hTERT- and hCTLA4Ig-expressing human bone marrow-derived mesenchymal stem cells: in vitro and in vivo characterization and osteogenic differentiation

Telomeres and Telomerase in the Control of Stem Cells

Stem cells serve as a source of cellular material in embryogenesis and postnatal growth and regeneration. This requires significant proliferative potential ensured by sufficient telomere length. Telomere attrition in the stem cells and their niche cells can result in the exhaustion of the regenerative potential of high-turnover organs, causing or contributing to the onset of age-related diseases. In this review, stem cells are examined in the context of the current telomere-centric theory of cell aging, which assumes that telomere shortening depends not just on the number of cell doublings (mitotic clock) but also on the influence of various internal and external factors. The influence of the telomerase and telomere length on the functional activity of different stem cell types, as well as on their aging and prospects of use in cell therapy applications, is discussed.

Astragaloside IV Improves Tibial Defect in Rats and Promotes Proliferation and Osteogenic Differentiation of hBMSCs through MiR-124-3p.1/STAT3 Axis

Astragaloside IV (AST-IV) facilitates the proliferation and migration of osteoblast-like cells. We sought to explore the effect and potential mechanism of AST-IV on regeneration of tibial defects. To reveal the effect of AST-IV on regeneration of tibial defects in rat, HE staining and microcomputed tomography (μCT) were performed on tibial bone. The binding relationship between miR-124-3p.1 and STAT3 was analyzed by TargetScan V7.2 and a dual-luciferase reporter assay. Human bone marrow mesenchymal stromal/stem cells (hBMSCs) were identified by morphological observation and flow-cytometric analysis. To reveal the effect and mechanism of AST-IV on phenotypes of hBMSCs, hBMSCs were treated with AST-IV, miR-124-3p.1 mimic, and pcDNA-STAT3, and cell viability, cell cycle, ALP activity, and calcium deposition of hBMSCs in vitro were determined by MTT, flow-cytometric analysis, ELISA, and Alizarin red staining, respectively. The expressions of osteoblast marker molecules (RUNX2, OCN, Smad4), miR-124-3p.1, and STAT3 were indicated by RT-qPCR and Western blot. AST-IV decreased miR-124-3p.1 expression, increased STAT3 expression in tibial bone defects, and promoted regeneration of tibial bone defects in a concentration-dependent manner. The hBMSCs appeared spindle-shaped and were positive for CD105, but negative for CD34. MiR-124-3p.1 negatively regulated STAT3 expression in hBMSCs under osteogenic conditions. AST-IV promoted viability, cell cycle, ALP activity, and osteogenic differentiation of hBMSCs along with increased expressions of osteoblast marker molecules, which was partially reversed by miR-124-3p.1 overexpression. However, the effect of miR-124-3p.1 overexpression on hBMSCs was also partially reversed by STAT3 overexpression. AST-IV improves tibial defects in rats and promotes proliferation and osteogenic differentiation of hBMSCs through the miR-124-3p.1/STAT3 axis.

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.

Molecular Phenotyping of Telomerized Human Bone Marrow Skeletal Stem Cells Reveals a Genetic Program of Enhanced Proliferation and Maintenance of Differentiation Responses

Long-term in vitro expansion of bone marrow stromal (skeletal) stem cells (also known as human mesenchymal stem cells [hMSC]) is associated with replicative senescence and impaired functions. We have previously reported that telomerization of hMSC through hTERT overexpression led to bypassing a replicative senescence phenotype and improved in vitro and in vivo functions. However, the molecular consequence of telomerization is poorly characterized. Thus, we compared the molecular phenotype of a well-studied telomerized hMSC (hMSC-TERT) cell line with primary hMSC. At a cellular level, both cell populations exhibited strong concordance for the known hMSC CD markers, similar responses to osteoblast (OB) differentiation induction, and formed heterotopic bone in vivo. Overall gene expression was highly correlated between both cell types with an average Pearson's correlation coefficient (R2) between the gene expression of all primary hMSC and all hMSC-TERT samples of 0.95 (range 0.93-0.96). Quantitative analysis of gene expression of CD markers, OB cell markers, and transcription factors (TF) showed a high degree of similarity between the two cell populations (72%, 77%, and 81%, respectively). The hMSC-TERT population was enriched mainly for genes associated with cell cycle and cell cycle signaling when compared with primary hMSC. Other enrichment was observed for genes involved in cell adhesion and skeletal system development and immune response pathways. Interestingly, hMSC-TERT shared a telomerization signature with upregulation of cancer/testis antigens, MAGE, and PAGE genes. Our data demonstrate that the enhanced biological characteristics of hMSC after telomerization are mainly due to enhanced expression of cell proliferation genes, whereas gene expression responses to differentiation are maintained. © 2018 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Bone tissue engineering strategy based on the synergistic effects of silicon and strontium ions

Multipotent human bone marrow mesenchymal stem cells (hBMSCs) are commonly used as seed cells in bone tissue engineering, but their clinical application is limited due to two challenges. One is the expansion of hBMSCs without loss of the stemness, and the other is the stimulation of osteogenic differentiation of hBMSCs when combined with biomaterials. In this study we demonstrated an approach by firstly elucidating the functional effects and optimal concentrations of Si and Sr ions on the proliferation and osteogenic differentiation of hBMSCs, and then designing bioactive bioceramic/alginate hydrogels which could release Si and Sr bioactive ions in the same optimal concentrations range for activation of the cells in vivo. The results showed that Si and Sr ions could synergistically stimulate cell proliferation without losing the stemness. Furthermore, at higher concentrations, Si and Sr ions stimulated osteogenic differentiation instead of enhancing proliferation. The designed bioactive hydrogels revealed activity to stimulate not only the osteogenic differentiation of encapsulated hBMSCs, but also the blood vessel formation in vivo. These results suggested that the design of biomaterials based on the biological function of different material elements was an effective approach for bone tissue engineering applications.

STATEMENT OF SIGNIFICANCE

The clinical application of multipotent human bone marrow mesenchymal stem cells (hBMSCs) in bone tissue engineering is limited due to two challenges. One is the expansion of cells without loss of the stemness, and the other is the stimulation of osteogenic differentiation of hBMSCs within the biomaterial scaffolds. Herein, we demonstrated an approach by firstly elucidating the functional effects and optimal concentrations of Si and Sr ions on the proliferation without losing stemness and osteogenic differentiation of hBMSCs, and then designing a bioactive bioceramic/alginate hydrogel which could release Si and Sr ions for in vivo activation of cells. The bioactive hydrogels revealed activity to stimulate not only osteogenic differentiation of encapsulated hBMSCs, but also the blood vessel formation in vivo. Our work provided an effective approach to design effective biomaterials for tissue engineering.

Non-invasive in vivo molecular imaging of intra-articularly transplanted immortalized bone marrow stem cells for osteoarthritis treatment

Pathophysiology of osteoarthritis (OA) is characterized by progressive loss of articular cartilage in the knee-joints. To impart regenerative ability in lowly metabolizing chondrocytes, the bone marrow stem cells (BMSCs) has recently been recognized as a superior alternative treatment for OA. However, study of primary BMSCs-mediated chondrogenesis is difficult due to progressive cellular aging and replicative senescence. To obtain a therapeutic cell population for OA, BMSCs were immortalized by human papilloma virus (HPV)-16 E6/E7 along with mCherry luciferase (mCL), a gene marker for non-invasive imaging, and designated as iBMSCs-mCL. Next, their cell morphology, population doubling time (PDT) and colony forming ability (CFU) were evaluated. Furthermore, pluripotency and immunophenotypic markers were investigated. To deduce therapeutic ability, iBMSCs-mCL were intra-articularly injected into right knee of anterior cruciate ligament transaction (ACLT)-OA mice model and tracked through non-invasive bioluminescence imaging. Cell morphology of iBMSCs-mCL was similar to parental BMSCs. PDT and CFU ability of iBMSCs-mCLs were significantly increased. Pluripotency and immunophenotypic markers were highly expressed in iBMSC-mCL. Long-term survival and tri-lineage differentiation particularly chondrogenic potential of iBMSCs-mCL were also demonstrated in vitro and then in vivo which was monitored through non-invasive imaging. Intensive bioluminescent signals in iBMSCs-mCL administered knee-joint indicated a marked in vivo survival and proliferation of iBMSCs-mCL. Immunohistochemical staining for type II collagen (IHC of Col II) and alcian blue & safranin o staining of proteoglycans also corroborated cartilage regeneration by iBMSCs-mCL. Conclusively, iBMSCs-mCL maintains stemness and in vivo cartilage regeneration potential suggesting a promising avenue for development of OA therapeutics.

Chemical and Physical Approaches to Extend the Replicative and Differentiation Potential of Stem Cells

Cell therapies using mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) are increasing in regenerative medicine, with applications to a growing number of aging-associated dysfunctions and degenerations. For successful therapies, a certain mass of cells is needed, requiring extensive ex vivo expansion of the cells. However, the proliferation of both MSCs and EPCs is limited as a result of telomere shortening-induced senescence. As cells approach senescence, their proliferation slows down and differentiation potential decreases. Therefore, ways to delay senescence and extend the replicative lifespan these cells are needed. Certain proteins and pathways play key roles in determining the replicative lifespan by regulating ROS generation, damage accumulation, or telomere shortening. And, their agonists and gene activators exert positive effects on lifespan. In many of the treatments, importantly, the lifespan is extended with the retention of differentiation potential. Furthermore, certain culture conditions, including the use of specific atmospheric conditions and culture substrates, exert positive effects on not only the proliferation rate, but also the extent of proliferation and differentiation potential as well as lineage determination. These strategies and known underlying mechanisms are introduced in this review, with an evaluation of their pros and cons in order to facilitate safe and effective MSC expansion ex vivo.

Periostin promotes ectopic osteogenesis of CTLA4-modified bone marrow mesenchymal stem cells

The improved ectopic osteogenesis of cytotoxic T-lymphocyte-associated antigen 4-Ig-modified bone marrow mesenchymal stem cells (MSCs-CTLA4) has been demonstrated but the mechanisms involved remain to be determined. The extracellular matrix (ECM) has recently been reported to play a vital role in bone formation and periostin (POSTN) has been suggested as a key member in constructing the ECM in bone tissue. We found that POSTN expression in the MSCs-CTLA4 group is significantly enhanced compared with that in the MSCs group, not only in tissue-engineered bone (TEB) with femur heterotopic transplantation in vivo but also under the immune activation condition in vitro. This ectopic osteogenesis effect is in accordance with POSTN expression. We also found that the soluble POSTN treatment up-regulates osteogenic marker expression in MSCs, including runt-related transcription factor 2, collagen 1, osteocalcin, osterix, and alkaline phosphatase and calcium nodule formation. These effects are diminished when the soluble POSTN is neutralized. Our results demonstrate that POSTN promotes the osteogenic differentiation of MSCs and that CTLA4 enhances the ectopic osteogenesis of MSCs-CTLA4-based TEB, potentially by maintaining POSTN expression in xenotransplantation.

Derivation and characterization of sheep bone marrow-derived mesenchymal stem cells induced with telomerase reverse transcriptase

Bone marrow mesenchymal stem cells (BMSCs) are a type of adult stem cells with a wide range of potential applications. However, BMSCs have a limited life cycle under normal culturing conditions, which has hindered further study and application. Many studies have confirmed that cells modified by telomerase reverse transcriptase (TERT) can maintain the ability to proliferate in vitro over a long period of time. In this study, we constructed a gene expression vector to transfer TERT into sheep BMSCs, and evaluated whether the TERT cell strain was successfully transferred. The abilities of cell proliferation and differentiation were evaluated using the methods including growth curve determination, inheritance stability analysis, multi-directional induction and so on, and the results showed that the cell strain can be cultured to 40 generations, with a normal karyotype rate maintained at 88.24%, and that the cell strain can be transferred and differentiated into neurocytes and lipocytes, proving that it retains the multi-directional transdifferentiation ability.

Periostin Upregulates Wnt/β-Catenin Signaling to Promote the Osteogenesis of CTLA4-Modified Human Bone Marrow-Mesenchymal Stem Cells

The enhanced osteogenesis of mesenchymal stem cells (MSCs) modified by expression of cytotoxic T lymphocyte-associated antigen 4 (CTLA4) has been shown in previous studies, but the mechanism remains unknown. Here we found that the bone repair effect of CTLA4-modified MSCs in demineralized bone matrix (DBM) in a rabbit radius defect model was significantly better than that observed for unmodified MSCs in DBM or DBM alone, and the periostin (POSTN) expression in CTLA4-modified MSCs was significantly higher than that in unmodified MSCs both in vivo and in vitro. In addition, we also found that treatment of CTLA4-modified MSCs with soluble POSTN could inhibit the glycogen synthase kinase-3β activity and increase β-catenin expression through up-regulation of lipoprotein-related protein-6 phosphorylation to promote osteogenic differentiation, but blocking of integrin αvβ3, a receptor of POSTN, could suppress these effects. Our data demonstrated that POSTN expressed in response to CTLA4 can promote the osteogenesis of xenotransplanted MSCs through interaction with Wnt/β-catenin pathway.