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

Mesenchymal stem/stromal cells from human pluripotent stem cell-derived brain organoid enhance the ex vivo expansion and maintenance of hematopoietic stem/progenitor cells

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) are of great therapeutic value due to their role in maintaining the function of hematopoietic stem/progenitor cells (HSPCs). MSCs derived from human pluripotent stem cells represent an ideal alternative because of their unlimited supply. However, the role of MSCs with neural crest origin derived from HPSCs on the maintenance of HSPCs has not been reported.

METHODS

Flow cytometric analysis, RNA sequencing and differentiation ability were applied to detect the characteristics of stromal cells from 3D human brain organoids. Human umbilical cord blood CD34+ (UCB-CD34+) cells were cultured in different coculture conditions composed of stromal cells and umbilical cord MSCs (UC-MSCs) with or without a cytokine cocktail. The hematopoietic stroma capacity of stromal cells was tested in vitro with the LTC-IC assay and in vivo by cotransplantation of cord blood nucleated cells and stroma cells into immunodeficient mice. RNA and proteomic sequencing were used to detect the role of MSCs on HSPCs.

RESULTS

The stromal cells, derived from both H1-hESCs and human induced pluripotent stem cells forebrain organoids, were capable of differentiating into the classical mesenchymal-derived cells (osteoblasts, chondrocytes, and adipocytes). These cells expressed MSC markers, thus named pluripotent stem cell-derived MSCs (pMSCs). The pMSCs showed neural crest origin with CD271 expression in the early stage. When human UCB-CD34+ HSPCs were cocultured on UC-MSCs or pMSCs, the latter resulted in robust expansion of UCB-CD34+ HSPCs in long-term culture and efficient maintenance of their transplantability. Comparison by RNA sequencing indicated that coculture of human UCB-CD34+ HSPCs with pMSCs provided an improved microenvironment for HSC maintenance. The pMSCs highly expressed the Wnt signaling inhibitors SFRP1 and SFRP2, indicating that they may help to modulate the cell cycle to promote the maintenance of UCB-CD34+ HSPCs by antagonizing Wnt activation.

CONCLUSIONS

A novel method for harvesting MSCs with neural crest origin from 3D human brain organoids under serum-free culture conditions was reported. We demonstrate that the pMSCs support human UCB-HSPC expansion in vitro in a long-term culture and the maintenance of their transplantable ability. RNA and proteomic sequencing indicated that pMSCs provided an improved microenvironment for HSC maintenance via mechanisms involving cell-cell contact and secreted factors and suppression of Wnt signaling. This represents a novel method for large-scale production of MSCs of neural crest origin and provides a potential approach for development of human hematopoietic stromal cell therapy for treatment of dyshematopoiesis.

Awakening of Dormant Breast Cancer Cells in the Bone Marrow

Up to 40% of patients with breast cancer (BC) have metastatic cells in the bone marrow (BM) at the initial diagnosis of localized disease. Despite definitive systemic adjuvant therapy, these cells survive in the BM microenvironment, enter a dormant state and recur stochastically for more than 20 years. Once they begin to proliferate, recurrent macrometastases are not curable, and patients generally succumb to their disease. Many potential mechanisms for initiating recurrence have been proposed, but no definitive predictive data have been generated. This manuscript reviews the proposed mechanisms that maintain BC cell dormancy in the BM microenvironment and discusses the data supporting specific mechanisms for recurrence. It addresses the well-described mechanisms of secretory senescence, inflammation, aging, adipogenic BM conversion, autophagy, systemic effects of trauma and surgery, sympathetic signaling, transient angiogenic bursts, hypercoagulable states, osteoclast activation, and epigenetic modifications of dormant cells. This review addresses proposed approaches for either eliminating micrometastases or maintaining a dormant state.

Identification of the genetic central dogma in osteogenic differentiation of MSCs by osteoinductive medium from transcriptional data sets

Background

The genetic central dogma (GCD) has been demonstrated its essential function in many biological processes and diseases. However, its roles in the process of osteogenic differentiation of mesenchymal stem cells (MSCs) remain unclear.

Methods

In this project, we analyzed an online database of osteogenic differentiation of MSCs after 14 days and 28 days by osteoinductive medium (GSE83770). The differentially expressed genes were screened by GEO2R, with further conducting of KEGG pathways using DAVID. In addition, protein–protein interactions of the enriched pathways were performed using STRING with marked hub genes measured by the CytoHubba. Hub genes were verified by quantitative reverse‐transcription polymerase chain reaction.

Results

Results showed that six pathways related to GCD, including DNA replication, Aminoacyl‐tRNA biosynthesis, Mismatch repair, Ribosome, Spliceosome, and RNA degradation pathways enriched in the early stage (14 days vs. undifferentiated MSCs) of osteogenesis. The Lysosome pathway was highly enriched in the late stage (28 vs. 14 days) of osteogenesis, and Ribosome pathway plays a key role throughout the entire process (28 days vs. undifferentiated MSCs) of osteogenesis.

Conclusion

Both DNA replication and protein translation were functionally worked in the early stage of osteogenesis, whereas the Lysosome pathway was the only GCD‐related one in the late stage of osteogenesis. The GCD‐related Ribosome pathway occupied the entire process of osteogenesis.

We identified six pathways associated with genetic central dogma (DNA replication, Aminoacyl‐tRNA biosynthesis, Mismatch repair, Ribosome, Spliceosome, and RNA degradation pathways), which participated in the early stage of osteogenesis (0−14 days).

The Lysosome pathway plays a crucial role in the late stage of osteogenesis (14–28 days), whereas the Ribosome pathway participates in the entire process (28 days vs. undifferentiated mesenchymal stem cells) of osteogenesis.

Developmental analysis of reconstructed embryos of second-generation cloned transgenic goats

To improve the efficiency of the production of transgenic cloned goats by somatic cell nuclear transfer (SCNT), the development of reconstructed embryos of first-generation (G1) and second-generation (G2) cloned transgenic goats were compared and analyzed. Primary transgenic fetal fibroblasts were used as donor cells for G1 somatic cell nuclear transfer (SCNT). When the G1 transgenic embryos developed to 35 days in the recipient goats, transgenic fetal fibroblasts were isolated from them and used as donor cells for the G2 clone. In the G1 clones, the average fusion rate of reconstructed embryos was 73.62±2.9%, the average development rate (2-4 cells) was 33.96±2.36%, and the pregnancy rate of transplant recipients was 31.91%. In the G2 clones, the average fusion rate of the reconstructed embryos was 90.29±2.03%, the average development rate was 66.46±3.30%, and the pregnancy rate was 58.14%. These results indicate that in the G2 clones, the fusion rate of eggs, the development rate of reconstructed embryos, and the pregnancy rate of transplant recipients were significantly higher than those of G1 clones. We believe these results will lay a solid foundation for the efficient production of transgenic cloned animals in the future.

Osteoblastic adherence regulates hematopoietic stem cell self-renewal and differentiation: a conceptional in vitro and in vivo study

Background

Intrinsic factors related to self-renewal regulatory factors in hematopoietic stem cells are well known; however, limited information is available on extrinsic factors, such as the cell environment. Therefore, in this study, we analyzed the regulatory mechanism of hematopoietic stem cell self-renewal, focusing on the osteoblastic niche, and examined how adherence to osteoblasts affects stem cell differentiation.

Methods

For this experimental study, we developed a co-culture system for hematopoietic stem cells and osteoblasts, such that cells adhered to osteoblasts can be separated from those that do not. Murine Sca1-positive cells were separated into groups according to whether they were attached to osteoblasts or detached from osteoblasts, and each group was then subjected to colony assays and bone marrow transplantation experiments.

Results

Adhered Sca1-positive cells developed more secondary colonies than non-adhered Sca1-positive cells. Furthermore, in bone marrow transplantation experiments, adhered Sca1-positive cells showed successful engraftment. We explored the role of Polycomb genes in the regulation of cell fate and found that self-renewing cells attached to osteoblasts had high Bmi-1 expression and low Mel-18 expression, while this expression was reversed in differentiating cells.

Conclusions

Our results suggest that hematopoietic stem cells self-renew when they remain in osteoblastic niches after cell division. Further, when stem cells leave the niches, they undergo differentiation.

Single-Cell Integration Analysis of Heterotopic Ossification and Fibrocartilage Developmental Lineage: Endoplasmic Reticulum Stress Effector Xbp1 Transcriptionally Regulates the Notch Signaling Pathway to Mediate Fibrocartilage Differentiation

INTRODUCTION

Regeneration of fibrochondrocytes is essential for the healing of the tendon-bone interface (TBI), which is similar to the formation of neurogenic heterotopic ossification (HO). Through single-cell integrative analysis, this study explored the homogeneity of HO cells and fibrochondrocytes.

METHODS

This study integrated six datasets, namely, GSE94683, GSE144306, GSE168153, GSE138515, GSE102929, and GSE110993. The differentiation trajectory and key transcription factors (TFs) for HO occurrence were systematically analyzed by integrating single-cell RNA (scRNA) sequencing, bulk RNA sequencing, and assay of transposase accessible chromatin seq. The differential expression and enrichment pathways of TFs in heterotopically ossified tissues were identified.

RESULTS

HO that mimicked pathological cells was classified into HO1 and HO2 cell subsets. Results of the pseudo-temporal sequence analysis suggested that HO2 is a differentiated precursor cell of HO1. The analysis of integrated scRNA data revealed that ectopically ossified cells have similar transcriptional characteristics to cells in the fibrocartilaginous zone of tendons. The modified SCENIC method was used to identify specific transcriptional regulators associated with ectopic ossification. Xbp1 was defined as a common key transcriptional regulator of ectopically ossified tissues and the fibrocartilaginous zone of tendons. Subsequently, the CellPhoneDB database was completed for the cellular ligand-receptor analysis. With further pathway screening, this study is the first to propose that Xbp1 may upregulate the Notch signaling pathway through Jag1 transcription. Twenty-four microRNAs were screened and were found to be potentially associated with upregulation of XBP1 expression after acute ischemic stroke.

CONCLUSION

A systematic analysis of the differentiation landscape and cellular homogeneity facilitated a molecular understanding of the phenotypic similarities between cells in the fibrocartilaginous region of tendon and HO cells. Furthermore, by identifying Xbp1 as a hub regulator and by conducting a ligand-receptor analysis, we propose a potential Xbp1/Jag1/Notch signaling pathway.

Autophagic Mediators in Bone Marrow Niche Homeostasis

The bone marrow serves as a reservoir for a multifunctional assortment of stem, progenitor, and mature cells, located in functional anatomical micro-areas termed niches. Within the niche, hematopoietic and mesenchymal progenies establish a symbiotic relationship characterized by interdependency and interconnectedness. The fine-tuned physical and molecular interactions that occur in the niches guarantee physiological bone turnover, blood cell maturation and egression, and moderation of inflammatory and oxidative intramural stressful conditions. The disruption of bone marrow niche integrity causes severe local and systemic pathological settings, and thus bone marrow inhabitants have been the object of extensive study. In this context, research has revealed the importance of the autophagic apparatus for niche homeostatic maintenance. Archetypal autophagic players such as the p62 and the Atg family proteins have been found to exert a variety of actions, some autophagy-related and others not; they moderate the essential features of mesenchymal and hematopoietic stem cells and switch their operational schedules. This chapter focuses on our current understanding of bone marrow functionality and the role of the executive autophagic apparatus in the niche framework. Autophagic mediators such as p62 and Atg7 are currently considered the most important orchestrators of stem and mature cell dynamics in the bone marrow.

Dynamic Changes of the Bone Marrow Niche: Mesenchymal Stromal Cells and Their Progeny During Aging and Leukemia

Mesenchymal stromal cells (MSCs) are a heterogenous cell population found in a wide range of tissues in the body, known for their nutrient-producing and immunomodulatory functions. In the bone marrow (BM), these MSCs are critical for the regulation of hematopoietic stem cells (HSC) that are responsible for daily blood production and functional immunity throughout an entire organism's lifespan. Alongside other stromal cells, MSCs form a specialized microenvironment BM tissue called "niche" that tightly controls HSC self-renewal and differentiation. In addition, MSCs are crucial players in maintaining bone integrity and supply of hormonal nutrients due to their capacity to differentiate into osteoblasts and adipocytes which also contribute to cellular composition of the BM niche. However, MSCs are known to encompass a large heterogenous cell population that remains elusive and poorly defined. In this review, we focus on deciphering the BM-MSC biology through recent advances in single-cell identification of hierarchical subsets with distinct functionalities and transcriptional profiles. We also discuss the contribution of MSCs and their osteo-adipo progeny in modulating the complex direct cell-to-cell or indirect soluble factors-mediated interactions of the BM HSC niche during homeostasis, aging and myeloid malignancies. Lastly, we examine the therapeutic potential of MSCs for rejuvenation and anti-tumor remedy in clinical settings.

Role of ex vivo Expanded Mesenchymal Stromal Cells in Determining Hematopoietic Stem Cell Transplantation Outcome

Overall, the human organism requires the production of ∼1 trillion new blood cells per day. Such goal is achieved via hematopoiesis occurring within the bone marrow (BM) under the tight regulation of hematopoietic stem and progenitor cell (HSPC) homeostasis made by the BM microenvironment. The BM niche is defined by the close interactions of HSPCs and non-hematopoietic cells of different origin, which control the maintenance of HSPCs and orchestrate hematopoiesis in response to the body’s requirements. The activity of the BM niche is regulated by specific signaling pathways in physiological conditions and in case of stress, including the one induced by the HSPC transplantation (HSCT) procedures. HSCT is the curative option for several hematological and non-hematological diseases, despite being associated with early and late complications, mainly due to a low level of HSPC engraftment, impaired hematopoietic recovery, immune-mediated graft rejection, and graft-versus-host disease (GvHD) in case of allogenic transplant. Mesenchymal stromal cells (MSCs) are key elements of the BM niche, regulating HSPC homeostasis by direct contact and secreting several paracrine factors. In this review, we will explore the several mechanisms through which MSCs impact on the supportive activity of the BM niche and regulate HSPC homeostasis. We will further discuss how the growing understanding of such mechanisms have impacted, under a clinical point of view, on the transplantation field. In more recent years, these results have instructed the design of clinical trials to ameliorate the outcome of HSCT, especially in the allogenic setting, and when low doses of HSPCs were available for transplantation.

Robust generation of erythroid and multilineage hematopoietic progenitors from human iPSCs using a scalable monolayer culture system

One of the most promising objectives of clinical hematology is to derive engraftable autologous hematopoietic stem cells (HSCs) from human induced pluripotent stem cells (iPSCs). Progress in translating iPSC technologies to the clinic relies on the availability of scalable differentiation methodologies. In this study, human iPSCs were differentiated for 21 days using STEMdiff™, a monolayer-based approach for hematopoietic differentiation of human iPSCs that requires no replating, co-culture or embryoid body formation. Both hematopoietic and non-hematopoietic cells were functionally characterized throughout differentiation. In the hematopoietic fraction, an early transient population of primitive CD235a⁺ erythroid progenitor cells first emerged, followed by hematopoietic progenitors with multilineage differentiation activity in vitro but no long-term engraftment potential in vivo. In later stages of differentiation, a nearly exclusive production of definitive erythroid progenitors was observed. In the non-hematopoietic fraction, we identified a prevalent population of mesenchymal stromal cells and limited arterial vascular endothelium (VE), suggesting that the cellular constitution of the monolayer may be inadequate to support the generation of HSCs with durable repopulating potential. Quantitative modulation of WNT/β-catenin and activin/nodal/TGFβ signaling pathways with CHIR/SB molecules during differentiation enhanced formation of arterial VE, definitive multilineage and erythroid progenitors, but was insufficient to orchestrate the generation of engrafting HSCs. Overall, STEMdiff™ provides a clinically-relevant and readily adaptable platform for the generation of erythroid and multilineage hematopoietic progenitors from human pluripotent stem cells.

Contextual Regulation of Skeletal Physiology by Notch Signaling

PURPOSE OF REVIEW

This article reviews the past 2 years of research on Notch signaling as it relates to bone physiology, with the goal of reconciling seemingly discrepant findings and identifying fruitful areas of potential future research.

RECENT FINDINGS

Conditional animal models and high-throughput omics have contributed to a greater understanding of the context-dependent role of Notch signaling in bone. However, significant gaps remain in our understanding of how spatiotemporal context and epigenetic state dictate downstream Notch phenotypes. Biphasic activation of Notch signaling orchestrates progression of mesenchymal progenitor cells through the osteoblast lineage, but there is a limited understanding of ligand- and receptor-specific functions. Paracrine Notch signaling through non-osteoblastic cell types contributes additional layers of complexity, and we anticipate impactful future work related to the integration of these cell types and signaling mechanisms.

Vascular Stem/Progenitor Cell Migration and Differentiation in Atherosclerosis

SIGNIFICANCE

Atherosclerosis is a major cause for the death of human beings, and it takes place in large- and middle-sized arteries. The pathogenesis of the disease has been widely investigated, and new findings on vascular stem/progenitor cells could have an impact on vascular regeneration. Recent Advances: Recent studies have shown that abundant stem/progenitor cells present in the vessel wall are mainly responsible for cell accumulation in the intima during vascular remodeling. It has been demonstrated that the mobilization and recruitment of tissue-resident stem/progenitor cells give rise to endothelial and smooth muscle cells (SMCs) that participate in vascular repair and remodeling such as neointimal hyperplasia and arteriosclerosis. Interestingly, cell lineage tracing studies indicate that a large proportion of SMCs in neointimal lesions is derived from adventitial stem/progenitor cells.

CRITICAL ISSUES

The influence of stem/progenitor cell behavior on the development of atherosclerosis is crucial. An understanding of the regulatory mechanisms that control stem/progenitor cell migration and differentiation is essential for stem/progenitor cell therapy for vascular diseases and regenerative medicine.

FUTURE DIRECTIONS

Identification of the detailed process driving the migration and differentiation of vascular stem/progenitor cells during the development of atherosclerosis, discovery of the environmental cues, and signaling pathways that control cell fate within the vasculature will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis. Antioxid. Redox Signal. 00, 000-000.

The Bone Marrow Microenvironment in Health and Myeloid Malignancy

Hematopoietic stem cells (HSCs) interact dynamically with an intricate network of cells in the bone marrow (BM) microenvironment or niche. These interactions provide instructive cues that influence the production and lineage determination of different types of blood cells and maintenance of HSC quiescence. They also contribute to hematopoietic deregulation and hematological myeloid malignancies. Alterations in the BM niche are commonly observed in myeloid malignancies and contribute to the aberrant function of myelodysplastic and leukemia-initiating stem cells. In this work, we review how different components of the BM niche affect normal hematopoiesis, the molecular signals that govern this interaction, and how genetic changes in stromal cells or alterations in remodeled malignant BM niches contribute to myeloid malignancies. Understanding the intricacies between normal and malignant niches and their modulation may provide insights into developing novel therapeutics for blood disorders.

Strategies to retain properties of bone marrow-derived mesenchymal stem cells ex vivo

Mesenchymal stem cells (MSCs) have been extensively used for cell therapies and tissue engineering. The current MSC strategy requires a large quantity of cells for such applications, which can be achieved through cell expansion in culture. In the body, stem cell fate is largely determined by their microenvironment, known as the niche. The complex and dynamic stem cell niche provides physical, mechanical, and chemical cues to collaboratively regulate cell activities. It remains a great challenge to maintain the properties of MSCs in culture. Constructing a microenvironment as an engineered stem cell niche in culture to maintain MSC phenotypes, properties, and functions is a viable strategy to address the issue. Here, we review the current understanding of MSC behavior in the bone marrow niche, describe different strategies to engineer an in vitro microenvironment for maintaining MSC properties and functions, and discuss previous findings on environmental factors critical to the modulation of MSC activities in engineered microenvironments.

The osteoblastic niche in hematopoiesis and hematological myeloid malignancies

PURPOSE OF REVIEW

This review focuses on evidence highlighting the bidirectional crosstalk between the hematopoietic stem cell (HSC) and their surrounding stromal cells, with a particular emphasis on cells of the osteoblast lineage. The role and molecular functions of osteoblasts in normal hematopoiesis and in myeloid hematological malignancies is discussed.

RECENT FINDINGS

Cells of the osteoblast lineage have emerged as potent regulators of HSC expansion that regulate their recruitment and, depending on their stage of differentiation, their activity, proliferation and differentiation along the lymphoid, myeloid and erythroid lineages. In addition, mutations in mature osteoblasts or their progenitors induce myeloid malignancies. Conversely, signals from myelodysplastic cells can remodel the osteoblastic niche to favor self-perpetuation.

SUMMARY

Understanding cellular crosstalk between osteoblastic cells and HSCs in the bone marrow microenvironment is of fundamental importance for developing therapies against benign and malignant hematological diseases.

Soluble Factors on Stage to Direct Mesenchymal Stem Cells Fate

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are identified by in vitro plastic adherence, colony-forming capacity, expression of a panel of surface molecules, and ability to differentiate at least toward osteogenic, adipogenic, and chondrogenic lineages. They also produce trophic factors with immunomodulatory, proangiogenic, and antiapoptotic functions influencing the behavior of neighboring cells. On the other hand, a reciprocal regulation takes place; in fact, MSCs can be isolated from several tissues, and depending on the original microenvironment and the range of stimuli received from there, they can display differences in their essential characteristics. Here, we focus mainly on the bone tissue and how soluble factors, such as growth factors, cytokines, and hormones, present in this microenvironment can orchestrate bone marrow-derived MSCs fate. We also briefly describe the alteration of MSCs behavior in pathological settings such as hematological cancer, bone metastasis, and bone marrow failure syndromes. Overall, the possibility to modulate MSCs plasticity makes them an attractive tool for diverse applications of tissue regeneration in cell therapy. Therefore, the comprehensive understanding of the microenvironment characteristics and components better suited to obtain a specific MSCs response can be extremely useful for clinical use.

The bone marrow pericyte: an orchestrator of vascular niche

The concept of pericyte has been changing over years. This cell type was believed to possess only a function of trophic support to endothelial cells and to maintain vasculature stabilization. In the last years, the discovery of multipotent ability of perivascular populations led to the concept of vessel/wall niche. Likewise, several perivascular populations have been identified in animal and human bone marrow. In this review, we provide an overview on bone marrow perivascular population, their cross-talk with other niche components, relationship with bone marrow stromal stem cells, and similarities and differences with the perivascular population of the vessel/wall niche. Finally, we focus on the regenerative potential of these cells and the forthcoming challenges related to their use as cell therapy products.