Wnt5a regulates hematopoietic stem cell proliferation and repopulation through the Ryk receptor

Transplantation of Wnt5a-modified Bone Marrow Mesenchymal Stem Cells Promotes Recovery After Spinal Cord Injury via the PI3K/AKT Pathway

Spinal cord injury (SCI) is a severe neurological condition that can lead to paralysis or even death. This study explored the potential benefits of bone marrow mesenchymal stem cell (BMSC) transplantation for repairing SCI. BMSCs also differentiate into astrocytes within damaged spinal cord tissues hindering the cell transplantation efficacy, therefore it is crucial to enhance their neuronal differentiation rate to facilitate spinal cord repair. Wnt5a, an upstream protein in the non-classical Wnt signaling pathway, has been implicated in stem cell migration, differentiation, and neurite formation but its role in the neuronal differentiation of BMSCs remains unclear. Thus, this study investigated the role and underlying mechanisms of Wnt5a in promoting neuronal differentiation of BMSCs both in vivo and in vitro. Wnt5a enhanced neuronal differentiation of BMSCs in vitro while reducing astrocyte differentiation. Additionally, high-throughput RNA sequencing revealed a correlation between Wnt5a and phosphoinositide 3-kinase (PI3K)/protein kinase B(AKT) signaling, which was confirmed by the use of the PI3K inhibitor LY294002 to reverse the effects of Wnt5a on BMSC neuronal differentiation. Furthermore, transplantation of Wnt5a-modified BMSCs into SCI rats effectively improved the histomorphology (Hematoxylin and eosin [H&E], Nissl and Luxol Fast Blue [LFB] staining), motor function scores (Footprint test and Basso-Beattie-Bresnahan [BBB]scores)and promoted neuron production, axonal formation, and remodeling of myelin sheaths (microtubule associated protein-2 [MAP-2], growth-associated protein 43 [GAP43], myelin basic protein [MBP]), while reducing astrocyte production (glial fibrillary acidic protein [GFAP]). Therefore, targeting the Wnt5a/PI3K/AKT pathway could enhance BMSC transplantation for SCI treatment.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

WNT Signaling in Stem Cells: A Look into the Non-Canonical Pathway

Tissue homeostasis is crucial for multicellular organisms, wherein the loss of cells is compensated by generating new cells with the capacity for proliferation and differentiation. At the origin of these populations are the stem cells, which have the potential to give rise to cells with both capabilities, and persevere for a long time through the self-renewal and quiescence. Since the discovery of stem cells, an enormous effort has been focused on learning about their functions and the molecular regulation behind them. Wnt signaling is widely recognized as essential for normal and cancer stem cell. Moreover, β-catenin-dependent Wnt pathway, referred to as canonical, has gained attention, while β-catenin-independent Wnt pathways, known as non-canonical, have remained conspicuously less explored. However, recent evidence about non-canonical Wnt pathways in stem cells begins to lay the foundations of a conceivably vast field, and on which we aim to explain this in the present review. In this regard, we addressed the different aspects in which non-canonical Wnt pathways impact the properties of stem cells, both under normal conditions and also under disease, specifically in cancer.

Role of Cytokine-Inducible SH2 Domain-Containing (CISH) Protein in the Regulation of Erythropoiesis

The cytokine-inducible SH2 domain-containing (CISH) protein was the first member of the suppressor of cytokine signaling (SOCS) family of negative feedback regulators discovered, being identified in vitro as an inducible inhibitor of erythropoietin (EPO) signaling. However, understanding of the physiological role played by CISH in erythropoiesis has remained limited. To directly assess the function of CISH in this context, mice deficient in CISH were characterized with respect to developmental, steady-state, and EPO-induced erythropoiesis. CISH was strongly expressed in the fetal liver, but CISH knockout (KO) mice showed only minor disruption of primitive erythropoiesis. However, adults exhibited mild macrocytic anemia coincident with subtle perturbation particularly of bone marrow erythropoiesis, with EPO-induced erythropoiesis blunted in the bone marrow of KO mice but enhanced in the spleen. Cish was expressed basally in the bone marrow with induction following EPO stimulation in bone marrow and spleen. Overall, this study indicates that CISH participates in the control of both basal and EPO-induced erythropoiesis in vivo.

WNT16b promotes the proliferation and self-renewal of human limbal epithelial stem/progenitor cells via activating the calcium/calcineurin A/NFATC2 pathway

Our previous finding revealed that WNT16b promoted the proliferation of human limbal epithelial stem cells (hLESCs) through a β-catenin independent pathway. Here, we aimed to explore its underlying molecular mechanism and evaluate its potential in the treatment of limbal stem cell deficiency (LSCD). Based on the findings of mRNA-sequencing, the expression of key molecules in WNT/calcineurin A/NFATC2 signalling pathway was investigated in WNT16b-co-incubated hLESCs and control hLESCs. An epithelial wound healing model was established on Wnt16b-KO mice to confirm the regulatory effect of WNT16b in vivo. The therapeutic potential of WNT16b-co-incubated hLESCs was also evaluated in mice with LSCD. Our findings showed that WNT16b bound with Frizzled7, promoted the release of Ca2+ and activated calcineurin A and NFATC2. With the translocation of NFATC2 into cell nucleus and the activation of HDAC3, WDR5 and GCN5L2, the expression of H3K4me3, H3K14ac and H3K27ac in the promoter regions of FoxM1 and c-MYC increased, which led to hLESC proliferation. The effect of the WNT16b/calcium/calcineurin A/NFATC2 pathway on LESC homeostasis maintenance and corneal epithelial repair was confirmed in Wnt16b-KO mice. Moreover, WNT16b-coincubated hLESCs could reconstruct a stable ocular surface and inhibit corneal neovascularization in mice with LSCD. In conclusion, WNT16b enhances the proliferation and maintains the stemness of hLESCs by activating the non-canonical calcium/calcineurin A/NFATC2 pathway in vitro and in vivo, and accelerates corneal epithelial wound healing.

The antitumor effects of WNT5A against hematological malignancies

The bone marrow (BM) microenvironment (niche) is abnormally altered in acute myeloid leukemia (AML), leading to deficient secretion of proteins, soluble factors, and cytokines by mesenchymal stromal cells (MSC) that modifies the crosstalk between MSC and hematopoietic cells. We focused on a WNT gene/protein family member, WNT5A, which is downregulated in leukemia and correlated with disease progression and poor prognosis. We demonstrated that WNT5A protein upregulated the WNT non-canonical pathway only in leukemic cells, without modulating normal cell behavior. We also introduced a novel WNT5A-mimicking compound, Foxy-5. Our results showed reduction of crucial biological functions that are upregulated in leukemia cells, including ROS generation, cell proliferation, and autophagy, as well as G0/G1 cell cycle arrest. Additionally, Foxy-5 induced early-stage macrophage cell differentiation, a crucial process during leukemia development. At a molecular level, Foxy-5 led to the downregulation of two overexpressed leukemia pathways, PI3K and MAPK, which resulted in a disarrangement of actin polymerization with consequent impairment of CXCL12-induced chemotaxis. Notably, in a novel tri-dimensional bone marrow-mimicking model, Foxy-5 led to reduced leukemia cell growth and similar results were observed in a xenograft in vivo model. Overall, our findings highlight the pivotal role of WNT5A in leukemia and demonstrate that Foxy-5 acts as a specific antineoplastic agent in leukemia, counterbalancing several leukemic oncogenic processes related to the crosstalk in the bone marrow niche, and represents a promising therapeutic option for AML. WNT5A, a WNT gene/protein family member, is naturally secreted by mesenchymal stromal cells and contributes to the maintenance of the bone marrow microenvironment. WNT5A downregulation is correlated with disease progression and poor prognosis. The treatment with Foxy-5, a WNT5A mimetizing compound, counterbalanced several leukemogenic processes that are upregulated in leukemia cells, including ROS generation, cell proliferation, and autophagy and disruption of PI3K and MAPK signaling pathways.

RYK Gene Expression Associated with Drug Response Variation of Temozolomide and Clinical Outcomes in Glioma Patients

Temozolomide (TMZ) chemotherapy is an important tool in the treatment of glioma brain tumors. However, variable patient response and chemo-resistance remain exceptionally challenging. Our previous genome-wide association study (GWAS) identified a suggestively significant association of SNP rs4470517 in the RYK (receptor-like kinase) gene with TMZ drug response. Functional validation of RYK using lymphocytes and glioma cell lines resulted in gene expression analysis indicating differences in expression status between genotypes of the cell lines and TMZ dose response. We conducted univariate and multivariate Cox regression analyses using publicly available TCGA and GEO datasets to investigate the impact of RYK gene expression status on glioma patient overall (OS) and progression-free survival (PFS). Our results indicated that in IDH mutant gliomas, RYK expression and tumor grade were significant predictors of survival. In IDH wildtype glioblastomas (GBM), MGMT status was the only significant predictor. Despite this result, we revealed a potential benefit of RYK expression in IDH wildtype GBM patients. We found that a combination of RYK expression and MGMT status could serve as an additional biomarker for improved survival. Overall, our findings suggest that RYK expression may serve as an important prognostic or predictor of TMZ response and survival for glioma patients.

Redox-Regulation in Cancer Stem Cells

Cancer stem cells (CSCs) represent a small subset of slowly dividing cells with tumor-initiating ability. They can self-renew and differentiate into all the distinct cell populations within a tumor. CSCs are naturally resistant to chemotherapy or radiotherapy. CSCs, thus, can repopulate a tumor after therapy and are responsible for recurrence of disease. Stemness manifests itself through, among other things, the expression of stem cell markers, the ability to induce sphere formation and tumor growth in vivo, and resistance to chemotherapeutics and irradiation. Stemness is maintained by keeping levels of reactive oxygen species (ROS) low, which is achieved by enhanced activity of antioxidant pathways. Here, cellular sources of ROS, antioxidant pathways employed by CSCs, and underlying mechanisms to overcome resistance are discussed.

Canonical Wnt: a safeguard and threat for erythropoiesis

Myeloid dysplastic syndrome (MDS) reflects a preleukemic bone marrow (BM) disorder with limited treatment options and poor disease survival. As only a minority of MDS patients are eligible for curative hematopoietic stem cell transplantation, there is an urgent need to develop alternative treatment options. Chronic activation of Wnt/β-catenin has been implicated to underlie MDS formation and recently assigned to drive MDS transformation to acute myeloid leukemia. Wnt/β-catenin signaling therefore may harbor a pharmaceutical target to treat MDS and/or prevent leukemia formation. However, targeting the Wnt/β-catenin pathway will also affect healthy hematopoiesis in MDS patients. The control of Wnt/β-catenin in healthy hematopoiesis is poorly understood. Whereas Wnt/β-catenin is dispensable for steady-state erythropoiesis, its activity is essential for stress erythropoiesis in response to BM injury and anemia. Manipulation of Wnt/β-catenin signaling in MDS may therefore deregulate stress erythropoiesis and even increase anemia severity. Here, we provide a comprehensive overview of the most recent and established insights in the field to acquire more insight into the control of Wnt/β-catenin signaling in healthy and inefficient erythropoiesis as seen in MDS.

Cellular components of the hematopoietic niche and their regulation of hematopoietic stem cell function

PURPOSE OF REVIEW

Development and functions of hematopoietic stem cells (HSC) are regulated by multiple cellular components of the hematopoietic niche. Here we review the recent advances in studying the role of three such components -- osteoblasts, osteomacs, and megakaryocytes and how they interact with each other in the hematopoietic niche to regulate HSC.

RECENT FINDINGS

Recent advances in transgenic mice models, scRNA-seq, transcriptome profile, proteomics, and live animal imaging have revealed the location of HSC within the bone and signaling molecules required for the maintenance of the niche. Interaction between megakaryocytes, osteoblasts and osteomacs enhances hematopoietic stem and progenitor cells (HSPC) function. Studies also revealed the niche as a dynamic entity that undergoes cellular and molecular changes in response to stress. Aging, which results in reduced HSC function, is associated with a decrease in endosteal niches and osteomacs as well as reduced HSC--megakaryocyte interactions.

SUMMARY

Novel approaches to study the cellular components of the niche and their interactions to regulate HSC development and functions provided key insights about molecules involved in the maintenance of the hematopoietic system. Furthermore, these studies began to build a more comprehensive model of cellular interactions and dynamics in the hematopoietic niche.

WNT5A from the fetal liver vascular niche supports human fetal liver hematopoiesis

The human fetal liver is a critical organ for prenatal hematopoiesis, the study of which offers insights into niche signals that regulate the fates of hematopoietic stem and progenitor cells (HSPCs) during fetal development. Here, we demonstrate that human fetal liver endothelium uniquely supports the maturation and expansion of multilineage HSPCs. Specifically, co-culture of fetal liver-derived immature CD43+CD45- hematopoietic cells with human fetal liver endothelial cells (ECs) led to a profound increase in the numbers of phenotypic CD45+CD34+ HSPCs and multilineage colony-forming progenitors generated in vitro, when compared to co-culture with ECs derived from other organs. We further identified a supportive role for EC-derived WNT5A in this process via gain- and loss-of-function studies within ECs. Our study emphasizes the importance of the organ-specific endothelial niche in supporting hematopoietic development and provides novel insight into signals that may facilitate HSPC expansion in vitro for clinical applications.

The Dual Role of ROS in Hematological Malignancies: Stem Cell Protection and Cancer Cell Metastasis

BACKGROUND AND OBJECTIVE

Reactive oxygen species (ROS) play crucial role in hematopoiesis, regulation of differentiation, self-renewal, and the balance between quiescence and proliferation of hematopoietic stem cells (HSCs). The HSCs are a small population of undifferentiated cells that reside in the bone marrow (BM) and can undergo self-renewal by giving rise to mature cells.

METHODS

Relevant literature was identified through a PubMed search (2000-2019) of English-language papers using the following terms: reactive oxygen species, hematopoietic stem cell, leukemic stem cell, leukemia and chemotherapy.

RESULTS

HSCs are very sensitive to high levels of ROS and increased production of ROS have been attributed to HSC aging. HSC aging induced by both cell intrinsic and extrinsic factors is linked to impaired HSC self-renewal and regeneration. In addition, the elevated ROS levels might even trigger differentiation of Leukemic stem cells (LSCs) and ROS may be involved in the initiation and progression of hematological malignancies, such as leukemia.

CONCLUSION

Targeting genes involved in ROS in LSCs and HSCs are increasingly being used as a critical target for therapeutic interventions. Appropriate concentration of ROS may be an optimal therapeutic target for treatment of leukemia during chemotherapy, but still more studies are required to better understanding of the of ROS role in blood disorders.

Cell-intrinsic Wnt4 promotes hematopoietic stem and progenitor cell self-renewal

Although intracellular Wnt signaling pathways need to be tightly regulated to promote hematopoietic stem cell self-renewal, the source and identity of important Wnt ligands in the bone marrow is still largely unknown. The noncanonical ligand Wnt4 is expressed in the bone marrow as well as in the stroma, and its overexpression in fetal liver cells facilitates thymic recovery; however, its impact on adult hematopoietic stem cell function remains unclear. Here, we report that the deletion of Wnt4 from hematopoietic cells in mice (Wnt4^Δ/Δ ) resulted in decreased lymphopoiesis at steady state. This was likely at least in part due to the increased proinflammatory environment present in the bone marrow of Wnt4^Δ/Δ mice. Wnt4^Δ/Δ hematopoietic stem cells displayed reduced reconstitution capacity in serial transplants, thus demonstrating defective self-renewal, and they expanded poorly in response to lipopolysaccharide stimulation. This appeared to be the result of the absence of Wnt4 in stem/progenitor cells, as myeloid-restricted Wnt4 deletion had no notable effect. Finally, we observed that Wnt4^Δ/Δ stem/progenitor cells were more quiescent, presenting enhanced levels of stress-associated JNK phosphorylation and p16^INK4a expression, likely contributing to the reduced expansion observed in transplants. In conclusion, our results identify a new, largely autocrine role for Wnt4 in hematopoietic stem cell self-renewal, suggesting that regulation of Wnt signaling in hematopoiesis may not need Wnt secretion and could be independent of morphogen gradients.

Endothelial Jak3 expression enhances pro-hematopoietic angiocrine function in mice

Jak3 is the only non-promiscuous member of the Jak family of secondary messengers. Studies to date have focused on understanding and targeting the cell-autonomous role of Jak3 in immunity, while functional Jak3 expression outside the hematopoietic system remains largely unreported. We show that Jak3 is expressed in endothelial cells across hematopoietic and non-hematopoietic organs, with heightened expression in the bone marrow. The bone marrow niche is understood as a network of different cell types that regulate hematopoietic function. We show that the Jak3-/- bone marrow niche is deleterious for the maintenance of long-term repopulating hematopoietic stem cells (LT-HSCs) and that JAK3-overexpressing endothelial cells have increased potential to expand LT-HSCs in vitro. This work may serve to identify a novel function for a highly specific tyrosine kinase in the bone marrow vascular niche and to further characterize the LT-HSC function of sinusoidal endothelium.

Aging and leukemic evolution of hematopoietic stem cells under various stress conditions

Hematopoietic stem cells (HSCs) have self-renewal capacity and differentiation potential into all lineages of blood cells throughout the lifetime of an organism. The function of HSCs gradually changes during aging. To date, various stress factors influencing HSC aging have been identified. The increased production of reactive oxygen species and DNA damage responses are causatively attributed to HSC aging. The increased apolarity is a prominent feature of aged HSCs, whereas it is less obvious in young HSCs. The bone marrow (BM) microenvironment niche is a crucial factor for HSC aging. Mesenchymal stem cells show skewed differentiation during aging, which leads to decreased bone formation and increased adipogenesis. The accumulation of adipocytes confers negative effects on hematopoiesis. Loss of sympathetic nerve fibers or adrenoreceptor β3 signaling induces premature HSC and niche aging. Epigenetic regulators such as polycomb group proteins and the sirtuin family of proteins act to prevent premature aging. Targeting these factors, several rejuvenation strategies for aged HSCs have been employed in mice. However, we still do not know whether these strategies can be extrapolated to human HSCs. Aging is frequently accompanied by the development of clonal hematopoiesis, which is called age-related clonal hematopoiesis (ARCH) or clonal hematopoiesis of indeterminate potential (CHIP). Most ARCH/CHIP mutations occur in genes encoding epigenetic regulators including DNMT3A, TET2, and ASXL1, which suggests the relevance of epigenetic drift during the aging process. ARCH/CHIP is a strong risk factor for subsequent hematologic cancer. Notably, it also has an impact on the development of non-malignant disorders such as coronary heart disease. Further studies are warranted to decipher the complete picture of molecular crosstalk that regulates HSC aging.

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.

Ryk modulates the niche activity of mesenchymal stromal cells by fine-tuning canonical Wnt signaling

The importance of modulating the intensity of Wnt signaling has been highlighted in various biological models, but their mechanisms remain unclear. In this study, we found that Ryk—an atypical Wnt receptor with a pseudokinase domain—has a Wnt-modulating effect in bone marrow stromal cells to control hematopoiesis-supporting activities. We first found that Ryk is predominantly expressed in the mesenchymal stromal cells (MSCs) of the bone marrow (BM) compared with hematopoietic cells. Downregulation of Ryk in MSCs decreased their clonogenic activity and ability to support self-renewing expansion of primitive hematopoietic progenitors (HPCs) in response to canonical Wnt ligands. In contrast, under high concentrations of Wnt, Ryk exerted suppressive effects on the transactivation of target genes and HPC-supporting effects in MSCs, thus fine-tuning the signaling intensity of Wnt in BM stromal cells. This ability of Ryk to modulate the HPC-supporting niche activity of MSCs was abrogated by induction of deletion mutants of Ryk lacking the intracellular domain or extracellular domain, indicating that the pseudokinase-containing intracellular domain mediates the Wnt-modulating effects in response to extracellular Wnt ligands. These findings indicate that the ability of the BM microenvironment to respond to extracellular signals and support hematopoiesis may be fine-tuned by Ryk via modulation of Wnt signaling intensity to coordinate hematopoietic activity.

Steady production of immune and blood cells depends on a signaling protein that helps maintain stable stem cell populations within the bone marrow. Hematopoietic stem cells (HSCs), which give rise to blood cells, reside within a supportive “niche” surrounded by mesenchymal stromal cells (MSCs), with extensive communication between the two populations. Researchers led by Il-Hoan Oh at The Catholic University of Korea, Seoul, have now identified a mechanism that MSCs employ to stabilize the niche environment through fine-tuning the signaling intensity of Wnt. Oh and colleagues focused on a signaling pathway that controls the undifferentiated state of HSCs, and showed that these signals are specifically modulated by an MSC protein known as Ryk. Without Ryk, MSCs can no longer promote HSC proliferation. However, when these signals are excessively strong, Ryk helps suppress proliferation to keep HSC numbers under control.

Doxycycline-Dependent Self-Inactivation of CRISPR-Cas9 to Temporally Regulate On- and Off-Target Editing

Exome and deep sequencing of cells treated with a panel of lentiviral guide RNA demonstrate that both on- and off-target editing proceed in a time-dependent manner. Thus, methods to temporally control Cas9 activity would be beneficial. To address this need, we describe a "self-inactivating CRISPR (SiC)" system consisting of a single guide RNA that deactivates the Streptococcus pyogenes Cas9 nuclease in a doxycycline-dependent manner. This enables defined, temporal control of Cas9 activity in any cell type and also in vivo. Results show that SiC may enable a reduction in off-target editing, with less effect on on-target editing rates. This tool facilitates diverse applications including (1) the timed regulation of genetic knockouts in hard-to-transfect cells using lentivirus, including human leukocytes for the identification of glycogenes regulating leukocyte-endothelial cell adhesion; (2) genome-wide lentiviral sgRNA (single guide RNA) library applications where Cas9 activity is ablated after allowing pre-determined editing times. Thus, stable knockout cell pools are created for functional screens; and (3) temporal control of Cas9-mediated editing of myeloid and lymphoid cells in vivo, both in mouse peripheral blood and bone marrow. Overall, SiC enables temporal control of gene editing and may be applied in diverse application including studies that aim to reduce off-target genome editing.

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.

Cellular and epigenetic drivers of stem cell ageing

Adult tissue stem cells have a pivotal role in tissue maintenance and regeneration throughout the lifespan of multicellular organisms. Loss of tissue homeostasis during post-reproductive lifespan is caused, at least in part, by a decline in stem cell function and is associated with an increased incidence of diseases. Hallmarks of ageing include the accumulation of molecular damage, failure of quality control systems, metabolic changes and alterations in epigenome stability. In this Review, we discuss recent evidence in support of a novel concept whereby cell-intrinsic damage that accumulates during ageing and cell-extrinsic changes in ageing stem cell niches and the blood result in modifications of the stem cell epigenome. These cumulative epigenetic alterations in stem cells might be the cause of the deregulation of developmental pathways seen during ageing. In turn, they could confer a selective advantage to mutant and epigenetically drifted stem cells with altered self-renewal and functions, which contribute to the development of ageing-associated organ dysfunction and disease.

Knockdown of long noncoding RNA WNT5A-AS restores the fate of neural stem cells exposed to sevoflurane via inhibiting WNT5A/Ryk-ROS signaling

Long noncoding RNAs (lncRNAs) have been implicated in neurogenesis. LncRNA WNT5A-AS is upregulated in neural stem cells (NSCs), the proliferation of which is inhibited by sevoflurane. Thus, we hypothesized that knocking down of lncRNA WNT5A-AS may restore the fate of NSCs exposed to sevoflurane. To test this hypothesis, NSCs obtained from postnatal Sprague-Dawley rats were exposed to 2.4% sevoflurane or control gas for 6 h. Bioinformatics analysis, quantitative PCR and RNA interference technology were used to identify the properties of lncRNA WNT5A-AS. Cell proliferation was assessed using counting a Cell Counting Kit-cell 8 assay, a 5-ethynyl-2'-deoxyuridine incorporation assay, and a plate cloning assay. Cell survival was detected by flow cytometry, which was also used to examine the levels of reactive oxygen species (ROS) and the cell cycle. The levels of WNT5A and receptor tyrosine kinase (Ryk) were measured via Western blotting. LncRNA WNT5A-AS was identified to have low coding potency and to be located on the antisense strand of WNT5A. The level of upregulated lncRNA WNT5A-AS was positively correlated with that of WNT5A in response to sevoflurane exposure. The knockdown of lncRNA WNT5A-AS promoted the proliferation and survival of NSCs, whereas it suppressed the WNT5A/Ryk-ROS signaling and drove cell cycle processes. Taken together, findings strongly suggest that the inhibition of lncRNA WNT5A-AS can rescue the fate of NSCs. In addition, WNT5A/Ryk-ROS signaling might be a downstream target of lncRNA WNT5A-AS.

Quiescence: Good and Bad of Stem Cell Aging

Stem cells are required for lifelong homeostasis and regeneration of tissues and organs in mammals, but the function of stem cells declines during aging. To preserve stem cells during life, they are kept in a quiescent state with low metabolic and low proliferative activity. However, activation of quiescent stem cells - an essential process for organ homeostasis/regeneration - requires concerted and faithful regulation of multiple molecular circuits controlling biosynthetic processes, repair mechanisms, and metabolic activity. Thus, while protecting stem cell maintenance, quiescence comes at the cost of vulnerability during the process of stem cell activation. Here we discuss molecular and biochemical processes regulating stem cells' maintenance in and exit from quiescence and how age-related failures of these circuits can contribute to organism aging.

Identification of the X-linked germ cell specific miRNAs (XmiRs) and their functions

MicroRNAs (miRNAs) play a critical role in multiple aspects of biology. Dicer, an RNase III endonuclease, is essential for the biogenesis of miRNAs, and the germ cell-specific Dicer1 knockout mouse shows severe defects in gametogenesis. How miRNAs regulate germ cell development is still not fully understood. In this study, we identified germ cell-specific miRNAs (miR-741-3p, miR-871-3p, miR-880-3p) by analyzing published RNA-seq data of mouse. These miRNA genes are contiguously located on the X chromosome near other miRNA genes. We named them X chromosome-linked miRNAs (XmiRs). To elucidate the functions of XmiRs, we generated knockout mice of these miRNA genes using the CRISPR/Cas9-mediated genome editing system. Although no histological abnormalities were observed in testes of F0 mice in which each miRNA gene was disrupted, a deletion covering miR-871 and miR-880 or covering all XmiRs (ΔXmiRs) resulted in arrested spermatogenesis in meiosis in a few seminiferous tubules, indicating their redundant functions in spermatogenesis. Among candidate targets of XmiRs, we found increased expression of a gene encoding a WNT receptor, FZD4, in ΔXmiRs testis compared with that in wildtype testis. miR-871-3p and miR-880-3p repressed the expression of Fzd4 via the 3′-untranslated region of its mRNA. In addition, downstream genes of the WNT/β-catenin pathway were upregulated in ΔXmiRs testis. We also found that miR-871, miR-880, and Fzd4 were expressed in spermatogonia, spermatocytes and spermatids, and overexpression of miR-871 and miR-880 in germ stem cells in culture repressed their increase in number and Fzd4 expression. Previous studies indicated that the WNT/β-catenin pathway enhances and represses proliferation and differentiation of spermatogonia, respectively, and our results consistently showed that stable β-catenin enhanced GSC number. In addition, stable β-catenin partially rescued reduced GSC number by overexpression of miR-871 and miR-880. The results together suggest that miR-871 and miR-880 cooperatively regulate the WNT/β-catenin pathway during testicular germ cell development.

Integrating Enhancer Mechanisms to Establish a Hierarchical Blood Development Program

Hematopoietic development requires the transcription factor GATA-2, and GATA-2 mutations cause diverse pathologies, including leukemia. GATA-2-regulated enhancers increase Gata2 expression in hematopoietic stem/progenitor cells and control hematopoiesis. The +9.5-kb enhancer activates transcription in endothelium and hematopoietic stem cells (HSCs), and its deletion abrogates HSC generation. The -77-kb enhancer activates transcription in myeloid progenitors, and its deletion impairs differentiation. Since +9.5^-/- embryos are HSC deficient, it was unclear whether the +9.5 functions in progenitors or if GATA-2 expression in progenitors solely requires -77. We further dissected the mechanisms using -77;+9.5 compound heterozygous (CH) mice. The embryonic lethal CH mutation depleted megakaryocyte-erythrocyte progenitors (MEPs). While the +9.5 suffices for HSC generation, the -77 and +9.5 must reside on one allele to induce MEPs. The -77 generated burst-forming unit-erythroid through the induction of GATA-1 and other GATA-2 targets. The enhancer circuits controlled signaling pathways that orchestrate a GATA factor-dependent blood development program.

The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca²⁺ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.

EDAG promotes the expansion and survival of human CD34+ cells

EDAG is multifunctional transcriptional regulator primarily expressed in the lin^loc^-kit⁺Sca-1⁺ hematopoietic stem cells (HSC) and CD34⁺ progenitor cells. Previous studies indicate that EDAG is required for maintaining hematopoietic lineage commitment balance. Here using ex vivo culture and HSC transplantation models, we report that EDAG enhances the proliferative potential of human cord blood CD34⁺ cells, increases survival, prevents cell apoptosis and promotes their repopulating capacity. Moreover, EDAG overexpression induces rapid entry of CD34⁺ cells into the cell cycle. Gene expression profile analysis indicate that EDAG knockdown leads to down-regulation of various positive cell cycle regulators including cyclin A, B, D, and E. Together these data provides novel insights into EDAG in regulation of expansion and survival of human hematopoietic stem/progenitor cells.

Non-canonical Wnt signaling regulates neural stem cell quiescence during homeostasis and after demyelination

Adult neural stem cells (NSCs) reside in a specialized microenvironment, the subventricular zone (SVZ), which provides them with unique signaling cues to control their basic properties and prevent their exhaustion. While the signaling mechanisms that regulate NSC lineage progression are well characterized, the molecular mechanisms that trigger the activation of quiescent NSCs during homeostasis and tissue repair are still unclear. Here, we uncovered that the NSC quiescent state is maintained by Rho-GTPase Cdc42, a downstream target of non-canonical Wnt signaling. Mechanistically, activation of Cdc42 induces expression of molecules involved in stem cell identity and anchorage to the niche. Strikingly, during a demyelination injury, downregulation of non-canonical Wnt-dependent Cdc42 activity is necessary to promote activation and lineage progression of quiescent NSCs, thereby initiating the process of tissue repair.

Following demyelination injury, neural stem cells (NSCs) in the subventricular zone switch to an activated state. Here, the authors show that a transient shift from non-canonical to canonical Wnt signaling is necessary for activation of quiescent NSCs to achieve tissue homeostasis and brain repair.

BET Inhibitors Suppress ALDH Activity by Targeting ALDH1A1 Super-Enhancer in Ovarian Cancer

The emergence of tumor cells with certain stem-like characteristics, such as high aldehyde dehydrogenase (ALDH) activity due to ALDH1A1 expression, contributes to chemotherapy resistance and tumor relapse. However, clinically applicable inhibitors of ALDH activity have not been reported. There is evidence to suggest that epigenetic regulation of stem-related genes contributes to chemotherapy efficacy. Here, we show that bromodomain and extraterminal (BET) inhibitors suppress ALDH activity by abrogating BRD4-mediated ALDH1A1 expression through a super-enhancer element and its associated enhancer RNA. The clinically applicable small-molecule BET inhibitor JQ1 suppressed the outgrowth of cisplatin-treated ovarian cancer cells both in vitro and in vivo Combination of JQ1 and cisplatin improved the survival of ovarian cancer-bearing mice in an orthotopic model. These phenotypes correlate with inhibition of ALDH1A1 expression through a super-enhancer element and other stem-related genes in promoter regions bound by BRD4. Thus, targeting the BET protein BRD4 using clinically applicable small-molecule inhibitors, such as JQ1, is a promising strategy for targeting ALDH activity in epithelial ovarian cancer. Cancer Res; 76(21); 6320-30. ©2016 AACR.

Diverse regulation of mammary epithelial growth and branching morphogenesis through noncanonical Wnt signaling

The mammary gland consists of an adipose tissue that, in a process called branching morphogenesis, is invaded by a ductal epithelial network comprising basal and luminal epithelial cells. Stem and progenitor cells drive mammary growth, and their proliferation is regulated by multiple extracellular cues. One of the key regulatory pathways for these cells is the β-catenin-dependent, canonical wingless-type MMTV integration site family (WNT) signaling pathway; however, the role of noncanonical WNT signaling within the mammary stem/progenitor system remains elusive. Here, we focused on the noncanonical WNT receptors receptor tyrosine kinase-like orphan receptor 2 (ROR2) and receptor-like tyrosine kinase (RYK) and their activation by WNT5A, one of the hallmark noncanonical WNT ligands, during mammary epithelial growth and branching morphogenesis. We found that WNT5A inhibits mammary branching morphogenesis in vitro and in vivo through the receptor tyrosine kinase ROR2. Unexpectedly, WNT5A was able to enhance mammary epithelial growth, which is in contrast to its next closest relative WNT5B, which potently inhibits mammary stem/progenitor proliferation. We found that RYK, but not ROR2, is necessary for WNT5A-mediated promotion of mammary growth. These findings provide important insight into the biology of noncanonical WNT signaling in adult stem/progenitor cell regulation and development. Future research will determine how these interactions go awry in diseases such as breast cancer.

The non-canonical Wnt receptor Ryk regulates hematopoietic stem cell repopulation in part by controlling proliferation and apoptosis

The development of blood and immune cells requires strict control by various signaling pathways in order to regulate self-renewal, differentiation and apoptosis in stem and progenitor cells. Recent evidence indicates critical roles for the canonical and non-canonical Wnt pathways in hematopoiesis. The non-canonical Wnt pathway is important for establishment of cell polarity and cell migration and regulates apoptosis in the thymus. We here investigate the role of the non-canonical Wnt receptor Ryk in hematopoiesis and lymphoid development. We show that there are dynamic changes in Ryk expression during development and in different hematopoietic tissues. Functionally, Ryk regulates NK cell development in a temporal fashion. Moreover, Ryk-deficient mice show diminished, but not absent self-renewal of hematopoietic stem cells (HSC), via effects on mildly increased proliferation and apoptosis. Thus, Ryk deficiency in HSCs from fetal liver reduces their quiescence, leading to proliferation-induced apoptosis and decreased self-renewal.

Noncanonical Wnt5a-Ca(2+) -NFAT signaling axis in pesticide induced bone marrow aplasia mouse model: A study to explore the novel mechanism of pesticide toxicity

According to case-control studies, long-term pesticide exposure can cause bone marrow aplasia like hematopoietic degenerative disease leading to impaired hematopoiesis and increased risk of aplastic anemia in human subjects. However, the exact mechanism of pesticide mediated hematotoxicity still remains elusive. In this study, we investigated the role of noncanonical Wnt signaling pathway, a crucial regulator of adult hematopoiesis, in pesticide induced bone marrow aplasia mouse model. Aplasia mouse model was developed following inhalation and dermal exposure of 5% aqueous mixture of common agriculturally used pesticides for 6 h/day for 5 days a week up to 90 days. After that, blood hemogram, marrow smear, cellularity, scanning electron microscopy, extramedullary hematopoiesis and flowcytometric expression analysis of noncanonical Wnt signaling components, such as Wnt 5a, fzd5, NFAT, IFN-γ, intracellular Ca(2+) level were evaluated in the bone marrow hematopoietic stem/progenitor compartment of the control and pesticide induced aplasia groups of animals. Results showed that pesticide exposed mice were anemic with peripheral blood pancytopenia, hypocellular degenerative marrow, and extramedullary hematopoiesis in the spleen. Upon pesticide exposure, Wnt 5a expression was severely downregulated with a decline in intracellular Ca(2+) level. Moreover, downstream of Wnt5a, we observed sharp downregulation of NFATc2 transcription factor expression, the major target of pesticide toxicity and its target molecule IFN-γ. Taken together, our result suggests that deregulation of Wnt5a-Ca(2+) -NFAT signaling axis in the hematopoietic stem/progenitor compartment plays a crucial role behind the pathogenesis of pesticide mediated bone marrow aplasia by limiting primitive hematopoietic stem cells' ability to maintain hematopoietic homeostasis and reconstitution mechanism in vivo during xenobiotic stress leading to ineffective hematopoiesis and evolution of bone marrow aplasia. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1163-1175, 2016.

Enhanced Hematopoietic Stem Cell Self-Renewal-Promoting Ability of Clonal Primary Mesenchymal Stromal/Stem cells Versus Their Osteogenic Progeny

Long-term self-renewing hematopoietic stem cell (LT-HSC) homeostasis within the bone marrow (BM) of adult mammals is regulated by complex interactions between LT-HSC and a number of niche-associated cell types including mesenchymal stromal/stem cells (MSC), osteoblasts (OB), macrophage, and neuronal cells in close proximity with the vasculature. Here, we cloned and functionally characterized a murine BM MSC subpopulation that was uniformly Nestin⁺ Lepr ⁺ Sca-1⁺ CD146⁺ and could be stably propagated with high colony-forming unit fibroblast re-cloning efficiency. MSC synergized with SCF and IL-11 to support a 20-fold expansion in true LT-HSC after 10-days of in vitro coculture. Optimal stimulation of LT-HSC expansion was minimally dependent on Notch signaling but was significantly enhanced by global inhibition of Wnt signaling. The self-renewal-promoting activity of MSC was progressively lost when MSC clones were differentiated into mature OB. This suggests that the stage of osteoblast development may significantly impact the ability of osteolineage cells to support LT-HSC homeostasis in vivo. Stem Cells 2017;35:473-484.

Cofactors of LIM Domains Associate with Estrogen Receptor α to Regulate the Expression of Noncoding RNA H19 and Corneal Epithelial Progenitor Cell Function

Cofactors of LIM domain proteins, CLIM1 and CLIM2, are widely expressed transcriptional cofactors that are recruited to gene regulatory regions by DNA-binding proteins, including LIM domain transcription factors. In the cornea, epithelium-specific expression of a dominant negative (DN) CLIM under the keratin 14 (K14) promoter causes blistering, wounding, inflammation, epithelial hyperplasia, and neovascularization followed by epithelial thinning and subsequent epidermal-like differentiation of the corneal epithelium. The defects in corneal epithelial differentiation and cell fate determination suggest that CLIM may regulate corneal progenitor cells and the transition to differentiation. Consistent with this notion, the K14-DN-Clim corneal epithelium first exhibits increased proliferation followed by fewer progenitor cells with decreased proliferative potential. In vivo ChIP-sequencing experiments with corneal epithelium show that CLIM binds to and regulates numerous genes involved in cell adhesion and proliferation, including limbally enriched genes. Intriguingly, CLIM associates primarily with non-LIM homeodomain motifs in corneal epithelial cells, including that of estrogen receptor α. Among CLIM targets is the noncoding RNA H19 whose deregulation is associated with Silver-Russell and Beckwith-Wiedemann syndromes. We demonstrate here that H19 negatively regulates corneal epithelial proliferation. In addition to cell cycle regulators, H19 affects the expression of multiple cell adhesion genes. CLIM interacts with estrogen receptor α at the H19 locus, potentially explaining the higher expression of H19 in female than male corneas. Together, our results demonstrate an important role for CLIM in regulating the proliferative potential of corneal epithelial progenitors and identify CLIM downstream target H19 as a regulator of corneal epithelial proliferation and adhesion.

WNT5A promotes stemness characteristics in nasopharyngeal carcinoma cells leading to metastasis and tumorigenesis

Nasopharyngeal carcinoma (NPC) has the highest metastasis rate among head and neck cancers with unclear mechanism. WNT5A belongs to the WNT family of cysteine-rich secreted glycoproteins. Our previous high-throughput gene expression profiling revealed that WNT5A was up-regulated in highly metastatic cells. In the present study, we first confirmed the elevated expression of WNT5A in metastatic NPC tissues at both the mRNA and protein levels. We then found that WNT5A promoted epithelial-mesenchymal transition (EMT) in NPC cells, induced the accumulation of CD24-CD44+ cells and side population, which are believed to be cancer stem cell characteristics. Moreover, WNT5A promoted the migration and invasion of NPC cells in vitro, while in vivo treatment with recombinant WNT5A promoted lung metastasis. Knocking down WNT5A diminished NPC tumorigenesis in vivo. When elevated expression of WNT5A coincided with the elevated expression of vimentin in the primary NPC, the patients had a poorer prognosis. Among major signaling pathways, protein kinase C (PKC) signaling was activated by WNT5A in NPC cells. A positive feedback loop between WNT5A and phospho-PKC to promote EMT was also revealed. Taken together, these data suggest that WNT5A is an important molecule in promoting stem cell characteristics in NPC, leading to tumorigenesis and metastasis.

WNT-5A: signaling and functions in health and disease

WNT-5A plays critical roles in a myriad of processes from embryonic morphogenesis to the maintenance of post-natal homeostasis. WNT-5A knock-out mice fail to survive and present extensive structural malformations. WNT-5A predominantly activates β-catenin-independent WNT signaling cascade but can also activate β-catenin signaling to relay its diverse cellular effects such as cell polarity, migration, proliferation, cell survival, and immunomodulation. Moreover, aberrant WNT-5A signaling is associated with several human pathologies such as cancer, fibrosis, and inflammation. Thus, owing to its diverse functions, WNT-5A is a crucial signaling molecule currently under intense investigation with efforts to not only delineate its signaling mechanisms and functions in physiological and pathological conditions, but also to develop strategies for its therapeutic targeting.

Receptor tyrosine kinase expression of circulating tumor cells in small cell lung cancer

Small cell lung cancer (SCLC) has a poor prognosis and is found disseminated at first presentation in the majority of cases. The cell biological mechanisms underlying metastasis and drug resistance are not clear. SCLC is characterized by high numbers of circulating tumor cells (CTCs) and we were able to expand several CTC lines ex vivo and to relate chitinase-3-like-1/YKL-40 (CHI3L1) as marker. Availability of expanded SCLC CTC cells allowed for a screening of receptor tyrosine kinases (RTKs) expressed. The metastatic CHI3L1-negative SCLC cell line SCLC26A, established from a pleural effusion was used for comparison. The CTC cell line BHGc10 was found to exhibit increased expression of RYK, AXL, Tie-1, Dtk, ROR1/2, several ephrins (Eph) and FGF/EGF receptors compared to SCLC26A. All of these RTKs have been associated with cell motility, invasion and poor prognosis in diverse cancer entities without knowledge of their association with CTCs. The identification of RYK, AXL and ROR1/2 as pseudokinases, lacking activity, seems to be related to the observed failure of RTK inhibitors in SCLC. These kinases are involved in the noncanonical WNT pathway and their expression in SCLC CTCs represents a cancer stem cell-like phenotype.

Activation of OCT4 enhances ex vivo expansion of human cord blood hematopoietic stem and progenitor cells by regulating HOXB4 expression

Although hematopoietic stem cells (HSC) are the best characterized and the most clinically used adult stem cells, efforts are still needed to understand how to best ex vivo expand these cells. Here we present our unexpected finding that OCT4 is involved in the enhancement of cytokine-induced expansion capabilities of human cord blood (CB) HSC. Activation of OCT4 by Oct4-activating compound 1 (OAC1) in CB CD34(+) cells enhanced ex vivo expansion of HSC, as determined by a rigorously defined set of markers for human HSC, and in vivo short-term and long-term repopulating ability in NSG mice. Limiting dilution analysis revealed that OAC1 treatment resulted in 3.5-fold increase in the number of SCID repopulating cells (SRCs) compared with that in day 0 uncultured CD34(+) cells and 6.3-fold increase compared with that in cells treated with control vehicle. Hematopoietic progenitor cells, as assessed by in vitro colony formation, were also enhanced. Furthermore, we showed that OAC1 treatment led to OCT4-mediated upregulation of HOXB4. Consistently, siRNA-mediated knockdown of HOXB4 expression suppressed effects of OAC1 on ex vivo expansion of HSC. Our study has identified the OCT4-HOXB4 axis in ex vivo expansion of human CB HSC.

Frizzled-6 Regulates Hematopoietic Stem/Progenitor Cell Survival and Self-Renewal

Adult hematopoietic stem/progenitor cell (HSPC) numbers remain stable in the absence of external stressors. After bone marrow (BM) transplant, HSPCs need to expand substantially to repopulate the BM and replenish the peripheral blood cell pool. In this study, we show that a noncanonical Wnt receptor, Frizzled-6 (Fzd6), regulates HSPC expansion and survival in a hematopoietic cell-intrinsic manner. Fzd6 deficiency increased the ratio of Flt3(hi) multipotent progenitors to CD150(+) stem cells in the mouse BM, suggesting defective stem cell maintenance. Competitive transplantation experiments demonstrated that Fzd6(-) (/) (-) HSPCs were able to home to the BM but were severely impaired in their capacity to reconstitute a lethally irradiated host. Lack of Fzd6 resulted in a strong activation of caspase-3 and a gradual loss of donor HSPCs and peripheral blood granulocytes. Fzd6 was also necessary for the efficient HSPC expansion during emergency hematopoiesis. Mechanistically, Fzd6 is a negative regulator of Cdc42 clustering in polarized cells. Furthermore, β-catenin-dependent signaling may be disinhibited in Fzd6(-) (/) (-) HSPCs. Collectively, our data reveal that Fzd6 has an essential role in HSPC maintenance and survival. Noncanonical Wnt-Fzd6 signaling pathway could thus present an interesting target for promoting HSPC expansion and multilineage hematopoietic recovery after transplant.

Wnts are dispensable for differentiation and self-renewal of adult murine hematopoietic stem cells

Wnt signaling controls early embryonic hematopoiesis and dysregulated β-catenin is implicated in leukemia. However, the role of Wnts and their source in adult hematopoiesis is still unclear, and is clinically important as upstream Wnt inhibitors enter clinical trials. We blocked Wnt secretion in hematopoietic lineages by targeting Porcn, a membrane-bound O-acyltransferase that is indispensable for the activity and secretion of all vertebrate Wnts. Surprisingly, deletion of Porcn in Rosa-CreER(T2)/Porcn(Del), MX1-Cre/Porcn(Del), and Vav-Cre/Porcn(Del) mice had no effects on proliferation, differentiation, or self-renewal of adult hematopoietic stem cells. Targeting Wnt secretion in the bone marrow niche by treatment with a PORCN inhibitor, C59, similarly had no effect on hematopoiesis. These results exclude a role for hematopoietic PORCN-dependent Wnts in adult hematopoiesis. Clinical use of upstream Wnt inhibitors is not likely to be limited by effects on hematopoiesis.

Human epicardial cell-conditioned medium contains HGF/IgG complexes that phosphorylate RYK and protect against vascular injury

AIMS

The aim of this study was to evaluate the paracrine activity of human epicardial-derived cells (hEPDCs) to screen for secreted vasoprotective factors and develop therapeutics to treat vascular reperfusion injury.

METHODS AND RESULTS

Epicardial cells support cardiac development, repair, and remodelling after injury in part, through paracrine activity. We hypothesized that secreted ligands from hEPDCs would protect vascular integrity after myocardial infarction (MI) with reperfusion. During simulated ischaemia in culture (24-48 h), concentrated hEPDC-conditioned medium (EPI CdM) increased survival of primary cardiac endothelial cells. In a rat MI model, EPI CdM treatment reduced vascular injury in vivo after reperfusion. By phospho-receptor tyrosine kinase (RTK) arrays, ELISA, and neutralizing antibody screens, we identified hepatocyte growth factor (HGF) as a key vasoprotective factor in EPI CdM. Unexpectedly, we observed that some of the HGF in EPI CdM formed complexes with polyclonal IgG. Following reperfusion, preparations of HGF/IgG complexes provided greater vascular protection than free HGF with IgG. HGF/IgG complexes localized to blood vessels in vivo and increased HGF retention time after administration. In subsequent screens, we found that 'related to tyrosine kinase' (RYK) receptor was phosphorylated after exposure of cardiac endothelial cells to HGF/IgG complexes, but not to free HGF with IgG. The enhanced protection conferred by HGF/IgG complexes was lost after antibody blockade of RYK. Notably, the HGF/IgG complex is the first 'ligand' shown to promote phosphorylation of RYK.

CONCLUSION

Early treatment with HGF/IgG complexes after myocardial ischaemia with reperfusion may rescue tissue through vasoprotection conferred by c-Met and RYK signalling.

Neural Differentiation of Human Adipose Tissue-Derived Stem Cells Involves Activation of the Wnt5a/JNK Signalling

Stem cells are a powerful resource for cell-based transplantation therapies, but understanding of stem cell differentiation at the molecular level is not clear yet. We hypothesized that the Wnt pathway controls stem cell maintenance and neural differentiation. We have characterized the transcriptional expression of Wnt during the neural differentiation of hADSCs. After neural induction, the expressions of Wnt2, Wnt4, and Wnt11 were decreased, but the expression of Wnt5a was increased compared with primary hADSCs in RT-PCR analysis. In addition, the expression levels of most Fzds and LRP5/6 ligand were decreased, but not Fzd3 and Fzd5. Furthermore, Dvl1 and RYK expression levels were downregulated in NI-hADSCs. There were no changes in the expression of ß-catenin and GSK3ß. Interestingly, Wnt5a expression was highly increased in NI-hADSCs by real time RT-PCR analysis and western blot. Wnt5a level was upregulated after neural differentiation and Wnt3, Dvl2, and Naked1 levels were downregulated. Finally, we found that the JNK expression was increased after neural induction and ERK level was decreased. Thus, this study shows for the first time how a single Wnt5a ligand can activate the neural differentiation pathway through the activation of Wnt5a/JNK pathway by binding Fzd3 and Fzd5 and directing Axin/GSK-3ß in hADSCs.

Standard sub-thermoneutral caging temperature influences radiosensitivity of hematopoietic stem and progenitor cells

The production of new blood cells relies on a hierarchical network of hematopoietic stem and progenitor cells (HSPCs). To maintain lifelong hematopoiesis, HSPCs must be protected from ionizing radiation or other cytotoxic agents. For many years, murine models have been a valuable source of information regarding factors that either enhance or reduce the survival of HSPCs after exposure of marrow to ionizing radiation. In a recent series of studies, however, it has become clear that housing-related factors such as the cool room temperature required for laboratory mice can exert a surprising influence on the outcome of experiments. Here we report that the mild, but chronic cold-stress endured by mice housed under these conditions exerts a protective effect on HSPCs after both non-lethal and lethal doses of total body irradiation (TBI). Alleviation of this cold-stress by housing mice at a thermoneutral temperature (30°C) resulted in significantly greater baseline radiosensitivity to a lethal dose of TBI with more HSPCs from mice housed at thermoneutral temperature undergoing apoptosis following non-lethal TBI. Cold-stressed mice have elevated levels of norepinephrine, a key molecule of the sympathetic nervous system that binds to β-adrenergic receptors. We show that blocking this signaling pathway in vivo through use of the β-blocker propanolol completely mitigates the protective effect of cold-stress on HSPC apoptosis. Collectively this study demonstrates that chronic stress endured by the standard housing conditions of laboratory mice increases the resistance of HSPCs to TBI-induced apoptosis through a mechanism that depends upon β-adrenergic signaling. Since β-blockers are commonly prescribed to a wide variety of patients, this information could be important when predicting the clinical impact of HSPC sensitivity to TBI.

Paracrine WNT5A Signaling Inhibits Expansion of Tumor-Initiating Cells

It is not well understood how paracrine communication between basal and luminal cell populations in the mammary gland affects tumorigenesis. During ErbB2-induced mammary tumorigenesis, enriched mammary stem cells that represent a subpopulation of basal cells exhibit enhanced tumorigenic capacity compared with the corresponding luminal progenitors. Transcript profiling of tumors derived from basal and luminal tumor-initiating cells (TIC) revealed preferential loss of the noncanonical Wnt ligand WNT5A in basal TIC-derived tumors. Heterozygous loss of WNT5A was correlated with shorter survival of breast cancer patients. In a mouse model of ErbB2-induced breast cancer, Wnt5a heterozygosity promoted tumor multiplicity and pulmonary metastasis. As a TGFβ substrate, luminal cell-produced WNT5A induced a feed-forward loop to activate SMAD2 in a RYK and TGFβR1-dependent manner to limit the expansion of basal TIC in a paracrine fashion, a potential explanation for the suppressive effect of WNT5A in mammary tumorigenesis. Our results identify the WNT5A/RYK module as a spatial regulator of the TGFβ-SMAD signaling pathway in the context of mammary gland development and carcinogenesis, offering a new perspective on tumor suppression provided by basal-luminal cross-talk in normal mammary tissue.

Related-to-receptor tyrosine kinase receptor regulates hematopoietic stem and progenitor sensitivity to myelosuppressive injury in mice

Maintaining a careful balance between quiescence and proliferation of hematopoietic stem and progenitor cells (HSPCs) is necessary for lifelong blood formation. Previously, we demonstrated that the Wnt5a ligand inhibits HSPC proliferation through a functional interaction with a noncanonical Wnt ligand receptor termed 'related-to-receptor tyrosine kinase' (Ryk). Expression of Ryk on HSPCs in vivo is associated with a lower rate of proliferation, and, following treatment with fluorouracil (5-FU), the percentage of Ryk(+/high) HSPCs increased and the percentage of Ryk(-/low) HSPCs decreased. Based on these data, we hypothesized that one function of the Ryk receptor is to protect HSPCs from the effects of myeloablative agents. We found that Ryk expression on HSPCs is associated with lower rates of apoptosis following 5-FU and radiation. Transient inhibition of Ryk signaling in vivo resulted in increased hematopoietic-stem-cell proliferation and decreased hematopoietic-stem-cell function in bone marrow transplant assays. Furthermore, inhibition of Ryk signaling sensitized HSPCs to 5-FU treatment in association with increased levels of reactive oxygen species. Together, these results demonstrated an association between Ryk expression and survival of HSPCs following suppressive injury.

Hematopoietic stem cell niche maintenance during homeostasis and regeneration

The bone marrow niche has mystified scientists for many years, leading to widespread investigation to shed light into its molecular and cellular composition. Considerable efforts have been devoted toward uncovering the regulatory mechanisms of hematopoietic stem cell (HSC) niche maintenance. Recent advances in imaging and genetic manipulation of mouse models have allowed the identification of distinct vascular niches that have been shown to orchestrate the balance between quiescence, proliferation and regeneration of the bone marrow after injury. Here we highlight the recently discovered intrinsic mechanisms, microenvironmental interactions and communication with surrounding cells involved in HSC regulation, during homeostasis and in regeneration after injury and discuss their implications for regenerative therapy.

Wnt5a signaling increases IL-12 secretion by human dendritic cells and enhances IFN-γ production by CD4+ T cells

Wnt5a is a secreted pleiotropic glycoprotein produced in an inflammatory state by a wide spectrum of ubiquitous cell populations. Recently, we demonstrated that Wnt5a skews the differentiation of human monocyte derived dendritic cells (moDCs) to a tolerogenic functional state. In this study we focus our interest on the role of this Wnt ligand after DC differentiation, during their maturation and function. We show that the expression of Wnt receptors is tightly regulated during the life cycle of DCs suggesting a differential responsiveness to Wnt signaling conditioned by their differentiation stage and the maturational stimuli. Furthermore, we confirm that Wnt5a is the main non-canonical Wnt protein expressed by DCs and its production increases upon specific stimuli. Exogenous Wnt5a improved the endocytic capacity of immature DCs but it is not a stimulatory signal on its own, slightly affecting the maturation and function of DCs. However, knocking down Wnt5a gene expression in maturing DCs demonstrates that DC-derived Wnt5a is necessary for normal IL-12 secretion and plays a positive role during the development of Th1 responses. Wnt5a acts both in autocrine and paracrine ways. Thus, human naive CD4(+) T cells express Wnt receptors and, the addition of Wnt5a during CD3/CD28 stimulation enhances IL-2 and IFN-γ production. Taken together these results suggest a time-dependent role for Wnt5a during inflammatory responses conditioned by the differentiation stage of cellular targets.