Chondrogenic differentiation of cultured human mesenchymal stem cells from marrow

Advantages and challenges of stem cell therapy for osteoarthritis (Review)

Osteoarthritis (OA) is a degenerative disorder of the cartilage and is one of the leading causes of disability, particularly amongst the elderly, wherein patients with advanced-stage OA experience chronic pain and functional impairment of the limbs, thus resulting in a significantly reduced quality of life. The currently available treatments primarily revolve around symptom management, and is thus palliative rather than curative. The aim of the present review is to briefly discuss the limitations of some of the currently available treatments for patients with OA, and highlight the value of the potential use of stem cells in cellular therapy, which is widely regarded as the breakthrough that can address the present unmet medical needs for treatment of degenerative diseases, such as OA. The advantages of stem cell therapy, particularly mesenchymal stem cells, and the challenges involved are also discussed in this review.

Naturally-derived protein extract from Gryllus bimaculatus improves antioxidant properties and promotes osteogenic differentiation of hBMSCs

Naturally-derived proteins or peptides are promising biopolymers for tissue engineering applications owing to their health-promoting activity. Herein, we extracted proteins (~90%) from two-spotted cricket (Gryllus bimaculatus) and evaluated their osteoinductive potential in human bone marrow-derived mesenchymal stem cells (hBMSCs) under in vitro conditions. The extracted protein isolate was analyzed for the amino acid composition and the mass distribution of the constituent peptide fraction. Fourier transform infrared (FTIR) spectroscopy was used to determine the presence of biologically significant functional groups. The cricket protein isolate (CPI) exhibited characteristic protein peaks in the FTIR spectrum. Notably, an enhanced cell viability was observed in the presence of the extracted proteins, showing their biocompatibility. The CPI also exhibited antioxidant properties in a concentration-dependent manner. More significant mineralization was observed in the CPI-treated cells than in the control, suggesting their osteoinductive potential. The upregulation of the osteogenic marker genes (Runx2, ALP, OCN, and BSP) in CPI treated media compared with the control supports their osteoinductive nature. Therefore, cricket-derived protein isolates could be used as functional protein isolate for tissue engineering applications, especially for bone regeneration.

Investigating the role of culture conditions on hypertrophic differentiation in human cartilage endplate cells

Cartilage endplate degeneration/calcification has been linked to the onset and progression of intervertebral disc degeneration and there is a critical need to understand mechanisms, such as hypertrophic differentiation, of cartilage endplate degeneration/calcification to inform treatment strategies for discogenic back pain. In vitro cell culture conditions capable of inducing hypertrophic differentiation are used to study pathophysiological mechanisms in articular chondrocytes, but culture conditions capable of inducing a hypertrophic cartilage endplate cell phenotype have yet to be explored. The goal of this study was to investigate the role of culture conditions capable of inducing hypertrophic differentiation in articular chondrocytes on hypertrophic differentiation in human cartilage endplate cells. Isolated human cartilage endplate cells were cultured as pellets for 21 days at either 5% O₂ (physiologic for cartilage) or 20.7% O₂ (hyperoxic) and treated with 10% fetal bovine serum or Wnt agonist, two stimuli used to induce hypertrophic differentiation in articular chondrocytes. Cartilage endplate cells did not exhibit a hypertrophic cell morphology in response to fetal bovine serum or Wnt agonist but did display other hallmarks of chondrocyte hypertrophy and degeneration such as hypertrophic gene and protein expression, and a decrease in healthy proteoglycans and an increase in fibrous collagen accumulation. These findings demonstrate that cartilage endplate cells take on a degenerative phenotype in response to hypertrophic stimuli in vitro, but do not undergo classical changes in morphology associated with hypertrophic differentiation regardless of oxygen levels, highlighting potential differences in the response of cartilage endplate cells versus articular chondrocytes to the same stimuli.

Recent Trends in Multipotent Human Mesenchymal Stem/Stromal Cells: Learning from History and Advancing Clinical Applications

Early cell biology reports demonstrated the presence of cells with stem-like properties in bone marrow, with both hematopoietic and mesenchymal lineages. Over the years, various investigations have purified and characterized mesenchymal stromal/stem cells (MSCs) from different human tissues as cells with multilineage differentiation potential under the appropriate conditions. Due to their appealing characteristics and versatile potentials, MSCs are leveraged in many applications in medicine such as oncology, bioprinting, and as recent as therapeutics discovery and innovation for COVID-19. To date, studies indicate that MSCs have varied differentiation capabilities into different cell types, and demonstrate immunomodulating and anti-inflammatory properties. Different microenvironments or niche for MSCs and their resulting heterogeneity may influence attendant cellular behavior and differentiation capacity. The potential clinical applications of MSCs and exosomes derived from these cells have led to an avalanche of research reports on their properties and hundreds of clinical trials being undertaken. There is ample reason to think, as discussed in this expert review that the future looks bright and promising for MSC research, with many clinical trials under way to ascertain their clinical utility. This review provides a synthesis of the latest advances and trends in MSC research to allow for broad and critically informed use of MSCs. Early observations of the presence of these cells in the bone marrow and their remarkable differentiation capabilities and immunomodulation are also presented.

pNaSS-Grafted PCL Film-Guided rAAV TGF-β Gene Therapy Activates the Chondrogenic Activities in Human Bone Marrow Aspirates

Scaffold-guided viral gene therapy is a novel, powerful tool to enhance the processes of tissue repair in articular cartilage lesions by the delivery and overexpression of therapeutic genes in a noninvasive, controlled release manner based on a procedure that may protect the gene vehicles from undesirable host immune responses. In this study, we examined the potential of transferring a recombinant adeno-associated virus (rAAV) vector carrying a sequence for the highly chondroregenerative transforming growth factor beta (TGF-β), using poly(ɛ-caprolactone) (PCL) films functionalized by the grafting of poly(sodium styrene sulfonate) (pNaSS) in chondrogenically competent bone marrow aspirates as future targets for therapy in cartilage lesions. Effective overexpression of TGF-β in the aspirates by rAAV was achieved upon delivery using pNaSS-grafted and ungrafted PCL films for up to 21 days (the longest time point evaluated), with superior levels using the grafted films, compared with respective conditions without vector coating. The production of rAAV-mediated TGF-β by pNaSS-grafted and ungrafted PCL films significantly triggered the biological activities and chondrogenic processes in the samples (proteoglycan and type-II collagen deposition and cell proliferation), while containing premature mineralization and hypertrophy relative to the other conditions, with overall superior effects supported by the pNaSS-grafted films. These observations demonstrate the potential of PCL film-assisted rAAV TGF-β gene transfer as a convenient, off-the-shelf technique to enhance the reparative potential of the bone marrow in patients in future approaches for improved cartilage repair.

Human myoblasts differentiate in various mesenchymal lineages and inhibit allogeneic T cell proliferation through an indolamine 2,3 dioxygenase dependent pathway

Muscle stem cells (MuSC) are considered as a reliable source of therapeutic cells to restore diseased muscles. However in most cases, injected MuSC-derived myoblasts are rapidly destroyed by the host immune response, which impairs the beneficial effect. By contrast, human mesenchymal stromal cells (MSC), have been reported to exhibit potent immune regulatory functions. Thus, we investigated, in vitro, the multipotent differentiation- and immunosuppressive capacities of human myoblasts and compared these features with those of human MSC. Myoblasts shared numerous cell surface markers with MSC, including CD73, CD90, CD105 and CD146. Both cell type were negative for HLA-DR and CD45, CD34 and CD31. CD56, a myogenic marker, was expressed by myoblasts exclusively. Myoblasts displayed multipotent potential capabilities with differentiation in chondrocytes, adipocytes and osteoblasts in vitro. Myoblasts also inhibited allogenic T cell proliferation in vitro in a dose dependent manner, very similarly to MSC. This effect was partly mediated via the activation of indolamine 2,3 dioxygenase enzyme (IDO) after IFNγ exposure. Altogether, these data demonstrate that human myoblasts can differentiate in various mesenchymal linages and exhibit powerful immunosuppressive properties in vitro. Such features may open new therapeutic strategies for MuSC-derived myoblasts.

Hydrogel microspheres for spatiotemporally controlled delivery of RNA and silencing gene expression within scaffold-free tissue engineered constructs

Delivery systems for controlled release of RNA interference (RNAi) molecules, including small interfering (siRNA) and microRNA (miRNA), have the potential to direct stem cell differentiation for regenerative musculoskeletal applications. To date, localized RNA delivery platforms in this area have focused predominantly on bulk scaffold-based approaches, which can interfere with cell-cell interactions important for recapitulating some native musculoskeletal developmental and healing processes in tissue regeneration strategies. In contrast, scaffold-free, high density human mesenchymal stem cell (hMSC) aggregates may provide an avenue for creating a more biomimetic microenvironment. Here, photocrosslinkable dextran microspheres (MS) encapsulating siRNA-micelles were prepared via an aqueous emulsion method and incorporated within hMSC aggregates for localized and sustained delivery of bioactive siRNA. siRNA-micelles released from MS in a sustained fashion over the course of 28 days, and the released siRNA retained its ability to transfect cells for gene silencing. Incorporation of fluorescently labeled siRNA (siGLO)-laden MS within hMSC aggregates exhibited tunable siGLO delivery and uptake by stem cells. Incorporation of MS loaded with siRNA targeting green fluorescent protein (siGFP) within GFP-hMSC aggregates provided sustained presentation of siGFP within the constructs and prolonged GFP silencing for up to 15 days. This platform system enables sustained gene silencing within stem cell aggregates and thus shows great potential in tissue regeneration applications. STATEMENT OF SIGNIFICANCE: This work presents a new strategy to deliver RNA-nanocomplexes from photocrosslinked dextran microspheres for tunable presentation of bioactive RNA. These microspheres were embedded within scaffold-free, human mesenchymal stem cell (hMSC) aggregates for sustained gene silencing within three-dimensional cell constructs while maintaining cell viability. Unlike exogenous delivery of RNA within culture medium that suffers from diffusion limitations and potential need for repeated transfections, this strategy provides local and sustained RNA presentation from the microspheres to cells in the constructs. This system has the potential to inhibit translation of hMSC differentiation antagonists and drive hMSC differentiation toward desired specific lineages, and is an important step in the engineering of high-density stem cell systems with incorporated instructive genetic cues for application in tissue regeneration.

Ectopic models recapitulating morphological and functional features of articular cartilage

BACKGROUND

Articular cartilage is an extremely specialized connective tissue which covers all diarthrodial joints. Implantation of chondrogenic cells without or with additional biomaterial scaffolds in ectopic locationsin vivo generates substitutes of cartilage with structural and functional characteristics that are used in fundamental investigations while also serving as a basis for translational studies.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant ectopic models, among which subcutaneous, intramuscular, and kidney capsule transplantation and elaborates on implanted cells and biomaterial scaffolds and on their use to recapitulate morphological and functional features of articular cartilage. Although the absence of a physiological joint environment and biomechanical stimuli is the major limiting factor, ectopic models are an established component for articular cartilage research aiming to generate a bridge between in vitro data and the clinically more relevant translational orthotopic in vivo models when their limitations are considered.

Trends in Articular Cartilage Tissue Engineering: 3D Mesenchymal Stem Cell Sheets as Candidates for Engineered Hyaline-Like Cartilage

Articular cartilage defects represent an inciting factor for future osteoarthritis (OA) and degenerative joint disease progression. Despite multiple clinically available therapies that succeed in providing short term pain reduction and restoration of limited mobility, current treatments do not reliably regenerate native hyaline cartilage or halt cartilage degeneration at these defect sites. Novel therapeutics aimed at addressing limitations of current clinical cartilage regeneration therapies increasingly focus on allogeneic cells, specifically mesenchymal stem cells (MSCs), as potent, banked, and available cell sources that express chondrogenic lineage commitment capabilities. Innovative tissue engineering approaches employing allogeneic MSCs aim to develop three-dimensional (3D), chondrogenically differentiated constructs for direct and immediate replacement of hyaline cartilage, improve local site tissue integration, and optimize treatment outcomes. Among emerging tissue engineering technologies, advancements in cell sheet tissue engineering offer promising capabilities for achieving both in vitro hyaline-like differentiation and effective transplantation, based on controlled 3D cellular interactions and retained cellular adhesion molecules. This review focuses on 3D MSC-based tissue engineering approaches for fabricating “ready-to-use” hyaline-like cartilage constructs for future rapid in vivo regenerative cartilage therapies. We highlight current approaches and future directions regarding development of MSC-derived cartilage therapies, emphasizing cell sheet tissue engineering, with specific focus on regulating 3D cellular interactions for controlled chondrogenic differentiation and post-differentiation transplantation capabilities.

Growth differentiation factor 5 in cartilage and osteoarthritis: A possible therapeutic candidate

Growth differentiation factor 5 (GDF-5) is essential for cartilage development and homeostasis. The expression and function of GDF-5 are highly associated with the pathogenesis of osteoarthritis (OA). OA, characterized by progressive degeneration of joint, particularly in cartilage, causes severe social burden. However, there is no effective approach to reverse the progression of this disease. Over the past decades, extensive studies have demonstrated the protective effects of GDF-5 against cartilage degeneration and defects. Here, we summarize the current literature describing the role of GDF-5 in development of cartilage and joints, and the association between the GDF-5 gene polymorphisms and OA susceptibility. We also shed light on the protective effects of GDF-5 against OA in terms of direct GDF-5 supplementation and modulation of the GDF-5-related signalling. Finally, we discuss the current limitations in the application of GDF-5 for the clinical treatment of OA. This review provides a comprehensive insight into the role of GDF-5 in cartilage and emphasizes GDF-5 as a potential therapeutic candidate in OA.

The effects of 3D culture on the expansion and maintenance of nucleus pulposus progenitor cell multipotency

INTRODUCTION

Low back pain (LBP) is a global health concern. Increasing evidence implicates intervertebral disk (IVD) degeneration as a major contributor. In this respect, tissue-specific progenitors may play a crucial role in tissue regeneration, as these cells are perfectly adapted to their niche. Recently, a novel progenitor cell population was described in the nucleus pulposus (NP) that is positive for Tie2 marker. These cells have self-renewal capacity and in vitro multipotency potential. However, extremely low numbers of the NP progenitors limit the feasibility of cell therapy strategies.

OBJECTIVE

Here, we studied the influence of the culture method and of the microenvironment on the proliferation rate and the differentiation potential of human NP progenitors in vitro.

METHOD

Cells were obtained from human NP tissue from trauma patients. Briefly, the NP tissue cells were cultured in two-dimensional (2D) (monolayer) or three-dimensional (3D) (alginate beads) conditions. After 1 week, cells from 2D or 3D culture were expanded on fibronectin-coated flasks. Subsequently, expanded NP cells were then characterized by cytometry and tri-lineage differentiation, which was analyzed by qPCR and histology. Moreover, experiments using Tie2+ and Tie2- NP cells were also performed.

RESULTS

The present study aims to demonstrate that 3D expansion of NP cells better preserves the Tie2+ cell populations and increases the chondrogenic and osteogenic differentiation potential compared to 2D expansion. Moreover, the cell sorting experiments reveal that only Tie2+ cells were able to maintain the pluripotent gene expression if cultured in 3D within alginate beads. Therefore, our results highly suggest that the maintenance of the cell's multipotency is mainly, but not exclusively, due to the higher presence of Tie2+ cells due to 3D culture.

CONCLUSION

This project not only might have a scientific impact by evaluating the influence of a two-step expansion protocol on the functionality of NP progenitors, but it could also lead to an innovative clinical approach.

Challenges and Innovations in Osteochondral Regeneration: Insights from Biology and Inputs from Bioengineering toward the Optimization of Tissue Engineering Strategies

Due to the extremely high incidence of lesions and diseases in aging population, it is critical to put all efforts into developing a successful implant for osteochondral tissue regeneration. Many of the patients undergoing surgery present osteochondral fissure extending until the subchondral bone (corresponding to a IV grade according to the conventional radiographic classification by Berndt and Harty). Therefore, strategies for functional tissue regeneration should also aim at healing the subchondral bone and joint interface, besides hyaline cartilage. With the ambition of contributing to solving this problem, several research groups have been working intensively on the development of tailored implants that could promote that complex osteochondral regeneration. These implants may be manufactured through a wide variety of processes and use a wide variety of (bio)materials. This review aimed to examine the state of the art regarding the challenges, advantages, and drawbacks of the current strategies for osteochondral regeneration. One of the most promising approaches relies on the principles of additive manufacturing, where technologies are used that allow for the production of complex 3D structures with a high level of control, intended and predefined geometry, size, and interconnected pores, in a reproducible way. However, not all materials are suitable for these processes, and their features should be examined, targeting a successful regeneration.

Human Osteochondral Explants: Reliable Biomimetic Models to Investigate Disease Mechanisms and Develop Personalized Treatments for Osteoarthritis

Introduction

Likely due to ignored heterogeneity in disease pathophysiology, osteoarthritis (OA) has become the most common disabling joint disease, without effective disease-modifying treatment causing a large social and economic burden. In this study we set out to explore responses of aged human osteochondral explants upon different OA-related perturbing triggers (inflammation, hypertrophy and mechanical stress) for future tailored biomimetic human models.

Methods

Human osteochondral explants were treated with IL-1β (10 ng/ml) or triiodothyronine (T3; 10 nM) or received 65% strains of mechanical stress (65% MS). Changes in chondrocyte signalling were determined by expression levels of nine genes involved in catabolism, anabolism and hypertrophy. Breakdown of cartilage was measured by sulphated glycosaminoglycans (sGAGs) release, scoring histological changes (Mankin score) and mechanical properties of cartilage.

Results

All three perturbations (IL-1β, T3 and 65% MS) resulted in upregulation of the catabolic genes MMP13 and EPAS1. IL-1β abolished COL2A1 and ACAN gene expression and increased cartilage degeneration, reflected by increased Mankin scores and sGAGs released. Treatment with T3 resulted in a high and significant upregulation of the hypertrophic markers COL1A1, COL10A1 and ALPL. However, 65% MS increased sGAG release and detrimentally altered mechanical properties of cartilage.

Conclusion

We present consistent and specific output on three different triggers of OA. Perturbation with the pro-inflammatory IL-1β mainly induced catabolic chondrocyte signalling and cartilage breakdown, while T3 initiated expression of hypertrophic and mineralization markers. Mechanical stress at a strain of 65% induced catabolic chondrocyte signalling and changed cartilage matrix integrity. The major strength of our ex vivo models was that they considered aged, preserved, human cartilage of a heterogeneous OA patient population. As a result, the explants may reflect a reliable biomimetic model prone to OA onset allowing for development of different treatment modalities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40744-021-00287-y.

3D printed silica-gelatin hybrid scaffolds of specific channel sizes promote collagen Type II, Sox9 and Aggrecan production from chondrocytes

Inorganic/organic hybrids have co-networks of inorganic and organic components, with the aim of obtaining synergy of the properties of those components. Here, a silica-gelatin sol-gel hybrid "ink" was directly 3D printed to produce 3D grid-like scaffolds, using a coupling agent, 3-glycidyloxypropyl)trimethoxysilane (GPTMS), to form covalent bonds between the silicate and gelatin co-networks. Scaffolds were printed with 1 mm strut separation, but the drying method affected the final architecture and properties. Freeze drying produced <40 μm struts and large ~700 μm channels. Critical point drying enabled strut consolidation, with ~160 μm struts and ~200 μm channels, which improved mechanical properties. This architecture was critical to cellular response: when chondrocytes were seeded on the scaffolds with 200 μm wide pore channels in vitro, collagen Type II matrix was preferentially produced (negligible amount of Type I or X were observed), indicative of hyaline-like cartilaginous matrix formation, but when pore channels were 700 μm wide, Type I collagen was prevalent. This was supported by Sox9 and Aggrecan expression. The scaffolds have potential for regeneration of articular cartilage regeneration, particularly in sports medicine cases.

Increased Mesenchymal Stem Cell Functionalization in Three-Dimensional Manufacturing Settings for Enhanced Therapeutic Applications

Mesenchymal stem/stromal cell (MSC) exist within their in vivo niches as part of heterogeneous cell populations, exhibiting variable stemness potential and supportive functionalities. Conventional extensive 2D in vitro MSC expansion, aimed at obtaining clinically relevant therapeutic cell numbers, results in detrimental effects on both cellular characteristics (e.g., phenotypic changes and senescence) and functions (e.g., differentiation capacity and immunomodulatory effects). These deleterious effects, added to the inherent inter-donor variability, negatively affect the standardization and reproducibility of MSC therapeutic potential. The resulting manufacturing challenges that drive the qualitative variability of MSC-based products is evident in various clinical trials where MSC therapeutic efficacy is moderate or, in some cases, totally insufficient. To circumvent these limitations, various in vitro/ex vivo techniques have been applied to manufacturing protocols to induce specific features, attributes, and functions in expanding cells. Exposure to inflammatory cues (cell priming) is one of them, however, with untoward effects such as transient expression of HLA-DR preventing allogeneic therapeutic schemes. MSC functionalization can be also achieved by in vitro 3D culturing techniques, in an effort to more closely recapitulate the in vivo MSC niche. The resulting spheroid structures provide spatial cell organization with increased cell–cell interactions, stable, or even enhanced phenotypic profiles, and increased trophic and immunomodulatory functionalities. In that context, MSC 3D spheroids have shown enhanced “medicinal signaling” activities and increased homing and survival capacities upon transplantation in vivo. Importantly, MSC spheroids have been applied in various preclinical animal models including wound healing, bone and osteochondral defects, and cardiovascular diseases showing safety and efficacy in vivo. Therefore, the incorporation of 3D MSC culturing approach into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved without requiring ex vivo stimulatory regimes. In the present review, we discuss the MSC functionalization in 3D settings and how this strategy can contribute to an improved MSC-based product for safer and more effective therapeutic applications.

Pluripotency and immunomodulatory signatures of canine induced pluripotent stem cell-derived mesenchymal stromal cells are similar to harvested mesenchymal stromal cells

With a view towards harnessing the therapeutic potential of canine mesenchymal stromal cells (cMSCs) as modulators of inflammation and the immune response, and to avoid the issues of the variable quality and quantity of harvested cMSCs, we examined the immunomodulatory properties of cMSCs derived from canine induced pluripotent stem cells (ciMSCs), and compared them to cMSCs harvested from adipose tissue (cAT-MSC) and bone marrow (cBM-MSC). A combination of deep sequencing and quantitative RT-PCR of the ciMSC transcriptome confirmed that ciMSCs express more genes in common with cBM-MSCs and cAT-MSCs than with the ciPSCs from which they were derived. Both ciMSCs and harvested cMSCs express a range of pluripotency factors in common with the ciPSCs including NANOG, POU5F1 (OCT-4), SOX-2, KLF-4, LIN-28A, MYC, LIF, LIFR, and TERT. However, ESRRB and PRDM-14, both factors associated with naïve, rather than primed, pluripotency were expressed only in the ciPSCs. CXCR-4, which is essential for the homing of MSCs to sites of inflammation, is also detectable in ciMSCs, cAT- and cBM-MSCs, but not ciPSCs. ciMSCs constitutively express the immunomodulatory factors iNOS, GAL-9, TGF-β1, PTGER-2α and VEGF, and the pro-inflammatory mediators COX-2, IL-1β and IL-8. When stimulated with the canine pro-inflammatory cytokines tumor necrosis factor-α (cTNF-α), interferon-γ (cIFN-γ), or a combination of both, ciMSCs upregulated their expression of IDO, iNOS, GAL-9, HGF, TGF-β1, PTGER-2α, VEGF, COX-2, IL-1β and IL-8. When co-cultured with mitogen-stimulated lymphocytes, ciMSCs downregulated their expression of iNOS, HGF, TGF-β1 and PTGER-2α, while increasing their expression of COX-2, IDO and IL-1β. Taken together, these findings suggest that ciMSCs possess similar immunomodulatory capabilities as harvested cMSCs and support further investigation into their potential use for the management of canine immune-mediated and inflammatory disorders.

Endoglin Level Is Critical for Cartilage Tissue Formation In Vitro by Passaged Human Chondrocytes

Transforming growth factor beta (TGFβ) signaling is required for in vitro chondrogenesis. In animal models of osteoarthritis (OA), TGFβ receptor alterations are detected in chondrocytes in severe OA cartilage. It is not known whether such changes are dependent on the grade of human OA and if they affect chondrogenesis. Thus, the purpose of this study was to determine if human OA chondrocytes obtained from low-grade or high-grade disease could form cartilage tissue and to assess the role of the co-receptors, endoglin (ENG) and TGFβ receptor 3 (TGFBRIII), in the regulation of this tissue generation in vitro. We hypothesized that the grade of OA disease would not affect the ability of cells to form cartilage tissue and that the TGFβ co-receptor, ENG, would be critical to regulating tissue formation. Chondrocytes isolated from low-grade OA or high-grade OA human articular cartilage (AC) were analyzed directly (P0) or passaged in monolayer to P2. Expression of the primary TGFβ receptor ALK5, and the co-receptors ENG and TGFβRIII, was assessed by image flow cytometry. To assess the ability to form cartilaginous tissue, cells were placed in three-dimensional culture at high density and cultured in chondrogenic media containing TGFβ3. ENG knockdown was used to determine its role in regulating tissue formation. Overall, grade-specific differences in expression of ALK5, ENG, and TGFβRIII in primary or passaged chondrocytes were not detected; however, ENG expression increased significantly after passaging. Despite the presence of ALK5, P0 cells did not form cartilaginous tissue. In contrast, P2 cells derived from low-grade and high-grade OA AC formed hyaline-like cartilaginous tissues of similar quality. Knockdown of ENG in P2 cells inhibited cartilaginous tissue formation compared to controls indicating that the level of ENG protein expression is critical for in vitro chondrogenesis by passaged articular chondrocytes. This study demonstrates that it is not the grade of OA, but the levels of ENG in the presence of ALK5 that influences the ability of human passaged articular chondrocytes to form cartilaginous tissue in vitro in 3D culture. This has implications for cartilage repair therapies. Impact statement These findings are important clinically, given the limited availability of osteoarthritis (OA) cartilage tissue. Being able to use cells from all grades of OA will increase our ability to obtain sufficient cells for cartilage repair. In addition, it is possible that endoglin (ENG) levels, in the presence of ALK5 expression, may be suitable to use as biomarkers to identify cells able to produce cartilage.

Tissue-Adhesive Chondroitin Sulfate Hydrogel for Cartilage Reconstruction

Chondroitin sulfate (CS), the main component of cartilage extracellular matrix, has attracted attention as a biomaterial for cartilage tissue engineering. However, current CS hydrogel systems still have limitations for application in successful cartilage tissue engineering owing to their unsuitable degradation kinetics, insufficient mechanical similarity, and lack of integration with the native cartilage tissue. In this study, using mussel adhesive-inspired catechol chemistry, we developed a functional CS hydrogel that exhibits tunable physical and mechanical properties as well as excellent tissue adhesion for efficient integration with native tissues. Various properties of the developed catechol-functionalized CS (CS-CA) hydrogel, including swelling, degradation, mechanical properties, and adhesiveness, could be tailored by varying the conjugation ratio of the catechol group to the CS backbone and the concentration of the CS-CA conjugates. CS-CA hydrogels exhibited significantly increased modulus (∼10 kPa) and superior adhesive properties (∼3 N) over conventional CS hydrogels (∼hundreds Pa and ∼0.05 N). In addition, CS-CA hydrogels incorporating decellularized cartilage tissue dice promoted the chondrogenic differentiation of human adipose-derived mesenchymal stem cells by providing a cartilage-like microenvironment. Finally, the transplantation of autologous cartilage dice using tissue-adhesive CS-CA hydrogels enhanced cartilage integration with host tissue and neo-cartilage formation owing to favorable physical, mechanical, and biological properties for cartilage formation. In conclusion, our study demonstrated the potential utility of the CS-CA hydrogel system in cartilage tissue reconstruction.

Current status of regenerative medicine in osteoarthritis

The high prevalence of osteoarthritis (OA), as well as the current lack of disease-modifying drugs for OA, has provided a rationale for regenerative medicine as a possible treatment modality for OA treatment. In this editorial, the current status of regenerative medicine in OA including stem cells, exosomes, and genes is summarized along with the author’s perspectives. Despite a tremendous interest, so far there is very little evidence proving the efficacy of this modality for clinical application. As symptomatic relief is not sufficient to justify the high cost associated with regenerative medicine, definitive structural improvement that would last for years or decades and obviate or delay the need for joint arthroplasty is essential for regenerative medicine to retain a place among OA treatment methods.

Cite this article: Bone Joint Res 2021;10(2):134–136.

The lower in vitro chondrogenic potential of canine adipose tissue-derived mesenchymal stromal cells (MSC) compared to bone marrow-derived MSC is not improved by BMP-2 or BMP-6

Mesenchymal stromal cells (MSC) are used for cell-based treatment for canine osteoarthritis (OA). Compared with human MSCs, detailed information on the functional characterisation of canine MSCs is limited. In particular, the chondrogenic differentiation of canine adipose tissue-derived MSCs (cAT-MSCs) is challenging. In this study, we aimed to compare cAT-MSCs with bone marrow-derived MSCs (cBM-MSCs), focusing specifically on their in vitro chondrogenic potential, with or without bone morphogenetic proteins (BMP). cBM-MSCs and cAT-MSCs were characterised using flow cytometry and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The chondrogenic differentiation potential of all cMSC preparations in the presence of TGF-β1 alone or when supplemented with 10, 100, or 250 ng/mL BMP-2 or BMP-6 was investigated using RT-qPCR, and biochemical, histochemical and immunohistological analyses. Both cBM-MSCs and cAT-MSCs expressed the surface markers CD90, CD73, and CD29, and were negative for CD45 and CD34, although the expression of CD73 and CD271 varied with donor and tissue origin. Interestingly, expression of ACAN and SOX9 was higher in cBM-MSCs than cAT-MSCs. In contrast with cBM-MSCs, cAT-MSCs could not differentiate toward the chondrogenic lineage without BMP-2/-6, and their in vitro chondrogenesis was inferior to cBM-MSCs with BMP-2/-6. Thus, cAT-MSCs have lower in vitro chondrogenic capacity than cBM-MSC under the studied culture conditions with 10, 100, or 250 ng/mL BMP-2 or BMP-6. Therefore, further characterisation is necessary to explore the potential of cAT-MSCs for cell-based OA treatments.

Quantitative Proteomic Profiling of Small Molecule Treated Mesenchymal Stem Cells Using Chemical Probes

The differentiation of human adipose derived stem cells toward a neural phenotype by small molecules has been a vogue topic in the last decade. The characterization of the produced cells has been explored on a broad scale, examining morphological and specific surface protein markers; however, the lack of insight into the expression of functional proteins and their interactive partners is required to further understand the extent of the process. The phenotypic characterization by proteomic profiling allows for a substantial in-depth analysis of the molecular machinery induced and directing the cellular changes through the process. Herein we describe the temporal analysis and quantitative profiling of neural differentiating human adipose-derived stem cells after sub-proteome enrichment using a bisindolylmaleimide chemical probe. The results show that proteins enriched by the Bis-probe were identified reproducibly with 133, 118, 126 and 89 proteins identified at timepoints 0, 1, 6 and 12, respectively. Each temporal timepoint presented several shared and unique proteins relative to neural differentiation and their interactivity. The major protein classes enriched and quantified were enzymes, structural and ribosomal proteins that are integral to differentiation pathways. There were 42 uniquely identified enzymes identified in the cells, many acting as hubs in the networks with several interactions across the network modulating key biological pathways. From the cohort, it was found by gene ontology analysis that 18 enzymes had direct involvement with neurogenic differentiation.

Innovative Tissue-Engineered Strategies for Osteochondral Defect Repair and Regeneration: Current Progress and Challenges

Clinical treatments for the repair of osteochondral defects (OCD) are merely palliative, not completely curative, and thus enormously unfulfilled challenges. With the in-depth studies of biology, medicine, materials, and engineering technology, the conception of OCD repair and regeneration should be renewed. During the past decades, many innovative tissue-engineered approaches for repairing and regenerating damaged osteochondral units have been widely explored. Various scaffold-free and scaffold-based strategies, such as monophasic, biphasic, and currently fabricated multiphasic and gradient architectures have been proposed and evaluated. Meanwhile, progenitor cells and tissue-specific cells have also been intensively investigated in vivo as well as ex vivo. Concerning bioactive factors and drugs, they have been combined with scaffolds and/or living cells, and even released in a spatiotemporally controlled manner. Although tremendous progress has been achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications. Here, the osteochondral unit structure, its defect classifications, and diagnosis are summarized. Commonly used clinical reparative techniques, tissue-engineered strategies, emerging 3D-bioprinting technologies, and the status of their clinical applications are discussed. Existing challenges to translation are also discussed and potential solutions for future R&D directions are proposed.

Fabrication of hyaline-like cartilage constructs using mesenchymal stem cell sheets

Cell and tissue engineering approaches for articular cartilage regeneration increasingly focus on mesenchymal stem cells (MSCs) as allogeneic cell sources, based on availability and innate chondrogenic potential. Many MSCs exhibit chondrogenic potential as three-dimensional (3D) cultures (i.e. pellets and seeded biomaterial scaffolds) in vitro; however, these constructs present engraftment, biocompatibility, and cell functionality limitations in vivo. Cell sheet technology maintains cell functionality as scaffold-free constructs while enabling direct cell transplantation from in vitro culture to targeted sites in vivo. The present study aims to develop transplantable hyaline-like cartilage constructs by stimulating MSC chondrogenic differentiation as cell sheets. To achieve this goal, 3D MSC sheets are prepared, exploiting spontaneous post-detachment cell sheet contraction, and chondrogenically induced. Results support 3D MSC sheets' chondrogenic differentiation to hyaline cartilage in vitro via post-contraction cytoskeletal reorganization and structural transformations. These 3D cell sheets' initial thickness and cellular densities may also modulate MSC-derived chondrocyte hypertrophy in vitro. Furthermore, chondrogenically differentiated cell sheets adhere directly to cartilage surfaces via retention of adhesion molecules while maintaining the cell sheets' characteristics. Together, these data support the utility of cell sheet technology for fabricating scaffold-free, hyaline-like cartilage constructs from MSCs for future transplantable articular cartilage regeneration therapies.

Characterization of Mesenchymal Stem Cell Differentiation within Miniaturized 3D Scaffolds through Advanced Microscopy Techniques

Three-dimensional culture systems and suitable substrates topographies demonstrated to drive stem cell fate in vitro by mechanical conditioning. For example, the Nichoid 3D scaffold remodels stem cells and shapes nuclei, thus promoting stem cell expansion and stemness maintenance. However, the mechanisms involved in force transmission and in biochemical signaling at the basis of fate determination are not yet clear. Among the available investigation systems, confocal fluorescence microscopy using fluorescent dyes enables the observation of cell function and shape at the subcellular scale in vital and fixed conditions. Contrarily, nonlinear optical microscopy techniques, which exploit multi-photon processes, allow to study cell behavior in vital and unlabeled conditions. We apply confocal fluorescence microscopy, coherent anti-Stokes Raman scattering (CARS), and second harmonic generation (SHG) microscopy to characterize the phenotypic expression of mesenchymal stem cells (MSCs) towards adipogenic and chondrogenic differentiation inside Nichoid scaffolds, in terms of nuclear morphology and specific phenotypic products, by comparing these techniques. We demonstrate that the Nichoid maintains a rounded nuclei during expansion and differentiation, promoting MSCs adipogenic differentiation while inhibiting chondrogenesis. We show that CARS and SHG techniques are suitable for specific estimation of the lipid and collagenous content, thus overcoming the limitations of using unspecific fluorescent probes.

Safety Considerations in 3D Bioprinting Using Mesenchymal Stromal Cells

Three-dimensional (3D) bioprinting has demonstrated great potential for the fabrication of biomimetic human tissues and complex graft materials. This technology utilizes bioinks composed of cellular elements placed within a biomaterial. Mesenchymal stromal cells (MSCs) are an attractive option for cell selection in 3D bioprinting. MSCs can be isolated from a variety of tissues, can pose vast proliferative capacity and can differentiate to multiple committed cell types. Despite their promising properties, the use of MSCs has been associated with several drawbacks. These concerns are related to the ex vivo manipulation throughout the process of 3D bioprinting. The herein manuscript aims to present the current evidence surrounding these events and propose ways to minimize the risks to the patients following widespread expansion of 3D bioprinting in the medical field.

Naringin and bone marrow mesenchymal stem cells repair articular cartilage defects in rabbit knees through the transforming growth factor-β superfamily signaling pathway

The present study aimed to assess the effect of a combination of naringin and rabbit bone marrow mesenchymal stem cells (BMSCs) on the repair of cartilage defects in rabbit knee joints and to assess possible involvement of the transforming growth factor-β (TGF-β) signaling pathway in this process. After establishing an articular cartilage defect model in rabbit knees, 20 New Zealand rabbits were divided into a sham operation group (Sham), a model group (Mod), a naringin treatment group (Nar), a BMSC group (BMSCs) and a naringin + BMSC group (Nar/BMSCs). At 12 weeks after treatment, the cartilage was evaluated using the International Cartilage Repair Society (ICRS)'s macroscopic evaluation of cartilage repair scale, the ICRS's visual histological assessment scale, the Modified O'Driscoll grading system, histological staining (hematoxylin and eosin staining, toluidine blue staining and safranin O staining) and immunohistochemical staining (type-II collagen, TGF-β3 and SOX-9 immunostaining). Using the above grading systems to quantify the extent of repair, histological quantification and macro quantification of joint tissue repair showed that the Nar/BMSCs group displayed repair after treatment in comparison to the untreated Mod group. Among the injury model groups (Mod, Nar, BMSCs and Nar/BMSCs), the Nar/BMSCs group displayed the highest degree of morphological repair. The results of histological and immunohistochemical staining of the repaired region of the joint defect indicated that the BMSCs had a satisfactory effect on the repair of the joint structure but had a poor effect on the repair of cartilage quality. The Nar/BMSCs group displayed satisfactory therapeutic effects on both repair of the joint structure and cartilage quality. The expression level of type-II collagen was high in the Nar/BMSCs group. Additionally, staining of TGF-β3 and SOX-9 in the Nar/BMSCs group was the strongest compared with that of any other group in the present study. Naringin and/BMSCs together demonstrated a more efficient repair effect on articular cartilage defects in rabbit knees than the use of either treatment alone in terms of joint structure and cartilage quality. One potential mechanism of naringin action may be through activation and continuous regulation of the TGF-β superfamily signaling pathway, which can promote BMSCs to differentiate into chondrocytes.

Lessons from joint development for cartilage repair in the clinic

More than 250 years ago, William Hunter stated that when cartilage is destroyed it never recovers. In the last 20 years, the understanding of the mechanisms that lead to joint formation and the knowledge that some of these mechanisms are reactivated in the homeostatic responses of cartilage to injury has offered an unprecedented therapeutic opportunity to achieve cartilage regeneration. Very large investments in ambitious clinical trials are finally revealing that, although we do not have perfect medicines yet, disease modification is a feasible possibility for human osteoarthritis.

Enhanced Osteogenic Differentiation of Human Mesenchymal Stem Cells on Amine-Functionalized Titanium Using Humidified Ammonia Supplied Nonthermal Atmospheric Pressure Plasma

The surface molecular chemistry, such as amine functionality, of biomaterials plays a crucial role in the osteogenic activity of relevant cells and tissues during hard tissue regeneration. Here, we examined the possibilities of creating amine functionalities on the surface of titanium by using the nonthermal atmospheric pressure plasma jet (NTAPPJ) method with humidified ammonia, and the effects on human mesenchymal stem cell (hMSC) were investigated. Titanium samples were subjected to NTAPPJ treatments using nitrogen (N-P), air (A-P), or humidified ammonia (NA-P) as the plasma gas, while control (C-P) samples were not subjected to plasma treatment. After plasma exposure, all treatment groups showed increased hydrophilicity and had more attached cells than the C-P. Among the plasma-treated samples, the A-P and NA-P showed surface oxygen functionalities and exhibited greater cell proliferation than the C-P and N-P. The NA-P additionally showed surface amine-related functionalities and exhibited a higher level of alkaline phosphatase activity and osteocalcin expression than the other samples. The results can be explained by increases in fibronectin absorption and focal adhesion kinase gene expression on the NA-P samples. These findings suggest that NTAPPJ technology with humidified ammonia as a gas source has clinical potential for hard tissue generation.

Recapitulation of cartilage/bone formation using iPSCs via biomimetic 3D rotary culture approach for developmental engineering

The recapitulation of cartilage/bone formation via guiding induced pluripotent stem cells (iPSCs) differentiation toward chondrogenic mesoderm lineage is an ideal approach to investigate cartilage/bone development and also for cartilage/bone regeneration. However, current induction protocols are time-consuming and complicated to follow. Here, we established a rapid and efficient approach that directly induce iPSCs differentiation toward chondrogenic mesoderm lineage by regulating the crucial Bmp-4 and FGF-2 signaling pathways using a 3D rotary suspension culture system. The mechanical stimulation from 3D rotary suspension accelerates iPSCs differentiation toward mesodermal and subsequent chondrogenic lineage via the Bmp-4-Smad1 and Tgf-β-Smad2/3 signaling pathways, respectively. The scaffold-free homogenous cartilaginous pellets or hypertrophic cartilaginous pellets derived from iPSCs within 28 days were capable of articular cartilage regeneration or vascularized bone regeneration via endochondral ossification in vivo, respectively. This biomimetic culture approach will contribute to research related to cartilage/bone development, regeneration, and hence to therapeutic applications in cartilage-/bone-related diseases.

Mesenchymal Stem/Progenitor Cells: The Prospect of Human Clinical Translation

Mesenchymal stem/progenitor cells (MSCs) are key players in regenerative medicine, relying principally on their differentiation/regeneration potential, immunomodulatory properties, paracrine effects, and potent homing ability with minimal if any ethical concerns. Even though multiple preclinical and clinical studies have demonstrated remarkable properties for MSCs, the clinical applicability of MSC-based therapies is still questionable. Several challenges exist that critically hinder a successful clinical translation of MSC-based therapies, including but not limited to heterogeneity of their populations, variability in their quality and quantity, donor-related factors, discrepancies in protocols for isolation, in vitro expansion and premodification, and variability in methods of cell delivery, dosing, and cell homing. Alterations of MSC viability, proliferation, properties, and/or function are also affected by various drugs and chemicals. Moreover, significant safety concerns exist due to possible teratogenic/neoplastic potential and transmission of infectious diseases. Through the current review, we aim to highlight the major challenges facing MSCs' human clinical translation and shed light on the undergoing strategies to overcome them.

Protein-reactive nanofibrils decorated with cartilage-derived decellularized extracellular matrix for osteochondral defects

Cartilage defect is difficult to heal due to its avascular properties. Implantation of mesenchymal stem cell is one of the most promising approach for regenerating cartilage defects. Here we prepared polymeric nanofibrils decorated with cartilage-derived decellularized extracellular matrix (dECM) as a chondroinductive scaffold material for cartilage repair. To fabricate nanofibrils, eletrospun PCL nanofibers were fragmented by subsequent mechanical and chemical process. The nanofibrils were surface-modified with poly(glycidyl methacrylate) (PGMA@NF) via surface-initiated atom transfer radical polymerization (SI-ATRP). The epoxy groups of PGMA@NF were subsequently reacted with dECM prepared from bovine articular cartilage. Therefore, the cartilage-dECM-decorated nanofibrils structurally and biochemically mimic cartilage-specific microenvironment. Once adipose-derived stem cells (ADSCs) were self-assembled with the cartilage-dECM-decorated nanofibrils by cell-directed association, they exhibited differentiation hallmarks of chondrogenesis without additional biologic additives. ADSCs in the nanofibril composites significantly increased expression of chondrogenic gene markers in comparison to those in pellet culture. Furthermore, ADSC-laden nanofibril composites filled the osteochondral defects compactly due to their clay-like texture. Thus, the ADSC-laden nanofibril composites supported the long-term regeneration of 12 weeks without matrix loss during joint movement. The defects treated with the ADSC-laden PGMA@NF significantly facilitated reconstruction of their cartilage and subchondral bone ECM matrices compared to those with ADSC-laden nanofibrils, non-specifically adsorbing cartilage-dECM without surface decoration of PGMA.

Runx2 silencing promotes adipogenesis via down-regulation of DLK1 in chondrogenic differentiating MSCs

BACKGROUND

For cartilage regeneration, stem cells are a promising cell source; however, even the advances made in the differentiation of stem cells into precursor-differentiated cartilage cells have not been successful with respect to reprograming these cells to achieve complete differentiation and fully functioning cells until now. Previous findings suggest that Runx2 plays a major role in chondrocyte differentiation and maturation. Although targeting Runx2 has enhanced some chondrocyte properties, the adipogenic lineage shift has eventually occurred in these cells. The present study mainly aimed to reveal the mechanism of this adipogenesis.

METHODS

To create inducible artificial shRNA-miR expressing vectors, the designed short hairpin RNAs (shRNAs) were inserted into the pri-mir-30 backbone, cloned into lentiviral pLVET-Tet-on, and transducted into mesenchymal stem cells (MSCs). Runx2 gene was silenced in MSCs either for 1 week or 4 weeks and cultured in the chondrogenic medium. At days 7, 14 and 28, cells were harvested, and chondrogenesis, adipogenesis and hypertrophic states were examined using histochemical staining and a real-time polymerase chain reaction assay.

RESULTS

The results showed that the designed shRNA-miR effectively targeted Runx2 in mRNA and protein levels. Chondrogenic markers were up-regulated in constantly silenced Runx2 group; however, adipogenic markers and fat droplets appeared gradually. DLK1 gene was also significantly down-regulated in this group, and overexpression of DLK1 abrogated adipogenesis in the Runx2 targeted group.

CONCLUSIONS

Based on these results, it can be concluded that DLK1 is responsible for the lineage shift in Runx2 targeted chondrogenic differentiating MSCs.

3D Bioprinting of osteochondral tissue substitutes - in vitro-chondrogenesis in multi-layered mineralized constructs

For the generation of multi-layered full thickness osteochondral tissue substitutes with an individual geometry based on clinical imaging data, combined extrusion-based 3D printing (3D plotting) of a bioink laden with primary chondrocytes and a mineralized biomaterial phase was introduced. A pasty calcium phosphate cement (CPC) and a bioink based on alginate-methylcellulose (algMC) - both are biocompatible and allow 3D plotting with high shape fidelity - were applied in monophasic and combinatory design to recreate osteochondral tissue layers. The capability of cells reacting to chondrogenic biochemical stimuli inside the algMC-based 3D hydrogel matrix was assessed. Towards combined osteochondral constructs, the chondrogenic fate in the presence of CPC in co-fabricated and biphasic mineralized pattern was evaluated. Majority of expanded and algMC-encapsulated cells survived the plotting process and the cultivation period, and were able to undergo redifferentiation in the provided environment to produce their respective extracellular matrix (ECM) components (i.e. sulphated glycosaminoglycans, collagen type II), examined after 3 weeks. The presence of a mineralized zone as located in the physiological calcified cartilage region suspected to interfere with chondrogenesis, was found to support chondrogenic ECM production by altering the ionic concentrations of calcium and phosphorus in in vitro culture conditions.

Mesenchymal stem cells-derived cartilage micropellets: A relevant in vitro model for biomechanical and mechanobiological studies of cartilage growth

The prevalence of diseases that affect the articular cartilage is increasing due to population ageing, but the current treatments are only palliative. One innovative approach to repair cartilage defects is tissue engineering and the use of mesenchymal stem/stromal cells (MSCs). Although the combination of MSCs with biocompatible scaffolds has been extensively investigated, no product is commercially available yet. This could be explained by the lack of mechanical stimulation during in vitro culture and the absence of proper and stable cartilage matrix formation, leading to poor integration after implantation. The objective of the present study was to investigate the biomechanical behaviour of MSC differentiation in micropellets, a well-defined 3D in vitro model of cartilage differentiation and growth, in view of tissue engineering applications. MSC micropellet chondrogenic differentiation was induced by exposure to TGFβ3. At different time points during differentiation (35 days of culture), their global mechanical properties were assessed using a very sensitive compression device coupled to an identification procedure based on a finite element parametric model. Micropellets displayed both a non-linear strain-induced stiffening behaviour and a dissipative behaviour that increased from day 14 to day 29, with a maximum instantaneous Young's modulus of 179.9 ± 18.8 kPa. Moreover, chondrocyte gene expression levels were strongly correlated with the observed mechanical properties. This study indicates that cartilage micropellets display the biochemical and biomechanical characteristics required for investigating and recapitulating the different stages of cartilage development.

rAAV-Mediated Overexpression of SOX9 and TGF-β via Carbon Dot-Guided Vector Delivery Enhances the Biological Activities in Human Bone Marrow-Derived Mesenchymal Stromal Cells

Scaffold-assisted gene therapy is a highly promising tool to treat articular cartilage lesions upon direct delivery of chondrogenic candidate sequences. The goal of this study was to examine the feasibility and benefits of providing highly chondroreparative agents, the cartilage-specific sex-determining region Y-type high-mobility group 9 (SOX9) transcription factor or the transforming growth factor beta (TGF-β), to human bone marrow-derived mesenchymal stromal cells (hMSCs) via clinically adapted, independent recombinant adeno-associated virus (rAAV) vectors formulated with carbon dots (CDs), a novel class of carbon-dominated nanomaterials. Effective complexation and release of a reporter rAAV-lacZ vector was achieved using four different CDs elaborated from 1-citric acid and pentaethylenehexamine (CD-1); 2-citric acid, poly(ethylene glycol) monomethyl ether (MW 550 Da), and N,N-dimethylethylenediamine (CD-2); 3-citric acid, branched poly(ethylenimine) (MW 600 Da), and poly(ethylene glycol) monomethyl ether (MW 2 kDa) (CD-3); and 4-citric acid and branched poly(ethylenimine) (MW 600 Da) (CD-4), allowing for the genetic modification of hMSCs. Among the nanoparticles, CD-2 showed an optimal ability for rAAV delivery (up to 2.2-fold increase in lacZ expression relative to free vector treatment with 100% cell viability for at least 10 days, the longest time point examined). Administration of therapeutic (SOX9, TGF-β) rAAV vectors in hMSCs via CD-2 led to the effective overexpression of each independent transgene, promoting enhanced cell proliferation (TGF-β) and cartilage matrix deposition (glycosaminoglycans, type-II collagen) for at least 21 days relative to control treatments (CD-2 lacking rAAV or associated to rAAV-lacZ), while advantageously restricting undesirable type-I and -X collagen deposition. These results reveal the potential of CD-guided rAAV gene administration in hMSCs as safe, non-invasive systems for translational strategies to enhance cartilage repair.

Adipose-Derived Mesenchymal Stem Cell Treatments and Available Formulations

PURPOSE OF REVIEW

The use of human adipose-derived mesenchymal stem cells (ADSCs) has gained attention due to its potential to expedite healing and the ease of harvesting; however, clinical evidence is limited, and questions concerning optimal method of delivery and long-term outcomes remain unanswered.

RECENT FINDINGS

Administration of ADSCs in animal models has been reported to aid in improved healing benefits with enhanced repair biomechanics, superior gross histological appearance of injury sites, and higher concentrations of growth factors associated with healing compared to controls. Recently, an increasing body of research has sought to examine the effects of ADSCs in humans. Several available processing techniques and formulations for ADSCs exist with evidence to suggest benefits with the use of ADSCs, but the superiority of any one method is not clear. Evidence from the most recent clinical studies available demonstrates promising outcomes following treatment of select musculoskeletal pathologies with ADSCs despite reporting variability among ADSCs harvesting and processing; these include (1) healing benefits and pain improvement for rotator cuff and Achilles tendinopathies, (2) improvements in pain and function in those with knee and hip osteoarthritis, and (3) improved cartilage regeneration for osteochondral focal defects of the knee and talus. The limitation to most of this literature is the use of other therapeutic biologics in combination with ADSCs. Additionally, many studies lack control groups, making establishment of causation inappropriate. It is imperative to perform higher-quality studies using consistent, predictable control populations and to standardize formulations of ADSCs in these trials.

Additive manufactured, highly resilient, elastic, and biodegradable poly(ester)urethane scaffolds with chondroinductive properties for cartilage tissue engineering

Articular cartilage was thought to be one of the first tissues to be successfully engineered. Despite the avascular and non-innervated nature of the tissue, the cells within articular cartilage – chondrocytes – account for a complex phenotype that is difficult to be maintained in vitro. The use of bone marrow–derived stromal cells (BMSCs) has emerged as a potential solution to this issue. Differentiation of BMSCs toward stable and non-hypertrophic chondrogenic phenotypes has also proved to be challenging. Moreover, hyaline cartilage presents a set of mechanical properties – relatively high Young's modulus, elasticity, and resilience – that are difficult to reproduce. Here, we report on the use of additive manufactured biodegradable poly(ester)urethane (PEU) scaffolds of two different structures (500 μm pore size and 90° or 60° deposition angle) that can support the loads applied onto the knee while being highly resilient, with a permanent deformation lower than 1% after 10 compression-relaxation cycles. Moreover, these scaffolds appear to promote BMSC differentiation, as shown by the deposition of glycosaminoglycans and collagens (in particular collagen II). At gene level, BMSCs showed an upregulation of chondrogenic markers, such as collagen II and the Sox trio, to higher or similar levels than that of traditional pellet cultures, with a collagen II/collagen I relative expression of 2–3, depending on the structure of the scaffold. Moreover, scaffolds with different pore architectures influenced the differentiation process and the final BMSC phenotype. These data suggest that additive manufactured PEU scaffolds could be good candidates for cartilage tissue regeneration in combination with microfracture interventions.

Nasal Chondrocyte-Derived Soluble Factors Affect Chondrogenesis of Cocultured Mesenchymal Stem Cells

To investigate the effect of soluble factors released from human nasal chondrocytes (NCs) on cocultured human bone marrow mesenchymal stem cells (MSCs) and NC tissue-engineered constructs. Cartilage engineered from pure NCs on a three-dimensional (3D) porous collagen scaffold was cultured indirectly in a Transwell system with cartilage engineered from a direct coculture of human bone marrow-derived MSCs and NCs on a 3D porous collagen scaffold. The soluble factors were measured in the conditioned media from the different chambers of the Transwell system. Engineered cartilage from cocultures exposed to the pure NC construct exhibited reduced chondrogenic potential relative to control constructs, shown by reduced extracellular matrix deposition and increased expression of hypertrophic markers. Analysis of the soluble factors within the conditioned media showed an increase in inflammatory cytokines in the coculture chamber exposed to the pure NC construct. Principal component analysis revealed that the majority of the data variance could be explained by proinflammatory factors and hypertrophic chondrogenesis. In conclusion, our data suggest that inflammatory cytokines derived from NCs reduce the chondrogenic potential of coculture engineered cartilage through the induction of hypertrophic chondrogenesis. Impact statement The use of engineered cartilage from cocultured nasal chondrocytes (NCs) and mesenchymal stem cells for nasal cartilage reconstruction may be problematic. Our data suggest that the soluble factors from surrounding native NCs in the cartilage to be fixed can compromise the quality of the engineered cartilage if used in reconstructive surgery.

Cytoprotective effects of antioxidant supplementation on mesenchymal stem cell therapy

Mesenchymal stem cells (MSCs) are earmarked as perfect candidates for cell therapy and tissue engineering due to their capacity to differentiate into different cell types. However, their potential for application in regenerative medicine declines when the levels of the reactive oxygen and nitrogen species (RONS) increase from the physiological levels, a phenomenon which is at least inevitable in ex vivo cultures and air-exposed damaged tissues. Increased levels of RONS can alter the patterns of osteogenic and adipogenic differentiation and inhibit proliferation, as well. Besides, oxidative stress enhances senescence and cell death, thus lowering the success rates of the MSC engraftment. Hence, in this review, we have selected some representatives of antioxidants and newly emerged nano antioxidants in three main categories, including chemical compounds, biometabolites, and protein precursors/proteins, which are proved to be effective in the treatment of MSCs. We will focus on how antioxidants can be applied to optimize the clinical usage of the MSCs and their associated signaling pathways. We have also reviewed several paralleled properties of some antioxidants and nano antioxidants which can be simultaneously used in real-time imaging, scaffolding techniques, and other applications in addition to their primary antioxidative function.

Current Status and Future Prospects of Genome-Scale Metabolic Modeling to Optimize the Use of Mesenchymal Stem Cells in Regenerative Medicine

Mesenchymal stem cells are a promising source for externally grown tissue replacements and patient-specific immunomodulatory treatments. This promise has not yet been fulfilled in part due to production scaling issues and the need to maintain the correct phenotype after re-implantation. One aspect of extracorporeal growth that may be manipulated to optimize cell growth and differentiation is metabolism. The metabolism of MSCs changes during and in response to differentiation and immunomodulatory changes. MSC metabolism may be linked to functional differences but how this occurs and influences MSC function remains unclear. Understanding how MSC metabolism relates to cell function is however important as metabolite availability and environmental circumstances in the body may affect the success of implantation. Genome-scale constraint based metabolic modeling can be used as a tool to fill gaps in knowledge of MSC metabolism, acting as a framework to integrate and understand various data types (e.g., genomic, transcriptomic and metabolomic). These approaches have long been used to optimize the growth and productivity of bacterial production systems and are being increasingly used to provide insights into human health research. Production of tissue for implantation using MSCs requires both optimized production of cell mass and the understanding of the patient and phenotype specific metabolic situation. This review considers the current knowledge of MSC metabolism and how it may be optimized along with the current and future uses of genome scale constraint based metabolic modeling to further this aim.

Long non-coding RNA GRASLND enhances chondrogenesis via suppression of the interferon type II signaling pathway

The roles of long noncoding RNAs (lncRNAs) in musculoskeletal development, disease, and regeneration remain poorly understood. Here, we identified the novel lncRNA GRASLND (originally named RNF144A-AS1) as a regulator of mesenchymal stem cell (MSC) chondrogenesis. GRASLND, a primate-specific lncRNA, is upregulated during MSC chondrogenesis and appears to act directly downstream of SOX9, but not TGF-β3. We showed that the silencing of GRASLND resulted in lower accumulation of cartilage-like extracellular matrix in a pellet assay, while GRASLND overexpression – either via transgene ectopic expression or by endogenous activation via CRISPR-dCas9-VP64 – significantly enhanced cartilage matrix production. GRASLND acts to inhibit IFN-γ by binding to EIF2AK2, and we further demonstrated that GRASLND exhibits a protective effect in engineered cartilage against interferon type II. Our results indicate an important role of GRASLND in regulating stem cell chondrogenesis, as well as its therapeutic potential in the treatment of cartilage-related diseases, such as osteoarthritis.

Enhanced Chondrogenic Differentiation Activities in Human Bone Marrow Aspirates via sox9 Overexpression Mediated by pNaSS-Grafted PCL Film-Guided rAAV Gene Transfer

BACKGROUND

The delivery of therapeutic genes in sites of articular cartilage lesions using non-invasive, scaffold-guided gene therapy procedures is a promising approach to stimulate cartilage repair while protecting the cargos from detrimental immune responses, particularly when targeting chondroreparative bone marrow-derived mesenchymal stromal cells in a natural microenvironment like marrow aspirates.

METHODS

Here, we evaluated the benefits of providing a sequence for the cartilage-specific sex-determining region Y-type high-mobility group box 9 (SOX9) transcription factor to human marrow aspirates via recombinant adeno-associated virus (rAAV) vectors delivered by poly(ε-caprolactone) (PCL) films functionalized via grafting with poly(sodium styrene sulfonate) (pNaSS) to enhance the marrow chondrogenic potential over time.

RESULTS

Effective sox9 overexpression was observed in aspirates treated with pNaSS-grafted or ungrafted PCL films coated with the candidate rAAV-FLAG-hsox9 (FLAG-tagged rAAV vector carrying a human sox9 gene sequence) vector for at least 21 days relative to other conditions (pNaSS-grafted and ungrafted PCL films without vector coating). Overexpression of sox9 via rAAV sox9/pNaSS-grafted or ungrafted PCL films led to increased biological and chondrogenic differentiation activities (matrix deposition) in the aspirates while containing premature osteogenesis and hypertrophy without impacting cell proliferation, with more potent effects noted when using pNaSS-grafted films.

CONCLUSIONS

These findings show the benefits of targeting patients' bone marrow via PCL film-guided therapeutic rAAV (sox9) delivery as an off-the-shelf system for future strategies to enhance cartilage repair in translational applications.

Combined Effect of Midazolam and Bone Morphogenetic Protein-2 for Differentiation Induction from C2C12 Myoblast Cells to Osteoblasts

In drug repositioning research, a new concept in drug discovery and new therapeutic opportunities have been identified for existing drugs. Midazolam (MDZ) is an anesthetic inducer used for general anesthesia. Here, we demonstrate the combined effects of bone morphogenetic protein-2 (BMP-2) and MDZ on osteogenic differentiation. An immortalized mouse myoblast cell line (C2C12 cell) was cultured in the combination of BMP-2 and MDZ (BMP-2+MDZ). The differentiation and signal transduction of C2C12 cells into osteoblasts were investigated at biological, immunohistochemical, and genetic cell levels. Mineralized nodules formed in C2C12 cells were characterized at the crystal engineering level. BMP-2+MDZ treatment decreased the myotube cell formation of C2C12 cells, and enhanced alkaline phosphatase activity and expression levels of osteoblastic differentiation marker genes. The precipitated nodules consisted of randomly oriented hydroxyapatite nanorods and nanoparticles. BMP-2+MDZ treatment reduced the immunostaining for both α1 and γ2 subunits antigens on the gamma-aminobutyric acid type A (GABAA) receptor in C2C12 cells, but enhanced that for BMP signal transducers. Our investigation showed that BMP-2+MDZ has a strong ability to induce the differentiation of C2C12 cells into osteoblasts and has the potential for drug repositioning in bone regeneration.

Chondrogenic Differentiation from Induced Pluripotent Stem Cells Using Non-Viral Minicircle Vectors

Human degenerative cartilage has low regenerative potential. Chondrocyte transplantation offers a promising strategy for cartilage treatment and regeneration. Currently, chondrogenesis using human pluripotent stem cells (hiPSCs) is accomplished using human recombinant growth factors. Here, we differentiate hiPSCs into chondrogenic pellets using minicircle vectors. Minicircles are a non-viral gene delivery system that can produce growth factors without integration into the host genome. We generated minicircle vectors containing bone morphogenetic protein 2 (BMP2) and transforming growth factor beta 3 (TGFβ3) and delivered them to mesenchymal stem cell-like, hiPSC-derived outgrowth (OG) cells. Cell pellets generated using minicircle-transfected OG cells successfully differentiated into the chondrogenic lineage. The implanted minicircle-based chondrogenic pellets recovered the osteochondral defects in rat models. This work is a proof-of-concept study that describes the potential application of minicircle vectors in cartilage regeneration using hiPSCs.

Animal mesenchymal stem cell research in cartilage regenerative medicine - a review

Healing of articular cartilage is a major clinical challenge as it also lacks a direct vasculature and nerves, and carries a limited number of resident chondrocytes that do not proliferate easily. Damaged articular cartilages are usually replaced by fibrocartilages, which are mechanically and structurally weaker and less resilient. Regenerative medicine involving stem cells is considered to have a definitive potential to overcome the limitations associated with the currently available surgical methods of cartilage repair. Among various stem cell types, mesenchymal stem cells (MSCs) are preferred for clinical applications. These cells can be readily derived from various sources and have the ability to trans-differentiate into various tissue-specific cells, including those of the cartilage by the process of chondrogenesis. Compared to embryonic or induced pluripotent stem cells (iPSCs), no ethical or teratogenic issues are associated with MSCs. These stem cells are being extensively evaluated for the treatment of joint affections and the results appear promising. Unlike human medicine, in veterinary medicine, the literature on stem cell research for cartilage regeneration is limited. This review, therefore, aims to comprehensively discuss the available literature and pinpoint the achievements and limitations associated with the use of MSCs for articular cartilage repair in animal species.