Aging of mesenchymal stem cells

The role of adult mesenchymal stem cells (MSC) in tissue maintenance and regeneration has received significant attention of late. Questions arise to what extent these cells are either subject to, or causes of aging; whether age-related changes in these cells are due to intrinsic factors or induced by the somatic environment. This review collates and examines recent data in support of these different theories. By means of introduction, a brief overview is given of current MSC definitions and their basic role in tissue regeneration followed by a comparative analysis of gerontological studies involving MSC. Evidence for extrinsic aging and various aging markers relating to morphology, proliferation, signalling, senescence markers, telomeres and telomerase, and other indicators is discussed. We observe that while the literature might often appear to conflict, many apparent discrepancies are attributable to inconsistent methods of extracting and isolating MSC which in fact contains various subsets of adult stem cells, varying not only in their differentiation potential but also in their vulnerability to senescence--ranging from quasi-somatic lifespan to perennial vigour. Thus, mesenchymal stem cells emerge as both subject to and key mediators of organismal aging.     

Stem cell differentiation to epidermal lineages on electrospun nanofibrous substrates for skin tissue engineering

Bone marrow (BM) mesenchymal stem cells (MSC) capable of differentiating along the epidermal lineage on engineered nanofibrous scaffolds have great potential for bionanomaterial-cell transplantation therapy of skin wounds. MSC have been the focus of many tissue engineering studies, mainly because of their multipotential properties. We investigated the potential of human BM-derived MSC for epidermal cell differentiation in vitro on electrospun collagen/poly(l-lactic acid)-co-poly(3-caprolactone) (Coll/PLLCL) nanofibrous scaffolds. PLLCL and Coll/PLLCL nanofibrous scaffolds were fabricated by an electrospinning process and their chemical and mechanical characterization carried out by scanning electron microscopy (SEM), water contact angle determination, Fourier transform infrared spectroscopy, and tensile testing. The differentiation of MSC was carried out using epidermis inducing factors, including epidermal growth factor (EGF) and 1,25-dihydroxyvitamin D(3), in culture medium. The proliferation of MSC evaluated by cell proliferation assay showed that the number of cells grown on Coll/PLLCL nanofibrous scaffolds was significantly higher than those on PLLCL scaffolds. The SEM results showed that MSC differentiated on Coll/PLLCL nanofibrous scaffolds showed a round keratinocyte morphology and expressed keratin 10, filaggrin and partial involucrin protein by immunofluorescent microscopic studies. The interaction of MSC and nanofibers was studied and we concluded that the electrospun Coll/PLLCL nanofibers could mimic the native skin extracellular matrix environment and are promising substrates for advanced skin tissue engineering. Our studies on the differentiation of MSC along the epidermal lineage on nanofibrous scaffolds suggest their potential application in skin regeneration without regional differentiation.     

Hepatic differentiation potential of commercially available human mesenchymal stem cells

The ready availability and low immunogenicity of commercially available mesenchymal stem cells (MSC) render them a potential cell source for the development of therapeutic products. With cell source a major bottleneck in hepatic tissue engineering, we investigated whether commercially available human MSC (hMSC) can transdifferentiate into the hepatic lineage. Based on previous studies that find rapid gain of hepatic genes in bone marrow-derived stem cells cocultured with liver tissue, we used a similar approach to drive hepatic differentiation by coculturing the hMSC with rat livers treated or untreated with gadolinium chloride (GdCl(3)). After a 24-hour coculture period with liver tissue injured by GdCl(3) in a Transwell configuration, approximately 34% of the cells differentiated into albumin-expressing cells. Cocultured cells were subsequently maintained with growth factors to complete the hepatic differentiation. Cocultured cells expressed more hepatic gene markers, and had higher metabolic functions and P450 activity than cells that were only differentiated with growth factors. In conclusion, commercially available hMSC do show hepatic differentiation potential, and a liver microenvironment in culture can provide potent cues to accelerate and deepen the differentiation. The ability to generate hepatocyte-like cells from a commercially available cell source would find interesting applications in liver tissue engineering.     

Two distinct stem cell lineages in murine bone marrow

Mesenchymal stem cells (MSC), a distinct type of adult stem cell, are easy to isolate, culture, and manipulate in ex vivo culture. These cells have great plasticity and potential for therapeutic application, but their properties are poorly understood because of their low frequency and the lack of knowledge on cell surface markers and their location of origin. The present study was designed to address the undefined lineage relationship of hematopoietic and mesenchymal stem cells. Genetically marked, highly purified hematopoietic stem cells (HSCs) were transplanted into wild-type animals and, after bone marrow repopulation, the progeny were rigorously investigated for differentiation potential into mesenchymal tissues by analyzing in vitro differentiation into mesenchymal tissues. None/very little of the hematopoietic cells contributed to colony-forming units fibroblast activity and mesenchymal cell differentiation; however, unfractionated bone marrow cells resulted in extensive replacement of not only hematopoietic cells but also mesenchymal cells, including MSCs. As a result, we concluded that purified HSCs have no significant potency to differentiate into mesenchymal lineage. The data strongly suggest that hematopoietic cells and mesenchymal lineage cells are derived from individual lineage-specific stem cells. In addition, we succeeded in visualizing mesenchymal lineage cells using in vivo microimaging and immunohistochemistry. Flow cytometric analysis revealed CD140b (PDGFRbeta) could be a specific marker for mesenchymal lineage cells. The results may reinforce the urgent need for a more comprehensive view of the mesenchymal stem cell identity and characteristics. Disclosure of potential conflicts of interest is found at the end of this article.     

The effect of aging on the pluripotential capacity and regenerative potential of human periodontal ligament stem cells

Multipotent postnatal stem cells can be isolated from human periodontal ligaments (PDLs) and have the potential for large-scale expansion, offering a reliable cell source for clinical use in periodontal regenerative therapies. However, the effects of aging on the mesenchymal stem cell (MSC) properties of these cells remain undefined. The aims of this study were to isolate and characterize the periodontal ligament stem cells (PDLSCs) derived from human impacted third molars of donors of different ages and to compare their pluripotential capacity and regenerative potential. PDL tissues were obtained from 90 surgically extracted third molars and divided into four groups according to the donor's age. For each group, the colony-forming ability, proliferative capacity, migratory potential, cell surface antigens, differentiation ability, alkaline phosphatase activity, and gene expression of the PDLSCs were contrastively evaluated and quantified for statistical analysis. The in?vivo tissue regenerative potential of PDLSCs was assessed by an in?vivo ectopic transplantation model. It was found that human PDLSCs were successfully isolated and characterized as MSCs in all 90 teeth. PDLSCs derived from donors of different ages were successfully differentiated under an osteogenic and adipogenic microenvironment. The proliferative and migratory potential and the differentiation capacity of PDLSCs decreased as age increased (p?相似文献   

Cell senescence: a challenge in cartilage engineering and regeneration

Cartilage defects, most commonly caused by aging and degenerative disease, have become the primary target of cartilage tissue engineering due to a lack of effective treatments and limited regenerative abilities. The limited success of autologous chondrocyte implantation necessitates the development of alternative cell sources. Adult mesenchymal stem cells (MSCs) with multiple lineage differentiation potentials from various sources can supplement the shortage of human autologous chondrocytes. However, cell senescence presents a big challenge for large-scale ex vivo expansion and maintenance of MSC stemness. In this review, we will summarize some potential factors resulting in cell senescence during cartilage tissue engineering, including ex vivo expansion, donor age, and degenerative diseases, and the challenge in the identification of senescent cells. The presence of senescence-associated β-galacotosidase and DNA damage, accumulation of reactive oxygen species, the decline of DNA replication and telomerase activity, and shortened telomere length is indicative of senescence, but none of them are specific. To some extent, growth factors, antioxidants, serum deprivation, or platelet-rich plasma treatment as well as low oxygen have been successful in retarding cell senescence. Recently, decellurized extracellular matrix, especially decellularized stem cell matrix, has emerged as a more promising tool in retaining cells in a younger state. Some potential signaling pathways in cell senescence will also be discussed for their potential involvement in cartilage regeneration despite the fact that comprehensive mechanisms are still under investigation.     

Origin and differentiation of human and murine stroma

Stromal cells generated in long-term cultures appear to follow a vascular smooth muscle differentiation pathway. Such a pathway, comprising several steps hallmarked by the expression of cytoskeletal and extracellular matrix markers, is found not only for bone marrow stromal cells, but also for stromal cells generated from the different developmental sites of hematopoiesis (yolk sac, aorta-gonad-mesonephros region, fetal liver, and spleen). Factors responsible for this differentiation pathway and its functional significance are discussed. The mesenchymal founder cell might be, at least for bone marrow, a mesenchymal stem cell (MSC), giving rise to stromal cells, endothelial cells, adipocytes, osteoblasts, and chondrocytes. A feature that distinguishes the MSC lineage from that of the hematopoietic stem cell lineage is that differentiation pathways are not strictly delineated, since even apparently fully differentiated cells from a given lineage have the potential to convert into another lineage (phenotype "plasticity") and intermediate cell phenotypes are observed. A stochastic Repression/Induction model that would account for this plasticity is proposed.     

A New Chapter for Mesenchymal Stem Cells: Decellularized Extracellular Matrices

From orthopedic to neurological disorders, stem cells are used as platforms to understand disease mechanisms and considered as novel and promising treatment options, especially when the valid therapeutic approaches are unavailable or ineffective. There are different stem cell types in the literature, however the spindle-shaped, colony forming and multilineage-differentiating cells, also known as mesenchymal stem cells (MSC) are very popular, as MSC can be isolated from different tissues with minimal ethical concerns and without tumor formations, which make them easily accessible and widely used in vitro and in vivo studies. In the literature, MSC have been shown to have therapeutic effects and orchestrate the healing process via their mobilization, migration, differentiation capacities, immunomodulation properties and/or secretion of bioactive factors. Nowadays, MSC derived extracellular matrices (ECM), which are part of the secreted/produced bioactive molecules from MSC; draw attention of researchers due to their key roles in cell biology. Several groups have isolated ECM from in vitro cultured MSC using different methods of decellularization techniques for tissue-engineering approaches. According to current knowledge, decellularized ECM (dECM) influence growth, adhesion, differentiation, migration, apoptosis, proliferation, and phenotype of cells, covering almost all cellular events. In this comprehensive review we focused on MSC and the isolation methods and effects of MSC derived dECM (MSC-dECM).     

Mechanical Signals As a Non-Invasive Means to Influence Mesenchymal Stem Cell Fate, Promoting Bone and Suppressing the Fat Phenotype

Pluripotent mesenchymal stem cells (MSCs) are considered ideal therapeutic targets in regenerative medicine, as they hold the capacity to differentiate into higher order connective tissues. The potential to harness MSCs for disease treatment and acceleration of repair will ultimately depend on an improved understanding of how physical and/or chemical signals regulate their activity, and the ability of exogenous stimuli to enhance MSC proliferation and define MSC fate. Recent appreciation that bone marrow osteoprogenitors are inversely proportional to adipocyte precursors suggests that their shared progenitor, the MSC, will commit to one lineage at the cost of the other. This interrelationship may contribute to the phenotype of sedentary subjects who have more fat and less bone, while conversely, to the outcome of exercise being less fat and more bone. Mechanical biasing of MSC lineage selection suggests that physical signals may influence the quantity of both fat and bone through developmental, as well as metabolic or adaptive pathways. Considered with the recent finding that low magnitude mechanical signals (LMMS) suppress the development of subcutaneous and visceral fat without elevating energy expenditure, this indicates that MSCs are ideally positioned as mechanosensitive elements central to musculoskeletal adaptation, but that the signals needn't be large to be influential. The biasing of MSC differentiation by mechanical signals represents a unique means by which adiposity can be inhibited while simultaneously promoting a better skeleton, and may provide the basis for a safe, non-invasive, non-pharmacologic strategy to prevent both obesity and osteoporosis, yet uniquely - without targeting the resident fat or bone cell.     

The role of epigenetic modifications in the osteogenic differentiation of adipose-derived stem cells

ABSTRACT

Over the last decade, stem cells have drawn extensive attention from scientists due to their full potential in tissue engineering, gene therapy, and cell therapy. Adipose-derived stem cells (ADSCs), which represent one type of mesenchymal stem cell (MSC), hold great promise in bone tissue engineering due to their painless collection procedure, their ability to self-renew and their multi-lineage differentiation properties. Major epigenetic mechanisms, which involve DNA methylation, histone modifications and RNA interference (RNAi), are known to represent one of the determining factors of ADSC fate and differentiation. Understanding the epigenetic modifications of ADSCs may provide a clue for improving stem cell therapy in bone repair and regeneration. The aim of this review is to present the recent advances in understanding the epigenetic mechanisms that facilitate ADSC differentiation into an osteogenic lineage, in addition to the characteristics of the main epigenetic modifications.     

Lithium enhanced cell proliferation and differentiation of mesenchymal stem cells to neural cells in rat spinal cord

Lithium has been shown to inhibit apoptosis of neural progenitor cells (NPCs) and promote differentiation of NPCs. However, there was rare data to discuss the effects of lithium on neural differentiation of mesenchymal stem cells (MSCs). Here, we investigated the potential promotion of lithium to MSC proliferation and neural differentiation in vitro and after transplanted into the ventral horn of rat spinal cord in vivo. We found that lithium possesses the ability to promote proliferation of GFP-MSCs in a dose dependent manner as verified by growth curve and bromodeoxyuridine (BrdU) incorporation assays; While in neural induction medium, lithium (0.1 mM) promotes neural differentiation of GFP-MSCs as verified by immunostaining and quantitative analysis. After transplantation of GFP-MSCs into the rat spinal cord, lithium treatment enhanced cell survival and neural differentiation after transplantation as verified by immunohistochemistry. These data suggested that lithium could be a potential drug to augment the therapeutic efficiency of MSCs transplantation therapy in central nervous system (CNS) disorders.     

Distinct gene expression profile of human mesenchymal stem cells in comparison to skin fibroblasts employing cDNA microarray analysis of 9600 genes

Broad differentiation capacity has been described for mesenchymal stem cells (MSC) from human bone marrow. We sought to identify genes associated with the immature state and pluripotency of this cell type. To prove the pluripotent state of the MSC, differentiation into osteocytes, adipocytes, and chondrocytes was performed in vitro. In contrast, normal skin cells did not harbor these differentiation abilities. We compared the expression profile of human bone marrow MSC with cDNA from one primary human skin cell line as control, using a cDNA chip providing 9600 genes. The identity of all relevant genes was confirmed by direct sequencing. Data of gene array expression were corroborated employing quantitative PCR analysis. About 80 genes were differently expressed more than threefold in MSC compared to mature skin fibroblasts. Interestingly, primary human MSC were found to upregulate a number of genes important for embryogenesis such as distal-less homeo box 5, Eyes absent homolog 2, inhibitor of DNA binding 3, and LIM protein. In contrast, mesenchymal lineage genes were downregulated in MSC in comparison to skin cells. We also detected expression of some genes involved in neural development, indicating the broad differentiation capabilities of MSC. We conclude that human mesenchymal stem cells harbor an expression profile distinct from mature skin fibroblast, and genes associated with developmental processes and stem cell function are highly expressed in adult mesenchymal stem cells.     

Mesenchymal Stem Cells as a Treatment for Peripheral Arterial Disease: Current Status and Potential Impact of Type II Diabetes on Their Therapeutic Efficacy

Mesenchymal stem cells (MSCs), due to their paracrine, transdifferentiation, and immunosuppressive effects, hold great promise as a therapy for peripheral arterial disease. Diabetes is an important risk factor for peripheral arterial disease; however, little is known of how type II diabetes affects the therapeutic function of MSCs. This review summarizes the current status of preclinical and clinical studies that have been performed to determine the efficacy of MSCs in the treatment of peripheral arterial disease. We also present findings from our laboratory regarding the impact of type II diabetes on the therapeutic efficacy of MSCs neovascularization after the induction of hindlimb ischemia. In our studies, we documented that experimental type II diabetes in db/db mice impaired MSCs’ therapeutic function by favoring their differentiation towards adipocytes, while limiting their differentiation towards endothelial cells. Moreover, type II diabetes impaired the capacity of MSCs to promote neovascularization in the ischemic hindlimb. We further showed that these impairments of MSC function and multipotency were secondary to hyperinsulinemia-induced, Nox4-dependent oxidant stress in db/db MSCs. Should human MSCs display similar oxidant stress-induced impairment of function, these findings might permit greater leverage of the potential of MSC transplantation, particularly in the setting of diabetes or other cardiovascular risk factors, as well as provide a therapeutic approach by reversing the oxidant stress of MSCs prior to transplantation.     

Short-term BMP-2 expression is sufficient for in vivo osteochondral differentiation of mesenchymal stem cells

Currently available murine models to evaluate mesenchymal stem cell (MSC) differentiation are based on cell injection at ectopic sites such as muscle or skin. Due to the importance of environmental factors on the differentiation capacities of stem cells in vivo, we investigated whether the peculiar synovial/cartilaginous environment may influence the lineage specificity of bone morphogenetic protein (BMP)-2-engineered MSCs. To this aim, we used the C3H10T1/2-derived C9 MSCs that express BMP-2 under control of the doxycycline (Dox)-repressible promoter, Tet-Off, and showed in vitro, using the micropellet culture system that C9 MSCs kept their potential to differentiate toward chondrocytes. Implantation of C9 cells, either into the tibialis anterior muscles or into the joints of CB17-severe combined immunodeficient bg mice led to the formation of cartilage and bone filled with bone marrow as soon as day 10. However, no differentiation was observed after injection of na?ve MSCs or C9 cells that were repressed to secrete BMP-2 by Dox addition. The BMP-2-induced differentiation of adult MSCs is thus independent of soluble factors present in the local environment of the synovial/cartilaginous tissues. Importantly, we demonstrated that a short-term expression of the BMP-2 growth factor is necessary and sufficient to irreversibly induce bone formation, suggesting that a stable genetic modification of MSCs is not required for stem cell-based bone/cartilage engineering.     

Mechanism of metformin: Inhibition of DNA damage and proliferative activity in Drosophila midgut stem cell

Age-related changes in stem cells could have a profound impact on tissue aging and the development of age-related diseases such as cancer. However, the effects of metformin, a recently recognized anti-cancer drug, on stem cell aging remain largely unknown. In the present study, an experiment was set up to investigate the underlying mechanism of metformin's beneficial effects on age-related changes in intestinal stem cells (ISCs) derived from Drosophila midgut. Results showed that metformin reduced age- and oxidative stress-related accumulation of DNA damage marked by Drosophila γH2AX foci and 8-oxo-dG in ISCs and progenitor cells. Metformin also inhibited age and- oxidative stress-related ISC hyperproliferation as well as intestinal hyperplasia. Our study further revealed that the inhibitory effects of metformin on DNA damage accumulation may be due to the down-regulation of age-related and oxidative stress-induced AKT activity. These data indicate that metformin has beneficial effects on age-related changes in ISCs derived from Drosophila midgut. Further, our results suggest a possible impact of DNA damage on stem cell genomic instability, which leads to the development of age-related diseases. Additionally, our study suggests that Drosophila midgut stem cells can be a suitable model system for studying stem cell biology and stem cell aging.     

Mesenchymal stem cell-derived extracellular vesicle-based therapies protect against coupled degeneration of the central nervous and vascular systems in stroke

Stem cell-based treatments have been suggested as promising candidates for stroke. Recently, mesenchymal stem cells (MSCs) have been reported as potential therapeutics for a wide range of diseases. In particular, clinical trial studies have suggested MSCs for stroke therapy. The focus of MSC treatments has been directed towards cell replacement. However, recent research has lately highlighted their paracrine actions. The secretion of extracellular vesicles (EVs) is offered to be the main therapeutic mechanism of MSC therapy. However, EV-based treatments may provide a wider therapeutic window compared to tissue plasminogen activator (tPA), the traditional treatment for stroke. Exosomes are nano-sized EVs secreted by most cell types, and can be isolated from conditioned cell media or body fluids such as plasma, urine, and cerebrospinal fluid (CSF). Exosomes apply their effects through targeting their cargos such as microRNAs (miRs), DNAs, messenger RNAs, and proteins at the host cells, which leads to a shift in the behavior of the recipient cells. It has been indicated that exosomes, in particular their functional cargoes, play a significant role in the coupled pathogenesis and recovery of stroke through affecting the neurovascular unit (NVU). Therefore, it seems that exosomes could be utilized as diagnostic and therapeutic tools in stroke treatment. The miRs are small endogenous non-coding RNA molecules which serve as the main functional cargo of exosomes, and apply their effects as epigenetic regulators. These versatile non-coding RNA molecules are involved in various stages of stroke and affect stroke-related factors. Moreover, the involvement of aging-induced changes to specific miRs profile in stroke further highlights the role of miRs. Thus, miRs could be utilized as diagnostic, prognostic, and therapeutic tools in stroke. In this review, we discuss the roles of stem cells, exosomes, and their application in stroke therapy. We also highlight the usage of miRs as a therapeutic choice in stroke therapy.     

Research on stem cells as candidates to be differentiated into hepatocytes

Liver diseases have become one of the most important causes of morbidity and mortality in the world. Cell therapy and liver transplantation are though to be two treatment options well accepted. However, the shortage of cells sources in cytotherapy and the lack of liver donor in liver transplantation are the major obstacles for the performance of these treatment methods. It urged us to find new origins of extra-hepatic cells. A number of recent studies show that extra-hepatic mesenchymal stem cells (MSC) from different tissues can be differentiated into hepatocytes like cells (HLC). Several hepatic differentiation protocols of MSC have been published in recent years, based on cellular stimulation with exogenous cytokines/growth factors, co-culture with fetal or adult hepatocytes, 2- or 3-dimensional (2D, 3D) matrices to favor differentiation. Independently from the starting stem cells population used, some minimal criteria must be fulfilled to ensure therapeutic success: in vitro expandability, expression of hepatic like surface markers, with hepatic cell functions, and minimal or absent immunogenicity in the recipient host. In this review, we focused on stem cells originated from bone marrow, umbilical cord and adipose tissue which are widely investigated in recent years and have been proved to have liver regenerative potential, the factors used to differentiate stem cells to hepatocyte-like cells and the methods used to investigate these cells.