New MSC: MSCs as pericytes are Sentinels and gatekeepers

Omonijo F, A Ganai N, M. Ibeagha-Awemu E, Mudasir Ahmad S. Immunotherapy in mastitis: state of knowledge, research gaps and way forward

Mastitis is an inflammatory condition that affects dairy cow's mammary glands. Traditional treatment approaches with antibiotics are increasingly leading to challenging scenarios such as antimicrobial resistance. In order to mitigate the unwanted side effects of antibiotics, alternative strategies such as those that harness the host immune system response, also known as immunotherapy, have been implemented. Immunotherapy approaches to treat bovine mastitis aims to enhance the cow's immune response against pathogens by promoting pathogen clearance, and facilitating tissue repair. Various studies have demonstrated the potential of immunotherapy for reducing the incidence, duration and severity of mastitis. Nevertheless, majority of reported therapies are lacking in specificity hampering their broad application to treat mastitis. Meanwhile, advancements in mastitis immunotherapy hold great promise for the dairy industry, with potential to provide effective and sustainable alternatives to traditional antibiotic-based approaches. This review synthesizes immunotherapy strategies, their current understanding and potential future perspectives. The future perspectives should focus on the development of precision immunotherapies tailored to address individual pathogens/group of pathogens, development of combination therapies to address antimicrobial resistance, and the integration of nano- and omics technologies. By addressing research gaps, the field of mastitis immunotherapy can make significant strides in the control, treatment and prevention of mastitis, ultimately benefiting both animal and human health/welfare, and environment health.

Comparative single-cell transcriptional and proteomic atlas of clinical-grade injectable mesenchymal source tissues

Bone marrow aspirate concentrate (BMAC) and adipose-derived stromal vascular fraction (ADSVF) are the most marketed stem cell therapies to treat a variety of conditions in the general population and elite athletes. Both tissues have been used interchangeably clinically even though their detailed composition, heterogeneity, and mechanisms of action have neither been rigorously inventoried nor compared. This lack of information has prevented investigations into ideal dosages and has facilitated anecdata and misinformation. Here, we analyzed single-cell transcriptomes, proteomes, and flow cytometry profiles from paired clinical-grade BMAC and ADSVF. This comparative transcriptional atlas challenges the prevalent notion that there is one therapeutic cell type present in both tissues. We also provide data of surface markers that may enable isolation and investigation of cell (sub)populations. Furthermore, the proteome atlas highlights intertissue and interpatient heterogeneity of injected proteins with potentially regenerative or immunomodulatory capacities. An interactive webtool is available online.

Possibilities and efficiency of MSC co-transfection for gene therapy

Mesenchymal stem/stromal cells (MSCs) are not only capable of self-renewal, trans-differentiation, homing to damaged tissue sites and immunomodulation by secretion of trophic factors but are also easy to isolate and expand. Because of these characteristics, they are used in numerous clinical trials for cell therapy including immune and neurological disorders, diabetes, bone and cartilage diseases and myocardial infarction. However, not all trials have successful outcomes, due to unfavourable microenvironmental factors and the heterogenous nature of MSCs. Therefore, genetic manipulation of MSCs can increase their prospect. Currently, most studies focus on single transfection with one gene. Even though the introduction of more than one gene increases the complexity, it also increases the effectivity as different mechanism are triggered, leading to a synergistic effect. In this review we focus on the methodology and efficiency of co-transfection, as well as the opportunities and pitfalls of these genetically engineered cells for therapy.

Peripheral 5-HT/HTR6 axis is responsible for obesity-associated hypertension

Hypertension is one of the major life-threatening complications of obesity. Recently adipose multipotent mesenchymal stromal cells (MSCs) were implicated to the pathogenesis of obesity-associated hypertension. These cells amplify noradrenaline-induced vascular cell contraction via cAMP-mediated signaling pathway. In this study we tested the ability of several cAMP-mediated hormones to affect the adrenergic sensitivity of MSCs and their associated contractility. Despite that adipose MSCs express a plethora of receptors capable of cAMP signaling activation, only 5-HT was able to elevate α1A-adrenoceptor-induced Ca2+ signaling in MSCs. Furthermore, 5-HT markedly enhanced noradrenaline-induced MSCs contractility. Using HTR isoform-specific antagonists followed by CRISPRi-mediated knockdown, we identified that the observed 5-HT effect on MSCs was mediated by the HTR6 isoform. This receptor was previously associated exclusively with 5-HT central nervous system activity. Discovered effect of HTR6 on MSCs contractility points to it as a potential therapeutic target for the prevention and treatment of obesity-associated hypertension.

Fundamentals and Translational Applications of Stem Cells and Biomaterials in Dental, Oral and Craniofacial Regenerative Medicine

Regenerative dental medicine continuously expands to improve treatments for prevalent clinical problems in dental and oral medicine. Stem cell based translational opportunities include regenerative therapies for tooth restoration, root canal therapy, and inflammatory processes (e.g., periodontitis). The potential of regenerative approaches relies on the biological properties of dental stem cells. These and other multipotent somatic mesenchymal stem cell (MSC) types can in principle be applied as either autologous or allogeneic sources in dental procedures. Dental stem cells have distinct developmental origins and biological markers that determine their translational utility. Dental regenerative medicine is supported by mechanistic knowledge of the molecular pathways that regulate dental stem cell growth and differentiation. Cell fate determination and lineage progression of dental stem cells is regulated by multiple cell signaling pathways (e.g., WNTs, BMPs) and epigenetic mechanisms, including DNA modifications, histone modifications, and non-coding RNAs (e.g., miRNAs and lncRNAs). This review also considers a broad range of novel approaches in which stem cells are applied in combination with biopolymers, ceramics, and composite materials, as well as small molecules (agonistic or anti-agonistic ligands) and natural compounds. Materials that mimic the microenvironment of the stem cell niche are also presented. Promising concepts in bone and dental tissue engineering continue to drive innovation in dental and non-dental restorative procedures.

Tendon stem/progenitor cells are promising reparative cell sources for multiple musculoskeletal injuries of concomitant articular cartilage lesions associated with ligament injuries

BACKGROUND

Trauma-related articular cartilage lesions usually occur in conjunction with ligament injuries. Torn ligaments are frequently reconstructed with tendon autograft and has been proven to achieve satisfactory clinical outcomes. However, treatments for the concomitant articular cartilage lesions are still very insufficient. The current study was aimed to evaluate whether stem cells derived from tendon tissue can be considered as an alternative reparative cell source for cartilage repair.

METHODS

Primary human tendon stem/progenitor cells (hTSPCs) were isolated from 4 male patients (32 ± 8 years) who underwent ACL reconstruction surgery with autologous semitendinosus and gracilis tendons. The excessive tendon tissue after graft preparation was processed for primary cell isolation with an enzyme digestion protocol. Decellularization cartilage matrix (DCM) was used to provide a chondrogenic microenvironment for hTSPCs. Cell viability, cell morphology on the DCM, as well as their chondrogenic differentiation were evaluated.

RESULTS

DAPI staining and DNA quantitative analysis (61.47 μg per mg dry weight before and 2.64 μg/mg after decellularization) showed that most of the cells in the cartilage lacuna were removed after decellularization process. Whilst, the basic structure of the cartilage tissue was preserved and the main ECM components, collagen type II and sGAG were retained after decellularization, which were revealed by DMMB assay and histology. Live/dead staining and proliferative assay demonstrated that DCM supported attachment, survival and proliferation of hTSPCs with an excellent biocompatibility. Furthermore, gene expression analysis indicated that chondrogenic differentiation of hTSPC was induced by the DCM microenvironment, with upregulation of chondrogenesis-related marker genes, COL 2 and SOX9, without the use of exogenous growth factors.

CONCLUSION

DCM supported hTSPCs attachment and proliferation with high biocompatibility. Moreover, TSPCs underwent a distinct chondrogenesis after the induction of a chondrogenic microenvironment provided by DCM. These results indicated that TSPCs are promising reparative cell sources for promoting cartilage repair. Particularly, in the cohort that articular cartilage lesions occur in conjunction with ligament injuries, autologous TSPCs can be isolated from a portion of the tendon autograph harvested for ligaments reconstruction. In future clinical practice, combined ligament reconstruction with TSPCs- based therapy for articular cartilage repair can to be considered to achieve superior repair of these associated injuries, in which autologous TSPCs can be isolated from a portion of the tendon autograph harvested for ligaments reconstruction.

The U.S. Food and Drug Administration, the mechanism of action, and other considerations for cell-based therapy candidates

The focus of this Commentary is to introduce cell-based therapy in the context of how I believe the U.S. Food and Drug Administration (FDA) might establish criteria for the approval of clinical trials that could eventually lead to the final marketplace approval of these medically relevant, cell-based therapeutic products. It is important to emphasize that regulatory agencies have set up practices and procedures that are based on many years of evaluating pharmaceutically provided drugs. To consider cell-based therapies as single action drugs is inappropriate given the complexity of this technology. The regulatory agencies have been slowly reevaluating the criteria by which they allow clinical trials using cell-based therapies to proceed. This commentary focuses on a few key aspects of such considerations and provides suggestions for modifying the standard criteria.

Regenerative methods in osteoarthritis

Osteoarthritis (OA) is the most common type of arthritis that can affect all joint structures. The primary goals of osteoarthritis treatment are to alleviate pain, reduce functional limitations, and improve quality of life. Despite its high prevalence, treatment options for osteoarthritis are limited, with most therapeutic approaches focusing on symptom management. Tissue engineering and regenerative strategies based on biomaterials, cells, and other bioactive molecules have emerged as viable options for osteoarthritis cartilage repair. Platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) are the most commonly used regenerative therapies today to protect, restore, or increase the function of damaged tissues. Despite promising results, there is conflicting evidence regarding the efficacy of regenerative therapies, and their efficacy remains unknown. The data suggest that more research and standardization are required for the use of these therapies in osteoarthritis. This article provides an overview of the application of MSCs and PRP applications.

Global Research Trends of Exosomes in the Central Nervous System: A Bibliometric and Visualized Analysis

OBJECTIVE

Exosomes in the central nervous system (CNS) have become an attractive area of research with great value. However, few bibliometric analysis has been conducted. The study aimed to visualize the scientific trends and research hotspots of exosomes in the CNS by bibliometric analysis.

METHODS

All potential articles and reviews on exosomes in the CNS published in English from 2001 to 2021 were extracted from the Web of Science Core Collection. The visualization knowledge maps of critical indicators, including countries/regions, institutions, authors, journals, references, and keywords, were generated by CiteSpace and VOSviewer software. Besides, each domain's quantitative and qualitative analysis was also considered.

RESULTS

A total of 2,629 papers were included. The number of exosomes-related publications and citations regarding CNS increased yearly. These publications came from 2,813 institutions in 77 countries/regions, led by the United States and China. Harvard University was the most influential institution, while the National Institutes of Health was the most critical funding source. We identified 14,468 authors, among which Kapogiannis D had the most significant number of articles and the highest H-index, while Théry C was the most frequently co-cited. The cluster analysis of keywords generated 13 clusters. In summary, the topic of biogenesis, biomarker, and drug delivery will serve as hotspots in future research.

CONCLUSION

Exosomes-related CNS research has gained considerable attention in the past 20 years. The sources and biological functions of exosomes and their promising role in diagnosing and treating CNS diseases are considered hotspots in this field. The clinical translation of the results from exosomes-related CNS research will be of great importance in the future.

Dynamics of Ex Vivo Mesenchymal Stromal Cell Potency under Continuous Perfusion

Mesenchymal stromal cells (MSCs) are a candidate for cell immunotherapy due to potent immunomodulatory activity found in their secretome. Though studies on their secreted substances have been reported, the time dynamics of MSC potency remain unclear. Herein, we report on the dynamics of MSC secretome potency in an ex vivo hollow fiber bioreactor using a continuous perfusion cell culture system that fractionated MSC-secreted factors over time. Time-resolved fractions of MSC-conditioned media were evaluated for potency by incubation with activated immune cells. Three studies were designed to characterize MSC potency under: (1) basal conditions, (2) in situ activation, and (3) pre-licensing. Results indicate that the MSC secretome is most potent in suppressing lymphocyte proliferation during the first 24 h and is further stabilized when MSCs are prelicensed with a cocktail of pro-inflammatory cytokines, IFNγ, TNFα, and IL-1β. The evaluation of temporal cell potency using this integrated bioreactor system can be useful in informing strategies to maximize MSC potency, minimize side effects, and allow greater control for the duration of ex vivo administration approaches.

Therapeutic Perspectives for Inflammation and Senescence in Osteoarthritis Using Mesenchymal Stem Cells, Mesenchymal Stem Cell-Derived Extracellular Vesicles and Senolytic Agents

Osteoarthritis (OA) is the most common cause of disability worldwide among the elderly. Alarmingly, the incidence of OA in individuals less than 40 years of age is rising, likely due to the increase in obesity and post-traumatic osteoarthritis (PTOA). In recent years, due to a better understanding of the underlying pathophysiology of OA, several potential therapeutic approaches targeting specific molecular pathways have been identified. In particular, the role of inflammation and the immune system has been increasingly recognized as important in a variety of musculoskeletal diseases, including OA. Similarly, higher levels of host cellular senescence, characterized by cessation of cell division and the secretion of a senescence-associated secretory phenotype (SASP) within the local tissue microenvironments, have also been linked to OA and its progression. New advances in the field, including stem cell therapies and senolytics, are emerging with the goal of slowing disease progression. Mesenchymal stem/stromal cells (MSCs) are a subset of multipotent adult stem cells that have demonstrated the potential to modulate unchecked inflammation, reverse fibrosis, attenuate pain, and potentially treat patients with OA. Numerous studies have demonstrated the potential of MSC extracellular vesicles (EVs) as cell-free treatments that comply with FDA regulations. EVs, including exosomes and microvesicles, are released by numerous cell types and are increasingly recognized as playing a critical role in cell-cell communication in age-related diseases, including OA. Treatment strategies for OA are being developed that target senescent cells and the paracrine and autocrine secretions of SASP. This article highlights the encouraging potential for MSC or MSC-derived products alone or in combination with senolytics to control patient symptoms and potentially mitigate the progression of OA. We will also explore the application of genomic principles to the study of OA and the potential for the discovery of OA phenotypes that can motivate more precise patient-driven treatments.

Isolation and cultivation as well as in situ identification of MSCs from equine dental pulp and periodontal ligament

Introduction

The lifelong eruption places a great demand on the dental pulp and periodontal ligament (PDL) of horse teeth. Cells within the pulp and PDL seem to play a key role during this remodeling.

Methods

In this study, we isolated and cultivated MSCs (medicinal signaling cells) from dental pulp, PDL and retrobulbar fat of four horses. Subsequently, we analyzed them by flow cytometry and immunohistochemistry to determine and compare their characteristics. In addition, we localized these cells within the tissue structure via immunohistochemistry of histological sections. For these analyses, several surface markers were applied.

Results

The described method illustrates a feasible approach to isolate and cultivate MSCs from equine dental pulp and PDL. In the flow cytometry a vast majority of cultivated cells were positive for CD90 and CD40 and negative for CD11a/18, CD45, CD105 and MHCII suggesting that these cells feature characteristics of MSCs. Immunohistochemistry of histological pulp and PDL sections showed the localization of CD90 positive cells especially in the perivascular region and the subodontoblastic layer.

Discussion

Our findings indicate that the isolation and cultivation of MSCs from equine dental pulp and PDL is feasible although an elaborate and complicated harvesting protocol is required. MSCs isolated from dental pulp and PDL are regarded as candidates for new therapeutical approaches in equine dental medicine like regeneration of periodontal lesions, enhancement of periodontal re-attachment after dental replantation and stimulation of pulp-obliteration and apexification in combination with endodontic therapies.

The roles and therapeutic potentialof mesenchymal stem/stromal cells and their extracellular vesicles in tendinopathies

Tendinopathies encompass a highly prevalent, multi-faceted spectrum of disorders, characterized by activity-related pain, compromised function, and propensity for an extended absence from sport and the workplace. The pathophysiology of tendinopathy continues to evolve. For decades, it has been related primarily to repetitive overload trauma but more recently, the onset of tendinopathy has been attributed to the tissue's failed attempt to heal after subclinical inflammatory and immune challenges (failed healing model). Conventional tendinopathy management produces only short-term symptomatic relief and often results in incomplete repair or healing leading to compromised tendon function. For this reason, there has been increased effort to develop therapeutics to overcome the tissue's failed healing response by targeting the cellular metaplasia and pro-inflammatory extra-cellular environment. On this basis, stem cell-based therapies have been proposed as an alternative therapeutic approach designed to modify the course of the various tendon pathologies. Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells often referred to as "medicinal signaling cells" due to their immunomodulatory and anti-inflammatory properties that can produce a pro-regenerative microenvironment in pathological tendons. However, the adoption of MSCs into clinical practice has been limited by FDA regulations and perceived risk of adverse events upon infusion in vivo. The introduction of cell-free approaches, such as the extracellular vesicles of MSCs, has encouraged new perspectives for the treatment of tendinopathies, showing promising short-term results. In this article, we review the most recent advances in MSC-based and MSC-derived therapies for tendinopathies. Preclinical and clinical studies are included with comment on future directions of this rapidly developing therapeutic modality, including the importance of understanding tissue loading and its relationship to any treatment regimen.

CD146+ Endometrial-Derived Mesenchymal Stem/Stromal Cell Subpopulation Possesses Exosomal Secretomes with Strong Immunomodulatory miRNA Attributes

The perivascular localization of endometrial mesenchymal stem/stromal cells (eMSC) allows them to sense local and distant tissue damage, promoting tissue repair and healing. Our hypothesis is that eMSC therapeutic effects are largely exerted via their exosomal secretome (eMSC EXOs) by targeting the immune system and angiogenic modulation. For this purpose, EXOs isolated from Crude and CD146+ eMSC populations were compared for their miRNA therapeutic signatures and immunomodulatory functionality under inflammatory conditions. eMSC EXOs profiling revealed 121 in Crude and 88 in CD146+ miRNAs, with 82 commonly present in both populations. Reactome and KEGG analysis of miRNAs highly present in eMSC EXOs indicated their involvement among others in immune system regulation. From the commonly present miRNAs, four miRNAs (hsa-miR-320e, hsa-miR-182-3p, hsa-miR-378g, hsa-let-7e-5p) were more enriched in CD146+ eMSC EXOs. These miRNAs are involved in macrophage polarization, T cell activation, and regulation of inflammatory cytokine transcription (i.e., TNF-α, IL-1β, and IL-6). Functionally, stimulated macrophages exposed to eMSC EXOs demonstrated a switch towards an alternate M2 status and reduced phagocytic capacity compared to stimulated alone. However, eMSC EXOs did not suppress stimulated human peripheral blood mononuclear cell proliferation, but significantly reduced secretion of 13 pro-inflammatory molecules compared to stimulated alone. In parallel, two anti-inflammatory proteins, IL-10 and IL-13, showed higher secretion, especially upon CD146+ eMSC EXO exposure. Our study suggests that eMSC, and even more, the CD146+ subpopulation, possess exosomal secretomes with strong immunomodulatory miRNA attributes. The resulting evidence could serve as a foundation for eMSC EXO-based therapeutics for the resolution of detrimental aspects of tissue inflammation.

Prrx1 marks stem cells for bone, white adipose tissue and dermis in adult mice

Specialized connective tissues, including bone and adipose tissues, control various physiological activities, including mineral and energy homeostasis. However, the identity of stem cells maintaining these tissues throughout adulthood remains elusive. By conducting genetic lineage tracing and cell depletion experiments in newly generated knock-in Cre/CreER^T2 lines, we show here that rare Prrx1-expressing cells act as stem cells for bone, white adipose tissue and dermis in adult mice, which are indispensable for the homeostasis and repair of these tissues. Single-cell profiling reveals the cycling and multipotent nature of Prrx1-expressing cells and the stemness of these cells is further validated by transplantation assays. Moreover, we identify the cell surface markers for Prrx1-expressing stem cells and show that the activities of these stem cells are regulated by Wnt signaling. These findings expand our knowledge of connective tissue homeostasis/regeneration and may help improve stem-cell-based therapies.

Perinatal derivatives: How to best validate their immunomodulatory functions

Perinatal tissues, mainly the placenta and umbilical cord, contain a variety of different somatic stem and progenitor cell types, including those of the hematopoietic system, multipotent mesenchymal stromal cells (MSCs), epithelial cells and amnion epithelial cells. Several of these perinatal derivatives (PnDs), as well as their secreted products, have been reported to exert immunomodulatory therapeutic and regenerative functions in a variety of pre-clinical disease models. Following experience with MSCs and their extracellular vesicle (EV) products, successful clinical translation of PnDs will require robust functional assays that are predictive for the relevant therapeutic potency. Using the examples of T cell and monocyte/macrophage assays, we here discuss several assay relevant parameters for assessing the immunomodulatory activities of PnDs. Furthermore, we highlight the need to correlate the in vitro assay results with preclinical or clinical outcomes in order to ensure valid predictions about the in vivo potency of therapeutic PnD cells/products in individual disease settings.

Pathophysiology of Sepsis and Genesis of Septic Shock: The Critical Role of Mesenchymal Stem Cells (MSCs)

The treatment of sepsis and septic shock remains a major public health issue due to the associated morbidity and mortality. Despite an improvement in the understanding of the physiological and pathological mechanisms underlying its genesis and a growing number of studies exploring an even higher range of targeted therapies, no significant clinical progress has emerged in the past decade. In this context, mesenchymal stem cells (MSCs) appear more and more as an attractive approach for cell therapy both in experimental and clinical models. Pre-clinical data suggest a cornerstone role of these cells and their secretome in the control of the host immune response. Host-derived factors released from infected cells (i.e., alarmins, HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (e.g., LPS, peptidoglycans) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of cytokines/chemokines and growth factors that influence, respectively, immune cell recruitment and stem cell mobilization. However, the way in which MSCs exert their beneficial effects in terms of survival and control of inflammation in septic states remains unclear. This review presents the interactions identified between MSCs and mediators of immunity and tissue repair in sepsis. We also propose paradigms related to the plausible roles of MSCs in the process of sepsis and septic shock. Finally, we offer a presentation of experimental and clinical studies and open the way to innovative avenues of research involving MSCs from a prognostic, diagnostic, and therapeutic point of view in sepsis.

Possible disease-protective roles of fibroblasts in cancer and fibrosis and their therapeutic application

Cancer and fibrotic diseases are characterized by continuous inflammation, tissue wounds, and injuries. Cancer is a "wound that does not heal," and the uncontrolled proliferation of cancer cells disrupts normal tissue integrity and induces stromal fibroinflammatory reactions. Fibroblasts proliferate extensively in the stroma, playing a major role in the development of these diseases. There has been considerable evidence that fibroblasts contribute to fibrosis and tissue stiffening and promote disease progression via multiple mechanisms. However, recent emerging findings, mainly derived from single-cell transcriptomic analysis, indicated that fibroblasts are functionally heterogeneous, leading to the hypothesis that both disease-promoting and -restraining fibroblasts exist. We recently showed that a fibroblast population, defined by the expression of the glycosylphosphatidylinositol-anchored membrane protein Meflin may suppress but not promote fibrotic response and disease progression in cancer and fibrotic diseases. Although currently hypothetical, the primary function of Meflin-positive fibroblasts may be tissue repair after injury and cancer initiation occurred. This observation has led to the proposal of a potential therapy that converts the phenotype of fibroblasts from pro-tumor to anti-tumor. In this short review, we summarize our recent findings on the function of Meflin in the context of cancer and fibrotic diseases and discuss how we can utilize this knowledge on fibroblasts in translational medicine. We also discuss several aspects of the interpretation of survival analysis data, such as Kaplan-Meier analysis, to address the function of specific genes expressed in fibroblasts.

Perivascular Mesenchymal Stem/Stromal Cells, an Immune Privileged Niche for Viruses?

Mesenchymal stem cells (MSCs) play a critical role in response to stress such as infection. They initiate the removal of cell debris, exert major immunoregulatory activities, control pathogens, and lead to a remodeling/scarring phase. Thus, host-derived ‘danger’ factors released from damaged/infected cells (called alarmins, e.g., HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (LPS, single strand RNA) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of growth factors and chemoattractant molecules that influence immune cell recruitment and stem cell mobilization. MSC, in an ultimate contribution to tissue repair, may also directly trans- or de-differentiate into specific cellular phenotypes such as osteoblasts, chondrocytes, lipofibroblasts, myofibroblasts, Schwann cells, and they may somehow recapitulate their neural crest embryonic origin. Failure to terminate such repair processes induces pathological scarring, termed fibrosis, or vascular calcification. Interestingly, many viruses and particularly those associated to chronic infection and inflammation may hijack and polarize MSC’s immune regulatory activities. Several reports argue that MSC may constitute immune privileged sanctuaries for viruses and contributing to long-lasting effects posing infectious challenges, such as viruses rebounding in immunocompromised patients or following regenerative medicine therapies using MSC. We will herein review the capacity of several viruses not only to infect but also to polarize directly or indirectly the functions of MSC (immunoregulation, differentiation potential, and tissue repair) in clinical settings.

Fat Stem Cells Combined with Complement C3 Inhibits the Progress of Type 2 Diabetes in Rats

This study assessed the effect of fat stem cells combined with complement C3 on Wnt/β-catenin pathway in type 2 diabetic rats. 30 male rats were randomly and equally divided into group of type 2 diabetes (intraperitoneal injection of urea with cephalosporins at a dose of 30 mg/kg and fed with high sugar and fat), type 2 diabetes+adipose stem cells+C3 group (after adipose stem cells+C3 group) and control group. Rats in adipose stem cells+C3 group received administration of stem cells and C3. The model of type 2 diabetic rats was successfully constructed. The blood glucose of type 2 diabetic rats and fat stem cell+C3 group was significantly higher than 11.1 mmol/L. Adipocyte was induced to be differentiated into islet cells depending on insulin secretion and glucose concentration. The combination of complement C3 improved the glucose sensitivity in type 2 diabetic rats. Compared with diabetic group, β-catenin and TCF in fat stem cell+C3 group were significantly decreased (P < 0.05). In conclusion, fat stem cells combined with complement C3 inhibit the disease progression in type 2 diabetic rats possibly by inhibiting the activation of Wnt/β-catenin signaling pathway.

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.

Cell Based Treatment of Autoimmune Diseases in Children

Mesenchymal stem cells have recently been recoined as medicinal signaling cells (MSC) for their ability to promote tissue homeostasis through immune modulation, angiogenesis and tropism. During the last 20 years, there has been a plethora of publications using MSC in adults and to lesser extent neonates on a variety of illnesses. In parts of the world, autologous and allogeneic MSCs have been purified and used to treat a range of autoimmune conditions, including graft versus host disease, Crohn's disease, multiple sclerosis, refractory systemic lupus erythematosus and systemic sclerosis. Generally, these reports are not part of stringent clinical trials but are of note for good outcomes with minimal side effects. This review is to summarize the current state of the art in MSC therapy, with a brief discussion of cell preparation and safety, insights into mechanisms of action, and a review of published reports of MSC treatment of autoimmune diseases, toward the potential application of MSC in treatment of children with severe autoimmune diseases using multicenter clinical trials and treatment algorithms.

Intra-Articular Injections of Autologous Adipose Tissue or Platelet-Rich Plasma Comparably Improve Clinical and Functional Outcomes in Patients with Knee Osteoarthritis

The use of biologic therapies for the management of knee osteoarthritis (OA) has largely increased in recent years. The purpose of this study was to evaluate the efficiency and the therapeutic potential of platelet-rich plasma (PRP) and autologous adipose tissue (AAT) injections as a treatment for knee OA. Sixty participants were enrolled in the study: 20 healthy ones and 40 with minimal to moderate knee OA (KL I-III). The OA patients were randomly assigned either to the PRP or to the AAT group. The PRP samples showed a low expression level of NF-κB-responsive gene CCL5 and high expression levels of classic inflammatory and TNF-l INF responses. The AAT injection product was prepared using a Lipogems device, and its regenerative potential as well as the ability for expansion of mesenchymal stem cells were tested in the cell culture conditions. The patient assessments were carried out five times. Significant improvement was observed regardless of the treatment method in the VAS, KOOS, WOMAC and IKDC 2000 subjective evaluations as well as in the functional parameters. Intra-articular injections of AAT or PRP improved pain, symptoms, quality of life and functional capacity with a comparable effectiveness in the patients with mild to moderate knee osteoarthritis.

Extruded Nucleoli of Human Dental Pulp Cells

Background and Objectives: The dental pulp stem cells are highly proliferative and can differentiate into various cell types, including endothelial cells. We aimed to evaluate the ultrastructural characteristics of the human dental pulp cells of the permanent frontal teeth. Materials and Methods: Human adult bioptic dental pulp was collected from n = 10 healthy frontal teeth of five adult patients, prior to prosthetic treatments for aesthetic purposes. Tissues were examined under transmission electron microscopy. Results: We identified cells with a peculiar trait: giant nucleoli resembling intranuclear endoplasmic reticulum, which mimicked extrusion towards the cytoplasm. These were either partly embedded within the nuclei, the case in which their adnuclear side was coated by marginal heterochromatin and the abnuclear side was coated by a thin rim of ribosomes, or were apparently isolated from the nuclei, while still being covered by ribosomes. Conclusions: Similar electron microscopy features were previously reported in the human endometrium, as nucleolar channel system; or R-Rings induced by Nopp140. To our knowledge, this is the first report of extruded nucleolar structure in the dental pulp. Moreover, the aspect of giant extruded nucleoli was not previously reported in any human cell type, although similar evidence was gathered in other species as well as in plants.

The promising role of autologous and allogeneic mesenchymal stromal cells in managing knee osteoarthritis. What is beyond Mesenchymal stromal cells?

Mesenchymal stromal cells (MSCs) express a wide range of properties anticipated to be beneficial for treating genetic, mechanical, and age-related degeneration in diseases such as osteoarthritis (OA). Although contemporary conservative management of OA is successful in many patients with mild-moderate OA, it often fails to improve symptoms in many patients who are not a candidate for any surgical management. Further, existing conservative treatment strategies do not prevent the progression of the disease and therefore fail to provide a long-term pain-free life. On the other hand, tremendous progress has been taking place in the exciting field of regenerative medicine involving MSCs (autologous and allogeneic), with promising translation taking place from basic science to the bedside. In this review, we comprehensively discuss the potential role of MSCs in treating OA, both autologous and off-the-shelf, allogeneic stem cells. Further, newer therapies are in the offing to treat OA, such as exosomes and growth factors.

Human Cardiac Organoids to Model COVID-19 Cytokine Storm Induced Cardiac Injuries

Acute cardiac injuries occur in 20-25% of hospitalized COVID-19 patients. Despite urgent needs, there is a lack of 3D organotypic models of COVID-19 hearts for mechanistic studies and drug testing. Herein, we demonstrate that human cardiac organoids (hCOs) are a viable platform to model the cardiac injuries caused by COVID-19 hyperinflammation. As IL-1βis an upstream cytokine and a core COVID-19 signature cytokine, it was used to stimulate hCOs to induce the release of a milieu of proinflammatory cytokines that mirror the profile of COVID-19 cytokine storm. The IL-1 β treated hCOs recapitulated transcriptomic, structural, and functional signatures of COVID-19 hearts. The comparison of IL-1β treated hCOs with cardiac tissue from COVID-19 autopsies illustrated the critical roles of hyper-inflammation in COVID-19 cardiac insults and indicated the cardioprotective effects of endothelium. The IL-1β treated hCOs also provide a viable model to assess the efficacy and potential side effects of immunomodulatory drugs, as well as the reversibility of COVID-19 cardiac injuries at baseline and simulated exercise conditions.

Is Long COVID a State of Systemic Pericyte Disarray?

The most challenging aspect of Post-Acute Sequelae of SARS-CoV-2 Infection (PASC) or Long COVID remains for the discordance between the viral damage from acute infection in the recent past and susceptibility of Long COVID without clear evidence of post infectious inflammation or autoimmune reactions. In this communication we propose that disarray of pericytes plays a central role in emerge of Long COVID. We assume pericytes are agents with “Triple-A” qualities, i.e., analyze-adapt and advance, necessary for sustainability of host homeostasis. Based on this view, we further suggest Long COVID may provide a model system to integrate system theory and complex adaptive systems to explore a new class of maladies those are currently not well defined and with no remedies.

Human Organ-on-a-Chip Microphysiological Systems to Model Musculoskeletal Pathologies and Accelerate Therapeutic Discovery

Human Microphysiological Systems (hMPS), otherwise known as organ- and tissue-on-a-chip models, are an emerging technology with the potential to replace in vivo animal studies with in vitro models that emulate human physiology at basic levels. hMPS platforms are designed to overcome limitations of two-dimensional (2D) cell culture systems by mimicking 3D tissue organization and microenvironmental cues that are physiologically and clinically relevant. Unlike animal studies, hMPS models can be configured for high content or high throughput screening in preclinical drug development. Applications in modeling acute and chronic injuries in the musculoskeletal system are slowly developing. However, the complexity and load bearing nature of musculoskeletal tissues and joints present unique challenges related to our limited understanding of disease mechanisms and the lack of consensus biomarkers to guide biological therapy development. With emphasis on examples of modeling musculoskeletal tissues, joints on chips, and organoids, this review highlights current trends of microphysiological systems technology. The review surveys state-of-the-art design and fabrication considerations inspired by lessons from bioreactors and biological variables emphasizing the role of induced pluripotent stem cells and genetic engineering in creating isogenic, patient-specific multicellular hMPS. The major challenges in modeling musculoskeletal tissues using hMPS chips are identified, including incorporating biological barriers, simulating joint compartments and heterogenous tissue interfaces, simulating immune interactions and inflammatory factors, simulating effects of in vivo loading, recording nociceptors responses as surrogates for pain outcomes, modeling the dynamic injury and healing responses by monitoring secreted proteins in real time, and creating arrayed formats for robotic high throughput screens. Overcoming these barriers will revolutionize musculoskeletal research by enabling physiologically relevant, predictive models of human tissues and joint diseases to accelerate and de-risk therapeutic discovery and translation to the clinic.

The Impact of Inflammatory Immune Reactions of the Vascular Niche on Organ Fibrosis

Inflammation is a type of defense response against tissue damage, and can be mediated by lymphocytes and macrophages. Fibrosis is induced by tissue injury and inflammation, which leads to an increase in fibrous connective tissue in organs and a decrease in organ parenchyma cells, finally leading to organ dysfunction or even failure. The vascular niche is composed of endothelial cells, pericytes, macrophages, and hematopoietic stem cells. It forms a guiding microenvironment for the behavior of adjacent cells, and mainly exists in the microcirculation, including capillaries. When an organ is damaged, the vascular niche regulates inflammation and affects the repair of organ damage in a variety of ways, such as via its angiocrine function and transformation of myofibroblasts. In this paper, the main roles of vascular niche in the process of organ fibrosis and its mechanism of promoting the progress of fibrosis through inflammatory immunoregulation are summarized. It was proposed that the vascular niche should be regarded as a new therapeutic target for organ fibrosis, suggesting that antifibrotic effects could be achieved by regulating macrophages, inhibiting endothelial-mesenchymal transition, interfering with the angiocrine function of endothelial cells, and inhibiting the transformation of pericytes into myofibroblasts, thus providing new ideas for antifibrosis drug research.

Osteogenically differentiated mesenchymal stem cells promote the apoptosis of human umbilical vein endothelial cells in vitro

The absence of blood vessels in tissue engineered bone often leads to necrosis of internal cells after implantation, ultimately affecting the process of bone repair. Herein, mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs) were cocultured to induce osteogenesis and angiogenesis. Based on the findings, the number of HUVECs in the coculture system increased in the growth medium group, but decreased in the osteogenic induction medium (OIM) group. Considering that the paracrine effects of MSCs had changed, we tested the genes expression of osteogenically differentiated MSCs. The expression of osteogenic genes in MSCs increased during osteogenesis. Further, the expression levels of pigment epithelial-derived factor (PEDF) gene and protein, an antivascular factor, were also increased. To verify whether MSCs promote HUVECs apoptosis via PEDF, PEDF was silenced via siRNA. The conditioned medium of differentiated MSCs with PEDF silencing significantly improved the proliferation and apoptosis of HUVECs. Based on further experiments, PEDF mediated the apoptosis and proliferation of HUVECs through p53, BAX/BCL-2, FAS, and c-Caspase-3. However, when PEDF was silenced with siRNA, the osteogenic potential of MSCs was affected. The results of this study provide a theoretical basis for the construction of prevascularized bone tissues in vitro.

H19 Overexpression Improved Efficacy of Mesenchymal Stem Cells in Ulcerative Colitis by Modulating the miR-141/ICAM-1 and miR-139/CXCR4 Axes

Overexpression of C-X-C motif chemokine receptor 4 (CXCR4) and intercellular cell adhesion molecule-1 (ICAM-1) may promote homing of mesenchymal stem cells (MSC). In this study, we treated ulcerative colitis animals with MSC preconditioned with or without H19 and compared the therapeutic effect of MSC and MSC-H19. We evaluated the regulatory relationship of H19 vs. miR-141/miR-139 and miR-141/miR-139 vs. ICAM-1/CXCR4. We established an ulcerative colitis mouse model to assess the effect of MSC and MSC-H19. H19 was found to bind to miR-141 and miR-139. The activity of H19 was strongly decreased in cells c-transfected with miR-141/miR-139 and WT H19. ICAM-1 was confirmed to be targeted by miR-141 and CXCR4 was targeted by miR-139. The H19 expression showed a negative regulatory relationship with the miR-141 and miR-139 expression but a positive regulatory relationship with the ICAM-1 and CXCR4 expression. In summary, the overexpression of H19 in MSC downregulated miR-139 and miR-141, thus increasing the activity of their targets ICAM-1 and CXCR4, respectively, to exhibit therapeutic effects in ulcerative colitis.

Pharmacological effects of ex vivo mesenchymal stem cell immunotherapy in patients with acute kidney injury and underlying systemic inflammation

Mesenchymal stem cells (MSCs) have natural immunoregulatory functions that have been explored for medicinal use as a cell therapy with limited success. A phase Ib study was conducted to evaluate the safety and immunoregulatory mechanism of action of MSCs using a novel ex vivo product (SBI-101) to preserve cell activity in patients with severe acute kidney injury. Pharmacological data demonstrated MSC-secreted factor activity that was associated with anti-inflammatory signatures in the molecular and cellular profiling of patient blood. Systems biology analysis captured multicompartment effects consistent with immune reprogramming and kidney tissue repair. Although the study was not powered for clinical efficacy, these results are supportive of the therapeutic hypothesis, namely, that treatment with SBI-101 elicits an immunotherapeutic response that triggers an accelerated phenotypic switch from tissue injury to tissue repair. Ex vivo administration of MSCs, with increased power of testing, is a potential new biological delivery paradigm that assures sustained MSC activity and immunomodulation.

Paracoccidioides brasiliensis activates mesenchymal stem cells through TLR2, TLR4, and Dectin-1

Numerous researchers have described the potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) for the treatment of various infectious and inflammatory diseases. However, contrary to what has been reported, the transplantation of BM-MSCs in a mouse model of Paracoccidioides brasiliensis-induced pulmonary fibrosis exacerbated the inflammatory process and fibrosis, worsening the course of the infection. The aim of this work was to determine whether P. brasiliensis exerts an immunomodulatory effect on BM-MSCs. The results indicate that P. brasiliensis can activate BM-MSCs through a mechanism dependent on TLR2, TLR4 and Dectin-1. In addition, it was found that these fungal cells can adhere and internalize within BM-MSCs. Nonetheless, this process did not affect the survival of the fungus and on the contrary, triggered the expression of inflammatory mediators such as IL-6, IL-17, TNF-α, and TGF-β. The present findings correlate with the loss of a fungicidal effect and poor control of the fungus, evidenced by the count of the colony-forming units. Previously reported in vivo results are thus confirmed, showing that P. brasiliensis induces an inflammatory profile in BM-MSCs when producing pro-inflammatory molecules that amplify such response. Numerous researchers have described the potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) for the treatment of various infectious and inflammatory diseases. However, contrary to what has been reported, the transplantation of BM-MSCs in a mouse model of Paracoccidioides brasiliensis-induced pulmonary fibrosis exacerbated the inflammatory process and fibrosis, worsening the course of the infection. The aim of this work was to determine whether P. brasiliensis exerts an immunomodulatory effect on BM-MSCs. The results indicate that P. brasiliensis can activate BM-MSCs through a mechanism dependent on TLR2, TLR4 and Dectin-1. In addition, it was found that these fungal cells can adhere and internalize within BM-MSCs. Nonetheless, this process did not affect the survival of the fungus and on the contrary, triggered the expression of inflammatory mediators such as IL-6, IL-17, TNF-α, and TGF-β. The present findings correlate with the loss of a fungicidal effect and poor control of the fungus, evidenced by the count of the colony-forming units. Previously reported in vivo results are thus confirmed, showing that P. brasiliensis induces an inflammatory profile in BM-MSCs when producing pro-inflammatory molecules that amplify such response.

In vitro cellular and proteome assays identify Wnt pathway and CDKN2A-regulated senescence affected in mesenchymal stem cells from mice after a chronic LD gamma irradiation in utero

Reliable data on the effects of chronic prenatal exposure to low dose (LD) of ionizing radiation in humans are missing. There are concerns about adverse long-term effects that may persist throughout postnatal life of the offspring. Due to their slow cell cycle kinetics and life-long residence time in the organism, mesenchymal stem cells (MSCs) are more susceptible to low level genotoxic stress caused by extrinsic multiple LD events. The aim of this study was to investigate the effect of chronic, prenatal LD gamma irradiation to the biology of MSCs later in life. C3H mice were exposed in utero to chronic prenatal irradiation of 10 mGy/day over a period of 3 weeks. Two years later, MSCs were isolated from the bone marrow and analyzed in vitro for their radiosensitivity, for cellular senescence and for DNA double-strand break recognition after a second acute gamma-irradiation. In addition to these cellular assays, changes in protein expression were measured using HPLC-MS/MS and dysregulated molecular signaling pathways identified using bioinformatics. We observed radiation-induced proteomic changes in MSCs from the offspring of in utero irradiated mice (leading to ~ 9.4% of all detected proteins being either up- or downregulated) as compared to non-irradiated controls. The proteomic changes map to regulation pathways involved in the extracellular matrix, the response to oxidative stress, and the Wnt signaling pathway. In addition, chronic prenatal LD irradiation lead to an increased rate of in vitro radiation-induced senescence later in life and to an increased number of residual DNA double-strand breaks after 4 Gy irradiation, indicating a remarkable interaction of in vivo radiation in combination with a second acute dose of in vitro radiation. This study provides the first insight into a molecular mechanism of persistent MSC damage response by ionizing radiation exposure during prenatal time and will help to predict therapeutic safety and efficacy with respect to a clinical application of stem cells.

Culture Substrates for Improved Manufacture of Mesenchymal Stromal Cell Therapies

Recent developments in mesenchymal stromal cell (MSC) therapies have increased the demand for tools to improve their manufacture, including the selection of optimal culture substrate materials. While many clinical manufacturers use planar tissue culture plastic (TCP) surfaces for MSC production, others have begun exploring the use of alternative culture substrates that present a variety of spatial, mechanical, and biochemical cues that influence cell expansion and resulting cell quality. In this review, the effects of culture and material properties distinct from traditional planar TCP surfaces on MSC proliferation, surface marker expression, and commonly used indications for therapeutic potency are examined. The different properties summarized include the use of alternative culture formats such as cellular aggregates or 3D scaffolds, as well as the effects of culture substrate stiffness and presentation of specific adhesive ligands and topographical cues. Specific substrate properties can be related to greater cell expansion and improvement in specific therapeutic functionalities, demonstrating the utility of culture materials in further improving the clinical-scale manufacture of highly secretory MSC products.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Biofabrication of vasculature in microphysiological models of bone

Bone contains a dense network of blood vessels that are essential to its homoeostasis, endocrine function, mineral metabolism and regenerative functions. In addition, bone vasculature is implicated in a number of prominent skeletal diseases, and bone has high affinity for metastatic cancers. Despite vasculature being an integral part of bone physiology and pathophysiology, it is often ignored or oversimplified inin vitrobone models. However, 3D physiologically relevant vasculature can now be engineeredin vitro, with microphysiological systems (MPS) increasingly being used as platforms for engineering this physiologically relevant vasculature. In recent years, vascularised models of bone in MPSs systems have been reported in the literature, representing the beginning of a possible technological step change in how bone is modelledin vitro. Vascularised bone MPSs is a subfield of bone research in its nascency, however given the impact of MPSs has had inin vitroorgan modelling, and the crucial role of vasculature to bone physiology, these systems stand to have a substantial impact on bone research. However, engineering vasculature within the specific design restraints of the bone niche is significantly challenging given the different requirements for engineering bone and vasculature. With this in mind, this paper aims to serve as technical guidance for the biofabrication of vascularised bone tissue within MPS devices. We first discuss the key engineering and biological considerations for engineering more physiologically relevant vasculaturein vitrowithin the specific design constraints of the bone niche. We next explore emerging applications of vascularised bone MPSs, and conclude with a discussion on the current status of vascularised bone MPS biofabrication and suggest directions for development of next generation vascularised bone MPSs.

Novel cell sources for bone regeneration

A plethora of both acute and chronic conditions, including traumatic, degenerative, malignant, or congenital disorders, commonly induce bone disorders often associated with severe persisting pain and limited mobility. Over 1 million surgical procedures involving bone excision, bone grafting, and fracture repair are performed each year in the U.S. alone, resulting in immense levels of public health challenges and corresponding financial burdens. Unfortunately, the innate self-healing capacity of bone is often inadequate for larger defects over a critical size. Moreover, as direct transplantation of committed osteoblasts is hindered by deficient cell availability, limited cell spreading, and poor survivability, an urgent need for novel cell sources for bone regeneration is concurrent. Thanks to the development in stem cell biology and cell reprogramming technology, many multipotent and pluripotent cells that manifest promising osteogenic potential are considered the regenerative remedy for bone defects. Considering these cells' investigation is still in its relative infancy, each of them offers their own particular challenges that must be conquered before the large-scale clinical application.

Recent Trends in Multipotent Human Mesenchymal Stem/Stromal Cells: Learning from History and Advancing Clinical Applications

Early cell biology reports demonstrated the presence of cells with stem-like properties in bone marrow, with both hematopoietic and mesenchymal lineages. Over the years, various investigations have purified and characterized mesenchymal stromal/stem cells (MSCs) from different human tissues as cells with multilineage differentiation potential under the appropriate conditions. Due to their appealing characteristics and versatile potentials, MSCs are leveraged in many applications in medicine such as oncology, bioprinting, and as recent as therapeutics discovery and innovation for COVID-19. To date, studies indicate that MSCs have varied differentiation capabilities into different cell types, and demonstrate immunomodulating and anti-inflammatory properties. Different microenvironments or niche for MSCs and their resulting heterogeneity may influence attendant cellular behavior and differentiation capacity. The potential clinical applications of MSCs and exosomes derived from these cells have led to an avalanche of research reports on their properties and hundreds of clinical trials being undertaken. There is ample reason to think, as discussed in this expert review that the future looks bright and promising for MSC research, with many clinical trials under way to ascertain their clinical utility. This review provides a synthesis of the latest advances and trends in MSC research to allow for broad and critically informed use of MSCs. Early observations of the presence of these cells in the bone marrow and their remarkable differentiation capabilities and immunomodulation are also presented.

3D bioprinting of prevascularised implants for the repair of critically-sized bone defects

For 3D bioprinted tissues to be scaled-up to clinically relevant sizes, effective prevascularisation strategies are required to provide the necessary nutrients for normal metabolism and to remove associated waste by-products. The aim of this study was to develop a bioprinting strategy to engineer prevascularised tissues in vitro and to investigate the capacity of such constructs to enhance the vascularisation and regeneration of large bone defects in vivo. From a screen of different bioinks, a fibrin-based hydrogel was found to best support human umbilical vein endothelial cell (HUVEC) sprouting and the establishment of a microvessel network. When this bioink was combined with HUVECs and supporting human bone marrow stem/stromal cells (hBMSCs), these microvessel networks persisted in vitro. Furthermore, only bioprinted tissues containing both HUVECs and hBMSCs, that were first allowed to mature in vitro, supported robust blood vessel development in vivo. To assess the therapeutic utility of this bioprinting strategy, these bioinks were used to prevascularise 3D printed polycaprolactone (PCL) scaffolds, which were subsequently implanted into critically-sized femoral bone defects in rats. Micro-computed tomography (µCT) angiography revealed increased levels of vascularisation in vivo, which correlated with higher levels of new bone formation. Such prevascularised constructs could be used to enhance the vascularisation of a range of large tissue defects, forming the basis of multiple new bioprinted therapeutics. STATEMENT OF SIGNIFICANCE: This paper demonstrates a versatile 3D bioprinting technique to improve the vascularisation of tissue engineered constructs and further demonstrates how this method can be incorporated into a bone tissue engineering strategy to improve vascularisation in a rat femoral defect model.

Human adventitial pericytes provide a unique source of anti-calcific cells for cardiac valve engineering: Role of microRNA-132-3p

AIMS

Tissue engineering aims to improve the longevity of prosthetic heart valves. However, the optimal cell source has yet to be determined. This study aimed to establish a mechanistic rationale supporting the suitability of human adventitial pericytes (APCs).

METHODS AND RESULTS

APCs were immunomagnetically sorted from saphenous vein leftovers of patients undergoing coronary artery bypass graft surgery and antigenically characterized for purity. Unlike bone marrow-derived mesenchymal stromal cells (BM-MSCs), APCs were resistant to calcification and delayed osteochondrogenic differentiation upon high phosphate (HP) induction, as assessed by cytochemistry and expression of osteogenic markers. Moreover, glycolysis was activated during osteogenic differentiation of BM-MSCs, whereas APCs showed no increase in glycolysis upon HP challenge. The microRNA-132-3p (miR-132), a known inhibitor of osteogenesis, was found constitutively expressed by APCs and upregulated following HP stimulation. The anti-calcific role of miR-132 was further corroborated by in silico analysis, luciferase assays in HEK293 cells, and transfecting APCs with miR-132 agomir and antagomir, followed by assessment of osteochondrogenic markers. Interestingly, treatment of swine cardiac valves with APC-derived conditioned medium conferred them with resistance to HP-induced osteogenesis, with this effect being negated when using the medium of miR-132-silenced APCs. Additionally, as an initial bioengineering step, APCs were successfully engrafted onto pericardium sheets, where they proliferated and promoted aortic endothelial cells attraction, a process mimicking valve endothelialization.

CONCLUSIONS

Human APCs are resistant to calcification compared with BM-MSCs and convey the anti-calcific phenotype to heart valves through miR-132. These findings may open new important avenues for prosthetic valve cellularization.

Characteristics of pre-metastatic niche: the landscape of molecular and cellular pathways

Metastasis is a major contributor to cancer-associated deaths. It involves complex interactions between primary tumorigenic sites and future metastatic sites. Accumulation studies have revealed that tumour metastasis is not a disorderly spontaneous incident but the climax of a series of sequential and dynamic events including the development of a pre-metastatic niche (PMN) suitable for a subpopulation of tumour cells to colonize and develop into metastases. A deep understanding of the formation, characteristics and function of the PMN is required for developing new therapeutic strategies to treat tumour patients. It is rapidly becoming evident that therapies targeting PMN may be successful in averting tumour metastasis at an early stage. This review highlights the key components and main characteristics of the PMN and describes potential therapeutic strategies, providing a promising foundation for future studies.

Mesenchymal stem cells as a double-edged sword in tumor growth: focusing on MSC-derived cytokines

Mesenchymal stem cells (MSCs) show homing capacity towards tumor sites. Numerous reports indicate that they are involved in multiple tumor-promoting processes through several mechanisms, including immunosuppression; stimulation of angiogenesis; transition to cancer-associated fibroblasts; inhibition of cancer cell apoptosis; induction of epithelial-mesenchymal transition (EMT); and increase metastasis and chemoresistance. However, other studies have shown that MSCs suppress tumor growth by suppressing angiogenesis, incrementing inflammatory infiltration, apoptosis and cell cycle arrest, and inhibiting the AKT and Wnt signaling pathways. In this review, we discuss the supportive and suppressive impacts of MSCs on tumor progression and metastasis. We also discuss MSC-based therapeutic strategies for cancer based on their potential for homing to tumor sites.

Mesenchymal stromal cells: Getting ready for clinical primetime

Mesenchymal stromal cells (MSC) are multipotent precursor cells that can be derived from a variety of tissue sources, with a working definition based on immunophenotyping and cell differentiation capacity. Despite historical roots in the field of tissue engineering, they have generated great interest as cell therapies for their immune regulatory function, which has led to numerous clinical trials for a range of inflammatory and autoimmune conditions. Importantly, due to the lack of traditional MHC expression and their expression of other immune regulatory proteins, they can be used from third party donors without generating a dangerous alloreactivity. After 20 years of clinical trials, they have earned themselves an excellent safety record but are currently only approved for use in Canada, New Zealand, Japan, South Korea and Europe due to a lack of consistent efficacy data. In the United States, the indication that has seen the most progress is steroid refractory acute graft-versus-host disease (SR-aGVHD). Issues with early clinical trials can be attributed to both challenges with defining optimal patient populations and trial design as well as limitations related to commercial manufacturing. Earlier this year, the encouraging data for a repeat Phase III trial in pediatric patients with SR-aGVHD was published. This review provides information on the proposed mechanism of action of MSCs, clinical utilization of MSCs with focus on SR-aGVHD and potential modalities that can improve the efficacy of MSCs.

Governmental Regulations and Increasing Food and Drug Administration Oversight of Regenerative Medicine Products: What's New in 2020?

The United States Food and Drug Administration (FDA) is responsible for protecting and promoting public health through rules and regulations. Over the past few years, the field of regenerative medicine and cell therapy have garnered significant interest, and this evolving new biology is changing fast and challenging regulatory bodies. The FDA has published a series of guidance documents outlining steps to protect consumers against potentially dangerous and unproven treatments. The agency has offered a grace period for "stem cell clinics" until November 2020 to come into compliance by obtaining Investigational New Drug applications and working to secure premarket approval of their products. With the documentation of hundreds of "stem cell clinics," the FDA needs to enforce the adherence to their outlined standards to protect patients. The aim of this review was to provide an overview of these FDA regulations and some current issues within the industry. The purpose is to educate and inform the musculoskeletal community about the current government regulations of this new expanding biology. LEVEL OF EVIDENCE: Level V, expert opinion.

Emerging Roles of Perivascular Mesenchymal Stem Cells in Synovial Joint Inflammation

In contrast to the significant advances in our understanding of the mesenchymal stem cell (MSC) populations in bone marrow (BM), little is known about the MSCs that are resident in the synovial joint and their possible roles in the tissue homeostasis, chronic inflammation as well as in repair. Neural crest is a transient embryonic structure, generating multipotential MSC capable of migrating along peripheral nerves and blood vessels to colonize most tissue types. In adult, these MSC can provide functional stromal support as a stem cell niche for lymphocyte progenitors for instance in the BM and the thymus. Critically, MSC have major immunoregulatory activities to control adverse inflammation and infection. These MSC will remain associated to vessels (perivascular (p) MSC) and their unique expression of markers such as myelin P0 and transcription factors (e.g. Gli1 and FoxD1) has been instrumental to develop transgenic mice to trace the fate of these cells in health and disease conditions. Intriguingly, recent investigations of chronic inflammatory diseases argue for an emerging role of pMSC in several pathological processes. In response to tissue injuries and with the release of host cell debris (e.g. alarmins), pMSC can detach from vessels and proliferate to give rise to either lipofibroblasts, osteoblasts involved in the ossification of arteries and myofibroblasts contributing to fibrosis. This review will discuss currently available data that suggest a role of pMSC in tissue homeostasis and pathogenesis of the synovial tissue and joints. Graphical abstract.

Single-cell transcriptomic analysis identifies extensive heterogeneity in the cellular composition of mouse Achilles tendons

Tendon is a dense connective tissue that stores and transmits forces between muscles and bones. Cellular heterogeneity is increasingly recognized as an important factor in the biological basis of tissue homeostasis and disease, yet little is known about the diversity of cell types that populate tendon. To address this, we determined the heterogeneity of cell populations within mouse Achilles tendons using single-cell RNA sequencing. In assembling a transcriptomic atlas of Achilles tendons, we identified 11 distinct types of cells, including three previously undescribed populations of tendon fibroblasts. Prior studies have indicated that pericytes, which are found in the vasculature of tendons, could serve as a potential source of progenitor cells for adult tendon fibroblasts. Using trajectory inference analysis, we provide additional support for the notion that pericytes are likely to be at least one of the progenitor cell populations for the fibroblasts that compose adult tendons. We also modeled cell-cell interactions and identified previously undescribed ligand-receptor signaling interactions involved in tendon homeostasis. Our novel and interactive tendon atlas highlights previously underappreciated heterogeneity between and within tendon cell populations. The atlas also serves as a resource to further the understanding of tendon extracellular matrix assembly and maintenance and in the design of therapies for tendinopathies.

The vascular nature of lung-resident mesenchymal stem cells

Human lungs bear their own reservoir of endogenous mesenchymal stem cells (MSCs). Although described as located perivascular, the cellular identity of primary lung MSCs remains elusive. Here we investigated the vascular nature of lung‐resident MSCs (LR‐MSCs) using healthy human lung tissue. LR‐MSCs predominately reside within the vascular stem cell niche, the so‐called vasculogenic zone of adult lung arteries. Primary LR‐MSCs isolated from normal human lung tissue showed typical MSC characteristics in vitro and were phenotypically and functionally indistinguishable from MSCs derived from the vascular wall of adult human blood vessels (VW‐MSCs). Moreover, LR‐MSCs expressed the VW‐MSC‐specific HOX code a characteristic to discriminate VW‐MSCs from phenotypical similar cells. Thus, LR‐MSC should be considered as VW‐MSCs. Immunofluorescent analyses of non‐small lung cancer (NSCLC) specimen further confirmed the vascular adventitia as stem cell niche for LR‐MSCs, and revealed their mobilization and activation in NSCLC progression. These findings have implications for understanding the role of MSC in normal lung physiology and pulmonary diseases, as well as for the rational design of additional therapeutic approaches.