Extracellular matrix deposited by synovium-derived stem cells delays replicative senescent chondrocyte dedifferentiation and enhances redifferentiation

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

Mechanisms underlying the cell-matrixed nerve grafts repairing peripheral nerve defects

Decellularized extracellular matrix (dECM), with its distinct biological properties, has gained significant attention as a natural biomaterial. Leveraging its potentials, we successfully developed a three-dimensional matrix-based oriented nerve graft by encapsulating a fibrous scaffold with multilayered conformationally intact and biologically active human bone marrow mesenchymal stem cell-derived decellularized extracellular matrix (hBMSC-dECM). Convincingly, the hBMSC-dECM group exhibited comparable functional recoveries to the autograft group by postoperative week 12. In the comprehensive analysis, the molecular regulations in the hBMSC-dECM group were more intricate and nuanced compared to the autograft group. Nevertheless, both groups displayed similar molecular regulatory processes in terms of vascularization and extracellular matrix. Notably, the hBMSC-dECM group demonstrated sustained high levels of regulation in axon and myelin regeneration at week 12, while the immunomodulation returned to the normal levels after peaking at week 2. Collectively, our findings illustrated the satisfactory construction of a cell-matrixed nerve graft that established a microenvironment conducive to nerve regeneration, and elucidated the distinct molecular regulation patterns and characteristics associated with different repair modes.

Bioinspired collagen-gelatin-hyaluronic acid-chondroitin sulfate tetra-copolymer scaffold biomimicking native cartilage extracellular matrix facilitates chondrogenesis of human synovium-derived stem cells

The microenvironment plays a crucial role in stem cell differentiation, and a scaffold that mimics native cartilaginous extracellular components can promote chondrogenesis. In this study, a collagen-gelatin-hyaluronic acid-chondroitin sulfate tetra-copolymer scaffold with composition and architecture similar to those of hyaline cartilage was fabricated using a microfluidic technique and compared with a pure gelatin scaffold. The newly designed biomimetic scaffold had a swelling ratio of 1278 % ± 270 %, a porosity of 77.68 % ± 11.70 %, a compressive strength of 1005 ± 174 KPa, and showed a good resilience against compression force. Synovium-derived stem cells (SDSCs) seeded into the tetra-copolymer scaffold attached to the scaffold firmly and exhibited good mitochondrial activity, high cell survival with a pronounced glycosaminoglycan production. SDSCs cultured on the tetra-copolymer scaffold with chondrogenic induction exhibited upregulated mRNA expression of COL2A1, ChM-1, Nrf2, TGF-β1, and BMP-7. Ex vivo study revealed that the SDSC-tetra-copolymer scaffold regenerated cartilage-like tissue in SCID mice with abundant type II collagen and S-100 production. BMP7 and COL2A1 expression in the tetra-copolymer scaffold group was much higher than that in the gelatin scaffold group ex vivo. The tetra-copolymer scaffold thus exhibits strong chondrogenic capability and will facilitate cartilage tissue engineering.

Comparison of decellularization protocols for cultured cell-derived extracellular matrix-Effects on decellularization efficacy, extracellular matrix retention, and cell functions

The in vitro reconstruction of the extracellular matrix (ECM) is required in tissue engineering and regenerative medicine because the ECM can regulate cell functions in vivo. For ECM reconstruction, a decellularization technique is used. ECM reconstructed by decellularization (dECM) is prepared from tissues/organs and cultured cells. Although decellularization methods have been optimized for tissue-/organ-derived dECM, the methods for cultured cell-derived dECM have not yet been optimized. Here, two physical (osmotic shocks) and five chemical decellularization methods are compared. The decellularization efficacies were changed according to the decellularization methods used. Among them, only the Triton X-100 and Tween 20 treatments could not decellularize completely. Additionally, when the efficacies were compared among different types of cells (monolayered cells with/without strong cell adhesion, multilayered cells), the efficacies were decreased for multilayered cells or cells with strong cell adhesion. Retained ECM contents tended to be greater in the dECM prepared by osmotic shocks than in those prepared by chemical methods. The contents impacted cell adhesion, shapes, growth and intracellular signal activation on the dECM. The comparison would be helpful for the optimization of decellularization methods for cultured cells, and it could also provide new insights into developing milder decellularization methods for tissues and organs.

Functional acellular matrix for tissue repair

In view of their low immunogenicity, biomimetic internal environment, tissue- and organ-like physicochemical properties, and functionalization potential, decellularized extracellular matrix (dECM) materials attract considerable attention and are widely used in tissue engineering. This review describes the composition of extracellular matrices and their role in stem-cell differentiation, discusses the advantages and disadvantages of existing decellularization techniques, and presents methods for the functionalization and characterization of decellularized scaffolds. In addition, we discuss progress in the use of dECMs for cartilage, skin, nerve, and muscle repair and the transplantation or regeneration of different whole organs (e.g., kidneys, liver, uterus, lungs, and heart), summarize the shortcomings of using dECMs for tissue and organ repair after refunctionalization, and examine the corresponding future prospects. Thus, the present review helps to further systematize the application of functionalized dECMs in tissue/organ transplantation and keep researchers up to date on recent progress in dECM usage.

Matrix from urine stem cells boosts tissue-specific stem cell mediated functional cartilage reconstruction

Articular cartilage has a limited capacity to self-heal once damaged. Tissue-specific stem cells are a solution for cartilage regeneration; however, ex vivo expansion resulting in cell senescence remains a challenge as a large quantity of high-quality tissue-specific stem cells are needed for cartilage regeneration. Our previous report demonstrated that decellularized extracellular matrix (dECM) deposited by human synovium-derived stem cells (SDSCs), adipose-derived stem cells (ADSCs), urine-derived stem cells (UDSCs), or dermal fibroblasts (DFs) provided an ex vivo solution to rejuvenate human SDSCs in proliferation and chondrogenic potential, particularly for dECM deposited by UDSCs. To make the cell-derived dECM (C-dECM) approach applicable clinically, in this study, we evaluated ex vivo rejuvenation of rabbit infrapatellar fat pad-derived stem cells (IPFSCs), an easily accessible alternative for SDSCs, by the abovementioned C-dECMs, in vivo application for functional cartilage repair in a rabbit osteochondral defect model, and potential cellular and molecular mechanisms underlying this rejuvenation. We found that C-dECM rejuvenation promoted rabbit IPFSCs' cartilage engineering and functional regeneration in both ex vivo and in vivo models, particularly for the dECM deposited by UDSCs, which was further confirmed by proteomics data. RNA-Seq analysis indicated that both mesenchymal-epithelial transition (MET) and inflammation-mediated macrophage activation and polarization are potentially involved in the C-dECM-mediated promotion of IPFSCs' chondrogenic capacity, which needs further investigation.

Constructing a highly bioactive tendon-regenerative scaffold by surface modification of tissue-specific stem cell derived extracellular matrix

Developing highly bioactive scaffold materials to promote stem cell migration, proliferation and tissue-specific differentiation is a crucial requirement in current tissue engineering and regenerative medicine. Our previous work has demonstrated that the decellularized tendon slices (DTSs) are able to promote stem cell proliferation and tenogenic differentiation in vitro and show certain pro-regenerative capacity for rotator cuff tendon regeneration in vivo. In this study, we present a strategy to further improve the bioactivity of the DTSs for constructing a novel highly bioactive tendon-regenerative scaffold by surface modification of tendon-specific stem cell-derived extracellular matrix (tECM), which is expected to greatly enhance the capacity of scaffold material in regulating stem cell behavior, including migration, proliferation and tenogenic differentiation. We prove that the modification of tECM could change the highly aligned surface topographical cues of the DTSs, retain the surface stiffness of the DTSs and significantly increase the content of multiple ECM components in the tECM-DTSs. As a result, the tECM-DTSs dramatically enhance the migration, proliferation as well as tenogenic differentiation of rat bone marrow-derived stem cells compared with the DTSs. Collectively, this strategy would provide a new way for constructing ECM-based biomaterials with enhanced bioactivity for in situ tendon regeneration applications.

Decellularized extracellular matrix mediates tissue construction and regeneration

Contributing to organ formation and tissue regeneration, extracellular matrix (ECM) constituents provide tissue with three-dimensional (3D) structural integrity and cellular-function regulation. Containing the crucial traits of the cellular microenvironment, ECM substitutes mediate cell-matrix interactions to prompt stem-cell proliferation and differentiation for 3D organoid construction in vitro or tissue regeneration in vivo. However, these ECMs are often applied generically and have yet to be extensively developed for specific cell types in 3D cultures. Cultured cells also produce rich ECM, particularly stromal cells. Cellular ECM improves 3D culture development in vitro and tissue remodeling during wound healing after implantation into the host as well. Gaining better insight into ECM derived from either tissue or cells that regulate 3D tissue reconstruction or organ regeneration helps us to select, produce, and implant the most suitable ECM and thus promote 3D organoid culture and tissue remodeling for in vivo regeneration. Overall, the decellularization methodologies and tissue/cell-derived ECM as scaffolds or cellular-growth supplements used in cell propagation and differentiation for 3D tissue culture in vitro are discussed. Moreover, current preclinical applications by which ECM components modulate the wound-healing process are reviewed.

Strategies for Articular Cartilage Repair and Regeneration

Articular cartilage is an avascular tissue, with limited ability to repair and self-renew. Defects in articular cartilage can induce debilitating degenerative joint diseases such as osteoarthritis. Currently, clinical treatments have limited ability to repair, for they often result in the formation of mechanically inferior cartilage. In this review, we discuss the factors that affect cartilage homeostasis and function, and describe the emerging regenerative approaches that are informing the future treatment options.

Anti-hypertrophic effect of synovium-derived stromal cells on costal chondrocytes promotes cartilage repairs

Background

Costal chondrocytes (CCs), as a promising donor cell source for cell-based therapy for cartilage repair, have strong tendency of hypertrophy and calcification, which limited CCs from further application in cartilage regenerative medicine. Synovium-derived stromal cells (SDSCs), have shown their beneficial effect for chondrocytes to maintain phenotype. This study aims to investigate whether SDSCs could help CCs to maintain chondrogenic phenotype and suppress hypertrophic differentiation in cartilage repairs.

Methods

CCs were directly cocultured with SDSCs in pellet or indirectly cocultured using a conditioned medium in vitro for 3 weeks. Cartilage matrix formation and hypertrophic differentiation of CCs were analyzed by RT-PCR, biochemical assays, and histological staining. Cocultured pellets were implanted into the osteochondral defects made on the femoral groove of the rats. Then, macroscopic and histological evaluations were performed.

Results

Pellets formed by CCs alone and CCs cocultured with SDSCs reveal equal cartilage matrix deposition. However, the gene expression of type X collagen was significantly downregulated in cocultured pellets. Immunohistochemistry analysis revealed suppressed expression of type X collagen in cocultured pellets, indicating SDSCs may suppress hypertrophic differentiation of chondrocytes. Further in indirect coculture experiment, SDSCs suppressed type X collagen expression as well and promoted the proliferation of CCs, indicating SDSCs may influence CCs by paracrine mechanism. The pellets implanted in the osteochondral defects showed good restoration effects, whereas the grafts constructed with CCs and SDSCs showed lower type X expression levels.

Conclusion

These results suggest that SDSCs may maintain the phenotype of CCs and prevent the hypertrophic differentiation of CCs in cartilage repair.

The Translational Potential of this Article: CCs is a promising donor cell source for cell-based therapy for cartilage repair. Based on our study, cocultured with SDSCs weakened the tendency of hypertrophy and calcification of CCs, which provide a potential usage of SDSCs in CCs-based cartilage repair therapy to suppress newly formed cartilage calcification and improve clinical outcomes.

Strategies to Modulate the Redifferentiation of Chondrocytes

Because of the low self-healing capacity of articular cartilage, cartilage injuries and degenerations triggered by various diseases are almost irreversible. Previous studies have suggested that human chondrocytes cultured in vitro tend to dedifferentiate during the cell-amplification phase and lose the physiological properties and functions of the cartilage itself, which is currently a critical limitation in the cultivation of cartilage for tissue engineering. Recently, numerous studies have focused on the modulation of chondrocyte redifferentiation. Researchers discovered the effect of various conditions (extracellular environment, cell sources, growth factors and redifferentiation inducers, and gene silencing and overexpression) on the redifferentiation of chondrocytes during the in vitro expansion of cells, and obtained cartilage tissue cultured in vitro that exhibited physiological characteristics and functions that were similar to those of human cartilage tissue. Encouragingly, several studies reported positive results regarding the modulation of the redifferentiation of chondrocytes in specific conditions. Here, the various factors and conditions that modulate the redifferentiation of chondrocytes, as well as their limitations and potential applications and challenges are reviewed. We expect to inspire research in the field of cartilage repair toward the future treatment of arthropathy.

Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes

Autologous chondrocyte implantation (ACI) is a procedure used to treat articular cartilage injuries and prevent the onset of post-traumatic osteoarthritis. In vitro expansion of chondrocytes, a necessary step in ACI, results in the generation of senescent cells that adversely affect the quality and quantity of newly formed cartilage. Recently, a senolytic peptide, fork head box O transcription factor 4-D-Retro-Inverso (FOXO4-DRI), was reported to selectively kill the senescent fibroblasts. In this study, we hypothesized that FOXO4-DRI treatment could remove the senescent cells in the expanded chondrocytes, thus enhancing their potential in generating high-quality cartilage. To simulate the in vitro expansion for ACI, chondrocytes isolated from healthy donors were expanded to population doubling level (PDL) 9, representing chondrocytes ready for implantation. Cells at PDL3 were also used to serve as the minimally expanded control. Results showed that the treatment of FOXO4-DRI removed more than half of the cells in PDL9 but did not significantly affect the cell number of PDL3 chondrocytes. Compared to the untreated control, the senescence level in FOXO4-DRI treated PDL9 chondrocytes was significantly reduced. Based on the result from standard pellet culture, FOXO4-DRI pre-treatment did not enhance the chondrogenic potential of PDL9 chondrocytes. However, the cartilage tissue generated from FOXO4-DRI pretreated PDL9 cells displayed lower expression of senescence-relevant secretory factors than that from the untreated control group. Taken together, FOXO4-DRI is able to remove the senescent cells in PDL9 chondrocytes, but its utility in promoting cartilage formation from the in vitro expanded chondrocytes needs further investigation.

Applications of Biocompatible Scaffold Materials in Stem Cell-Based Cartilage Tissue Engineering

Cartilage, especially articular cartilage, is a unique connective tissue consisting of chondrocytes and cartilage matrix that covers the surface of joints. It plays a critical role in maintaining joint durability and mobility by providing nearly frictionless articulation for mechanical load transmission between joints. Damage to the articular cartilage frequently results from sport-related injuries, systemic diseases, degeneration, trauma, or tumors. Failure to treat impaired cartilage may lead to osteoarthritis, affecting more than 25% of the adult population globally. Articular cartilage has a very low intrinsic self-repair capacity due to the limited proliferative ability of adult chondrocytes, lack of vascularization and innervation, slow matrix turnover, and low supply of progenitor cells. Furthermore, articular chondrocytes are encapsulated in low-nutrient, low-oxygen environment. While cartilage restoration techniques such as osteochondral transplantation, autologous chondrocyte implantation (ACI), and microfracture have been used to repair certain cartilage defects, the clinical outcomes are often mixed and undesirable. Cartilage tissue engineering (CTE) may hold promise to facilitate cartilage repair. Ideally, the prerequisites for successful CTE should include the use of effective chondrogenic factors, an ample supply of chondrogenic progenitors, and the employment of cell-friendly, biocompatible scaffold materials. Significant progress has been made on the above three fronts in past decade, which has been further facilitated by the advent of 3D bio-printing. In this review, we briefly discuss potential sources of chondrogenic progenitors. We then primarily focus on currently available chondrocyte-friendly scaffold materials, along with 3D bioprinting techniques, for their potential roles in effective CTE. It is hoped that this review will serve as a primer to bring cartilage biologists, synthetic chemists, biomechanical engineers, and 3D-bioprinting technologists together to expedite CTE process for eventual clinical applications.

Heterogeneity of mesenchymal stem cells in cartilage regeneration: from characterization to application

Articular cartilage is susceptible to damage but hard to self-repair due to its avascular nature. Traditional treatment methods are not able to produce satisfactory effects. Mesenchymal stem cells (MSCs) have shown great promise in cartilage repair. However, the therapeutic effect of MSCs is often unstable partly due to their heterogeneity. Understanding the heterogeneity of MSCs and the potential of different types of MSCs for cartilage regeneration will facilitate the selection of superior MSCs for treating cartilage damage. This review provides an overview of the heterogeneity of MSCs at the donor, tissue source and cell immunophenotype levels, including their cytological properties, such as their ability for proliferation, chondrogenic differentiation and immunoregulation, as well as their current applications in cartilage regeneration. This information will improve the precision of MSC-based therapeutic strategies, thus maximizing the efficiency of articular cartilage repair.

Human Chondrocytes from Human Adipose Tissue-Derived Mesenchymal Stem Cells Seeded on a Dermal-Derived Collagen Matrix Sheet: Our Preliminary Results for a Ready to Go Biotechnological Cartilage Graft in Clinical Practice

Background

The articular cartilage is unique in that it contains only a single type of cell and shows poor ability for spontaneous healing. Cartilage tissue engineering which uses mesenchymal stem cells (MSCs) and adipose tissue-derived mesenchymal stem cells (AT-MSCs) is considered an attractive treatment for cartilage lesions and osteoarthritis. The establishment of cartilage regenerative medicine is an important clinical issue, but the search for cell sources able to restore cartilage integrity proves to be challenging. The aim of this study was to create cartilage grafts from the combination of AT-MSCs and collagen substrates.

Methods

Mesenchymal stem cells were obtained from human donors' adipose tissue, and collagen scaffold, obtained from human skin and cleaned from blood vessels, adipose tissues, and debris, which only preserve dermis and epidermis, were seeded and cultured on collagen substrates and differentiated to chondrocytes. The obtained chondrocyte extracellular matrix of cartilage was then evaluated for the expression of chondrocyte-/cartilage-specific markers, the Cartilage Oligomeric Matrix Protein (COMP), collagen X, alpha-1 polypeptide (COL10A1), and the Collagen II, Human Tagged ORF Clone (COL2A1) by using the reverse transcription polymerase chain reaction (RT-PCR).

Results

Our findings have shown that the dermal collagen may exert important effects on the quality of in vitro expanded chondrocytes, leading in this way that the influence of collagen skin matrix helps to produce highly active and functional chondrocytes for long-term cartilage tissue regeneration.

Conclusion

This research opens up the possibility of generating cartilage grafts with the precise purpose of improving the existing limitation in current clinical procedures.

Research Progress on Stem Cell Therapies for Articular Cartilage Regeneration

Injury of articular cartilage can cause osteoarthritis and seriously affect the physical and mental health of patients. Unfortunately, current surgical treatment techniques that are commonly used in the clinic cannot regenerate articular cartilage. Regenerative medicine involving stem cells has entered a new stage and is considered the most promising way to regenerate articular cartilage. In terms of theories on the mechanism, it was thought that stem cell-mediated articular cartilage regeneration was achieved through the directional differentiation of stem cells into chondrocytes. However, recent evidence has shown that the stem cell secretome plays an important role in biological processes such as the immune response, inflammation regulation, and drug delivery. At the same time, the stem cell secretome can effectively mediate the process of tissue regeneration. This new theory has attributed the therapeutic effect of stem cells to their paracrine effects. The application of stem cells is not limited to exogenous stem cell transplantation. Endogenous stem cell homing and in situ regeneration strategies have received extensive attention. The application of stem cell derivatives, such as conditioned media, extracellular vesicles, and extracellular matrix, is an extension of stem cell paracrine theory. On the other hand, stem cell pretreatment strategies have also shown promising therapeutic effects. This article will systematically review the latest developments in these areas, summarize challenges in articular cartilage regeneration strategies involving stem cells, and describe prospects for future development.

Mesenchymal stem cell-derived extracellular matrix (mECM): a bioactive and versatile scaffold for musculoskeletal tissue engineering

Mesenchymal stem cell-derived extracellular matrix (mECM) has received increased attention in the fields of tissue engineering and scaffold-assisted regeneration. mECM exhibits many unique characteristics, such as robust bioactivity, biocompatibility, ease of use, and the potential for autologous tissue engineering. As the use of mECM has increased in musculoskeletal tissue engineering, it should be noted that mECM generated from current methods has inherited insufficiencies, such as low mechanical properties and lack of internal architecture. In this review, we first summarize the development and use of mECM as a scaffold for musculoskeletal tissue regeneration and highlight our current progress on moving this technology toward clinical application. Then we review recent methods to improve the properties of mECM that will overcome current weaknesses. Lastly, we propose future studies that will pave the road for mECM application in regenerating tissues in humans.

Cell-derived decellularized extracellular matrix scaffolds for articular cartilage repair

Articular cartilage repair remains a great clinical challenge. Tissue engineering approaches based on decellularized extracellular matrix (dECM) scaffolds show promise for facilitating articular cartilage repair. Traditional regenerative approaches currently used in clinical practice, such as microfracture, mosaicplasty, and autologous chondrocyte implantation, can improve cartilage repair and show therapeutic effect to some degree; however, the long-term curative effect is suboptimal. As dECM prepared by proper decellularization procedures is a biodegradable material, which provides space for regeneration tissue growth, possesses low immunogenicity, and retains most of its bioactive molecules that maintain tissue homeostasis and facilitate tissue repair, dECM scaffolds may provide a biomimetic microenvironment promoting cell attachment, proliferation, and chondrogenic differentiation. Currently, cell-derived dECM scaffolds have become a research hotspot in the field of cartilage tissue engineering, as ECM derived from cells cultured in vitro has many advantages compared with native cartilage ECM. This review describes cell types used to secrete ECM, methods of inducing cells to secrete cartilage-like ECM and decellularization methods to prepare cell-derived dECM. The potential mechanism of dECM scaffolds on cartilage repair, methods for improving the mechanical strength of cell-derived dECM scaffolds, and future perspectives on cell-derived dECM scaffolds are also discussed in this review.

Dedifferentiation: inspiration for devising engineering strategies for regenerative medicine

Cell dedifferentiation is the process by which cells grow reversely from a partially or terminally differentiated stage to a less differentiated stage within their own lineage. This extraordinary phenomenon, observed in many physiological processes, inspires the possibility of developing new therapeutic approaches to regenerate damaged tissue and organs. Meanwhile, studies also indicate that dedifferentiation can cause pathological changes. In this review, we compile the literature describing recent advances in research on dedifferentiation, with an emphasis on tissue-specific findings, cellular mechanisms, and potential therapeutic applications from an engineering perspective. A critical understanding of such knowledge may provide fresh insights for designing new therapeutic strategies for regenerative medicine based on the principle of cell dedifferentiation.

Where is human-based cellular pharmaceutical R&D taking us in cartilage regeneration?

Lately, cellular-based cartilage joint therapies have gradually gained more attention, which leads to next generation bioengineering approaches in the development of cell-based medicinal products for human use in cartilage repair. The greatest hurdles of chondrocyte-based cartilage bioengineering are: (i) preferring the cell source; (ii) differentiation and expansion processes; (iii) the time necessary for chondrocyte expansion pre-implantation; and (iv) fixing the chondrocyte count in accordance with the lesion surface area of the patient in question. The chondrocyte presents itself to be the focal starting material for research and development of bioengineered cartilage-based medicinal products which promise the regeneration and restoration of non-orthopedic cartilage joint defects. Even though chondrocytes seem to be the first choice, inevitable complications related to proliferation, dedifferentation and redifferentiation are probable. Detailed studies are a necessity to fully investigate detailed culturing conditions, the chondrogenic strains of well-defined phenotypes and evaluation of the methods to be used in biomaterial production. Despite a majority of the current methods which aid amelioration of joint functionality, they are insufficient in fully restoring the natural structure and composition of the joint cartilage. Hence current studies have trended towards gene therapy, mesenchymal stem cells and tissue engineering practices. There are many studies addressing the outcomes of chondrocytes in the clinical scene, and many vital biomaterials have been developed for structuring the bioengineered cartilage. This study aims to convey to the audience the practical significance of chondrocyte-based clinical applications.

Synovium stem cell-derived matrix enhances anti-inflammatory properties of rabbit articular chondrocytes via the SIRT1 pathway

Autologous chondrocyte implantation (ACI) is a promising approach to repair cartilage defects; however, the cartilage trauma-induced inflammatory environment compromises its clinical outcomes. Cell-derived decellularized extracellular matrix (DECM) has been used as a culture substrate for mesenchymal stem cells (MSCs) to improve the cell proliferation and lineage-specific differentiation. In this study, DECM deposited by synovium-derived MSCs was used as an in vitro expansion system for rabbit articular chondrocytes and the response of DECM-expanded chondrocytes to pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was evaluated. Compared with those grown on tissue culture polystyrene (TCPS), the proliferation rate was significantly improved in DECM-expanded chondrocytes. TCPS- and DECM-expanded chondrocytes were isolated and induced to redifferentiation in a high-density pellet culture. DECM-expanded chondrocytes exerted a stronger resistance to 1 ng/mL of IL-1β than TCPS-expanded cells, but the production of cartilage matrix in both groups was inhibited by 5 ng/mL of IL-1β. When exposed to 1 or 5 ng/mL of TNF-α, DECM-expanded chondrocytes showed higher levels of cartilage matrix synthesis than TCPS-expanded cells. In addition, the gene expression of IL-1β- or TNF-α-induced matrix degrading enzymes (MMP3, MMP9, MMP13, and ADAMTS5) was significantly lower in DECM-expanded chondrocytes than TCPS-expanded cells. Furthermore, we found that SIRT1 inhibition by nicotinamide completely counteracted the protective effect of DECM on chondrocytes in the presence of IL-1β or TNF-α, indicating that the SIRT1 signaling pathway was involved in the DECM-mediated enhancement of anti-inflammatory properties of chondrocytes. Taken together, this work suggests that stem cell-derived DECM is a superior culture substrate for in vitro chondrocyte expansion by improving proliferation and enhancing the anti-inflammatory properties of chondrocytes. DECM-expanded chondrocytes with enhanced anti-inflammatory properties hold great potential in clinically ACI-based cartilage repair.

[Research progress in treatment of knee osteoarthritis by paracrine effect of stem cells]

Objective

To review the advances in utilizing paracrine effect of stem cells in knee osteoarthritis (OA) treatment.

Methods

The researches in applying stem cells derived conditioned medium, extracellular matrix, exosomes, and microvesicles in knee OA treatment and cartilage repair were reviewed and analyzed.

Results

The satisfying outcomes of using different products of stem cells paracrine effect in knee OA condition as well as cartilage defect is revealed in studies in vitro and in vivo. The mechanism including suppressing the intraarticular inflammation, the apoptosis of chondrocytes, and the degradation of cartilage matrix, while enhancing the synthesis of cartilage matrix, the differentiation of in-situ stem cells into chondrocytes and the migration to the affected area. The effectiveness can be further improved supplemented with the tissue engineering methods or gene modification.

Conclusion

Compared with the traditional stem cell therapy, applying the products from paracrine effect of stem cells in knee OA treatment is more economical and safer, presenting great potential in clinical practice.

Extracellular matrix derived by human umbilical cord-deposited mesenchymal stem cells accelerates chondrocyte proliferation and differentiation potential in vitro

The extracellular matrix (ECM) is a dynamic and intricate three-dimensional (3D) microenvironment with excellent biophysical, biomechanical, and biochemical properties that may directly or indirectly regulate cell behavior, including proliferation, adhesion, migration, and differentiation. Compared with tissue-derived ECM, cell-derived ECM potentially has more advantages, including less potential for pathogen transfer, fewer inflammatory or anti-host immune responses, and a closer resemblance to the native ECM microenvironment. Different types of cell-derived ECM, such as adipose stem cells, synovium-derived stem cells and bone marrow stromal cells, their effects on articular chondrocytes which have been researched. In this study, we aimed to develop a 3D cell culture substrate using decellularized ECM derived from human umbilical cord-derived mesenchymal stem cells (hUCMSCs), and evaluated the effects on articular chondrocytes. We evaluated the morphology and components of hUCMSC-derived ECM using physical and chemical methods. Morphological, histological, immunohistochemical, biochemical, and real-time PCR analyses demonstrated that proliferation and differentiation capacity of chondrocytes using the 3D hUCMSC-derived ECM culture substrate was superior to that using non-coated two-dimensional plastic culture plates. In conclusion, 3D decellularized ECM derived from hUCMSCs offers a tissue-specific microenvironment for in vitro culture of chondrocytes, which not only markedly promoted chondrocyte proliferation but also preserved the differentiation capacity of chondrocytes. Therefore, our findings suggest that a 3D cell-derived ECM microenvironment represents a promising prospect for autologous chondrocyte-based cartilage tissue engineering and regeneration. The hUCMSC-derived ECM as a biomaterial is used for the preparation of scaffold or hybrid scaffold products which need to further study in the future.

Extracellular matrix derived from chondrocytes promotes rapid expansion of human primary chondrocytes in vitro with reduced dedifferentiation

A significant expansion of autologous chondrocytes in vitro is required for cell-based cartilage repair. However, the in vitro expansion of chondrocytes under standard culture conditions inevitably leads to the dedifferentiation of chondrocytes and contributes to suboptimal clinical outcomes. To address this challenge, we focused our efforts on developing an improved in vitro expansion protocol, which shortens the expansion time with decreased dedifferentiation. It is known that the tissue microenvironment plays a critical role in regulating the cellular functions of resident cells and provides guidance in tissue-specific regeneration. We hypothesized that chondrocyte extracellular matrix (ECM) mimics a native microenvironment and that it may support chondrocyte expansion in vitro. To test this hypothesis, we prepared decellularized ECMs from allogeneic human articular chondrocytes (HAC) (AC-ECM) and bone marrow stromal cells (BM-ECM) and studied their effects on the in vitro expansion of primary HAC. The differential composition and physical properties of these two ECMs were revealed by mass spectrometry and atomic force microscopy. Compared with standard tissue culture polystyrene (TCP) or BM-ECM, HAC cultured on AC-ECM proliferated faster and maintained the highest ratio of COL2A1/COL1A1. Furthermore, a pellet culture study demonstrated that cells expanded on AC-ECM produced a more cartilage-like ECM than cells expanded on BM-ECM or TCP. This is the first report on modulating chondrocyte expansion and dedifferentiation using cell type-specific ECM and on identifying AC-ECM as a preferred substrate for in vitro expansion of HAC cell-based therapies. STATEMENT OF SIGNIFICANCE: To reduce the dedifferentiation of chondrocytes during in vitro expansion, cell type-specific extracellular matrix (ECM), which mimics a native microenvironment, was prepared from human articular chondrocytes (AC-ECM) or bone marrow stromal cells (BM-ECM). As demonstrated by mass spectrometry and atomic force microscopy, AC-ECM and BM-ECM have differential ECM compositions and physical characteristics. Human articular chondrocytes (HAC) expanded faster and maintained a better chondrocyte phenotype on AC-ECM than on BM-ECM or a standard culture surface. AC-ECM has potential to be developed for expanding HAC for cell-based therapies.

Transcriptome-Wide Analysis of Human Chondrocyte Expansion on Synoviocyte Matrix

Human chondrocytes are expanded and used in autologous chondrocyte implantation techniques and are known to rapidly de-differentiate in culture. These chondrocytes, when cultured on tissue culture plastic (TCP), undergo both phenotypical and morphological changes and quickly lose the ability to re-differentiate to produce hyaline-like matrix. Growth on synoviocyte-derived extracellular matrix (SDECM) reduces this de-differentiation, allowing for more than twice the number of population doublings (PD) whilst retaining chondrogenic capacity. The goal of this study was to apply RNA sequencing (RNA-Seq) analysis to examine the differences between TCP-expanded and SDECM-expanded human chondrocytes. Human chondrocytes from three donors were thawed from primary stocks and cultured on TCP flasks or on SDECM-coated flasks at physiological oxygen tension (5%) for 4 passages. During log expansion, RNA was extracted from the cell layer (70–90% confluence) at passages 1 and 4. Total RNA was column-purified and DNAse-treated before quality control analysis and next-generation RNA sequencing. Significant effects on gene expression were observed due to both culture surface and passage number. These results offer insight into the mechanism of how SDECM provides a more chondrogenesis-preserving environment for cell expansion, the transcriptome-wide changes that occur with culture, and potential mechanisms for further enhancement of chondrogenesis-preserving growth.

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.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Functionality of decellularized matrix in cartilage regeneration: A comparison of tissue versus cell sources

Increasing evidence indicates that decellularized extracellular matrices (dECMs) derived from cartilage tissues (T-dECMs) or chondrocytes/stem cells (C-dECMs) can support proliferation and chondrogenic differentiation of cartilage-forming cells. However, few review papers compare the differences between these dECMs when they serve as substrates for cartilage regeneration. In this review, after an introduction of cartilage immunogenicity and decellularization methods to prepare T-dECMs and C-dECMs, a comprehensive comparison focuses on the effects of T-dECMs and C-dECMs on proliferation and chondrogenic differentiation of chondrocytes/stem cells in vitro and in vivo. Key factors within dECMs, consisting of microarchitecture characteristics and micromechanical properties as well as retained insoluble and soluble matrix components, are discussed in-depth for potential mechanisms underlying the functionality of these dECMs in regulating chondrogenesis. With this information, we hope to benefit dECM based cartilage engineering and tissue regeneration for future clinical application.

STATEMENT OF SIGNIFICANCE

The use of decellularized extracellular matrix (dECM) is becoming a promising approach for tissue engineering and regeneration. Compared to dECM derived from cartilage tissue, recently reported dECM from cell sources exhibits a distinct role in cell based cartilage regeneration. In this review paper, for the first time, tissue and cell based dECMs are comprehensively compared for their functionality in cartilage regeneration. This information is expected to provide an update for dECM based cartilage regeneration.

An injectable nucleus pulposus cell-modified decellularized scaffold: biocompatible material for prevention of disc degeneration

We developed a nucleus pulposus cell (NPC)-modulated decellularized small intestinal submucosa (SIS) scaffold, and assessed the ability of this material to prevent Intervertebral disc degeneration (IVD) degeneration. Decellularized porcine SIS was squashed into particles and the biological safety and efficiency of these particles were evaluated. Next, SIS particles were seeded with rabbit NPCs, cultured for two months in vitro, decellularized again and suspended for intervertebral injection. We demonstrated that use of the decellularization protocol resulted in the removal of cellular components with maximal retention of extracellular matrix. The xenogeneic decellularized SIS did not display cytotoxicity in vitro and its application prevented NPC degradation. Furthermore, the xenogeneic SIS microparticles were effective in preventing IVD progression in vivo in a rabbit disc degeneration model. In conclusion, our study describes an optimized method for decellularized SIS preparation and demonstrated that the material is safe and effective for treating IVD degeneration.

Mesenchymal stem cell-derived extracellular matrix enhances chondrogenic phenotype of and cartilage formation by encapsulated chondrocytes in vitro and in vivo

Mesenchymal stem cell derived extracellular matrix (MSC-ECM) is a natural biomaterial with robust bioactivity and good biocompatibility, and has been studied as a scaffold for tissue engineering. In this investigation, we tested the applicability of using decellularized human bone marrow derived MSC-ECM (hBMSC-ECM) as a culture substrate for chondrocyte expansion in vitro, as well as a scaffold for chondrocyte-based cartilage repair. hBMSC-ECM deposited by hBMSCs cultured on tissue culture plastic (TCP) was harvested, and then subjected to a decellularization process to remove hBMSCs. Compared with chondrocytes grown on TCP, chondrocytes seeded onto hBMSC-ECM exhibited significantly increased proliferation rate, and maintained better chondrocytic phenotype than TCP group. After being expanded to the same cell number and placed in high-density micromass cultures, chondrocytes from the ECM group showed better chondrogenic differentiation profile than those from the TCP group. To test cartilage formation ability, composites of hBMSC-ECM impregnated with chondrocytes were subjected to brief trypsin treatment to allow cell-mediated contraction, and folded to form 3-dimensional chondrocyte-impregnated hBMSC-ECM (Cell/ECM constructs). Upon culture in vitro in chondrogenic medium for 21 days, robust cartilage formation was observed in the Cell/ECM constructs. Similarly prepared Cell/ECM constructs were tested in vivo by subcutaneous implantation into SCID mice. Prominent cartilage formation was observed in the implanted Cell/ECM constructs 14 days post-implantation, with higher sGAG deposition compared to controls consisting of chondrocyte cell sheets. Taken together, these findings demonstrate that hBMSC-ECM is a superior culture substrate for chondrocyte expansion and a bioactive matrix potentially applicable for cartilage regeneration in vivo.

STATEMENT OF SIGNIFICANCE

Current cell-based treatments for focal cartilage defects face challenges, including chondrocyte dedifferentiation, need for xenogenic scaffolds, and suboptimal cartilage formation. We present here a novel technique that utilizes adult stem cell-derived extracellular matrix, as a culture substrate and/or encapsulation scaffold for human adult chondrocytes, for the repair of cartilage defects. Chondrocytes cultured in stem cell-derived matrix showed higher proliferation, better chondrocytic phenotype, and improved redifferentiation ability upon in vitro culture expansion. Most importantly, 3-dimensional constructs formed from chondrocytes folded within stem cell matrix manifested excellent cartilage formation both in vitro and in vivo. These findings demonstrate the suitability of stem cell-derived extracellular matrix as a culture substrate for chondrocyte expansion as well as a candidate bioactive matrix for cartilage regeneration.

Decellularized orthopaedic tissue-engineered grafts: biomaterial scaffolds synthesised by therapeutic cells

In orthopaedic surgery, the reconstruction of musculoskeletal defects is a constant challenge.

Advances for Treatment of Knee OC Defects

Osteochondral (OC) defects are prevalent among young adults and are notorious for being unable to heal. Although they are traumatic in nature, they often develop silently. Detection of many OC defects is challenging, despite the criticality of early care. Current repair approaches face limitations and cannot provide regenerative or long-standing solution. Clinicians and researchers are working together in order to develop approaches that can regenerate the damaged tissues and protect the joint from developing osteoarthritis. The current concepts of tissue engineering and regenerative medicine, which have brought many promising applications to OC management, are overviewed herein. We will also review the types of stem cells that aim to provide sustainable cell sources overcoming the limitation of autologous chondrocyte-based applications. The various scaffolding materials that can be used as extracellular matrix mimetic and having functional properties similar to the OC unit are also discussed.

Decellularized allogeneic intervertebral disc: natural biomaterials for regenerating disc degeneration

Intervertebral disc degeneration is associated with back pain and disc herniation. This study established a modified protocol for intervertebral disc (IVD) decellularization and prepared its extracellular matrix (ECM). By culturing mesenchymal stem cells (MSCs)(3, 7, 14 and 21 days) and human degenerative IVD cells (7 days) in the ECM, implanting it subcutaneously in rabbit and injecting ECM microparticles into degenerative disc, the biological safety and efficacy of decellularized IVD was evaluated both in vitro and in vivo. Here, we demonstrated that cellular components can be removed completely after decellularization and maximally retain the structure and biomechanics of native IVD. We revealed that allogeneic ECM did not evoke any apparent inflammatory reaction in vivo and no cytotoxicity was found in vitro. Moreover, IVD ECM can induce differentiation of MSCs into IVD-like cells in vitro. Furthermore, allogeneic ECM microparticles are effective on the treatment of rabbit disc degeneration in vivo. In conclusion, our study developed an optimized method for IVD decellularization and we proved decellularized IVD is safe and effective for the treatment of degenerated disc diseases.

Improved Chondrogenic Potential and Proteomic Phenotype of Porcine Chondrocytes Grown in Optimized Culture Conditions

For successful cartilage tissue engineering, the ability to generate a high number of chondrocytes in vitro while avoiding terminal differentiation or de-differentiation is critical. The ability to accomplish this by using the abundant and easily sampled costal cartilage could provide a practical alternative to the use of articular cartilage and mesenchymal stem cells. Chondrocytes isolated from pig costal cartilage were expanded in either serum-free medium with FGF2 (SFM) or fetal bovine serum-containing medium (SCM), under either high (21%) or low (5%) oxygen conditions. Overall, chondrocytes cultured in SFM and low oxygen (Low-SFM) demonstrated the highest cell growth rate (p < 0.05). The effect of passage number on the differentiation status of the chondrocytes was analyzed by alkaline phosphatase (AP) staining and real-time PCR for known chondrocyte quality markers. AP staining indicated that chondrocytes grown in SCM had a higher proportion of terminally differentiated (hypertrophic) chondrocytes (p < 0.05). At the mRNA level, expression ratios of ACAN/VCAN and COL2/COL1 were significantly higher (p < 0.05) in cells expanded in Low-SFM, indicating reduced de-differentiation. In vitro re-differentiation capacity was assessed after a 6-week induction, and chondrocytes grown in Low-SFM showed similar expression ratios of COL2/COL1 and ACAN/VCAN to native cartilage. Proteomic analysis of in vitro produced cartilage indicated that the Low-SFM condition most closely matched the proteomic profile of native costal and articular cartilage. In conclusion, Low-SFM culture conditions resulted in improved cell growth rates, reduced levels of de-differentiation during expansion, greater ability to re-differentiate into cartilage on induction, and an improved proteomic profile that resembles that of in vivo cartilage.

Preparation and characterization of small-diameter decellularized scaffolds for vascular tissue engineering in an animal model

BACKGROUND

The development of a suitable extracellular matrix (ECM) scaffold is the first step in vascular tissue engineering (VTE). Synthetic vascular grafts are available as an alternative to autologous vessels in large-diameter arteries (>8 mm) and medium-diameter arteries (6-8 mm). In small-diameter vessels (<6 mm), synthetic vascular grafts are of limited use due to poor patency rates. Compared with a vascular prosthesis, natural tissue ECM has valuable advantages. Despite considerable progress in recent years, identifying an optimal protocol to create a scaffold for use in small-diameter (<6 mm) fully natural tissue-engineered vascular grafts (TEVG), remains elusive. Although reports on different decellularization techniques have been numerous, combination of and comparison between these methods are scarce; therefore, we have compared five different decellularization protocols for making small-diameter (<6 mm) ECM scaffolds and evaluated their characteristics relative to those of fresh vascular controls.

RESULTS

The protocols differed in the choice of enzymatic digestion solvent, the use of non-ionic detergent, the durations of the individual steps, and UV crosslinking. Due to their small diameter and ready availability, rabbit arteria carotis were used as the source of the ECM scaffolds. The scaffolds were subcutaneously implanted in rats and the results were evaluated using various microscopy and immunostaining techniques.

CONCLUSIONS

Our findings showed that a 2 h digestion time with 1× EDTA, replacing non-ionic detergent with double-distilled water for rinsing and the application of UV crosslinking gave rise to an ECM scaffold with the highest biocompatibility, lowest cytotoxicity and best mechanical properties for use in vivo or in situ pre-clinical research in VTE in comparison.

Isolation and characterization of human articular chondrocytes from surgical waste after total knee arthroplasty (TKA)

BACKGROUND

Cartilage tissue engineering is a fast-evolving field of biomedical engineering, in which the chondrocytes represent the most commonly used cell type. Since research in tissue engineering always consumes a lot of cells, simple and cheap isolation methods could form a powerful basis to boost such studies and enable their faster progress to the clinics. Isolated chondrocytes can be used for autologous chondrocyte implantation in cartilage repair, and are the base for valuable models to investigate cartilage phenotype preservation, as well as enable studies of molecular features, nature and scales of cellular responses to alterations in the cartilage tissue.

METHODS

Isolation and consequent cultivation of primary human adult articular chondrocytes from the surgical waste obtained during total knee arthroplasty (TKA) was performed. To evaluate the chondrogenic potential of the isolated cells, gene expression of collagen type 2 (COL2), collagen 1 (COL1) and aggrecan (ACAN) was evaluated. Immunocytochemical staining of all mentioned proteins was performed to evaluate chondrocyte specific production.

RESULTS

Cartilage specific gene expression of COL2 and ACAN has been shown that the proposed protocol leads to isolation of cells with a high chondrogenic potential, possibly even specific phenotype preservation up to the second passage. COL1 expression has confirmed the tendency of the isolated cells dedifferentiation into a fibroblast-like phenotype already in the second passage, which confirms previous findings that higher passages should be used with care in cartilage tissue engineering. To evaluate the effectiveness of our approach, immunocytochemical staining of the evaluated chondrocyte specific products was performed as well.

DISCUSSION

In this study, we developed a protocol for isolation and consequent cultivation of primary human adult articular chondrocytes with the desired phenotype from the surgical waste obtained during TKA. TKA is a common and very frequently performed orthopaedic surgery during which both femoral condyles are removed. The latter present the ideal source for a simple and relatively cheap isolation of chondrocytes as was confirmed in our study.

A Protocol to Prepare Decellularized Stem Cell Matrix for Rejuvenation of Cell Expansion and Cartilage Regeneration

Traditional ex vivo expansion of adult stem cells yields an insufficient quantity of less potent cells. Here we describe the fabrication of decellularized matrix deposited by synovium-derived stem cells (SDSCs). This matrix could serve as a three-dimensional expansion system to rejuvenate cells for proliferation and tissue-specific differentiation potential, which could benefit cartilage regeneration. The decellularized stem cell matrix (DSCM) might be a powerful system for tissue engineering and regeneration.

Cellular senescence in aging and osteoarthritis

- It is well accepted that age is an important contributing factor to poor cartilage repair following injury, and to the development of osteoarthritis. Cellular senescence, the loss of the ability of cells to divide, has been noted as the major factor contributing to age-related changes in cartilage homeostasis, function, and response to injury. The underlying mechanisms of cellular senescence, while not fully understood, have been associated with telomere erosion, DNA damage, oxidative stress, and inflammation. In this review, we discuss the causes and consequences of cellular senescence, and the associated biological challenges in cartilage repair. In addition, we present novel strategies for modulation of cellular senescence that may help to improve cartilage regeneration in an aging population.

Environmental preconditioning rejuvenates adult stem cells' proliferation and chondrogenic potential

Adult stem cells are a promising cell source for cartilage regeneration. Unfortunately, due to donor age and ex vivo expansion, stem cell senescence becomes a huge hurdle for these cells to be used clinically. Increasing evidence indicates that environmental preconditioning is a powerful approach in promoting stem cells' ability to resist a harsh environment post-engraftment, such as hypoxia and inflammation. However, few reports organize and evaluate the literature regarding the rejuvenation effect of environmental preconditioning on stem cell proliferation and chondrogenic differentiation capacity, which are important variables for stem cell based tissue regeneration. This report aims to identify several critical environmental factors such as oxygen concentration, growth factors, and extracellular matrix and to discuss their preconditioning influence on stem cells' rejuvenation including proliferation and chondrogenic potential as well as underlying molecular mechanisms. We believe that environmental preconditioning based rejuvenation is a simpler and safer strategy to program pre-engraftment stem cells for better survival and enhanced proliferation and differentiation capacity without the undesired effects of some treatments, such as genetic manipulation.

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.

AIMP1 downregulation restores chondrogenic characteristics of dedifferentiated/degenerated chondrocytes by enhancing TGF-β signal

Dedifferentiation and degeneration of chondrocytes critically influences the efficiency of cartilage repair. One of the causes is the defect of transforming growth factor (TGF)-β signaling that promotes chondrogenic differentiation and degeneration. In the present study, we found that aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) negatively regulates TGF-β signaling via interactions with Smad2 and Smad3 in immunoprecipitation assay and luciferase assay. In addition, we observed that the AIMP1 expression level was significantly increased in osteoarthritis (OA) patient-derived degenerated chondrocytes compared with healthy control. So, we hypothesized that downregulation of AIMP1 using small-interfering RNA (siRNA) technology in dedifferentiated (collected at passage #6) and degenerated (obtained from OA-affected areas) chondrocytes could lead to recover TGF-β signaling in both chondrocytes. Indeed, AIMP1 downregulation restored TGF-β signaling by promoting phosphorylation of Smad2 and Smad3, which shows redifferentiated characteristics in both dedifferentiated and degenerated chondrocytes. Additionally, implantation analyses using in vivo mouse model clearly showed that AIMP1 downregulation resulted in the increased chondrogenic potential as well as the enhanced cartilage tissue formation in both dedifferentiated and degenerated chondrocytes. Histological analyses clarified that AIMP1 downregulation increased expression levels of collagen type II (Col II) and aggrecan, but not Col I expression. Taken together, these data indicate that AIMP1 downregulation using siRNA is a novel tool to restore TGF-β signaling and thereby increases the chondrogenic potential of dedifferentiated/degenerated chondrocytes, which could be further developed as a therapeutic siRNA to treat OA.

Chondrogenic priming of human fetal synovium-derived stem cells in an adult stem cell matrix microenvironment

Cartilage defects are a challenge to treat clinically due to the avascular nature of cartilage. Low immunogenicity and extensive proliferation and multidifferentiation potential make fetal stem cells a promising source for regenerative medicine. In this study, we aimed to determine whether fetal synovium-derived stem cells (FSDSCs) exhibited replicative senescence and whether expansion on decellularized extracellular matrix (dECM) deposited by adult SDSCs (AECM) promoted FSDSCs' chondrogenic potential. FSDSCs from passage 2 and 9 were compared for chondrogenic potential, using Alcian blue staining for sulfated glycosaminoglycans (GAGs), biochemical analysis for DNA and GAG amounts, and real-time PCR for chondrogenic genes including ACAN and COL2A1. Passage 3 FSDSCs were expanded for one passage on plastic flasks (PL), AECM, or dECM deposited by fetal SDSCs (FECM). During expansion, cell proliferation was evaluated using flow cytometry for proliferation index, stem cell surface markers, and resistance to hydrogen peroxide. During chondrogenic induction, expanded FSDSCs were evaluated for tri-lineage differentiation capacity. We found that cell expansion enhanced FSDSCs' chondrogenic potential at least up to passage 9. Expansion on dECMs promoted FSDSCs' proliferative and survival capacity and adipogenic differentiation but not osteogenic capacity. AECM-primed FSDSCs exhibited an enhanced chondrogenic potential.

Delineation of in vitro chondrogenesis of human synovial stem cells following preconditioning using decellularized matrix

As a tissue-specific stem cell for chondrogenesis, synovium-derived stem cells (SDSCs) are a promising cell source for cartilage repair. However, a small biopsy can only provide a limited number of cells. Cell senescence from both in vitro expansion and donor age presents a big challenge for stem cell based cartilage regeneration. Here we found that expansion on decellularized extracellular matrix (dECM) full of three-dimensional nanostructured fibers provided SDSCs with unique surface profiles, low elasticity but large volume as well as a fibroblast-like shape. dECM expanded SDSCs yielded larger pellets with intensive staining of type II collagen and sulfated glycosaminoglycans compared to those grown on plastic flasks while SDSCs grown in ECM yielded 28-day pellets with minimal matrix as evidenced by pellet size and chondrogenic marker staining, which was confirmed by both biochemical data and real-time PCR data. Our results also found lower levels of inflammatory genes in dECM expanded SDSCs that might be responsible for enhanced chondrogenic differentiation. Despite an increase in type X collagen in chondrogenically induced cells, dECM expanded cells had significantly lower potential for endochondral bone formation. Wnt and MAPK signals were actively involved in both expansion and chondrogenic induction of dECM expanded cells. Since young and healthy people can be potential donors for this matrix expansion system and decellularization can minimize immune concerns, human SDSCs expanded on this future commercially available dECM could be a potential cell source for autologous cartilage repair.

Synoviocyte Derived-Extracellular Matrix Enhances Human Articular Chondrocyte Proliferation and Maintains Re-Differentiation Capacity at Both Low and Atmospheric Oxygen Tensions

Background

Current tissue engineering methods are insufficient for total joint resurfacing, and chondrocytes undergo de-differentiation when expanded on tissue culture plastic. De-differentiated chondrocytes show poor re-differentiation in culture, giving reduced glycosaminoglycan (GAG) and collagen matrix accumulation. To address this, porcine synoviocyte-derived extracellular matrix and low (5%) oxygen tension were assessed for their ability to enhance human articular chondrocyte expansion and maintain re-differentiation potential.

Methods

Porcine synoviocyte matrices were devitalized using 3 non-detergent methods. These devitalized synoviocyte matrices were compared against tissue culture plastic for their ability to support human chondrocyte expansion. Expansion was further compared at both low (5%), and atmospheric (20%) oxygen tension on all surfaces. Expanded cells then underwent chondrogenic re-differentiation in aggregate culture at both low and atmospheric oxygen tension. Aggregates were assessed for their GAG and collagen content both biochemically and histologically.

Results

Human chondrocytes expanded twice as fast on devitalized synoviocyte matrix vs. tissue culture plastic, and cells retained their re-differentiation capacity for twice the number of population doublings. There was no significant difference in growth rate between low and atmospheric oxygen tension. There was significantly less collagen type I, collagen type II, aggrecan and more MMP13 expression in cells expanded on synoviocyte matrix vs. tissue culture plastic. There were also significant effects due to oxygen tension on gene expression, wherein there was greater collagen type I, collagen type II, SOX9 and less MMP13 expression on tissue culture plastic compared to synoviocyte matrix. There was a significant increase in GAG, but not collagen, accumulation in chondrocyte aggregates re-differentiated at low oxygen tension over that achieved in atmospheric oxygen conditions.

Conclusions

Synoviocyte-derived matrix supports enhanced expansion of human chondrocytes such that the chondrocytes are maintained in a state from which they can re-differentiate into a cartilage phenotype after significantly more population doublings. Also, low oxygen tension supports GAG, but not collagen, accumulation. These findings are a step towards the production of a more functional, tissue engineered cartilage.

Transforming growth factor beta signaling is essential for the autonomous formation of cartilage-like tissue by expanded chondrocytes

Cartilage is a tissue with limited self-healing potential. Hence, cartilage defects require surgical attention to prevent or postpone the development of osteoarthritis. For cell-based cartilage repair strategies, in particular autologous chondrocyte implantation, articular chondrocytes are isolated from cartilage and expanded in vitro to increase the number of cells required for therapy. During expansion, the cells lose the competence to autonomously form a cartilage-like tissue, that is in the absence of exogenously added chondrogenic growth factors, such as TGF-βs. We hypothesized that signaling elicited by autocrine and/or paracrine TGF-β is essential for the formation of cartilage-like tissue and that alterations within the TGF-β signaling pathway during expansion interfere with this process. Primary bovine articular chondrocytes were harvested and expanded in monolayer culture up to passage six and the formation of cartilage tissue was investigated in high density pellet cultures grown for three weeks. Chondrocytes expanded for up to three passages maintained the potential for autonomous cartilage-like tissue formation. After three passages, however, exogenous TGF-β1 was required to induce the formation of cartilage-like tissue. When TGF-β signaling was blocked by inhibiting the TGF-β receptor 1 kinase, the autonomous formation of cartilage-like tissue was abrogated. At the initiation of pellet culture, chondrocytes from passage three and later showed levels of transcripts coding for TGF-β receptors 1 and 2 and TGF-β2 to be three-, five- and five-fold decreased, respectively, as compared to primary chondrocytes. In conclusion, the autonomous formation of cartilage-like tissue by expanded chondrocytes is dependent on signaling induced by autocrine and/or paracrine TGF-β. We propose that a decrease in the expression of the chondrogenic growth factor TGF-β2 and of the TGF-β receptors in expanded chondrocytes accounts for a decrease in the activity of the TGF-β signaling pathway and hence for the loss of the potential for autonomous cartilage-like tissue formation.

Cell-based articular cartilage repair: the link between development and regeneration

Clinical efforts to repair damaged articular cartilage (AC) currently face major obstacles due to limited intrinsic repair capacity of the tissue and unsuccessful biological interventions. This highlights a need for better therapeutic strategies. This review summarizes the recent advances in the field of cell-based AC repair. In both animals and humans, AC defects that penetrate into the subchondral bone marrow are mainly filled with fibrocartilaginous tissue through the differentiation of bone marrow mesenchymal stem cells (MSCs), followed by degeneration of repaired cartilage and osteoarthritis (OA). Cell therapy and tissue engineering techniques using culture-expanded chondrocytes, bone marrow MSCs, or pluripotent stem cells with chondroinductive growth factors may generate cartilaginous tissue in AC defects but do not form hyaline cartilage-based articular surface because repair cells often lose chondrogenic activity or result in chondrocyte hypertrophy. The new evidence that AC and synovium develop from the same pool of precursors with similar gene profiles and that synovium-derived chondrocytes have stable chondrogenic activity has promoted use of synovium as a new cell source for AC repair. The recent finding that NFAT1 and NFAT2 transcription factors (TFs) inhibit chondrocyte hypertrophy and maintain metabolic balance in AC is a significant advance in the field of AC repair. The use of synovial MSCs and discovery of upstream transcriptional regulators that help maintain the AC phenotype have opened new avenues to improve the outcome of AC regeneration.