549, H157, etc). Our studies identified Wnt11 and Wnt5a as regulators of cadherin expression and potentiated relocation of β-catenin to the nucleus as an important step in decreased cellular adhesion. The presented data identifies additional details in the regulation of SCC that can aid identification of therapeutic drug targets in the future.

Efficient cardiomyogenic differentiation of bone marrow mesenchymal stromal cells by combination of Wnt11 and bone morphogenetic protein 2

Wnt11 and bone morphogenetic protein 2 (BMP-2) are key signaling factors for stem cell differentiation into functional cardiomyocytes (CMs). In this study, we elucidate the biological effect of BMP-2 and Wnt11 on bone marrow mesenchymal stromal cells (BM-MSCs) that differentiate into myocardial-like cells in a simulated myocardial microenvironment in vitro. A cell co-culture system was established with recombinant Wnt11 treatment of NIH/3T3 cells and CMs. BMP-2 was added in a diverse schedule to induce cardiomyogenic differentiation of BM-MSCs co-cultured under various conditions. The levels of cardiac-specific markers Nkx2.5, α-myosin heavy chain ( α-MHC), β-myosin heavy chain ( β-MHC) and cardiac troponin I (cTnI) were determined by reverse transcriptase polymerase chain reaction and immunocytochemistry to evaluate cardiomyogenic differentiation. Wnt11 or BMP-2 used on their own to differentiate BM-MSCs resulted in no expression of α-MHC and cTnI. Wnt11 alone in a myocardial microenvironment enhanced cardiomyogenic differentiation. BMP-2 demonstrated a dose-dependent effect on BM-MSC differentiation into myocardial-like cells. Addition of BMP to BM-MSCs at various time points resulted in varying effects on cardiomyogenic differentiation. The combination of Wnt11 and BMP-2 treatment in a temporal manner significantly enhanced cardiomyogenic differentiation of BM-MSCs, with high expressions of α-MHC, β-MHC, Nkx2.5 and cTnI upon co-culture with CMs. Our study demonstrates that the combination of Wnt11 and BMP-2 effectively promotes cardiomyogenic differentiation of BM-MSCs in vitro. The synergistic effect of Wnt11 and BMP-2 on the cardiomyogenic differentiation of BM-MSCs is further enhanced in a myocardial microenvironment.

Attenuated Wnt/β-catenin signalling mediates methotrexate chemotherapy-induced bone loss and marrow adiposity in rats

Cancer chemotherapy often causes significant bone loss, marrow adiposity and haematopoietic defects, yet the underlying mechanisms and recovery potential remain unclear. Wnt/β-catenin signalling is integral to the regulation of osteogenesis, adipogenesis and haematopoiesis; using a rat model, the current study investigated roles of this signalling pathway in changes to bone marrow stromal and haematopoietic cell differentiation after chemotherapy with methotrexate (MTX), a commonly used antimetabolite. MTX treatment in rats (5 daily administrations at 0.75 mg/kg) has previously been found to decrease bone volume and increase marrow fat, which was associated with increased osteoclastogenesis in haematopoietic cells and with an osteogenesis to adipogenesis switch in bone marrow stromal cells of treated rats. In the current study, on day 6 after the first MTX dose we found that accompanying these changes as well as a suppressed haematopoietic cellularity but increased granulocyte/macrophage differentiation potential, there was an increase in mRNA expression of Wnt antagonists sFRP-1 and Dkk-1 in bone, a reduction in nuclear β-catenin protein in bone marrow stromal cells, and decreased mRNA levels of β-catenin target genes lef-1, cyclin D1 and survivin, suggesting reduced activation of Wnt/β-catenin signalling in the bone during MTX-induced damage. Concurrent administration of BIO, a GSK-3β inhibitor that stabilises β-catenin, partially abrogated the MTX-induced transient changes in osteogenic/adipogenic commitment, granulocyte/macrophage lineage differentiation and osteoclast number. These findings demonstrate a potentially important role of Wnt/β-catenin signalling in MTX chemotherapy-induced cellular changes to the bone marrow microenvironment.

CTNNB1 signaling in sertoli cells downregulates spermatogonial stem cell activity via WNT4

Constitutive activation of the WNT signaling effector CTNNB1 (β-catenin) in the Sertoli cells of the Ctnnb1^tm1Mmt/+;Amhr2^{tm3(cre)Bhr/+} mouse model results in progressive germ cell loss and sterility. In this study, we sought to determine if this phenotype could be due to a loss of spermatogonial stem cell (SSC) activity. Reciprocal SSC transplants between Ctnnb1^tm1Mmt/+;Amhr2^{tm3(cre)Bhr/+} and wild-type mice showed that SSC activity is lost in Ctnnb1^tm1Mmt/+;Amhr2^{tm3(cre)Bhr/+} testes over time, whereas the mutant testes could not support colonization by wild-type SSCs. Microarray analyses performed on cultured Sertoli cells showed that CTNNB1 induces the expression of genes associated with the female sex determination pathway, which was also found to occur in Ctnnb1^tm1Mmt/+;Amhr2^{tm3(cre)Bhr/+} testes. One CTNNB1 target gene encoded the secreted signaling molecule WNT4. We therefore tested the effects of WNT4 on SSC-enriched germ cell cultures, and found that WNT4 induced cell death and reduced SSC activity without affecting cell cycle. Conversely, conditional inactivation of Wnt4 in the Ctnnb1^tm1Mmt/+;Amhr2^{tm3(cre)Bhr/+} model rescued spermatogenesis and male fertility, indicating that WNT4 is the major effector downstream of CTNNB1 responsible for germ cell loss. Furthermore, WNT4 was found to signal via the CTNNB1 pathway in Sertoli cells, suggesting a self-reinforcing positive feedback loop. Collectively, these data indicate for the first time that ectopic activation of a signaling cascade in the stem cell niche depletes SSC activity through a paracrine factor. These findings may provide insight into the pathogenesis of male infertility, as well as embryonic gonadal development.

Wnt11 in 2011 - the regulation and function of a non-canonical Wnt

Genetic studies of Wnt11 have revealed many insights into the roles and regulation of Wnt11, particularly during development. New tools to study Wnt11 have recently become available, making it timely to review the literature regarding this unique Wnt family member. In this study, we focus on mammalian Wnt11, describing its main sites of expression during development, and how the Wnt11 gene is regulated. We highlight an emerging theme in which canonical Wnt signals regulate Wnt11 expression through transcription factors in addition to, or other than, Tcf/LEF family members. We also discuss the frizzled family and other receptors that bind to Wnt11, the intracellular kinases and small GTPases that act downstream of Wnt11, and the effects of Wnt11 on Wnt/β-catenin signalling. Finally, we elaborate on the relevance of Wnt11 to human cancer, where it appears to be important both for proliferation and/or survival during normal differentiation and for migration/invasion.

Wnt signaling and cardiac differentiation

The Wnt family of secreted glycoproteins participates in a wide array of biological processes, including cellular differentiation, proliferation, survival, apoptosis, adhesion, angiogenesis, hypertrophy, and aging. The canonical Wnt signaling primarily utilizes β-catenin-mediated activation of transcription, while the noncanonical mechanisms involve a calcium-dependent protein kinase C-mediated Wnt/Ca(2+) pathway and a dishevelled-dependent c-Jun N-terminal kinase-mediated planar cell polarity pathway. Although both canonical and noncanonical Wnts have been implicated in cardiac specification, morphogenesis, and differentiation; the molecular events remain unclear and often depend on the cell type and biological context. In this regard, growing evidence indicates that Wnt11 is able to induce cardiogenesis not only during embryonic development but also in adult cells. The cardiogenic properties of Wnt11 may prove useful for preprogramming adult stem cells before myocardial transplantation. Further, elucidation of the molecular steps in Wnt11-induced cardiac differentiation will be necessary to enhance the outcomes of cardiac cell therapy.

GATA6 reporter gene reveals myocardial phenotypic heterogeneity that is related to variations in gap junction coupling

This study examined transgenic mice whose expression of a β-galactosidase (lacZ) reporter is driven by a GATA6 gene enhancer. Previous investigations established that transcription of the transgene was associated with precardiac mesoderm and primary heart tube myocardium, which decreased progressively, so that its expression was no longer observed within ventricular myocardium by midgestation. Expression of this reporter in the adult was investigated for insights into myocyte homeostasis and cardiovascular biology. Morphometric analysis determined that <1% of myocytes, often found in small clusters, express this GATA6-associated reporter in the adult heart. LacZ expression was also found in the ascending aorta. Myocardial expression of the transgene was not associated with a proliferative phenotype or new myocyte formation, as lacZ-positive myocytes neither labeled with cell division markers nor following 5-bromodeoxyuridine pulse-chase experimentation. Despite exhibiting normal adherens junctions, these myocytes appeared to exhibit decreased connexin 43 gap junctions. Treatment with the gap junctional blocker heptanol both in vivo and in culture elevated myocardial β-galactosidase activity, suggesting that deficient gap junctional communication underlies expression of the transgenic reporter. LacZ expression within the myocardium was also enhanced in response to cryoinjury and isoproterenol-induced hypertrophy. These results reveal a previously uncharacterized phenotypic heterogeneity in the myocardium and suggest that decreased gap junctional coupling leads to induction of a signaling pathway that utilizes a unique GATA6 enhancer. Upregulation of lacZ reporter gene expression following cardiac injury indicates this transgenic mouse may serve as a model for examining the transition of the heart from healthy to pathological states.

Genome-wide screen reveals WNT11, a non-canonical WNT gene, as a direct target of ETS transcription factor ERG

E26 transforming sequence-related gene (ERG) is a transcription factor involved in normal hematopoiesis and is dysregulated in leukemia. ERG mRNA overexpression was associated with poor prognosis in a subset of patients with T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Herein, a genome-wide screen of ERG target genes was conducted by chromatin immunoprecipitation-on-chip (ChIP-chip) in Jurkat cells. In this screen, 342 significant annotated genes were derived from this global approach. Notably, ERG-enriched targets included WNT signaling genes: WNT11, WNT2, WNT9A, CCND1 and FZD7. Furthermore, chromatin immunoprecipitation (ChIP) of normal and primary leukemia bone marrow material also confirmed WNT11 as a target of ERG in six of seven patient samples. A larger sampling of patient diagnostic material revealed that ERG and WNT11 mRNA were co-expressed in 80% of AML (n=30) and 40% in T-ALL (n=30) bone marrow samples. Small interfering RNA (siRNA)-mediated knockdown of ERG confirmed downregulation of WNT11 transcripts. Conversely, in a tet-on ERG-inducible assay, WNT11 transcripts were co-stimulated. A WNT pathway agonist, 6-bromoindirubin-3-oxime (BIO), was used to determine the effect of cell growth on the ERG-inducible cells. The addition of BIO resulted in an ERG-dependent proliferative growth advantage over ERG-uninduced cells. Finally, ERG induction prompted morphological transformation whereby round unpolarized K562 cells developed elongated protrusions and became polarized. This morphological transformation could effectively be inhibited with BIO and with siRNA knockdown of WNT11. In conclusion, ERG transcriptional networks in leukemia converge on WNT signaling targets. Specifically, WNT11 emerged as a direct target of ERG. Potent ERG induction promoted morphological transformation through WNT11 signals. The findings in this study unravel new ERG-directed molecular signals that may contribute to the resistance of current therapies in acute leukemia patients with poor prognosis characterized by high ERG mRNA expression.

Maintenance of HSC by Wnt5a secreting AGM-derived stromal cell line

OBJECTIVE

The microenvironment wherein hematopoietic stem cells (HSC) reside orchestrates HSC self-renewal vs. differentiation decisions. Stromal cells derived from ontogenically divergent hematopoietic microenvironments can support HSC in vitro and have been used to decipher factors that influence HSC fate decisions. Employing stromal cell lines derived from the aorta-gonad-mesonephros and embryonic liver, we aim to identify secreted factors that maintain/expand HSC in vitro.

MATERIALS AND METHODS

We cultured murine lineage antigen-negative (Lin(-)) bone marrow cells in transwells above the UG26-1B6, urogenital ridge-, and EL08-1D2, embryonic liver-derived cell lines. We, also, performed real-time quantitative PCR analysis to identify differentially expressed genes from the Wnt family of proteins in ontogenically different stromal cell lines.

RESULTS

Lin(-) murine bone marrow cells maintained for 3 weeks in transwells above UG26-1B6 but not EL08-1D2 cells contained competitive repopulating HSC. Addition of as few as 25% UG26-1B6 cells to EL08-1D2 feeders led to maintenance of HSC in noncontact cultures, validating soluble factors are secreted by the UG26-1B6 cells. As we found that Wnt5a was significantly higher expressed in UG26-1B6 than EL08-1D2 cells, we added Wnt5a to EL08-1D2 transwell cultures or an antibody against Wnt5a to UG26-1B6 transwell cultures. Addition of Wnt5a to EL08-1D2 transwell cultures restored maintenance of HSC, whereas addition of an anti-Wnt5a antibody to UG26-1B6 transwell cultures inhibited maintenance of competitive repopulating HSC.

CONCLUSIONS

We demonstrate that stromal cell lines generated from embryonic microenvironments provide a tool to identify secreted proteins that play a role in the maintenance of HSC, and that at least one of the factors produced by UG26-1B6 cells responsible for preserving HSC is Wnt5a.

Role of Wnt canonical pathway in hematological malignancies

Wnt canonical signaling pathway plays a diverse role in embryonic development and maintenance of organs and tissues in adults. It has been observed that Wnt/β-catenin signaling pathway is involved in the pathogenesis of many carcinomas. Moreover, Wnt/β-catenin pathway has been revealed to be associated with angiogenesis. Wnt canonical pathway signaling has great potential as a therapeutic target. It has been disclosed that some hematological malignancies, such as chronic lymphocytic leukemia, mantle cell lymphoma, may occur partly due to the constitutive activation of Wnt canonical signaling pathway. This review will summarize the latest development in Wnt canonical signaling pathway and its roles in tumorigenesis and angiogenesis.

Transcriptional down-regulation of the Wnt antagonist SFRP1 in haematopoietic cells of patients with different risk types of MDS

Secreted frizzled related protein 1 (SFRP1) is an extracellular antagonist of the Wnt signalling pathway that plays an important role in the pathogenesis of solid tumours and haematopoietic malignancies. SFRP1 has been observed to be transcriptionally down-regulated due to hypermethylation in acute and chronic leukaemia, but so far not in myelodysplastic syndrome (MDS). Moreover, it has been shown that the epigenetic inactivation of SFRP1 correlates with an overexpression of the Wnt receptor Frizzled 3 (Fzd3) in acute leukaemia. Using real-time quantitative reverse transcription polymerase chain reaction (RT-PCR) we examined mRNA expression of SFRP1 and Fzd3 in bone marrow cells derived from 121 patients with different risk types of MDS, acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL). We employed pyrosequencing to quantify promoter DNA methylation in MDS and acute leukaemia. We detected significant lower mRNA transcription of SFRP1 in MDS compared to healthy individuals. However, DNA sequence mutations or frequent elevated DNA methylation levels of the SFRP1 promoter could not be observed in MDS but in AML and ALL as previously reported. The expression levels of Fzd3 were up-regulated in both acute leukaemia and MDS. Our data show a significant transcriptional down-regulation of SFRP1 as a common event in AML, ALL and - as demonstrated for the first time - in MDS. An inactivation of SFRP1 and the transcriptional up-regulation of Fzd3 seem to be associated with an activation of the Wnt signalling pathway in these haematopoietic diseases.

Wnt and Notch signaling pathways selectively regulating hematopoiesis

Hematopoietic stem and progenitor cells (HSPCs) are the source of all blood cells in the adult body. The pool of HSPCs is formed during embryogenesis process through a well-characterized succession of intra-embryonic regions and organs. The spatial and temporal restrictions in definitive hematopoietic development and the signaling molecules involved are of great interest as these may prove useful for generating and expanding these clinically important cell populations ex vivo. To elucidate the mechanism by which definitive HSPCs expand during this limited developmental time frame, we analyzed the spatial and temporal programmed gene expression patterns of Wnt and Notch signaling members during hematopoietic development. Genes related to the Wnt signaling pathway were up-regulated in E10.5 aorta-gonad-mesonephros (AGM) and E14.5 fetal liver corresponding to the inherent proliferation potential of hematopoietic progenitors, whereas genes related to the Notch signaling pathway were identified as up-regulated in E10.5 AGM, and bone marrow coincides with the maintenance of undifferentiation state of hematopoietic progenitors. Our findings suggest that Wnt and Notch signalings are integrated and are selectively regulating hematopoiesis. The spatial and temporal balance between Wnt and Notch signaling orchestrates the precise progression of hematopoietic progenitors.

Characterization of Wnt/beta-catenin signalling in osteoclasts in multiple myeloma

We recently showed that increasing Wnt/beta-catenin signalling in the bone marrow microenvironment or in multiple myeloma (MM) cells clearly suppresses osteoclastogenesis in SCID-hu mice; however, this regulation of osteoclastogenesis could result directly from activation of Wnt/beta-catenin signalling in osteoclasts or indirectly from effects on osteoblasts. The present studies characterized Wnt/beta-catenin signalling and its potential role in osteoclasts. Systematic analysis of expression of WNT, FZD, LRP and TCF gene families demonstrated that numerous Wnt-signalling components were expressed in human osteoclasts from patients with MM. Functional Wnt/beta-catenin signalling was identified by accumulation of total and active beta-catenin and increases in Dvl-3 protein in response to Wnt3a or LiCl. Furthermore, Wnt-induced increases in beta-catenin and Dvl-3 were attenuated by Wnt antagonists Dkk1 and sFRP1. Finally, Wnt3a-induced TCF/LEF transcriptional activity suggests that canonical Wnt signalling is active in osteoclasts. Supernatants from dominant-negative-beta-catenin-expressing osteoblast clones significantly stimulated tartrate-resistant acid phosphatase-positive osteoclast formation from primary MM-derived osteoclasts, compared with supernatants from control cells. These results suggested that Wnt/beta-catenin signalling is active in osteoclasts in MM and is involved in osteoclastogenesis in bone marrow, where it acts as a negative regulator of osteoclast formation in an osteoblast-dependent manner in MM.

Noncanonical Wnt signaling orchestrates early developmental events toward hematopoietic cell fate from human embryonic stem cells

During human development, signals that govern lineage specification versus expansion of cells committed to a cell fate are poorly understood. We demonstrate that activation of canonical Wnt signaling by Wnt3a promotes proliferation of human embryonic stem cells (hESCs)--precursors already committed to the hematopoietic lineage. In contrast, noncanonical Wnt signals, activated by Wnt11, control exit from the pluripotent state and entry toward mesoderm specification. Unique to embryoid body (EB) formation of hESCs, Wnt11 induces development and arrangement of cells expressing Brachyury that coexpress E-cadherin and Frizzled-7 (Fzd7). Knockdown of Fzd7 expression blocks Wnt11-dependent specification. Our study reveals an unappreciated role for noncanonical Wnt signaling in hESC specification that involves development of unique mesoderm precursors via morphogenic organization within human EBs.

Noncanonical Wnt11 signaling and cardiomyogenic differentiation

Although the molecular details remain unclear, Wnt signaling via both canonical and noncanonical pathways is integral to cardiac specification and morphogenesis. A growing body of evidence also suggests substantial overlap between these supposedly discrete pathways in cell- and context-dependent manners. The ability of Wnt11 to induce cardiomyogenesis both during embryonic development and in adult cells makes it an attractive candidate for preprogramming cells for cardiac repair. This review primarily discusses various aspects of noncanonical Wnt signaling in cardiogenesis with particular emphasis on Wnt11.

MicroRNA profiling identifies miR-34a and miR-21 and their target genes JAG1 and WNT1 in the coordinate regulation of dendritic cell differentiation

MicroRNAs (miRNAs, miRs) modulate a multitude of cellular events. Here, we identify functional miRNA-protein networks that regulate human monocyte-derived dendritic cell (MDDC) differentiation. miRNA profiling revealed stage-specific differential expression of 20 miRNAs during days 1, 3, and 5 of MDDC differentiation. To identify and prioritize miRNA-protein networks for functional validation, we developed a target ranking algorithm that incorporates many features of miRNA regulatory networks. This system prioritized miR-21, miR-34a, and their cognate targets WNT1 and JAG1 for functional validation. Inhibition of both miR-21 and miR-34a stalled MDDC differentiation, as quantified by DC-SIGN/CD14 expression ratios, showing cooperative involvement of these miRNAs in MDDC differentiation. We confirmed that the 3' untranslated regions of WNT1 and JAG1 were functional targets of these miRNAs and provide evidence that these targets were translationally suppressed. Significantly, exogenously added Wnt-1 and Jagged-1 also stalled MDDC differentiation, suggesting that miRNA-mediated inhibition of endogenous WNT1 and JAG1 expression was important for proper MDDC differentiation. Finally, inhibition of miR-21 and miR-34a, or addition of Wnt-1 and Jagged-1, led to a decrease in endocytic capacity, a key function of immature DCs. Thus, our novel approach identified and validated some miRNA-protein networks involved in phenotypic and functional MDDC differentiation.

Epigenetic dysregulation of secreted Frizzled-related proteins in multiple myeloma

We analysed the clinical impact of epigenetic dysregulation of the Wnt pathway in malignant plasma cell disorders. In multiple myeloma (MM) cell lines, aberrant promoter hypermethylation of the secreted Frizzled-related protein (SFRP) genes was a common event, and hypermethylation of SFRP1,-2 and -5 was associated with transcriptional silencing. Among 76 primary patient samples, the frequency of aberrant methylation was 35.5% for SFRP1, 52.6% for SFRP2, 1.3% for SFRP4 and 6.9% for SFRP5. Hypermethylation of SFRP1 and -2 genes was detected in monoclonal gammopathy of undetermined significance and all MM stages including plasma cell leukaemia (PCL), while SFRP5 methylation was restricted to advanced MM stages and PCL. Our data indicate that epigenetic silencing of Wnt antagonists is an early event in MM pathogenesis and that SFRP5 hypermethylation may play a role in disease progression.

Wnt5a and Wnt11 interact in a maternal Dkk1-regulated fashion to activate both canonical and non-canonical signaling in Xenopus axis formation

Wnt signaling in development and adult tissue homeostasis requires tight regulation to prevent patterning abnormalities and tumor formation. Here, we show that the maternal Wnt antagonist Dkk1 downregulates both the canonical and non-canonical signaling that are required for the correct establishment of the axes of the Xenopus embryo. We find that the target Wnts of Dkk activity are maternal Wnt5a and Wnt11, and that both Wnts are essential for canonical and non-canonical signaling. We determine that Wnt5a and Wnt11 form a previously unrecognized complex. This work suggests a new aspect of Wnt signaling: two Wnts acting in a complex together to regulate embryonic patterning.

Dissection of sets of genes that control the character of wnt5a-deficient mouse calvarial cells

Wnts (wingless and int-related proteins) are a family of secreted cysteine-rich glycoproteins, expressed in a variety of tissues in developing embryos, thought to be involved in cell fate specification and stem cell commitment. To identify the specific Wnts involved in osteoblastic differentiation of human mesenchymal stem cells (hMSCs), we performed degenerative RT-PCR cloning method to amplify Wnt-encoding cDNAs expressed during osteoblastic differentiation of hMSCs in vitro and during hMSC-directed ectopic osteogenesis in the severe combined immunodeficient (SCID) mouse host. WNT5A was found to be the dominant Wnt expressed during osteoblastic differentiation of hMSCs both in vitro and in vivo. RT-PCR further revealed that hWNT5A and its receptor Frizzled family member 5 (hFZD5) was up-regulated during osteoblastic differentiation compared to uncommitted hMSCs. To evaluate the function of Wnt5a, calvarial cells were obtained from Wnt5a(-/-), Wnt5a(+/-), and wild type mice. Wnt5a(-/-) cells showed significantly slower growth when compared to Wnt5a(+/-) and wild type cells. Gene expression profiles of the Wnt5a(-/-) calvarial cells as compared to wild type cells were evaluated using microarray analysis. 255 genes exhibited at least 2-fold changes in expression. Clusters of genes regulating cell cycle, cell proliferation and cell growth, and gene transcription were altered with absence of Wnt5a expression. In addition, genes regulating osteoblastic differentiation including Runx2, osterix, and alkaline phosphatase (ALP) were shown to be down-regulated in Wnt5a(-/-) cells. In conclusion, Wnt5a is highly expressed during osteoblastic differentiation. Its function during mesenchymal stem cell differentiation as well as cell growth was suggested by comparing the gene expression profile of calvarial cells from the Wnt5a(-/-) and wild type mice.

Activation of Wnt signaling in cKit-ITD mediated transformation and imatinib sensitivity in acute myeloid leukemia

The Wnt-signaling pathway plays a critical role in directing cell fate during embryogenesis and also in the pathogenesis of cancer. In leukemia, it is well described that activating internal tandem duplications (ITD) mutations in receptor tyrosine kinases like cKit or Flt3 confer to the pathogenesis of cancer. Here, we analyzed whether Wnt-signaling plays a role in cKit-ITD mediated transformation. Stably transfected 32D cells with cKit-ITD cells had higher beta-Catenin protein levels compared to the cKit-WT. Analysis of beta-Catenin mRNA and protein levels revealed that beta-Catenin was regulated at post-transcriptional level in cKit-ITD as well as Flt3-ITD compared to the wildtype. Signaling analyses revealed higher-phosphorylation of GSK3beta by oncogenic cKit-ITD. Moreover, activation of Wnt signaling was confirmed by constitutive activation of c-myc luciferase by cKit-ITD cells. Importantly, using dominant negative TCF4, we show that activation of Wnt signaling plays an important role in cKit mediated transformation of myeloid cells. Application of specific receptor tyrosine kinase inhibitors for Flt3 or cKit result in a decrease of beta-Catenin that underwent with a decrease of GSK3beta phosphorylation, suggesting an indirect mechanism of beta-Catenin regulation by oncogenic receptor tyrosine kinases in both ITD mutations. Our study shows the importance of activation of Wnt signaling in leukemia and suggests as attractive target for future therapeutical approaches.

Epigenetic inactivation of secreted Frizzled-related proteins in acute myeloid leukaemia

The Wnt signalling pathway has a key function in stem cell maintenance and differentiation of haematopoietic progenitors. Secreted Frizzled-related protein genes (SFRPs), functioning as Wnt signalling antagonists, have been found to be downregulated by promoter hypermethylation in many tumours. To analyse epigenetic dysregulation of SFRPs in acute myeloid leukaemia (AML), we examined the promoter methylation status of SFRP1, -2, -4 and -5 in AML cell lines by methylation-specific polymerase chain reaction (MSP). Aberrant CpG island methylation was found for all four SFRP genes. By real-time reverse transcription-PCR, corresponding transcriptional silencing for SFRP1 and -2 was demonstrated and treatment of cell lines with 5-aza-2'-deoxycytidine resulted in re-expression. The methylation status of the SFRP genes was analysed in 100 specimens obtained from AML patients at diagnosis. The frequencies of aberrant methylation among the patient samples were 29% for SFRP1, 19% for SFRP2, 0% for SFRP4 and 9% for SFRP5. For SFRP2, a correlation between promoter hypermethylation and transcriptional downregulation was found in primary AML samples. Among AML cases with a favourable karyotype, hypermethylation of SFRP genes was restricted to patients with core binding factor (CBF) leukaemia, and aberrant methylation of the SFRP2 promoter was an adverse risk factor for survival in CBF leukaemia.

Hematopoietic contribution to skeletal muscle regeneration in acid alpha-glucosidase knockout mice

Recent studies have shown that cells from bone marrow (BM) can give rise to differentiated skeletal muscle fibers. However, the mechanisms and identities of the cell types involved remain unknown. We performed BM transplantation in acid alpha-glucosidase (GAA) knockout mice, a model of glycogen storage disease type II, and our observations suggested that the BM cells contribute to skeletal muscle fiber formation. Furthermore, we showed that most CD45+:Sca1+ cells have a donor character in regenerating muscle of recipient mice. Based on these findings, CD45+:Sca1+ cells were sorted from regenerating muscles. The cell number was increased with granulocyte colony-stimulating factor after cardiotoxin injury, and the cells were transplanted directly into the tibialis anterior (TA) muscles of GAA knockout mice. Sections of the TA muscles stained with anti-laminin-alpha2 antibody showed that the number of CD45+:Sca1+ cells contributing to muscle fiber formation and glycogen levels were decreased in transplanted muscles. Our results indicated that hematopoietic stem cells, such as CD45+:Sca1+ cells, are involved in skeletal muscle regeneration.

Seminiferous tubule degeneration and infertility in mice with sustained activation of WNT/CTNNB1 signaling in sertoli cells

WNT/CTNNB1 signaling is involved in the regulation of multiple embryonic developmental processes, adult tissue homeostasis, abd cell fate determination and differentiation. Many WNTs and components of the WNT/CTNNB1 signaling pathway are expressed in the testis, but their physiological roles in this organ are largely unknown. To elucidate the role(s) of WNT/CTNNB1 signaling in the testis, transgenic Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ mice were generated to obtain sustained activation of the WNT/CTNNB1 pathway in both Leydig and Sertoli cells. Male Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ mice were sterile because of testicular atrophy starting at 5 wk of age, associated with degeneration of seminiferous tubules and the progressive loss of germ cells. Although Cre activity was expected in Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ Leydig cells, no evidence of Cre-mediated recombination of the floxed allele or of WNT/CTNNB1 pathway activation could be obtained, and testosterone levels were comparable to age-matched controls, suggesting that genetic recombination was inefficient in Leydig cells. Conversely, sustained WNT/CTNNB1 pathway activation was obtained in Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ Sertoli cells. The latter often exhibited morphological characteristics suggestive of incomplete differentiation that appeared in a manner coincident with germ cell loss, and this was accompanied by an increase in the expression of the immature Sertoli cell marker AMH. In addition, a poorly differentiated, WT1-positive somatic cell population accumulated in multilayered foci near the basement membrane of many seminiferous tubules. Together, these data suggest that the WNT/CTNNB1 pathway regulates Sertoli cell functions critical to their capacity to support spermatogenesis in the postnatal testis.

Noncanonical Wnt11 signaling is sufficient to induce cardiomyogenic differentiation in unfractionated bone marrow mononuclear cells

BACKGROUND

Despite the frequent clinical use of adult unfractionated bone marrow mononuclear cells (BMMNCs) for cardiac repair, whether these cells are capable of undergoing cardiomyogenic differentiation in vitro remains uncertain. In addition, the role of Wnt signaling in cardiomyogenic differentiation of adult cells is unclear.

METHODS AND RESULTS

Unfractionated BMMNCs were isolated from adult mice via Ficoll-Paque density-gradient centrifugation and cultured in the presence of Wnt3a or Wnt11. In control BMMNCs, Wnt11 was not expressed, whereas the expression of markers of pluripotency (Oct-4 and Nanog), as well as that of Wnt3a and beta-catenin, decreased progressively during culture. Exposure to Wnt3a rescued beta-catenin expression and markedly increased the expression of Oct-4 and Nanog, concomitant with increased cell proliferation and CD45 expression. In contrast, exposure to ectopically expressed noncanonical Wnt11 markedly decreased the expression of Oct-4 and Nanog and induced mRNA expression (quantitative real-time reverse-transcription polymerase chain reaction) of cardiac-specific genes (Nkx2.5, GATA-4, atrial natriuretic peptide, alpha- and beta-myosin heavy chain, and cardiac troponin T) by day 3 with subsequent progression to a pattern characteristic of the cardiac fetal gene program. After 21 days, 27.6+/-0.6% and 29.6+/-1.4% of BMMNCs expressed the cardiac-specific antigens cardiac myosin heavy chain and cardiac troponin T, respectively (immunocytochemistry), indicating cardiomyogenic lineage commitment. Wnt11-induced cardiac-specific expression was completely abolished by the protein kinase C inhibitor bisindolylmaleimide I, partially abolished by the c-Jun-N-terminal kinase inhibitor SP600125, and attenuated by the Wnt inhibitor Dickkopf-1.

CONCLUSIONS

In adult density-gradient separated BMMNCs, canonical Wnt3a promotes stemness, proliferation, and hematopoietic commitment, whereas noncanonical signaling via Wnt11 induces robust cardiomyogenic differentiation in a protein kinase C- and c-Jun-N-terminal kinase-dependent manner.

Canonical and non-canonical Wnts differentially affect the development potential of primary isolate of human bone marrow mesenchymal stem cells

This study examines the role of Wnt signaling events in regulating the differential potential of mesenchymal stem cells (MSCs) from adult bone marrow (BM). Immunohistochemical analysis of BM revealed co-localization of Wnt5a protein, a non-canonical Wnt, with CD45(+) cells and CD45(-) STRO-1(+) cells, while Wnt3a expression, a canonical Wnt, was associated with the underlying stroma matrix, suggesting that Wnts may regulate MSCs in their niche in BM. To elucidate the role of Wnts in MSC development, adult human BM-derived mononuclear cells were maintained as suspension cultures to recapitulate the marrow cellular environment, in serum-free, with the addition of Wnt3a and Wnt5a protein. Results showed that Wnt3a increased cell numbers and expanded the pool of MSCs capable of colony forming unit -- fibroblast (CFU-F) and CFU -- osteoblast (O), while Wnt5a maintained cell numbers and CFU-F and CFU-O numbers. However, when cells were cultured directly onto tissue culture plastic, Wnt5a increased the number of CFU-O relative to control conditions. These findings suggest the potential dual role of Wnt5a in the maintenance of MSCs in BM and enhancing osteogenesis ex vivo. Our work provides evidence that Wnts can function as mesenchymal regulatory factors by providing instructive cues for the recruitment, maintenance, and differentiation of MSCs.

Gene expression profiling during differentiation of human monocytes to macrophages or dendritic cells

Macrophages and dendritic cells (DC) are APC, which regulate innate and adaptive immune responses. Macrophages function locally mainly, maintaining inflammatory responses in tissues, whereas DC take up microbes, mature, and migrate to local lymph nodes to present microbial antigens to naïve T cells to elicit microbe-specific immune responses. Blood monocytes can be differentiated in vitro to macrophages or DC by GM-CSF or GM-CSF + IL-4, respectively. In the present study, we performed global gene expression analyses using Affymetrix HG-U133A Gene Chip oligonucleotide arrays during macrophage and DC differentiation. During the differentiation process, 340 and 350 genes were up-regulated, and 190 and 240 genes were down-regulated in macrophages and DC, respectively. There were also more that 200 genes, which were expressed differentially in fully differentiated macrophages and DC. Macrophage-specific genes include, e.g., CD14, CD163, C5R1, and FcgammaR1A, and several cell surface adhesion molecules, cytokine receptors, WNT5A and its receptor of the Frizzled family FZD2, fibronectin, and FcepsilonR1A were identified as DC-specific. Our results reveal significant differences in gene expression profiles between macrophages and DC, and these differences can partially explain the functional differences between these two important cell types.

The emerging role of Wnt signaling in the pathogenesis of acute myeloid leukemia

Wnt signaling plays an important role in stem cell self-renewal and proliferation. Aberrant activation of Wnt signaling and its downstream targets are intimately linked with several types of cancer with colon cancer being the best-studied example. However, recent results also suggest an important role of Wnt signaling in normal as well as leukemic hematopoietic stem cells. Aberrant activation of Wnt signaling and downstream effectors has been demonstrated in acute myeloid leukemia. Here, mutant receptor tyrosine kinases, such as Flt3 and chimeric transcription factors such as promyelocytic leukemia-retinoic acid receptor-alpha and acute myeloid leukemia1-ETO, induce downstream Wnt signaling events. These findings suggest that the Wnt signaling pathway is an important target in several leukemogenic pathways and may provide a novel opportunity for targeting leukemic stem cells.

The Wnt/beta-catenin pathway regulates Gli-mediated Myf5 expression during somitogenesis

Canonical Wnt/beta-catenin signaling regulates the activation of the myogenic determination gene Myf5 at the onset of myogenesis, but the underlying molecular mechanism is unknown. Here, we report that the Wnt signal is transduced in muscle progenitor cells by at least two Frizzled (Fz) receptors (Fz1 and/or Fz6), through the canonical beta-catenin pathway, in the epaxial domain of newly formed somites. We show that Myf5 activation is dramatically reduced by blocking the Wnt/beta-catenin pathway in somite progenitor cells, whereas expression of activated beta-catenin is sufficient to activate Myf5 in somites but not in the presomitic mesoderm. In addition, we identified Tcf/Lef sequences immediately 5' to the Myf5 early epaxial enhancer. These sites determine the correct spatiotemporal expression of Myf5 in the epaxial domain of the somite, mediating the synergistic action of the Wnt/beta-catenin and the Shh/Gli pathways. Taken together, these results demonstrate that Myf5 is a direct target of Wnt/beta-catenin, and that its full activation requires a cooperative interaction between the canonical Wnt and the Shh/Gli pathways in muscle progenitor cells.

Parathyroid hormone: A novel tool for treating bone marrow depletion in cancer patients caused by chemotherapeutic drugs and ionizing radiation

Between 1958 and the late 1970s it was learned that PTH (the parathyroid hormone) could directly stimulate the initiation of DNA replication by murine CFU-S (colony-forming unit-spleen) cells via cyclic AMP, stimulate the proliferation of normal and X-irradiated murine and rat bone marrow cells, control hematopoiesis, and increase the survival of X-irradiated mice and rats when injected any time between 18h before and 3h after X-irradiation. Since then, it has been shown that the hematopoietic stem cell niche consists of PTH receptor-bearing, osteoblastic trabecular bone-lining cells that maintain the stem cells' (HSCs') proliferatively quiescent 'stemness' by various gene up-regulating and down-regulating signals caused by the tight adhesion of the HSCs to the osteoblastic niche-lining cells. Stimulating the osteoblastic lining cells with recombinant human PTH-(1-34) (Forteo) causes a cyclic AMP-mediated enlargement of the HSC pool and promotes bone marrow transplant engraftment and growth and the survival of lethally irradiated mice. But this is only the beginning of the exploitation of the PTHs for marrow engraftment. It must now be determined whether the marrow engraftment-enhancing action of this potent bone growth-stimulating PTH can be extended from mice to rats and monkeys. It must be determined whether two other PTH peptides, rhPTH-(1-84) [Preos]and [Leu(27)]cyclo(Glu(22)-Lys(26))hPTH-(1-31)NH(2) [Ostabolin-C]) are as effective as or better than rhPTH-(1-34)(Forteo). Since, all three peptides are on the market, or nearing the market, for safely and strongly stimulating bone growth and treating osteoporosis one or all of them may become valuable tools for safely promoting the engraftment of peripherally harvested HSCs in cancer patients whose bone marrows have been 'emptied' by chemotherapeutic drugs or ionizing radiation.

Expression of beta-catenin by acute myeloid leukemia cells predicts enhanced clonogenic capacities and poor prognosis

Activation of the Wnt/beta-catenin pathway has recently been shown to be crucial to the establishment of leukemic stem cells in chronic myeloid leukemia. We sought to determine whether beta-catenin was correlated to clonogenic capacity also in the acute myeloid leukemia (AML) setting. Eighty-two patients were retrospectively evaluated for beta-catenin expression by Western blot. beta-Catenin was expressed (although at various protein levels) in 61% of patients, and was undetectable in the remaining cases. In our cohort, beta-catenin expression was correlated with the clonogenic proliferation of AML-colony forming cells (AML-CFC or CFU-L) in methylcellulose in the presence of 5637-conditioned medium, and more strikingly with self-renewing of leukemic cells, as assessed in vitro by a re-plating assay. In survival analyses, beta-catenin appeared as a new independent prognostic factor predicting poor event-free survival and shortened overall survival (both with P<0.05). Furthermore, variations in beta-catenin protein levels were dependent on post-transcriptional mechanisms involving the Wnt/beta-catenin pathway only in leukemic cells. Indeed, beta-catenin negative leukemic cells were found to increase beta-catenin in response to Wnt3a agonist in contrast to normal counterparts. Altogether, our data pave the way to the evaluation of Wnt pathway inhibition as a new rationale for eradicating the clonogenic pool of AML cells.

Analysis of the human fetal liver hematopoietic microenvironment

In the adult, hematopoietic stem cells (HSCs) are resident in the bone marrow (BM) compartment and are in direct association with the BM stromal microenvironment. However, human adult HSCs are largely quiescent and undergo limited self-renewal. This is in contrast to the higher frequency of cycling HSCs undergoing self-renewal during fetal development when hematopoiesis is transiently localized to the fetal liver (FL), suggesting that FL provides a more conducive microenvironment to support HSCs. Here, we provide phenotypic and molecular characterization of primary human FL stromal cells capable of supporting human repopulating progenitors. Qualitative and quantitative analysis revealed several properties unique to FL stromal cells compared to adult BM-derived stroma that included a greater than 10-fold enhanced proliferative capacity of FL stromal vs adult BM, and a 2-fold increase in the number of N-cadherin- and osteopontin-expressing cells. Supportive of extrinsic influences likely to modulate HSC expansion, global gene expression microarray analysis revealed that FL stroma has higher expression of regulators of the Wnt signaling pathway compared to adult BM stroma, which demonstrated an increased expression of the Notch signaling pathway. Our results suggest that human FL stromal cells provide a unique microenvironment to HSCs compared to adult BM stroma by controlling Wnt signaling of HSCs during human fetal hematopoietic development, while Notch signaling is tightly regulated by the HSC microenvironment in the adult. We propose that the human HSC niche is ontogenically controlled during human development to provide appropriate expansion of fetal HSCs and subsequent maintenance of adult HSCs.

Blood-Borne Stem Cells Differentiate into Vascular and Cardiac Lineages During Normal Development

Recent investigations have indicated that hematopoietic stem cells (HSCs) have the potential to differentiate into multiple non-blood cell lineages and contribute to the cellular regeneration of various tissues and multiple organs. Most studies to date on HSC potential have examined the adult, focusing on their potential to repair tissue under pathological conditions (e.g., ischemic injury, organ failure). Comparatively little is known about the physiological role of HSCs in normal tissue homeostasis in the adult, and even less of their contribution to organogenesis during prenatal development. This study reports the contribution of blood-borne cells to various organ systems of the developing embryo using a quail-chick parabiosis model. Under these conditions, the developing circulatory systems fuse between ED6-ED8, resulting in free exchange of circulating cells. Cells of quail origin, identified by quail-specific antibodies at ED15, were found in numerous organs of the parabiotic chick embryo. Circulating cells contributed to developing vasculature, where they differentiated into endothelial, smooth muscle, and adventitial tissues. In the heart, differentiation of circulating cells into cardiomyocytes was demonstrated using double immunolabeling for QCPN and sarcomeric actin or myosin. These results were confirmed by intramyocardial injection of quail bone marrow cells that were found to express markers of myocytes, coronary smooth muscle, and epicardium. Experiments using lacZ-transgenic chick embryos for a second positive cellular marker showed that fusion between chick and quail cells was a rare event. These results suggest that during development, multipotent cells are present in the embryonic circulation and home into different organs where they undergo tissue-specific differentiation. Moreover, the demonstration that blood-borne cells contribute to the development of various organs lends credence to claims that hematopoietic stem cells have utility for treating diseased or damaged tissues in the adult.

CpG Island Methylation and Expression of the Secreted Frizzled-Related Protein Gene Family in Chronic Lymphocytic Leukemia

B-cell chronic lymphocytic leukemia (CLL) is characterized by a clonal accumulation of mature neoplastic B cells indicating disruption of apoptosis. Restriction Landmark Genome Scanning was done to identify novel target genes silenced by CpG island methylation in CLL. Secreted frizzled-related protein 4 (SFRP4), a negative regulator of the Wnt signaling pathway, was found to be frequently methylated in CLL samples. Wnt signaling has been shown to control normal apoptotic behavior and is required for normal B-cell development whereas aberrant activation of this pathway has been observed in CLL. We show aberrant DNA methylation and silencing of SFRP4, as well as of additional SFRP family members, in primary CLL samples. Induction of their expression in a dose-dependent manner following treatment with a demethylating agent, 5-aza-2'-deoxycytidine, was shown. Of the five SFRP family members studied in detail, SFRP1 was hypermethylated and down-regulated in all CLL patient samples studied, suggesting that this epigenetic event is a critical step during leukemogenesis. Our results suggest that silencing of SFRPs by CpG island methylation is one possible mechanism contributing to aberrant activation of Wnt signaling pathway in CLL.

BMP signaling and stem cell regulation

Stem cells play an essential role in cellular specialization and pattern formation during embryogenesis and in tissue regeneration in adults. This is mainly due to a stem cell's ability to replenish itself (self-renewal) and, at the same time, produce differentiated progeny. Realization of these special stem cell features has changed the prospective of the field. However, regulation of stem cell self-renewal and maintenance of its potentiality require a complicated regulatory network of both extracellular cues and intrinsic programs. Understanding how signaling regulates stem cell behavior will shed light on the molecular mechanisms underlying stem cell self-renewal. In this review, we focus on comparing the progress of recent research regarding the roles of the BMP signaling pathway in different stem cell systems, including embryonic stem cells, germline stem cells, hematopoietic stem cells, and intestinal stem cells. We hope this comparison, together with a brief look at other signaling pathways, will bring a more balanced view of BMP signaling in regulation of stem cell properties, and further point to a general principle that self-renewal of stem cells may require a combination of maintenance of proliferation potential, inhibition of apoptosis, and blocking of differentiation.

The role of Wnt signaling in cancer and stem cells

The Wingless-Int (Wnt) signaling pathway has been widely investigated in recent years. Initially, its role regulating cell proliferation and survival during embryogenesis aroused the interest of researchers. Later, the focus was placed on the link between aberrant Wnt pathway activation and human cancer. The improper function of Wnt signaling components can lead to aberrant cell proliferation and cancer. Mutations in the adenomatous polyposis coli and β-catenin genes first implicated Wnt signaling in carcinogenesis. Over time, a wealth of evidence has indicated that amplification or inhibition of other components might also play a role in human cancers. In addition, Wnt signaling pathways also play a crucial role in normal tissue regeneration and stem cell self-renewal, raising the possibility of controlling immature tumor stem cells.

Multiple stem cell populations contribute to the formation of the myocardium

Owing to the very rapid growth of the vertebrate embryo following fertilization, an efficient circulatory system needs to be established during the initial stages of development. For that reason, the first functional organ that develops in both the bird and mammalian embryo is the heart. Until recently, the narrative of cardiac development was portrayed in a straightforward manner, with all the myocardium in the mature heart being generated from the expansion of an original pool of myocardial cells present in the early gastrula. It is now known that the story of the developing myocardium is more dynamic, as it is comprises cellular components of multiple ancestries. The de novo addition of myocytes to the developing heart occurs at various points during embryogenesis, as cardiac muscle takes on new members by the absorption of cells that either reside in neighboring nonmuscle tissue or come into contact with the myocardium by entering the heart upon migration or via the circulation. This article reviews what is presently known about cellular populations that contribute to the myocardium and examine reasons why the embryo utilizes multiple cellular sources for forming the cardiac muscle.

Long-term functional impairment of hemopoietic progenitor cells engineered to express the S1 catalytic subunit of pertussis toxin

OBJECTIVE

A large body of data suggests that pertussis toxin (PTX)-sensitive G protein signals in mature and immature hemopoietic cells control their migration patterns in vitro and in vivo. These effects were derived after treatment of cells or animals with PTX. To circumvent several inherent problems of PTX holotoxin treatment, we expressed the S1 catalytic activity of PTX, thus blocking Gi protein signaling, in 32D murine myeloid progenitor cells and in primary human CD34+ cells, and studied its functional consequences.

METHODS

S1 was expressed using viral vectors. Effects of Gi protein blockade on proliferation, migration, adhesion, and gene expression were tested in vitro.

RESULTS

S1 expression was nontoxic for the cells; expression and function were stable long-term and not overridden by compensatory mechanisms. S1-transduced 32D cells and primary CD34+ cells migrated poorly and did not contract their cytoskeleton upon treatment with the chemoattractant stromal cell-derived factor -1 (SDF-1), similar to the phenotype induced by PTX treatment. Gene expression studies comparing S1-transduced and control 32D cells uncovered four genes, expression of which was regulated by Gi protein blockade. Of interest, although SDF-1 signaling was inhibited, comparison between SDF-1-treated and untreated cells suggests that SDF-1 stimulation does not depend on de novo gene expression in these cells. Furthermore, when injected into nonobese diabetic/severe combined immunodeficient mice, seeding of S1-expressing 32D cells to bone marrow was largely blocked.

CONCLUSION

Expression of S1 is an effective approach for studying long-term functional consequences of Gi protein blockade in hemopoietic cells in vitro and in vivo.