H2O2 accumulation mediates differentiation capacity alteration, but not proliferative decline, in senescent human fetal mesenchymal stem cells

Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD+/SIRT1 axis

BACKGROUND

The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation.

METHODS

Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45- MSCs.

RESULTS

Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD+), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD+, with oral NAD+ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days.

CONCLUSIONS

We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD+-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.

Mesenchymal Stem Cells and Exosomes: A Novel Therapeutic Approach for Corneal Diseases

The cornea, with its delicate structure, is vulnerable to damage from physical, chemical, and genetic factors. Corneal transplantation, including penetrating and lamellar keratoplasties, can restore the functions of the cornea in cases of severe damage. However, the process of corneal transplantation presents considerable obstacles, including a shortage of available donors, the risk of severe graft rejection, and potentially life-threatening complications. Over the past few decades, mesenchymal stem cell (MSC) therapy has become a novel alternative approach to corneal regeneration. Numerous studies have demonstrated the potential of MSCs to differentiate into different corneal cell types, such as keratocytes, epithelial cells, and endothelial cells. MSCs are considered a suitable candidate for corneal regeneration because of their promising therapeutic perspective and beneficial properties. MSCs compromise unique immunomodulation, anti-angiogenesis, and anti-inflammatory properties and secrete various growth factors, thus promoting corneal reconstruction. These effects in corneal engineering are mediated by MSCs differentiating into different lineages and paracrine action via exosomes. Early studies have proven the roles of MSC-derived exosomes in corneal regeneration by reducing inflammation, inhibiting neovascularization, and angiogenesis, and by promoting cell proliferation. This review highlights the contribution of MSCs and MSC-derived exosomes, their current usage status to overcome corneal disease, and their potential to restore different corneal layers as novel therapeutic agents. It also discusses feasible future possibilities, applications, challenges, and opportunities for future research in this field.

Impact of exogenous hydrogen peroxide on osteogenic differentiation of broiler chicken compact bones derived mesenchymal stem cells

The effects of hydrogen peroxide (H₂O₂) on the osteogenic differentiation of primary chicken mesenchymal stem cells (MSCs) were investigated. MSCs were subjected to an osteogenic program and exposed to various concentrations of H₂O₂ for 14 days. Results showed that high concentrations of H₂O₂ (200 and 400 nM) significantly increased pro-apoptotic marker CASP8 expression and impaired osteogenic differentiation, as indicated by decreased mRNA expression levels of osteogenesis-related genes and reduced in vitro mineralization. In contrast, long-term H₂O₂ exposure promoted basal expression of adipogenic markers at the expense of osteogenesis in MSCs during osteogenic differentiation, and increased intracellular reactive oxygen species (ROS) production, as well as altered antioxidant enzyme gene expression. These findings suggest that long-term H₂O₂-induced ROS production impairs osteogenic differentiation in chicken MSCs under an osteogenic program.

Increased production of 8-oxo-7,8-dihydroguanine in human urine, a novel biomarker of osteoporosis

Osteoporosis is a worldwide disease that seriously affects the quality of life and survival rate of the elderly. The detection of bone biomarkers will provide supplementary information of bone mineral density, contributing to the accurate diagnosis of osteoporosis and better health care for prevention. This study aimed to investigate the efficacy of oxidative stress markers-8-oxo-7,8-dihydroguanine (8-oxoGsn) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGsn) in the assessment of osteoporosis. We conducted a cross-sectional study among menopausal women with a mean (standard deviation) age of 62.967 (7.798) years old (n = 151). Participants were recruited for the bone mineral density (BMD) assessment, blood and urinary samples. Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine and 8-oxo-7,8-dihydro-guanine concentrations were measured by ultra performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS). The urinary 8-oxoGsn/Cre value differed significantly between normal and osteoporotic participants (p < 0.001), while the 8-oxodGsn/Cre value did not (p = 0.720). Even after adjusting for the age and body mass index, the BMD was still associated with urinary 8-oxoGsn/Cre value. ROC analysis showed that 8-oxoGsn has a strong diagnostic value for osteoporosis (AUC =0.744). The results show for the first time that 8-oxoGsn may be a biomarker for the future diagnosis of osteoporosis in women.

Changes in tumor suppressors and inflammatory responses during hydrogen peroxide-induced senescence in rat fibroblasts

Cell proliferation and senescence are processes induced by oxidative stress. In this study, we aimed to establish a cellular model of rapid proliferation and senescence of rat tail-tip fibroblasts by hydrogen peroxide(H₂O₂), a well-known oxidant. On this basis, changes in oxidative stress, inflammatory response and cell cycle of fibroblasts were studied. After H₂O₂ treatment, cell counting and flow cytometry results showed that 50μM of H₂O₂ for 12h and 100μM for 8h effectively promoted fibroblast proliferation, while 500μM rapidly led to cell cycle arrest. In addition, stimulation with H₂O₂ at a concentration of 50μM also promoted the inflammatory effects of the cells. At a concentration of 100μM H₂O₂, the cellular antioxidant system began to collapse at 8h and began to affect cellular activity. 500μM of H₂O₂ at 4h the levels of senescence-associated β-galactosidase, a marker of senescence and oxidative stress, were almost positive in fibroblasts. In addition, we found that the risk of fibroblasts carcinogenesis increased with increased H₂O₂ stimulation. The results of this study indicate that H₂O₂ can cause rapid proliferation and senescence of fibroblasts and that its mechanism of action may be mainly through influencing cellular antioxidant systems, cellular inflammatory responses and cell cycle.

Melatonin Improves the Resistance of Oxidative Stress-Induced Cellular Senescence in Osteoporotic Bone Marrow Mesenchymal Stem Cells

Accumulation of senescent bone marrow-derived mesenchymal stem cells (BMMSCs) has led to an age-related bone loss. However, the role of stem cell senescence in estrogen deficiency-induced osteoporosis remains elusive. Though melatonin plays a vital role in bone metabolism regulation, the underlying mechanisms of melatonin-mediated antiosteoporosis are partially elucidated. Therefore, this study purposed to explore (1) whether estrogen deficiency causes cellular senescence of BMMSCs, and if so, (2) the potential of melatonin in preventing bone loss via senescence signaling inhibition. BMMSCs derived from ovariectomized (OVX) rats (OVX BMMSCs) showed an impaired osteogenic capacity, albeit having comparable levels of senescence biomarkers than the sham cells. When exposed to low levels of hydrogen peroxide (H₂O₂), OVX BMMSCs rapidly exhibited senescence-associated phenotypes such as the increased activity of senescence-associated β-galactosidase (SA-β-gal) and upregulation of cell cycle inhibitors. Notably, the in vitro treatment with melatonin hindered H₂O₂-induced senescence in OVX BMMSCs and restored their osteogenic capacity. Treatment with either SIRT1 inhibitor (sirtinol) or melatonin receptor antagonists (luzindole and 4-P-PDOT) eliminated melatonin protective effects, thus indicating its potential in preventing stem cell senescence via SIRT1 activation through the melatonin membrane receptors. Following in vivo intravenous administration with melatonin, it successfully protected the bone microstructure and preserved the antisenescence property of BMMSCs in OVX rats. Collectively, our findings demonstrated that melatonin protected against estrogen deficiency-related bone loss by improving the resistance of BMMSCs to cellular senescence. Therefore, melatonin-mediated antisenescence effect on stem cells provides vital information to facilitate the development of a novel and effective strategy for treating postmenopausal OP.

Mesenchymal Stem Cell-Based Therapy as a New Approach for the Treatment of Systemic Sclerosis

Systemic sclerosis (SSc) is an intractable autoimmune disease with unmet medical needs. Conventional immunosuppressive therapies have modest efficacy and obvious side effects. Targeted therapies with small molecules and antibodies remain under investigation in small pilot studies. The major breakthrough was the development of autologous haematopoietic stem cell transplantation (AHSCT) to treat refractory SSc with rapidly progressive internal organ involvement. However, AHSCT is contraindicated in patients with advanced visceral involvement. Mesenchymal stem cells (MSCs) which are characterized by immunosuppressive, antifibrotic and proangiogenic capabilities may be a promising alternative option for the treatment of SSc. Multiple preclinical and clinical studies on the use of MSCs to treat SSc are underway. However, there are several unresolved limitations and safety concerns of MSC transplantation, such as immune rejections and risks of tumour formation, respectively. Since the major therapeutic potential of MSCs has been ascribed to their paracrine signalling, the use of MSC-derived extracellular vesicles (EVs)/secretomes/exosomes as a "cell-free" therapy might be an alternative option to circumvent the limitations of MSC-based therapies. In the present review, we overview the current knowledge regarding the therapeutic efficacy of MSCs in SSc, focusing on progresses reported in preclinical and clinical studies using MSCs, as well as challenges and future directions of MSC transplantation as a treatment option for patients with SSc.

Advances in mesenchymal stem cell therapy for immune and inflammatory diseases: Use of cell-free products and human pluripotent stem cell-derived mesenchymal stem cells

Mesenchymal stem cell therapy (MSCT) for immune and inflammatory diseases continues to be popular based on progressive accumulation of preclinical mechanistic evidence. This has led to further expansion in clinical indications from graft rejection, autoimmune diseases, and osteoarthritis, to inflammatory liver and pulmonary diseases including COVID‐19. A clear trend is the shift from using autologous to allogeneic MSCs, which can be immediately available as off‐the‐shelf products. In addition, new products such as cell‐free exosomes and human pluripotent stem cell (hPSC)‐derived MSCs are exciting developments to further prevalent use. Increasing numbers of trials have now published results in which safety of MSCT has been largely demonstrated. While reports of therapeutic endpoints are still emerging, efficacy can be seen for specific indications—including graft‐vs‐host‐disease, strongly Th17‐mediated autoimmune diseases, and osteoarthritis—which are more robustly supported by mechanistic preclinical evidence. In this review, we update and discuss outcomes in current MSCT clinical trials for immune and inflammatory disease, as well as new innovation and emerging trends in the field.

In Vitro Generation of Vascular Wall-Typical Mesenchymal Stem Cells (VW-MSC) from Murine Induced Pluripotent Stem Cells Through VW-MSC-Specific Gene Transfer

Among the adult stem cells, multipotent mesenchymal stem cells (MSCs) turned out to be a promising option for cell-based therapies for the treatment of various diseases including autoimmune and cardiovascular disorders. MSCs bear a high proliferation and differentiation capability and exert immunomodulatory functions while being still clinically safe. As tissue-resident stem cells, MSCs can be isolated from various tissue including peripheral or umbilical cord blood, placenta, blood, fetal liver, lung, adipose tissue, and blood vessels, although the most commonly used source for MSCs is the bone marrow. However, the proportion of MSCs in primary isolates from adult tissue biopsies is rather low, and therefore MSCs must be intensively expanded in vitro before the MSCs find particular use in therapies that may require extensive and repetitive cell replacement. Therefore, more easily accessible sources of MSCs are needed. Here, we present a detailed protocol to generate tissue-typical MSCs by direct linage conversion using transcription factors defining target MSC identity from murine induced pluripotent stem cells (iPSCs).

Protocol for human placental mesenchymal stem cell therapy in a murine model of intra-abdominal infection of hypervirulent Klebsiella

Hypervirulent Klebsiella pneumoniae (hvKP) strains cause extra-pulmonary infections such as intra-abdominal infection (IAI) even in healthy individuals due to its resistance to polymorphonuclear neutrophil (PMN) killing and a high incidence of multidrug resistance. To assess whether human placental mesenchymal stem cell (PMSC) therapy can be an effective treatment option, we established a murine model of hvKP-IAI to evaluate immune cell modulation and bacterial clearance for this highly lethal infection. This protocol can rapidly assess potential therapies for severe bacterial IAIs.

For complete details on the use and execution of this protocol, please refer to Wang et al. (2020).

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PMSC treatment in a mouse model of hvKP-induced intra-abdominal infection

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Isolation of mouse peritoneal immune cells without affixing mice to a dissecting board

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Analysis of PMN, T, and NK cells in peritoneal washings

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Determination of bacterial CFUs in hvKP-infected peritoneal fluid

A Rapid and Highly Predictive in vitro Screening Platform for Osteogenic Natural Compounds Using Human Runx2 Transcriptional Activity in Mesenchymal Stem Cells

The rapid aging of worldwide populations had led to epidemic increases in the incidence of osteoporosis (OP), but while treatments are available, high cost, adverse effects, and poor compliance continue to be significant problems. Naturally occurring plant-based compounds including phytoestrogens can be good and safe candidates to treat OP, but screening for osteogenic capacity has been difficult to achieve, largely due to the requirement of using primary osteoblasts or mesenchymal stem cells (MSCs), the progenitors of osteoblasts, to conduct time-consuming in vitro and in vivo osteogenic assay. Taking advantage of MSC osteogenic capacity and utilizing a promoter reporter assay for Runx2, the master osteogenesis transcription factor, we developed a rapid in vitro screening platform to screen osteogenic small molecules including natural plant-based compounds. We screened eight plant-derived compounds from different families including flavonoids, polyphenolic compounds, alkaloids, and isothiocyanates for osteogenic capacity using the human RUNX2-promoter luciferase reporter (hRUNX2-luc) transduced into the mouse MSC line, C3H10T1/2, with daidzein-a well-studied osteogenic phytoestrogen-as a positive control. Classical in vitro and in vivo osteogenesis assays were performed using primary murine and human bone marrow MSCs (BMMSCs) to validate the accuracy of this rapid screening platform. Using the MSC/hRUNX2-luc screening platform, we were able not only to shorten the selection process for osteogenic compounds from 3∼4 weeks to just a few days but also simultaneously perform comparisons between multiple compounds to assess relative osteogenic potency. Predictive analyses revealed nearly absolute correlation of the MSC/hRUNX2-luc reporter platform to the in vitro classical functional assay of mineralization using murine BMMSCs. Validation using human BMMSCs with in vitro mineralization and in vivo osteogenesis assays also demonstrated nearly absolute correlation to the MSC/hRUNX2-luc reporter results. Our findings therefore demonstrate that the MSC/hRUNX2 reporter platform can accurately, rapidly, and robustly screen for candidate osteogenic compounds and thus be relevant for therapeutic application in OP.

Genetic modification by overexpression of target gene in mesenchymal stromal cell for treating liver diseases

Different hepatoxic factors cause irreversible liver injury, leading to liver failure, cirrhosis, and cancer in mammals. Liver transplantation is the only effective strategy, which can improve the prognosis of patients with end-stage liver diseases, but it is limited by liver donor shortage, expensive costs, liver graft rejection and dysfunction, and recurring liver failure. Recently, mesenchymal stromal cells (MSCs) isolated from various tissues are regarded as the main stem cell type with therapeutic effects in liver diseases because of their hepatogenic differentiation, anti-inflammatory, immuoregulatory, anti-apoptotic, antifibrotic, and antitumor capacities. To further improve the therapeutic effects of MSCs, multiple studies showed that genetically engineered MSCs have increased regenerative capacities and are able to more effectively inhibit cell death. Moreover, they are able to secrete therapeutic proteins for attenuating liver injury in liver diseases. In this review, we mainly focus on gene overexpression for reprogramming MSCs to increase their therapeutic effects in treating various liver diseases. We described the potential mechanisms of MSCs with gene overexpression in attenuating liver injury, and we recommend further expansion of experiments to discover more gene targets and optimized gene delivery methods for MSC-based regenerative medicine. We also discussed the potential hurdles in genetic engineering MSCs. In conclusion, we highlight that we need to overcome all scientific hurdles before genetically modified MSC therapy can be translated into clinical practices for patients with liver diseases.

Alteration of fatty acid oxidation by increased CPT1A on replicative senescence of placenta-derived mesenchymal stem cells

Background

Human placenta-derived mesenchymal stem cells (PD-MSCs) are powerful sources for cell therapy in regenerative medicine. However, a limited lifespan by senescence through mechanisms that are well unknown is the greatest obstacle. In the present study, we first demonstrated the characterization of replicative senescent PD-MSCs and their possible mitochondrial functional alterations.

Methods

Human PD-MSCs were cultured to senescent cells for a long period of time. The cells of before passage number 8 were early cells and after passage number 14 were late cells. Also, immortalized cells of PD-MSCs (overexpressed hTERT gene into PD-MSCs) after passage number 14 were positive control of non-senescent cells. The characterization and mitochondria analysis of PD-MSCs were explored with long-term cultivation.

Results

Long-term cultivation of PD-MSCs exhibited increases of senescent markers such as SA-β-gal and p21 including apoptotic factor, and decreases of proliferation, differentiation potential, and survival factor. Mitochondrial dysfunction was also observed in membrane potential and metabolic flexibility with enlarged mitochondrial mass. Interestingly, we founded that fatty acid oxidation (FAO) is an important metabolism in PD-MSCs, and carnitine palmitoyltransferase1A (CPT1A) overexpressed in senescent PD-MSCs. The inhibition of CPT1A induced a change of energy metabolism and reversed senescence of PD-MSCs.

Conclusions

These findings suggest that alteration of FAO by increased CPT1A plays an important role in mitochondrial dysfunction and senescence of PD-MSCs during long-term cultivation.

Melatonin restores the osteoporosis-impaired osteogenic potential of bone marrow mesenchymal stem cells by preserving SIRT1-mediated intracellular antioxidant properties

Postmenopausal osteoporosis (OP) is one of the most common bone diseases that affects millions of aging women. Reduced osteogenesis and increased oxidative stress have been implicated in bone marrow mesenchymal stem cells (BMMSCs) derived from OP patients. Melatonin has shown positive effects on osteoblast differentiation and bone formation; however, it was unknown whether melatonin could restore OP-impaired osteogenic potential of BMMSCs and what the underlying mechanisms entailed. The objective of this study is to investigate (1) whether melatonin can restore the impaired osteogenic potential of OP BMMSCs by preserving their antioxidant functions, and if so, (2) whether intravenous administration of melatonin can prevent OP-induced bone loss in ovariectomized (OVX) rats. Ovariectomies were performed in female rats and BMMSCs were isolated from the osteoporotic rats 3 months later. In vitro treatment with melatonin successfully improved the osteogenic differentiation of OP BMMSCs, as evidenced by increased levels of matrix mineralization and osteoblast-specific genes. In melatonin-treated OP BMMSCs, intracellular oxidative stress was significantly attenuated, while levels of intracellular antioxidant enzymes were noticeably up-regulated - particularly superoxide dismutase 2 (SOD2) and glutathione peroxidase 1 (GPX1). Silent information regulator type 1 (SIRT1) was involved in the melatonin-mediated recovery of osteogenesis and antioxidant functions. Meanwhile, in vivo injections of melatonin via the tail vein successfully ameliorated the bone micro-architecture in ovariectomized rat femurs. Further experiments confirmed that BMMSCs derived from melatonin-treated OVX rats exerted well-preserved antioxidant properties and osteogenic potential. Our findings demonstrate that the administration of melatonin is a promising strategy for treating patients with postmenopausal OP by preserving the antioxidant properties and osteogenic potential of their BMMSCs.

Melatonin promotes the BMP9-induced osteogenic differentiation of mesenchymal stem cells by activating the AMPK/β-catenin signalling pathway

Background

Mesenchymal stem cells (MSCs) play a crucial role in maintaining the dynamic balance of bone metabolism. Melatonin may have a regulatory effect on bone metabolism by regulating the lineage commitment and differentiation signalling pathways of MSCs. Among the BMP families, the osteogenesis of BMP9 is considered to be one of the strongest in MSCs. Here, we explored whether melatonin and BMP9 act synergistically on MSC osteogenic differentiation.

Methods

The C3H10T1/2 osteogenic differentiation function induced by melatonin synergizes with BMP9, as detected by the expression of osteogenic markers at different periods. The result was further confirmed by foetal limb explant culture and in vivo stem cell implantation experiments. The effects of the AMPK/β-catenin pathway on the osteogenic differentiation of C3H10T1/2 cells were evaluated by Western blotting.

Results

Melatonin combined with BMP9 significantly enhanced the expression of osteogenic markers at different periods in C3H10T1/2 cells, effectively enhancing BMP9-induced bone formation in cultured foetal explants and ectopic bone formation in vivo in stem cell transplantation experiments. Melatonin increases the expression of BMP9 in C3H10T1/2 cells and induces Smad1/5/8 translocation from the cytoplasm to the nucleus. In addition, melatonin and BMP9 synergistically promote AMPK and β-catenin phosphorylation, which can be largely eliminated by AMPK siRNA pretreatment.

Conclusions

Melatonin and BMP9 in C3H10T1/2 cells synergistically promote osteogenic differentiation at least in part by activating the AMPK/β-catenin signalling pathway.

Current Trends and Future Perspective of Mesenchymal Stem Cells and Exosomes in Corneal Diseases

The corneal functions (transparency, refractivity and mechanical strength) deteriorate in many corneal diseases but can be restored after corneal transplantation (penetrating and lamellar keratoplasties). However, the global shortage of transplantable donor corneas remains significant and patients are subject to life-long risk of immune response and graft rejection. Various studies have shown the differentiation of multipotent mesenchymal stem cells (MSCs) into various corneal cell types. With the unique properties of immunomodulation, anti-angiogenesis and anti-inflammation, they offer the advantages in corneal reconstruction. These effects are widely mediated by MSC differentiation and paracrine signaling via exosomes. Besides the cell-free nature of exosomes in circumventing the problems of cell-fate control and tumorigenesis, the vesicle content can be genetically modified for optimal therapeutic affinity. The pharmacology and toxicology, xeno-free processing with sustained delivery, scale-up production in compliant to Good Manufacturing Practice regulations, and cost-effectiveness are the current foci of research. Routes of administration via injection, topical and/or engineered bioscaffolds are also explored for its applicability in treating corneal diseases.

Production of Mesenchymal Stem Cells Through Stem Cell Reprogramming

Mesenchymal stem cells (MSCs) possess a broad spectrum of therapeutic applications and have been used in clinical trials. MSCs are mainly retrieved from adult or fetal tissues. However, there are many obstacles with the use of tissue-derived MSCs, such as shortages of tissue sources, difficult and invasive retrieval methods, cell population heterogeneity, low purity, cell senescence, and loss of pluripotency and proliferative capacities over continuous passages. Therefore, other methods to obtain high-quality MSCs need to be developed to overcome the limitations of tissue-derived MSCs. Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), are considered potent sources for the derivation of MSCs. PSC-derived MSCs (PSC-MSCs) may surpass tissue-derived MSCs in proliferation capacity, immunomodulatory activity, and in vivo therapeutic applications. In this review, we will discuss basic as well as recent protocols for the production of PSC-MSCs and their in vitro and in vivo therapeutic efficacies. A better understanding of the current advances in the production of PSC-MSCs will inspire scientists to devise more efficient differentiation methods that will be a breakthrough in the clinical application of PSC-MSCs.

Bone marrow mesenchymal stem cells suppress growth and promote the apoptosis of glioma U251 cells through downregulation of the PI3K/AKT signaling pathway

Mesenchymal stem cells (MSCs), with the capacity for self-renewal and differentiation into multiple cell types, exhibit the property of homing towards tumor sites and immunosuppression and have been used as tumor-tropic vectors for tumor therapy. However, few studies have investigated the underlying molecular mechanisms that link MSCs to targeted tumor cells. In this study, we elucidated the inhibitory effects and mechanisms of human bone marrow mesenchymal stem cells (hBMSCs) on human glioma U251 cells using a co-culture system in vitro. The anti-tumor activity of co-cultured hBMSCs was assessed by morphological changes, the MTT assay, and Hoechst 33258 staining. Cell apoptosis and cell cycle distribution were evaluated by flow cytometry. Cell migration and invasion were evaluated using a 24-well Transwell chamber. A proteomics approach was used to identify differentially expressed proteins after hBMSCs treatment in U251 cells, and quantitative polymerase chain reaction was used to validate the results. Bioinformatics analyses were also implemented to better understand the identified proteins, and Western blotting analyses were used to analyze the associated proteins. The results showed that hBMSCs could inhibit cell proliferation and induce cell cycle arrest in the G1 phase, resulting in apoptosis of U251 cells. Transwell and Matrigel invasion assays showed that hBMSCs reduced the migration and invasion of U251 cells. Using proteomics, 11 differentially expressed proteins were identified and observed. Bioinformatics analyses indicated that the identified proteins participated in several biological processes and exhibited various molecular functions, mainly related to the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway. Moreover, hBMSCs regulated changes in proteins linked to cell apoptosis and cell cycle progression and inhibited the epithelial-mesenchymal transition (EMT)-like and PI3K/AKT pathway. Taken together, the findings in our study suggest that hBMSCs inhibit U251 cells proliferation and the EMT-like by downregulating the PI3K/AKT signaling pathway, which indicates that hBMSCs have a potential antitumor characteristics and should be further explored in future glioma therapy.

A prospect of cell immortalization combined with matrix microenvironmental optimization strategy for tissue engineering and regeneration

Cellular senescence is a major hurdle for primary cell-based tissue engineering and regenerative medicine. Telomere erosion, oxidative stress, the expression of oncogenes and the loss of tumor suppressor genes all may account for the cellular senescence process with the involvement of various signaling pathways. To establish immortalized cell lines for research and clinical use, strategies have been applied including internal genomic or external matrix microenvironment modification. Considering the potential risks of malignant transformation and tumorigenesis of genetic manipulation, environmental modification methods, especially the decellularized cell-deposited extracellular matrix (dECM)-based preconditioning strategy, appear to be promising for tissue engineering-aimed cell immortalization. Due to few review articles focusing on this topic, this review provides a summary of cell senescence and immortalization and discusses advantages and limitations of tissue engineering and regeneration with the use of immortalized cells as well as a potential rejuvenation strategy through combination with the dECM approach.

Mechanical stretch induces antioxidant responses and osteogenic differentiation in human mesenchymal stem cells through activation of the AMPK-SIRT1 signaling pathway

Mesenchymal stem cells (MSCs) are promising cell sources for regenerative medicine. Growing evidence has indicated that mechanical stimuli are crucial for their lineage-specific differentiation. However, the effect of mechanical loading on redox balance and the intracellular antioxidant system in MSCs was unknown. In this study, human bone marrow-derived MSCs (BM-MSCs) were subjected to cyclic stretch at the magnitude of 2.5%, 5%, and 10%. Cell proliferation, intracellular reactive oxygen species (ROS), expression of antioxidant enzymes, and osteogenic differentiation were evaluated. RNA was extracted and subjected to DNA microarray analysis. Sirtinol and compound C were used to investigate the underlying mechanisms involved silent information regulator type 1 (SIRT1) and AMP-activated protein kinase (AMPK). Our results showed that mechanical stretch at appropriate magnitudes increased cell proliferation, up-regulated extracellular matrix organization, and down-regulated matrix disassembly. After 3 days of stretch, intracellular ROS in BM-MSCs were decreased but the levels of antioxidant enzymes, especially superoxide dismutase 1 (SOD1), were up-regulated. Osteogenesis was improved by 5% stretch rather than 10% stretch, as evidenced by increased matrix mineralization and osteogenic marker gene expression. The expression of SIRT1 and phosphorylation of AMPK were enhanced by mechanical stretch; however, inhibition of SIRT1 or AMPK abrogated the stretch-induced antioxidant effect on BM-MSCs and inhibited the stretch-mediated osteogenic differentiation. Our findings reveal that mechanical stretch induced antioxidant responses, attenuated intracellular ROS, and improved osteogenesis of BM-MSCs. The stretch-induced antioxidant effect was through activation of the AMPK-SIRT1 signaling pathway. Our findings demonstrated that appropriate mechanical stimulation can improve MSC antioxidant functions and benefit bone regeneration.

Alcohol Induces Cellular Senescence and Impairs Osteogenic Potential in Bone Marrow-Derived Mesenchymal Stem Cells

Aims

Chronic and excessive alcohol consumption is a high-risk factor for osteoporosis. Bone marrow-derived mesenchymal stem cells (BM-MSCs) play an important role in bone formation; however, they are vulnerable to ethanol (EtOH). The purpose of this research was to investigate whether EtOH could induce premature senescence in BM-MSCs and subsequently impair their osteogenic potential.

Methods

Human BM-MSCs were exposed to EtOH ranging from 10 to 250 mM. Senescence-associated β-galactosidase (SA-β-gal) activity, cell cycle distribution, cell proliferation and reactive oxygen species (ROS) were evaluated. Mineralization and osteoblast-specific gene expression were evaluated during osteogenesis in EtOH-treated BM-MSCs. To investigate the role of silent information regulator Type 1 (SIRT1) in EtOH-induced senescence, resveratrol (ResV) was used to activate SIRT1 in EtOH-treated BM-MSCs.

Results

EtOH treatments resulted in senescence-associated phenotypes in BM-MSCs, such as decreased cell proliferation, increased SA-β-gal activity and G0/G1 cell cycle arrest. EtOH also increased the intracellular ROS and the expression of senescence-related genes, such as p16INK4α and p21. The down-regulated levels of SIRT1 accompanied with suppressed osteogenic differentiation were confirmed in EtOH-treated BM-MSCs. Activation of SIRT1 by ResV partially counteracted the effects of EtOH by decreasing senescence markers and rescuing the inhibited osteogenesis.

Conclusion

EtOH treatments induced premature senescence in BM-MSCs in a dose-dependent manner that was responsible for EtOH-impaired osteogenic differentiation. Activation of SIRT1 was effective in ameliorating EtOH-induced senescence phenotypes in BMSCs and could potentially lead to a new strategy for clinically preventing or treating alcohol-induced osteoporosis.

Short summary

Ethanol (EtOH) treatments induce premature senescence in marrow-derived mesenchymal stem cells in a dose-dependent manner that is responsible for EtOH-impaired osteogenic differentiation. Activation of SIRT1 is effective in ameliorating EtOH-induced senescence phenotypes, which potentially leads to a new strategy for clinically treating alcohol-induced osteoporosis.

Current Strategies to Generate Human Mesenchymal Stem Cells In Vitro

Mesenchymal stem cells (MSCs) are heterogeneous multipotent stem cells that are involved in the development of mesenchyme-derived evolving structures and organs during ontogeny. In the adult organism, reservoirs of MSCs can be found in almost all tissues where MSCs contribute to the maintenance of organ integrity. The use of these different MSCs for cell-based therapies has been extensively studied over the past years, which highlights the use of MSCs as a promising option for the treatment of various diseases including autoimmune and cardiovascular disorders. However, the proportion of MSCs contained in primary isolates of adult tissue biopsies is rather low and, thus, vigorous ex vivo expansion is needed especially for therapies that may require extensive and repetitive cell substitution. Therefore, more easily and accessible sources of MSCs are needed. This review summarizes the current knowledge of the different strategies to generate human MSCs in vitro as an alternative method for their applications in regenerative therapy.

Murine Bone Marrow Mesenchymal Stromal Cells Respond Efficiently to Oxidative Stress Despite the Low Level of Heme Oxygenases 1 and 2

AIMS

Mesenchymal stromal cells (MSCs) are heterogeneous cells from adult tissues that are able to differentiate in vitro into adipocytes, osteoblasts, or chondrocytes. Such cells are widely studied in regenerative medicine. However, the success of cellular therapy depends on the cell survival. Heme oxygenase-1 (HO-1, encoded by the Hmox1 gene), an enzyme converting heme to biliverdin, carbon monoxide, and Fe²⁺, is cytoprotective and can affect stem cell performance. Therefore, our study aimed at assessing whether Hmox1 is critical for survival and functions of murine bone marrow MSCs.

RESULTS

Both MSC Hmox1^+/+ and Hmox1^-/- showed similar phenotype, differentiation capacities, and production of cytokines or growth factors. Hmox1^+/+ and Hmox1^-/- cells showed similar survival in response to 50 μmol/L hemin even in increased glucose concentration, conditions that were unfavorable for Hmox1^-/- bone marrow-derived proangiogenic cells (BDMC). Hmox1^+/+ MSCs but not fibroblasts retained low ROS levels even after prolonged incubation with 50 μmol/L hemin, although both cell types have a comparable Hmox1 expression and similarly increase its levels in response to hemin. MSCs Hmox1^-/- treated with hemin efficiently induced expression of a vast panel of antioxidant genes, especially enzymes of the glutathione pathway. Innovation and Conclusion: Hmox1 overexpression is a popular strategy to enhance viability and performance of MSCs after the transplantation. However, murine MSCs Hmox1^-/- do not differ from wild-type MSCs in phenotype and functions. MSC Hmox1^-/- show better resistance to hemin than fibroblasts and BDMCs and rapidly react to the stress by upregulation of quintessential genes in antioxidant response. Antioxid. Redox Signal. 00, 000-000.

Spontaneous up-regulation of SIRT1 during osteogenesis contributes to stem cells' resistance to oxidative stress

Osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs) is a central event in bone formation. However, oxidative stress has a deleterious impact on BM-MSC osteogenesis. In this study, we hypothesized that oxidative stress influenced BM-MSC osteogenesis differently in the early or late stages, in which silent information regulator type 1 (SIRT1) played a critical role. A continuous exposure to sublethal concentrations of hydrogen peroxide (H₂ O₂ ), ranging from 25 to 100 µM for 21 days, resulted in the complete inhibition of BM-MSC osteogenesis. We found that a 7-day treatment with H₂ O₂ inhibited the lineage commitment of BM-MSCs toward osteoblasts, as evidenced by a significant reduction of alkaline phosphatase activity (a typical marker for early osteogenesis). However, moderate oxidative stress did not affect late-differentiated BM-MSCs, as there were comparable levels of matrix mineralization (a typical marker for late osteogenesis). In addition, we observed a spontaneous up-regulation of SIRT1 and intracellular antioxidant enzymes such as superoxide dismutase 2, catalase, and glutathione peroxidase 1, which accounted for the enhanced resistance to oxidative stress upon osteogenic differentiation. Activation of SIRT1 by resveratrol rescued the effect of H₂ O₂ on early-differentiated BM-MSCs and inhibition of SIRT1 by nicotinamide intensified the effect of H₂ O₂ on late-differentiated BM-MSCs, indicating that the SIRT1-mediated pathway was actively involved in MSC osteogenesis and antioxidant mechanisms. Our findings uncovered the relationship between SIRT1 and resistance to H₂ O₂ -induced oxidative stress during BM-MSC osteogenesis, which could provide a new strategy for protecting MSCs from extracellular oxidative stress.

Differentiation of Mesenchymal Stem Cells from Human Induced Pluripotent Stem Cells Results in Downregulation of c-Myc and DNA Replication Pathways with Immunomodulation Toward CD4 and CD8 Cells

Multilineage tissue-source mesenchymal stem cells (MSCs) possess strong immunomodulatory properties and are excellent therapeutic agents, but require constant isolation from donors to combat replicative senescence. The differentiation of human induced pluripotent stem cells (iPSCs) into MSCs offers a renewable source of MSCs; however, reports on their immunomodulatory capacity have been discrepant. Using MSCs differentiated from iPSCs reprogrammed using diverse cell types and protocols, and in comparison to human embryonic stem cell (ESC)-MSCs and bone marrow (BM)-MSCs, we performed transcriptome analyses and assessed for functional immunomodulatory properties. Differentiation of MSCs from iPSCs results in decreased c-Myc expression and its downstream pathway along with a concomitant downregulation in the DNA replication pathway. All four lines of iPSC-MSCs can significantly suppress in vitro activated human peripheral blood mononuclear cell (PBMC) proliferation to a similar degree as ESC-MSCs and BM-MSCs, and modulate CD4 T lymphocyte fate from a type 1 helper T cell (Th1) and IL-17A-expressing (Th17) cell fate to a regulatory T cell (Treg) phenotype. Moreover, iPSC-MSCs significantly suppress cytotoxic CD8 T proliferation, activation, and differentiation into type 1 cytotoxic T (Tc1) and IL-17-expressing CD8 T (Tc17) cells. Coculture of activated PBMCs with human iPSC-MSCs results in an overall shift of secreted cytokine profile from a pro-inflammatory environment to a more immunotolerant milieu. iPSC-MSC immunomodulation was also validated in vivo in a mouse model of induced inflammation. These findings support that iPSC-MSCs possess low oncogenicity and strong immunomodulatory properties regardless of cell-of-origin or reprogramming method and are good potential candidates for therapeutic use. Stem Cells 2018;36:903-914.

Melatonin alleviates oxidative stress-inhibited osteogenesis of human bone marrow-derived mesenchymal stem cells through AMPK activation

Oxidative stress plays an important role in the pathogenesis of aging-related osteoporosis through the increased bone resorption or reduced bone formation. Melatonin, which can exert beneficial actions through antioxidant, anti-inflammatory, and bone-preserving effects, shows promise in preventing oxidative stress-inhibited osteogenesis. However, specific mechanisms by which melatonin rescues oxidative stress-inhibited osteogenesis of human mesenchymal stem cells (MSCs) have not been fully elucidated yet. We therefore investigated whether activation of AMPK by melatonin regulates the antagonistic crosstalk between oxidative stress and osteogenic differentiation in human MSCs. Melatonin treatment significantly enhanced osteogenic differentiation of human MSCs through activation of AMPK and upregulation of FOXO3a and RUNX2 which were known as master transcription factors responsible for the mechanistic link between oxidative stress and osteogenic phenotype. Osteogenic differentiation determined by calcium deposition was significantly increased by melatonin treatment against oxidative stress. In addition, melatonin treatment reconstituted activation of AMPK and expression of FOXO3a and RUNX2 inhibited by oxidative stress. Overall, these results demonstrate that melatonin enhances osteogenic differentiation of human MSCs and restores oxidative stress-inhibited osteogenesis through AMPK activation in human MSCs, suggesting that activation of AMPK by melatonin may represent a promising new therapeutic strategy for treating metabolic bone diseases such as osteoporosis.

Oxidative stress induces imbalance of adipogenic/osteoblastic lineage commitment in mesenchymal stem cells through decreasing SIRT1 functions

With rapidly ageing populations worldwide, the incidence of osteoporosis has reached epidemic proportions. Reactive oxygen species (ROS), a by‐product of oxidative stress and ageing, has been thought to induce osteoporosis by inhibiting osteogenic differentiation of mesenchymal stem cells (MSCs). However, specific mechanisms of how ROS results in alterations on MSC differentiation capacity have been inconsistently reported. We found that H₂O₂, an ROS, simultaneously induced MSC lineage commitment towards adipogenesis and away from osteogenesis at the functional as well as transcriptional level. In addition, H₂O₂ decreased the activities of SIRT1, a histone deacetylase and longevity gene. By silencing and reconstituting SIRT1 in MSCs, we demonstrated that H₂O₂ exerted its disparate effects on adipogenic/osteoblastic lineage commitment mainly through modulating SIRT1 expression levels. Treatment with resveratrol, a SIRT1 agonist, can also reverse this ROS‐induced adipogenesis/osteogenesis lineage imbalance. Moreover, SIRT1 regulation of RUNX2 transcriptional activity was mediated through deacetylation of the ROS‐sensitive transcription factor FOXO3a. Taken together, our data implicate SIRT1 as playing a vital role in ROS‐directed lineage commitment of MSCs by modulating two lineages simultaneously. Our findings on the critical role of SIRT1 in ROS/age‐related perturbations of MSC differentiation capacity highlight this molecule as a target for maintenance of MSC stemness as well as a potential anabolic target in osteoporosis.

Demyelination induced by oxidative stress is regulated by sphingosine 1-phosphate receptors

Oxidative stress is a pathological condition defined as an imbalance between production and removal of reactive oxygen species. This process causes structural cell damage, disrupts DNA repair and induces mitochondrial dysfunction. Many in vitro studies have used direct bolus application of H₂ O₂ to investigate the role of oxidative stress in cell culture. In this study, using mouse organotypic cerebellar slice cultures, the effects of H₂ O₂ -induced oxidative stress on myelination state were examined, using bolus concentrations of H₂ O₂ (0.1-1 mM) and low-continuous H₂ O₂ (∼20 μM) generated from glucose oxidase and catalase (GOX-CAT). Using these models, the potential therapeutic effects of pFTY720, an oral therapy used in multiple sclerosis, was also examined. We found bolus treatment of H₂ O₂ (0.5 mM) and, for the first time, low-continuous H₂ O₂ (GOX-CAT) to induce demyelination in organotypic slices. Both bolus H₂ O₂ and GOX-CAT treatments significantly decreased vimentin expression in these slice cultures as well as increased cell death in isolated astrocyte cultures. Importantly, pre-treatment with pFTY720 significantly attenuated both bolus H₂ O₂ and GOX-CAT-induced demyelination and the GOX-CAT-induced decrease in vimentin in cerebellar slices, without altering levels of the proinflammatory cytokines such as IL-6 and CX3CL1. We also observed increased SMI-32 immunoreactivity in the white matter tract induced by GOX-CAT indicating axonal damage, which was remarkably attenuated by pFTY720. Taken together, this data establishes a novel GOX-CAT model of demyelination and demonstrates that pFTY720 can act independently of inflammatory cytokines to attenuate decreases in vimentin, as well as axonal damage and demyelination induced by oxidative stress.

In Vitro Generation of Vascular Wall-Resident Multipotent Stem Cells of Mesenchymal Nature from Murine Induced Pluripotent Stem Cells

The vascular wall (VW) serves as a niche for mesenchymal stem cells (MSCs). In general, tissue-specific stem cells differentiate mainly to the tissue type from which they derive, indicating that there is a certain code or priming within the cells as determined by the tissue of origin. Here we report the in vitro generation of VW-typical MSCs from induced pluripotent stem cells (iPSCs), based on a VW-MSC-specific gene code. Using a lentiviral vector expressing the so-called Yamanaka factors, we reprogrammed tail dermal fibroblasts from transgenic mice containing the GFP gene integrated into the Nestin-locus (NEST-iPSCs) to facilitate lineage tracing after subsequent MSC differentiation. A lentiviral vector expressing a small set of recently identified human VW-MSC-specific HOX genes then induced MSC differentiation. This direct programming approach successfully mediated the generation of VW-typical MSCs with classical MSC characteristics, both in vitro and in vivo.

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In vitro generation of (VW)-typical MSCs from iPSCs based on a specific HOX code

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Reprogrammed fibroblasts (NEST-iPSCs) facilitated lineage tracing

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A lentiviral vector expressing HOXB7, HOXC6, and HOXC8 induced MSC differentiation

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Generated VW-MSCs showed classical MSC characteristics in vitro and in vivo

c-Maf regulates pluripotency genes, proliferation/self-renewal, and lineage commitment in ROS-mediated senescence of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are therapeutically relevant multilineage and immunomodulatory progenitors. Ex vivo expansion of these rare cells is necessary for clinical application and can result in detrimental senescent effects, with mechanisms still largely unknown. We found that vigorous ex vivo expansion of human adipose tissue-derived MSCs (hAMSCs) results in proliferative decline, cell cycle arrest, and altered differentiation capacity. This senescent phenotype was associated with reactive oxygen species (ROS) accumulation, and with increased expression of G1 cell -cycle inhibitors— p15^INK4b and p16^INK4a — but decreased expression of pluripotency genes—Oct-4, Sox-2, Nanog, and c-Myc—as well as c-Maf a co-factor of MSC lineage-specific transcription factor and sensitive to oxidative stress. These global changes in the transcriptional and functional programs of proliferation, differentiation, and self-renewal were all mediated by ROS-induced suppression of c-Maf, as evidenced by binding of c-Maf to promoter regions of multiple relevant genes in hAMSCs which could be reduced by exogenous ROS. Our findings implicate the strong effects of ROS on multiple stem cell functions with a central role for c-Maf in stem cell senescence.

The oncometabolite R-2-hydroxyglutarate activates NF-κB-dependent tumor-promoting stromal niche for acute myeloid leukemia cells

Mutations of isocitrate dehydrogenase 1 (IDH1) and IDH2 in acute myeloid leukemia (AML) cells produce the oncometabolite R-2-hydroxyglutarate (R-2HG) to induce epigenetic alteration and block hematopoietic differentiation. However, the effect of R-2HG released by IDH-mutated AML cells on the bone marrow microenvironment is unclear. Here, we report that R-2HG induces IκB kinase-independent activation of NF-κB in bone marrow stromal cells. R-2HG acts via a reactive oxygen species/extracellular signal-regulated kinase (ERK)-dependent pathway to phosphorylate NF-κB on the Thr254 residue. This phosphorylation enhances the interaction of NF-κB and the peptidyl-prolyl cis-trans isomerase PIN1 and increases the protein stability and transcriptional activity of NF-κB. As a consequence, R-2HG enhances NF-κB-dependent expression of cytokines including IL-6, IL-8 and complement 5a to stimulate proliferation of AML cells. In addition, R-2HG also upregulates vascular endothelial adhesion molecule 1 and CXCR4 in stromal cells to enhance the contact between AML and stromal cells and attenuates chemotherapy-induced apoptosis. More importantly, we validated the R-2HG-activated gene signature in the primary bone marrow stromal cells isolated from IDH-mutated AML patients. Collectively, our results suggest that AML cell-derived R-2HG may be helpful for the establishment of a supportive bone marrow stromal niche to promote AML progression via paracrine stimulation.

Human pluripotent stem cell (PSC)-derived mesenchymal stem cells (MSCs) show potent neurogenic capacity which is enhanced with cytoskeletal rearrangement

Mesenchymal stem cells (MSCs) are paraxial mesodermal progenitors with potent immunomodulatory properties. Reports also indicate that MSCs can undergo neural-like differentiation, offering hope for use in neurodegenerative diseases. However, ex vivo expansion of these rare somatic stem cells for clinical use leads to cellular senescence. A newer source of MSCs derived from human pluripotent stem cells (PSC) can offer the 'best-of-both-worlds' scenario, abrogating the concern of teratoma formation while preserving PSC proliferative capacity. PSC-derived MSCs (PSC-MSCs) also represent MSCs at the earliest developmental stage, and we found that these MSCs harbor stronger neuro-differentiation capacity than post-natal MSCs. PSC-MSCs express higher levels of neural stem cell (NSC)-related genes and transcription factors than adult bone marrow MSCs at baseline, and rapidly differentiate into neural-like cells when cultured in either standard neurogenic differentiation medium (NDM) or when the cytoskeletal modulator RhoA kinase (ROCK) is inhibited. Interestingly, when NDM is combined with ROCK inhibition, PSC-MSCs undergo further commitment, acquiring characteristics of post-mitotic neurons including nuclear condensation, extensive dendritic growth, and neuron-restricted marker expression including NeuN, β-III-tubulin and Doublecortin. Our data demonstrates that PSC-MSCs have potent capacity to undergo neural differentiation and also implicate the important role of the cytoskeleton in neural lineage commitment.

Current View on Osteogenic Differentiation Potential of Mesenchymal Stromal Cells Derived from Placental Tissues

Mesenchymal stromal cells (MSC) isolated from human term placental tissues possess unique characteristics, including their peculiar immunomodulatory properties and their multilineage differentiation potential. The osteogenic differentiation capacity of placental MSC has been widely disputed, and continues to be an issue of debate. This review will briefly discuss the different MSC populations which can be obtained from different regions of human term placenta, along with their unique properties, focusing specifically on their osteogenic differentiation potential. We will present the strategies used to enhance osteogenic differentiation potential in vitro, such as through the selection of subpopulations more prone to differentiate, the modification of the components of osteo-inductive medium, and even mechanical stimulation. Accordingly, the applications of three-dimensional environments in vitro and in vivo, such as non-synthetic, polymer-based, and ceramic scaffolds, will also be discussed, along with results obtained from pre-clinical studies of placental MSC for the regeneration of bone defects and treatment of bone-related diseases.

Culturing on decellularized extracellular matrix enhances antioxidant properties of human umbilical cord-derived mesenchymal stem cells

Human umbilical cord-derived mesenchymal stem cells (UC-MSCs) have attracted great interest in clinical application because of their regenerative potential and their lack of ethical issues. Our previous studies showed that decellularized cell-deposited extracellular matrix (ECM) provided an in vivo-mimicking microenvironment for MSCs and facilitated in vitro cell expansion. This study was conducted to analyze the cellular response of UC-MSCs when culturing on the ECM, including reactive oxygen species (ROS), intracellular antioxidative enzymes, and the resistance to exogenous oxidative stress. After decellularization, the architecture of cell-deposited ECM was characterized as nanofibrous, collagen fibrils and the matrix components were identified as type I and III collagens, fibronectin, and laminin. Compared to tissue culture polystyrene (TCPS) plates, culturing on ECM yielded a 2-fold increase of UC-MSC proliferation and improved the percentage of cells in the S phase by 2.4-fold. The levels of intracellular ROS and hydrogen peroxide (H2O2) in ECM-cultured cells were reduced by 41.7% and 82.9%, respectively. More importantly, ECM-cultured UC-MSCs showed enhanced expression and activity of intracellular antioxidative enzymes such as superoxide dismutase and catalase, up-regulated expression of silent information regulator type 1, and suppressed phosphorylation of p38 mitogen-activated protein kinase. Furthermore, a continuous treatment with exogenous 100μM H2O2 dramatically inhibited osteogenic differentiation of UC-MSCs cultured on TCPS, but culturing on ECM retained the differentiation capacity for matrix mineralization and osteoblast-specific marker gene expression. Collectively, by providing sufficient cell amounts and enhancing antioxidant capacity, decellularized ECM can be a promising cell culture platform for in vitro expansion of UC-MSCs.

Assessment of the Immunomodulatory Properties of Human Mesenchymal Stem Cells (MSCs)

The immunomodulatory properties of multilineage human mesenchymal stem cells (MSCs) appear to be highly relevant for clinical use towards a wide-range of immune-related diseases. Mechanisms involved are increasingly being elucidated and in this article, we describe the basic experiment to assess MSC immunomodulation by assaying for suppression of effector leukocyte proliferation. Representing activation, leukocyte proliferation can be assessed by a number of techniques, and we describe in this protocol the use of the fluorescent cellular dye carboxyfluorescein succinimidyl ester (CFSE) to label leukocytes with subsequent flow cytometric analyses. This technique can not only assess proliferation without radioactivity, but also the number of cell divisions that have occurred as well as allowing for identification of the specific population of proliferating cells and intracellular cytokine/factor expression. Moreover, the assay can be tailored to evaluate specific populations of effector leukocytes by magnetic bead surface marker selection of single peripheral blood mononuclear cell populations prior to co-culture with MSCs. The flexibility of this co-culture assay is useful for investigating cellular interactions between MSCs and leukocytes.

Human Placenta-Derived Multipotent Cells (hPDMCs) Modulate Cardiac Injury: From Bench to Small and Large Animal Myocardial Ischemia Studies

Cardiovascular disease is the leading cause of death globally, and stem cell therapy remains one of the most promising strategies for regeneration or repair of the damaged heart. We report that human placenta-derived multipotent cells (hPDMCs) can modulate cardiac injury in small and large animal models of myocardial ischemia (MI) and elucidate the mechanisms involved. We found that hPDMCs can undergo in vitro cardiomyogenic differentiation when cocultured with mouse neonatal cardiomyocytes. Moreover, hPDMCs exert strong proangiogenic responses in vitro toward human endothelial cells mediated by secretion of hepatocyte growth factor, growth-regulated oncogene-α, and interleukin-8. To test the in vivo relevance of these results, small and large animal models of acute MI were induced in mice and minipigs, respectively, by permanent left anterior descending (LAD) artery ligation, followed by hPDMC or culture medium-only implantation with follow-up for up to 8 weeks. Transplantation of hPDMCs into mouse heart post-acute MI induction improved left ventricular function, with significantly enhanced vascularity in the cell-treated group. Furthermore, in minipigs post-acute MI induction, hPDMC transplantation significantly improved myocardial contractility compared to the control group ( p=0.016) at 8 weeks postinjury. In addition, tissue analysis confirmed that hPDMC transplantation induced increased vascularity, cardiomyogenic differentiation, and antiapoptotic effects. Our findings offer evidence that hPDMCs can modulate cardiac injury in both small and large animal models, possibly through proangiogenesis, cardiomyogenesis, and suppression of cardiomyocyte apoptosis. Our study offers mechanistic insights and preclinical evidence on using hPDMCs as a therapeutic strategy to treat severe cardiovascular diseases.

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.

Quantitative analysis of NRF2 pathway reveals key elements of the regulatory circuits underlying antioxidant response and proliferation of ovarian cancer cells

Cells are constantly exposed to Reactive Oxygen Species (ROS) produced both endogenously to meet physiological requirements and from exogenous sources. While endogenous ROS are considered as important signalling molecules, high uncontrollable ROS are detrimental. It is unclear how cells can achieve a balance between maintaining physiological redox homeostasis and robustly activate the antioxidant system to remove exogenous ROS. We have utilised a Systems Biology approach to understand how this robust adaptive system fulfils homeostatic requirements of maintaining steady-state ROS and growth rate, while undergoing rapid readjustment under challenged conditions. Using a panel of human ovarian and normal cell lines, we experimentally quantified and established interrelationships between key elements of ROS homeostasis. The basal levels of NRF2 and KEAP1 were cell line specific and maintained in tight correlation with their growth rates and ROS. Furthermore, perturbation of this balance triggered cell specific kinetics of NRF2 nuclear-cytoplasmic relocalisation and sequestration of exogenous ROS. Our experimental data were employed to parameterise a mathematical model of the NRF2 pathway that elucidated key response mechanisms of redox regulation and showed that the dynamics of NRF2-H2O2 regulation defines a relationship between half-life, total and nuclear NRF2 level and endogenous H2O2 that is cell line specific.

Age-related decreases of serum-response factor levels in human mesenchymal stem cells are involved in skeletal muscle differentiation and engraftment capacity

Skeletal muscle (SkM) comprise ∼40% of human body weight. Injury or damage to this important tissue can result in physical disability, and in severe cases is difficult for its endogenous stem cell-the satellite cell-to reverse effectively. Mesenchymal stem cells (MSC) are postnatal progenitor/stem cells that possess multilineage mesodermal differentiation capacity, including toward SkM. Adult bone marrow (BM) is the best-studied source of MSCs; however, aging also decreases BMMSC numbers and can adversely affect differentiation capacity. Therefore, we asked whether human sources of developmentally early stage mesenchymal stem cells (hDE-MSCs) isolated from embryonic stem cells, fetal bone, and term placenta could be cellular sources for SkM repair. Under standard muscle-inducing conditions, hDE-MPCs differentiate toward a SkM lineage rather than cardiomyocytic or smooth muscle lineages, as evidenced by increased expression of SkM-associated markers and in vitro myotube formation. In vivo transplantation revealed that SkM-differentiated hDE-MSCs can efficiently incorporate into host SkM tissue in a mouse model of SkM injury. In contrast, adult BMMSCs do not express SkM-associated genes after in vitro SkM differentiation nor engraft in vivo. Further investigation of possible factors responsible for this difference in SkM differentiation potential revealed that, compared with adult BMMSCs, hDE-MSCs expressed higher levels of serum response factor (SRF), a transcription factor critical for SkM lineage commitment. Moreover, knockdown of SRF in hDE-MSCs resulted in decreased expression of SkM-related genes after in vitro differentiation and decreased in vivo engraftment. Our results implicate SRF as a key factor in age-related SkM differentiation capacity of MSCs, and demonstrate that hDE-MSCs are possible candidates for SkM repair.

Rescue of proinflammatory cytokine-inhibited chondrogenesis by the antiarthritic effect of melatonin in synovium mesenchymal stem cells via suppression of reactive oxygen species and matrix metalloproteinases

Cartilage repair by mesenchymal stem cells (MSCs) often occurs in diseased joints in which the inflamed microenvironment impairs chondrogenic maturation and causes neocartilage degradation. In this environment, melatonin exerts an antioxidant effect by scavenging free radicals. This study aimed to investigate the anti-inflammatory and chondroprotective effects of melatonin on human MSCs in a proinflammatory cytokine-induced arthritic environment. MSCs were induced toward chondrogenesis in the presence of interleukin-1β (IL-1β) or tumor necrosis factor α (TNF-α) with or without melatonin. Levels of intracellular reactive oxygen species (ROS), hydrogen peroxide, antioxidant enzymes, and cell viability were then assessed. Deposition of glycosaminoglycans and collagens was also determined by histological analysis. Gene expression of chondrogenic markers and matrix metalloproteinases (MMPs) was assessed by real-time polymerase chain reaction. In addition, the involvement of the melatonin receptor and superoxide dismutase (SOD) in chondrogenesis was investigated using pharmacologic inhibitors. The results showed that melatonin significantly reduced ROS accumulation and increased SOD expression. Both IL-1β and TNF-α had an inhibitory effect on the chondrogenesis of MSCs, but melatonin successfully restored the low expression of cartilage matrix and chondrogenic genes. Melatonin prevented cartilage degradation by downregulating MMPs. The addition of luzindole and SOD inhibitors abrogated the protective effect of melatonin associated with increased levels of ROS and MMPs. These results demonstrated that proinflammatory cytokines impair the chondrogenesis of MSCs, which was rescued by melatonin treatment. This chondroprotective effect was potentially correlated to decreased ROS, preserved SOD, and suppressed levels of MMPs. Thus, melatonin provides a new strategy for promoting cell-based cartilage regeneration in diseased or injured joints.

Role of SIRT1 and AMPK in mesenchymal stem cells differentiation

The differentiation capabilities of mesenchymal stem cells (MSCs) compromise with age and with in vitro passages which could impair the efficacy of cell therapy and tissue engineering. However, how to maintain these capabilities is not fully understood. Calorie restriction (CR, decreasing caloric intake by 30-40%) could extend longevity and reduce aging-related diseases. Recent studies revealed that CR could influence the lineage determination of stem cells including MSCs. Two important mediators of CR might be silent mating type information regulation 2 homolog 1 (SIRT1), a NAD(+)-dependent deacetylase, and AMP-activated protein kinase (AMPK), an energy-sensing kinase. Evidences are mounting that both SIRT1 and AMPK play important roles in cell fate determination of MSCs. Herein, we intend to sum up our understanding about the role of SIRT1 and AMPK in osteogenic and adipogenic potential of MSCs. Metabolic process of MSCs differentiation and the putative interplay of SIRT1 and AMPK in this process was also discussed.

Inhibition of nuclear Nox4 activity by plumbagin: effect on proliferative capacity in human amniotic stem cells

Human amniotic fluid stem cells (AFSC) with multilineage differentiation potential are novel source for cell therapy. However, in vitro expansion leads to senescence affecting differentiation and proliferative capacities. Reactive oxygen species (ROS) have been involved in the regulation of stem cell pluripotency, proliferation, and differentiation. Redox-regulated signal transduction is coordinated by spatially controlled production of ROS within subcellular compartments. NAD(P)H oxidase family, in particular Nox4, has been known to produce ROS in the nucleus; however, the mechanisms and the meaning of this function remain largely unknown. In the present study, we show that Nox4 nuclear expression (nNox4) increases during culture passages up to cell cycle arrest and the serum starvation causes the same effect. With the decrease of Nox4 activity, obtained with plumbagin, a decline of nuclear ROS production and of DNA damage occurs. Moreover, plumbagin exposure reduces the binding between nNox4 and nucleoskeleton components, as Matrin 3. The same effect was observed also for the binding with phospho-ERK, although nuclear ERK and P-ERK are unchanged. Taken together, we suggest that nNox4 regulation may have important pathophysiologic effects in stem cell proliferation through modulation of nuclear signaling and DNA damage.

Nutrient-sensing pathways and metabolic regulation in stem cells

Stem cells exert precise regulation to maintain a balance of self-renewal and differentiation programs to sustain tissue homeostasis throughout the life of an organism. Recent evidence suggests that this regulation is modulated, in part, via metabolic changes and modifications of nutrient-sensing pathways such as mTOR and AMPK. It is becoming increasingly clear that stem cells inhibit oxidative phosphorylation in favor of aerobic glycolysis for energy production. Recent progress has detailed the molecular mechanisms of this metabolic phenotype and has offered insight into new metabolic pathways that may be involved in stem cell homeostasis.