A comprehensive review on mesenchymal stem cell growth and senescence

Stem cell-based therapy for fibrotic diseases: mechanisms and pathways

Fibrosis is a pathological process, that could result in permanent scarring and impairment of the physiological function of the affected organ; this condition which is categorized under the term organ failure could affect various organs in different situations. The involvement of the major organs, such as the lungs, liver, kidney, heart, and skin, is associated with a high rate of morbidity and mortality across the world. Fibrotic disorders encompass a broad range of complications and could be traced to various illnesses and impairments; these could range from simple skin scars with beauty issues to severe rheumatologic or inflammatory disorders such as systemic sclerosis as well as idiopathic pulmonary fibrosis. Besides, the overactivation of immune responses during any inflammatory condition causing tissue damage could contribute to the pathogenic fibrotic events accompanying the healing response; for instance, the inflammation resulting from tissue engraftment could cause the formation of fibrotic scars in the grafted tissue, even in cases where the immune system deals with hard to clear infections, fibrotic scars could follow and cause severe adverse effects. A good example of such a complication is post-Covid19 lung fibrosis which could impair the life of the affected individuals with extensive lung involvement. However, effective therapies that halt or slow down the progression of fibrosis are missing in the current clinical settings. Considering the immunomodulatory and regenerative potential of distinct stem cell types, their application as an anti-fibrotic agent, capable of attenuating tissue fibrosis has been investigated by many researchers. Although the majority of the studies addressing the anti-fibrotic effects of stem cells indicated their potent capabilities, the underlying mechanisms, and pathways by which these cells could impact fibrotic processes remain poorly understood. Here, we first, review the properties of various stem cell types utilized so far as anti-fibrotic treatments and discuss the challenges and limitations associated with their applications in clinical settings; then, we will summarize the general and organ-specific mechanisms and pathways contributing to tissue fibrosis; finally, we will describe the mechanisms and pathways considered to be employed by distinct stem cell types for exerting anti-fibrotic events.

Effects of royal jelly on the antisenescence, mitochondrial viability and osteogenic differentiation capacity of umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that have the ability to self-renew and regulate paracrine signalling and immune system processes. MSCs have extensive clinical applications in regeneration, functional reconstruction and cellular therapies. However, studies are needed to discover ways to improve the properties of MSCs, such as differentiation, and prevent senescence in culture, which are both very important for cell therapies. Royal jelly (RJ) is a nutritional substance produced by worker bees that contains a substantial amounts of proteins that are beneficial for cell growth and proliferation. RJ is widely used in traditional medicine today, and due to the specific components in its content, it has been reported to have antioxidant, antiproliferative, antimicrobial, neuroprotective, anti-inflammatory, immunomodulatory and anti-ageing properties. In our study, human Wharton's jelly mesenchymal stem cells (WJ-MSCs) derived from umbilical cord matrix were grown in culture medium supplemented with RJ. The control group comprised minimum essential medium (MEM) and 10% foetal bovine serum (FBS); RJ groups were formed using MEM, 10% FBS and 0.075 mg/ml or 0.150 mg/ml RJ. In our study, we evaluated the effect of RJ on WJ-MSC growth by MTT assay, proliferating cell nuclear antigen ELISA, β-galactosidase activity assay, MitoTracker Green staining and differentiation tests in adipogenic, osteogenic and chondrogenic cell lines. It was observed that the number of mitochondria increased, senescence decreased and osteogenic differentiation increased after differentiation induction after the addition of RJ to MSC culture. In general, the results of this study indicate that WJ-MSCs enhance mitochondrial numbers and important cellular activities, such as antisenescence and osteogenic differentiation, and with increasing evidence from further studies, RJ supplementation may be found beneficial for the use of MSCs in bone engineering regenerative medicine or cell therapy.

A new option for bone regeneration: a rapid methodology for cellularization of allograft with human bone marrow stromal cells with in vivo bone-forming potential

The treatment of severe musculoskeletal injuries, such as loss of bone tissue and consolidation disorders, requires bone transplantation, and the success of this bone reconstruction depends on the grafts transplant's osteogenic, osteoconductive, and osteoinductive properties. Although the gold standard is autograft, it is limited by availability, morbidity, and infection risk. Despite their low capacity for osteoinduction and osteogenesis, decellularized bone allografts have been used in the search for alternative therapeutic strategies to improve bone regeneration. Considering that bone marrow stromal cells (BMSCs) are responsible for the maintenance of bone turnover throughout life, we believe that associating BMSCs with allograft could produce a material that is biologically similar to autologous bone graft. For this reason, this study evaluated the osteogenic potential of bone allograft cellularized with BMSCs. First, BMSC was characterized and allograft decellularization was confirmed by histology, scanning electron microscopy, and DNA quantification. Subsequently, the BMSCs and allografts were associated and evaluated for adhesion, proliferation, and in vitro and in vivo osteogenic potential. We demonstrated that, after 2 hours, BMSCs had already adhered to the surface of allografts and remained viable for 14 days. In vitro osteogenic assays indicated increased osteogenic potential of allografts compared with beta-tricalcium phosphate (β-TCP). In vivo transplantation assays in immunodeficient mice confirmed the allograft's potential to induce bone formation, with significantly better results than β-TCP. Finally, our results indicate that allograft can provide structural support for BMSC adhesion, offering a favorable microenvironment for cell survival and differentiation and inducing new bone formation. Taken together, our data indicate that this rapid methodology for cellularization of allograft with BMSCs might be a new therapeutic alternative in regenerative medicine and bone bioengineering.

Mass Cytometry as a Tool for Investigating Senescence in Multiple Model Systems

Cellular senescence is a durable cell cycle arrest as a result of the finite proliferative capacity of cells. Senescence responds to both intrinsic and extrinsic cellular stresses, such as aging, mitochondrial dysfunction, irradiation, and chemotherapy. Here, we report on the use of mass cytometry (MC) to analyze multiple model systems and demonstrate MC as a platform for senescence analysis at the single-cell level. We demonstrate changes to p16 expression, cell cycling fraction, and histone tail modifications in several established senescent model systems and using isolated human T cells. In bone marrow mesenchymal stromal cells (BMSCs), we show increased p16 expression with subsequent passage as well as a reduction in cycling cells and open chromatin marks. In WI-38 cells, we demonstrate increased p16 expression with both culture-induced senescence and oxidative stress-induced senescence (OSIS). We also use Wanderlust, a trajectory analysis tool, to demonstrate how p16 expression changes with histone tail modifications and cell cycle proteins. Finally, we demonstrate that repetitive stimulation of human T cells with CD3/CD28 beads induces an exhausted phenotype with increased p16 expression. This p16-expressing population exhibited higher expression of exhaustion markers such as EOMES and TOX. This work demonstrates that MC is a useful platform for studying senescence at a single-cell protein level, and is capable of measuring multiple markers of senescence at once with high confidence, thereby improving our understanding of senescent pathways.

TLR4 downregulation by the RNA-binding protein PUM1 alleviates cellular aging and osteoarthritis

Dysfunction of mRNA or RNA-binding proteins (RBPs) causes cellular aging and age-related degenerative diseases; however, information regarding the mechanism through which RBP-mediated posttranscriptional regulation affects cellular aging and related disease processes is limited. In this study, PUM1 was found to be associated with the self-renewal capacity and aging process of human mesenchymal stem cells (MSC). PUM1 interacted with the 3'-untranslated region of Toll-like receptor 4 (TLR4) to suppress TLR4 mRNA translation and regulate the activity of nuclear factor-κB (NF-κB), a master regulator of the aging process in MSCs. PUM1 overexpression protected MSCs against H₂O₂-induced cellular senescence by suppressing TLR4-mediated NF-κB activity. TLR4-mediated NF-κB activation is a key regulator in osteoarthritis (OA) pathogenesis. PUM1 overexpression enhanced the chondrogenic potential of MSCs even under the influence of inflammation-inducing factors, such as lipopolysaccharide (LPS) or interleukin-1β (IL-1β), whereas the chondrogenic potential was reduced following the PUM1 knockdown-mediated TLR4 activation. PUM1 levels decreased under inflammatory conditions in vitro and during OA progression in human and mouse disease models. PUM1 knockdown in human chondrocytes promoted chondrogenic phenotype loss, whereas PUM1 overexpression protected the cells from inflammation-mediated disruption of the chondrogenic phenotype. Gene therapy using a lentiviral vector encoding mouse PUM1 showed promise in preserving articular cartilage integrity in OA mouse models. In conclusion, PUM1 is a novel suppressor of MSC aging, and the PUM1-TLR4 regulatory axis represents a potential therapeutic target for OA.

A Novel 3D Culture System Using a Chitin-Based Polysaccharide Material Produces High-Quality Allogeneic Human UCMSCs with Dispersed Sphere Morphology

Mesenchymal stem cell (MSC) transplantation, in particular allogeneic transplantation, is a promising therapy for a variety of diseases. However, before performing allograft treatment it is necessary to find suitable donors, establish culture methods that maintain cell quality, and reduce cell production costs. Here, we present a new method of producing allogeneic MSCs combining human umbilical cord-derived mesenchymal stem cells (UCMSCs) and chitin-based polysaccharide fibers (Cellhesion^® MS). UCMSC numbers significantly increased, and cells grew as dispersed spheres on Cellhesion^® MS. Subsequent biological analyses showed that the expression levels of stemness-related and migration-related genes were significantly upregulated, including octamer-binding transcription factor 4 (OCT4), Nanog homeobox (NANOG), and C-X-C chemokine receptor type 4 (CXCR4). The secretion levels of paracrine factors such as prostaglandin E2 (PGE₂), TNFα-stimulating gene (TSG)-6, fibroblast growth factor 2 (bFGF), and Angiogenin (Ang) from UCMSCs using Cellhesion^® MS were significantly higher than with microcarrier and U-bottom plate culture. In addition, culture supernatant from UCMSCs with Cellhesion^® MS had better angiogenic potential than that from monolayer cultured UCMSCs. Furthermore, we succeeded in a scaled-up culture of UCMSCs with Cellhesion^® MS using a closed culture bag. Therefore, Cellhesion^® MS is a key material for producing high-quality UCMSCs in a three-dimensional (3D) culture system.

Exploring microenvironment strategies to delay mesenchymal stem cell senescence

Mesenchymal stem cells (MSCs) have recently emerged as an important candidate for cell therapy and tissue regeneration. However, some limitations in translational research and therapies still exist, such as insufficient cell supply, inadequate differentiation potential, and decreased immune capacity, all of which result from replicative senescence during long-term in vitro culture. In vitro, stem cells lack a protective microenvironment owing to the absence of physical and biochemical cues compared with the in vivo niche, which provides dynamic physicochemical and biological cues. This difference results in accelerated aging after long-term in vitro culture. Therefore, it remains a great challenge to delay replicative senescence in culture. Constructing a microenvironment to delay replicative senescence of MSCs by maintaining their phenotypes, properties, and functions is a feasible strategy to solve this problem and has made measurable progress both in preclinical studies and clinical trials. Here, we review the current knowledge on the characteristics of senescent MSCs, explore the molecular mechanisms of MSCs senescence, describe the niche of MSCs, and discuss some current microenvironment strategies to delay MSCs replicative senescence that can broaden their range of therapeutic applications.

Long term expansion profile of mesenchymal stromal cells at protein nanosheet-stabilised bioemulsions for next generation cell culture microcarriers

Tremendous progress in the identification, isolation and expansion of stem cells has allowed their application in regenerative medicine and tissue engineering, and their use as advanced in vitro models. As a result, stem cell manufacturing increasingly requires scale up, parallelisation and automation. However, solid substrates currently used for the culture of adherent cells are poorly adapted for such applications, owing to their difficult processing from cell products, relatively high costs and their typical reliance on difficult to recycle plastics and microplastics. In this work, we show that bioemulsions formed of microdroplets stabilised by protein nanosheets displaying strong interfacial mechanics are well-suited for the scale up of adherent stem cells such as mesenchymal stromal cells (MSCs). We demonstrate that, over multiple passages (up to passage 10), MSCs retain comparable phenotypes when cultured on such bioemulsions, solid microcarriers (Synthemax II) and classic 2D tissue culture polystyrene. Phenotyping (cell proliferation, morphometry, flow cytometry and differentiation assays) of MSCs cultured for multiple passages on these systems indicate that, although stemness is lost at late passages when cultured on these different substrates, stem cell phenotypes remained comparable between different culture conditions, at any given passage. Hence our study validates the use of bioemulsions for the long term expansion of adherent stem cells and paves the way to the design of novel 3D bioreactors based on microdroplet microcarriers.

Intravenous administration of allogeneic Wharton jelly-derived mesenchymal stem cells for treatment of dogs with congestive heart failure secondary to myxomatous mitral valve disease

OBJECTIVE

To evaluate whether mesenchymal stem cells (MSCs) can be safely administered IV to dogs with congestive heart failure (CHF) secondary to myxomatous mitral valve disease (MMVD) to improve cardiac function and prolong survival time.

ANIMALS

10 client-owned dogs with CHF secondary to MMVD.

PROCEDURES

Dogs with an initial episode of CHF secondary to MMVD were enrolled in a double-blind, placebo-controlled clinical trial. Five dogs in the MSC group received allogeneic Wharton jelly-derived MSCs (2 × 10⁶ cells/kg, IV), and 5 dogs in the placebo group received a 1% solution of autologous serum (IV) for 3 injections 3 weeks apart. Cell-release criteria included trilineage differentiation, expression of CD44 and CD90 and not CD34 and major histocompatability complex class II, normal karyotype, and absence of contamination by pathogenic microorganisms. Patients were followed for 6 months or until death or euthanasia. Echocardiographic data, ECG findings, serum cardiac biomarker concentrations, CBC, and serum biochemical analysis results were obtained prior to and 4 hours after the first injection and every 3 months after the final injection.

RESULTS

Lymphocyte and eosinophil counts decreased significantly 4 hours after injection, and monocytes decreased significantly only in dogs that received an MSC injection. No significant differences were seen in the echocardiographic variables, ECG results, serum cardiac biomarker concentrations, survival time, and time to first diuretic drug dosage escalation between the 2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE

This study showed that MSCs can be easily collected from canine Wharton jelly as an allogeneic source of MSCs and can be safely delivered IV to dogs with CHF secondary to MMVD.

Cellhesion VP enhances the immunomodulating potential of human mesenchymal stem cell-derived extracellular vesicles

Mesenchymal stem cell (MSC) transplantation is a promising therapy for regenerative medicine. However, MSCs grown under two-dimensional (2D) culture conditions differ significantly in cell shape from those in the body, with downregulated stemness genes and secretion of paracrine factors. Here, we evaluated the effect of 3D culture using Cellhesion VP, a water-insoluble material composed of chitin-based polysaccharide fibers, on the characteristics of human Wharton's jelly-derived MSCs (hMSCs). Cellhesion VP significantly increased cell proliferation after retrieval. Transcriptome analyses suggested that genes involved in cell stemness, migration ability, and extracellular vesicle (EV) production were enhanced by 3D culture. Subsequent biochemical analyses showed that the expression levels of stemness genes including OCT4, NANOG, and SSEA4 were upregulated and migration capacity was elevated in 3D-cultured hMSCs. In addition, EV production was significantly elevated in 3D cells, which contained a distinct protein profile from 2D cells. Gene and drug connectivity analyses revealed that the 2D and 3D EVs had similar functions as immunomodulators; however, 3D EVs had completely distinct therapeutic profiles for various infectious and metabolic diseases based on activation of disease-associated signaling pathways. Therefore, EVs from Cellhesion VP-primed hMSCs offer a new treatment for immune and metabolic diseases.

Use of a novel Screen-Enrich-Combine(-biomaterials) Circulating System to fill a 3D-printed open Ti6Al4V frame with mesenchymal stem cells/β-tricalcium phosphate to repair complex anatomical bone defects in load-bearing areas

Background

Repairing complex anatomical load-bearing bone defects is difficult because it requires the restoration of the load-bearing function, reconstructing the anatomical shape, and repair by regenerated bone. We previously developed a Screen–Enrich–Combine(-biomaterials) Circulating System (SECCS) for rapid intraoperative enrichment of autologous bone marrow mesenchymal stem cells (MSCs) to enhance the osteogenic ability of porous bone substitutes. In this study, we prepared a 3D-printed Ti6A14V macroporous frame matching the defect shape to provide early load-bearing support and evaluated the efficacy of filling the frame with SECCS-processed MSCs/beta tricalcium phosphate (β-TCP) for long-term bone growth.

Methods

Fifteen 2-year-old goats were involved in this study, and the lateral part of their distal femur was removed by an electric saw and was fitted by a matching electron beam melting technology-prepared (EBM) Ti6Al4V frame. Three types of frames, filled with nothing, pure porous β-TCP, or SECCS-processed MSCs/β-TCP, were fixed onto the defect site. Repair efficacy was evaluated by X-ray radiography, computed tomography (CT), histology, and histomorphometry.

Results

In the basic regular hexagon printing unit, the combined side width (w) and the inscribed circle diameter (d) determines the printing frame’s mechanical strength. The compressive load was significantly higher for w=1.9 mm, d=4.4 mm than for w=1.7 mm, d=4.0 mm or w=2.0 mm, d=5.0 mm (P<0.05). The EBM-prepared Ti6Al4V defect-matched frame was well maintained 9 months after implantation. The MSCs successfully adhered to the wall of the porous β-TCP in the SECCS-processed group and had spread fully in the test samples. Each goat in the MSCs/β-TCP–the filled group, had approximately 31,321.7±22,554.7 of MSCs and a larger area of new bone growth inside the frame than the control and blank areas groups.

Conclusions

Filling the 3D-printed Ti6Al4V large-aperture frame with osteogenic materials achieved biological reconstruction over a larger area of regenerated bone to repair complex anatomical weight-bearing bone defects under the condition of early frame-supported load bearing. MSCs/β-TCP prepared by SECCS can be used as a filling material for this type of bone defect to obtain more efficacious bone repair.

Primary Cilia as a Biomarker in Mesenchymal Stem Cells Senescence: Influencing Osteoblastic Differentiation Potency Associated with Hedgehog Signaling Regulation

Bone tissue engineering-based therapy for bone lesions requires the expansion of seeding cells, such as autologous mesenchymal stem cells (MSCs). A major obstacle to this process is the loss of the phenotype and differentiation capacity of MSCs subjected to passage. Recent studies have suggested that primary cilia, primordial organelles that transduce multiple signals, particularly hedgehog signals, play a role in senescence. Therefore, we explored the relationships among senescence, primary cilia, and hedgehog signaling in MSCs. Ageing of MSCs by expansion in vitro was accompanied by increased cell doubling time. The osteogenic capacity of aged MSCs at passage 4 was compromised compared to that of primary cells. P4 MSCs exhibited reductions in the frequency and length of primary cilia associated with decreased intensity of Arl13b staining on cilia. Senescence also resulted in downregulation of the expression of hedgehog components and CDKN2A. Suppression of ciliogenesis reduced the gene expression of both Gli1, a key molecule in the hedgehog signaling pathway and ALP, a marker of osteoblastic differentiation. This study demonstrated that the senescence of MSCs induced the loss of osteoblastic differentiation potency and inactivated hedgehog signaling associated with attenuated ciliogenesis, indicating that primary cilia play a mediating role in and are biomarkers of MSC senescence; thus, future antisenescence strategies involving manipulation of primary cilia could be developed.

Depletion of SNRNP200 inhibits the osteo-/dentinogenic differentiation and cell proliferation potential of stem cells from the apical papilla

BACKGROUND

Tissue regeneration mediated by mesenchymal stem cells (MSCs) is deemed a desirable way to repair teeth and craniomaxillofacial tissue defects. Nevertheless, the molecular mechanisms about cell proliferation and committed differentiation of MSCs remain obscure. Previous researches have proved that lysine demethylase 2A (KDM2A) performed significant function in the regulation of MSC proliferation and differentiation. SNRNP200, as a co-binding factor of KDM2A, its potential effect in regulating MSCs' function is still unclear. Therefore, stem cells from the apical papilla (SCAPs) were used to investigate the function of SNRNP200 in this research.

METHODS

The alkaline phosphatase (ALP) activity assay, Alizarin Red staining, and osteogenesis-related gene expressions were used to examine osteo-/dentinogenic differentiation potential. Carboxyfluorescein diacetate, succinimidyl ester (CFSE) and cell cycle analysis were applied to detect the cell proliferation. Western blot analysis was used to evaluate the expressions of cell cycle-related proteins.

RESULTS

Depletion of SNRNP200 caused an obvious decrease of ALP activity, mineralization formation and the expressions of osteo-/dentinogenic genes including RUNX2, DSPP, DMP1 and BSP. Meanwhile, CFSE and cell cycle assays revealed that knock-down of SNRNP200 inhibited the cell proliferation and blocked cell cycle at the G2/M and S phase in SCAPs. In addition, it was found that depletion of SNRNP200 up-regulated p21 and p53, and down-regulated the CDK1, CyclinB, CyclinE and CDK2.

CONCLUSIONS

Depletion of SNRNP200 repressed osteo-/dentinogenic differentiation potentials and restrained cell proliferation through blocking cell cycle progression at the G2/M and S phase, further revealing that SNRNP200 has crucial effects on preserving the proliferation and differentiation potentials of dental tissue-derived MSCs.

Enhancement of bone marrow aspirate concentrate with local self-healing corticotomies

Bone marrow aspirate concentrate (BMAC) is a potentially useful biological product for bone regeneration. This study investigated whether BMAC can be enriched by local minor corticotomies. Five 4-month-old domestic pigs were used with each pig undergoing two minor corticotomies at one randomly-selected tibia. Two weeks after the operation, bone marrow was aspirated from both tibiae and processed into BMAC samples. The amount of mesenchymal stem cells (MSCs) and the concentration of several regenerative growth factors contained in BMAC, as well as the proliferative and osteogenic differentiation capacity of MSCs, were compared between the corticotomy and the control sides. Another four weeks later, healing of the corticotomies was evaluated by radiographic and histological methods. The results demonstrated that BMAC from the corticotomy side contained significantly more MSCs than the control side. MSCs from the corticotomy side also proliferated significantly faster and tended to have stronger osteogenic differentiation than those from the control side. In contrast, the protein concentration of TGF-β, BMP-2 and PDGF contained in BMAC was only minimally changed by the corticotomies. The corticotomies in all pigs healed uneventfully, showing complete obliteration of the corticotomy gaps on CT images. Comparison between the two sides showed that the corticotomy side had thicker and denser cortical bone and more abundant osteogenic cell differentiation than the control side. These findings suggest that the quantity and proliferative/osteogenic differentiation capacity of MSCs contained in local BMAC can be enhanced by minor corticotomies, and spontaneous healing of the corticotomy can be completed within 6 weeks of the operation.

A bone matrix-simulating scaffold to alleviate replicative senescence of mesenchymal stem cells during long-term expansion

Replicative senescence during in vitro augmentation, which is mostly induced by the loss of physiological microenvironment, hinders the application of mesenchymal stem cells (MSCs) in the clinic. Here, we investigated whether MSCs senescence could be prevented by bio-scaffold mimicking the natural tissue matrix. Human umbilical cord mesenchymal stem cells (hUCMSCs) exhibited a senescent phenotype during a long-term passage in the conventional culture dish. To fabricate the bone matrix, a naturally based matrix composed of nano-hydroxyapatite/chitosan/poly lactide-co-glycolide (nHA/CS/PLGA) was produced. Long-term passage resulted in an obvious increase in the expression of senescence markers and a reduction in the expression of master genes involved in tissue regeneration. Functional assay confirmed that nHA/CS/PLGA scaffold preserved the proliferation and differentiation of hUCMSCs even after being passaged 27 times. Moreover, in vivo ectopic bone formation assay revealed that the bone formation of hUCMSCs cultured on the nano-scaffolds for the long term was as robust as the cells in the early passage. In summary, our results demonstrate that nHA/CS/PLGA scaffold effectively preserves the stemness and youth of hUCMSCs in the long-term passage. Taken advantage of its compatibility and bioactivity, nHA/CS/PLGA scaffold is of great potential in large-scale expansion of MSCs for stem cell therapy and tissue engineering.

Recombinant Klotho Protects Human Periodontal Ligament Stem Cells by Regulating Mitochondrial Function and the Antioxidant System during H2O2-Induced Oxidative Stress

Human periodontal ligament stem cells (hPDLSCs) are a favourable source for tissue engineering, but oxidative stress conditions during cell culture and transplantation could affect stem cell viability and stemness, leading to failed regeneration. The aim of this study was to evaluate the antioxidant and protective effects of Klotho, an antiageing protein, against cell damage and the loss of osteogenesis in hPDLSCs in H₂O₂-induced oxidative environments. H₂O₂ was used as an exogenous reactive oxygen species (ROS) to induce oxidative stress. Recombinant human Klotho protein was administered before H₂O₂ treatment. Multitechniques were used to assess antioxidant activity, cell damage, and osteogenic ability of hPDLSCs in oxidative stress and the effects of Klotho on hPDLSCs. Mitochondrial function was analyzed by an electron microscopy scan of cellular structure, mitochondrial DNA copy number, and cellular oxygen consumption rate (OCR). Furthermore, we explored the pathway by which Klotho may function to regulate the antioxidant system. We found that pretreatment with recombinant human Klotho protein could enhance SOD activity and reduce intracellular oxidative stress levels. Klotho reduced H₂O₂-induced cellular damage and eventually maintained the osteogenic differentiation potential of hPDLSCs. Notably, Klotho promoted mitochondrial function and activated antioxidants by negatively regulating the PI3K/AKT/FoxO1 pathway. The findings suggest that Klotho protein enhanced the antioxidative ability of hPDLSCs and protected stem cell viability and stemness from H₂O₂-induced oxidative stress by restoring mitochondrial functions and the antioxidant system.

Enhancement of Mesenchymal Stem Cell-Driven Bone Regeneration by Resveratrol-Mediated SOX2 Regulation

Mesenchymal stem cells (MSCs) are an attractive cell source for regenerative medicine. However, MSCs age rapidly during long-term ex vivo culture and lose their therapeutic potential before they reach effective cell doses (ECD) for cell therapy. Thus, a prerequisite for effective MSC therapy is the development of cell culture methods to preserve the therapeutic potential during long-term ex vivo cultivation. Resveratrol (RSV) has been highlighted as a therapeutic candidate for bone disease. Although RSV treatment has beneficial effects on bone-forming cells, in vivo studies are lacking. The current study showed that long-term (6 weeks from primary culture date)-cultured MSCs with RSV induction retained their proliferative and differentiation potential despite reaching ECD. The mechanism of RSV action depends entirely on the SIRT1-SOX2 axis in MSC culture. In a rat calvarial defect model, RSV induction significantly improved bone regeneration after MSC transplantation. This study demonstrated an example of efficient MSC therapy for treating bone defects by providing a new strategy using the plant polyphenol RSV.

Spermatogenesis Recovery Potentials after Transplantation of Adipose Tissue-Derived Mesenchymal Stem Cells Cultured with Growth Factors in Experimental Azoospermic Mouse Models

Objective

Approximately 1% of the male population suffers from obstructive or non-obstructive azoospermia. Previous in vitro studies have successfully differentiated mesenchymal stem cells (MSCs) into germ cells. Because of immune- modulating features, safety, and simple isolation, adipose tissue-derived MSCs (AT-MSCs) are good candidates for such studies. However, low availability is the main limitation in using these cells. Different growth factors have been investigated to overcome this issue. In the present study, we aimed to comparatively assess the performance of AT-MSCs cultured under the presence or absence of three different growth factors, epidermal growth factor (EGF), leukemia inhibitory factor (LIF) and glial cell line-derived neurotrophic factor (GDNF), following transplantation in testicular torsion-detorsion mice

Materials and Methods

This was an experimental study in which AT-MSCs were first isolated from male Naval Medical Research Institute (NMRI) mice. Then, the mice underwent testicular torsion-detorsion surgery and received bromodeoxyuridine (BrdU)-labeled AT-MSCs into the lumen of seminiferous tubules. The transplanted cells had been cultured in different conditioned media, containing the three growth factors and without them. The expression of germ cell-specific markers was evaluated with real-time polymerase chain reaction (PCR) and western-blot. Moreover, immunohistochemical staining was used to trace the labeled cells.

Results

The number of transplanted AT-MSCs resided in the basement membrane of seminiferous tubules significantly increased after 8 weeks. The expression levels of Gcnf and Mvh genes in the transplanted testicles by AT-MSCs cultured in the growth factors-supplemented medium was greater than those in the control group (P<0.001 and P<0.05, respectively). The expression levels of the c-Kit and Scp3 genes did not significantly differ from the control group.

Conclusion

Our findings showed that the use of EGF, LIF and GDNF to culture AT-MSCs can be very helpful in terms of MSC survival and localization.

Anti-aging effects exerted by Tetramethylpyrazine enhances self-renewal and neuronal differentiation of rat bMSCs by suppressing NF-kB signaling

In order to improve the therapeutic effects of mesenchymal stem cell (MSC)-based therapies for a number of intractable neurological disorders, a more favorable strategy to regulate the outcome of bone marrow MSCs (bMSCs) was examined in the present study. In view of the wide range of neurotrophic and neuroprotective effects, Tetramethylpyrazine (TMP), a biologically active alkaloid isolated from the herbal medicine Ligusticum wallichii, was used. It was revealed that treatment with 30–50 mg/l TMP for 4 days significantly increased cell viability, alleviated senescence by suppressing NF-κB signaling, and promoted bMSC proliferation by regulating the cell cycle. In addition, 40–50 mg/l TMP treatment may facilitate the neuronal differentiation of bMSCs, verified in the present study by presentation of neuronal morphology and expression of neuronal markers: microtubule-associated protein 2 (MAP-2) and neuron-specific enolase (NSE). The quantitative real-time polymerase chain reaction (qRT-PCR) revealed that TMP treatment may promote the expression of neurogenin 1 (Ngn1), neuronal differentiation 1 (NeuroD) and mammalian achaete–scute homolog 1 (Mash1). In conclusion, 4 days of 40–50 mg/l TMP treatment may significantly delay bMSC senescence by suppressing NF-κB signaling, and enhancing the self-renewal ability of bMSCs, and their potential for neuronal differentiation.

Identification of senescent cells in multipotent mesenchymal stromal cell cultures: Current methods and future directions

Regardless of their tissue of origin, multipotent mesenchymal stromal cells (MSCs) are commonly expanded in vitro for several population doublings to achieve a sufficient number of cells for therapy. Prolonged MSC expansion has been shown to result in phenotypical, morphological and gene expression changes in MSCs, which ultimately lead to the state of senescence. The presence of senescent cells in therapeutic MSC batches is undesirable because it reduces their viability, differentiation potential and trophic capabilities. Additionally, senescent cells acquire senescence-activated secretory phenotype, which may not only induce apoptosis in the neighboring host cells following MSC transplantation, but also trigger local inflammatory reactions. This review outlines the current and promising new methodologies for the identification of senescent cells in MSC cultures, with a particular emphasis on non-destructive and label-free methodologies. Technologies allowing identification of individual senescent cells, based on new surface markers, offer potential advantage for targeted senescent cell removal using new-generation senolytic agents, and subsequent production of therapeutic MSC batches fully devoid of senescent cells. Methods or a combination of methods that are non-destructive and label-free, for example, involving cell size and spectroscopic measurements, could be the best way forward because they do not modify the cells of interest, thus maximizing the final output of therapeutic-grade MSC cultures. The further incorporation of machine learning methods has also recently shown promise in facilitating, automating and enhancing the analysis of these measured data.

Melatonin plays critical role in mesenchymal stem cell-based regenerative medicine in vitro and in vivo

Although stem cells have emerged as promising sources for regenerative medicine, there are many potential safety hazards for their clinical application, including tumorigenicity, an availability shortage, senescence, and sensitivity to toxic environments. Mesenchymal stem cells (MSCs) have various advantages compared to other stem cells, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); thus, MSCs have been intensely investigated in recent studies. However, they are placed in a harsh environment after isolation and transplantation, and the adverse microenvironment substantially reduces the viability and therapeutic effects of MSCs. Intriguingly, melatonin (MT), which is primarily secreted by the pineal organ, has been found to influence the fate of MSCs during various physiological and pathological processes. In this review, we will focus on the recent progress made regarding the influence of MT on stem cell biology and its implications for regenerative medicine. In addition, several biomaterials have been proven to significantly improve the protective effects of MT on MSCs by controlling the release of MT. Collectively, MT will be a promising agent for enhancing MSC activities and the regenerative capacity via the regulation of reactive oxygen species (ROS) generation and the release of immune factors in regenerative medicine.

[The mechanism of bone marrow-derived mesenchymal stem cells excessive senescence in severe aplastic anemia mouse model]

目的

探讨重型再生障碍性贫血（SAA）模型小鼠骨髓间充质干细胞（BM-MSC）过度衰老的机制。

方法

选择BALB/c小鼠40只，随机分为正常组20只、SAA组20只。应用白消安灌胃联合IFN-γ腹腔注射诱导建立SAA小鼠模型；分离培养两组小鼠的BM-MSC。观察BM-MSC细胞形态和细胞骨架；CCK-8和流式细胞术检测细胞增殖与细胞周期情况；比较衰老相关β-半乳糖苷酶（Senescence-associated β-Galactosidase, SA-β-gal）的染色阳性细胞比例；Western blot法检测mTOR蛋白的表达水平。

结果

正常组小鼠的BM-MSC细胞呈纺锤状、边界清晰，应力纤维平行排列、整齐；而SAA小鼠的BM-MSC细胞体积增大，呈平铺、边界不清状，应力纤维紊乱模糊。CCK-8结果显示，SAA小鼠的BM-MSC的增殖速率较正常组缓慢，在第2天开始差异有统计学意义（P<0.05）。SAA组小鼠BM-MSC的G₀/G₁期细胞比率[（77.461±1.567）%对（46.045±2.055）%，t=−34.384，P<0.001]、SA-β-gal阳性细胞比例[（75±11）%对（28±8）%，t=15.454，P<0.001]较正常组升高；SAA小鼠BM-MSC的mTOR表达水平高于正常小鼠。

结论

SAA小鼠模型中BM-MSC是衰老的MSC，且mTOR通路激活可能是导致其衰老发生的机制。

Direct Control of Stem Cell Behavior Using Biomaterials and Genetic Factors

Stem cells have recently emerged as an important candidate for cell therapy. However, some major limitations still exist such as a small quantity of cell supply, senescence, and insufficient differentiation efficiency. Therefore, there is an unmet need to control stem cell behavior for better clinical performance. Since native microenvironment factors including stem cell niche, genetic factors, and growth factors direct stem cell fate cooperatively, user-specified in vitro settings are required to understand the regulatory roles and effects of each factor, thereby applying the factors for improved cell therapy. Among others, various types of biomaterials and transfection method have been employed as key tools for development of the in vitro settings. This review focuses on the current strategies to improve stemness maintenance, direct differentiation, and reprogramming using biomaterials and genetic factors without any aids from additional biochemicals and growth factors.

Role of Prion protein-EGFR multimolecular complex during neuronal differentiation of human dental pulp-derived stem cells

Cellular prion protein (PrP^C) is expressed in a wide variety of stem cells in which regulates their self-renewal as well as differentiation potential. In this study we investigated the presence of PrP^C in human dental pulp-derived stem cells (hDPSCs) and its role in neuronal differentiation process. We show that hDPSCs expresses early PrP^C at low concentration and its expression increases after two weeks of treatment with EGF/bFGF. Then, we analyzed the association of PrP^C with gangliosides and EGF receptor (EGF-R) during neuronal differentiation process. PrP^C associates constitutively with GM2 in control hDPSCs and with GD3 only after neuronal differentiation. Otherwise, EGF-R associates weakly in control hDPSCs and more markedly after neuronal differentiation. To analyze the functional role of PrP^C in the signal pathway mediated by EGF/EGF-R, a siRNA PrP was applied to ablate PrP^C and its function. The treatment with siRNA PrP significantly prevented Akt and ERK1/2 phosphorylation induced by EGF. Moreover, siRNA PrP treatment significantly prevented neuronal-specific antigens expression induced by EGF/bFGF, indicating that cellular prion protein is essential for EGF/bFGF-induced hDPSCs differentiation. These results suggest that PrP^C interact with EGF-R within lipid rafts, playing a role in the multimolecular signaling complexes involved in hDPSCs neuronal differentiation.

Dicer1 downregulation by multiple myeloma cells promotes the senescence and tumor-supporting capacity and decreases the differentiation potential of mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMMSCs) facilitate the growth of multiple myeloma (MM) cells, but the underlying mechanisms remain unclear. This study demonstrates that the senescence of MM-MSCs significantly increased, as evidenced by a decrease in proliferation and increase in the number of cells positive for senescence-associated β-galactosidase activity. Senescent MM-MSCs displayed decreased differentiation potential and increased tumor-supporting capacity. Dicer1 knockdown in the MSCs of healthy controls promoted cellular senescence and tumor-supporting capacity, while decreasing the differentiation capacity. Dicer1 overexpression in MM-MSCs reversed the effects on differentiation and reduced cellular senescence. In addition, decreased expression of the microRNA-17 family was identified as a favorable element responsible for increasing senescence, with the expression of p21 increased in Dicer1 knockdown cells. Furthermore, we observed decreased expression of miR-93 and miR-20a in MM-MSCs, while upregulation of miR-93/miR-20a decreased cellular senescence, as evidenced by the increased p21 expression. Importantly, we found that myeloma cells could induce the senescence of MSCs from healthy controls, as observed from the decreased expression of Dicer1 and miR-93/miR-20a and increased expression of p21. Overall, MM cells downregulate Dicer1 in MSCs, which leads to senescence; in turn, senescent MSCs promote MM cell growth, which most likely contributes to disease progression.

Comparative characterization of SHED and DPSCs during extended cultivation in vitro

Dental pulp stem cells (DPSCs) and stem cells from human exfoliated deciduous teeth (SHED) are types of human dental tissue-derived mesenchymal stem cells (MSCs). These cells possess a capacity for self-renewal, multilineage differentiation potential and immunomodulatory functions. Previous studies have reported that DPSCs and SHED may be beneficial in regenerative treatments and immunotherapy. The substantial expansion of cells in vitro is a prerequisite to obtaining adequate cell numbers required for cell-based therapy. However, the regeneration and clinical potential of MSCs diminishes with long-term cell culture amplification. To assess the alterations in SHED and DPSCs characteristics that underlie cellular senescence and result from extended in vitro amplification, the biological properties of SHED and DPSCs at passages 4 (P4) and 20 (P20) were compared. The cells underwent senescence following serial expansion to P20, as determined by altered cell morphology, decreased proliferation and migration capacity, attenuated differentiation potential, elevated senescence-associated β-galactosidase (SA-β-gal)-positive rates and increased apoptosis. The phenotypic changes were also accompanied by a marked increase in the expression of p53, p21 and p16^Ink4a. The present study also identified that senescent DPSCs exhibited an increased number of positive cells in SA-β-gal staining and demonstrated varying expressions of p53, p21 and p16^Ink4a in comparison with SHED, indicating the involvement of diverse pathways in cellular senescence during long-term sequential in vitro culture and passage. Furthermore, at early and late passages, SHED exhibited a higher proliferation rate and osteogenic differentiation capability when compared with DPSCs. In addition, both cell types maintained their characteristic immunophenotype during long-term cultivation, while the expression levels of CD73 were higher in SHED at P20. The present study concluded that notable alterations were exhibited in SHED and DPSCs during the process of extensive expansion in vitro and the results may provide guidance for the selection of safe and effective expanded SHED and DPSCs for regenerative medicine and therapy.

SIRT1-dependent anti-senescence effects of cell-deposited matrix on human umbilical cord mesenchymal stem cells

Human umbilical cord-derived mesenchymal stem cells (UC-MSCs) are considered an attractive cell source for tissue regeneration. However, environmental oxidative stress can trigger premature senescence in MSCs and thus compromises their regenerative potential. Extracellular matrix (ECM) derived from MSCs has been shown to facilitate cell proliferation and multi-lineage differentiation. This investigation evaluated the effect of cell-deposited decellularized ECM (DECM) on oxidative stress-induced premature senescence in UC-MSCs. Sublethal dosages of H₂ O₂ , ranging from 50 μm to 200 μm, were used to induce senescence in MSCs. We found that DECM protected UC-MSCs from oxidative stress-induced premature senescence. When treated with H₂ O₂ at the same concentration, cell proliferation of DECM-cultured UC-MSCs was twofold higher than those on standard tissue culture polystyrene (TCPS). After exposure to 100 μm H₂ O₂ , fewer senescence-associated β-galactosidase-positive cells were observed on DECM than those on TCPS (17.6  ±  4.0% vs. 60.4  ±  6.2%). UC-MSCs cultured on DECM also showed significantly lower levels of senescence-related regulators, such as p16^INK4α and p21. Most importantly, DECM preserved the osteogenic differentiation potential of UC-MSCs with premature senescence. The underlying molecular mechanisms involved the silent information regulator type 1 (SIRT1)-dependent signalling pathway, confirmed by the fact that the SIRT1 inhibitor nicotinamide counteracted the DECM-mediated anti-senescent effect. Collagen type I, rather than fibronectin, partially contributed to the protective effect of decellularized matrix. These findings provide a new strategy of using stem cell-deposited matrix to overcome the challenge of cellular senescence and to facilitate the clinical application of MSCs in regenerative medicine. Copyright © 2017 John Wiley & Sons, Ltd.

The replicative senescent mesenchymal stem / stromal cells defect in DNA damage response and anti-oxidative capacity

Replicative senescence and potential malignant transformation are great limitations in the clinical application of bone marrow-derived mesenchymal stem / stromal cells (MSCs). An abnormal DNA damage response may result in genomic instability, which is an integral component of aging and tumorigenesis. However, the effect of aging on the DNA damage response in MSCs is currently unknown. In the present study, we evaluated the DNA damage response induced by oxidative stress and DNA double-strand breaks in human bone marrow-derived MSCs. After long-term cell culture, replicative senescent MSCs (sMSCs) were characterized by a poor proliferation rate, high senescence-associated β-galactosidase activity, and enhanced expression of P53 and P16. Features of the DNA damage response in these sMSCs were then compared with those from early-passage MSCs. The sMSCs were more sensitive to hydrogen peroxide and bleomycin treatment with respect to cell viability and apoptosis induction. Combined with the comet assay, γH2AX foci characterization and reactive oxygen species detection were used to demonstrate that the antioxidant and DNA repair ability of sMSCs are attenuated. This result could be explained, at least in part, by the downregulation of anti-oxidation and DNA repair genes, including Cu/Zn-SOD, GPX, CAT, OGG1, XRCC1, Ku70, BRCA2 and XRCC4. In conclusion, MSCs aging is associated with a reduction in the DNA repair and anti-oxidative capacity.

Developmental Programming: Impact of Prenatal Testosterone Excess on Steroidal Machinery and Cell Differentiation Markers in Visceral Adipocytes of Female Sheep

Prenatal testosterone (T)-treated female sheep manifest reduced adipocyte size and peripheral insulin resistance. The small adipocyte phenotype may reflect defects in adipogenesis and its steroidal machinery. To test whether prenatal T treatment from gestational days 30 to 90 alters the visceral adipose tissue (VAT) steroidal machinery and reduces adipocyte differentiation, we examined expression of the steroidogenic enzymes, steroid receptors, and adipocyte differentiation markers at fetal day 90 and postnatal ages 10 and 21 months. Because gestational T treatment increases fetal T and maternal insulin, the contributions of these were assessed by androgen receptor antagonist or insulin sensitizer cotreatment, either separately (at fetal day 90 and 21 months of age time points) or together (10 months of age). The effects on adipogenesis were assessed in the VAT-derived mesenchymal stem cells (AT-MSCs) from pre- and postpubertal time points to evaluate the effects of pubertal steroidal changes on adipogenesis. Our results show that VAT manifests potentially a predominant estrogenic intracrine milieu (increased aromatase and estrogen receptor α) and reduced differentiation markers at fetal day 90 and postnatal 21 months of age. These changes appear to involve both androgenic and metabolic pathways. Preliminary findings suggest that prenatal T treatment reduces adipogenesis, decreases expression of differentiation, and increases expression of commitment markers at both pre- and postpubertal time points. Together, these findings suggest that (1) increased commitment of AT-MSCs to adipocyte lineage and decreased differentiation to adipocytes may underlie the small adipocyte phenotype of prenatal T-treated females and (2) excess T-induced changes in steroidal machinery in the VAT likely participate in the programming/maintenance of this defect.

The Flavonoid Glabridin Induces OCT4 to Enhance Osteogenetic Potential in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are a promising tool for studying intractable diseases. Unfortunately, MSCs can easily undergo cellular senescence during in vitro expansion by losing stemness. The aim of this study was to improve the stemness and differentiation of MSCs by using glabridin, a natural flavonoid. Assessments of cell viability, cell proliferation, β-galactosidase activity, differentiation, and gene expression by reverse transcription PCR were subsequently performed in the absence or presence of glabridin. Glabridin enhanced the self-renewal capacity of MSCs, as indicated by the upregulation of the OCT4 gene. In addition, it resulted in an increase in the osteogenic differentiation potential by inducing the expression of osteogenesis-related genes such as DLX5 and RUNX2. We confirmed that glabridin improved the osteogenesis of MSCs with a significant elevation in the expression of OSTEOCALCIN and OSTEOPONTIN genes. Taken together, these results suggest that glabridin enhances osteogenic differentiation of MSCs with induction of the OCT4 gene; thus, glabridin could be useful for stem cell-based therapies.

Hepatic differentiation of mouse bone marrow‑derived mesenchymal stem cells using a novel 3D culture system

The development of novel culture systems that mimic the in vivo microenvironment may be beneficial for inducing the differentiation of stem cells and promoting liver function. In the present study, spheroid cultures and decellularized liver scaffolds (DLSs) were utilized to obtain differentiated hepatocyte-like cells. Mouse bone marrow (BM)-derived mesenchymal stem cells (MSCs) self-aggregated into spheroids under low-attachment conditions and implanted into the DLSs via a negative pressure suction device. The Albp-ZsGreen adenoviral vector was utilized for real-time monitoring of hepatocyte-like cell differentiation. To detect the differentiation stages of the MSCs, immunostaining of hepatocyte markers and functional analysis was performed. Compared with traditional 2D monolayer induction, mouse BM-MSCs spheroids and DLSs in 3D culture generated greater yields of mature, differentiated hepatocytes. In conclusion, this 3D culture system may provide a strategy for generating hepatocyte-like cells for portable liver micro-organs, and aid clinical hepatocyte transplantation and liver tissue engineering.

Effects of Lobeglitazone, a New Thiazolidinedione, on Osteoblastogenesis and Bone Mineral Density in Mice

BACKGROUND

Bone strength is impaired in patients with type 2 diabetes mellitus despite an increase in bone mineral density (BMD). Thiazolidinedione (TZD), a peroxisome proliferator activated receptor γ agonist, promotes adipogenesis, and suppresses osteoblastogenesis. Therefore, its use is associated with an increased risk of fracture. The aim of this study was to examine the in vitro and in vivo effects of lobeglitazone, a new TZD, on bone.

METHODS

MC3T3E1 and C3H10T1/2 cells were cultured in osteogenic medium and exposed to lobeglitazone (0.1 or 1 μM), rosiglitazone (0.4 μM), or pioglitazone (1 μM) for 10 to 14 days. Alkaline phosphatase (ALP) activity, Alizarin red staining, and osteoblast marker gene expression were analyzed. For in vivo experiments, 6-month-old C57BL/6 mice were treated with vehicle, one of two doses of lobeglitazone, rosiglitazone, or pioglitazone. BMD was assessed using a PIXImus2 instrument at the baseline and after 12 weeks of treatment.

RESULTS

As expected, in vitro experiments showed that ALP activity was suppressed and the mRNA expression of osteoblast marker genes RUNX2 (runt-related transcription factor 2) and osteocalcin was significantly attenuated after rosiglitazone treatment. By contrast, lobeglitazone at either dose did not inhibit these variables. Rosiglitazone-treated mice showed significantly accelerated bone loss for the whole bone and femur, but BMD did not differ significantly between the lobeglitazone-treated and vehicle-treated mice.

CONCLUSION

These findings suggest that lobeglitazone has no detrimental effects on osteoblast biology and might not induce side effects in the skeletal system.

Immune dysfunctionality of replicative senescent mesenchymal stromal cells is corrected by IFNγ priming

Industrial-scale expansion of mesenchymal stromal cells (MSCs) is often used in clinical trials, and the effect of replicative senescence on MSC functionality is of mechanistic interest. Senescent MSCs exhibit cell-cycle arrest, cellular hypertrophy, and express the senescent marker β-galactosidase. Although both fit and senescent MSCs display intact lung-homing properties in vivo, senescent MSCs acquire a significant defect in inhibiting T-cell proliferation and cytokine secretion in vitro. IFNγ does not upregulate HLA-DR on senescent MSCs, whereas its silencing did not reverse fit MSCs' immunosuppressive properties. Secretome analysis of MSC and activated peripheral blood mononuclear cell coculture demonstrate that senescent MSCs are significantly defective in up (vascular endothelial growth factor [VEGF], granulocyte colony-stimulating factor [GCSF], CXCL10, CCL2) or down (IL-1ra, IFNγ, IL-2r, CCL4, tumor necrosis factor-α, IL-5) regulating cytokines/chemokines. Unlike indoleamine 2,3 dioxygenase (IDO), silencing of CXCL9, CXCL10, CXCL11, GCSF, CCL2, and exogenous addition of VEGF, fibroblast growth factor-basic do not modulate MSCs' immunosuppressive properties. Kynurenine levels were downregulated in senescent MSC cocultures compared with fit MSC counterparts, and exogenous addition of kynurenine inhibits T-cell proliferation in the presence of senescent MSCs. IFNγ prelicensing activated several immunomodulatory genes including IDO in fit and senescent MSCs at comparable levels and significantly enhanced senescent MSCs' immunosuppressive effect on T-cell proliferation. Our results define immune functional defects acquired by senescent MSCs, which are reversible by IFNγ prelicensing.

Mitochondrial DNA Hypomethylation Is a Biomarker Associated with Induced Senescence in Human Fetal Heart Mesenchymal Stem Cells

Background. Fetal heart can regenerate to restore its normal anatomy and function in response to injury, but this regenerative capacity is lost within the first week of postnatal life. Although the specific molecular mechanisms remain to be defined, it is presumed that aging of cardiac stem or progenitor cells may contribute to the loss of regenerative potential. Methods. To study this aging-related dysfunction, we cultured mesenchymal stem cells (MSCs) from human fetal heart tissues. Senescence was induced by exposing cells to chronic oxidative stress/low serum. Mitochondrial DNA methylation was examined during the period of senescence. Results. Senescent MSCs exhibited flattened and enlarged morphology and were positive for the senescence-associated beta-galactosidase (SA-β-Gal). By scanning the entire mitochondrial genome, we found that four CpG islands were hypomethylated in close association with senescence in MSCs. The mitochondrial COX1 gene, which encodes the main subunit of the cytochrome c oxidase complex and contains the differentially methylated CpG island 4, was upregulated in MSCs in parallel with the onset of senescence. Knockdown of DNA methyltransferases (DNMT1, DNMT3a, and DNMT3B) also upregulated COX1 expression and induced cellular senescence in MSCs. Conclusions. This study demonstrates that mitochondrial CpG hypomethylation may serve as a critical biomarker associated with cellular senescence induced by chronic oxidative stress.

Senescence of mesenchymal stem cells (Review)

Mesenchymal stem cells (MSCs) have been used in cell-based therapy for various diseases, due to their immunomodulatory and inflammatory effects. However, the function of MSCs is known to decline with age, a process that is called senescence. To date, the process of MSC senescence remains unknown as in-depth understanding of the mechanisms involved in cellular senescence is lacking. First, senescent MSCs are so heterogeneous that not all of them express the same phenotypic markers. In addition, the genes and signaling pathways which regulate this process in MSCs are still unknown. Thus, an understanding of the molecular processes controlling MSC senescence is crucial to determining the drivers and effectors of age-associated MSC dysfunction. Moreover, the proper use of MSCs for clinical application requires a general understanding of the MSC aging process. Furthermore, such knowledge is essential for the development of therapeutic interventions that can slow or reverse age-related degenerative changes to enhance repair processes and maintain healthy function in aging tissues. To further clarify the properties of senescent cells, as well as to present significant findings from studies on the mechanisms of cellular aging, we summarize these biological features in the senescence of MSCs in this scenario. This review summarizes recent advances in our understanding of the markers and differentiation potential indicating MSC senescence, as well as factors affecting MSC senescence with particular emphasis on the roles of oxidative stress, intrinsic changes in telomere shortening, histone deacetylase and DNA methyltransferase, genes and signaling pathways and immunological properties.

3D culture increases pluripotent gene expression in mesenchymal stem cells through relaxation of cytoskeleton tension

Three‐dimensional (3D) culture has been shown to improve pluripotent gene expression in mesenchymal stem cells (MSCs), but the underlining mechanisms were poorly understood. Here, we found that the relaxation of cytoskeleton tension of MSCs in 3D culture was critically associated with the expressional up‐regulation of Nanog. Cultured in spheroids, MSCs showed decreased integrin‐based cell–matrix adhesion but increased cadherin‐based cell–cell interaction. Different from that in 2D culture, where MSCs exhibited branched and multiple‐directed F‐actin stress bundles at the cell edge and strengthened stress fibres transversing the cell body, MSCs cultured in spheroids showed compact cell body, relaxed cytoskeleton tension with very thin cortical actin filament outlining the cell, and increased expression of Nanog along with reduced levels of Suv39h1 (H3K9 methyltransferase) and H3K9me3. Notably, pharmaceutical inhibition of actin polymerization with cytochalasin D or silencing Suv39h1 expression with siRNA in 2D‐cultured MSCs elevated the expression of Nanog via H3K9 demethylation. Thus, our data suggest that 3D culture increases the expression of Nanog through the relaxation of actin cytoskeleton, which mediates reduced Suv39h1 and H3K9me3 levels.

Construction of bioengineered hepatic tissue derived from human umbilical cord mesenchymal stem cells via aggregation culture in porcine decellularized liver scaffolds

BACKGROUND

An individualized, tissue-engineered liver suitable for transplanting into a patient with liver disease would be of great benefit to the patient and the healthcare system. The tissue-engineered liver would possess the functions of the original healthy organ. Two fields of study, (i) using decellularized tissue as cell scaffolding, and (ii) stem cell differentiation into functional cells, are coming together to make this concept feasible. The decellularized liver scaffolds (DLS) can interact with cells to promote cell differentiation and signal transduction and three-dimensional (3D) stem cell aggregations can maintain the phenotypes and improve functions of stem cells after differentiation by undergoing cell-cell contact. Although the effects of DLS and stem cell aggregation culture have been intensively studied, few observations about the interaction between the two have been achieved.

METHODS

We established a method that combines the use of decellularized liver scaffolds and aggregation culture of MSCs (3D-DLS) and explored the effects of the two on hepatic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs) in bioengineered hepatic tissue.

RESULTS

A higher percentage of albumin-producing cells, higher levels of liver-specific transcripts, higher urea cycle-related transcripts, and lower levels of stem cell-specific transcripts were observed in the 3D-DLS group when compared to that of hUC-MSCs in monolayer culture (2D), aggregation culture (3D), monolayer on DLS culture (2D-DLS). The gene arrays also indicated that 3D-DLS induced the differentiation from the hUC-MSC phenotype to the PHH phenotype. Liver-specific proteins albumin, CK-18, and glycogen storage were highly positive in the 3D-DLS group. Albumin secretion and ammonia conversion to urea were more effective with a higher cell survival rate in the 3D-DLS group for 14 days.

CONCLUSION

This DLS and aggregation combination culture system provides a novel method to improve hepatic differentiation, maintain phenotype of hepatocyte-like cells and sustain survival for 14 days in vitro. This is a promising strategy to use to construct bioengineered hepatic tissue.

Poly-L-lysine Prevents Senescence and Augments Growth in Culturing Mesenchymal Stem Cells Ex Vivo

Mesenchymal stem cells (MSCs) possess great therapeutic potential. Efficient in vitro expansion of MSCs is however necessary for their clinical application. The extracellular matrix (ECM) provides structural and biochemical support to the surrounding cells, and it has been used as a coating substrate for cell culture. In this study, we have aimed to improve the functionality and stemness of MSCs during culture using poly-L-lysine (PLL). Functionality of MSCs was analysed by cell cycle analysis, differentiation assay, β-galactosidase staining, and RT-PCR. Furthermore, we assessed the global gene expression profile of MSCs on uncoated and PLL-coated plates. MSCs on PLL-coated plates exhibited a faster growth rate with increased S-phase and upregulated expression of the stemness markers. In addition, their osteogenic differentiation potential was increased, and genes involved in cell adhesion, FGF-2 signalling, cell cycle, stemness, cell differentiation, and cell proliferation were upregulated, compared to that of the MSCs cultured on uncoated plates. We also confirmed that MSCs on uncoated plates expressed higher β-galactosidase than the MSCs on PLL-coated plates. We demonstrate that PLL provides favourable microenvironment for MSC culture by reversing the replicative senescence. This method will significantly contribute to effective preparation of MSCs for cellular therapy.

Site-Specific Characteristics of Bone Marrow Mesenchymal Stromal Cells Modify the Effect of Aging on the Skeleton

Bone is a self-renewing tissue. Bone marrow mesenchymal stromal cells (BMSCs) are located in the adult skeleton and are believed to be involved in the maintenance of skeletal homeostasis throughout life. With increasing age, the ability of the skeleton to repair itself decreases, possibly due to the reduced functional capacity of BMSCs. Recent evidence has suggested the existence of at least two populations of BMSCs with different embryonic origins that cannot be interchanged during stem cell recruitment: craniofacial BMSCs (neural crest origin) and appendicular BMSCs (mesoderm origin). Questions arise as to whether the site-specific characteristics alter the effect of aging on the skeleton. In this study, the effects of biological aging on human BMSCs were compared with BMSCs derived from the craniofacial bone versus those derived from the appendicular skeleton. The phenotype, proliferation, and functional characteristics (osteogenic differentiation, cytokine secretion, and bone formation in vivo) of the BMSCs were investigated. The results demonstrated that the proliferative capacity and osteogenic differentiation of the BMSCs decrease significantly with age both in vitro and in vivo. For age-matched groups, the osteogenic differentiation capacity of alveolar BMSCs was higher than that of femoral BMSCs in the middle-aged and old groups, while there was no significant difference for the young groups. Compared with old alveolar BMSCs, old femoral BMSCs had a significantly longer population doubling time, a smaller colony-forming population, and less bone formation in vivo, while there was no significant difference for the young and middle-aged groups. Distinct differences in the expression of cytokine factors were also found. In conclusion, human BMSCs display an age-related decrease in functional capacity, and embryonic origins may play a critical role in mediating the aging rate of BMSCs. These data provide novel insights into the skeletal site-specific characteristics of aged BMSCs.

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.

System-wide survey of proteomic responses of human bone marrow stromal cells (hBMSCs) to in vitro cultivation

Human bone marrow stromal cells (hBMSCs, also loosely called bone marrow-derived mesenchymal stem cells) are the subject of increasing numbers of clinical trials and laboratory research. Our group recently reported on the optimization of a workflow for a sensitive proteomic study of hBMSCs. Here, we couple this workflow with a label-free protein quantitation method to investigate the molecular responses of hBMSCs to long-term in vitro passaging. We explored the proteomic responses of hBMSCs by assessing the expression levels of proteins at early passage (passage 3, P3) and late passage (P7). We used multiple biological as well as technical replicates to ensure that the detected proteomic changes are repeatable between cultures and thus likely to be biologically relevant. Over 1700 proteins were quantified at three passages and a list of differentially expressed proteins was compiled. Bioinformatics-based network analysis and term enrichment revealed that metabolic pathways are largely altered, where many proteins in the glycolytic, pentose phosphate, and TCA pathways were shown to be largely upregulated in late passages. We also observed significant proteomic alterations in functional categories including apoptosis, and ER-based protein processing and sorting following in vitro cell aging. We posit that the comprehensive map outlined in this report of affected phenotypes as well as the underpinning molecular factors tremendously benefit the effort to uncovering targets that are not just used only to monitor cell fitness but can be employed to slowdown the in vitro aging process in hBMSCs and hence ensure manufacturing of cells with known quality, efficacy and stability.

SIRT1 directly regulates SOX2 to maintain self-renewal and multipotency in bone marrow-derived mesenchymal stem cells

SOX2 is crucial for the maintenance of the self-renewal capacity and multipotency of mesenchymal stem cells (MSCs); however, the mechanism by which SOX2 is regulated remains unclear. Here, we report that RNA interference of sirtuin 1 (SIRT1) in human bone marrow (BM)-derived MSCs leads to a decrease of SOX2 protein, resulting in the deterioration of the self-renewal and differentiation capacities of BM-MSCs. Using immunoprecipitation, we demonstrated direct binding between SIRT1 and SOX2 in HeLa cells overexpressing SOX2. We further discovered that the RNA interference of SIRT1 induces the acetylation, nuclear export, and ubiquitination of SOX2, leading to proteasomal degradation in BM-MSCs. SOX2 suppression by trichostatin A (TSA), a known histone deacetylase inhibitor, was reverted by treatment with resveratrol (0.1 and 1 µM), a known activator of SIRT1 in BM-MSCs. Furthermore, 0.1 and 1 µM resveratrol reduced TSA-mediated acetylation and ubiquitination of SOX2 in BM-MSCs. SIRT1 activation by resveratrol enhanced the colony-forming ability and differentiation potential to osteogenic and adipogenic lineages in a dose-dependent manner. However, the enhancement of self-renewal and multipotency by resveratrol was significantly decreased to basal levels by RNA interference of SOX2. These results strongly suggest that the SIRT1-SOX2 axis plays an important role in maintaining the self-renewal capability and multipotency of BM-MSCs. In conclusion, our findings provide evidence for positive SOX2 regulation by post-translational modification in BM-MSCs through the inhibition of nuclear export and subsequent ubiquitination, and demonstrate that SIRT1-mediated deacetylation contributes to maintaining SOX2 protein in the nucleus.

Melatonin reverses H2 O2 -induced premature senescence in mesenchymal stem cells via the SIRT1-dependent pathway

Mesenchymal stem cells (MSCs) represent an attractive source for stem cell-based regenerative therapy, but they are vulnerable to oxidative stress-induced premature senescence in pathological conditions. We previously reported antioxidant and antiarthritic effects of melatonin on MSCs against proinflammatory cytokines. In this study, we hypothesized that melatonin could protect MSCs from premature senescence induced by hydrogen peroxide (H2 O2 ) via the silent information regulator type 1 (SIRT1)-dependent pathway. In response to H2 O2 at a sublethal concentration of 200 μm, human bone marrow-derived MSCs (BM-MSCs) underwent growth arrest and cellular senescence. Treatment with melatonin before H2 O2 exposure cannot significantly prevent premature senescence; however, treatment with melatonin subsequent to H2 O2 exposure successfully reversed the senescent phenotypes of BM-MSCs in a dose-dependent manner. This result was made evident by improved cell proliferation, decreased senescence-associated β-galactosidase activity, and the improved entry of proliferating cells into the S phase. In addition, treatment with 100 μm melatonin restored the osteogenic differentiation potential of BM-MSCs that was inhibited by H2 O2 -induced premature senescence. We also found that melatonin attenuated the H2 O2 -stimulated phosphorylation of p38 mitogen-activated protein kinase, decreased expression of the senescence-associated protein p16(INK) (4α) , and increased SIRT1. Further molecular experiments revealed that luzindole, a nonselective antagonist of melatonin receptors, blocked melatonin-mediated antisenescence effects. Inhibition of SIRT1 by sirtinol counteracted the protective effects of melatonin, suggesting that melatonin reversed the senescence in cells through the SIRT1-dependent pathway. Together, these findings lay new ground for understanding oxidative stress-induced premature senescence and open perspectives for therapeutic applications of melatonin in stem cell-based regenerative medicine.

Mesenchymal Stem Cells Derived from Peripheral Blood Retain Their Pluripotency, but Undergo Senescence During Long-Term Culture

Peripheral blood-derived mesenchymal stem cells (PB-MSCs) show promise as a source of cells for autologous transplantation because they can be harvested through minimally invasive procedures. To ensure adequate numbers of cells for transplantation and tissue regeneration, PB-MSCs must first be cultured and expanded in vitro, but whether long-term passage modifies their properties has been poorly understood. In this study we triggered production of PB-MSCs in rabbits using granulocyte colony-stimulating factor (G-CSF) and AMD3100, and then isolated and expanded the cells in culture until they reached a state of senescence, usually after about 20 passages. Cultures of low-, middle-, and high-passage numbers were compared in terms of morphology, proliferative capacity, phenotype, differentiation potential, apoptosis, metabolic indicators, and senescence. As passage number increased, MSCs retained their elongated spindle shape, but became larger and flatter, slowed in growth gradually, and increased proportion of cells showed G1 arrest. The proportions of apoptotic cells, production of reactive oxygen species (ROS), and ADP/ATP ratio increased with passage number. Expression of senescence-associated β-galactosidase increased, while telomerase activity decreased. On the other hand, cultures did not show significant changes in phenotype or lose their ability to differentiate into three lineages as passage number increased. These results suggest that PB-MSCs maintain their stem cell properties during prolonged culturing, but they undergo senescence that may be due to apoptosis and production of ROS. These findings may help to standardize in vitro production of PB-MSCs for tissue engineering.

Wip1 knockout inhibits the proliferation and enhances the migration of bone marrow mesenchymal stem cells

Mesenchymal stem cells (MSCs), a unique population of multipotent adult progenitor cells originally found in bone marrow (BM), are extremely useful for multifunctional therapeutic approaches. However, the growth arrest and premature senescence of MSCs in vitro prevent the in-depth characterization of these cells. In addition, the regulatory factors involved in MSCs migration remain largely unknown. Given that protein phosphorylation is associated with the processes of MSCs proliferation and migration, we focused on wild-type p53-inducible phosphatase-1 (Wip1), a well-studied modulator of phosphorylation, in this study. Our results showed that Wip1 knockout significantly inhibited MSCs proliferation and induced G2-phase cell-cycle arrest by reducing cyclinB1 expression. Compared with WT-MSCs, Wip1(-/-) MSCs displayed premature growth arrest after six passages in culture. Transwell and scratch assays revealed that Wip1(-/-) MSCs migrate more effectively than WT-MSCs. Moreover, the enhanced migratory response of Wip1(-/-) MSCs may be attributed to increases in the induction of Rac1-GTP activity, the pAKT/AKT ratio, the rearrangement of filamentous-actin (f-actin), and filopodia formation. Based on these results, we then examined the effect of treatment with a PI3K/AKT and Rac1 inhibitor, both of which impaired the migratory activity of MSCs. Therefore, we propose that the PI3K/AKT/Rac1 signaling axis mediates the Wip1 knockout-induced migration of MSCs. Our findings indicate that the principal function of Wip1 in MSCs transformation is the maintenance of proliferative capacity. Nevertheless, knocking out Wip1 increases the migratory capacity of MSCs. This dual effect of Wip1 provides the potential for purposeful routing of MSCs.

Characterization of bone marrow-derived mesenchymal stem cells in aging

Adult mesenchymal stem cells are a resource for autologous and allogeneic cell therapies for immune-modulation and regenerative medicine. However, patients most in need of such therapies are often of advanced age. Therefore, the effects of the aged milieu on these cells and their intrinsic aging in vivo are important considerations. Furthermore, these cells may require expansion in vitro before use as well as for future research. Their aging in vitro is thus also an important consideration. Here, we focus on bone marrow mesenchymal stem cells (BMSCs), which are unique compared to other stem cells due to their support of hematopoietic cells in addition to contributing to bone formation. BMSCs may be sensitive to age-related diseases and could perpetuate degenerative diseases in which bone remodeling is a contributory factor. Here, we review (1) the characterization of BMSCs, (2) the characterization of in vivo-aged BMSCs, (3) the characterization of in vitro-aged BMSCs, and (4) potential approaches to optimize the performance of aged BMSCs. This article is part of a Special Issue entitled "Stem Cells and Bone".

Down-regulation of Dicer1 promotes cellular senescence and decreases the differentiation and stem cell-supporting capacities of mesenchymal stromal cells in patients with myelodysplastic syndrome

Although it has been reported that mesenchymal stromal cells are unable to provide sufficient hematopoietic support in myelodysplastic syndrome, the underlying mechanisms remain elusive. In this study, we found that mesenchymal stromal cells from patients with myelodysplastic syndrome displayed a significant increase in senescence, as evidenced by their decreased proliferative capacity, flattened morphology and increased expression of SA-β-gal and p21. Senescent mesenchymal stromal cells from patients had decreased differentiation potential and decreased stem cell support capacity. Gene knockdown of Dicer1, which was down-regulated in mesenchymal stromal cells from patients, induced senescence. The differentiation and stem cell-supporting capacities were significantly inhibited by Dicer1 knockdown. Overexpression of Dicer1 in mesenchymal stromal cells from patients reversed cellular senescence and enhanced stem cell properties. Furthermore, we identified reduced expression in the microRNA-17 family (miR-17-5p, miR-20a/b, miR-106a/b and miR-93) as a potential factor responsible for increased p21 expression, a key senescence mediator, in Dicer1 knockdown cells. Moreover, we found that miR-93 and miR-20a expression levels were significantly reduced in mesenchymal stromal cells from patients and miR-93/miR-20a gain of function resulted in a decrease of cellular senescence. Collectively, the results of our study show that mesenchymal stromal cells from patients with myelodysplastic syndrome are prone to senescence and that Dicer1 down-regulation promotes cellular senescence and decreases the differentiation and stem cell-supporting capacities of mesenchymal stromal cells. Dicer1 down-regulation seems to contribute to the insufficient hematopoietic support capacities of mesenchymal stromal cells from patients with myelodysplastic syndrome.

SIRT1 ameliorates age-related senescence of mesenchymal stem cells via modulating telomere shelterin

Mesenchymal stem cells (MSCs) senescence is an age-related process that impairs the capacity for tissue repair and compromises the clinical use of autologous MSCs for tissue regeneration. Here, we describe the effects of SIRT1, a NAD⁺-dependent deacetylase, on age-related MSCs senescence. Knockdown of SIRT1 in young MSCs induced cellular senescence and inhibited cell proliferation whereas overexpression of SIRT1 in aged MSCs reversed the senescence phenotype and stimulated cell proliferation. These results suggest that SIRT1 plays a key role in modulating age-induced MSCs senescence. Aging-related proteins, P16 and P21 may be downstream effectors of the SIRT1-mediated anti-aging effects. SIRT1 protected MSCs from age-related DNA damage, induced telomerase reverse transcriptase (TERT) expression and enhanced telomerase activity but did not affect telomere length. SIRT1 positively regulated the expression of tripeptidyl peptidase 1 (TPP1), a component of the shelterin pathway that protects chromosome ends from DNA damage. Together, the results demonstrate that SIRT1 quenches age-related MSCs senescence by mechanisms that include enhanced TPP1 expression, increased telomerase activity and reduced DNA damage.