Loss of EfnB1 in the osteogenic lineage compromises their capacity to support hematopoietic stem/progenitor cell maintenance

Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD+/SIRT1 axis

BACKGROUND

The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation.

METHODS

Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45- MSCs.

RESULTS

Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD+), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD+, with oral NAD+ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days.

CONCLUSIONS

We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD+-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.

EPH/Ephrin Signaling in Normal Hematopoiesis and Hematologic Malignancies: Deciphering Their Intricate Role and Unraveling Possible New Therapeutic Targets

Erythropoietin-producing hepatocellular carcinoma receptors (EPHs) represent the largest family of receptor tyrosine kinases (RTKs). EPH interaction with ephrins, their membrane-bound ligands, holds a pivotal role in embryonic development, while, though less active, it is also implicated in various physiological functions during adult life. In normal hematopoiesis, different patterns of EPH/ephrin expression have been correlated with hematopoietic stem cell (HSC) maintenance and lineage-committed hematopoietic progenitor cell (HPC) differentiation, as well as with the functional properties of their mature offspring. Research in the field of hematologic malignancies has unveiled a rather complex involvement of the EPH/ephrinsignaling pathway in the pathophysiology of these neoplasms. Aberrations in genetic, epigenetic, and protein levels have been identified as possible players implicated both in tumor progression and suppression, while correlations have also been highlighted regarding prognosis and response to treatment. Initial efforts to therapeutically target the EPH/ephrin axis have been undertaken in the setting of hematologic neoplasia but are mainly confined to the preclinical level. To this end, deciphering the complexity of this signaling pathway both in normal and malignant hematopoiesis is necessary.

Sticky, Adaptable, and Many-sided: SAM protein versatility in normal and pathological hematopoietic states

With decades of research seeking to generalize sterile alpha motif (SAM) biology, many outstanding questions remain regarding this multi-tool protein module. Recent data from structural and molecular/cell biology has begun to reveal new SAM modes of action in cell signaling cascades and biomolecular condensation. SAM-dependent mechanisms underlie blood-related (hematologic) diseases, including myelodysplastic syndromes and leukemias, prompting our focus on hematopoiesis for this review. With the increasing coverage of SAM-dependent interactomes, a hypothesis emerges that SAM interaction partners and binding affinities work to fine tune cell signaling cascades in developmental and disease contexts, including hematopoiesis and hematologic disease. This review discusses what is known and remains unknown about the standard mechanisms and neoplastic properties of SAM domains and what the future might hold for developing SAM-targeted therapies.

Construction of three-gene-based prognostic signature and analysis of immune cells infiltration in children and young adults with B-acute lymphoblastic leukemia

Background

Although B‐acute lymphoblastic leukemia (B‐ALL) patients' survival has been improved dramatically, some cases still relapse. This study aimed to explore the prognosis‐related novel differentially expressed genes (DEGs) for predicting the overall survival (OS) of children and young adults (CAYAs) with B‐ALL and analyze the immune‐related factors contributing to poor prognosis.

Methods

GSE48558 and GSE79533 from Gene Expression Omnibus (GEO) and clinical sample information and mRNA‐seq from Therapeutically Applicable Research to Generate Effective Treatments (TARGET) database were retrieved. Prognosis‐related key genes were enrolled to build a Cox proportional model using multivariate Cox regression. Five‐year OS of patients, clinical characteristic relevance and clinical independence were assessed based on the model. The mRNA levels of prognosis‐related genes were validated in our samples and the difference of immune cells composition between high‐risk and low‐risk patients were compared.

Results

One hundred and twelve DEGs between normal B cells and B‐ALL cells were identified based on GSE datasets. They were mainly participated in protein binding and HIF‐1 signaling pathway. One hundred and eighty‐nine clinical samples were enrolled in the study, both Kaplan–Meier (KM) analysis and univariate Cox regression analysis showed that CYBB, BCL2A1, IFI30, and EFNB1 were associated with prognosis, CYBB, BCL2A1, and EFNB1 were used to construct prognostic risk model. Moreover, compared to clinical indicators, the three‐gene signature was an independent prognostic factor for CAYAs with B‐ALL. Finally, the mRNA levels of CYBB, BCL2A1, and EFNB1 were significantly lower in B‐ALL group as compared to controls. The high‐risk group had a significantly higher percentage of infiltrated immune cells.

Conclusion

We constructed a novel three‐gene signature with independent prognostic factor for predicting 5‐year OS of CAYAs with B‐ALL. Additionally, we discovered the difference of immune cells composition between high‐risk and low‐risk groups. This study may help to customize individual treatment and improve prognosis of CAYAs with B‐ALL.

High CD34 surface expression in BCP-ALL predicts poor induction therapy response and is associated with altered expression of genes related to cell migration and adhesion

Minimal residual disease (MRD) constitutes the most important prognostic factor in B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL). Flow cytometry is widely used in MRD assessment, yet little is known regarding the effect of different immunophenotypic subsets on outcome. In this study of 200 BCP‐ALL patients, we found that a CD34‐positive, CD38 dim‐positive, nTdT dim‐positive immunophenotype on the leukemic blasts was associated with poor induction therapy response and predicted an MRD level at the end of induction therapy (EOI) of ≥ 0.001. CD34 expression was strongly and positively associated with EOI MRD, whereas CD34‐negative patients had a low relapse risk. Further, CD34 expression increased from diagnosis to relapse. CD34 is a stemness‐associated cell‐surface molecule, possibly involved in cell adhesion/migration or survival. Accordingly, genes associated with stemness were overrepresented among the most upregulated genes in CD34‐positive leukemias, and protein–protein interaction networks showed an overrepresentation of genes associated with cell migration, cell adhesion, and negative regulation of apoptosis. The present work is the first to demonstrate a CD34‐negative immunophenotype as a good prognostic factor in ALL, whereas high CD34 expression is associated with poor therapy response and an altered gene expression profile reminiscent of migrating cancer stem‐like cells.

A senescence stress secretome is a hallmark of therapy-related myeloid neoplasm stromal tissue occurring soon after cytotoxic exposure

Therapy-related myeloid neoplasm (tMN) is considered a direct consequence of DNA damage in hematopoietic stem cells. Despite increasing recognition that altered stroma can also drive leukemogenesis, the functional biology of the tMN microenvironment remains unknown. We performed multiomic (transcriptome, DNA damage response, cytokine secretome and functional profiling) characterization of bone marrow stromal cells from tMN patients. Critically, we also compared (i) patients with myeloid neoplasm and another cancer but without cytotoxic exposure, (ii) typical primary myeloid neoplasm, and (iii) age-matched controls to decipher the microenvironmental changes induced by cytotoxics vs. neoplasia. Strikingly, tMN exhibited a profoundly senescent phenotype with induction of CDKN1A and β-Galactosidase, defective phenotype, and proliferation. Moreover, tMN stroma showed delayed DNA repair and defective adipogenesis. Despite their dormant state, tMN stromal cells were metabolically highly active with a switch toward glycolysis and secreted multiple pro-inflammatory cytokines indicative of a senescent-secretory phenotype that inhibited adipogenesis. Critically, senolytics not only eliminated dormant cells, but also restored adipogenesis. Finally, sequential patient sampling showed senescence phenotypes are induced within months of cytotoxic exposure, well prior to the onset of secondary cancer. Our data underscores a role of senescence in the pathogenesis of tMN and provide a valuable resource for future therapeutics.

Loss of tyrosine kinase receptor Ephb2 impairs proliferation and stem cell activity of spermatogonia in culture†

Germline stem and progenitor cells can be extracted from the adult mouse testis and maintained long-term in vitro. Yet, the optimal culture conditions for preserving stem cell activity are unknown. Recently, multiple members of the Eph receptor family were detected in murine spermatogonia, but their roles remain obscure. One such gene, Ephb2, is crucial for maintenance of somatic stem cells and was previously found enriched at the level of mRNA in murine spermatogonia. We detected Ephb2 mRNA and protein in primary adult spermatogonial cultures and hypothesized that Ephb2 plays a role in maintenance of stem cells in vitro. We employed CRISPR-Cas9 targeting and generated stable mutant SSC lines with complete loss of Ephb2. The characteristics of Ephb2-KO cells were interrogated using phenotypic and functional assays. Ephb2-KO SSCs exhibited reduced proliferation compared to wild-type cells, while apoptosis was unaffected. Therefore, we examined whether Ephb2 loss correlates with activity of canonical pathways involved in stem cell self-renewal and proliferation. Ephb2-KO cells had reduced ERK MAPK signaling. Using a lentiviral transgene, Ephb2 expression was rescued in Ephb2-KO cells, which partially restored signaling and proliferation. Transplantation analysis revealed that Ephb2-KO SSCs cultures formed significantly fewer colonies than WT, indicating a role for Ephb2 in preserving stem cell activity of cultured cells. Transcriptome analysis of wild-type and Ephb2-KO SSCs identified Dppa4 and Bnc1 as differentially expressed, Ephb2-dependent genes that are potentially involved in stem cell function. These data uncover for the first time a crucial role for Ephb2 signaling in cultured SSCs.

Eph-Ephrin Signaling Mediates Cross-Talk Within the Bone Microenvironment

Skeletal integrity is maintained through the tightly regulated bone remodeling process that occurs continuously throughout postnatal life to replace old bone and to repair skeletal damage. This is maintained primarily through complex interactions between bone resorbing osteoclasts and bone forming osteoblasts. Other elements within the bone microenvironment, including stromal, osteogenic, hematopoietic, endothelial and neural cells, also contribute to maintaining skeletal integrity. Disruption of the dynamic interactions between these diverse cellular systems can lead to poor bone health and an increased susceptibility to skeletal diseases including osteopenia, osteoporosis, osteoarthritis, osteomalacia, and major fractures. Recent reports have implicated a direct role for the Eph tyrosine kinase receptors and their ephrin ligands during bone development, homeostasis and skeletal repair. These membrane-bound molecules mediate contact-dependent signaling through both the Eph receptors, termed forward signaling, and through the ephrin ligands, referred to as reverse signaling. This review will focus on Eph/ ephrin cross-talk as mediators of hematopoietic and stromal cell communication, and how these interactions contribute to blood/ bone marrow function and skeletal integrity during normal steady state or pathological conditions.

Heterogeneity of murine periosteum progenitors involved in fracture healing

The periosteum is the major source of cells involved in fracture healing. We sought to characterize progenitor cells and their contribution to bone fracture healing. The periosteum is highly enriched with progenitor cells, including Sca1+ cells, fibroblast colony-forming units, and label-retaining cells compared to the endosteum and bone marrow. Using lineage tracing, we demonstrate that alpha smooth muscle actin (αSMA) identifies long-term, slow-cycling, self-renewing osteochondroprogenitors in the adult periosteum that are functionally important for bone formation during fracture healing. In addition, Col2.3CreER-labeled osteoblast cells contribute around 10% of osteoblasts but no chondrocytes in fracture calluses. Most periosteal osteochondroprogenitors following fracture can be targeted by αSMACreER. Previously identified skeletal stem cell populations were common in periosteum but contained high proportions of mature osteoblasts. We have demonstrated that the periosteum is highly enriched with skeletal progenitor cells, and there is heterogeneity in the populations of cells that contribute to mature lineages during periosteal fracture healing.

Crosstalk between skeletal and neural tissues is critical for skeletal health

Emerging evidence in the literature describes a physical and functional association between the neural and skeletal systems that forms a neuro-osteogenic network. This communication between bone cells and neural tissues within the skeleton is important in facilitating bone skeletal growth, homeostasis and repair. The growth and repair of the skeleton is dependent on correct neural innervation for correct skeletal developmental growth and fracture repair, while pathological conditions such as osteoporosis are accelerated by disruptions to sympathetic innervation. To date, different molecular mechanisms have been reported to mediate communication between bone and neural populations. This review highlights the important role of various cell surface receptors, cytokines and associated ligands as potential regulators of skeletal development, homeostasis, and repair, by mediating interactions between the skeletal and nervous systems. Specifically, this review describes how Bone Morphogenetic Proteins (BMPs), Eph/ephrin, Chemokine CXCL12, Calcitonin Gene-related Peptide (CGRP), Netrins, Neurotrophins (NTs), Slit/Robo and the Semaphorins (Semas) contribute to the cross talk between bone cells and peripheral nerves, and the importance of these interactions in maintaining skeletal health.

Markers for Identification of Postnatal Skeletal Stem Cells In Vivo

PURPOSE OF REVIEW

The adult skeleton contains stem cells involved in growth, homeostasis, and healing. Mesenchymal or skeletal stem cells are proposed to provide precursors to osteoblasts, chondrocytes, marrow adipocytes, and stromal cells. We review the evidence for existence and functionality of different skeletal stem cell pools, and the tools available for identifying or targeting these populations in mouse and human tissues.

RECENT FINDINGS

Lineage tracing and single cell-based techniques in mouse models indicate that multiple pools of stem cells exist in postnatal bone. These include growth plate stem cells, stem and progenitor cells in the diaphysis, reticular cells that only form bone in response to injury, and injury-responsive periosteal stem cells. New staining protocols have also been described for prospective isolation of human skeletal stem cells. Several populations of postnatal skeletal stem and progenitor cells have been identified in mice, and we have an increasing array of tools to target these cells. Most Cre models lack a high degree of specificity to define single populations. Human studies are less advanced and require further efforts to refine methods for identifying stem and progenitor cells in adult bone.

Conditional knockout of ephrinB1 in osteogenic progenitors delays the process of endochondral ossification during fracture repair

The Eph receptor tyrosine kinase ligand, ephrinB1 (EfnB1) is important for correct skeletal and cartilage development, however, the role of EfnB1 in fracture repair is unknown. This study investigated the role of EfnB1 during fracture repair where EfnB1 expression increased significantly at 1 and 2 weeks post fracture in C57Bl/6 wildtype mice, coinciding with the haematoma, soft callus formation/remodelling stages, respectively. To investigate the specific role of EfnB1 within the osteogenic lineage during fracture repair, male mice with a conditional deletion of EfnB1 in the osteogenic lineage (EfnB1_OB^fl/O), driven by the Osterix (Osx) promoter, and their male Osx:Cre counterparts were subject to a femoral fracture with internal fixation. Two weeks post fracture micro computed tomography (μCT) analysis revealed that EfnB1_OB^fl/O mice displayed a significant decrease in bone volume relative to tissue volume within the fracture callus. This was attributed to an alteration in the distribution of osteoclasts within the fracture site, a significant elevation in cartilaginous tissue and reduction in the osteoprogenitor population and calcein labelled bone within the fracture site of EfnB1_OB^fl/O mice. Supportive in vitro studies demonstrated that under osteogenic conditions, cultured EfnB1_OB^fl/O stromal cells derived from the 2 week fracture site exhibited a reduced capacity to produce mineral and decreased expression of the osteogenic gene, Osterix, when compared to Osx:Cre controls. These findings suggest that the loss of EfnB1 delays the fracture repair process. The present study confirmed that EFNB1 activation in human BMSC, following stimulation with soluble-EphB2 resulted in de-phosphorylation of TAZ, demonstrating similarities in EfnB1 signalling between human and mouse stromal populations. Overall, the present study provides evidence that loss of EfnB1 in the osteo/chondrogenic lineages delays the soft callus formation/remodelling stages of the fracture repair process.

Eph/ephrin Signaling and Biology of Mesenchymal Stromal/Stem Cells

Mesenchymal stromal/stem cells (MSCs) have emerged as important therapeutic agents, owing to their easy isolation and culture, and their remarkable immunomodulatory and anti-inflammatory properties. However, MSCs constitute a heterogeneous cell population which does not express specific cell markers and has important problems for in vivo homing, and factors regulating their survival, proliferation, and differentiation are largely unknown. Accordingly, in the present article, we review the current evidence on the relationships between Eph kinase receptors, their ephrin ligands, and MSCs. These molecules are involved in the adult homeostasis of numerous tissues, and we and other authors have demonstrated their expression in human and murine MSCs derived from both bone marrow and adipose tissue, as well as their involvement in the MSC biology. We extend these studies providing new results on the effects of Eph/ephrins in the differentiation and immunomodulatory properties of MSCs.