New MSC: MSCs as pericytes are Sentinels and gatekeepers

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.

Engineering Brain-Specific Pericytes from Human Pluripotent Stem Cells

Pericytes (PCs) are a type of perivascular cells that surround endothelial cells of small blood vessels. In the brain, PCs show heterogeneity depending on their position within the vasculature. As a result, PC interactions with surrounding endothelial cells, astrocytes, and neuron cells play a key role in a wide array of neurovascular functions such as regulating blood-brain barrier (BBB) permeability, cerebral blood flow, and helping to facilitate the clearance of toxic cellular molecules. Therefore, a reliable method of engineering brain-specific PCs from human induced pluripotent stem cells (hiPSCs) is critical in neurodegenerative disease modeling. This review summarizes brain-specific PC differentiation of hiPSCs through mesoderm and neural crest induction. Key signaling pathways (platelet-derived growth factor-B [PDGF-B], transforming growth factor [TGF]-β, and Notch signaling) regulating PC function, PC interactions with adjacent cells, and PC differentiation from hiPSCs are also discussed. Specifically, PDGF-BB-platelet-derived growth factor receptor β signaling promotes PC cell survival, TGF-β signal transduction facilitates PC attachment to endothelial cells, and Notch signaling is critical in vascular development and arterial-venous specification. Furthermore, current challenges facing the use of hiPSC-derived PCs are discussed, and their ongoing uses in neurodegenerative disease modeling are identified. Further investigations into PCs and surrounding cell interactions are needed to characterize the roles of brain PCs in various neurodegenerative disorders. Impact statement This article summarizes the work related to brain-specific pericytes (PCs) derived from human pluripotent stem cells (hPSCs). In particular, key signaling pathways regulating PC function, PC interactions with adjacent cells, and PC differentiation from hPSCs were discussed. Furthermore, current challenges facing the use of hPSC-derived PCs were identified, and their ongoing uses in neurodegenerative disease modeling were discussed. The review highlights the important role of cell-cell interactions in blood-brain barrier (BBB) models and neurodegeneration. The summarized findings are significant for establishing pluripotent stem cell-based BBB models toward the applications in drug screening and disease modeling.

Scleraxis is required for the growth of adult tendons in response to mechanical loading

Scleraxis is a basic helix-loop-helix transcription factor that plays a central role in promoting tenocyte proliferation and matrix synthesis during embryonic tendon development. However, the role of scleraxis in the growth and adaptation of adult tendons is not known. We hypothesized that scleraxis is required for tendon growth in response to mechanical loading and that scleraxis promotes the specification of progenitor cells into tenocytes. We conditionally deleted scleraxis in adult mice using a tamoxifen-inducible Cre-recombinase expressed from the Rosa26 locus (ScxΔ) and then induced tendon growth in Scx+ and ScxΔ adult mice via plantaris tendon mechanical overload. Compared with the WT Scx+ group, ScxΔ mice demonstrated blunted tendon growth. Transcriptional and proteomic analyses revealed significant reductions in cell proliferation, protein synthesis, and extracellular matrix genes and proteins. Our results indicate that scleraxis is required for mechanically stimulated adult tendon growth by causing the commitment of CD146+ pericytes into the tenogenic lineage and by promoting the initial expansion of newly committed tenocytes and the production of extracellular matrix proteins.

Transcriptomic Analysis of Human Mesenchymal Stem Cell Therapy in Incontinent Rat Injured Urethra

Periurethral human mesenchymal stem cell (hMSC) injections are associated with functional improvement in animal models of postpartum stress urinary incontinence (SUI). However, limited data exist on the role of hMSCs in modulating gene expression in tissue repair after urethral injury. To this end, we quantified temporal gene expression modulation in hMSCs, and in injured rat urethral tissue, using RNA-seq in an animal model of SUI, over a 3-day period following urethral injury, and local hMSC injection. We injected PKH fluorescent-labeled hMSC into the periurethral space of rats following a 4 h vaginal distention (VD) (three rats per time point). Control rats underwent VD injury only, and all animals were euthanized at 12, 24, 36, 72 h postinjury. Rat urethral and vaginal tissues were frozen and sectioned. Fluorescent labeled hMSCs were distinguished from adjacent, unlabeled rat urethral tissue. RNA was prepared from hMSCs and urethral tissue obtained by laser dissection of frozen tissue sections and sequenced on an Illumina HiSeq 2500. Differentially expressed genes (DEGs) over 72 h were evaluated using a two-group t-test (p < 0.05). Our transcriptional analyses identified candidate genes involved in tissue injury that were broadly sorted by injury and exposure to hMSC throughout the first 72 h of acute phase of injury. DEGs in treated urethra, compared with untreated urethra, were functionally associated with tissue repair, angiogenesis, neurogenesis, and oxidative stress suppression. DEGs included a variety of cytokines, extracellular matrix stabilization and regeneration genes, cytokine signaling modification, cell cycle regulation, muscle differentiation, and stabilization. Moreover, our results revealed DEG changes in hMSCs (PKH-labeled) harvested from injured urethra. The expressions are related to DNA damage repair, transcription activation, stem cell regulation, cell survival, apoptosis, self-renewal, cell proliferation, migration, and injury response. Impact statement Stress urinary incontinence (SUI) affects nearly half of women over 40, resulting in reduced quality of life and increased health care cost. Development of SUI is multifactorial and strongly associated with vaginal delivery. While stem cell therapy in animal models of SUI and limited preliminary clinical trials demonstrate functional improvement of SUI, the role of stem cell therapy in modulating tissue repair is unclear impeding advanced clinical trials. Our work provides a new understanding of the transcriptional mechanisms with which human mesenchymal stem cells improve acute injury repair thus guiding the development of cell-based therapies for women with nonacute established SUI.

Modifying MSC Phenotype to Facilitate Bone Healing: Biological Approaches

Healing of fractures and bone defects normally follows an orderly series of events including formation of a hematoma and an initial stage of inflammation, development of soft callus, formation of hard callus, and finally the stage of bone remodeling. In cases of severe musculoskeletal injury due to trauma, infection, irradiation and other adverse stimuli, deficient healing may lead to delayed or non-union; this results in a residual bone defect with instability, pain and loss of function. Modern methods of mechanical stabilization and autologous bone grafting are often successful in achieving fracture union and healing of bone defects; however, in some cases, this treatment is unsuccessful because of inadequate biological factors. Specifically, the systemic and local microenvironment may not be conducive to bone healing because of a loss of the progenitor cell population for bone and vascular lineage cells. Autologous bone grafting can provide the necessary scaffold, progenitor and differentiated lineage cells, and biological cues for bone reconstruction, however, autologous bone graft may be limited in quantity or quality. These unfavorable circumstances are magnified in systemic conditions with chronic inflammation, including obesity, diabetes, chronic renal disease, aging and others. Recently, strategies have been devised to both mitigate the necessity for, and complications from, open procedures for harvesting of autologous bone by using minimally invasive aspiration techniques and concentration of iliac crest bone cells, followed by local injection into the defect site. More elaborate strategies (not yet approved by the U.S. Food and Drug Administration-FDA) include isolation and expansion of subpopulations of the harvested cells, preconditioning of these cells or inserting specific genes to modulate or facilitate bone healing. We review the literature pertinent to the subject of modifying autologous harvested cells including MSCs to facilitate bone healing. Although many of these techniques and technologies are still in the preclinical stage and not yet approved for use in humans by the FDA, novel approaches to accelerate bone healing by modifying cells has great potential to mitigate the physical, economic and social burden of non-healing fractures and bone defects.

Mesenchymal Stromal Cell Bioreactor for Ex Vivo Reprogramming of Human Immune Cells

Bone marrow mesenchymal stromal cells (MSCs) have been studied for decades as potent immunomodulators. Clinically, they have shown some promise but with limited success. Here, we report the ability of a scalable hollow fiber bioreactor to effectively maintain ideal MSC function as a single population while also being able to impart an immunoregulatory effect when cultured in tandem with an inflamed lymphocyte population. MSCs were seeded on the extraluminal side of hollow fibers within a bioreactor where they indirectly interact with immune cells flowing within the lumen of the fibers. MSCs showed a stable and predictable metabolite and secreted factor profile during several days of perfusion culture. Exposure of bioreactor-seeded MSCs to inflammatory stimuli reproducibly switched MSC secreted factor profiles and altered microvesicle composition. Furthermore, circulating, activated human peripheral blood mononuclear cells (PBMCs) were suppressed by MSC bioreactor culture confirmed by a durable change in their immunophenotype and function. This platform was useful to study a model of immobilized MSCs and circulating immune cells and showed that monocytes play an important role in MSC driven immunomodulation. This coculture technology can have broad implications for use in studying MSC-immune interactions under flow conditions as well as in the generation of ex vivo derived immune cellular therapeutics.

Signature quality attributes of CD146+ mesenchymal stem/stromal cells correlate with high therapeutic and secretory potency

CD146⁺ bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs) play key roles in the perivascular niche, skeletogenesis, and hematopoietic support; however, comprehensive evaluation of therapeutic potency has yet to be determined. In this study, in vitro inflammatory priming to crude human BM-MSCs (n = 8) captured a baseline of signature responses, including enriched CD146⁺ with coexpression of CD107a^High , CXCR4^High , and LepR^High , transcriptional profile, enhanced secretory capacity, and robust immunomodulatory secretome and function, including immunopotency assays (IPAs) with stimulated immune cells. These signatures were significantly more pronounced in CD146⁺ (POS)-sorted subpopulation than in the CD146^- (NEG). Mechanistically, POS BM-MSCs showed a markedly higher secretory capacity with significantly greater immunomodulatory and anti-inflammatory protein production upon inflammatory priming compared with the NEG BM-MSCs. Moreover, IPAs with stimulated peripheral blood mononuclear cells and T lymphocytes demonstrated robust immunosuppression mediated by POS BM-MSC while inducing significant frequencies of regulatory T cells. in vivo evidence showed that POS BM-MSC treatment promoted pronounced M1-to-M2 macrophage polarization, ameliorating inflammation/fibrosis of knee synovium and fat pad, unlike treatment with NEG BM-MSCs. These data correlate the expression of CD146 with innately higher immunomodulatory and secretory capacity, and thus therapeutic potency. This high-content, reproducible evidence suggests that the CD146⁺ (POS) MSC subpopulation are the mediators of the beneficial effects achieved using crude BM-MSCs, leading to translational implications for improving cell therapy and manufacturing.

Stem-cell therapy for erectile dysfunction: a review of clinical outcomes

The prevalence of erectile dysfunction (ED) has increased in recent decades. Although many treatments offer some benefits for patients with ED, unmet therapeutic needs remain, and promising new approaches are under investigation. One of these approaches is the use of stem-cell (SC) therapy for ED. We comprehensively reviewed the published literature and ongoing phase 1 and phase 2 trials and identified 27 trials by using SC therapy to treat ED. Of the 27 trials, three have been withdrawn, nine have published results, six are complete but without published results, and nine trials are ongoing or have an "unknown" status. Our analysis revealed that SC therapy represents a promising option to treat ED, although published data exist for less than 100 patients. Large placebo-controlled trials with longer follow-up are needed to confirm the long-term safety and efficacy of SC therapy for ED.

Pericyte-Mediated Tissue Repair through PDGFRβ Promotes Peri-Infarct Astrogliosis, Oligodendrogenesis, and Functional Recovery after Acute Ischemic Stroke

Post-stroke functional recovery can occur spontaneously during the subacute phase; however, how post-stroke fibrotic repair affects functional recovery is highly debated. Platelet-derived growth factor receptor β (PDGFRβ)-expressing pericytes are responsible for post-stroke fibrotic repair within infarct areas; therefore, we examined peri-infarct neural reorganization and functional recovery after permanent middle cerebral artery occlusion (pMCAO) using pericyte-deficient Pdgfrb^+/- mice. Time-dependent reduction of infarct area sizes, i.e., repair, was significantly impaired in Pdgfrb^+/- mice with recovery of cerebral blood flow (CBF) in ischemic areas attenuated by defective leptomeningeal arteriogenesis and intrainfarct angiogenesis. Peri-infarct astrogliosis, accompanied by increased STAT3 phosphorylation, was attenuated in Pdgfrb^+/- mice. Pericyte-conditioned medium (PCM), particularly when treated with platelet-derived growth factor subunit B (PDGFB) homodimer (PDGF-BB; PCM/PDGF-BB), activated STAT3 and enhanced the proliferation and activity of cultured astrocytes. Although peri-infarct proliferation of oligodendrocyte (OL) precursor cells (OPCs) was induced promptly after pMCAO regardless of intrainfarct repair, OPC differentiation and remyelination were significantly attenuated in Pdgfrb^+/- mice. Consistently, astrocyte-CM (ACM) promoted OPC differentiation and myelination, which were enhanced remarkably by adding PCM/PDGF-BB to the medium. Post-stroke functional recovery correlated well with the extent and process of intrainfarct repair and peri-infarct oligodendrogenesis. Overall, pericyte-mediated intrainfarct fibrotic repair through PDGFRβ may promote functional recovery through enhancement of peri-infarct oligodendrogenesis as well as astrogliosis after acute ischemic stroke.

Friend or Foe? Essential Roles of Osteoclast in Maintaining Skeletal Health

Heightened activity of osteoclast is considered to be the culprit in breaking the balance during bone remodeling in pathological conditions, such as osteoporosis. As a “foe” of skeletal health, many antiosteoporosis therapies aim to inhibit osteoclastogenesis. However, bone remodeling is a dynamic process that requires the subtle coordination of osteoclasts and osteoblasts. Severe suppression of osteoclast differentiation will impair bone formation because of the coupling effect. Thus, understanding the complex roles of osteoclast in maintaining proper bone remodeling is highly warranted to develop better management of osteoporosis. This review aimed to determine the varied roles of osteoclasts in maintaining skeletal health and to highlight the positive roles of osteoclasts in maintaining normal bone remodeling. Generally, osteoclasts interact with osteocytes to initiate targeted bone remodeling and have crosstalk with mesenchymal stem cells and osteoblasts via secreted factors or cell-cell contact to promote bone formation. We believe that a better outcome of bone remodeling disorders will be achieved when proper strategies are made to coordinate osteoclasts and osteoblasts in managing such disorders.

Safety and efficacy of a mesenchymal stem cell intramammary therapy in dairy cows with experimentally induced Staphylococcus aureus clinical mastitis

Although, antibiotics are effective in the treatment of bovine mastitis, they do not address the regeneration of mammary glandular tissue and have been associated to the increment in antimicrobial resistance worldwide. Considering the necessity of alternative therapies for this disease of high economic impact and the reported regenerative and antibacterial effects of mesenchymal stem cell (MSCs), we evaluated the safety and efficacy of an allogenic MSC-based intramammary therapy in dairy cows with experimentally induced Staphylococcus aureus clinical mastitis. In a safety trial, heifers were inoculated intramammarily with a 2.5 × 10⁷-suspension of bovine fetal AT-MSCs on experimental days 1 and 10. Animals were evaluated clinically on a daily basis during a 20-day experimental period and blood samples were collected for hemogram determination and peripheral blood leukocytes (PBLs) isolation. In an efficacy trial, Holstein Friesian cows were inoculated with S. aureus and treated intramammarily with vehicle (NEG; days 4 and 10), antibiotics (ATB; days 4 and 5) or a suspension of 2.5 × 10⁷ AT-MSCs (MSC; days 4 and 5). Cows were clinically evaluated daily and milk samples were collected for somatic cell count (SCC) and colony forming units (CFU). Blood samples were collected for serum haptoglobin and amyloid A determination. Intramammary administration of two doses of bovine fetal AT-MSCs in healthy cows did not induce changes in clinical or hematological variables, and gene expression profiles in PBLs associated to activation (CD4, CD8, CD25, CD62L and CD69) and proinflammatory cytokines (CCL2, CCL5, IL2, CXCL3, IFNγ, and TNFα). Quarters of MSC group of cows had similar SCC log/mL in milk compared to infected quarters of ATB or NEG cows. However, quarters of MSC cows had lower CFU log/mL in milk compared to quarters of NEG cows. Intramammarily inoculation of repeated doses of 2.5 × 10⁷ allogenic AT-MSCs did not induce clinical or immunological response in healthy cows. Moreover, MSC-intramammary treatment reduced bacterial count in milk of cows with S. aureus clinical mastitis compared to untreated cows. This work provides initial evidence for the safety and efficacy of an allogenic MSC-based intramammary therapy for the treatment of bovine mastitis.

Allogeneic adipose-derived mesenchymal stem cell sheet that produces neurological improvement with angiogenesis and neurogenesis in a rat stroke model

OBJECTIVE

Stem cell therapy is a promising strategy for the treatment of severe cerebral ischemia. However, targeting sufficient grafted cells to the affected area remains challenging. Choosing an adequate transplantation method for the CNS appears crucial for this therapy to become a clinical reality. The authors used a scaffold-free cell sheet as a translational intervention. This method involves the use of cell sheet layers and allows the transplantation of a large number of cells, locally and noninvasively. The authors evaluated the effectiveness of allogeneic adipose tissue-derived mesenchymal stem cell sheets in a rat model of stroke.

METHODS

The animals, subjected to middle cerebral artery occlusion, were randomly divided in two groups: one in which a cell sheet was transplanted and the other in which a vehicle was used (n = 10/group). Over a period of 14 days after transplantation, the animals' behavior was evaluated, after which brain tissue samples were removed and fixed, and the extent of angiogenesis and infarct areas was evaluated histologically.

RESULTS

Compared to the vehicle group, in the cell sheet group functional angiogenesis and neurogenesis were significantly increased, which resulted in behavioral improvement. Transplanted cells were identified within newly formed perivascular walls as pericytes, a proportion of which were functional. Newly formed blood vessels were found within the cell sheet that had anastomosed to the cerebral blood vessels in the host.

CONCLUSIONS

The transplantation approach described here is expected to provide not only a paracrine effect but also a direct cell effect resulting in cell replacement that protects the damaged neurovascular unit. The behavioral improvement seen with this transplantation approach provides the basis for further research on cell sheet-based regenerative treatment as a translational treatment for patients with stroke.

Mesenchymal Stem Cells Decrease Oxidative Stress in the Bowels of Interleukin-10 Knockout Mice

Background/Aims: Inflammatory bowel disease (IBD) is an autoimmune disease characterized by chronic inflammation mainly in the large intestine. The interleukin-10 knockout (IL-10 KO) mouse is a well-known animal model of IBD that develops spontaneous intestinal inflammation resembling Crohn's disease. Oxidative stress is considered to be the leading cause of cell and tissue damage. Reactive oxygen species (ROS) can cause direct cell injury and/or indirect cell injury by inducing the secretion of cytokines from damaged cells. This study evaluated the effects of mesenchymal stem cell (MSC) on the progression of IBD. Methods: In this study, human bone marrow-derived MSCs were injected into IL-10 KO mice (MSC). Oxidative stress and inflammation levels were evaluated in the large intestine and compared with those in control IL-10 KO mice (CON) and normal wild-type control mice (Wild). Results: The levels of ROS (superoxide and hydrogen peroxidase) and a secondary end-product of lipid peroxidation (malondialdehyde) were considerably higher in the CON, while superoxide dismutase and catalase levels were lower in the MSC. Inflammation-related marker (interferon-γ, tumor necrosis factor-α, IL-4, and CD8) expression and inflammatory histological changes were much less pronounced in MSC than in CON. Conclusions: MSCs affect the redox balance, leading to the suppression of IBD.

Are Liver Pericytes Just Precursors of Myofibroblasts in Hepatic Diseases? Insights from the Crosstalk between Perivascular and Inflammatory Cells in Liver Injury and Repair

Cirrhosis, a late form of liver disease, is characterized by extensive scarring due to exacerbated secretion of extracellular matrix proteins by myofibroblasts that develop during this process. These myofibroblasts arise mainly from hepatic stellate cells (HSCs), liver-specific pericytes that become activated at the onset of liver injury. Consequently, HSCs tend to be viewed mainly as myofibroblast precursors in a fibrotic process driven by inflammation. Here, the molecular interactions between liver pericytes and inflammatory cells such as macrophages and neutrophils at the first moments after injury and during the healing process are brought into focus. Data on HSCs and pericytes from other tissues indicate that these cells are able to sense pathogen- and damage-associated molecular patterns and have an important proinflammatory role in the initial stages of liver injury. On the other hand, further data suggest that as the healing process evolves, activated HSCs play a role in skewing the initial proinflammatory (M1) macrophage polarization by contributing to the emergence of alternatively activated, pro-regenerative (M2-like) macrophages. Finally, data suggesting that some HSCs activated during liver injury could behave as hepatic progenitor or stem cells will be discussed.

NFATc1+CD31+CD45- circulating multipotent stem cells derived from human endocardium and their therapeutic potential

Many studies have shown the existence of cardiac stem cells in the myocardium and epicardial progenitor cells in the epicardium. However, the characteristics of stem cells in the endocardium has not been fully elucidated. In this study, we investigated the origin of newly identified cells in the blood and their therapeutic potential. The new population of cells, identified from human peripheral blood, was quite different from previously reported stem cells. These newly identified cells, which we named Circulating Multipotent Stem (CiMS) cells, were multipotent, and therefore differentiated into multiple lineages in vitro and in vivo. In order to determine the origin of these cells, we collected peripheral blood from a group of patients who underwent bone marrow, liver, heart, or kidney transplantation. We identified the endocardium as the origin of these cells because the Short Tandem Repeat profile of CiMS cells from the recipient had changed from the recipient's profile to the donor's profile after heart transplantation. CiMS cells significantly increased after stimuli to the endocardium, such as catheter ablation for arrhythmia or acute myocardial infarction. CiMS cells circulate in human peripheral blood and are easily obtainable, suggesting that these cells could be a promising tool for cell therapy.

Bone Marrow Niches for Skeletal Progenitor Cells and their Inhabitants in Health and Disease

The bone marrow hosts skeletal progenitor cells which have most widely been referred to as Mesenchymal Stem or Stromal Cells (MSCs), a heterogeneous population of adult stem cells possessing the potential for self-renewal and multilineage differentiation. A consensus agreement on minimal criteria has been suggested to define MSCs in vitro, including adhesion to plastic, expression of typical surface markers and the ability to differentiate towards the adipogenic, osteogenic and chondrogenic lineages but they are critically discussed since the differentiation capability of cells could not always be confirmed by stringent assays in vivo. However, these in vitro characteristics have led to the notion that progenitor cell populations, similar to MSCs in bone marrow, reside in various tissues. MSCs are in the focus of numerous (pre)clinical studies on tissue regeneration and repair. Recent advances in terms of genetic animal models enabled a couple of studies targeting skeletal progenitor cells in vivo. Accordingly, different skeletal progenitor cell populations could be identified by the expression of surface markers including nestin and leptin receptor. While there are still issues with the identity of, and the overlap between different cell populations, these studies suggested that specific microenvironments, referred to as niches, host and maintain skeletal progenitor cells in the bone marrow. Dynamic mutual interactions through biological and physical cues between niche constituting cells and niche inhabitants control dormancy, symmetric and asymmetric cell division and lineage commitment. Niche constituting cells, inhabitant cells and their extracellular matrix are subject to influences of aging and disease e.g. via cellular modulators. Protective niches can be hijacked and abused by metastasizing tumor cells, and may even be adapted via mutual education. Here, we summarize the current knowledge on bone marrow skeletal progenitor cell niches in physiology and pathophysiology. We discuss the plasticity and dynamics of bone marrow niches as well as future perspectives of targeting niches for therapeutic strategies.

Potential Role of MSC/Cancer Cell Fusion and EMT for Breast Cancer Stem Cell Formation

Solid tumors comprise of maturated cancer cells and self-renewing cancer stem-like cells (CSCs), which are associated with various other nontumorigenic cell populations in the tumor microenvironment. In addition to immune cells, endothelial cells, fibroblasts, and further cell types, mesenchymal stroma/stem-like cells (MSC) represent an important cell population recruited to tumor sites and predominantly interacting with the different cancer cells. Breast cancer models were among the first to reveal distinct properties of CSCs, however, the cellular process(es) through which these cells are generated, maintained, and expanded within neoplastic tissues remains incompletely understood. Here, we discuss several possible scenarios that are not mutually exclusive but may even act synergistically: fusion of cancer cells with MSC to yield hybrid cells and/or the induction of epithelial-mesenchymal transition (EMT) in breast cancer cells by MSC, which can relay signals for retrodifferentiation and eventually, the generation of breast CSCs (BCSCs). In either case, the consequences may be promotion of self-renewal capacity, tumor cell plasticity and heterogeneity, an increase in the cancer cells' invasive and metastatic potential, and the acquisition of resistance mechanisms towards chemo- or radiotherapy. While specific signaling mechanisms involved in each of these properties remain to be elucidated, the present review article focusses on a potential involvement of cancer cell fusion and EMT in the development of breast cancer stem cells.

Marker Expression of Interstitial Cells in Human Skeletal Muscle: An Immunohistochemical Study

There is a growing recognition that myogenic stem cells are influenced by their microenvironment during regeneration. Several interstitial cell types have been described as supportive for myoblasts. In this role, both the pericyte as a possible progenitor for mesenchymal stem cells, and interstitial cells in the endomysium have been discussed. We have applied immunohistochemistry on normal and pathological human skeletal muscle using markers for pericytes, or progenitor cells and found a cell type co-expressing CD10, CD34, CD271, and platelet-derived growth factor receptor α omnipresent in the endomysium. The marker profile of these cells changed dynamically in response to muscle damage and atrophy, and they proliferated in response to damage. The cytology and expression profile of the CD10+ cells indicated a capacity to participate in myogenesis. Both morphology and indicated function of these cells matched properties of several previously described interstitial cell types. Our study suggests a limited number of cell types that could embrace many of these described cell types. Our study indicate that the CD10+, CD34+, CD271+, and platelet-derived growth factor receptor α+ cells could have a supportive role in human muscle regeneration, and thus the mechanisms by which they exert their influence could be implemented in stem cell therapy.

CDKN2B upregulation prevents teratoma formation in multipotent fibromodulin-reprogrammed cells

Tumorigenicity is a well-documented risk to overcome for pluripotent or multipotent cell applications in regenerative medicine. To address the emerging demand for safe cell sources in tissue regeneration, we established a novel, protein-based reprogramming method that does not require genome integration or oncogene activation to yield multipotent fibromodulin (FMOD)-reprogrammed (FReP) cells from dermal fibroblasts. When compared with induced pluripotent stem cells (iPSCs), FReP cells exhibited a superior capability for bone and skeletal muscle regeneration with markedly less tumorigenic risk. Moreover, we showed that the decreased tumorigenicity of FReP cells was directly related to an upregulation of cyclin-dependent kinase inhibitor 2B (CDKN2B) expression during the FMOD reprogramming process. Indeed, sustained suppression of CDKN2B resulted in tumorigenic, pluripotent FReP cells that formed teratomas in vivo that were indistinguishable from iPSC-derived teratomas. These results highlight the pivotal role of CDKN2B in cell fate determination and tumorigenic regulation and reveal an alternative pluripotent/multipotent cell reprogramming strategy that solely uses FMOD protein.

The multifaceted role of mesenchymal stem cells in cancer

Mesenchymal stem cells (MSCs) are multipotent stem cells derived from the mesoderm that give rise to several mesenchymal lineages, including osteoblasts, adipocytes, chondrocytes and myocytes. Their potent ability to home to tumors coupled with their differentiation potential and immunosuppressive function positions MSCs as key regulators of tumor fate. Here we review the existing knowledge on the involvement of MSCs in multiple tumor-promoting processes, including angiogenesis, epithelial-mesenchymal transition, metastasis, immunosuppression and therapy resistance. We also discuss the clinical potential of MSC-based therapy for cancer.

Comparative analysis of in vitro proliferative, migratory and pro-angiogenic potentials of bovine fetal mesenchymal stem cells derived from bone marrow and adipose tissue

Mesenchymal stem cells (MSCs) are found in virtually all tissues, where they self-renew and differentiate into multiple cell types. Cumulative data indicate that MSCs secrete paracrine factors that may play key roles in the treatment of various acute and chronic pathological conditions in diverse animal species including cattle. The aim of the present study was to compare the potentials for proliferation, migration and pro-angiogenesis of bovine fetal BM-MSCs and AT-MSCs under in vitro conditions. Growth curves and population doubling time (PDT) were determined for BM-MSCs and AT-MSCs in order to compare in vitro cell proliferation potentials. The ability of BM-MSCs and AT-MSCs to migrate was evaluated by scratch plate and transwell migration assays. The pro-angiogenic potential of conditioned medium from BM-MSCs and AT-MSCs was compared using an endothelial cell (EC) tubule formation assay. BM-MSCs displayed higher proliferation curves and doubled their populations in fewer days compared to AT-MSCs. No significant differences were detected in the number of migrant cells between BM-MSCs and AT-MSCs; however, a higher migration value was detected for BM-MSCs compared to fibroblasts (FBs), and a higher number of migrant cells were attracted by DMEM supplemented with 5% fetal bovine serum (FBS) compared to stromal cell-derived factor-1 (SDF-1). More tubules of ECs were formed after exposure to concentrated conditioned medium from AT-MSCs compared to BM-MSCs, FBs or DMEM controls. Despite common mesodermal origin, BM-MSCs display higher proliferative capacity and lower pro-angiogenic potential compared to AT-MSCs; however, both cell types possess similar migratory ability.

Mesenchymal stem cells: From regeneration to cancer

Mesenchymal stem cells (MSCs) are multipotent tissue stem cells that differentiate into a number of mesodermal tissue types, including osteoblasts, adipocytes, chondrocytes and myofibroblasts. MSCs were originally identified in the bone marrow (BM) of humans and other mammals, but recent studies have shown that they are multilineage progenitors in various adult organs and tissues. MSCs that localize at perivascular sites function to rapidly respond to external stimuli and coordinate with the vascular and immune systems to accomplish the wound healing process. Cancer, considered as wounds that never heal, is also accompanied by changes in MSCs that parallels the wound healing response. MSCs are now recognized as key players at distinct steps of tumorigenesis. In this review, we provide an overview of the function of MSCs in wound healing and cancer progression with the goal of providing insight into the development of novel MSC-manipulating strategies for clinical cancer treatment.

Studying Heterotypic Cell⁻Cell Interactions in the Human Brain Using Pluripotent Stem Cell Models for Neurodegeneration

Human cerebral organoids derived from induced pluripotent stem cells (iPSCs) provide novel tools for recapitulating the cytoarchitecture of the human brain and for studying biological mechanisms of neurological disorders. However, the heterotypic interactions of neurovascular units, composed of neurons, pericytes (i.e., the tissue resident mesenchymal stromal cells), astrocytes, and brain microvascular endothelial cells, in brain-like tissues are less investigated. In addition, most cortical organoids lack a microglia component, the resident immune cells in the brain. Impairment of the blood-brain barrier caused by improper crosstalk between neural cells and vascular cells is associated with many neurodegenerative disorders. Mesenchymal stem cells (MSCs), with a phenotype overlapping with pericytes, have promotion effects on neurogenesis and angiogenesis, which are mainly attributed to secreted growth factors and extracellular matrices. As the innate macrophages of the central nervous system, microglia regulate neuronal activities and promote neuronal differentiation by secreting neurotrophic factors and pro-/anti-inflammatory molecules. Neuronal-microglia interactions mediated by chemokines signaling can be modulated in vitro for recapitulating microglial activities during neurodegenerative disease progression. In this review, we discussed the cellular interactions and the physiological roles of neural cells with other cell types including endothelial cells and microglia based on iPSC models. The therapeutic roles of MSCs in treating neural degeneration and pathological roles of microglia in neurodegenerative disease progression were also discussed.

Human Diseased Articular Cartilage Contains a Mesenchymal Stem Cell-Like Population of Chondroprogenitors with Strong Immunomodulatory Responses

Background: osteoarthritic human articular cartilage (AC)-derived cartilage cells (CCs) with same-donor bone marrow (BMSCs) and adipose tissue (ASCs)-derived mesenchymal stem cells were compared, in terms of stemness features, and secretory and immunomodulatory responses to inflammation. Methods: proteoglycan 4 (PRG4) presence was evaluated in AC and CCs. MSCs and CCs (n = 8) were cultured (P1 to P4) and characterized for clonogenicity, nanog homeobox (NANOG), and POU class 5 homeobox 1 (POU5F1) expression, immunotypification, and tri-lineage differentiation. Their basal and interleukin-1β (IL-1β)-stimulated expression of matrix metalloproteases (MMPs), tissue inhibitors (TIMPs), release of growth factors, and cytokines were analyzed, along with the immunomodulatory ability of CCs. Results: PRG4 was mainly expressed in the intact AC surface, whereas shifted to the intermediate zone in damaged cartilage and increased its expression in CCs upon culture. All cells exhibited a similar phenotype and stemness maintenance over passages. CCs showed highest chondrogenic ability, no adipogenic potential, a superior basal secretion of growth factors and cytokines, the latter further increased after inflammatory stimulation, and an immunomodulatory behavior. All stimulated cells shared an increased MMP expression without a corresponding TIMP production. Conclusion: based on the observed features, CCs obtained from pathological joints may constitute a potential tissue-specific therapeutic target or agent to improve damaged cartilage healing, especially damage caused by inflammatory/immune mediated conditions.

Less Vertebral Bone Mass after Treatment with Macitentan in Mice: A Pilot Study

Purpose

Blood vessels and skeleton interact together. Endothelin-1 is a potent vasoconstrictor and also has an effect on bone metabolism. The dual antagonist to both endothelin-1 type A and B receptors, Macitentan, has been approved for clinical management of pulmonary arterial hypertension while little is known about the secondary effect of the drug on spine. We aimed to answer how vertebral bone mass responded to Macitentan treatment in mice.

Methods

Sixteen male balb/c mice at 6 months were randomly assigned into 2 groups. Vehicle and Macitentan were administrated via intraperitoneal injection to Control group and Treatment group, respectively, for 4 months. At sacrifice, plasma endothelin-1 was evaluated with ELISA and vertebral bone mass was evaluated with Microcomputed Tomography and histological analysis.

Results

We found higher plasma endothelin-1 level (p<0.01) and less vertebral bone mass (p<0.05) in Treatment group compared to controls. Moreover, less osteoblasts and more osteoclasts were observed in the vertebral trabecular bone in the Treatment group compared to controls, by immunohistochemistry of the cell-specific markers.

Conclusions

Treatment with Macitentan is associated with significant lower vertebral bone mass and therefore the secondary effect of dual antagonists to endothelin-1 receptors on the skeleton should be monitored and investigated in clinical practice. Both osteoblasts and osteoclasts may be involved while the molecular mechanism needs to be further explored.

Synovium extra cellular matrices seeded with transduced mesenchymal stem cells stimulate chondrocyte maturation in vitro and cartilage healing in clinically-induced rat-knee lesions in vivo

Osteoarthritis (OA) is a progressive disease associated with cartilage injury and its inherently limited repair capability. Synovium-based cellular constructs (sConstructs) are proposed as possible treatments. Equine sConstructs were produced from decellularized synovium-based extracellular matrix scaffolds (sECM) seeded with synovium-derived mesenchymal stem cells (sMSC), and engineered to express green fluorescent protein (GFP), or bone morphogenetic protein-2 (BMP-2). Survival, distribution, and chondrogenic potential of the sConstructs in vitro and in vivo were assessed. sConstructs in co-culture with chondrocytes increased chondrocyte proliferation, viability, and Col II production, greatest in BMP-2-sConstructs. Chondrocyte presence increased the production of hyaluronic acid (HA), proteoglycan (PG), and BMP-2 by the sConstructs in a positive feedback loop. sECM alone, or GFP- or BMP-2-sConstructs were implanted in synovium adjacent to clinically created full-thickness rat-knee cartilage lesions. At 5 weeks, the lesion area and implants were resected. Gross anatomy, adjacent articulate cartilage growth and subchondral bone repair were scored; and peripheral, central and cartilage lesion measurements taken. For all scores and measurements, sConstruct implants were significantly greater than controls, greatest with the BMP-2-sConstructs. Immunohistochemistry demonstrated migration of endogenous cells into the sECM, with greater cellularity in the constructs with intense positive GFP staining confirming engraftment of implanted sMSC and continued gene expression. In summary, exposing cartilage to sConstructs was chondrogenic in vitro and in vivo, and resulted in substantially increased growth in vivo. This effect was mediated, in part, by soluble ECM and cell factors and upregulation of anabolic growth proteins, such as BMP-2. This work is "proof of concept" that sConstructs surgically implanted adjacent to cartilage damage can significantly improve cartilage and subchondral bone repair, and potentially prevent the progression of OA.

Experimental Strategies of Mesenchymal Stem Cell Propagation: Adverse Events and Potential Risk of Functional Changes

Mesenchymal stem cells (MSCs) are attractive candidates for cell-based tissue repair approaches. Hundreds of clinical trials using MSCs have been completed and many others are still being investigated. For most therapeutic applications, MSC propagation in vitro is often required. However, ex vivo culture condition is not fully physiological and may affect biological properties of MSCs including their regenerative potential. Moreover, both cell cryopreservation and labelling procedure prior to infusion may have the negative impact on their expected effect in vivo. The incidence of MSC transformation during in vitro culture should be also taken into consideration before using cells in stem cell therapy. In our review, we focused on different aspects of MSC propagation that might influence their regenerative properties of MSC. We also discussed the influence of different factors that might abolish MSC proliferation and differentiation as well as potential impact of stem cell senescence and aging. Despite of many positive therapeutic effects of MSC therapy, one has to be conscious about potential cell changes that could appear during manufacturing of MSCs.

Identification of miRNA Reference Genes in Extracellular Vesicles from Adipose Derived Mesenchymal Stem Cells for Studying Osteoarthritis

Osteoarthritis (OA) leads to chronic pain and disability, and traditional conservative treatments are not effective in the long term. The intra-articular injection of mesenchymal stem cells (MSCs) is considered a novel therapy for OA whose efficacy mainly relies on the adaptive release of paracrine molecules which are either soluble or extracellular vesicles (EVs) embedded. The correct quantification of EV-miRNAs using reliable reference genes (RGs) is a crucial step in optimizing this future therapeutic cell-free approach. The purpose of this study is to rate the stabilities of literature-selected proposed RGs for EV-miRNAs in adipose derived-MSCs (ASCs). EVs were isolated by ultracentrifugation from ASCs cultured with or without inflammatory priming mimicking OA synovial fluid condition. Expression of putative RGs (let-7a-5p, miR-16-5p, miR-23a-3p, miR-26a-5p, miR-101-3p, miR-103a-3p, miR-221-3p, miR-423-5p, miR-425-5p, U6 snRNA) was scored by using the algorithms geNorm, NormFinder, BestKeeper and ΔCt method. miR-16a-5p/miR-23a-3p yielded the most stable RGs, whereas let-7a-5p/miR-425-5p performed poorly. Outcomes were validated by qRT-PCR on miR-146a-5p, reported to be ASC-EVs enriched and involved in OA. Incorrect RG selection affected the evaluation of miR-146a-5p abundance and modulation by inflammation, with both values resulting strongly donor-dependent. Our findings demonstrated that an integrated approach of multiple algorithms is necessary to identify reliable, stable RGs for ASC-EVs miRNAs evaluation. A correct approach would increase the accuracy of embedded molecule assessments aimed to develop therapeutic strategies for the treatment of OA based on EVs.

Human Fetal Cardiac Mesenchymal Stromal Cells Differentiate In Vivo into Endothelial Cells and Contribute to Vasculogenesis in Immunocompetent Mice

Mesenchymal stromal cells (MSCs) have shown great potential as a treatment for systemic inflammatory diseases, but their local regenerative properties are highly tissue- and site specific. Previous studies have demonstrated that adult human MSCs respond to inflammatory cytokines through the release of paracrine factors that stimulate angiogenesis, but they do not themselves differentiate into vascular structures in vivo. In this study, we used human fetal cardiac MSCs (hfcMSCs) harvested during the first trimester of heart development and injected them into the subcutaneous tissue of normal immunocompetent mice treated with short-term costimulation blockade for tolerance induction. When hfcMSCs were transplanted subcutaneously together with Matrigel matrix, they contributed to vasculogenesis through differentiation into endothelial cells and generation of the basal membrane protein Laminin α4. These characteristics of hfcMSCs are similar to the mesodermal progenitors giving rise to the developing heart and they may be useful for treatment of ischemic injuries.

CD248: A therapeutic target in cancer and fibrotic diseases

CD248/endosialin/TEM1 is a type 1 transmembrane glycoprotein found on the plasma membrane of activated mesenchymal cells. CD248 functions during embryo development and is either not expressed or found at very low levels in adult tissues. CD248 is expressed at high levels by malignant sarcoma cells, by the pericyte component of tumor vasculature and by mesenchymal cells in some fibrotic diseases. CD248 is being targeted by several experimental therapeutics including antibodies, antibody drug conjugates, as an antigen for CART cells and in therapeutic vaccines. Although the function of CD248 has yet to be fully elucidated, this protein is a potential broad scope therapeutic target.

TRPV4-mediated calcium signaling in mesenchymal stem cells regulates aligned collagen matrix formation and vinculin tension

Microarchitectural cues drive aligned fibrillar collagen deposition in vivo and in biomaterial scaffolds, but the cell-signaling events that underlie this process are not well understood. Utilizing a multicellular patterning model system that allows for observation of intracellular signaling events during collagen matrix assembly, we investigated the role of calcium (Ca²⁺) signaling in human mesenchymal stem cells (MSCs) during this process. We observed spontaneous Ca²⁺ oscillations in MSCs during fibrillar collagen assembly, and hypothesized that the transient receptor potential vanilloid 4 (TRPV4) ion channel, a mechanosensitive Ca²⁺-permeable channel, may regulate this signaling. Inhibition of TRPV4 nearly abolished Ca²⁺ signaling at initial stages of collagen matrix assembly, while at later times had reduced but significant effects. Importantly, blocking TRPV4 activity dramatically reduced aligned collagen fibril assembly; conversely, activating TRPV4 accelerated aligned collagen formation. TRPV4-dependent Ca²⁺ oscillations were found to be independent of pattern shape or subpattern cell location, suggesting this signaling mechanism is necessary for aligned collagen formation but not sufficient in the absence of physical (microarchitectural) cues that force multicellular alignment. As cell-generated mechanical forces are known to be critical to the matrix assembly process, we examined the role of TRPV4-mediated Ca²⁺ signaling in force generated across the load-bearing focal adhesion protein vinculin within MSCs using an FRET-based tension sensor. Inhibiting TRPV4 decreased tensile force across vinculin, whereas TRPV4 activation caused a dynamic unloading and reloading of vinculin. Together, these findings suggest TRPV4 activity regulates forces at cell-matrix adhesions and is critical to aligned collagen matrix assembly by MSCs.

Bone Marrow-Derived and Adipose-Derived Mesenchymal Stem Cell Therapy in Primary Knee Osteoarthritis: A Narrative Review

Regenerative medicine in the context of musculoskeletal injury is a broad term that offers potential therapeutic solutions to restore or repair damaged tissue. The current focus in recent literature and clinical practice has been on cell based therapy. In particular, much attention has been centered on autologous bone marrow concentrate and adipose-derived mesenchymal stem cells (MSCs) for cartilage and tendon disorders. This article provides an overview of MSC-derived therapy and offers a comprehensive review of adipose- and bone marrow-derived MSC therapy in primary knee osteoarthritis. LEVEL OF EVIDENCE: IV.

Equine Cord Blood Mesenchymal Stromal Cells Have Greater Differentiation and Similar Immunosuppressive Potential to Cord Tissue Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) are the most common cell population studied for therapeutic use in veterinary medicine. MSCs obtained from neonatal sources such as umbilical cord tissue (CT-MSCs) or cord blood (CB-MSCs) are appealing due to the non-invasive nature of procurement and the time allowed for characterization of cells before use. However, it remains unclear as to whether CB- or CT-MSCs have equivalent progenitor and non-progenitor functions. CB-MSCs have been shown to have superior chondrogenic potential to MSCs from other sources, whereas their immunomodulatory capacity does not seem to vary significantly. Using equine CB-MSCs and CT-MSCs from the same donors, we hypothesized that MSCs from both sources would have a similar immunophenotype, that CB-MSCs would be more amenable to differentiation, and that they can equally suppress lymphocyte proliferation. We evaluated cells from both sources for "classic" equine MSC markers CD90, CD105, CD29, and CD44, as well as pericyte markers CD146, NG2, and α-SMA. Contrary to our hypothesis, CB-MSCs showed mid- to high expression of pericyte surface markers CD146 and NG2, whereas expression in CT-MSCs was absent. On trilineage differentiation, CB-MSCs were more osteogenic and chondrogenic based on alkaline phosphatase activity and glycosaminoglycan content, respectively. Finally, using a mononuclear cell (MNC) suppression assay, we determined that both CB-MSCs and CT-MSCs are capable of suppressing stimulated MNC proliferation to a similar degree. We have determined that the choice of MSC tissue source should be made with the intended application in mind. This appears to be particularly relevant if pursuing a progenitor-based treatment strategy.

Mesenchymal stromal cells-exosomes: a promising cell-free therapeutic tool for wound healing and cutaneous regeneration

Cutaneous regeneration at the wound site involves several intricate and dynamic processes which require a series of coordinated interactions implicating various cell types, growth factors, extracellular matrix (ECM), nerves, and blood vessels. Mesenchymal stromal cells (MSCs) take part in all the skin wound healing stages playing active and beneficial roles in animal models and humans. Exosomes, which are among the key products MSCs release, mimic the effects of parental MSCs. They can shuttle various effector proteins, messenger RNA (mRNA) and microRNAs (miRNAs) to modulate the activity of recipient cells, playing important roles in wound healing. Moreover, using exosomes avoids many risks associated with cell transplantation. Therefore, as a novel type of cell-free therapy, MSC-exosome -mediated administration may be safer and more efficient than whole cell. In this review, we provide a comprehensive understanding of the latest studies and observations on the role of MSC-exosome therapy in wound healing and cutaneous regeneration. In addition, we address the hypothesis of MSCs microenvironment extracellular vesicles (MSCs-MEVs) or MSCs microenvironment exosomes (MSCs-MExos) that need to take stock of and solved urgently in the related research about MSC-exosomes therapeutic applications. This review can inspire investigators to explore new research directions of MSC-exosome therapy in cutaneous repair and regeneration.

Stem cells in the treatment of diabetes mellitus - Focus on mesenchymal stem cells

Diabetes mellitus type 1 and type 2 have become a global epidemic with dramatically increasing incidences. Poorly controlled diabetes is associated with severe life-threatening complications. Beside traditional treatment with insulin and oral anti-diabetic drugs, clinicians try to improve patient's care by cell therapies using embryonic stem cells (ESC), induced pluripotent stem cells (iPSC) and adult mesenchymal stem cells (MSC). ESC display a virtually unlimited plasticity, including the differentiation into insulin producing β-cells, but they raise ethical concerns and bear, like iPSC, the risk of tumours. IPSC may further inherit somatic mutations and remaining somatic transcriptional memory upon incomplete re-programming, but allow the generation of patient/disease-specific cell lines. MSC avoid such issues but have not been successfully differentiated into β-cells. Instead, MSC and their pericyte phenotypes outside the bone marrow have been recognized to secrete numerous immunomodulatory and tissue regenerative factors. On this account, the term 'medicinal signaling cells' has been proposed to define the new conception of a 'drug store' for injured tissues and to stay with the MSC nomenclature. This review presents the biological background and the resulting clinical potential and limitations of ESC, iPSC and MSC, and summarizes the current status quo of cell therapeutic concepts and trials.

Pericytes in Bone Marrow

Bone marrow environments are composed of multiple cell types, most of which are thought to be derived from mesenchymal stem cells. In mouse bone marrow, stromal cells with CD45^- Tie2^- CD90^- CD51⁺ CD105⁺ phenotype, Nestin-GFP⁺, CXCL12-abundant reticular (CAR) cells, PDGFRα⁺ Sca-1⁺ or CD51⁺ PDGFRα⁺, and Prx-1-derived CD45^- Ter119^- PDGFRα⁺ Sca-1⁺ populations select for MSC activity. There is evidence that these stromal cell populations display some significant overlap with each other and comprise important cellular constituents of the hematopoietic stem cell niche. Moreover, these mesenchymal cell populations share characteristics in their location as they all are found around bone marrow vessels (can be called "pericytes"). In this chapter, with reviewing the recent literatures, how the pericytes relate to physiological and pathological hematopoiesis is argued.

Rescue from lethal acute radiation syndrome (ARS) with severe weight loss by secretome of intramuscularly injected human placental stromal cells

BACKGROUND

Most current cell-based regenerative therapies are based on the indirect induction of the affected tissues repair. Xenogeneic cell-based treatment with expanded human placenta stromal cells, predominantly from fetal origin (PLX-RAD cells), were shown to mitigate significantly acute radiation syndrome (ARS) following high dose irradiation in mice, with expedited regain of weight loss and haematopoietic function. The current mechanistic study explores the indirect effect of the secretome of PLX-RAD cells in the rescue of the irradiated mice.

METHODS

The mitigation of the ARS was investigated following two intramuscularly (IM) injected 2 × 10⁶ PLX-RAD cells, 1 and 5 days following 7.7 Gy irradiation. The mice survival rate and their blood or bone marrow (BM) cell counts were followed up and correlated with multiplex immunoassay of a panel of related human proteins of PLX-RAD derived secretome, as well as endogenous secretion of related mouse proteins. PLX-RAD secretome was also tested in vitro for its effect on the induction of the migration of BM progenitors.

RESULTS

A 7.7 Gy whole body mice irradiation resulted in ~25% survival by 21 days. Treatment with two IM injections of 2 × 10⁶ PLX-RAD cells on days 1 and 5 after irradiation mitigated highly significantly the subsequent lethal ARS, with survival rate increase to nearly 100% and fast regain of the initial weight loss (P < 0,0001). This was associated with a significant faster haematopoiesis recovery from day 9 onwards (P < 0.01). Nine out of the 65 human proteins tested were highly significantly elevated in the mouse circulation, peaking on days 6-9 after irradiation, relative to negligible levels in non-irradiated PLX-RAD injected mice (P < 0.01). The highly elevated proteins included human G-CSF, GRO, MCP-1, IL-6 and lL-8, reaching >500 pg/mL, while MCP-3, ENA, Eotaxin and fractalkine levels ranged between ~60-160pg/mL. The detected radiation-induced PLX-RAD secretome correlated well with the timing of the fast haematopoiesis regeneration. The radiation-induced PLX-RAD secretome seemed to reinforce the delayed high levels secretion of related mouse endogenous cytokines, including GCSF, KC, MCP-1 and IL-6. Additional supportive in vitro studies also confirmed the ability of cultured PLX-RAD secretome to induce accelerated migration of BM progenitors.

CONCLUSIONS

A well-regulated and orchestrated secretion of major pro-regenerative BM supporting secretome in high dose irradiated mice, treated with xenogeneic IM injected PLX-RAD cells, can explain the observed mitigation of ARS. This seemed to coincide with faster haematopoiesis regeneration, regain of severe weight loss and the increased survival rate. The ARS-related stress signals activating the IM injected PLX-RAD cells for the remote secretion of the relevant human proteins deserve further investigation.

Mesenchymal Stem Cell Functionalization for Enhanced Therapeutic Applications

IMPACT STATEMENT

Culture expansion of MSCs has detrimental effects on various cell characteristics and attributes (e.g., phenotypic changes and senescence), which, in addition to inherent interdonor variability, negatively impact the standardization and reproducibility of their therapeutic potential. The identification of innate distinct functional MSC subpopulations, as well as the description of ex vivo protocols aimed at maintaining phenotypes and enhancing specific functions have the potential to overcome these limitations. The incorporation of those approaches into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved.

Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells

Blood vessels composed of endothelial cells (ECs) contact with mesenchymal stem cells (MSCs) in different tissues, suggesting possible interaction between these 2 types of cells. We hypothesized that endothelin-1 (ET1), a secreted paracrine factor of ECs, can differentially direct the lineages of adipose-derived stem cells (ASCs) and bone marrow-derived MSCs (BMSCs). Predifferentiated ASCs and BMSCs were treated with ET1 for 2 cell passages and then induced for multilineage differentiation. Our results showed that adipogenesis of ET1-pretreated ASCs and osteogenesis of ET1-pretreated BMSCs were increased compared to those of control cells. The effect of ET1 on enhancing adipogenesis of ASCs and osteogenesis of BMSCs was attenuated by blocking endothelin receptor type A (ETAR) and/or endothelin receptor type B (ETBR). Western blot analysis indicated that regulation by ET1 was mediated through activation of the protein kinase B and ERK1/2 signaling pathways. We analyzed subpopulations of ASCs and BMSCs with or without ETAR and/or ETBR, and we found that ETAR⁺/ETBR^- and ETAR^-/ETBR⁺ subpopulations of ASCs and those of BMSCs pretreated with ET1 were prone to turning into adipocytes and osteoblasts, respectively, after differentiation induction. Our findings provide insight into the differential regulation of MSC specification by ET1, which may help develop viable approaches for tissue regeneration.-Lee, M.-S., Wang, J., Yuan, H., Jiao, H., Tsai, T.-L., Squire, M. W., Li, W.-J. Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells.

Regenerative Sports Medicine: Past, Present, and Future (Adapted From the PASSOR Legacy Award Presentation; AAPMR; October 2016)

Regenerative medicine has shown dramatic expanse and evolution in the past decade. Within that milieu, physiatrists are taking an active role in research, clinical care delivery, and education. The purpose of this review is to provide a balance among evidence, theory, experience, clinical trends, and the foreseeable future. We focus on the literature that reports the research with the best methodology in each practice area, recognizing that the level of evidence varies substantially among different treatment modalities and conditions. The following elements are included: an overview of the evolution of currently available regenerative techniques, evidence base for each available modality (prolotherapy, platelet rich plasma, bone marrow aspirate concentrate and stem cells, adipose-derived stem cells, and amniotic tissue products), general principles in the application of these treatments, and discussion and a vision of what lies ahead. We expect that practitioners will use this review to facilitate clinical decision making and to provide a core knowledge base to assist when counseling patients. LEVEL OF EVIDENCE: IV.

Role of TGF‑β1 expressed in bone marrow‑derived mesenchymal stem cells in promoting bone formation in a rabbit femoral defect model

Bone defects represent a major clinical and socioeconomic problem without suitable treatment options. Previous studies have shown that transforming growth factor β1 (TGF‑β1) is important in the development of various diseases. The present study aimed to investigate the therapeutic potential of rabbit bone marrow‑derived mesenchymal stem cells (BMSCs) expressing TGF‑β1 in the treatment of rabbit femoral defects. First, rabbit BMSCs were identified and cultured. TGF‑β1 was then stably overexpressed in the rabbit BMSCs by lentivirus transfection, which was expressed at a high level in the femoral defects treated with TGF‑β1‑overexpressing BMSCs, compared with PBS‑treated controls. In addition, the TGF‑β1‑overexpressing BMSCs promoted new bone formation in the rabbit femoral defect model, and increased the expression of bone‑related markers at week 2 and week 6. Therefore, the study demonstrated that BMSCs overexpressing TGF‑β1 may provide a novel therapeutic option for femoral defects.