Cellular Heterogeneity of Mesenchymal Stem/Stromal Cells in the Bone Marrow

Application of mesenchymal stem/stromal cells in periodontal regeneration: Opportunities and challenges

Guided tissue regeneration (GTR) has been widely used in the periodontal treatment of intrabony and furcation defects for nearly four decades. The treatment outcomes have shown effectiveness in reducing pocket depth, improving attachment gain and bone filling in periodontal tissue. Although applying GTR could reconstruct the periodontal tissue, the surgical indications are relatively narrow, and some complications and race ethic problems bring new challenges. Therefore, it is challenging to achieve a consensus concerning the clinical benefits of GTR. With the appearance of stem cell-based regenerative medicine, mesenchymal stem/stromal cells (MSCs) have been considered a promising cell resource for periodontal regeneration. In this review, we highlight preclinical and clinical periodontal regeneration using MSCs derived from distinct origins, including non-odontogenic and odontogenic tissues and induced pluripotent stem cells, and discuss the transplantation procedures, therapeutic mechanisms, and concerns to evaluate the effectiveness of MSCs.

Advantages and disadvantages of various hydrogel scaffold types: A research to improve the clinical conversion rate of loaded MSCs-Exos hydrogel scaffolds

Mesenchymal stem cell-derived exosomes(MSCs-Exos) offer promising therapeutic potential for a wide range of tissues and organs such as bone/cartilage, nerves, skin, fat, and endocrine organs. In comparison to the application of mesenchymal stem cells (MSCs), MSCs-Exos address critical challenges related to rejection reactions and ethical concerns, positioning themselves as a promising cell-free therapy. As exosomes are extracellular vesicles, their effective delivery necessitates the use of carriers. Consequently, the selection of hydrogel materials as scaffolds for exosome delivery has become a focal point of contemporary research. The diversity of hydrogel scaffolds, which can take various forms such as injectable types, dressings, microneedles, and capsules, leads to differing choices among researchers for treating diseases within the same domain. This variability in hydrogel materials poses challenges for the translation of findings into clinical practice. The review highlights the potential of hydrogel-loaded exosomes in different fields and introduces the advantages and disadvantages of different forms of hydrogel applications. It aims to provide a multifunctional and highly recognized hydrogel scaffold option for tissue regeneration at specific sites, improve clinical translation efficiency, and benefit the majority of patients.

Investigation of MSC potency metrics via integration of imaging modalities with lipidomic characterization

Mesenchymal stem/stromal cell (MSC) therapies have had limited success so far in clinical trials due in part to heterogeneity in immune-responsive phenotypes. Therefore, techniques to characterize these properties of MSCs are needed during biomanufacturing. Imaging cell shape, or morphology, has been found to be associated with MSC immune responsivity-but a direct relationship between single-cell morphology and function has not been established. We used label-free differential phase contrast imaging and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to evaluate single-cell morphology and explore relationships with lipid metabolic immune response. In interferon gamma (IFN-γ)-stimulated MSCs, we found higher lipid abundances from the ceramide-1-phosphate (C1P), phosphatidylcholine (PC), LysoPC, and triglyceride (TAG) families that are involved in cell immune function. Furthermore, we identified differences in lipid signatures in morphologically defined MSC subpopulations. The use of single-cell optical imaging coupled with single-cell spatial lipidomics could assist in optimizing the MSC production process and improve mechanistic understanding of manufacturing process effects on MSC immune activity and heterogeneity.

Optimization of transplantation methods using isolated mesenchymal stem/stromal cells: clinical trials of inflammatory bowel diseases as an example

Mesenchymal stem/stromal cells (MSCs) are distributed in various tissues and are used in clinical applications as a source of transplanted cells because of their easy harvestability. Although MSCs express numerous cell-surface antigens, single-cell analyses have revealed a highly heterogeneous cell population depending on the original tissue and donor conditions, including age and interindividual differences. This heterogeneity leads to differences in their functions, such as multipotency and immunomodulatory effects, making it challenging to effectively treat targeted diseases. The therapeutic efficacy of MSCs is controversial and depends on the implantation site. Thus, there is no established recipe for the transplantation of MSCs (including the type of disease, type of origin, method of cell culture, form of transplanted cells, and site of delivery). Our recent preclinical study identified appropriate MSCs and their suitable transplantation routes in a mouse model of inflammatory bowel disease (IBD). Three-dimensional (3D) cultures of MSCs have been demonstrated to enhance their properties and sustain engraftment at the lesion site. In this note, we explore the methods of MSC transplantation for treating IBDs, especially Crohn's disease, from clinical trials published over the past decade. Given the functional changes in MSCs in 3D culture, we also investigate the clinical trials using 3D constructs of MSCs and explore suitable diseases that might benefit from this approach. Furthermore, we discuss the advantages of the prospective isolation of MSCs in terms of interindividual variability. This note highlights the need to define the method of MSC transplantation, including interindividual variability, the culture period, and the transplantation route.

Murine bone-derived mesenchymal stem cells undergo molecular changes after a single passage in culture

The rarity of the mesenchymal stem cell (MSC) population poses a significant challenge for MSC research. Therefore, these cells are often expanded in vitro, prior to use. However, long-term culture has been shown to alter primary MSC properties. Additionally, early passage primary MSCs in culture are often assumed to represent the primary MSC population in situ, however, little research has been done to support this. Here, we compared the transcriptomic profiles of murine MSCs freshly isolated from the bone marrow to those that had been expanded in culture for 10 days. We identified that a single passage in culture extensively altered MSC molecular signatures associated with cell cycling, differentiation and immune response. These findings indicate the critical importance of the MSC source, highlighting the need for optimization of culture conditions to minimize the impact on MSC biology and a transition towards in vivo methodologies for the study of MSC function.

Towards Stem Cell Therapy for Critical-Sized Segmental Bone Defects: Current Trends and Challenges on the Path to Clinical Translation

The management and reconstruction of critical-sized segmental bone defects remain a major clinical challenge for orthopaedic clinicians and surgeons. In particular, regenerative medicine approaches that involve incorporating stem cells within tissue engineering scaffolds have great promise for fracture management. This narrative review focuses on the primary components of bone tissue engineering-stem cells, scaffolds, the microenvironment, and vascularisation-addressing current advances and translational and regulatory challenges in the current landscape of stem cell therapy for critical-sized bone defects. To comprehensively explore this research area and offer insights for future treatment options in orthopaedic surgery, we have examined the latest developments and advancements in bone tissue engineering, focusing on those of clinical relevance in recent years. Finally, we present a forward-looking perspective on using stem cells in bone tissue engineering for critical-sized segmental bone defects.

Potential Therapeutic Use of Stem Cells for Prion Diseases

Prion diseases are neurodegenerative disorders that are progressive, incurable, and deadly. The prion consists of PrPSc, the misfolded pathogenic isoform of the cellular prion protein (PrPC). PrPC is involved in a variety of physiological functions, including cellular proliferation, adhesion, differentiation, and neural development. Prion protein is expressed on the membrane surface of a variety of stem cells (SCs), where it plays an important role in the pluripotency and self-renewal matrix, as well as in SC differentiation. SCs have been found to multiply the pathogenic form of the prion protein, implying their potential as an in vitro model for prion diseases. Furthermore, due to their capability to self-renew, differentiate, immunomodulate, and regenerate tissue, SCs are prospective cell treatments in many neurodegenerative conditions, including prion diseases. Regenerative medicine has become a new revolution in disease treatment in recent years, particularly with the introduction of SC therapy. Here, we review the data demonstrating prion diseases' biology and molecular mechanism. SC biology, therapeutic potential, and its role in understanding prion disease mechanisms are highlighted. Moreover, we summarize preclinical studies that use SCs in prion diseases.

Towards standardization of human adipose-derived stromal cells secretomes

The secretome of adipose-derived stromal cells (ASC) is a heterogeneous mixture of components with a beneficial influence on cellular microenvironments. As such, it represents a cell-free alternative in regenerative medicine therapies. Pathophysiological conditions increase the therapeutic capacity of ASC and, with this, the benefits of the secretome. Such conditions can be partially mimicked in vitro by adjusting culturing conditions. Secretomics, the unbiased analysis of a cell secretome by mass spectrometry, is a powerful tool to describe the composition of ASC secretomes. In this proteomics databases review, we compared ASC secretomic studies to retrieve persistently reported proteins resulting from the most explored types of culturing conditions used in research, i.e., exposure to normoxia, hypoxia, or cytokines. Our comparisons identified only eight common proteins within ASC normoxic secretomes, no commonalities within hypoxic ASC secretomes, and only nine within secretomes of ASC exposed to proinflammatory cytokines. Within these, and regardless of the culturing condition that stimulated secretion, a consistent presence of extracellular matrix-related pathways associated with such proteins was identified. Confounders such as donors' age, sex, body mass index, the anatomical area where ASC were harvested, secretome collection method, data description, and how the data is shared with the scientific community are discussed as factors that might explain our outcomes. We conclude that standardization is imperative as the currently available ASC secretomic studies do not facilitate solid conclusions on the therapeutic value of different ASC secretomes.

Dissecting the Interrelationship between COVID-19 and Diabetes Mellitus

COVID-19 disease, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to enormous morbidity and mortality worldwide. After gaining entry into the human host, the virus initially infects the upper and lower respiratory tract, subsequently invading multiple organs, including the pancreas. While on one hand, diabetes mellitus (DM) is a significant risk factor for severe COVID-19 infection and associated death, recent reports have shown the onset of DM in COVID-19-recovered patients. SARS-CoV-2 infiltrates the pancreatic islets and activates stress response and inflammatory signaling pathways, impairs glucose metabolism, and consequently leads to their death. Indeed, the pancreatic autopsy samples of COVID-19 patients reveal the presence of SARS-CoV-2 particles in β-cells. The current review describes how the virus enters the host cells and activates an immunological response. Further, it takes a closer look into the interrelationship between COVID-19 and DM with the aim to provide mechanistic insights into the process by which SARS-CoV-2 infects the pancreas and mediates dysfunction and death of endocrine islets. The effects of known anti-diabetic interventions for COVID-19 management are also discussed. The application of mesenchymal stem cells (MSCs) as a future therapy for pancreatic β-cells damage to reverse COVID-19-induced DM is also emphasized.

From Teeth to Therapy: A Review of Therapeutic Potential within the Secretome of Stem Cells from Human Exfoliated Deciduous Teeth

Stem cells derived from human exfoliated deciduous teeth (SHED) have emerged as an alternative stem cell source for cell therapy and regenerative medicine because they are readily available, pose fewer ethical concerns, and have low immunogenicity and tumourigenicity. SHED offer a number of advantages over other dental stem cells, including a high proliferation rate with the potential to differentiate into multiple developmental lineages. The therapeutic effects of SHED are mediated by multiple mechanisms, including immunomodulation, angiogenesis, neurogenesis, osteogenesis, and adipogenesis. In recent years, there is ample evidence that the mechanism of action of SHED is mainly due to its paracrine action, releasing a wide range of soluble factors such as cytokines, chemokines, and trophic factors (also known as 'secretome') into the local tissue microenvironment to promote tissue survival and recovery. This review provides an overview of the secretome derived from SHED and highlights the bioactive molecules involved in tissue regeneration and their potential applications in regenerative medicine.

Consequences of HIV infection in the bone marrow niche

Dysregulation of the bone marrow niche resulting from the direct and indirect effects of HIV infection contributes to haematological abnormalities observed in HIV patients. The bone marrow niche is a complex, multicellular environment which functions primarily in the maintenance of haematopoietic stem/progenitor cells (HSPCs). These adult stem cells are responsible for replacing blood and immune cells over the course of a lifetime. Cells of the bone marrow niche support HSPCs and help to orchestrate the quiescence, self-renewal and differentiation of HSPCs through chemical and molecular signals and cell-cell interactions. This narrative review discusses the HIV-associated dysregulation of the bone marrow niche, as well as the susceptibility of HSPCs to infection by HIV.

Single-Cell RNA-Seq Reveals LRRC75A-Expressing Cell Population Involved in VEGF Secretion of Multipotent Mesenchymal Stromal/Stem Cells Under Ischemia

Human multipotent mesenchymal stromal/stem cells (MSCs) have been utilized in cell therapy for various diseases and their clinical applications are expected to increase in the future. However, the variation in MSC-based product quality due to the MSC heterogeneity has resulted in significant constraints in the clinical utility of MSCs. Therefore, we hypothesized that it might be important to identify and ensure/enrich suitable cell subpopulations for therapies using MSC-based products. In this study, we aimed to identify functional cell subpopulations to predict the efficacy of angiogenic therapy using bone marrow-derived MSCs (BM-MSCs). To assess its angiogenic potency, we observed various levels of vascular endothelial growth factor (VEGF) secretion among 11 donor-derived BM-MSC lines under in vitro ischemic culture conditions. Next, by clarifying the heterogeneity of BM-MSCs using single-cell RNA-sequencing analysis, we identified a functional cell subpopulation that contributed to the overall VEGF production in BM-MSC lines under ischemic conditions. We also found that leucine-rich repeat-containing 75A (LRRC75A) was more highly expressed in this cell subpopulation than in the others. Importantly, knockdown of LRRC75A using small interfering RNA resulted in significant inhibition of VEGF secretion in ischemic BM-MSCs, indicating that LRRC75A regulates VEGF secretion under ischemic conditions. Therefore, LRRC75A may be a useful biomarker to identify cell subpopulations that contribute to the angiogenic effects of BM-MSCs. Our work provides evidence that a strategy based on single-cell transcriptome profiles is effective for identifying functional cell subpopulations in heterogeneous MSC-based products.

Factors Influencing the Yield of Progenitor Cells in Bone Marrow Aspiration Concentrate—A Retrospective Analysis of 58 Patients

This study aims to identify the role of subjective factors (age, sex, and comorbidities) and procedure-specific factors (aspiration volume) in influencing the yield of progenitor cells in bone marrow aspiration concentrate (BMAC) harvested from the iliac crest. A retrospective analysis was conducted on 58 patients (male:female = 31:27; mean age: 52.56 ± 18.14 years) who underwent BMAC therapy between January 2020 and June 2021. The factors analyzed include individual factors such as age, sex, and comorbid conditions, and procedural factors such as aspirate volume. The mononuclear cell (MNC) count and colony-forming unit (CFU) assay were used to assess the yield of progenitors in the aspirate. Pearson’s correlation test was performed for the age, aspirate volume, and outcome parameters, such as MNC and CFU. We used the chi-square test to analyze the role of sex and comorbidities on cellular yield. The mean volume of aspirate used for BMAC therapy was 66.65 (±17.82) mL. The mean MNC count of the BMAC was 19.94 (±16.34) × 106 cells, which formed 11 (±12) CFUs. Evidence of statistically significant positive associations was noted between the CFUs developed from the BMAC and the MNC count within them (r = 0.95, p < 0.001). The sex of the individual did not play any significant role in MNC count (p = 0.092) or CFUs formed (p = 0.448). The age of the individual showed evidence of a statistically significant negative association with the MNC count (r = −0.681, p < 0.001) and CFUs (r = −0.693, p < 0.001), as did the aspiration volume with the MNC count (r = −0.740, p < 0.001) and CFUs (r = −0.629, p < 0.001). We also noted a significant reduction in the MNC count (p = 0.002) and CFUs formed (p = 0.004) when the patients presented comorbidities. Individual factors such as age, comorbid conditions, and procedure factors such as aspirate volume significantly affected the yield of progenitor cells in the BMAC. The sex of the individual did not influence the yield of progenitor cells in BMAC.

Health Literacy among Japanese College Students: Association with Healthy Lifestyle and Subjective Health Status

The improvement of health literacy (HL) is a critical issue for college students who are in the transitional period to adulthood and are establishing their subsequent lifestyles. The present study aimed to evaluate the current state of HL among college students and to explore the factors that influence HL. Moreover, it investigated the relationship between HL and health conditions. For this study, the researchers conducted an online survey of college students. The questionnaire consisted of the Japanese version of the 47-item European Health Literacy Survey Questionnaire (HLS-EU-Q47), which is a self-assessment tool for HL that covers the major health issues of college students and health-related quality of life. The study analyzed 1049 valid responses. Based on the HLS-EU-Q47 total score, 85% of the participants exhibited problematic or unsatisfactory HL levels. Participants who reported high levels of healthy lifestyles obtained high HL scores. High levels of HL were associated with high levels of subjective health. Results from quantitative text analysis suggested that specific mindsets were correlated with high levels of competency in appraising health information among male students. In the future, educational intervention programs for college students need to be established to improve HL levels.

Cellular niches for hematopoietic stem cells in bone marrow under normal and malignant conditions

Throughout adult life, most lineages of blood cells, including immune cells, are generated from hematopoietic stem cells (HSCs) in the bone marrow. HSCs are thought to require special microenvironments, termed niches, for their maintenance in the bone marrow; however, the identity of the HSC cellular niche has been a subject of long-standing debate. Although diverse candidates have been proposed so far, accumulated studies demonstrate that the bone marrow-specific population of fibroblastic reticular cells with long processes, termed CXC chemokine ligand 12-abundant reticular cells (which overlap strongly with leptin receptor-expressing cells), termed CAR/LepR⁺ cells, are the pivotal cellular component of niches for HSCs and lymphoid progenitors. Sinusoidal endothelial cells (ECs) are also important for hematopoietic homeostasis and regeneration. Hematopoiesis is altered dynamically by various stimuli such as inflammation, infection, and leukemia, all of which affect cellular niches and alter their function. Therefore, it is important to consider situations in which stimuli affect HSCs, either via direct interaction or indirectly via the hematopoietic niches. In this review, the dynamics of cellular niches in the steady state and disease are described, with a focus on CAR/LepR⁺ cells and ECs.

Bone Marrow Avatars: Mimicking Hematopoiesis in a Dish

SUMMARY

Faithful recapitulation of human bone marrow complexity has been a major challenge for the sci-entific community for many years. In this issue of Cancer Discovery, Khan and colleagues present an improved induced pluripotent stem cell differentiation protocol that generates bone marrow organoids re-creating key characteristics of human marrow. See related article by Khan et al., p. 364 (8).

Multipotent Mesenchymal Stromal Cells from Porcine Bone Marrow, Implanted under the Kidney Capsule, form an Ectopic Focus Containing Bone, Hematopoietic Stromal Microenvironment, and Muscles

Multipotent mesenchymal stromal cells (MSCs) are an object of intense investigation due to their therapeutic potential. MSCs have been well studied in vitro, while their fate after implantation in vivo has been poorly analyzed. We studied the properties of MSCs from the bone marrow (BM-MSC) before and after implantation under the renal capsule using a mini pig model. Autologous BM-MSCs were implanted under the kidney capsule. After 2.5 months, ectopic foci containing bones, foci of ectopic hematopoiesis, bone marrow stromal cells and muscle cells formed. Small pieces of the implant were cultivated as a whole. The cells that migrated out from these implants were cultured, cloned, analyzed and were proven to meet the most of criteria for MSCs, therefore, they are designated as MSCs from the implant-IM-MSCs. The IM-MSC population demonstrated high proliferative potential, similar to BM-MSCs. IM-MSC clones did not respond to adipogenic differentiation inductors: 33% of clones did not differentiate, and 67% differentiated toward an osteogenic lineage. The BM-MSCs revealed functional heterogeneity after implantation under the renal capsule. The BM-MSC population consists of mesenchymal precursor cells of various degrees of differentiation, including stem cells. These newly discovered properties of mini pig BM-MSCs reveal new possibilities in terms of their manipulation.

The Role of Diets and Dietitians for Para-Athletes: A Pilot Study Based on Interviews

Efforts to provide nutrition support to para-athletes have not been established to date, and are far behind those established for athletes without disabilities. In the present study, we attempted to clarify the actual situation regarding dietary challenges of para-athletes. The aim of this study was to obtain clues to effective intervention methods that encourage the practice of sports nutrition. Six active elite para-athletes (30–70 years, four males) and a female physical therapist without physical disability participated in semi-structured interviews. All para-athletes had lower-limb disabilities and participated in the international wheelchair sports competitions (tennis, softball, and table tennis, with 2–26 years of player history). The interview items were on the ideal diet for improving competitive performance, evaluation of their typical diets, and the role of the dietitian as support. Responses obtained from participants were analyzed using quantitative content analysis by language analysis software. There are differences in the ideal diet based on the characteristics of the sport, but most participants believed that a nutritionally well-balanced diet with abundant vegetables was ideal for improving competitive performance. Para-athletes who use a wheelchair daily pay attention to their total calorie intake, because gaining weight is a critical issue for operating their wheelchairs and transferring themselves to and from their wheelchairs. Despite their world-class competition levels, none of them received routine dietary advice from dietitians. Some para-athletes did not even feel the need to engage with dietitians. Even for these para-athletes at a high level of competition, the “ideal diet” they considered was not always the optimal diet for improving their competitive performance. In addition, there are various barriers to practicing their optimal diet due to disability characteristics. Dietitians need to understand these barriers, their concerns and conflicts, and how to help them plan the optimal diet to improve their performance and maintain overall health.

Shining a light on hematopoietic stem cells

A combination of light and electron microscopy has revealed further details about the location and interactions of hematopoietic stem and progenitor cells.

The Choice of Anticoagulant Influences the Characteristics of Bone Marrow Aspirate Concentrate and Mesenchymal Stem Cell Bioactivity In Vitro

Bone marrow aspirate concentrate (BMC) is commonly used as a therapeutic agent to resolve orthopedic injuries, using its unique cellularity to reduce inflammation and prime the region for repair. The aspiration of the bone marrow is performed using either sodium citrate (SC) or heparin sodium (HS) as an anticoagulant and processed via centrifugation to concentrate the cellular constituents. To date, the consideration of the impact of the two commonly used anticoagulants on the mesenchymal stem/stromal cell (MSC) population has been overlooked. The current study assesses the differences in the BMCs produced using 15% SC and HS at 1,000 U/mL or 100 U/mL final v./v. as an anticoagulant using in vitro metrics including total nucleated cell counts (TNC) and viability, the ability for mesenchymal stromal/stem cells (MSCs) to establish colony-forming units with fibroblast morphology (CFU-f), and cytokine expression profile of the MSC cultures. Our findings demonstrate that HS-derived BMC cultures result in higher CFU-f formation and CFU-f frequency at both concentrations assessed compared to SC-derived BMC cultures. In addition, there were significant differences in 27% (7 of 26) of the cytokines quantified in HS-derived BMC cultures compared to SC-derived BMC cultures with implications for MSC plasticity and self-renewal.

One of the Primary Functions of Tissue-Resident Pluripotent Pericytes Cells May Be to Regulate Normal Organ Growth and Maturation: Implications for Attempts to Repair Tissues Later in Life

Adult mesenchymal stem cells were reported more than 30 years ago. Since then, their potential to repair and regenerate damaged or diseased tissues has been studied intensively in both preclinical models and human trials. Most of the need for such tissue repair/regeneration is in older populations, so much of the effort has been performed with autologous cells in older patients. However, success has been difficult to achieve. In the literature, it has been noted that such progenitor cells from younger individuals often behave with more vigorous activity and are functionally enhanced compared to those from older individuals or animals. In addition, cells with the characteristics of mesenchymal stem cells or pluripotent mesenchymal regulatory cells exist in nearly all tissues and organs as pericytes since fetal life. Such evidence raises the possibility that one of the primary roles of these organ-specific cells is to regulate organ growth and maturation, and then subsequently play a role in the maintenance of organ integrity. This review will discuss the evidence to support this concept and the implications of such a concept regarding the use of these progenitor cells for the repair and regeneration of tissues damaged by injury or disease later in life. For the latter, it may be necessary to return the organ-specific progenitor cells to the functional state that contributed to their effectiveness during growth and maturation rather than attempting to use them after alterations imposed during the aging process have been established and their function compromised.

Odontogenic MSC Heterogeneity: Challenges and Opportunities for Regenerative Medicine

Cellular heterogeneity refers to the genetic and phenotypic differences among cells, which reflect their various fate choices, including viability, proliferation, self-renewal probability, and differentiation into different lineages. In recent years, research on the heterogeneity of mesenchymal stem cells has made some progress. Odontogenic mesenchymal stem cells share the characteristics of mesenchymal stem cells, namely, good accessibility, low immunogenicity and high stemness. In addition, they also exhibit the characteristics of vasculogenesis and neurogenesis, making them attractive for tissue engineering and regenerative medicine. However, the usage of mesenchymal stem cell subgroups differs in different diseases. Furthermore, because of the heterogeneity of odontogenic mesenchymal stem cells, their application in tissue regeneration and disease management is restricted. Findings related to the heterogeneity of odontogenic mesenchymal stem cells urgently need to be summarized, thus, we reviewed studies on odontogenic mesenchymal stem cells and their specific subpopulations, in order to provide indications for further research on the stem cell regenerative therapy.

Lateral Mesoderm-Derived Mesenchymal Stem Cells With Robust Osteochondrogenic Potential and Hematopoiesis-Supporting Ability

Mesenchymal stem cells (MSCs) are among the most promising cell sources for the treatment of various diseases. Nonetheless, the therapeutic efficacy in clinical trials has been inconsistent due to the heterogeneity of MSCs, which may be partially attributed to their undefined developmental origins. The lateral mesoderm is also a developmental source of MSCs that constitute appendicular skeletal elements in the developing vertebrate embryo. However, it is difficult to isolate homogeneous lateral mesoderm (LM)-derived MSCs from bone tissues or bone marrow due to the lack of understanding of their characteristics. Herein, we successfully established an efficient differentiation protocol for the derivation of MSCs with a LM origin from human pluripotent stem cells (hPSCs) under specific conditions. LM-MSCs resembled bone marrow-derived MSCs (BMSCs) with regard to cell surface markers, global gene profiles, and immunoregulatory activity and showed a homeodomain transcription factor (HOX) gene expression pattern typical of skeletal MSCs in long bones. Moreover, we demonstrated that LM-MSCs had an increased osteogenic/chondrogenic differentiation capacity and hematopoietic support potential compared to BMSCs. These homogeneous LM-MSCs may serve as a powerful tool for elucidating their precise role in bone formation and hematopoiesis and could be a potentially ideal cell source for therapeutic applications.

Recent updates on the biological basis of heterogeneity in bone marrow stromal cells/skeletal stem cells

Based on studies over the last several decades, the self-renewing skeletal lineages derived from bone marrow stroma could be an ideal source for skeletal tissue engineering. However, the markers for osteogenic precursors; i.e., bone marrowderived skeletal stem cells (SSCs), in association with other cells of the marrow stroma (bone marrow stromal cells, BMSCs) and their heterogeneous nature both in vivo and in vitro remain to be clarified. This review aims to highlight: i) the importance of distinguishing BMSCs/SSCs from other "mesenchymal stem/stromal cells", and ii) factors that are responsible for their heterogeneity, and how these factors impact on the differentiation potential of SSCs towards bone. The prospective role of SSC enrichment, their expansion and its impact on SSC phenotype is explored. Emphasis has also been given to emerging single cell RNA sequencing approaches in scrutinizing the unique population of SSCs within the BMSC population, along with their committed progeny. Understanding the factors involved in heterogeneity may help researchers to improvise their strategies to isolate, characterize and adopt best culture practices and source identification to develop standard operating protocols for developing reproducible stem cells grafts. However, more scientific understanding of the molecular basis of heterogeneity is warranted that may be obtained from the robust high-throughput functional transcriptomics of single cells or clonal populations.

The long and winding road: homeostatic and disordered haematopoietic microenvironmental niches: a narrative review

Haematopoietic microenvironmental niches have been described as the 'gatekeepers' for the blood and immune systems. These niches change during ontogeny, with the bone marrow becoming the predominant site of haematopoiesis in post-natal life under steady state conditions. To determine the structure and function of different haematopoietic microenvironmental niches, it is essential to clearly define specific haematopoietic stem and progenitor cell subsets during ontogeny and to understand their temporal appearance and anatomical positioning. A variety of haematopoietic and non-haematopoietic cells contribute to haematopoietic stem and progenitor cell niches. The latter is reported to include endothelial cells and mesenchymal stromal cells (MSCs), skeletal stem cells and/or C-X-C motif chemokine ligand 12-abundant-reticular cell populations, which form crucial components of these microenvironments under homeostatic conditions. Dysregulation or deterioration of such cells contributes to significant clinical disorders and diseases worldwide and is associated with the ageing process. A critical appraisal of these issues and of the roles of MSC/C-X-C motif chemokine ligand 12-abundant-reticular cells and the more recently identified skeletal stem cell subsets in bone marrow haematopoietic niche function under homeostatic conditions and during ageing will form the basis of this research review. In the context of haematopoiesis, clinical translation will deal with lessons learned from the vast experience garnered from the development and use of MSC therapies to treat graft versus host disease in the context of allogeneic haematopoietic transplants, the recent application of these MSC therapies to treating emerging and severe coronavirus disease 2019 (COVID-19) infections, and, given that skeletal stem cell ageing is one proposed driver for haematopoietic ageing, the potential contributions of these stem cells to haematopoiesis in healthy bone marrow and the benefits and challenges of using this knowledge for rejuvenating the age-compromised bone marrow haematopoietic niches and restoring haematopoiesis.

Transcriptome Sequencing Reveals Key Genes in Three Early Phases of Osteogenic, Adipogenic, and Chondrogenic Differentiation of Bone Marrow Mesenchymal Stem Cells in Rats

Bone mesenchymal stem cells (BMSCs) of multi-directional differentiation and reproductive activity are attractive candidates for bone and cartilage repair. However, the molecular mechanisms underlying the early phase of osteogenesis, adipogenesis, and chondrogenesis of BMSCs are still far from understood. In the current study, BMSCs are isolated from rats, and the gene expressions during the initiation of differentiation (phase I), lineage acquisition (phase II), and early lineage progression (phase III) of three-directional differentiation of BMSCs were detected by using high-throughput sequencing. Then, 356, 540, and 299 differentially expressed genes (DEGs) were identified in phases I, II, and III of osteogenesis, respectively. The numbers are 507, 287, and 428 for adipogenesis, respectively, and 412, 336, and 513 for chondrogenesis, respectively. Time-dependent expression patterns of genes were also validated during three-directional differentiation in BMSCs. Hub genes including Ccna2, Cdc20, and Il6 may act as common participants in initiating osteogenesis, adipogenesis, and chondrogenesis. Mex3b, Sertad1, and Hopx showed an enhanced expression throughout three early phases during the osteogenic differentiation but no significant change in other two-directional differentiation. A similar pattern of Dtx4 and Ibsp expression occurred in adipogenesis and chondrogenesis, respectively. Our findings will help understand the underlying mechanism determining the differentiation fate of BMSCs and provide theoretical support for the clinical treatment of osteoporosis, osteoarthritis, and other age-related bone diseases.

Novel Insights into the Stemness and Immune Privilege of Mesenchymal Stem Cells from Human Wharton Jelly by Single-Cell RNA Sequencing

BACKGROUND Fundamental and clinical interest in mesenchymal stem cells (MSCs) has risen dramatically over the past 3 decades. The immunomodulatory and differentiation abilities are the main mechanisms in vitro and in vivo. However, increasing evidence casts doubt on the stemness and immunogenicity of MSCs. MATERIAL AND METHODS We conducted a high-throughput 10x RNA sequencing and Smart-seq2 scRNA-seq analysis to reveal gene expression of Wharton jelly MSCs (WJ-MSCs) at a single-cell level. Multipotent differentiation, subpopulations, marker genes, human leucocyte antigen (HLA) gene expression, and cell cluster trajectory analysis were evaluated. RESULTS The WJ-MSCs had considerable heterogeneity between cells in terms of gene expression. They highly, partially, and hardly expressed genes related to mesodermal differentiation, endodermal differentiation, and ectodermal differentiation, respectively. Some cells seem to be bipotent or unipotent stem cells. Further, Monocle and cell cluster trajectory analysis demonstrated that 1 of the 3 divided clusters performed as stem cells, accounting for 12.6% of the population. The marker genes for a stem cell cluster were CRIM1, GLS, PLOD2, NEXN, ACTR2, FN1, MBNL1, LMOD1, COL3A1, NCL, SEC62, EPRS, COL5A2, COL8A1, and VCAN. In addition, the MSCs also highly, partially, and hardly expressed HLA-I antigen genes, HLA-II genes, and the HLA-G gene, respectively, indicating that MSCs probably have immunogenicity. A Kyoto Encyclopedia of Genes and Genomes pathway analysis of the 3 clusters demonstrated that they were mainly connected with viral infectious diseases, cancer, and endocrine and metabolic disorders. The most expressed transcription factors were zf-C2H2, HMG/HMGY, and Homeobox. CONCLUSIONS We found that only a subpopulation of WJ-MSCs are real stem cells and WJ-MSCs probably do not have immune privilege.

Transcriptome Sequencing Reveals Key Genes in Three Early Phases of Osteogenic, Adipogenic, and Chondrogenic Differentiation of Bone Marrow Mesenchymal Stem Cells in Rats

Bone mesenchymal stem cells (BMSCs) of multi-directional differentiation and reproductive activity are attractive candidates for bone and cartilage repair. However, the molecular mechanisms underlying the early phase of osteogenesis, adipogenesis, and chondrogenesis of BMSCs are still far from understood. In the current study, BMSCs are isolated from rats, and the gene expressions during the initiation of differentiation (phase I), lineage acquisition (phase II), and early lineage progression (phase III) of three-directional differentiation of BMSCs were detected by using high-throughput sequencing. Then, 356, 540, and 299 differentially expressed genes (DEGs) were identified in phases I, II, and III of osteogenesis, respectively. The numbers are 507, 287, and 428 for adipogenesis, respectively, and 412, 336, and 513 for chondrogenesis, respectively. Time-dependent expression patterns of genes were also validated during three-directional differentiation in BMSCs. Hub genes including Ccna2, Cdc20, and Il6 may act as common participants in initiating osteogenesis, adipogenesis, and chondrogenesis. Mex3b, Sertad1, and Hopx showed an enhanced expression throughout three early phases during the osteogenic differentiation but no significant change in other two-directional differentiation. A similar pattern of Dtx4 and Ibsp expression occurred in adipogenesis and chondrogenesis, respectively. Our findings will help understand the underlying mechanism determining the differentiation fate of BMSCs and provide theoretical support for the clinical treatment of osteoporosis, osteoarthritis, and other age-related bone diseases.

Effective Label-Free Sorting of Multipotent Mesenchymal Stem Cells from Clinical Bone Marrow Samples

Mesenchymal stem cells (MSC) make up less than 1% of the bone marrow (BM). Several methods are used for their isolation such as gradient separation or centrifugation, but these methodologies are not direct and, thus, plastic adherence outgrowth or magnetic/fluorescent-activated sorting is required. To overcome this limitation, we investigated the use of a new separative technology to isolate MSCs from BM; it label-free separates cells based solely on their physical characteristics, preserving their native physical properties, and allows real-time visualization of cells. BM obtained from patients operated for osteochondral defects was directly concentrated in the operatory room and then analyzed using the new technology. Based on cell live-imaging and the sample profile, it was possible to highlight three fractions (F1, F2, F3), and the collected cells were evaluated in terms of their morphology, phenotype, CFU-F, and differentiation potential. Multipotent MSCs were found in F1: higher CFU-F activity and differentiation potential towards mesenchymal lineages compared to the other fractions. In addition, the technology depletes dead cells, removing unwanted red blood cells and non-progenitor stromal cells from the biological sample. This new technology provides an effective method to separate MSCs from fresh BM, maintaining their native characteristics and avoiding cell manipulation. This allows selective cell identification with a potential impact on regenerative medicine approaches in the orthopedic field and clinical applications.

Isolation and Characterization of Tissue Resident CD29-Positive Progenitor Cells in Livestock to Generate a Three-Dimensional Meat Bud

The current process of meat production using livestock has significant effects on the global environment, including high emissions of greenhouse gases. In recent years, cultured meat has attracted attention as a way to acquire animal proteins. However, the lack of markers that isolate proliferating cells from bovine tissues and the complex structure of the meat make it difficult to culture meat in a dish. In this study, we screened 246 cell-surface antibodies by fluorescence-activated cell sorting for their capacity to form colonies and their suitability to construct spheroid “meat buds”. CD29+ cells (Ha2/5 clone) have a high potency to form colonies and efficiently proliferate on fibronectin-coated dishes. Furthermore, the meat buds created from CD29+ cells could differentiate into muscle and adipose cells in a three-dimensional structure. The meat buds embedded in the collagen gel proliferated in the matrix and formed large aggregates. Approximately 10 trillion cells can theoretically be obtained from 100 g of bovine tissue by culturing and amplifying them using these methods. The CD29+ cell characteristics of bovine tissue provide insights into the production of meat alternatives in vitro.