Adult bone marrow stem/progenitor cells (MSCs) are preconditioned by microenvironmental "niches" in culture: a two-stage hypothesis for regulation of MSC fate

Scalable manufacture of therapeutic mesenchymal stromal cell products on customizable microcarriers in vertical wheel bioreactors that improve direct visualization, product harvest, and cost

BACKGROUND AIMS

Human mesenchymal stromal cells (hMSCs) and their secreted products show great promise for treatment of musculoskeletal injury and inflammatory or immune diseases. However, the path to clinical utilization is hampered by donor-tissue variation and the inability to manufacture clinically relevant yields of cells or their products in a cost-effective manner. Previously we described a method to produce chemically and mechanically customizable gelatin methacryloyl (GelMA) microcarriers for culture of hMSCs. Herein, we demonstrate scalable GelMA microcarrier-mediated expansion of induced pluripotent stem cell (iPSC)-derived hMSCs (ihMSCs) in 500 mL and 3L vertical wheel bioreactors, offering several advantages over conventional microcarrier and monolayer-based expansion strategies.

METHODS

Human mesenchymal stromal cells derived from induced pluripotent cells were cultured on custom-made spherical gelatin methacryloyl microcarriers in single-use vertical wheel bioreactors (PBS Biotech). Cell-laden microcarriers were visualized using confocal microscopy and elastic light scattering methodologies. Cells were assayed for viability and differentiation potential in vitro by standard methods. Osteogenic cell matrix derived from cells was tested in vitro for osteogenic healing using a rodent calvarial defect assay. Immune modulation was assayed with an in vivo peritonitis model using Zymozan A.

RESULTS

The optical properties of GelMA microcarriers permit noninvasive visualization of cells with elastic light scattering modalities, and harvest of product is streamlined by microcarrier digestion. At volumes above 500 mL, the process is significantly more cost-effective than monolayer culture. Osteogenic cell matrix derived from ihMSCs expanded on GelMA microcarriers exhibited enhanced in vivo bone regenerative capacity when compared to bone morphogenic protein 2, and the ihMSCs exhibited superior immunosuppressive properties in vivo when compared to monolayer-generated ihMSCs.

CONCLUSIONS

These results indicate that the cell expansion strategy described here represents a superior approach for efficient generation, monitoring and harvest of therapeutic MSCs and their products.

Unravelling novel and pleiotropic genes for cannon bone circumference and bone mineral density in Yorkshire pigs

Leg weakness is a prevalent health condition in pig farms. The augmentation of cannon bone circumference and bone mineral density can effectively improve limb strength in pigs and alleviate leg weakness. This study measured forelimb cannon bone circumference (fCBC) and rear limb cannon bone circumference (rCBC) using an inelastic tapeline and rear limb metatarsal area bone mineral density (raBMD) using a dual-energy X-ray absorptiometry bone density scanner. The samples of Yorkshire castrated boars were genotyped using a 50K single-nucleotide polymorphism (SNP) array. The SNP-chip data were imputed to the level of whole-genome sequencing data (iWGS). This study used iWGS data to perform genome-wide association studies and identified novel significant SNPs associated with fCBC on SSC6, SSC12, and SSC13, rCBC on SSC12 and SSC14, and raBMD on SSC7. Based on the high phenotypic and genetic correlations between CBC and raBMD, multi-trait meta-analysis was performed to identify pleiotropic SNPs. A significant potential pleiotropic quantitative trait locus (QTL) regulating both CBC and raBMD was identified on SSC15. Bayes fine mapping was used to establish the confidence intervals for these novel QTLs with the most refined confidence interval narrowed down to 56 kb (15.11 to 15.17 Mb on SSC12 for fCBC). Furthermore, the confidence interval for the potential pleiotropic QTL on SSC15 in the meta-analysis was narrowed down to 7.45 kb (137.55 to137.56 Mb on SSC15). Based on the biological functions of genes, the following genes were identified as novel regulatory candidates for different phenotypes: DDX42, MYSM1, FTSJ3, and MECOM for fCBC; SMURF2, and STC1 for rCBC; RGMA for raBMD. Additionally, RAMP1, which was determined to be located 23.68 kb upstream of the confidence interval of the QTL on SSC15 in the meta-analysis, was identified as a potential pleiotropic candidate gene regulating both CBC and raBMD. These findings offered valuable insights for identifying pathogenic genes and elucidating the genetic mechanisms underlying CBC and BMD.

A new frontier in temporomandibular joint osteoarthritis treatment: Exosome-based therapeutic strategy

Temporomandibular joint osteoarthritis (TMJOA) is a debilitating degenerative disease with high incidence, deteriorating quality of patient life. Currently, due to ambiguous etiology, the traditional clinical strategies of TMJOA emphasize on symptomatic treatments such as pain relief and inflammation alleviation, which are unable to halt or reverse the destruction of cartilage or subchondral bone. A number of studies have suggested the potential application prospect of mesenchymal stem cells (MSCs)-based therapy in TMJOA and other cartilage injury. Worthy of note, exosomes are increasingly being considered the principal efficacious agent of MSC secretions for TMJOA management. The extensive study of exosomes (derived from MSCs, synoviocytes, chondrocytes or adipose tissue et al.) on arthritis recently, has indicated exosomes and their specific miRNA components to be potential therapeutic agents for TMJOA. In this review, we aim to systematically summarize therapeutic properties and underlying mechanisms of MSCs and exosomes from different sources in TMJOA, also analyze and discuss the approaches to optimization, challenges, and prospects of exosome-based therapeutic strategy.

Expression of proliferation-related genes in BM-MSC-treated ALL cells in hypoxia condition is regulated under the influence of epigenetic factors in-vitro

Mesenchymal stem cells affect ALL cell biology under hypoxic conditions. We studied survival, proliferation, expression, and promoter methylation levels of essential genes involved in expanding MOLT-4 cells co-cultured with BM-MSC under the hypoxic condition. Here, MOLT-4 cells were co-cultured with BMMSCs under hypoxic conditions. First, the apoptosis rate was evaluated by Flow cytometry. Then, MOLT-4 cells' proliferation rate was assessed using MTT assay, and the expressions and methylation rates of genes were determined by qRT-PCR and MS-qPCR, respectively. The results showed that although MOLT-4 cells proliferation and survival rates were reduced under hypoxic conditions, this reduction was not statistically significant. Also, we showed that hypoxic conditions caused upregulation of candidate genes and affected their methylation status. Besides, it was revealed that Pontin was downregulated, while KDM3A, SKP2, and AURKA had an upward trend in the presence of MOLT-4 cells plus BM-MSC. The co-culture of leukemia cells with BMMSCs under hypoxic conditions may be a potential therapeutic approach for ALL.

A scalable system for generation of mesenchymal stem cells derived from induced pluripotent cells employing bioreactors and degradable microcarriers

Human mesenchymal stem cells (hMSCs) are effective in treating disorders resulting from an inflammatory or heightened immune response. The hMSCs derived from induced pluripotent stem cells (ihMSCs) share the characteristics of tissue derived hMSCs but lack challenges associated with limited tissue sources and donor variation. To meet the expected future demand for ihMSCs, there is a need to develop scalable methods for their production at clinical yields while retaining immunomodulatory efficacy. Herein, we describe a platform for the scalable expansion and rapid harvest of ihMSCs with robust immunomodulatory activity using degradable gelatin methacryloyl (GelMA) microcarriers. GelMA microcarriers were rapidly and reproducibly fabricated using a custom microfluidic step emulsification device at relatively low cost. Using vertical wheel bioreactors, 8.8 to 16.3‐fold expansion of ihMSCs was achieved over 8 days. Complete recovery by 5‐minute digestion of the microcarriers with standard cell dissociation reagents resulted in >95% viability. The ihMSCs matched or exceeded immunomodulatory potential in vitro when compared with ihMSCs expanded on monolayers. This is the first description of a robust, scalable, and cost‐effective method for generation of immunomodulatory ihMSCs, representing a significant contribution to their translational potential.

Under hypoxic conditions, MSCs affect the expression and methylation level of survival-related genes in ALL independent of apoptosis pathways in vitro

Mesenchymal stem cells (MSCs) are one of the most prominent cells in the bone marrow. MSCs can affect acute lymphocytic leukemia (ALL) cells under hypoxic conditions. With this aim, we used MOLT-4 cells as simulators of ALL cells cocultured with bone marrow mesenchymal stem cells (BMMSCs) under hypoxic conditions in vitro. Then, mRNA and protein expression of the MAT2A, PDK1, and HK2 genes were evaluated by real-time PCR and Western blot which was also followed by apoptosis measurement by a flow-cytometric method. Next, the methylation status of the target genes was investigated by MS-qPCR. Additionally, candidate gene expressions were examined after treatment with rapamycin using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. We found that the mRNA expression of the candidate genes was augmented under the hypoxic condition in which MAT2A was upregulated in cocultured cells compared to MOLT-4, while HK2 and PDK1 were downregulated. Moreover, we found an association between gene expression and promoter methylation levels of target genes. Besides, expressions of the candidate genes were decreased, while their methylation levels were promoted following treatment with rapamycin. Our results suggest an important role for the BMMSC in regulating the methylation of genes involved in cell survival in hypoxia conditions; however, we found no evidence to prove the MSCs' effect on directing malignant lymphoblastic cells to apoptosis.

Borax induces osteogenesis by stimulating NaBC1 transporter via activation of BMP pathway

The intrinsic properties of mesenchymal stem cells (MSCs) make them ideal candidates for tissue engineering applications. Efforts have been made to control MSC behavior by using material systems to engineer synthetic extracellular matrices and/or include soluble factors in the media. This work proposes a simple approach based on ion transporter stimulation to determine stem cell fate that avoids the use of growth factors. Addition of borax alone, transported by the NaBC1-transporter, enhanced MSC adhesion and contractility, promoted osteogenesis and inhibited adipogenesis. Stimulated-NaBC1 promoted osteogenesis via the BMP canonical pathway (comprising Smad1/YAP nucleus translocation and osteopontin expression) through a mechanism that involves simultaneous NaBC1/BMPR1A and NaBC1/α₅β₁/α_vβ₃ co-localization. We describe an original function for NaBC1 transporter, besides controlling borate homeostasis, capable of stimulating growth factor receptors and fibronectin-binding integrins. Our results open up new biomaterial engineering approaches for biomedical applications by a cost-effective strategy that avoids the use of soluble growth factors.

Rico et al. propose a simple approach based on borax stimulation of NaBC1 transporter, which enhances FN-binding integrin-dependent mesenchymal stem cell adhesion and contractility, promotes osteogenesis and inhibits adipogenesis. Osteogenic differentiation depends on activation of the BMP pathway through a mechanism that involves simultaneous co-localization of NaBC1 with FN-binding integrins and BMPR1A.

Concurrent multi-lineage differentiation of mesenchymal stem cells through spatial presentation of growth factors

Severe tendon and ligament injuries are estimated to affect between 300 000 and 400 000 people annually. Surgical repairs of these injuries often have poor long-term clinical outcomes because of resection of the interfacial tissue-the enthesis-and subsequent stress concentration at the attachment site. A healthy enthesis consists of distinct regions of bone, fibrocartilage, and tendon, each with distinct cell types, extracellular matrix components, and architecture, which are important for tissue function. Tissue engineering, which has been proposed as a potential strategy for replacing this tissue, is currently limited by its inability to differentiate multiple lineages of cells from a single stem cell population within a single engineered construct. In this study, we develop a multi-phasic gelatin methacrylate hydrogel construct system for spatial presentation of proteins, which is then validated for multi-lineage differentiation towards the cell types of the bone-tendon enthesis. This study determines growth factor concentrations for differentiation of mesenchymal stem cells towards osteoblasts, chondrocytes/fibrochondrocytes, and tenocytes, which maintain similar differentiation profiles in 3D hydrogel culture as assessed by qPCR and immunofluorescence staining. Finally, it is shown that this method is able to guide heterogeneous and spatially confined changes in mesenchymal stem cell genes and protein expressions with the tendency to result in osteoblast-, fibrochondrocyte-, and tenocyte-like expression profiles. Overall, we demonstrate the utility of the culture technique for engineering other musculoskeletal tissue interfaces and provide a biochemical approach for recapitulating the bone-tendon enthesis in vitro.

Surface Tethering of Inflammation-Modulatory Nanostimulators to Stem Cells for Ischemic Muscle Repair

Stem cell transplantation has been a promising treatment for peripheral arterial diseases in the past decade. Stem cells act as living bioreactors of paracrine factors that orchestrate tissue regeneration. Prestimulated adipose-derived stem cells (ADSCs) have been proposed as potential candidates but have been met with challenges in activating their secretory activities for clinical use. Here, we propose that tethering the ADSC surface with nanoparticles releasing tumor necrosis factor α (TNFα), named nanostimulator, would stimulate cellular secretory activity in situ. We examined this hypothesis by complexing octadecylamine-grafted hyaluronic acid onto a liposomal carrier of TNFα. Hyaluronic acid increased the liposomal stability and association to CD44 on ADSC surface. ADSCs tethered with these TNFα carriers exhibited up-regulated secretion of proangiogenic vascular endothelial growth factor and immunomodulatory prosteoglandin E2 (PGE2) while decreasing secretion of antiangiogenic pigment epithelium-derived factors. Accordingly, ADSCs tethered with nanostimulators promoted vascularization in a 3D microvascular chip and enhanced recovery of perfusion, walking, and muscle mass in a murine ischemic hindlimb compared to untreated ADSCs. We propose that this surface tethering strategy for in situ stimulation of stem cells would replace the costly and cumbersome preconditioning process and expedite clinical use of stem cells for improved treatments of various injuries and diseases.

Mesenchymal Stromal/Stem Cells in Regenerative Medicine and Tissue Engineering

As a result of over five decades of investigation, mesenchymal stromal/stem cells (MSCs) have emerged as a versatile and frequently utilized cell source in the fields of regenerative medicine and tissue engineering. In this review, we summarize the history of MSC research from the initial discovery of their multipotency to the more recent recognition of their perivascular identity in vivo and their extraordinary capacity for immunomodulation and angiogenic signaling. As well, we discuss long-standing questions regarding their developmental origins and their capacity for differentiation toward a range of cell lineages. We also highlight important considerations and potential risks involved with their isolation, ex vivo expansion, and clinical use. Overall, this review aims to serve as an overview of the breadth of research that has demonstrated the utility of MSCs in a wide range of clinical contexts and continues to unravel the mechanisms by which these cells exert their therapeutic effects.

PGC-1α Controls Skeletal Stem Cell Fate and Bone-Fat Balance in Osteoporosis and Skeletal Aging by Inducing TAZ

Aberrant lineage specification of skeletal stem cells (SSCs) contributes to reduced bone mass and increased marrow adipose tissue (MAT) in osteoporosis and skeletal aging. Although master regulators of osteoblastic and adipogenic lineages have been identified, little is known about factors that are associated with MAT accumulation and osteoporotic bone loss. Here, we identify peroxisome-proliferator-activated receptor γ coactivator 1-α (PGC-1α) as a critical switch of cell fate decisions whose expression decreases with aging in human and mouse SSCs. Loss of PGC-1α promoted adipogenic differentiation of murine SSCs at the expense of osteoblastic differentiation. Deletion of PGC-1α in SSCs impaired bone formation and indirectly promoted bone resorption while enhancing MAT accumulation. Conversely, induction of PGC-1α attenuated osteoporotic bone loss and MAT accumulation. Mechanistically, PGC-1α maintains bone and fat balance by inducing TAZ. Our results suggest that PGC-1α is a potentially important therapeutic target in the treatment of osteoporosis and skeletal aging.

An Update on the Therapeutic Potential of Stem Cells

The seeming setbacks noted for stem cells underscore the need for experimental studies for safe and efficacious application to patients. Both clinical and experimental researchers have gained valuable knowledge on the characteristics of stem cells, and their behavior in different microenvironment. This introductory chapter focuses on adult mesenchymal stem cells (MSCs) based on the predominance in the clinic. MSCs can be influenced by inflammatory mediators to exert immune suppressive properties, commonly referred to as "licensing." Interestingly, while there are questions if other stem cells can be delivered across allogeneic barrier, there is no question on the ability of MSCs to provide this benefit. This property has been a great advantage since MSCs could be available for immediate application as "off-the-shelf" stem cells for several disorders, tissue repair and gene/drug delivery. Despite the benefit of MSCs, it is imperative that research continues with the various types of stem cells. The method needed to isolate these cells is outlined in this book. In parallel, safety studies are needed; particularly links to oncogenic event. In summary, this introductory chapter discusses several potential areas that need to be addressed for safe and efficient delivery of stem cells, and argue for the incorporation of microenvironmental factors in the studies. The method described in this chapter could be extrapolated to the field of chimeric antigen receptor T-cells (CAR-T). This will require application to stem cell hierarchy of memory T-cells.

AMPK Activation Mediated by Hinokitiol Inhibits Adipogenic Differentiation of Mesenchymal Stem Cells through Autophagy Flux

BACKGROUND AND PURPOSE

Hinokitiol, a natural monopenoid present in the essential oil of Calocedrus formosana heartwood, exerts potent anticancer, anti-inflammatory, antibacterial, and neuroprotective effects on various cells. However, the antiobesity effect of hinokitiol on adipocytes is unclear.

EXPERIMENTAL APPROACH

In this study, we observed that hinokitiol affected the differentiation to adipocytes in mesenchymal stem cells (MSCs). Hinokitiol was treated with 3-isobutyl-1-methylxanthine, insulin, and dexamethasone to induce differentiation and maturing adipocytes in cultured MSCs.

KEY RESULTS

Hinokitiol treatment of MSCs decreased their differentiation to mature adipocytes and increased AMPK phosphorylation in a concentration-dependent manner. Moreover, we confirmed that the antiadipogenic effect of hinokitiol was associated with autophagy. The levels of LC3-II decreased and those of p62 increased in hinokitiol-treated MSCs. The treatment of hinokitiol-treated MSCs with the autophagy activator, rapamycin, restored the hinokitiol-induced decrease in the adipocyte differentiation of MSCs. The inhibition of AMPK phosphorylation also suppressed hinokitiol-mediated inhibition of autophagy and antiadipogenic effects.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results indicated that AMPK activation and autophagy flux inhibition mediated by hinokitiol inhibited lipid accumulation and differentiation of MSCs to adipocytes and also suggest that differentiation of mesenchymal stem cells may be regulated by using the modulator of autophagy flux and AMPK signals including hinokitiol.

Exosomes derived from human umbilical cord mesenchymal stem cells protect against cisplatin-induced ovarian granulosa cell stress and apoptosis in vitro

Human umbilical cord mesenchymal stem cells (huMSCs) can treat primary ovarian insufficiency (POI) related to ovarian granulosa cell (OGC) apoptosis caused by cisplatin chemotherapy. Exosomes are a class of membranous vesicles with diameters of 30–200 nm that are constitutively released by eukaryotic cells. Exosomes mediate local cell-to-cell communication by transferring microRNAs and proteins. In the present study, we demonstrated the effects of exosomes derived from huMSCs (huMSC-EXOs) on a cisplatin-induced OGC model in vitro and discussed the preliminary mechanisms involved in these effects. We successfully extracted huMSC-EXOs from huMSC culture supernatant and observed the effective uptake of exosomes by cells with fluorescent staining. Using flow cytometry (with annexin-V/PI labelling), we found that huMSC-EXOs increased the number of living cells. Western blotting showed that the expression of Bcl-2 and caspase-3 were upregulated, whilst the expression of Bax, cleaved caspase-3 and cleaved PARP were downregulated to protect OGCs. These results suggest that huMSC-EXOs can be used to prevent and treat chemotherapy-induced OGC apoptosis in vitro. Therefore, this work provides insight and further evidence of stem cell function and indicates that huMSC-EXOs protect OGCs from cisplatin-induced injury in vitro.

The combination of nano-calcium sulfate/platelet rich plasma gel scaffold with BMP2 gene-modified mesenchymal stem cells promotes bone regeneration in rat critical-sized calvarial defects

BACKGROUND

Mesenchymal stem cells (MSCs) can be differentiated into an osteoblastic lineage in the presence of growth factors (GFs). Platelet-rich plasma (PRP), which can be easily isolated from whole blood, contains a large amount of GFs, and, therefore, promotes bone growth and regeneration. The main goal of this work was to develop and investigate the effect of a new sandwich-like bone scaffold which combines a nano-calcium sulfate (nCS) disc along with PRP fibrin gel (nCS/PRP) with BMP2-modified MSCs on bone repair and regeneration in rat critical-sized calvarial defects.

METHODS

We evaluated the cytotoxicity, osteogenic differentiation and mineralization effect of PRP extract on BMP2-modified MSCs and constructed a sandwich-like nCS/PRP scaffold (mimicking the nano-calcium matrix of bone and carrying multi GFs in the PRP) containing BMP2-modified MSCs. The capacity of this multifunctional bone regeneration system in promoting bone repair was assessed in vivo in a rat critical-sized (8 mm) calvarial bone defect model.

RESULTS

We developed an optimized nCS/PRP sandwich-like scaffold. Scanning electron microscopy (SEM) results showed that nCS/PRP are polyporous with an average pore diameter of 70-80 μm and the cells can survive in the nCS/PRP scaffold. PRP extract dramatically stimulated proliferation and differentiation of BMP2-modified MSCs in vitro. Our in vivo results showed that the combination of BMP2-modified MSCs and nCS/PRP scaffold dramatically increased new bone regeneration compared with the groups without PRP and/or BMP2.

CONCLUSIONS

nCS/PRP scaffolds containing BMP2-modified MSCs successfully promotes bone regeneration in critical-sized bone defects. This system could ultimately enable clinicians to better reconstruct the craniofacial bone and avoid donor site morbidity for critical-sized bone defects.

Efficient programming of human mesenchymal stem cell-derived hepatocytes by epigenetic regulations

BACKGROUND AND AIM

In view of its unique properties of detoxification and involvement of metabolic and biochemical functions, in vitro hepatocyte culture serves as a valuable material for drug screening and mechanistic analysis for pathology of liver diseases. The restriction of rapid de-differentiation and inaccessibility of human hepatocytes from routine clinical procedure, however, limits its use.

METHODS

To address this issue, the effort to direct human mesenchymal stem cells (hMSCs) into hepatocytes using a modified protocol was proposed. With the additional treatment of histone deacetylase inhibitor (HDACi) and DNA methyltransferase inhibitor (DNMTi), in vitro hMSC-derived hepatocytes were cultivated and their hepatic characteristics were examined.

RESULTS

By using a modified protocol, it was shown that Trichostatin A and 5-aza-2-deoxycitidine protected differentiating cells from death and could sufficiently trigger a wide range of liver-specific markers as well as liver functions including albumin production, glycogen storage, and urea cycle in hMSC-derived hepatocytes. The increased mRNA expression for hepatitis C virus (HCV) entry including CD81, Occludin, LDL receptor, and scavenger receptor class B type I in hMSC-derived hepatocytes was also detected, implying its potential to be utilized as an in vitro model to analyze dynamic HCV infection.

CONCLUSIONS

The present study successfully established a protocol to direct hMSCs into hepatocyte-like cells suggesting the beneficial impact to apply HDACi and DNMTi as potent modulators for hMSCs to liver differentiation.

Application of platelet-rich plasma with stem cells in bone and periodontal tissue engineering

Presently, there is a high paucity of bone grafts in the United States and worldwide. Regenerating bone is of prime concern due to the current demand of bone grafts and the increasing number of diseases causing bone loss. Autogenous bone is the present gold standard of bone regeneration. However, disadvantages like donor site morbidity and its decreased availability limit its use. Even allografts and synthetic grafting materials have their own limitations. As certain specific stem cells can be directed to differentiate into an osteoblastic lineage in the presence of growth factors (GFs), it makes stem cells the ideal agents for bone regeneration. Furthermore, platelet-rich plasma (PRP), which can be easily isolated from whole blood, is often used for bone regeneration, wound healing and bone defect repair. When stem cells are combined with PRP in the presence of GFs, they are able to promote osteogenesis. This review provides in-depth knowledge regarding the use of stem cells and PRP in vitro, in vivo and their application in clinical studies in the future.

Comparative study of adipose-derived stem cells and bone marrow-derived stem cells in similar microenvironmental conditions

Mesenchymal stem cells (MSCs), which were first isolated from the bone marrow, are now being extracted from various other tissues in the body, including the adipose tissue. The current study presents systematic evidence of how the adipose tissue-derived stem cells (ASCs) and bone marrow-derived mesenchymal stem cells (Bm-MSCs) behave when cultured in specific pro-adipogenic microenvironments. The cells were first characterized and identified as MSCs in terms of their morphology, phenotypic expression, self-renewal capabilities and multi-lineage potential. Subsequently, the proliferation and gene expression profiles of the cell populations cultured on two-dimensional (2D) adipose tissue extracellular matrix (ECM)-coated tissue culture plastic (TCP) and in three-dimensional (3D) AlgiMatrix® microenvironments were analyzed. Overall, it was found that adipogenesis was triggered in both cell populations due to the presence of adipose tissue ECM. However, in 3D microenvironments, ASCs and Bm-MSCs were predisposed to the adipogenic and osteogenic lineages respectively. Overall, findings from this study will contribute to ongoing efforts in adipose tissue engineering as well as provide new insights into the role of the ECM and cues provided by the immediate microenvironment for stem cell differentiation.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles Protect the Fetal Brain After Hypoxia-Ischemia

Preterm neonates are susceptible to perinatal hypoxic-ischemic brain injury, for which no treatment is available. In a preclinical animal model of hypoxic-ischemic brain injury in ovine fetuses, we have demonstrated the neuroprotective potential of systemically administered mesenchymal stromal cells (MSCs). The mechanism of MSC treatment is unclear but suggested to be paracrine, through secretion of extracellular vesicles (EVs). Therefore, we investigated in this study the protective effects of mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) in a preclinical model of preterm hypoxic-ischemic brain injury. Ovine fetuses were subjected to global hypoxia-ischemia by transient umbilical cord occlusion, followed by in utero intravenous administration of MSC-EVs. The therapeutic effects of MSC-EV administration were assessed by analysis of electrophysiological parameters and histology of the brain. Systemic administration of MSC-EVs improved brain function by reducing the total number and duration of seizures, and by preserving baroreceptor reflex sensitivity. These functional protections were accompanied by a tendency to prevent hypomyelination. Cerebral inflammation remained unaffected by the MSC-EV treatment. Our data demonstrate that MSC-EV treatment might provide a novel strategy to reduce the neurological sequelae following hypoxic-ischemic injury of the preterm brain. Our study results suggest that a cell-free preparation comprising neuroprotective MSC-EVs could substitute MSCs in the treatment of preterm neonates with hypoxic-ischemic brain injury, thereby circumventing the potential risks of systemic administration of living cells.

SIGNIFICANCE

Bone marrow-derived mesenchymal stromal cells (MSCs) show promise in treating hypoxic-ischemic injury of the preterm brain. Study results suggest administration of extracellular vesicles, rather than intact MSCs, is sufficient to exert therapeutic effects and avoids potential concerns associated with administration of living cells. The therapeutic efficacy of systemically administered mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) on hypoxia-ischemia-induced injury was assessed in the preterm ovine brain. Impaired function and structural injury of the fetal brain was improved following global hypoxia-ischemia. A cell-free preparation of MSC-EVs could substitute for the cellular counterpart in the treatment of preterm neonates with hypoxic-ischemic brain injury. This may open new clinical applications for "off-the-shelf" interventions with MSC-EVs.

Deubiquitinase MYSM1 Is Essential for Normal Bone Formation and Mesenchymal Stem Cell Differentiation

Deubiquitinase MYSM1 has been shown to play a critical role in hematopoietic cell differentiation and hematopoietic stem cell (HSC) maintenance. Mesenchymal stem cells (MSCs) are multipotent stromal cells within the bone marrow. MSCs are progenitors to osteoblasts, chondrocytes, adipocytes, and myocytes. Although, MSCs have been extensively studied, the roles of MYSM1 in these cells remain unclear. Here we describe the function of MYSM1 on MSC maintenance and differentiation. In this report, we found that Mysm1−/− mice had a lower bone mass both in long bone and calvaria compared with their control counterpart. Preosteoblasts from Mysm1−/− mice did not show changes in proliferation or osteogenesis when compared to WT mice. Conversely, Mysm1−/− MSCs showed enhanced autonomous differentiation and accelerated adipogenesis. Our results demonstrate that MYSM1 plays a critical role in MSC maintenance and differentiation. This study also underscores the biological significance of deubiquitinase activity in MSC function. Mysm1 may represent a potential therapeutic target for controlling MSC lineage differentiation, and possibly for the treatment of metabolic bone diseases such as osteoporosis.

CD200 expression in human cultured bone marrow mesenchymal stem cells is induced by pro-osteogenic and pro-inflammatory cues

Similar to other adult tissue stem/progenitor cells, bone marrow mesenchymal stem/stromal cells (BM MSCs) exhibit heterogeneity at the phenotypic level and in terms of proliferation and differentiation potential. In this study such a heterogeneity was reflected by the CD200 protein. We thus characterized CD200(pos) cells sorted from whole BM MSC cultures and we investigated the molecular mechanisms regulating CD200 expression. After sorting, measurement of lineage markers showed that the osteoblastic genes RUNX2 and DLX5 were up-regulated in CD200(pos) cells compared to CD200(neg) fraction. At the functional level, CD200(pos) cells were prone to mineralize the extra-cellular matrix in vitro after sole addition of phosphates. In addition, osteogenic cues generated by bone morphogenetic protein 4 (BMP4) or BMP7 strongly induced CD200 expression. These data suggest that CD200 expression is related to commitment/differentiation towards the osteoblastic lineage. Immunohistochemistry of trephine bone marrow biopsies further corroborates the osteoblastic fate of CD200(pos) cells. However, when dexamethasone was used to direct osteogenic differentiation in vitro, CD200 was consistently down-regulated. As dexamethasone has anti-inflammatory properties, we assessed the effects of different immunological stimuli on CD200 expression. The pro-inflammatory cytokines interleukin-1β and tumour necrosis factor-α increased CD200 membrane expression but down-regulated osteoblastic gene expression suggesting an additional regulatory pathway of CD200 expression. Surprisingly, whatever the context, i.e. pro-inflammatory or pro-osteogenic, CD200 expression was down-regulated when nuclear-factor (NF)-κB was inhibited by chemical or adenoviral agents. In conclusion, CD200 expression by cultured BM MSCs can be induced by both osteogenic and pro-inflammatory cytokines through the same pathway: NF-κB.

The Effects of Endocrine Disruptors on Adipogenesis and Osteogenesis in Mesenchymal Stem Cells: A Review

Endocrine-disrupting chemicals (EDCs) are prevalent in the environment, and epidemiologic studies have suggested that human exposure is linked to chronic diseases, such as obesity and diabetes. In vitro experiments have further demonstrated that EDCs promote changes in mesenchymal stem cells (MSCs), leading to increases in adipogenic differentiation, decreases in osteogenic differentiation, activation of pro-inflammatory cytokines, increases in oxidative stress, and epigenetic changes. Studies have also shown alteration in trophic factor production, differentiation ability, and immunomodulatory capacity of MSCs, which have significant implications to the current studies exploring MSCs for tissue engineering and regenerative medicine applications and the treatment of inflammatory conditions. Thus, the consideration of the effects of EDCs on MSCs is vital when determining potential therapeutic uses of MSCs, as increased exposure to EDCs may cause MSCs to be less effective therapeutically. This review focuses on the adipogenic and osteogenic differentiation effects of EDCs as these are most relevant to the therapeutic uses of MSCs in tissue engineering, regenerative medicine, and inflammatory conditions. This review will highlight the effects of EDCs, including organophosphates, plasticizers, industrial surfactants, coolants, and lubricants, on MSC biology.

Optimization of mesenchymal stem cells (MSCs) delivery dose and route in mice with acute liver injury by bioluminescence imaging

PURPOSE

Both experimental and initial clinical studies have shown the therapeutic potential of mesenchymal stem cells (MSCs) in liver disease. Noninvasive tracking of MSCs could facilitate its clinical translation. The purpose of this study was to optimize MSCs delivery dose and route in mice with acute liver injury using bioluminescence imaging (BLI) to track the cells.

PROCEDURES

MSCs were labeled with the Luc2-mKate2 dual-fusion reporter gene (MSCs-R). The fate of MSCs-R was tracked through in vivo BLI after administration of different doses or delivery through different routes.

RESULTS

When delivered via the superior mesenteric vein (SMV), the high-dose (1.0 × 10(6) and 5.0 × 10(5)) group mice demonstrated high liver BLI signal but also had lethal portal vein embolization (PVE). By contrast, no PVE and its related death occurred in the low-dose (2.5 × 10(5)) group mice. Thus, 2.5 × 10(5) is the optimal delivery dose. Three delivery routes, i.e., inferior vena cava (IVC), SMV, and intrahepatic (IH) injection, were also systematically compared. After IVC infusion, MSCs-R were quickly trapped inside the lungs, and no detectable homing to the liver and other organs was observed. By IH injection, lung entrapment was bypassed, but MSCs-R distribution was only localized in the injection region of the liver. By contrast, after SMV infusion, MSCs-R were dispersedly distributed and stayed as long as 7-day posttransplantation in the liver. The in vivo imaging results were further validated by ex vivo imaging, digital subtraction angiography (DSA), and tissue analysis. Therefore, SMV is the optimal MSCs delivery route for liver disease.

CONCLUSIONS

Collectively, BLI, which could dynamically and quantitatively track cellular location and survival, is useful in determining MSCs transplantation parameters.

Fractal heterogeneity in minimal matrix models of scars modulates stiff-niche stem-cell responses via nuclear exit of a mechanorepressor

Scarring is a long-lasting problem in higher animals, and reductionist approaches could aid in developing treatments. Here, we show that copolymerization of collagen I with polyacrylamide produces minimal matrix models of scars (MMMS), in which fractal-fibre bundles segregate heterogeneously to the hydrogel subsurface. Matrix stiffens locally-as in scars-while allowing separate control over adhesive-ligand density. The MMMS elicits scar-like phenotypes from mesenchymal stem cells (MSCs): cells spread and polarize quickly, increasing nucleoskeletal lamin-A yet expressing the 'scar marker' smooth muscle actin (SMA) more slowly. Surprisingly, expression responses to MMMS exhibit less cell-to-cell noise than homogeneously stiff gels. Such differences from bulk-average responses arise because a strong SMA repressor, NKX2.5, slowly exits the nucleus on rigid matrices. NKX2.5 overexpression overrides rigid phenotypes, inhibiting SMA and cell spreading, whereas cytoplasm-localized NKX2.5 mutants degrade in well-spread cells. MSCs thus form a 'mechanical memory' of rigidity by progressively suppressing NKX2.5, thereby elevating SMA in a scar-like state.

In Vitro Differentiation of Human Umbilical Cord Blood CD133(+)Cells into Insulin Producing Cells in Co-Culture with Rat Pancreatic Mesenchymal Stem Cells

Objective

Pancreatic stroma plays an important role in the induction of pancreatic cells by the use of close range signaling. In this respect, we presume that pancreatic mesenchymal cells (PMCs) as a fundamental factor of the stromal niche may have an effective role in differentiation of umbilical cord blood cluster of differentiation 133⁺ (UCB-CD133⁺) cells into newly-formed β-cells in vitro.

Materials and Methods

This study is an experimental research. The UCB-CD133⁺cells were purified by magnetic activated cell sorting (MACS) and differentiated into insulin producing cells (IPCs) in co-culture, both directly and indirectly with rat PMCs. Immunocytochemistry and enzyme linked immune sorbent assay (ELISA) were used to determine expression and production of insulin and C-peptide at the protein level.

Results

Our results demonstrated that UCB-CD133⁺differentiated into IPCs. Cells in islet-like clusters with (out) co-cultured with rat pancreatic stromal cells produced insulin and C-peptide and released them into the culture medium at the end of the induction protocol. However they did not respond well to glucose challenges.

Conclusion

Rat PMCs possibly affect differentiation of UCB-CD133⁺cells into IPCs by increasing the number of immature β-cells.

Mesenchymal stem cells in the treatment of type 1 diabetes mellitus

Diabetes mellitus type 1 is a form of diabetes mellitus that results from the autoimmune destruction of insulin-producing beta cells in the pancreas. The current gold standard therapy for pancreas transplantation has limitations because of the long list of waiting patients and the limited supply of donor pancreas. Mesenchymal stem cells (MSCs), a relatively new potential therapy in various fields, have already made their mark in the young field of regenerative medicine. Recent studies have shown that the implantation of MSCs decreases glucose levels through paracrine influences rather than through direct transdifferentiation into insulin-producing cells. Therefore, these cells may use pro-angiogenic and immunomodulatory effects to control diabetes following the cotransplantation with pancreatic islets. In this review, we present and discuss new approaches of using MSCs in the treatment of diabetes mellitus type 1.

Appropriate nonwoven filters effectively capture human peripheral blood cells and mesenchymal stem cells, which show enhanced production of growth factors

Scaffolds, growth factors, and cells are three essential components in regenerative medicine. Nonwoven filters, which capture cells, provide a scaffold that localizes and concentrates cells near injured tissues. Further, the cells captured on the filters are expected to serve as a local supply of growth factors. In this study, we investigated the growth factors produced by cells captured on nonwoven filters. Nonwoven filters made of polyethylene terephthalate (PET), biodegradable polylactic acid (PLA), or chitin (1.2-22 μm fiber diameter) were cut out as 13 mm disks and placed into cell-capturing devices. Human mesenchymal stem cells derived from adipose tissues (h-ASCs) and peripheral blood cells (h-PBCs) were captured on the filter and cultured to evaluate growth factor production. The cell-capture rates strongly depended on the fiber diameter and the number of filter disks. Nonwoven filter disks were composed of PET or PLA fibers with fiber diameters of 1.2-1.8 μm captured over 70% of leukocytes or 90% of h-ASCs added. The production of vascular endothelial growth factor (VEGF), transforming growth factor β1, and platelet-derived growth factor AB were significantly enhanced by the h-PBCs captured on PET or PLA filters. h-ASCs on PLA filters showed significantly enhanced production of VEGF. These enhancements varied with the combination of the nonwoven filter and cells. Because of the enhanced growth factor production, the proliferation of human fibroblasts increased in conditioned medium from h-PBCs on PET filters. This device consisting of nonwoven filters and cells should be investigated further for possible use in the regeneration of impaired tissues.

The effects of human keratinocyte coculture on human adipose-derived stem cells

The potential for adipose-derived stem cells to differentiate into keratinocyte-like cells has recently been receiving attention, stemming from the hypothesis that a bioengineered skin may be manufactured from these readily available mesenchymal stem cells. This study was conducted to evaluate the influence of human keratinocyte non-contact coculture on hADSCs. Human epidermal keratinocytes and hADSCs obtained by lipoaspiration were cultured in keratinogenic growth media, which were divided into the following groups: human adipose-derived stem cell (hADSC) monoculture, non-contact coculture of hADSCs and human keratinocytes and keratinocyte monoculture. Cell proliferation was assessed, and keratogenicity was analysed through immunocytochemistry and polymerase chain reaction of early, intermediate and late keratogenic markers. hADSCs cocultured with keratinocytes displayed enhanced proliferation compared with the monoculture group. After a 7-day coculture period, immunohistochemistry and polymerase chain reaction findings revealed the presence of specific keratinocyte markers in the coculture group. This study demonstrates that hADSCs cocultured with keratinocytes have the capacity to transdifferentiate into keratinocyte lineage cells, and suggests that adipose tissue may be a source of keratinocytes that may further be used in structuring the bioengineered skin.

Effects of tricalcium silicate cements on osteogenic differentiation of human bone marrow-derived mesenchymal stem cells in vitro

Tricalcium silicate cements have been successfully employed in the biomedical field as bioactive bone and dentin substitutes, with widely acclaimed osteoactive properties. This research analyzed the effects of different tricalcium silicate cement formulations on the temporal osteoactivity profile of human bone marrow-derived mesenchymal stem cells (hMW-MSCs). These cells were exposed to four commercially available tricalcium silicate cement formulations in osteogenic differentiation medium. After 1, 3, 7 and 10 days, quantitative real-time polymerase chain reaction and Western blotting were performed to detect expression of the target osteogenic markers ALP, RUNX2, OSX, OPN, MSX2 and OCN. After 3, 7, 14 and 21 days, alkaline phosphatase assay was performed to detect changes in intracellular enzyme level. An Alizarin Red S assay was performed after 28 days to detect extracellular matrix mineralization. In the presence of tricalcium silicate cements, target osteogenic markers were downregulated at the mRNA and protein levels at all time points. Intracellular alkaline phosphatase enzyme levels and extracellular mineralization of the experimental groups were not significantly different from the untreated control. Quantitative polymerase chain reaction results showed increases in downregulation of RUNX2, OSX, MSX2 and OCN with increasing time of exposure to the tricalcium silicate cements, while ALP showed peak downregulation at day 7. For Western blotting, OSX, OPN, MSX2 and OCN showed increased downregulation with increased exposure time to the tested cements. Alkaline phosphatase enzyme levels generally declined after day 7. Based on these results, it is concluded that tricalcium silicate cements do not induce osteogenic differentiation of hBM-MSCs in vitro.

Biomimetic nanocomposites to control osteogenic differentiation of human mesenchymal stem cells

The design of biomimetic nanomaterials that can directly influence the behavior of cells and facilitate the regeneration of tissues and organs has become an active area of research. Here, the production of materials based on nano-hydroxyapatite composites in scaffolds with nanofibrous and nanoporous topographies, designed to mimic the native bone matrix for applications in bone tissue engineering, is reported. Human mesenchymal stem cells grown on these nanocomposites are stimulated to rapidly produce bone minerals in situ, even in the absence of osteogenic supplements in the cell-culture medium. Nanocomposites comprising type I collagen and nano-hydroxyapatite are found to be especially efficient at inducing mineralization. When subcutaneously implanted into nude mice, this biomimetic nanocomposite is able to form a new bone matrix within only two weeks. Furthermore, when the nanocomposite is enriched with human mesenchymal stem cells before implantation, development of the bone matrix is accelerated to within one week. To the best of the authors' knowledge, this study provides the first clear in vitro and in vivo demonstration of osteoinduction controlled by the material characteristics of a biomimetic nanocomposite. This approach can potentially facilitate the translation of de novo bone-formation technologies to the clinic.

Adenovirus-mediated transfer of VEGF into marrow stromal cells combined with PLGA/TCP scaffold increases vascularization and promotes bone repair in vivo

INTRODUCTION

Large osseous defect remains a serious clinical problem due to the lack of sufficient blood supply and it has been proposed that this situation can be relieved by accelerating the formation of new vessels in the process of bone defect repair. The aim of this study was to develop a new type of artificial bone by transferring the VEGF gene into marrow stromal cells (MSCs) and seeding them into a porous scaffold.

MATERIAL AND METHODS

An adenovirus vector was employed to transfer the VEGF gene into MSCs and expression of the exogenous gene was confirmed by ELISA. Next the transduced cells were seeded into a collagen I modified PLGA/TCP scaffold. The constructed new complex artificial bone was then assessed for biocompatibility in vitro and blood vessel formation and bone formation in vivo.

RESULTS

We found that adenovirus mediated VEGF gene transfer into MSCs sustained VEGF expression in MSCs for 3 weeks. Porous scaffold PLGA/TCP made by rapid prototyping technology exhibited improved biocompatibility resulting from crosslinking with collagen I. Furthermore, the in vivo study showed that large amounts of blood vessels were detected histologically 1 week after artificial bone implantation, and significant bone formation was detected 8 weeks after implantation.

CONCLUSIONS

Our findings suggest that gene transfer of VEGF into MSCs combined with PLGA/TCP scaffold enhances bone repair in vivo by promoting vascularization.

Macromolecular crowding amplifies adipogenesis of human bone marrow-derived mesenchymal stem cells by enhancing the pro-adipogenic microenvironment

The microenvironment plays a vital role in both the maintenance of stem cells in their undifferentiated state (niche) and their differentiation after homing into new locations outside this niche. Contrary to conventional in-vitro culture practices, the in-vivo stem cell microenvironment is physiologically crowded. We demonstrate here that re-introducing macromolecular crowding (MMC) at biologically relevant fractional volume occupancy during chemically induced adipogenesis substantially enhances the adipogenic differentiation response of human bone marrow-derived mesenchymal stem cells (MSCs). Both early and late adipogenic markers were significantly up-regulated and cells accumulated 25-40% more lipid content under MMC relative to standard induction cocktails. MMC significantly enhanced deposition of extracellular matrix (ECM), notably collagen IV and perlecan, a heparan sulfate proteoglycan. As a novel observation, MMC also increased the presence of matrix metalloproteinase -2 in the deposited ECM, which was concomitant with geometrical ECM remodeling typical of adipogenesis. This suggested a microenvironment that was richer in both matrix components and associated ligands and was conducive to adipocyte maturation. This assumption was confirmed by seeding undifferentiated MSCs on decellularized ECM deposited by adipogenically differentiated MSCs, Adipo-ECM. On Adipo-ECM generated under crowding, MSCs differentiated much faster under a classical differentiation protocol. This was evidenced throughout the induction time course, by a significant up-regulation of both early and late adipogenic markers and a 60% higher lipid content on MMC-generated Adipo-ECM in comparison to standard induction on tissue culture plastic. This suggests that MMC helps build and endow the nascent microenvironment with adipogenic cues. Therefore, MMC initiates a positive feedback loop between cells and their microenvironment as soon as progenitor cells are empowered to build and shape it, and, in turn, are informed by it to respond by attaining a stable differentiated phenotype if so induced. This work sheds new light on the utility of MMC to tune the microenvironment to augment the generation of adipose tissue from differentiating human MSCs.

CD146 expression on mesenchymal stem cells is associated with their vascular smooth muscle commitment

Bone marrow mesenchymal stem cells (MSCs) are plastic adherent cells that can differentiate into various tissue lineages, including osteoblasts, adipocytes and chondrocytes. However, this progenitor property is not shared by all cells within the MSC population. In addition, MSCs vary in their proliferation capacity and expression of markers. Because of heterogeneity of CD146 expression in the MSC population, we compared CD146^−/Low and CD146^High cells under clonal conditions and after sorting of the non-clonal cell population to determine whether this expression is associated with specific functions. CD146^−/Low and CD146^High bone marrow MSCs did not differ in colony-forming unit-fibroblast number, osteogenic, adipogenic and chondrogenic differentiation or in vitro haematopoietic-supportive activity. However, CD146^−/Low clones proliferated slightly but significantly faster than did CD146^High clones. In addition, a strong expression of CD146 molecule was associated with a commitment to a vascular smooth muscle cell (VSMC) lineage characterized by a strong up-regulation of calponin-1 and SM22α expression and an ability to contract collagen matrix. Thus, within a bone marrow MSC population, certain subpopulations characterized by high expression of CD146, are committed towards a VSMC lineage.

Activation of human mesenchymal stem cells impacts their therapeutic abilities in lung injury by increasing interleukin (IL)-10 and IL-1RN levels

Acute respiratory distress syndrome (ARDS) is an important cause of morbidity and mortality, with no currently effective therapies. Several preclinical studies have shown that human mesenchymal stem cells (hMSCs) have therapeutic potential for patients with ARDS because of their immunomodulatory properties. The clinical use of hMSCs has some limitations, such as the extensive manipulation required to isolate the cells from bone marrow aspirates and the heterogeneity in their anti-inflammatory effect in animal models and clinical trials. The objective of this study was to improve the protective anti-inflammatory capacity of hMSCs by evaluating the consequences of preactivating hMSCs before use in a murine model of ARDS. We injected endotoxemic mice with minimally manipulated hMSCs isolated from the bone marrow of vertebral bodies with or without prior activation with serum from ARDS patients. Minimally manipulated hMSCs were more efficient at reducing lung inflammation compared with isolated and in vitro expanded hMSCs obtained from bone marrow aspirates. Where the most important effect was observed was with the activated hMSCs, independent of their source, which resulted in increased expression of interleukin (IL)-10 and IL-1 receptor antagonist (RN), which was associated with enhancement of their protective capacity by reduction of the lung injury score, development of pulmonary edema, and accumulation of bronchoalveolar lavage inflammatory cells and cytokines compared with nonactivated cells. This study demonstrates that a low manipulation during hMSC isolation and expansion increases, together with preactivation prior to the therapeutic use of hMSCs, would ensure an appropriate immunomodulatory phenotype of the hMSCs, reducing the heterogeneity in their anti-inflammatory effect.

Biophysical regulation of stem cell differentiation

Bone adaptation to its mechanical environment, from embryonic through adult life, is thought to be the product of increased osteoblastic differentiation from mesenchymal stem cells. In parallel with tissue-scale loading, these heterogeneous populations of multipotent stem cells are subject to a variety of biophysical cues within their native microenvironments. Bone marrow-derived mesenchymal stem cells-the most broadly studied source of osteoblastic progenitors-undergo osteoblastic differentiation in vitro in response to biophysical signals, including hydrostatic pressure, fluid flow and accompanying shear stress, substrate strain and stiffness, substrate topography, and electromagnetic fields. Furthermore, stem cells may be subject to indirect regulation by mechano-sensing osteocytes positioned to more readily detect these same loading-induced signals within the bone matrix. Such paracrine and juxtacrine regulation of differentiation by osteocytes occurs in vitro. Further studies are needed to confirm both direct and indirect mechanisms of biophysical regulation within the in vivo stem cell niche.

Paracrine effects and heterogeneity of marrow-derived stem/progenitor cells: relevance for the treatment of respiratory diseases

Stem cell-based treatment may represent a hope for the treatment of acute lung injury and pulmonary fibrosis, and other chronic lung diseases, such as cystic fibrosis, asthma and chronic obstructive pulmonary disease (COPD). It is well established in preclinical models that bone marrow-derived stem and progenitor cells exert beneficial effects on inflammation, immune responses and repairing of damage in virtually all lung-borne diseases. While it was initially thought that the positive outcome was due to a direct engraftment of these cells into the lung as endothelial and epithelial cells, paracrine factors are now considered the main mechanism through which stem and progenitor cells exert their therapeutic effect. This knowledge has led to the clinical use of marrow cells in pulmonary hypertension with endothelial progenitor cells (EPCs) and in COPD with mesenchymal stromal (stem) cells (MSCs). Bone marrow-derived stem cells, including hematopoietic stem/progenitor cells, MSCs, EPCs and fibrocytes, encompass a wide array of cell subsets with different capacities of engraftment and injured tissue-regenerating potential. The characterization/isolation of the stem cell subpopulations represents a major challenge to improve the efficacy of transplantation protocols used in regenerative medicine and applied to lung disorders.

Growing bone tissue-engineered niches with graded osteogenicity: an in vitro method for biomimetic construct assembly

The traditional bone tissue-engineering approach exploits mesenchymal stem cells (MSCs) to be seeded once only on three-dimensional (3D) scaffolds, hence, differentiated for a certain period of time and resulting in a homogeneous osteoblast population at the endpoint. However, after achieving terminal osteodifferentiation, cell viability is usually markedly compromised. On the other hand, naturally occurring osteogenesis results from the coexistence of MSC progenies at distinct differentiative stages in the same microenvironment. This diversification also enables long-term viability of the mature tissue. We report an easy and tunable in vitro method to engineer simple osteogenic cell niches in a biomimetic fashion. The niches were grown via periodic reseeding of undifferentiated MSCs on MSC/scaffold constructs, the latter undergoing osteogenic commitment. Time-fractioning of the seeded cell number during differentiation time of the constructs allowed graded osteogenic cell populations to be grown together on the same scaffolds (i.e., not only terminally differentiated osteoblasts). In such cell-dynamic systems, the overall differentiative stage of the constructs could also be tuned by varying the cell density seeded at each inoculation. In this way, we generated two different biomimetic niche models able to host good reservoirs of preosteoblasts and other osteoprogenitors after 21 culture days. At that time, the niche type resulting in 40.8% of immature osteogenic progenies and only 59.2% of mature osteoblasts showed a calcium content comparable to the constructs obtained with the traditional culture method (i.e., 100.03 ± 29.30 vs. 78.51 ± 28.50 pg/cell, respectively; p=not significant), the latter colonized only by fully differentiated osteoblasts showing exhausted viability. This assembly method for tissue-engineered constructs enabled a set of important parameters, such as viability, colonization, and osteogenic yield of the MSCs to be balanced on 3D scaffolds, thus achieving biomimetic in vitro models with graded osteogenicity, which are more complex and reliable than those currently used by tissue engineers.

Medical therapies with adult stem/progenitor cells (MSCs): a backward journey from dramatic results in vivo to the cellular and molecular explanations

There is currently great interest in the use of mesenchymal stem/stromal cells (MSCs) for the therapy of many diseases of animals and humans. However, we are still left with the serious challenges in explaining the beneficial effects of the cells. Hence, it is essential to work backward from dramatic results obtained in vivo to the cellular and molecular explanations in order to discover the secrets of MSCs. This review will focus on recent data that have changed the paradigms for understanding the therapeutic potentials of MSCs.

Therapeutic potential of bone marrow-derived mesenchymal stem cells for cutaneous wound healing

Despite advances in wound care, many wounds never heal and become chronic problems that result in significant morbidity and mortality to the patient. Cellular therapy for cutaneous wounds has recently come under investigation as a potential treatment modality for impaired wound healing. Bone marrow-derived mesenchymal stem cells (MSCs) are a promising source of adult progenitor cells for cytotherapy as they are easy to isolate and expand and have been shown to differentiate into various cell lineages. Early studies have demonstrated that MSCs may enhance epithelialization, granulation tissue formation, and neovascularization resulting in accelerated wound closure. It is currently unclear if these effects are mediated through cellular differentiation or by secretion of cytokines and growth factors. This review discusses the proposed biological contributions of MSCs to cutaneous repair and their clinical potential in cell-based therapies.

Current thoughts on the therapeutic potential of stem cell

Stem cells are considered as potential therapy for inflammatory disorders, tissue repair, and gene delivery, among others. The heterogeneity of a disease and the underlying disorder of a patient bring up the question on the method by which stem cells should be delivered. This summary discusses potential complex interactions among mediators at sites to tissue insults with stem cells. The chapter selects mesenchymal stem cells (MSCs) as a model, although the discussion is relevant to all stem cells. The review examines how MSCs and their differentiated cells can develop cross communication with soluble factors and cells within the region of tissue damage. Inflammatory cytokines, IL-1, TNFα, and TGFβ are selected to explain how they can affect the responses of MSCs, while predisposing the stem cells to oncogenic event. By understanding the varied functions of MSCs, one will be able to intervene to form a balance in functions, ultimately to achieve safety and efficient application. Cytokines can affect the expression of pluripotent genes such as REST and Oct-4. REST is a critical gene in the decision of a cell to express or repress neural genes. Since cytokines can affect microRNAs, the review incorporates this family of molecules as mediators of cytokine effects. IFNγ, although an inflammatory mediator, is central to the expression of MHC-II on MSCs. Therefore, it is included to discuss its role in the transplantation of stem cells across allogeneic barrier. In summary, this chapter discusses several potential areas that need to be addressed for safe and efficient delivery of stem cells, and argue for the incorporation of microenvironmental factors in the studies.

Age-related decline in osteoblastogenesis and 1α-hydroxylase/CYP27B1 in human mesenchymal stem cells: stimulation by parathyroid hormone

With aging, there is a decline in bone mass and in osteoblast differentiation of human mesenchymal stem cells (hMSCs) in vitro. Osteoblastogenesis can be stimulated with 1,25-dihydroxyvitamin D(3) [1,25(OH)(2) D(3) ] and, in some hMSCs, by the precursor 25-hydroxyvitamin D(3) (25OHD(3) ). CYP27B1/1α-hydroxylase activates 25OHD(3) and, to a variable degree, hMSCs express CYP27B1. In this study, we tested the hypotheses (i) that age affects responsiveness to 25OHD(3) and expression/activity of CYP27B1 in hMSCs and (ii) that parathyroid hormone (PTH) upregulates CYP27B1 in hMSCs, as it does in renal cells. There were age-related declines in osteoblastogenesis (n=8, P=0.0286) and in CYP27B1 gene expression (n=27, r= -0.498; P=0.008) in hMSCs. Unlike hMSCs from young subjects (≤50 years), hMSCs from older subjects (≥55 years) were resistant to 25OHD(3) stimulation of osteoblastogenesis. PTH1-34 (100 nm) provided hMSCs with responsiveness to 25OHD(3) (P=0.0313, Wilcoxon matched pairs test) and with two episodes of increased 1,25(OH)(2) D(3) synthesis, of cAMP response element binding protein (CREB) activation, and of CYP27B1 upregulation. Both increases in CYP27B1 expression by PTH were obliterated by CREB-siRNA or KG-501 (which specifically inhibits the downstream binding of activated CREB). Only the second period of CREB signaling was diminished by AG1024, an inhibitor of insulin-like growth factor-I receptor kinase. Thus, PTH stimulated hMSCs from elders with responsiveness to 25OHD(3) by upregulating expression/activity of CYP27B1 and did so through CREB and IGF-I pathways.

Hesperedin promotes MyoD-induced myogenic differentiation in vitro and in vivo

BACKGROUND AND PURPOSE

The bioflavonoid, hesperedin, promotes osteoblast differentiation in human mesenchymal stem cells, indicating an anabolic effect of hesperedin on bone metabolism. Murine bone marrow mesenchymal stem cells undergo myogenic differentiation as well as osteogenic differentiation. We therefore explored whether hesperedin modulates muscle cell differentiation.

EXPERIMENTAL APPROACH

Myoblast C2C12 cells were differentiated into muscle cells in the presence or absence of hesperedin. The effects of hesperedin on myogenic differentiation were determined by analysing specific muscle markers in vitro using reporter gene assays, immunoblotting, RT-PCR and DNA pull-down assays. In vivo, the effects of hesperedin were assessed using the freeze injury-induced muscle regeneration model in mice and daily injections of hesperedin for 6 days.

KEY RESULTS

Hesperedin promoted myogenic differentiation, in a dose-dependent manner, by increasing myogenin gene expression. MyoD-induced myogenin gene transcription was enhanced by hesperedin, as this bioflavonoid augmented the nuclear localization and myogenin promoter-binding of MyoD. In addition, hesperedin increased myogenin and muscle creatine kinase gene expression during myogenic differentiation from C3H10T1/2 mesenchymal stem cells in a MyoD-dependent manner and accelerated in vivo muscle regeneration induced by muscle injury.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that hesperedin promoted myogenic differentiation in vitro and in vivo through activation of MyoD-mediated myogenin expression, suggesting a beneficial role in promoting muscle regeneration, following injury.

Trichostatin a promotes cardiomyocyte differentiation of rat mesenchymal stem cells after 5-azacytidine induction or during coculture with neonatal cardiomyocytes via a mechanism independent of histone deacetylase inhibition

This study was to investigate the effect of trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, on cardiac differentiation of bone marrow mesenchymal stem cells (MSCs) in vitro. Rat MSCs were isolated and divided into six groups: 1) control; 2) 5-azacytidine treatment (5-aza, 10 μM); 3) treatment with TSA (100, 300, and 500 nM); 4) treatment with 5-aza followed by incubation with TSA; 5) coculture with neonatal cardiomyocytes (CMs); and 6) treatment with TSA then coculture with CMs. HDAC activity was significantly inhibited in TSA-treated cells with the maximal inhibition after 24 h of exposure to TSA at 300 nM. No changes in HDAC activity were observed in control, 5-aza-treated, or coculture groups. Following 7 days of differentiation, the expression of early cardiac transcription factors GATA-4, NKx2.5, MEF2c, and cardiac troponin T (cTnT) was increased by 6-8 times in the cells in 5-aza-treated, coculture, or TSA-treated groups over control as determined using real-time PCR, immunofluorescence staining, and Western blotting. However, the percent cTnT-positive cells were dramatically different with 0.7% for control, 10% for 5-aza-treated, 25% for coculture, and 4% for TSA-treated group (500 nM). TSA treatment of the cells pretreated with 5-aza or cocultured with CMs dramatically increased the expression of GATA-4, NKx2.5, and MEF2c by 35-50 times over control. The cTnT protein expression was also significantly increased by over threefold by TSA treatment (500 nM) in both 5-aza-treated and coculture group over control. The percent cTnT-positive cells in both 5-aza-pre-treated and coculture groups were significantly increased by TSA treatment after 1 week of differentiation by up to 92.6% (from 10.3% to 19.8%) and 23.9% (from 24.5% to 30.2%), respectively. These data suggested that TSA enhanced the cardiac differentiation of MSCs after 5-aza induction or during coculture with CMs through a mechanism beyond the inhibition of HDAC activity.

A comparative study of neural and mesenchymal stem cell-based carriers for oncolytic adenovirus in a model of malignant glioma

Glioblastoma multiforme is a primary malignancy of the central nervous system that is universally fatal due to its disseminated nature. Recent investigations have focused on the unique tumor-tropic properties of stem cells as a novel platform for targeted delivery of anticancer agents to the brain. Neural stem cells (NSCs) and mesenchymal stem cells (MSCs) both have the potential to function as cell carriers for targeted delivery of a glioma restricted oncolytic virus to disseminated tumor due to their reported tumor tropism. In this study, we evaluated NSCs and MSCs as cellular delivery vehicles for an oncolytic adenovirus in the context of human glioma. We report the first preclinical comparison of the two cell lines and show that, while both stem cell lines are able to support therapeutic adenoviral replication intracellularly, the amount of virus released from NSCs was a log higher than the MSC (p < 0.001). Moreover, only virus loaded NSCs that were administered intracranially in an orthotopic glioma model significantly prolonged the survival of tumor bearing animals (median survival for NSCs 68.5 days vs 44 days for MSCs, p < 0.002). Loading oncolytic adenovirus into NSCs and MSCs also led to expression of both pro- and anti-inflammatory genes and decreased vector-mediated neuroinflammation. Our results indicate that, despite possessing a comparable migratory capacity, NSCs display superior therapeutic efficacy in the context of intracranial tumors. Taken together, these findings argue in favor of NSCs as an effective cell carrier for antiglioma oncolytic virotherapy.

Could metabolic syndrome, lipodystrophy, and aging be mesenchymal stem cell exhaustion syndromes?

One of the most important and complex diseases of modern society is metabolic syndrome. This syndrome has not been completely understood, and therefore an effective treatment is not available yet. We propose a possible stem cell mechanism involved in the development of metabolic syndrome. This way of thinking lets us consider also other significant pathologies that could have similar etiopathogenic pathways, like lipodystrophic syndromes, progeria, and aging. All these clinical situations could be the consequence of a progressive and persistent stem cell exhaustion syndrome (SCES). The main outcome of this SCES would be an irreversible loss of the effective regenerative mesenchymal stem cells (MSCs) pools. In this way, the normal repairing capacities of the organism could become inefficient. Our point of view could open the possibility for a new strategy of treatment in metabolic syndrome, lipodystrophic syndromes, progeria, and even aging: stem cell therapies.

Monitoring human mesenchymal stromal cell differentiation by electrochemical impedance sensing

BACKGROUND AIMS

For their wide mesodermal differentiation potential, mesenchymal stromal/stem cells (MSC) are attractive candidates for tissue engineering. However, standardized quality control assays monitoring differentiation that are non-invasive and continuous over time are lacking.

METHODS

We employed a non-invasive assay, using two different systems, to discriminate osteogenic and adipogenic differentiation of MSC by monitoring impedance. Fibroblasts and keratinocytes served as non-specific controls. Impedance profiles were recorded comparing MSC from bone marrow and adipose tissue, either non-induced or induced for osteogenesis or adipogenesis, for 5-14 days, and correlated with differentiation markers assessed by reverse transcription-quantitative polymerase chain reaction and Western blot. Additionally, differentiation modulating effects of extracellular matrix components were analyzed.

RESULTS

Adhesion and growth-related impedance profiles of non-induced MSC roughly resembled those of fibroblasts, whereas keratinocytes differed significantly. Distinct from that, osteogenic induction of MSC revealed initially rapid and continuously rising impedance, corresponding to mineralized calcium matrix formation. Conversely, adipogenic induction caused shallower initial slopes and eventually declining profiles, corresponding to more compact, adipocyte-like cells with numerous lipid vacuoles. Pre-coating with either collagen type I or IV apparently favored osteogenesis and fibronectin adipogenesis. Impedance recordings correlated well with the extent of differentiation evaluated by histochemical staining and protein and gene expression.

CONCLUSIONS

Overall, our data demonstrate that impedance profiling offers a basis for standardized real-time, non-invasive high-throughput screening of MSC properties. It enables further testing of the influence of diffusible factors or extracellular matrix composites on MSC differentiation or maintenance of stemness, thus substantiating therapeutic application.

The cell surface proteome of human mesenchymal stromal cells

Background

Multipotent human mesenchymal stromal cells (hMSCs) are considered as promising biological tools for regenerative medicine. Their antibody-based isolation relies on the identification of reliable cell surface markers.

Methodology/Principal Findings

To obtain a comprehensive view of the cell surface proteome of bone marrow-derived hMSCs, we have developed an analytical pipeline relying on cell surface biotinylation of intact cells using cell impermeable, cleavable sulfo-NHS-SS-biotin to enrich the plasma membrane proteins and mass spectrometry for identification with extremely high confidence. Among the 888 proteins identified, we found ≈200 bona fide plasma membrane proteins including 33 cell adhesion molecules and 26 signaling receptors. In total 41 CD markers including 5 novel ones (CD97, CD112, CD239, CD276, and CD316) were identified. The CD markers are distributed homogenously within plastic-adherent hMSC populations and their expression is modulated during the process of adipogenesis or osteogenesis. Moreover, our in silico analysis revealed a significant difference between the cell surface proteome of hMSCs and that of human embryonic stem cells reported previously.

Conclusions/Significance

Collectively, our analytical methods not only provide a basis for further studies of mechanisms maintaining the multipotency of hMSCs within their niches and triggering their differentiation after signaling, but also a toolbox for a refined antibody-based identification of hMSC populations from different tissues and their isolation for therapeutic intervention.