Immortalisation with hTERT Impacts on Sulphated Glycosaminoglycan Secretion and Immunophenotype in a Variable and Cell Specific Manner

Meta-analysis of the Mesenchymal Stem Cells Immortalization Protocols: A Guideline for Regenerative Medicine

BACKGROUND

This systematic review describes the most common methodologies for immortalizing human and animal mesenchymal stem cells (MSCs). This study follows the rules of PRISMA and is registered in the Institutional Review Board of PROSPERO International of systematic reviews, numbered protocol code: CRD42020202465.

METHOD

The data search systematization was based on the words "mesenchymal stem cell" AND "immortalization." The search period for publications was between 2000 and 2022, and the databases used were SCOPUS, PUBMED, and SCIENCE DIRECT. The search strategies identified 384 articles: 229 in the SCOPUS database, 84 in PUBMED, and 71 in SCIENCE DIRECT. After screening by titles and abstracts, 285 articles remained. This review included thirty-nine articles according to the inclusion and exclusion criteria.

RESULT

In 28 articles, MSCs were immortalized from humans and 11 animals. The most used immortalization methodology was viral transfection. The most common immortalized cell type was the MSC from bone marrow, and the most used gene for immortalizing human and animal MSCs was hTERT (39.3%) and SV40T (54.5%), respectively.

CONCLUSION

Also, it was observed that although less than half of the studies performed tumorigenicity assays to validate the immortalized MSCs, other assays, such as qRT-PCR, colony formation in soft agar, karyotype, FISH, and cell proliferation, were performed in most studies on distinct MSC cell passages.

Generation of human immortalized chondrocytes from osteoarthritic and healthy cartilage : a new tool for cartilage pathophysiology studies

AIMS

After a few passages of in vitro culture, primary human articular chondrocytes undergo senescence and loss of their phenotype. Most of the available chondrocyte cell lines have been obtained from cartilage tissues different from diarthrodial joints, and their utility for osteoarthritis (OA) research is reduced. Thus, the goal of this research was the development of immortalized chondrocyte cell lines proceeded from the articular cartilage of patients with and without OA.

METHODS

Using telomerase reverse transcriptase (hTERT) and SV40 large T antigen (SV40LT), we transduced primary OA articular chondrocytes. Proliferative capacity, degree of senescence, and chondrocyte surface antigen expression in transduced chondrocytes were evaluated. In addition, the capacity of transduced chondrocytes to synthesize a tissue similar to cartilage and to respond to interleukin (IL)-1β was assessed.

RESULTS

Coexpression of both transgenes (SV40 and hTERT) were observed in the nuclei of transduced chondrocytes. Generated chondrocyte cell lines showed a high proliferation capacity and less than 2% of senescent cells. These cell lines were able to form 3D aggregates analogous to those generated by primary articular chondrocytes, but were unsuccessful in synthesizing cartilage-like tissue when seeded on type I collagen sponges. However, generated chondrocyte cell lines maintained the potential to respond to IL-1β stimulation.

CONCLUSION

Through SV40LT and hTERT transduction, we successfully immortalized chondrocytes. These immortalized chondrocytes were able to overcome senescence in vitro, but were incapable of synthesizing cartilage-like tissue under the experimental conditions. Nonetheless, these chondrocyte cell lines could be advantageous for OA investigation since, similarly to primary articular chondrocytes, they showed capacity to upregulate inflammatory mediators in response to the IL-1β cytokine.Cite this article: Bone Joint Res 2023;12(1):46-57.

Potency Assay Considerations for Cartilage Repair, Osteoarthritis and Use of Extracellular Vesicles

Articular cartilage covers the ends of bones in synovial joints acting as a shock absorber that helps movement of bones. Damage of the articular cartilage needs treatment as it does not repair itself and the damage can progress to osteoarthritis. In osteoarthritis all the joint tissues are involved with characteristic progressive cartilage degradation and inflammation. Autologous chondrocyte implantation is a well-proven cell-based treatment for cartilage defects, but a main downside it that it requires two surgeries. Multipotent, aka mesenchymal stromal cell (MSC)-based cartilage repair has gained attention as it can be used as a one-step treatment. It is proposed that a combination of immunomodulatory and regenerative capacities make MSC attractive for the treatment of osteoarthritis. Furthermore, since part of the paracrine effects of MSCs are attributed to extracellular vesicles (EVs), small membrane enclosed particles secreted by cells, EVs are currently being widely investigated for their potential therapeutic effects. Although MSCs have entered clinical cartilage treatments and EVs are used in in vivo efficacy studies, not much attention has been given to determine their potency and to the development of potency assays. This chapter provides considerations and suggestions for the development of potency assays for the use of MSCs and MSC-EVs for the treatment of cartilage defects and osteoarthritis.

Acrylamide-based hydrogels with distinct osteogenic and chondrogenic differentiation potential

Regeneration solutions for the osteochondral interface depth are limited, where multi-material implants have the potential to delaminate affecting the regeneration process and impacting the final integrity of tissue interface. Here we explore regionally mixed hydrogel networks, presenting distinct chemical features to determine their compatibility in supporting osteogenic or chondrogenic cell behaviour and differentiation. Poly(N-isopropylacrylamide) (pNIPAM) and poly(N-tert-butylacrylamide) (pNTBAM) hydrogels were assessed in terms of their chemical differences, mechanical strength, internal architecture, porosity and capacity to support cell viability, migration, and differentiation. pNTBAM polymerized with a Young’s modulus of up to 371 ± 31 kPa compared to the more flexible pNIPAM, 16.5 ± 0.6 kPa. Viability testing revealed biocompatibility of both hydrogels with significantly increased cell numbers observed in pNTBAM (500 ± 95 viable cells/mm²) than in pNIPAM (60 ± 3 viable cells/mm²) (P ≤ 0.05). Mineralization determined through alkaline phosphatase (ALP) activity, calcium ion and annexin A2 markers of mineralization) and osteogenic behaviour (collagen I expression) were supported in both hydrogels, but to a greater extent in pNTBAM. pNTBAM supported significantly elevated levels of chondrogenic markers as evidenced by collagen II and glycosaminoglycan expression in comparison to little or no evidence in pNIPAM (P ≤ 0.05). In conclusion, structurally similar, chemically distinct, acrylamide hydrogels display variable capacities in supporting osteochondral cell behaviours. These systems demonstrate spatial control of cell interaction through simple changes in monomer chemistry. Fine control over chemical presentation during the fabrication of biomaterial implants could lead to greater efficacy and targeted regeneration of semi-complex tissues.

Generation of Mesenchymal Cell Lines Derived from Aged Donors

Background: Mesenchymal stromal cells (MSCs) have the capacity for self-renewal and multi-differentiation, and for this reason they are considered a potential cellular source in regenerative medicine of cartilage and bone. However, research on this field is impaired by the predisposition of primary MSCs to senescence during culture expansion. Therefore, the aim of this study was to generate and characterize immortalized MSC (iMSC) lines from aged donors. Methods: Primary MSCs were immortalized by transduction of simian virus 40 large T antigen (SV40LT) and human telomerase reverse transcriptase (hTERT). Proliferation, senescence, phenotype and multi-differentiation potential of the resulting iMSC lines were analyzed. Results: MSCs proliferate faster than primary MSCs, overcome senescence and are phenotypically similar to primary MSCs. Nevertheless, their multi-differentiation potential is unbalanced towards the osteogenic lineage. There are no clear differences between osteoarthritis (OA) and non-OA iMSCs in terms of proliferation, senescence, phenotype or differentiation potential. Conclusions: Primary MSCs obtained from elderly patients can be immortalized by transduction of SV40LT and hTERT. The high osteogenic potential of iMSCs converts them into an excellent cellular source to take part in in vitro models to study bone tissue engineering.

Direct comparison of the immunogenicity of major histocompatibility complex-I and -II deficient mesenchymal stem cells in vivo

Mesenchymal stem cells (MSCs) play an important role in tissue engineering applications aiming at the regeneration or substitution of damaged tissues. In this context, off-the-shelf allogeneic MSCs would represent an attractive universal cell source. However, immune rejection is a major limitation for the clinical use of allogeneic MSCs. Immune rejection is mediated by the expression of major histocompatibility complexes (MHC)-I and -II on the donor cells. In this study, we eliminated MHC-I and/or MHC-II expression in human MSCs by using the CRISPR/Cas9 technology and investigated the effect of the individual or combined knockout of MHC-I and MHC-II on MSC survival after transplantation into immunocompetent mice. Elimination of MHC-I and/or MHC-II expression did not affect mesenchymal marker gene expression, viability, proliferation and the differentiation potential of MSCs in vitro. However, cell survival of transplanted MSCs was significantly elevated in MHC-I and MHC-II deficient MSCs. A direct side-by-side comparison does not reveal any significant difference in the immunogenicity of MHC-I and MHC-II knockout MSCs. Moreover, double knockout of MHC-I and MHC-II did not further increase in vivo cell survival of transplanted MSCs. Our results demonstrate that knockout of MHC-I and/or MHC-II represents an effective strategy to prevent immune rejection of allogeneic MSCs.

Immortalizing Mesenchymal Stromal Cells from Aged Donors While Keeping Their Essential Features

Human bone marrow-derived mesenchymal stromal cells (MSCs) obtained from aged patients are prone to senesce and diminish their differentiation potential, therefore limiting their usefulness for osteochondral regenerative medicine approaches or to study age-related diseases, such as osteoarthiritis (OA). MSCs can be transduced with immortalizing genes to overcome this limitation, but transduction of primary slow-dividing cells has proven to be challenging. Methods for enhancing transduction efficiency (such as spinoculation, chemical adjuvants, or transgene expression inductors) can be used, but several parameters must be adapted for each transduction system. In order to develop a transduction method suitable for the immortalization of MSCs from aged donors, we used a spinoculation method. Incubation parameters of packaging cells, speed and time of centrifugation, and valproic acid concentration to induce transgene expression have been adjusted. In this way, four immortalized MSC lines (iMSC#6, iMSC#8, iMSC#9, and iMSC#10) were generated. These immortalized MSCs (iMSCs) were capable of bypassing senescence and proliferating at a higher rate than primary MSCs. Characterization of iMSCs showed that these cells kept the expression of mesenchymal surface markers and were able to differentiate towards osteoblasts, adipocytes, and chondrocytes. Nevertheless, alterations in the CD105 expression and a switch of cell fate-commitment towards the osteogenic lineage have been noticed. In conclusion, the developed transduction method is suitable for the immortalization of MSCs derived from aged donors. The generated iMSC lines maintain essential mesenchymal features and are expected to be useful tools for the bone and cartilage regenerative medicine research.

Usefulness of Mesenchymal Cell Lines for Bone and Cartilage Regeneration Research

The unavailability of sufficient numbers of human primary cells is a major roadblock for in vitro repair of bone and/or cartilage, and for performing disease modelling experiments. Immortalized mesenchymal stromal cells (iMSCs) may be employed as a research tool for avoiding these problems. The purpose of this review was to revise the available literature on the characteristics of the iMSC lines, paying special attention to the maintenance of the phenotype of the primary cells from which they were derived, and whether they are effectively useful for in vitro disease modeling and cell therapy purposes. This review was performed by searching on Web of Science, Scopus, and PubMed databases from 1 January 2015 to 30 September 2019. The keywords used were ALL = (mesenchymal AND ("cell line" OR immortal*) AND (cartilage OR chondrogenesis OR bone OR osteogenesis) AND human). Only original research studies in which a human iMSC line was employed for osteogenesis or chondrogenesis experiments were included. After describing the success of the immortalization protocol, we focused on the iMSCs maintenance of the parental phenotype and multipotency. According to the literature revised, it seems that the maintenance of these characteristics is not guaranteed by immortalization, and that careful selection and validation of clones with particular characteristics is necessary for taking advantage of the full potential of iMSC to be employed in bone and cartilage-related research.

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.

Recellularization of decellularized adipose tissue-derived stem cells: role of the cell-secreted extracellular matrix in cellular differentiation

Adipose-derived stem cells (ASCs) are found in a location within the adipose tissue known as the stem cell niche. The ASCs in the niche are maintained in the quiescent state, and upon exposure to various microenvironmental triggers are prompted to undergo proliferation or differentiation. These microenvironmental triggers also modulate the extracellular matrix (ECM), which interacts with the cells through the cytoskeleton and induces downstream events inside the cells that bring about a change in cell behaviour. In response to these changes, the cells remodel the ECM, which will differ according to the type of tissue being formed by the cells. As the ECM itself plays an important role in the regulation of cellular differentiation, this study aims to explore the role of the cell-secreted ECM at various stages of differentiation of stem cells in triggering the differentiation of ASCs. To this end, the ASCs cultured in proliferation, osteogenic and adipogenic media were decellularized and the secreted ECM was characterized. Overall, it was found that osteo-differentiated ASCs produced higher amounts of collagen and glycosaminoglycans (GAG) compared to the undifferentiated and adipo-differentiated ASCs. The two types of differentiated ECMs were subsequently shown to trigger initial but not terminal differentiation of ASCs into osteo- and adipo-lineages respectively, as indicated by the upregulation of lineage specific markers. In addition, integrin subunits alpha (α) 6 and integrin beta (β) 1 were found to be produced by ASCs cultured on cell-secreted ECM-coated substrates, suggesting that the integrins α6 and β1 play an instrumental role in cell-ECM interactions. Taken together, this study demonstrates the importance of the ECM in cellular fate decisions and how ECM-coated substrates can potentially be used for various tissue engineering applications.

Ectopic Telomerase Expression Fails to Maintain Chondrogenic Capacity in Three-Dimensional Cultures of Clinically Relevant Cell Types

The poor healing capacity of cartilage and lack of effective treatment for associated disease and trauma makes it a strong candidate for a regenerative medicine approach. Potential therapies tested to date, although effective, have met with a number of intrinsic difficulties possibly related to limited autologous chondrocyte cell yield and quality of cartilage produced. A potential mechanism to bypass limited cell yields and improve quality of differentiation is to immortalize relevant cell types through the ectopic expression of telomerase. Pellet cultures of human chondrocytes (OK3), bone marrow mesenchymal stem cells (BMA13), and embryonic stem cell (H1 line)-derived cells (1C6) and their human telomerase reverse transcriptase (hTERT) transduced counterparts were maintained for 20 days in standard maintenance medium (MM) or transforming growth factor-β3-supplemented prochondrogenic medium (PChM). Pellets were assessed for volume and density by microcomputed tomography. Quantitative gene expression (COL1A2, COL2A1, COL3A1, COL6A3, COL10A1, ACAN, COMP, SOX9); sulfated glycosaminoglycans (sGAGs), and DNA quantification were performed. Histology and immunohistochemistry were used to determine matrix constituent distribution. Pellet culture in PChM resulted in significantly larger pellets with an overall increased density when compared with MM culture. Gene expression analysis revealed similarities in expression patterns between telomerase-transduced and parental cells in both MM and PChM. Of the three parental cell types examined OK3 and BMA13 produced similar amounts of pellet-associated sGAG in PChM (4.62 ± 1.20 and 4.91 ± 1.37 μg, respectively) with lower amounts in 1C6 (2.89 ± 0.52 μg), corresponding to 3.1, 2.3, and 1.6-fold increases from day 0. In comparison, telomerase-transduced cells all had much lower sGAG with OK3H at 2.74 ± 0.11 μg, BMA13H 1.29 ± 0.34 μg, and 1C6H 0.52 ± 0.01 μg corresponding to 1.2, 0.87, and 0.34-fold changes compared with day 0. Histology of day 20 pellets displayed reduced staining overall for collagens and sGAG in telomerase-transduced cells, most notably with alterations in aggrecan and collagen VI; all cells stained positively for collagen II. We conclude that while telomerase transduction may be an effective technique to extend cellular proliferative capacity, it is not sufficient in isolation to sustain a naive chondrogenic phenotype across multiple cell types.