Hematopoiesis and the behavior of hematopoietic stem and progenitor cells (HSPCs) are regulated by the bone marrow niche. Here, we introduce the major niche cell types in bone marrow and their response to stress condition. We highlight the hematopoietic response and bone marrow niche adaptation to inflammatory condition and non-hematopoietic diseases, which are not systematically summarized. These emerging data suggest targeting hematopoiesis and bone marrow niche may provide novel therapeutic target to precisely control the progression of the diseases.

Skeletal stem cells (SSCs) have been isolated from various tissues, including periosteum and bone marrow, where they exhibit key functions in bone biology and hematopoiesis, respectively. The role of periosteal SSCs (P-SSCs) in bone regeneration and healing has been extensively studied, but their ability to contribute to the bone marrow stroma is still under debate. In the present study, we characterized a mouse whole bone transplantation model that mimics the initial bone marrow necrosis and fatty infiltration seen after injury. Using this model and a lineage tracing approach, we observed the migration of P-SSCs into the bone marrow after transplantation. Once in the bone marrow, P-SSCs are phenotypically and functionally reprogrammed into bone marrow mesenchymal stem cells (BM-MSCs) that express high levels of hematopoietic stem cell niche factors such as Cxcl12 and Kitl. In addition, using ex vivo and in vivo approaches, we found that P-SSCs are more resistant to acute stress than BM-MSCs. These results highlight the plasticity of P-SSCs and their potential role in bone marrow regeneration after bone marrow injury.

The skeleton is one of the most structurally and compositionally diverse organ systems in the human body, depending on unique cellular dynamisms. Here, we integrate prospective isolation of human skeletal stem cells (hSSCs; CD45-CD235a-TIE2-CD31-CD146-PDPN+CD73+CD164+) from ten skeletal sites with functional assays and single-cell RNA sequencing (scRNA-seq) analysis to identify chondrogenic, osteogenic, stromal, and fibrogenic subtypes of hSSCs during development and their linkage to skeletal phenotypes. We map the distinct composition of hSSC subtypes across multiple skeletal sites and demonstrate their unique in vivo clonal dynamics. We find that age-related changes in bone formation and regeneration disorders stem from a pathological fibroblastic shift in the hSSC pool. Utilizing a Boolean algorithm, we uncover gene regulatory networks that dictate differences in the ability of hSSCs to generate specific skeletal tissues. Importantly, hSSC lineage dynamics are pharmacologically malleable, providing a new strategy to treat aberrant hSSC diversity central to aging and skeletal maladies.

Damage to articular cartilage, tendons, ligaments and entheses as a result of trauma, degeneration or inflammation in rheumatic diseases is prevalent. Regenerative medicine offers promising strategies for repairing damaged tissues, with the aim of restoring both their structure and function. While these strategies have traditionally relied on tissue engineering approaches using exogenous cells, interventions based on the activation of endogenous repair mechanisms are an attractive alternative. Key to advancing such approaches is a comprehensive understanding of the diversity of the stem and progenitor cells that reside in the adult synovial joint and how they function to repair damaged tissues. Advances in developmental biology have provided a lens through which to understand the origins, identities and functions of these cells, and insights into the roles of stem and progenitor cells in joint tissue repair, as well as their complex relationship with fibroblasts, have emerged. Integration of knowledge obtained through studies using advanced single-cell technologies will be crucial to establishing unified models of cell populations, lineage hierarchies and their molecular regulation. Ultimately, a more complete understanding of how cells repair tissues in adult life will guide the development of innovative pro-regenerative drugs, which are poised to enter clinical practice in musculoskeletal medicine.

In our aging society, the degeneration of the musculoskeletal system and adjacent tissues is a growing orthopedic concern. As bones age, they become more fragile, increasing the risk of fractures and injuries. Furthermore, tissues like cartilage accumulate damage, leading to widespread joint issues. Compounding this, the regenerative capacity of these tissues declines with age, exacerbating the consequences of fractures and cartilage deterioration. With rising demand for fracture and cartilage repair, bone-derived stem cells have attracted significant research interest. However, the therapeutic use of stem cells has produced inconsistent results, largely due to ongoing debates and uncertainties regarding the precise identity of the stem cells responsible for musculoskeletal growth, maintenance and repair. This review focuses on the potential to leverage endogenous skeletal stem cells (SSCs)-a well-defined population of stem cells with specific markers, reliable isolation techniques, and functional properties-in bone repair and cartilage regeneration. Understanding SSC behavior in response to injury, including their activation to a functional state, could provide insights into improving treatment outcomes. Techniques like microfracture surgery, which aim to stimulate SSC activity for cartilage repair, are of particular interest. Here, we explore the latest advances in how such interventions may modulate SSC function to enhance bone healing and cartilage regeneration.

CD146 plays a key role in cancer progression and metastasis. Cancer stem cells (CSCs) are responsible for tumor initiation, drug resistance, metastasis, and recurrence. In this study, we explored the role of CD146 in the regulation of liver CSCs. Here, we demonstrated that CD146 was highly expressed in liver CSCs. CD146 overexpression promoted the self-renewal ability and chemoresistance of Hepatocellular Carcinoma (HCC) cells in vitro and tumorigenicity in vivo. Inversely, knockdown of CD146 restrained these abilities. Mechanistically, CD146 activated the NF-κB signaling to up-regulate JAG2 expression and activated the Notch signaling, which resulted in increased stemness of HCC. Furthermore, JAG2 overexpression restored the Notch signaling activity, the stemness, and chemotherapeutic resistance caused by CD146 knockdown. These results demonstrated that CD146 positively regulates HCC stemness by activating the JAG2-NOTCH signaling. Combined targeting of CD146 and JAG2 may represent a novel therapeutic strategy for HCC treatment.

Periosteum-resident skeletal stem cells (SSCs) are essential for the growth, maintenance, and repair of the skeletal system. These cells exhibit self-renewal ability and clonal pluripotency. Compared to the diverse bone marrow mesenchymal stem cells (BMSCs), periosteal skeletal stem cells (P-SSCs) represent a purified stem cell population and are preferable for bone tissue engineering.

This review covers the histological structure of the periosteum, process of isolating and characterising P-SSCs, and spatiotemporal distribution and characteristics of P-SSCs from different lineages. Additionally, the roles of P-SSCs in bone injury, disease, and periosteal niche regulation are discussed.

Intramembrane and intraconal ossification of P-SSCs exhibits favourable therapeutic potential. Osteogenesis using P-SSCs is an ideal process for bone repair.

P-SSCs are vital for bone formation, maintenance, and repair. P-SSCs are essential components of the periosteal microenvironment. Therefore, it is essential to investigate their critical clinical applications and translational functions. By targeting and inducing endogenous stem cells, the in situ repair of bone defects can be facilitated, leading to the development of more effective novel therapies.

To enhance our understanding of the function of P-SSCs in bone repair and skeleton-related diseases, it is imperative to elucidate the current research status of P-SSCs and ascertain the prospective trajectory for their advancement and refinement in bone tissue engineering. P-SSCs are expected to play an expanded role in treating bone abnormalities, leading to the optimisation of bone tissue treatment.

Skeletal stem cells (SSCs) and related progenitors with osteogenic potential, collectively termed skeletal stem and/or progenitor cells (SSPCs), are crucial for providing osteoblasts for bone formation during homeostatic tissue turnover and fracture repair. Besides mediating normal bone physiology, they also have important roles in various metabolic bone diseases, including osteoporosis. SSPCs are of tremendous interest because they represent prime future targets for osteoanabolic therapies and bone regenerative medicine. Remarkable progress has been made in characterizing various SSC and SSPC populations in postnatal bone. SSPCs exist in the periosteum and within the bone marrow stroma, including subsets localizing around arteriolar and sinusoidal blood vessels; they can display osteogenic, chondrogenic, adipogenic and/or fibroblastic potential, and exert critical haematopoiesis-supportive functions. However, much remains to be clarified. By the current markers, bona fide SSCs are commonly contained within broader SSPC populations characterized by considerable heterogeneity and overlap, whose common versus specific functions in health and disease have not been fully unravelled. Here, we review the present knowledge of the identity, fates and relationships of SSPC populations in the postnatal bone environment, their contributions to bone maintenance, the changes observed upon ageing, and the effect of metabolic diseases such as osteoporosis and diabetes mellitus.

➢ Skeletal stem cells (SSCs) continually replenish mature cell populations to support skeletal homeostasis.➢ SSCs repopulate by self-renewal, have multilineage potential, and are long-lived in vivo.➢ SSCs express specific combinations of cell surface markers that reflect their lineage identity.➢ SSCs adapt to their anatomic environment to support regional differences in skeletal behavior and pathology.

SHEDs have demonstrated significant potential in cell therapy due to their superior proliferation rate, self-renewal and differentiation capacity (particularly neurogenesis attributed to their neural crest origin), and the less invasive procedure required for tissue collection compared to other stem cells. However, there is no established criterion to verify the minimum qualification to select one from numerous candidates, especially for SHEDs' cultured FBS-free medium for clinic application. For that, we performed a characteristic analysis containing the growth rate, colony-forming unit (CFU) number, average colony size, and migration capacity with hPL-cultured SHEDs from 21 different donors, and we suggest the result as a minimum standard to filter out unqualified candidates. In addition, in the secretome analysis to predict the paracrine effect, it was found that upregulated proteins compared to the control were related to angiogenesis, immune response, and BMP signaling, and this was found to have a strong correlation only with protein concentration. This study presents a minimum standard for selecting cell therapy candidates and suggests the protein concentration of a conditioned medium as a cost-effective tool to expect the paracrine effect of SHEDs.

The liver, as the largest metabolic and detoxification organ in mammals, metabolizes approximately 80-90% of drugs. However, drug-induced liver injury (DILI) is common and driven by factors such as individual variability, differences in liver metabolism, and improper drug use. Mesenchymal stem cells (MSCs), with their self-renewal and multipotent differentiation capabilities, offer therapeutic potential, but face challenges such as limited proliferation and increased apoptosis during in vitro expansion. Although MSCs exhibit low immunogenicity, they are often cleared by the host immune system, which limits their survival and engraftment. Glutathione peroxidase 3 (GPX3) is a key antioxidant enzyme that reduces reactive oxygen species (ROS), protecting cells from oxidative damage. CD47, also known as integrin-associated protein (IAP), helps cells evade immune clearance by binding to signal regulatory protein alpha (SIRPα) on the immune cells. Here, we used an acetaminophen (APAP)-induced DILI mouse model to evaluate the therapeutic efficacy of intravenously infused MSCs overexpressing GPX3 and CD47. Compared to unmodified MSCs, modified MSCs showed improved survival, reduced liver inflammation, and alleviated oxidative damage, offering enhanced protection against APAP-induced DILI.

Myelodysplastic syndrome (MDS) is a clonal disorder of hematopoietic stem cells (HSCs), characterized by ineffective hematopoiesis and a high risk of progression to acute myeloid leukemia. Elucidating the mechanism underlying the dysfunction of MDS-HSCs is crucial for exploring the pathogenesis of the syndrome. While previous studies have implicated mesenchymal stem cells (MSCs), a principal component of the bone marrow (BM) microenvironment, in the inhibition of normal hematopoiesis, the precise molecular mechanisms have not been fully elucidated. In this study, we investigated the effects of MSCs from MDS patients on hematopoietic functions of HSCs from a metabolic perspective.

MSCs were isolated from BM of MDS patients. The proliferation, apoptosis, differentiation and support for hematopoiesis of these cells were analyzed using CCK-8 assay, FC and induction medium and CFU (colony forming units) assay, respectively. Expression levels of metabolic molecules were used as indicators to screen MSCs with different metabolic pathways and were detected by RT-PCR and Western blotting. Exosome derived from MSCs were isolated from the culture supernatant and confirmed by Transmission Electron Microscope, Dynamic Light Scattering and Western blotting. The effects of these exosomes on HSCs were analyzed using the same methods as those used to assess MSCs function.

Our findings demonstrated that MDS-MSCs exhibited significant functional impairments, including reduced proliferation, impaired differentiation, diminished support for hematopoiesis, and increased apoptosis. Notably, we observed an upregulation of lipid metabolism in these MSCs, which appears to contribute to their dysfunction. Intriguingly, the aberrant lipid metabolic profile can be effectively reversed by the administration of etomoxir (ETO), an inhibitor of carnitine palmitoyltransferase 1A (CPT-1A). Furthermore, MSCs with enhanced lipid metabolism could transmit this dysfunction to HSCs through the secretion of exosomes that are enriched in CPT-1A.

We suggest that the MDS BM microenvironment disrupts MSCs metabolism by increasing the expression of CPT-1A, which impairs the ability to support normal HSCs. Interestingly, the suppressive effect is mediated by exosomes rich in CPT-1A, which derived from MSCs. These findings provide novel insights into MDS MSCs-metabolism-Exosome axis in ineffective hematopoiesis and offer new strategies for the treatment of MDS.

Hematopoiesis unfolds within the bone marrow niche where hematopoietic stem cells (HSCs) play a central role in continually replenishing blood cells. The hypoxic bone marrow environment imparts peculiar metabolic characteristics to hematopoietic processes. Here, we discuss the internal metabolism of HSCs and describe external influences exerted on HSC metabolism by the bone marrow niche environment. Importantly, we suggest that the metabolic environment and metabolic cues are intertwined with HSC cell fate, and are crucial for hematopoietic processes. Metabolic dysregulation within the bone marrow niche during acute stress, inflammation, and chronic inflammatory conditions can lead to reduced HSC vitality. Additionally, we raise questions regarding metabolic stresses imposed on HSCs during implementation of stem cell protocols such as allo-SCT and gene therapy, and the potential ramifications. Enhancing our comprehension of metabolic influences on HSCs will expand our understanding of pathophysiology in the bone marrow and improve the application of stem cell therapies.

Skeletal stem cells have been isolated from various tissues, including periosteum and bone marrow, where they exhibit key functions in bone biology and hematopoiesis, respectively. The role of periosteal skeletal stem cells in bone regeneration and healing has been extensively studied, but their ability to contribute to the bone marrow stroma is still under debate. In the present study, we characterized a whole bone transplantation model that mimics the initial bone marrow necrosis and fatty infiltration seen after injury. Using this model and a lineage tracing approach, we observed the migration of periosteal skeletal stem cells into the bone marrow after transplantation. Once in the bone marrow, periosteal skeletal stem cells are phenotypically and functionally reprogrammed into bone marrow mesenchymal stem cells that express high levels of hematopoietic stem cell niche factors such as Cxcl12 and Kitl. In addition, using ex vivo and in vivo approaches, we found that periosteal skeletal stem cells are more resistant to acute stress than bone marrow mesenchymal stem cells. These results highlight the plasticity of periosteal skeletal stem cells and their potential role in bone marrow regeneration after bone marrow injury.

During the transition from embryonic to adult life, the sites of hematopoiesis undergo dynamic shifts across various tissues. In adults, although bone marrow (BM) becomes the primary site for definitive hematopoiesis, the establishment of the BM niche for accommodating hematopoietic stem cells (HSCs) remains incompletely understood. Here, we reveal that perinatal BM mesenchymal stem cells (BMSCs) exhibit highly activated insulin-like growth factor 1 receptor (IGF1R) signaling compared with adult BMSCs (aBMSCs). Deletion of Igf1r in perinatal BMSCs (pBMSCs) hinders the transition of HSCs from the fetal liver to the BM in perinatal mice and disrupts hematopoiesis in adult individuals. Conversely, the deletion of Igf1r in aBMSCs, adipocytes, osteoblasts, or endothelial cells does not affect HSCs in the BM. Mechanistically, IGF1R signaling activates the transcription factor nuclear factor of activated T cells c1 in pBMSCs, which upregulates CXCL12 and other niche factors for HSC retention. Overall, IGF1R signaling in pBMSCs regulates the development of the BM niche for hematopoiesis.

Stem cell transplantation has proven effective in treating acute and chronic wounds, but its limitations, such as low cellular viability and the need for specialized transportation, highlight the necessity for alternative approaches. This review explores the potential of engineered exosomes, containing identified miRNAs/peptides, as a more stable and efficient cell-free therapy for regenerative medicine, particularly in wound healing. The discussion emphasizes the benefits of exosomes, including their stability, reduced damage, and consistent biological activity, paving the way for innovative applications like lyophilized exosomes, mist spray delivery, and exosome-based scaffolds. The exploration of cell-free therapy in this review holds promising implications for advancing wound-healing strategies.

A detailed examination of bone marrow (BM) aspiration and biopsy can provide clues regarding the course of the disease as well as the diagnostic features of myelodysplastic syndrome (MDS).

Our aim is to reveal the histomorphological features of MDS, investigate the impact of dysplasia types on prognosis, and highlight the importance of the microenvironment.

In 130 (93.5%) of 139 cases, Wright-Giemsa-stained BM aspiration slides were evaluated, and the dysplasia diversity was examined in detail. A regression analysis of dysplasia features significant for overall survival revealed that the presence of hyperlobulation in the megakaryocytic series (p = 0.014, odds ratio = 3.485) and the presence of an abnormal localization of immature progenitors (ALIP) (p = 0.010, odds ratio = 2.206) were significantly associated with poor prognosis. Additionally, an increase in the microvessel density (MVD) was found to be associated with a poor prognosis (p < 0.001). A multiple regression analysis identified that MVD is the most significant parameter (p = 0.014).

The diversity of dysplasia in BM aspiration and biopsy does not predict MDS subtypes; however, certain cytomorphological dysplasia types can provide insights regarding survival. The microenvironment's impact on MDS pathogenesis is undeniable, with ALIP and MVD presence and frequency being significant factors. Thus, BM histomorphological examination, beyond its diagnostic role, also offers prognostic insights.

Bone tissue provides structural support for our bodies, with the inner bone marrow (BM) acting as a hematopoietic organ. Within the BM tissue, two types of stem cells play crucial roles: mesenchymal stem cells (MSCs) (or skeletal stem cells) and hematopoietic stem cells (HSCs). These stem cells are intricately connected, where BM-MSCs give rise to bone-forming osteoblasts and serve as essential components in the BM microenvironment for sustaining HSCs. Despite the mid-20th century proposal of BM-MSCs, their in vivo identification remained elusive owing to a lack of tools for analyzing stemness, specifically self-renewal and multipotency. To address this challenge, Cre/loxP-based cell lineage tracing analyses are being employed. This technology facilitated the in vivo labeling of specific cells, enabling the tracking of their lineage, determining their stemness, and providing a deeper understanding of the in vivo dynamics governing stem cell populations responsible for maintaining hard tissues. This review delves into cell lineage tracing studies conducted using commonly employed genetically modified mice expressing Cre under the influence of LepR, Gli1, and Axin2 genes. These studies focus on research fields spanning long bones and oral/maxillofacial hard tissues, offering insights into the in vivo dynamics of stem cell populations crucial for hard tissue homeostasis.

Telomeres are pivotal determinants of cell stemness, organismal aging, and lifespan. Herein, we examined similarities in telomeres of Arabidopsis thaliana, mice, and humans. We report the common traits, which include their composition in multimers of TTAGGG sequences and their protection by specialized proteins. Moreover, given the link between telomeres, on the one hand, and cell proliferation and stemness on the other, we discuss the counterintuitive convergence between plants and mammals in this regard, focusing on the impact of niches on cell stemness. Finally, we suggest that tackling the study of telomere function and cell stemness by taking into consideration both plants and mammals can aid in the understanding of interconnections and contribute to research focusing on aging and organismal lifespan determinants.

Human induced pluripotent stem cells represent a scalable source of youthful tissue progenitors and secretomes for regenerative therapies. The aim of our study was to investigate the potential of conditioned medium (CM) from hiPSC-mesenchymal progenitors (hiPSC-MPs) to stimulate osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells (MSCs). We also investigated whether prolonged cultivation or osteogenic pre-differentiation of hiPSC-MPs could enhance the stimulatory activity of CM.

MSCs were isolated from 13 donors (age 20-90 years). CM derived from hiPSC-MPs was added to the MSC cultures and the effects on proliferation and osteogenic differentiation were examined after 14 days and 6 weeks. The stimulatory activity of hiPSC-MP-CM was compared with the activity of MSC-derived CM and with the activity of CM prepared from hiPSC-MPs pre-cultured in growth or osteogenic medium for 14 days. Comparative proteomic analysis of CM was performed to gain insight into the molecular components responsible for the stimulatory activity.

Primary bone marrow-derived MSC exhibited variability, with a tendency towards lower proliferation and tri-lineage differentiation in older donors. hiPSC-MP-CM increased the proliferation and alkaline phosphatase activity of MSC from several adult/aged donors after 14 days of continuous supplementation under osteogenic conditions. However, CM supplementation failed to improve the mineralization of MSC pellets after 6 weeks under osteogenic conditions. hiPSC-MP-CM showed greater enhancement of proliferation and ALP activity than CM derived from bone marrow-derived MSCs. Moreover, 14-day cultivation but not osteogenic pre-differentiation of hiPSC-MPs strongly enhanced CM stimulatory activity. Quantitative proteomic analysis of d14-CM revealed a distinct profile of components that formed a highly interconnected associations network with two clusters, one functionally associated with binding and organization of actin/cytoskeletal components and the other with structural constituents of the extracellular matrix, collagen, and growth factor binding. Several hub proteins were identified that were reported to have functions in cell-extracellular matrix interaction, osteogenic differentiation and development.

Our data show that hiPSC-MP-CM enhances early osteogenic differentiation of human bone marrow-derived MSCs and that prolonged cultivation of hiPSC-MPs enhances CM-stimulatory activity. Proteomic analysis of the upregulated protein components provides the basis for further optimization of hiPSC-MP-CM for bone regenerative therapies.

The efficiency of mesenchymal stem cells (MSCs) in treating myocardial infarction (MI) remains inconsistent, which limits their therapeutic applications. Therefore, exploring the mechanism for the inconsistent efficacy of MSCs and identification the criteria for screening MSCs are important for improving the efficiency of MSCs.

Mouse model after MI was utilized to test the role of MSCs from different donors and the functional subpopulation in improving cardiac function. Heterogeneity of MSCs was identified using single-cell RNA sequencing (scRNA-seq) of MSC-GY. GSEA and Scissor analyses were used to find the functional subpopulations of MSCs that promote angiogenesis. The role of functional subpopulations in promoting angiogenesis was verified by detecting the secretory proteins, the ratio of N-CADHERIN+/CD168- subpopulations in MSCs, and the tube formation, migration, and proliferation of HUVECs after treatment with conditional medium (CM) derived from different MSCs.

We found that umbilical cord-derived MSCs (UC-MSCs) from different donors have varied therapeutic efficacy in MI mice and UC-MSCs with higher therapeutic effectiveness exhibited the most potent pro-angiogenic effects by secreting elevated levels of angiogenesis-related proteins, such as MYDGF, VEGFA, and FGF2. ScRNA-seq of 10,463 UC-MSCs revealed that the N-CADHERIN+/CD168- subpopulation was closely associated with pro-angiogenic effects, and the ratio of this cell subpopulation was positively correlated with the angiogenic potential of MSCs. We also found that the N-CADHERIN+/CD168- subpopulation was the functional subpopulation of MSCs in improving cardiac function of MI mice.

Our study identified that the N-CADHERIN+/CD168- subpopulation was the functional subpopulation of MSCs in treating MI, which was essential for the development and utilization of MSCs in MI treatment.

Hematopoiesis within the bone marrow (BM) is a complex and tightly regulated process predominantly influenced by immune factors. Aging, diabetes, and obesity are significant contributors to BM niche damage, which can alter hematopoiesis and lead to the development of clonal hematopoiesis of intermediate potential (CHIP). Genetic/epigenetic alterations during aging could influence BM niche reorganization for hematopoiesis or clonal hematopoiesis. CHIP is driven by mutations in genes such as Tet2, Dnmt3a, Asxl1, and Jak2, which are associated with age-related hematological malignancies.

This literature review aims to provide an updated exploration of the functional aspects of BM niche cells within the hematopoietic microenvironment in the context of age-related hematological malignancies. The review specifically focuses on how immunological stressors modulate different signaling pathways that impact hematopoiesis.

An extensive review of recent studies was conducted, examining the roles of various BM niche cells in hematopoietic stem cell (HSC) trafficking and the development of age-related hematological malignancies. Emphasis was placed on understanding the influence of immunological stressors on these processes.

Recent findings reveal a significant microheterogeneity and temporal stochasticity of niche cells across the BM during hematopoiesis. These studies demonstrate that niche cells, including mesenchymal stem cells, osteoblasts, and endothelial cells, exhibit dynamic interactions with HSCs, significantly influenced by the BM microenvironment as the age increases. Immunosurveillance plays a crucial role in maintaining hematopoietic homeostasis, with alterations in immune signaling pathways contributing to the onset of hematological malignancies. Novel insights into the interaction between niche cells and HSCs under stress/aging conditions highlight the importance of niche plasticity and adaptability.

The involvement of age-induced genetic/epigenetic alterations in BM niche cells and immunological stressors in hematopoiesis is crucial for understanding the development of age-related hematological malignancies. This comprehensive review provides new insights into the complex interplay between niche cells and HSCs, emphasizing the potential for novel therapeutic approaches that target niche cell functionality and resilience to improve hematopoietic outcomes in the context of aging and metabolic disorders.

This review introduces novel concepts regarding the plasticity and adaptability of BM niche cells in response to immunological stressors and epigenetics. It proposes that targeted therapeutic strategies aimed at enhancing niche cell resilience could mitigate the adverse effects of aging, diabetes, and obesity on hematopoiesis and clonal hematopoiesis. Additionally, the review suggests that understanding the precise temporal and spatial dynamics of niche-HSC interactions and epigenetics influence may lead to innovative treatments for age-related hematological malignancies.

The current murine models of peri-implant osseointegration failure are associated with wear particles. However, the current clinical osseointegration failure is not associated with wear particles. Here, we develop a murine model of osseointegration failure not associated with wear particles and validate it by comparing the cellular composition of interfacial tissues with human samples collected during total joint arthroplasty revision for aseptic loosening.

Thirty-two 16-week-old female C57BL/6 mice underwent implantation with a press-fitted roughened titanium implant (Control, n = 11) to induce normal osseointegration and a press-fitted smooth polymethylmethacrylate implant (PMMA, n = 11), a loosely fitted smooth titanium implant (Smooth-Ti, n = 5) or a loosely fitted roughened titanium implant (Overdrill, n = 5) to induce osseointegration failure. Pullout testing was used to determine the strength of the bone-implant interface (n = 6 of each for Control and PMMA groups) at 2 weeks after implantation. Histology (n = 2/group) and immunofluorescence (n = 3/group) were used to determine the cellular composition of bone-implant interfacial tissue, and this was compared with two human samples.

Osseointegration failure was confirmed with grossly loosening implants and the presence of fibrous tissue identified via histology. The maximum pullout load in the PMMA group was 87% lower than in the Control group (2.8 ± 0.6 N vs. 21 ± 1.5 N, p < 0.001). With immunofluorescence, abundant fibroblasts (PDGFRα+ TCF4+ and PDGFRα+ Pu1+) were observed in osseointegration failure groups and the human samples, but not in controls. Interestingly, CD146+PDGFRα+ and LepR+PDGFRα+ mesenchymal progenitors, osteoblasts (OPN+), vascular endothelium (EMCN+) cells were observed in all groups, indicating dynamic osteogenic activity. Macrophages, only M2, were observed in conditions producing fibrous tissue.

In this newly developed non-wear-particle-related murine osseointegration failure model, the cellular composition of human and murine interfacial tissue implicates specific populations of fibroblasts in fibrous tissue formation and implies that these cells may derive from mesenchymal stem cells.

Mammalian hematopoietic stem cells (HSCs) emerge from the hemogenic endothelium in the major embryonic arteries. HSCs undergo a complex journey first migrating to the fetal liver (FL) and from there to the fetal bone marrow (FBM), where they mostly remain during adult life. In this process, a pool of adult HSCs is produced, which sustains lifelong hematopoiesis. Multiple cellular components support HSC maturation and expansion and modulate their response to environmental and developmental cues. While the adult HSC niche has been extensively studied over the last two decades, the niches present in the major embryonic arteries, FL, FBM and perinatal bone marrow (BM) are poorly described. Recent investigations highlight important differences among FL, FBM and adult BM niches and emphasize the important role that inflammation, microbiota and hormonal factors play regulating HSCs and their niches. We provide a review on our current understanding of these important cellular microenvironments across ontogeny. We mainly focused on mice, as the most widely used research model, and, when possible, include relevant insights from other vertebrates including birds, zebrafish, and human. Developing a comprehensive picture on these processes is critical to understand the earliest origins of childhood leukemia and to achieve multiple goals in regenerative medicine, such as mimicking HSC development in vitro to produce HSCs for broad transplantation purposes in leukemia, following chemotherapy, bone marrow failure, and in HSC-based gene therapy.

Early B cell factor 1 (EBF1) is a transcription factor expressed by multiple lineages of stromal cells within the bone marrow. While cultures of Ebf1-deficient cells have been demonstrated to have impaired differentiation into either the osteoblast or adipogenic lineage in vitro by several groups, in vivo there has been a nominal consequence of the loss of EBF1 on skeletal development. In this study we used Prx-cre driven deletion of Ebf1 to eliminate EBF1 from the entire mesenchymal lineage of the skeleton and resolve this discrepancy. We report here that EBF1 is expressed primarily in the Mesenchymal Stem and Progenitor Cell (MSPC)-Adipo, MSPC-Osteo, and the Early Mesenchymal Progenitors, and that loss of EBF1 has a plethora of consequences to maintenance of the skeleton throughout adulthood. Stroma from the Prx-cre;Ebf1fl/fl bones had impaired osteogenic differentiation, an age-dependent loss of CFU-F, and elevated senescence accompanying Ebf1-deletion. New bone formation was reduced after 3 months, and resulted in a quiescent bone environment with fewer osteoblasts and an accompanied reduction in osteoclast-mediated remodeling. Consequently, bones were less ductile at a younger age, and deletion of EBF1 dramatically impaired fracture repair. Disruption of EBF1 in perivascular populations also rearranged the vascular network within these bones and disrupted cytokine signaling from key hematopoietic niches resulting in anemia, reductions in B cells, and myeloid skewing of marrow hematopoietic lineages. Mechanistically we observed disrupted BMP signaling within Ebf1-deficient progenitors with reduced SMAD1-phosphorylation, and elevated secretion of the soluble BMP-inhibitor Gremlin from the MSPC-Adipo cells. Ebf1-deficient progenitors also exhibited posttranslational suppression of glucocorticoid receptor expression. Together, these results suggest that EBF1 signaling is required for mesenchymal progenitor mobilization to maintain the adult skeleton, and that the primary action of EBF1 in the early mesenchymal lineage is to promote proliferation, and differentiation of these perivascular cells to sustain a healthy tissue.

Human aging is linked to bone loss, resulting in bone fragility and an increased risk of fractures. This is primarily due to an age-related decline in the function of bone-forming osteoblastic cells and accelerated cellular senescence within the bone microenvironment. Here, we provide a detailed discussion of the hypothesis that age-related defective bone formation is caused by senescence of skeletal stem cells, as they are the main source of bone forming osteoblastic cells and influence the composition of bone microenvironment. Furthermore, this review discusses potential strategies to target cellular senescence as an emerging approach to treat age-related bone loss.

The human endometrium, lining the inner uterus, regenerates over 400 times uniquely during a woman's reproductive life. Endometrial stem cells (eSCs) enrich the tissue, resulting in a dense vascular network, significant angiogenic potential, and effective regeneration power. Being of natural angiogenic properties and proven effective in the treatment of vascular disorders, eSCs can be considered safe, reliable, and superior to other post-natal stem cells. Cluster of Differentiation 146 (CD146) has emerged as a pivotal marker associated with pericytes and endothelial cells for promoting angiogenesis. Endometrial cells with high CD146 expression could proliferate and differentiate into multiple lineages. This study will explore the role of CD146 in eSCs, focusing on the potential to boost the angiogenic and regenerative functions of the cells. The novelty of this study lies in the investigation of CD146 on eSC function, which may open new possibilities for eSC-based therapy in regenerative medicine and vascular disorders.

The study involved obtaining endometrial biopsies from active reproducing women to isolate and cultivate eSCs. eSCs were assessed for growth factor secretion pattern, characterized for their mesenchymal properties. Finally, eSCs were tested for their angiogenic potential by angiogenic gene expression profile and in-ovo chick embryo model. As aimed, to check the role of CD146 in eSC angiogenesis, CD146+ cells were magnetically sorted and cultured. The sorted cells underwent various analyses, including flowcytometry to identify mesenchymal markers and human growth factor panel to analyze growth factor secretion profiles The study evaluated the angiogenic potential of CD146 + cells using functional assays, including ring formation, endothelial differentiation, and wound scratch assays, to evaluate cell migration and healing capabilities. Molecular insights were obtained through chemokine and cytokine investigations In-ovo Chick model assay was conducted to check the angiogenic potential and evaluated through macroscopic as well as through immunohistochemistry.

Endometrial stem cells (eSCs) were successfully isolated using a combination of mechanical and enzymatic digestion, followed by culturing in complete DMEM media. The secretion profile of eSCs revealed significant production of various angiogenic growth factors, including Granulocyte macrophage colony-stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), Vascular endothelial growth factor (VEGF), Fibroblast growth factors (FGF), and Platelet derived growth factor AA (PDGF-AA). The angiogenic gene profile indicated upregulation of several angiogenic genes in eSCs. The mesenchymal nature of eSCs was demonstrated through surface marker analysis (Cluster of differentiation 73, Cluster of differentiation 90, Cluster of differentiation 105) and trilineage differentiation. The in-ovo chick model confirmed the angiogenic potential of eSCs. CD146+ cells, isolated via magnetic sorting, exhibited enhanced angiogenic potential. These cells secreted significant levels of angiogenic growth factors such as VEGF. In Matrigel assays, CD146+ cells formed endothelial ring structures more rapidly and persistently than unsorted eSCs. Semi-quantitative PCR confirmed their endothelial differentiation. CD146+ cells express various angiogenic chemokines such as CXCL5, CXCL8, CCL3, and CCL20 and cytokines such as GM-CSF, Interleukin-1β (IL-1β), Interleukin-6 (IL-6), PDGF AA/BB, Epidermal growth factor (EGF), Endothelin 1, Angiopoietin. In-ovo chick model assay showed that CD146+ cells had superior angiogenesis, with more nodes, junctions, and segments compared to eSCs and controls. Immunohistochemistry confirmed increased expression of endothelial markers (Cluster of differentiation 31, VEGF, Vascular associated protein (VAP), Von Willebrand factor (vWF) in CD146+ cells.

The study highlights the angiogenic potential of endometrial stem cells, particularly the CD146+ cell population. These cells promote angiogenesis, secreting growth factors and forming stable blood vessel structures. CD146+ cells have higher expression levels of VEGF and TGF-α, key factors in angiogenesis. This suggests CD146+ eSCs may be promising for therapeutic applications in vascular diseases requiring angiogenesis. Further research is needed.

The periosteum contains skeletal stem/progenitor cells that contribute to bone fracture healing. However, the in vivo identity of periosteal skeletal stem cells (P-SSCs) remains unclear, and membrane protein markers of P-SSCs that facilitate tissue engineering are needed. Here, we identified integral membrane protein 2A (Itm2a) enriched in SSCs using single-cell transcriptomics. Itm2a+ P-SSCs displayed clonal multipotency and self-renewal and sat at the apex of their differentiation hierarchy. Lineage-tracing experiments showed that Itm2a selectively labeled the periosteum and that Itm2a+ cells were preferentially located in the outer fibrous layer of the periosteum. The Itm2a+ cells rarely expressed CD34 or Osx, but expressed periosteal markers such as Ctsk, CD51, PDGFRA, Sca1, and Gli1. Itm2a+ P-SSCs contributed to osteoblasts, chondrocytes, and marrow stromal cells upon injury. Genetic lineage tracing using dual recombinases showed that Itm2a and Prrx1 lineage cells generated spatially separated subsets of chondrocytes and osteoblasts during fracture healing. Bone morphogenetic protein 2 (Bmp2) deficiency or ablation of Itm2a+ P-SSCs resulted in defects in fracture healing. ITM2A+ P-SSCs were also present in the human periosteum. Thus, our study identified a membrane protein marker that labels P-SSCs, providing an attractive target for drug and cellular therapy for skeletal disorders.

Adult hematopoietic stem and progenitor cells (HSPCs) reside in the bone marrow (BM) hematopoietic niche, which regulates HSPC quiescence, self-renewal, and commitment in a demand-adapted manner. Although the complex BM niche is responsible for adult hematopoiesis, evidence exists for simpler, albeit functional and more accessible, extramedullary hematopoietic niches. Inspired by the anecdotal description of retroperitoneal hematopoietic masses occurring at higher frequency upon hormonal dysregulation within the adrenal gland, we hypothesized that the adult adrenal gland could be induced into a hematopoietic-supportive environment in a systematic manner, thus revealing mechanisms underlying de novo niche formation in the adult. Here, we show that upon splenectomy and hormonal stimulation, the adult adrenal gland of mice can be induced to recruit and host functional HSPCs, capable of serial transplantation, and that this phenomenon is associated with de novo formation of platelet-derived growth factor receptor α/leptin receptor (PDGFRα+/LEPR+/-)-expressing stromal nodules. We further show in CXCL12-green fluorescent protein reporter mice that adrenal glands contain a stromal population reminiscent of the CXCL12-abundant reticular cells, which compose the BM HSPC niche. Mechanistically, HSPC homing to hormonally induced adrenal glands was found dependent on the CXCR4-CXCL12 axis. Mirroring our findings in mice, we found reticular CXCL12+ cells coexpressing master niche regulator FOXC1 in primary samples from human adrenal myelolipomas, a benign tumor composed of adipose and hematopoietic tissue. Our findings reignite long-standing questions regarding hormonal regulation of hematopoiesis and provide a novel model to facilitate the study of adult-specific inducible hematopoietic niches, which may pave the way to therapeutic applications.

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.

Bone marrow stem cells (BM-SCs) and their progeny play a central role in tissue repair and regeneration. In patients with chronic liver failure, bone marrow (BM) reserve is severally compromised and they showed marked defects in the resolution of injury and infection, leading to liver failure and the onset of decompensation. Whether BM failure is the cause or consequence of liver failure during cirrhosis is not known. In this study, we aimed to determine the underlying relationship between BM failure and regeneration failure in cirrhosis.

C57Bl/6(J) mice were used to develop chronic liver injury through intra-peritoneal administration of carbon tetrachloride (CCl4) for 15 weeks (0.1-0.5 ml/kg). Animals were sacrificed to study the transition of cirrhosis and BM defects. To restore the BM-SC reserve; healthy BM cells were infused via intra-BM infusion and assessed for changes in liver injury, regeneration, and BM-SC reserve.

Using a CCl4-induced animal - model of cirrhosis, we showed the loss of BM-SCs reserve occurred before regeneration failure and the onset of non-acute decompensation. Intra-BM infusion of healthy BM cells induced the repopulation of native hematopoietic stem cells (HSCs) in cirrhotic BM. Restoring BM-HSCs reserve augments liver macrophage-mediated clearance of infection and inflammation dampens neutrophil-mediated inflammation, accelerates fibrosis regression, enhances hepatocyte proliferation, and delays the onset of non-acute decompensation.

These findings suggest that loss of BM-HSCs reserve underlies the compromised innate immune function of the liver, drives regeneration failure, and the onset of non-acute decompensation. We further provide the proof-of-concept that rejuvenating BM-HSC reserve can serve as a potential therapeutic approach for preventing regeneration failure and transition to decompensated cirrhosis.

Hematopoietic stem cell transplantation (HSCT) remains an indispensable therapeutic strategy for various hematological diseases. This review discusses the pivotal role of bone marrow (BM) niches in influencing the efficacy of HSCT and evaluates the current animal models, emphasizing their limitations and the need for alternative models. Traditional animal models, mainly murine xenograft, have provided significant insights, but due to species-specific differences, are often constrained from accurately mimicking human physiological responses. These limitations highlight the importance of developing alternative models that can more realistically replicate human hematopoiesis. Emerging models that include BM organoids and BM-on-a-chip microfluidic systems promise enhanced understanding of HSCT dynamics. These models aim to provide more accurate simulations of the human BM microenvironment, potentially leading to improved preclinical assessments and therapeutic outcomes. This review highlights the complexities of the BM niche, discusses the limitations of current models, and suggests directions for future research using advanced model systems. [BMB Reports 2024; 57(8): 352-362].

Hematopoietic stem cells (HSCs) are the cornerstone of the hematopoietic system. HSCs sustain the continuous generation of mature blood derivatives while self-renewing to preserve a relatively constant pool of progenitors throughout life. Yet, long-term maintenance of functional HSCs exclusively takes place in association with their native tissue microenvironment of the bone marrow (BM). HSCs have been long proposed to reside in fixed and identifiable anatomical units found in the complex BM tissue landscape, which control their identity and fate in a deterministic manner. In the last decades, tremendous progress has been made in the dissection of the cellular and molecular fabric of the BM, the structural organization governing tissue function, and the plethora of interactions established by HSCs. Nonetheless, a holistic model of the mechanisms controlling HSC regulation in their niche is lacking to date. Here, we provide an overview of our current understanding of BM anatomy, HSC localization, and crosstalk within local cellular neighborhoods in murine and human tissues, and highlight fundamental open questions on how HSCs functionally integrate in the BM microenvironment.

In this review, we discuss the most recent scientific advances on the reciprocal regulatory interactions between the skeletal and hematopoietic stem cell niche, focusing on immunomodulation and its interplay with the cell's mitochondrial function, and how this impacts osteoimmune health during aging and disease.

Osteoimmunology investigates interactions between cells that make up the skeletal stem cell niche and immune system. Much work has investigated the complexity of the bone marrow microenvironment with respect to the skeletal and hematopoietic stem cells that regulate skeletal formation and immune health respectively. It has now become clear that these cellular components cooperate to maintain homeostasis and that dysfunction in their interaction can lead to aging and disease. Having a deeper, mechanistic appreciation for osteoimmune regulation will lead to better research perspective and therapeutics with the potential to improve the aging process, skeletal and hematologic regeneration, and disease targeting.

Mesenchymal stromal cells (MSCs) display heterogeneity in origin and functional role in tissue homeostasis. Subsets of MSCs derived from the neural crest express nestin and serve as niches in bone marrow, but the possibility of coaxing MSCs into nestin-expresing cells for enhanced supportive activity is unclear. In this study, as an approach to the chemical coaxing of MSC functions, we screened libraries of clinically approved chemicals to identify compounds capable of inducing nestin expression in MSCs. Out of 2000 clinical compounds, we chose vorinostat as a candidate to coax the MSCs into neural crest-like fates. When treated with vorinostat, MSCs exhibited a significant increase in the expression of genes involved in the pluripotency and epithelial-mesenchymal transition (EMT), as well as nestin and CD146, the markers for pericytes. In addition, these nestin-induced MSCs exhibited enhanced differentiation towards neuronal cells with the upregulation of neurogenic markers, including SRY-box transcription factor 2 (Sox2), SRY-box transcription factor 10 (Sox10) and microtubule associated protein 2 (Map2) in addition to nestin. Moreover, the coaxed MSCs exhibited enhanced supporting activity for hematopoietic progenitors without supporting leukemia cells. These results demonstrate the feasibility of the drug repositioning of MSCs to induce neural crest-like properties through the chemical coaxing of cell fates.