Chondrogenic differentiation of mesenchymal stem cells: challenges and unfulfilled expectations

Effects of adipose tissue-derived stromal vascular fraction on osteochondral defects treated by hyaluronic acid-based scaffold: An experimental study

OBJECTIVES

This study aims to evaluate the effect of adipose-derived stromal vascular fraction (SVF) on osteochondral defects treated by hyaluronic acid (HA)-based scaffold in a rabbit model.

MATERIALS AND METHODS

Eighteen white New Zealand rabbits were randomly grouped into the experimental group (n=9) and control group (n=9). In all groups, osteochondral defects were induced on the weight-bearing surfaces of the right femoral medial condyles, and a HA-based scaffold was applied to the defect area with microfractures (MFs). In this study, 1 mL of adipose-derived SVF was injected into the knee joints of the rabbits in the experimental group. For histological and macroscopic evaluation, four rabbits were randomly selected from each group at Week 4, and the remaining rabbits were sacrificed at the end of Week 8. Macroscopic assessments of all samples were performed based on the Brittberg scoring system, and microscopic evaluations were performed based on the O'Driscoll scores.

RESULTS

Samples were taken at Weeks 4 and 8. At Week 4, the O'Driscoll scores were significantly higher in the control group than the experimental group (p=0.038), while there was no significant difference in the Brittberg scores between the two groups (p=0.108). At Week 8, the O'Driscoll score and Brittberg scores were statistically higher in the experimental group than in the control group (p=0.008 and p=0.007, respectively). According to the microscopic evaluation, at the end of Week 8, the cartilage thickness was greater in the experimental group, and nearly all of the defect area was filled with hyaline cartilage.

CONCLUSION

Application of adipose-derived SVF with MF-HA-based scaffold was better than MF-HA-based scaffold treatment in improving osteochondral regeneration. Therefore, it can be used in combination with microfracture and scaffold to accelerate cartilage regeneration, particularly in the treatment of secondary osteoarthritis.

Electrochemiluminescence imaging of respiratory activity of cellular spheroids using sequential potential steps

The respiratory activity of cultured cells can be electrochemically monitored using scanning electrochemical microscopy (SECM) with high spatial resolution. However, in SECM, the electrode takes a long time to scan, limiting simultaneous measurements with large biological samples such as cell spheroids. Therefore, for rapid electrochemical imaging, a novel strategy is needed. Herein, we report electrochemiluminescence (ECL) imaging of spheroid respiratory activity for the first time using sequential potential steps. L-012, a luminol analog, was used as an ECL luminophore, and H₂O₂, a sensitizer for ECL of L-012, was generated by the electrochemical reduction of dissolved O₂. The ECL imaging visualized spheroid respiratory activity-evidenced by ECL suppression-corresponding to O₂ distribution around the spheroids. This method enabled the time-lapse imaging of respiratory activity in multiple spheroids with good spatial resolution comparable to that of SECM. Our work provides a promising high-throughput imaging strategy for elucidating spheroid cellular dynamics.

LncRNA DNM3OS regulates GREM2 via miR-127-5p to suppress early chondrogenic differentiation of rat mesenchymal stem cells under hypoxic conditions

Background

Improved chondrogenic differentiation of mesenchymal stem cells (MSCs) by genetic regulation is a potential method for regenerating articular cartilage. MiR-127-5p has been reported to promote cartilage differentiation of rat bone marrow MSCs (rMSCs); however, the regulatory mechanisms underlying hypoxia-stimulated chondrogenic differentiation remain unknown.

Methods

rMSCs were induced to undergo chondrogenic differentiation under normoxic or hypoxic conditions. Expression of lncRNA DNM3OS, miR-127-5p, and GREM2 was detected by quantitative real-time PCR. Proteoglycans were detected by Alcian blue staining. Western blot assays were performed to examine the relative levels of GREM2 and chondrogenic differentiation related proteins. Luciferase reporter assays were performed to assess the association among DNM3OS, miR-127-5p, and GREM2.

Results

MiR-127-5p levels were upregulated, while DNM3OS and GREM2 levels were downregulated in rMSCs induced to undergo chondrogenic differentiation, and those changes were attenuated by hypoxic conditions (1% O₂). Further in vitro experiments revealed that downregulation of miR-127-5p reduced the production of proteoglycans and expression of chondrogenic differentiation markers (COL1A1, COL2A1, SOX9, and ACAN) and osteo/chondrogenic markers (BMP-2, p-SMAD1/2). MiR-127-5p overexpression produced the opposite results in rMSCs induced to undergo chondrogenic differentiation under hypoxic conditions. GREM2 was found to be a direct target of miR-127-5p, which was suppressed in rMSCs undergoing chondrogenic differentiation. Moreover, DNM3OS could directly bind to miR-127-5p and inhibit chondrogenic differentiation of rMSCs via regulating GREM2.

Conclusions

Our study revealed a novel molecular pathway (DNM3OS/miR-127-5p/GREM2) that may be involved in hypoxic chondrogenic differentiation.

Bio-mimicking Shear Stress Environments for Enhancing Mesenchymal Stem Cell Differentiation

Mesenchymal stem cells (MSCs) are multipotent stromal cells, with the ability to differentiate into mesodermal (e.g., adipocyte, chondrocyte, hematopoietic, myocyte, osteoblast), ectodermal (e.g., epithelial, neural) and endodermal (e.g., hepatocyte, islet cell) lineages based on the type of induction cues provided. As compared to embryonic stem cells, MSCs hold a multitude of advantages from a clinical translation perspective, including ease of isolation, low immunogenicity and limited ethical concerns. Therefore, MSCs are a promising stem cell source for different regenerative medicine applications. The in vitro differentiation of MSCs into different lineages relies on effective mimicking of the in vivo milieu, including both biochemical and mechanical stimuli. As compared to other biophysical cues, such as substrate stiffness and topography, the role of fluid shear stress (SS) in regulating MSC differentiation has been investigated to a lesser extent although the role of interstitial fluid and vascular flow in regulating the normal physiology of bone, muscle and cardiovascular tissues is well-known. This review aims to summarise the current state-of-the-art regarding the role of SS in the differentiation of MSCs into osteogenic, cardiovascular, chondrogenic, adipogenic and neurogenic lineages. We will also highlight and discuss the potential of employing SS to augment the differentiation of MSCs to other lineages, where SS is known to play a role physiologically but has not yet been successfully harnessed for in vitro differentiation, including liver, kidney and corneal tissue lineage cells. The incorporation of SS, in combination with biochemical and biophysical cues during MSC differentiation, may provide a promising avenue to improve the functionality of the differentiated cells by more closely mimicking the in vivo milieu.

Extracellular Vesicles from Mesenchymal Stem Cells as Potential Treatments for Osteoarthritis

Osteoarthritis (OA) is a chronic degenerative disorder of the joint and its prevalence and severity is increasing owing to ageing of the population. Osteoarthritis is characterized by the degradation of articular cartilage and remodeling of the underlying bone. There is little understanding of the cellular and molecular processes involved in pathophysiology of OA. Currently the treatment for OA is limited to painkillers and anti-inflammatory drugs, which only treat the symptoms. Some patients may also undergo surgical procedures to replace the damaged joints. Extracellular vesicles (EV) play an important role in intercellular communications and their concentration is elevated in the joints of OA patients, although their mechanism is unclear. Extracellular vesicles are naturally released by cells and they carry their origin cell information to be delivered to target cells. On the other hand, mesenchymal stem cells (MSCs) are highly proliferative and have a great potential in cartilage regeneration. In this review, we provide an overview of the current OA treatments and their limitations. We also discuss the role of EV in OA pathophysiology. Finally, we highlight the therapeutic potential of MSC-derived EV in OA and their challenges.

Different phenotypes and chondrogenic responses of human menstrual blood and bone marrow mesenchymal stem cells to activin A and TGF-β3

BACKGROUND

Due to its low capacity for self-repair, articular cartilage is highly susceptible to damage and deterioration, which leads to the development of degenerative joint diseases such as osteoarthritis (OA). Menstrual blood-derived mesenchymal stem/stromal cells (MenSCs) are much less characterized, as compared to bone marrow mesenchymal stem/stromal cells (BMMSCs). However, MenSCs seem an attractive alternative to classical BMMSCs due to ease of access and broader differentiation capacity. The aim of this study was to evaluate chondrogenic differentiation potential of MenSCs and BMMSCs stimulated with transforming growth factor β (TGF-β3) and activin A.

METHODS

MenSCs (n = 6) and BMMSCs (n = 5) were isolated from different healthy donors. Expression of cell surface markers CD90, CD73, CD105, CD44, CD45, CD14, CD36, CD55, CD54, CD63, CD106, CD34, CD10, and Notch1 was analyzed by flow cytometry. Cell proliferation capacity was determined using CCK-8 proliferation kit and cell migration ability was evaluated by scratch assay. Adipogenic differentiation capacity was evaluated according to Oil-Red staining and osteogenic differentiation according to Alizarin Red staining. Chondrogenic differentiation (activin A and TGF-β3 stimulation) was investigated in vitro and in vivo (subcutaneous scaffolds in nude BALB/c mice) by expression of chondrogenic genes (collagen type II, aggrecan), GAG assay and histologically. Activin A protein production was evaluated by ELISA during chondrogenic differentiation in monolayer culture.

RESULTS

MenSCs exhibited a higher proliferation rate, as compared to BMMSCs, and a different expression profile of several cell surface markers. Activin A stimulated collagen type II gene expression and glycosaminoglycan synthesis in TGF-β3 treated MenSCs but not in BMMSCs, both in vitro and in vivo, although the effects of TGF-β3 alone were more pronounced in BMMSCs in vitro.

CONCLUSION

These data suggest that activin A exerts differential effects on the induction of chondrogenic differentiation in MenSCs vs. BMMSCs, which implies that different mechanisms of chondrogenic regulation are activated in these cells. Following further optimization of differentiation protocols and the choice of growth factors, potentially including activin A, MenSCs may turn out to be a promising population of stem cells for the development of cell-based therapies with the capacity to stimulate cartilage repair and regeneration in OA and related osteoarticular disorders.

Human nasal septal chondrocytes (NSCs) preconditioned on NSC-derived matrix improve their chondrogenic potential

Background

Extracellular matrix (ECM) has a profound effect on cell behaviors. In this study, we prepare a decellularized human nasal septal chondrocyte (NSC)-derived ECM (CHDM), as a natural (N-CHDM) or soluble form (S-CHDM), and investigate their impact on NSCs differentiation.

Methods

N-CHDM, S-CHDM were obtained from NSC. To evaluate function of NSC cultured on each substrate, gene expression using chondrogenic marker, and chondrogenic protein expression were tested. Preconditioned NSCs-loaded scaffolds were transplanted in nude mice for 3 weeks and analyzed.

Results

When cultivated on each substrate, NSCs exhibited similar cell spread area but showed distinct morphology on N-CHDM with significantly lower cell circularity. They were highly proliferative on N-CHDM than S-CHDM and tissue culture plastic (TCP), and showed more improved cell differentiation, as assessed via chondrogenic marker (Col2, Sox9, and Aggrecan) expression and immunofluorescence of COL II. We also investigated the effect of NSCs preconditioning on three different 2D substrates while NSCs were isolated from those substrates, subsequently transferred to 3D mesh scaffold, then cultivated them in vitro or transplanted in vivo. The number of cells in the scaffolds was similar to each other at 5 days but cell differentiation was notably better with NSCs preconditioned on N-CHDM, as assessed via real-time q-PCR, Western blot, and immunofluorescence. Moreover, when those NSCs-loaded polymer scaffolds were transplanted subcutaneously in nude mice for 3 weeks and analyzed, the NSCs preconditioned on the N-CHDM showed significantly advanced cell retention in the scaffold, more cells with a chondrocyte lacunae structure, and larger production of cartilage ECM (COL II, glycosaminoglycan).

Conclusions

Taken together, a natural form of decellularized ECM, N-CHDM would present an advanced chondrogenic potential over a reformulated ECM (S-CHDM) or TCP substrate, suggesting that N-CHDM may hold more diverse signaling cues, not just limited to ECM component.

Recent Developed Strategies for Enhancing Chondrogenic Differentiation of MSC: Impact on MSC-Based Therapy for Cartilage Regeneration

Articular cartilage is susceptible to damage, but its self-repair is hindered by its avascular nature. Traditional treatment methods are not able to achieve satisfactory repair effects, and the development of tissue engineering techniques has shed new light on cartilage regeneration. Mesenchymal stem cells (MSCs) are one of the most commonly used seed cells in cartilage tissue engineering. However, MSCs tend to lose their multipotency, and the composition and structure of cartilage-like tissues formed by MSCs are far from those of native cartilage. Thus, there is an urgent need to develop strategies that promote MSC chondrogenic differentiation to give rise to durable and phenotypically correct regenerated cartilage. This review provides an overview of recent advances in enhancement strategies for MSC chondrogenic differentiation, including optimization of bioactive factors, culture conditions, cell type selection, coculture, gene editing, scaffolds, and physical stimulation. This review will aid the further understanding of the MSC chondrogenic differentiation process and enable improvement of MSC-based cartilage tissue engineering.

Progress in the use of mesenchymal stromal cells for osteoarthritis treatment

LITERATURE REVIEW OF MSCS IN THE TREATMENT OF OSTEOARTHRITIS IN THE PAST FIVE YEARS: Osteoarthritis (OA) is one of the most common chronic joint diseases, with prominent symptoms caused by many factors. However, current medical interventions for OA have resulted in poor clinical outcomes, demonstrating that there are huge unmet medical needs in this area. Cell therapy has opened new avenues of OA treatment. Different sources of mesenchymal stromal cells (MSCs) may have different phenotypes and cellular functions. Pre-clinical and clinical studies have demonstrated the feasibility, safety and efficacy of MSC therapy. Mitogen-activated protein kinase, Wnt and Notch signaling pathways are involved in the chondrogenesis of MSC-mediated treatments. MSCs may also exert effective immunoregulatory and paracrine effects to stimulate tissue repair. Therapy with extracellular vesicles containing cytokines, which are secreted by MSCs, might be a potential treatment for OA.

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.

rAAV-Mediated Human FGF-2 Gene Therapy Enhances Osteochondral Repair in a Clinically Relevant Large Animal Model Over Time In Vivo

BACKGROUND

Osteochondral defects, if left untreated, do not heal and can potentially progress toward osteoarthritis. Direct gene transfer of basic fibroblast growth factor 2 (FGF-2) with the clinically adapted recombinant adeno-associated viral (rAAV) vectors is a powerful tool to durably activate osteochondral repair processes.

PURPOSE

To examine the ability of an rAAV-FGF-2 construct to target the healing processes of focal osteochondral injury over time in a large translational model in vivo versus a control gene transfer condition.

STUDY DESIGN

Controlled laboratory study.

METHODS

Standardized osteochondral defects created in the knee joints of adult sheep were treated with an rAAV human FGF-2 (hFGF-2) vector by direct administration into the defect relative to control (reporter) rAAV-lacZ gene transfer. Osteochondral repair was monitored using macroscopic, histological, immunohistological, and biochemical methods and by micro-computed tomography after 6 months.

RESULTS

Effective, localized prolonged FGF-2 overexpression was achieved for 6 months in vivo relative to the control condition without undesirable leakage of the vectors outside the defects. Such rAAV-mediated hFGF-2 overexpression significantly increased the individual histological parameter "percentage of new subchondral bone" versus lacZ treatment, reflected in a volume of mineralized bone per unit volume of the subchondral bone plate that was equal to a normal osteochondral unit. Also, rAAV-FGF-2 significantly improved the individual histological parameters "defect filling,""matrix staining," and "cellular morphology" and the overall cartilage repair score versus the lacZ treatment and led to significantly higher cell densities and significantly higher type II collagen deposition versus lacZ treatment. Likewise, rAAV-FGF-2 significantly decreased type I collagen expression within the cartilaginous repair tissue.

CONCLUSION

The current work shows the potential of direct rAAV-mediated FGF-2 gene therapy to enhance osteochondral repair in a large, clinically relevant animal model over time in vivo.

CLINICAL RELEVANCE

Delivery of therapeutic (hFGF-2) rAAV vectors in sites of focal injury may offer novel, convenient tools to enhance osteochondral repair in the near future.

Dielectrophoretic Characterization of Tenogenically Differentiating Mesenchymal Stem Cells

Tendons are collagenous musculoskeletal tissues that connect muscles to bones and transfer the forces necessary for movement. Tendons are susceptible to injury and heal poorly, with long-term loss of function. Mesenchymal stem cell (MSC)-based therapies are a promising approach for treating tendon injuries but are challenged by the difficulties of controlling stem cell fate and of generating homogenous populations of stem cells optimized for tenogenesis (differentiation toward tendon). To address this issue, we aim to explore methods that can be used to identify and ultimately separate tenogenically differentiated MSCs from non-tenogenically differentiated MSCs. In this study, baseline and tenogenically differentiating murine MSCs were characterized for dielectric properties (conductivity and permittivity) of their outer membrane and cytoplasm using a dielectrophoretic (DEP) crossover technique. Experimental results showed that unique dielectric properties distinguished tenogenically differentiating MSCs from controls after three days of tenogenic induction. A single shell model was used to quantify the dielectric properties and determine membrane and cytoplasm conductivity and permittivity. Together, cell responses at the crossover frequency, cell morphology, and shell models showed that changes potentially indicative of early tenogenesis could be detected in the dielectric properties of MSCs as early as three days into differentiation. Differences in dielectric properties with tenogenesis indicate that the DEP-based label-free separation of tenogenically differentiating cells is possible and avoids the complications of current label-dependent flow cytometry-based separation techniques. Overall, this work illustrates the potential of DEP to generate homogeneous populations of differentiated stem cells for applications in tissue engineering and regenerative medicine.

Mesenchymal stem cells in osteoarthritis therapy: a review

Osteoarthritis (OA) is a chronic joint disease that generally occurs worldwide with pain and disability. The progression is slow, and it is mostly diagnosed midlife and often disturbs the knees, hips, feet, hands, and spine. Sex, age, obesity, occupation, and hereditary factors are risk factors that increase the opportunity for OA. Physical examinations involving X-rays and MRI, joint fluid analysis and blood tests are common tools for the diagnosis of OA. Interventions including exercise, manual therapy, lifestyle modification, and medication can help relieve pain and maintain mobility in the affected joints, yet none of the therapies enables the promotion of regeneration of degenerated tissues. Mesenchymal stem cells (MSCs) are a promising source for the treatment of OA due to their multipotency for differentiation into chondrocytes and their ability to modulate the immune system. Herein, we review the pathogenesis and treatment of OA and address the current status of MSCs as a novel potential therapeutic agent in OA treatment.

Non-viral Gene Therapy for Osteoarthritis

Strategies for delivering nucleic acids into damaged and diseased tissues have been divided into two major areas: viral and non-viral gene therapy. In this mini-review article we discuss the application of gene therapy for the treatment of osteoarthritis (OA), one of the most common forms of arthritis. We focus primarily on non-viral gene therapy and cell therapy. We briefly discuss the advantages and disadvantages of viral and non-viral gene therapy and review the nucleic acid transfer systems that have been used for gene delivery into articular chondrocytes in cartilage from the synovial joint. Although viral gene delivery has been more popular due to its reported efficiency, significant effort has gone into enhancing the transfection efficiency of non-viral delivery, making non-viral approaches promising tools for further application in basic, translational and clinical studies on OA. Non-viral gene delivery technologies have the potential to transform the future development of disease-modifying therapeutics for OA and related osteoarticular disorders. However, further research is needed to optimize transfection efficiency, longevity and duration of gene expression.

Characterisation of ovine bone marrow-derived stromal cells (oBMSC) and evaluation of chondrogenically induced micro-pellets for cartilage tissue repair in vivo

Abstract

Bone marrow stromal cells (BMSC) show promise in cartilage repair, and sheep are the most common large animal pre-clinical model.

Objective

The objective of this study was to characterise ovine BMSC (oBMSC) in vitro, and to evaluate the capacity of chondrogenic micro-pellets manufactured from oBMSC or ovine articular chondrocytes (oACh) to repair osteochondral defects in sheep.

Design

oBMSC were characterised for surface marker expression using flow cytometry and evaluated for tri-lineage differentiation capacity. oBMSC micro-pellets were manufactured in a microwell platform, and chondrogenesis was compared at 2%, 5%, and 20% O₂. The capacity of cartilage micro-pellets manufactured from oBMSC or oACh to repair osteochondral defects in adult sheep was evaluated in an 8-week pilot study.

Results

Expanded oBMSC were positive for CD44 and CD146 and negative for CD45. The common adipogenic induction ingredient, 3-Isobutyl-1-methylxanthine (IBMX), was toxic to oBMSC, but adipogenesis could be restored by excluding IBMX from the medium. BMSC chondrogenesis was optimal in a 2% O₂ atmosphere. Micro-pellets formed from oBMSC or oACh appeared morphologically similar, but hypertrophic genes were elevated in oBMSC micro-pellets. While oACh micro-pellets formed cartilage-like repair tissue in sheep, oBMSC micro-pellets did not.

Conclusion

The sensitivity of oBMSC, compared to human BMSC, to IBMX in standard adipogenic assays highlights species-associated differences. Micro-pellets manufactured from oACh were more effective than micro-pellets manufactured from oBMSC in the repair of osteochondral defects in sheep. While oBMSC can be driven to form cartilage-like tissue in vitro, the effective use of these cells in cartilage repair will depend on the successful mitigation of hypertrophy and tissue integration.

Supplementary information

The online version contains supplementary material available at 10.1186/s13287-020-02045-3.

A single day of TGF-β1 exposure activates chondrogenic and hypertrophic differentiation pathways in bone marrow-derived stromal cells

Virtually all bone marrow-derived stromal cell (BMSC) chondrogenic induction cultures include greater than 2 weeks exposure to transforming growth factor-β (TGF-β), but fail to generate cartilage-like tissue suitable for joint repair. Herein we used a micro-pellet model (5 × 103 BMSC each) to determine the duration of TGF-β1 exposure required to initiate differentiation machinery, and to characterize the role of intrinsic programming. We found that a single day of TGF-β1 exposure was sufficient to trigger BMSC chondrogenic differentiation and tissue formation, similar to 21 days of TGF-β1 exposure. Despite cessation of TGF-β1 exposure following 24 hours, intrinsic programming mediated further chondrogenic and hypertrophic BMSC differentiation. These important behaviors are obfuscated by diffusion gradients and heterogeneity in commonly used macro-pellet models (2 × 105 BMSC each). Use of more homogenous micro-pellet models will enable identification of the critical differentiation cues required, likely in the first 24-hours, to generate high quality cartilage-like tissue from BMSC.

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.

Extracellular Vesicles from Adipose Tissue Stem Cells in Diabetes and Associated Cardiovascular Disease; Pathobiological Impact and Therapeutic Potential

Adipose tissue-derived stem cells (ADSCs) are pluripotent mesenchymal stem cells found in relatively high percentages in the adipose tissue and able to self-renew and differentiate into many different types of cells. “Extracellular vesicles (EVs), small membrane vesicular structures released during cell activation, senescence, or apoptosis, act as mediators for long distance communication between cells, transferring their specific bioactive molecules into host target cells”. There is a general consensus on how to define and isolate ADSCs, however, multiple separation and characterization protocols are being used in the present which complicate the results’ integration in a single theory on ADSCs’ and their derived factors’ way of action. Metabolic syndrome and type 2 diabetes mellitus (T2DM) are mainly caused by abnormal adipose tissue size, distribution and metabolism and so ADSCs and their secretory factors such as EVs are currently investigated as therapeutics in these diseases. Moreover, due to their relatively easy isolation and propagation in culture and their differentiation ability, ADSCs are being employed in preclinical studies of implantable devices or prosthetics. This review aims to provide a comprehensive summary of the current knowledge on EVs secreted from ADSCs both as diagnostic biomarkers and therapeutics in diabetes and associated cardiovascular disease, the molecular mechanisms involved, as well as on the use of ADSC differentiation potential in cardiovascular tissue repair and prostheses.

An integrated microfluidic device for stem cell differentiation based on cell-imprinted substrate designed for cartilage regeneration in a rabbit model

Separating cells from the body and cultivating them in vitro will alter the function of cells. Therefore, for optimal cell culture in the laboratory, conditions similar to those of their natural growth should be provided. In previous studies, it has been shown that the use of cellular shape at the culture surface can regulate cellular function. In this work, the efficiency of the imprinting method increased by using microfluidic chip design and fabrication. In this method, first, a cell-imprinted substrate of chondrocytes was made using a microfluidic chip. Afterwards, stem cells were cultured on a cell-imprinted substrate using a second microfluidic chip aligned with the substrate. Therefore, stem cells were precisely placed on the chondrocyte patterns on the substrate and their fibroblast-like morphology was changed to chondrocyte's spherical morphology after 14-days culture in the chip without using any chemical growth factor. After chondrogenic differentiation and in vitro assessments (real-time PCR and immunocytotoxicity), differentiated stem cells were transferred on a collagen-hyaluronic acid scaffold and transplanted in articular cartilage defect of the rabbit. After 6 months, the post-transplantation analysis showed that the articular cartilage defect had been successfully regenerated in differentiated stem cell groups in comparison with the controls. In conclusion, this study showed the potency of the imprinting method for inducing chondrogenicity in stem cells, which can be used in clinical trials due to the safety of the procedure.

Utility of direct 3D co-culture model for chondrogenic differentiation of mesenchymal stem cells on hyaluronan scaffold (Hyaff-11)

This study presents direct 2D and 3D co-culture model of mesenchymal stem cells (MSCs) line with chondrocytes isolated from patients with osteoarthritis (unaffected area). MSCs differentiation into chondrocytes after 14, 17 days was checked by estimation of collagen I, II, X, aggrecan expression using immunohistochemistry. Visualization, localization of cells on Hyaff-11 was performed using enzymatic technique and THUNDER Imaging Systems. Results showed, that MSCs/chondrocytes 3D co-culture induced suitable conditions for chondrocytes grow and MSCs differentiation than 2D monoculture. Despite that differentiated cells on Hyaff-11 expressed collagen X, they showed high collagen II (80%) and aggrecan (60%) expression with simultaneous decrease of collagen I expression (10%). The high concentration of differentiated cells on Hyaff-11, indicate that this structure has an impact on cells cooperation and communication. In conclusion, we suggest that high expression of collagen II and aggrecan in 3D co-culture model, indicate that cooperation between different subpopulations may have synergistic impact on MSCs chondrogenic potential. Revealed the high concentration and localization of cells growing in deeper layers of membrane in 3D co-culture, indicate that induced microenvironmental enhance cell migration within scaffold. Additionally, we suggest that co-culture model might be useful for construction a bioactive structure for cartilage tissue regeneration.

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.

Rheumatoid Arthritis: Applicability of Ready-to-Use Human Cartilaginous Cells for Screening of Compounds with TNF-Alpha Inhibitory Activity

In the context of modern drug discovery, there is an obvious advantage to designing phenotypic bioassays based on human disease-relevant cells that express disease-relevant markers. The specific aim of the study was to develop a convenient and reliable method for screening compounds with Tumor Necrosis Factor-alpha (TNF-α) inhibitory activity. This assay was developed using cryopreserved ready-to-use cartilage-derived cells isolated from juvenile donors diagnosed with polydactyly. It has been demonstrated that all donor (10 donors) cells were able to respond to TNF-α treatment by increased secretion of pro-inflammatory cytokine IL-6 into subcultural medium. Inhibition of TNF-α using commercially available TNF-α inhibitor etanercept resulted in a dose-dependent decrease in IL-6 production which was measured by Enzyme-Linked Immunosorbent Assay (ELISA). TNF-α dependent IL-6 production was detected in the cells after both their prolonged cultivation in vitro (≥20 passages) and cryopreservation. This phenotypic bioassay based on ready-to-use primary human cells was developed for detection of novel TNF-α inhibitory compounds and profiling of biosimilar drugs.

Metabolic Labeling to Probe the Spatiotemporal Accumulation of Matrix at the Chondrocyte-Hydrogel Interface

Hydrogels are engineered with biochemical and biophysical signals to recreate aspects of the native microenvironment and to control cellular functions such as differentiation and matrix deposition. This deposited matrix accumulates within the pericellular space and likely affects the interactions between encapsulated cells and the engineered hydrogel; however, there has been little work to study the spatiotemporal evolution of matrix at this interface. To address this, metabolic labeling is employed to visualize the temporal and spatial positioning of nascent proteins and proteoglycans deposited by chondrocytes. Within covalently crosslinked hyaluronic acid hydrogels, chondrocytes deposit nascent proteins and proteoglycans in the pericellular space within 1 d after encapsulation. The accumulation of this matrix, as measured by an increase in matrix thickness during culture, depends on the initial hydrogel crosslink density with decreased thicknesses for more crosslinked hydrogels. Encapsulated fluorescent beads are used to monitor the hydrogel location and indicate that the emerging nascent matrix physically displaces the hydrogel from the cell membrane with extended culture. These findings suggest that secreted matrix increasingly masks the presentation of engineered hydrogel cues and may have implications for the design of hydrogels in tissue engineering and regenerative medicine.

Orthotopic Bone Formation by Streamlined Engineering and Devitalization of Human Hypertrophic Cartilage

Most bones of the human body form and heal through endochondral ossification, whereby hypertrophic cartilage (HyC) is formed and subsequently remodeled into bone. We previously demonstrated that HyC can be engineered from human mesenchymal stromal cells (hMSC), and subsequently devitalized by apoptosis induction. The resulting extracellular matrix (ECM) tissue retained osteoinductive properties, leading to ectopic bone formation. In this study, we aimed at engineering and devitalizing upscaled quantities of HyC ECM within a perfusion bioreactor, followed by in vivo assessment in an orthotopic bone repair model. We hypothesized that the devitalized HyC ECM would outperform a clinical product currently used for bone reconstructive surgery. Human MSC were genetically engineered with a gene cassette enabling apoptosis induction upon addition of an adjuvant. Engineered hMSC were seeded, differentiated, and devitalized within a perfusion bioreactor. The resulting HyC ECM was subsequently implanted in a 10-mm rabbit calvarial defect model, with processed human bone (Maxgraft^®) as control. Human MSC cultured in the perfusion bioreactor generated a homogenous HyC ECM and were efficiently induced towards apoptosis. Following six weeks of in vivo implantation, microcomputed tomography and histological analyses of the defects revealed an increased bone formation in the defects filled with HyC ECM as compared to Maxgraft^®. This work demonstrates the suitability of engineered devitalized HyC ECM as a bone substitute material, with a performance superior to a state-of-the-art commercial graft. Streamlined generation of the devitalized tissue transplant within a perfusion bioreactor is relevant towards standardized and automated manufacturing of a clinical product.

Differential Production of Cartilage ECM in 3D Agarose Constructs by Equine Articular Cartilage Progenitor Cells and Mesenchymal Stromal Cells

Identification of articular cartilage progenitor cells (ACPCs) has opened up new opportunities for cartilage repair. These cells may be used as alternatives for or in combination with mesenchymal stromal cells (MSCs) in cartilage engineering. However, their potential needs to be further investigated, since only a few studies have compared ACPCs and MSCs when cultured in hydrogels. Therefore, in this study, we compared chondrogenic differentiation of equine ACPCs and MSCs in agarose constructs as monocultures and as zonally layered co-cultures under both normoxic and hypoxic conditions. ACPCs and MSCs exhibited distinctly differential production of the cartilaginous extracellular matrix (ECM). For ACPC constructs, markedly higher glycosaminoglycan (GAG) contents were determined by histological and quantitative biochemical evaluation, both in normoxia and hypoxia. Differential GAG production was also reflected in layered co-culture constructs. For both cell types, similar staining for type II collagen was detected. However, distinctly weaker staining for undesired type I collagen was observed in the ACPC constructs. For ACPCs, only very low alkaline phosphatase (ALP) activity, a marker of terminal differentiation, was determined, in stark contrast to what was found for MSCs. This study underscores the potential of ACPCs as a promising cell source for cartilage engineering.

Hurdles to uptake of mesenchymal stem cells and their progenitors in therapeutic products

Twenty-five years have passed since the first clinical trial utilising mesenchymal stomal/stem cells (MSCs) in 1995. In this time academic research has grown our understanding of MSC biochemistry and our ability to manipulate these cells in vitro using chemical, biomaterial, and mechanical methods. Research has been emboldened by the promise that MSCs can treat illness and repair damaged tissues through their capacity for immunomodulation and differentiation. Since 1995, 31 therapeutic products containing MSCs and/or progenitors have reached the market with the level of in vitro manipulation varying significantly. In this review, we summarise existing therapeutic products containing MSCs or mesenchymal progenitor cells and examine the challenges faced when developing new therapeutic products. Successful progression to clinical trial, and ultimately market, requires a thorough understanding of these hurdles at the earliest stages of in vitro pre-clinical development. It is beneficial to understand the health economic benefit for a new product and the reimbursement potential within various healthcare systems. Pre-clinical studies should be selected to demonstrate efficacy and safety for the specific clinical indication in humans, to avoid duplication of effort and minimise animal usage. Early consideration should also be given to manufacturing: how cell manipulation methods will integrate into highly controlled workflows and how they will be scaled up to produce clinically relevant quantities of cells. Finally, we summarise the main regulatory pathways for these clinical products, which can help shape early therapeutic design and testing.

Influence of Conditioned Media on the Re-Differentiation Capacity of Human Chondrocytes in 3D Spheroid Cultures

A major challenge of cell-based therapy for cartilage lesions is the preservation of the chondrogenic phenotype during ex vivo cell cultivation. In this in vitro study, the chondro-inductive capacity of two different hyaline cartilage-conditioned cell culture media on human chondrocytes in 3D spheroids was determined. Media were conditioned by incubation of 200 mg/mL vital or devitalized cartilage matrix in growth media over 35 days. The media were analyzed for the content of soluble procollagen type (Col) II and glycosaminoglycans (GAGs) as well as released TGF-β1, IGF-1 and IGFBP3. Unconditioned medium served as a negative control while the positive medium control was supplemented with TGF-β1 and IGF-1. Spheroid cultures prepared from human chondrocytes were cultivated at 37 °C, 5% CO₂ and 21% O₂ in the respective media and controls. After 14 and 35 days, the deposition of ECM components was evaluated by histological analysis. Vital cartilage-conditioned medium contained significantly higher levels of Col II and active TGF-β1 compared to medium conditioned with the devitalized cartilage matrix. Despite these differences, the incubation with vital as well as devitalized cartilage conditioned medium led to similar results in terms of deposition of proteoglycans and collagen type II, which was used as an indicator of re-differentiation of human chondrocytes in spheroid cultures. However, high density 3D cell cultivation showed a positive influence on re-differentiation.

Human Levels of MMP-1 in Degenerated Disks Can Be Mitigated by Signaling Peptides from Mesenchymal Stem Cells

Degradation of extracellular matrix (ECM) in intervertebral disks (IVDs) during IVD degeneration plays a vital role in low back pain (LBP). In healthy IVDs, synthesis and degradation of ECM are kept in balance by matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs. MMPs are enzymes responsible for ECM degradation, and their expression levels are known to increase in degenerated disks. However, the exact pathophysiological concentration of MMP-1 in the degenerated disks of patients with chronic LBP has not been reported previously. Factors secreted by human mesenchymal stem cells (hMSCs) have shown positive results in cell therapy of degenerated disks. The aim of this study was to investigate the pathophysiological MMP-1 concentration (in ng/mL) in degenerated disk tissue and to evaluate if conditioned media (CM) from hMSCs could mitigate the effects of MMP-1 at the detected levels in a 3D in vitro disk cell (DC) pellet model. Tissue levels of MMP-1 were quantified in disk tissue collected from 6 chronic LBP patients undergoing surgery. DC pellet cultures were performed to investigate the effects of MMP-1 alone and the effects of conditioned media (CM) in the presence of MMP-1. MMP-1 was introduced in the pellets on day 14 at concentrations of 5, 50, or 100 ng/mL. The pellets were harvested on day 28 and evaluated for cell viability, proliferation, and ECM production. The mean concentration of MMP-1 in disk tissue was 151 ng/mL. Results from pellet cultures demonstrated a higher number of viable cells, glycosaminoglycan production, and ECM accumulation in the CM group even in the presence of MMP-1 compared to the controls. However, the level decreased with increasing MMP-1 concentration. The results demonstrated that CM has the ability to mitigate matrix degradation property of MMP-1 up to 50 ng/mL suggesting that CM could potentially be used to treat early stages of disk degeneration.

Intermittent parathyroid hormone (1-34) supplementation of bone marrow stromal cell cultures may inhibit hypertrophy, but at the expense of chondrogenesis

Background

Bone marrow stromal cells (BMSC) have promise in cartilage tissue engineering, but for their potential to be fully realised, the propensity to undergo hypertrophy must be mitigated. The literature contains diverging reports on the effect of parathyroid hormone (PTH) on BMSC differentiation. Cartilage tissue models can be heterogeneous, confounding efforts to improve media formulations.

Methods

Herein, we use a novel microwell platform (the Microwell-mesh) to manufacture hundreds of small-diameter homogeneous micro-pellets and use this high-resolution assay to quantify the influence of constant or intermittent PTH(1–34) medium supplementation on BMSC chondrogenesis and hypertrophy. Micro-pellets were manufactured from 5000 BMSC each and cultured in standard chondrogenic media supplemented with (1) no PTH, (2) intermittent PTH, or (3) constant PTH.

Results

Relative to control chondrogenic cultures, BMSC micro-pellets exposed to intermittent PTH had reduced hypertrophic gene expression following 1 week of culture, but this was accompanied by a loss in chondrogenesis by the second week of culture. Constant PTH treatment was detrimental to chondrogenic culture.

Conclusions

This study provides further clarity on the role of PTH on chondrogenic differentiation in vitro and suggests that while PTH may mitigate BMSC hypertrophy, it does so at the expense of chondrogenesis.

Adipogenesis, Osteogenesis, and Chondrogenesis of Human Mesenchymal Stem/Stromal Cells: A Comparative Transcriptome Approach

Adipogenesis, osteogenesis and chondrogenesis of human mesenchymal stem/stromal cells (MSC) are complex and highly regulated processes. Over the years, several studies have focused on understanding the mechanisms involved in the MSC commitment to the osteogenic, adipogenic and/or chondrogenic phenotypes. High-throughput methodologies have been used to investigate the gene expression profile during differentiation. Association of data analysis of mRNAs, microRNAs, circular RNAs and long non-coding RNAs, obtained at different time points over these processes, are important to depict the complexity of differentiation. This review will discuss the results that were highlighted in transcriptome analyses of MSC undergoing adipogenic, osteogenic and chondrogenic differentiation. The focus is to shed light on key molecules, main signaling pathways and biological processes related to different time points of adipogenesis, osteogenesis and chondrogenesis.

Human pluripotent stem cell-derived chondroprogenitors for cartilage tissue engineering

The cartilage of joints, such as meniscus and articular cartilage, is normally long lasting (i.e., permanent). However, once damaged, especially in large animals and humans, joint cartilage is not spontaneously repaired. Compensating the lack of repair activity by supplying cartilage-(re)forming cells, such as chondrocytes or mesenchymal stromal cells, or by transplanting a piece of normal cartilage, has been the basis of therapy for biological restoration of damaged joint cartilage. Unfortunately, current biological therapies face problems on a number of fronts. The joint cartilage is generated de novo from a specialized cell type, termed a 'joint progenitor' or 'interzone cell' during embryogenesis. Therefore, embryonic chondroprogenitors that mimic the property of joint progenitors might be the best type of cell for regenerating joint cartilage in the adult. Pluripotent stem cells (PSCs) are expected to differentiate in culture into any somatic cell type through processes that mimic embryogenesis, making human (h)PSCs a promising source of embryonic chondroprogenitors. The major research goals toward the clinical application of PSCs in joint cartilage regeneration are to (1) efficiently generate lineage-specific chondroprogenitors from hPSCs, (2) expand the chondroprogenitors to the number needed for therapy without loss of their chondrogenic activity, and (3) direct the in vivo or in vitro differentiation of the chondroprogenitors to articular or meniscal (i.e., permanent) chondrocytes rather than growth plate (i.e., transient) chondrocytes. This review is aimed at providing the current state of research toward meeting these goals. We also include our recent achievement of successful generation of "permanent-like" cartilage from long-term expandable, hPSC-derived ectomesenchymal chondroprogenitors.

Piezoelectric stimulation by ultrasound facilitates chondrogenesis of mesenchymal stem cells

A cellular stimulation device utilizing an AT-cut quartz coverslip mounted on an ultrasonic live imaging chamber is developed to investigate the effect of piezoelectric stimulation. Two types of chambers deliver ultrasound at intensities ranging from 1 to 20 mW/cm² to mesenchymal stem cells (MSCs) seeded on the quartz coverslip. The quartz coverslip imposes additionally localized electric charges as it vibrates with the stimulation. The device was applied to explore whether piezoelectric stimulation can facilitate chondrogenesis of MSCs. The results suggest piezoelectric stimulation drove clustering of MSCs and consequently facilitated chondrogenesis of MSCs without the use of differentiation media.

A composite hydrogel-3D printed thermoplast osteochondral anchor as example for a zonal approach to cartilage repair: in vivo performance in a long-term equine model

Recent research has been focusing on the generation of living personalized osteochondral constructs for joint repair. Native articular cartilage has a zonal structure, which is not reflected in current constructs and which may be a cause of the frequent failure of these repair attempts. Therefore, we investigated the performance of a composite implant that further reflects the zonal distribution of cellular component both in vitro and in vivo in a long-term equine model. Constructs constituted of a 3D-printed poly(ϵ-caprolactone) (PCL) bone anchor from which reinforcing fibers protruded into the chondral part of the construct over which two layers of a thiol-ene cross-linkable hyaluronic acid/poly(glycidol) hybrid hydrogel (HA-SH/P(AGE-co-G)) were fabricated. The top layer contained Articular Cartilage Progenitor Cells (ACPCs) derived from the superficial layer of native cartilage tissue, the bottom layer contained mesenchymal stromal cells (MSCs). The chondral part of control constructs were homogeneously filled with MSCs. After six months in vivo, microtomography revealed significant bone growth into the anchor. Histologically, there was only limited production of cartilage-like tissue (despite persistency of hydrogel) both in zonal and non-zonal constructs. There were no differences in histological scoring; however, the repair tissue was significantly stiffer in defects repaired with zonal constructs. The sub-optimal quality of the repair tissue may be related to several factors, including early loss of implanted cells, or inappropriate degradation rate of the hydrogel. Nonetheless, this approach may be promising and research into further tailoring of biomaterials and of construct characteristics seems warranted.

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.

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

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

A human preadipocyte cell strain with multipotent differentiation capability as an in vitro model for adipogenesis

Murine 3T3 cell lines constitute a standard model system for in vitro study of mammalian adipogenesis although they do not faithfully reflect the biology of the human adipose cells. Several human adipose cell lines and strains have been used to recapitulate human adipogenesis in vitro, but to date there is no generally accepted in vitro model for human adipogenesis. We obtained a clonal strain of human subcutaneous adipose stromal cells, IPI-SA3-C4, and characterized its utility as an in vitro model for human subcutaneous adipogenesis. IPI-SA3-C4 cells showed a high proliferative potential for at least 30 serial passages, reached 70 cumulative population doublings and exhibited a population doubling time of 47 h and colony forming efficiency of 12% at the 57th cumulative population doublings. IPI-SA3-C4 cells remained diploid (46XY) even at the 56th cumulative population doublings and expressed the pluripotency markers POU5F1, NANOG, KLF4, and MYC even at 50th cumulative population doublings. Under specific culture conditions, IPI-SA3-C4 cells displayed cellular hallmarks and molecular markers of adipogenic, osteogenic, and chondrogenic lineages and showed adipogenic capacity even at the 66th cumulative population doublings. These characteristics show IPI-SA3-C4 cells as a promising potential model for human subcutaneous adipogenesis in vitro.

Repair of Osteochondral Defects With Predifferentiated Mesenchymal Stem Cells of Distinct Phenotypic Character Derived From a Nanotopographic Platform

BACKGROUND

Articular cartilage has a zonal architecture and biphasic mechanical properties. The recapitulation of surface lubrication properties with high compressibility of the deeper layers of articular cartilage during regeneration is essential in achieving long-term cartilage integrity. Current clinical approaches for cartilage repair, especially with the use of mesenchymal stem cells (MSCs), have yet to restore the hierarchically organized architecture of articular cartilage.

HYPOTHESIS

MSCs predifferentiated on surfaces with specific nanotopographic patterns can provide phenotypically stable and defined chondrogenic cells and, when delivered as a bilayered stratified construct at the cartilage defect site, will facilitate the formation of functionally superior cartilage tissue in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

MSCs were subjected to chondrogenic differentiation on specific nanopatterned surfaces. The phenotype of the differentiated cells was assessed by the expression of cartilage markers. The ability of the 2-dimensional nanopattern-generated chondrogenic cells to retain their phenotypic characteristics after removal from the patterned surface was tested by subjecting the enzymatically harvested cells to 3-dimensional fibrin hydrogel culture. The in vivo efficacy in cartilage repair was demonstrated in an osteochondral rabbit defect model. Repair by bilayered construct with specific nanopattern predifferentiated cells was compared with implantation with cell-free fibrin hydrogel, undifferentiated MSCs, and mixed-phenotype nanopattern predifferentiated MSCs. Cartilage repair was evaluated at 12 weeks after implantation.

RESULTS

Three weeks of predifferentiation on 2-dimensional nanotopographic patterns was able to generate phenotypically stable chondrogenic cells. Implantation of nanopatterned differentiated MSCs as stratified bilayered hydrogel constructs improved the repair quality of cartilage defects, as indicated by histological scoring, mechanical properties, and polarized microscopy analysis.

CONCLUSION

Our results indicate that with an appropriate period of differentiation, 2-dimensional nanotopographic patterns can be employed to generate phenotypically stable chondrogenic cells, which, when implanted as stratified bilayered hydrogel constructs, were able to form functionally superior cartilage tissue.

CLINICAL RELEVANCE

Our approach provides a relatively straightforward method of obtaining large quantities of zone-specific chondrocytes from MSCs to engineer a stratified cartilage construct that could recapitulate the zonal architecture of hyaline cartilage, and it represents a significant improvement in current MSC-based cartilage regeneration.

Transforming growth factor-beta stimulates human bone marrow-derived mesenchymal stem/stromal cell chondrogenesis more so than kartogenin

A previous study identified kartogenin (KGN) as a potent modulator of bone marrow mesenchymal stem/stromal cell (BMSC) chondrogenesis. This initial report did not contrast KGN directly against transforming growth factor-beta 1 (TGF-β1), the most common growth factor used in chondrogenic induction medium. Herein, we directly compared the in vitro chondrogenic potency of TGF-β1 and KGN using a high resolution micropellet model system. Micropellets were cultured for 7–14 days in medium supplemented with TGF-β1, KGN, or both TGF-β1 + KGN. Following 14 days of induction, micropellets exposed to TGF-β1 alone or TGF-β1 + KGN in combination were larger and produced more glycosominoglycan (GAG) than KGN-only cultures. When TGF-β1 + KGN was used, GAG quantities were similar or slightly greater than the TGF-β1-only cultures, depending on the BMSC donor. BMSC micropellet cultures supplemented with KGN alone contracted in size over the culture period and produced minimal GAG. Indicators of hypertrophy were not mitigated in TGF-β1 + KGN cultures, suggesting that KGN does not obstruct BMSC hypertrophy. KGN appears to have weak chondrogenic potency in human BMSC cultures relative to TGF-β1, does not obstruct hypertrophy, and may not be a viable alternative to growth factors in cartilage tissue engineering.

Angiogenic Potential of Tissue Engineered Cartilage From Human Mesenchymal Stem Cells Is Modulated by Indian Hedgehog and Serpin E1

With rising demand for cartilage tissue repair and replacement, the differentiation of mesenchymal stem cells (BMSCs) into cartilage tissue forming cells provides a promising solution. Often, the BMSC-derived cartilage does not remain stable and continues maturing to bone through the process of endochondral ossification in vivo. Similar to the growth plate, invasion of blood vessels is an early hallmark of endochondral ossification and a necessary step for completion of ossification. This invasion originates from preexisting vessels that expand via angiogenesis, induced by secreted factors produced by the cartilage graft. In this study, we aimed to identify factors secreted by chondrogenically differentiated bone marrow-derived human BMSCs to modulate angiogenesis. The secretome of chondrogenic pellets at day 21 of the differentiation program was collected and tested for angiogenic capacity using in vitro endothelial migration and proliferation assays as well as the chick chorioallantoic membrane (CAM) assay. Taken together, these assays confirmed the pro-angiogenic potential of the secretome. Putative secreted angiogenic factors present in this medium were identified by comparative global transcriptome analysis between murine growth plate cartilage, human chondrogenic BMSC pellets and human neonatal articular cartilage. We then verified by PCR eight candidate angiogenesis modulating factors secreted by differentiated BMSCs. Among those, Serpin E1 and Indian Hedgehog (IHH) had a higher level of expression in BMSC-derived cartilage compared to articular chondrocyte derived cartilage. To understand the role of these factors in the pro-angiogenic secretome, we used neutralizing antibodies to functionally block them in the conditioned medium. Here, we observed a 1.4-fold increase of endothelial cell proliferation when blocking IHH and 1.5-fold by Serpin E1 blocking compared to unblocked control conditioned medium. Furthermore, endothelial migration was increased 1.9-fold by Serpin E1 blocking and 2.7-fold by IHH blocking. This suggests that the pro-angiogenic potential of chondrogenically differentiated BMSC secretome could be further augmented through inhibition of specific factors such as IHH and Serpin E1 identified as anti-angiogenic factors.

Challenges Toward the Identification of Predictive Markers for Human Mesenchymal Stromal Cells Chondrogenic Potential

Human bone marrow derived mesenchymal stromal cells (BMSCs) represent a putative cell source candidate for tissue engineering-based strategies to repair cartilage and bone. However, traditional isolation of BMSCs by adhesion to plastic leads to very heterogeneous cell populations, accounting for high variability of chondrogenic differentiation outcome, both across donors and across clonally derived strains. Identification of putative surface markers able to select BMSC subpopulations with higher chondrogenic capacity (CC) and reduced variance in chondrogenic differentiation could aid the development of BMSC-based cartilage and bone regeneration approaches. With the goal to identify predictive markers for chondrogenic BMSC populations, we assessed the gene expression profile of single cell-derived clones with high and low CC. While a clustering between high and low CC clones was observed for one donor, donor-to-donor variability hampered the possibility to achieve conclusive results when different donors were considered. Nevertheless, increased NCAM1/CD56 expression correlated in clones derived from one donor with higher CC, the same trend was observed for three additional donors (even if no significance was achieved). Enriching multiclonal BMSCs for CD56⁺ expression led to an increase in CC, though still highly affected by donor-to-donor variability. Our study finally suggests that definition of predictive marker(s) for BMSCs chondrogenesis is challenged by the large donor heterogeneity of these cells, and by the high complexity and plasticity of the BMSCs system. Multiple pathways and external parameters may be indeed involved in determining the chondrogenic potential of BMSCs, making the identification of putative markers still an open issue. Stem Cells Translational Medicine 2019;8:194&11.

A Novel High-Throughput Screening Platform Identifies Itaconate Derivatives from Marine Penicillium antarcticum as Inhibitors of Mesenchymal Stem Cell Differentiation

Worldwide diffused diseases such as osteoarthritis, atherosclerosis or chronic kidney disease are associated with a tissue calcification process which may involve unexpected local stem cell differentiation. Current pharmacological treatments for such musculoskeletal conditions are weakly effective, sometimes extremely expensive and often absent. The potential to develop new therapies is represented by the discovery of small molecules modulating resident progenitor cell differentiation to prevent aberrant tissue calcification. The marine environment is a rich reserve of compounds with pharmaceutical potential and many novel molecules are isolated from macro and microorganisms annually. The potential of small molecules synthetized by marine filamentous fungi to influence the osteogenic and chondrogenic differentiation of human mesenchymal stem/stromal cells (hMSCs) was investigated using a novel, high-throughput automated screening platform. Metabolites synthetized by the marine-derived fungus Penicillium antarcticum were evaluated on the platform. Itaconic acid derivatives were identified as inhibitors of calcium elaboration into the matrix of osteogenically differentiated hMSCs and also inhibited hMSC chondrogenic differentiation, highlighting their capacity to impair ectopic calcification. Bioactive small molecule discovery is critical to address ectopic tissue calcification and the use of biologically relevant assays to identify naturally occurring metabolites from marine sources represents a strategy that can contribute to this effort.

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.

Investigation of the Effect of Secreted Factors from Mesenchymal Stem Cells on Disc Cells from Degenerated Discs

Low back pain is experienced by a large number of people in western countries and may be caused and influenced by many different pathologies and psychosocial factors including disc degeneration. Disc degeneration involves the increased expression of proinflammatory cytokines and matrix metalloproteinases (MMPs) in the disc environment, which leads to the loss of extracellular matrix (ECM) and the viability of the native disc cells (DCs). Treatment approaches using growth factors and cell therapy have been proposed due to the compelling results that growth factors and mesenchymal stem cells (MSCs) can influence the degenerated discs. The aim of this study was to investigate the effects of conditioned media (CM) from human MSCs (hMSCs) and connective tissue growth factor (CTGF) and TGF-β on disc cells, and hMSCs isolated from patients with degenerative discs and severe low back pain. The aim was also to examine the constituents of CM in order to study the peptides that could bring about intervertebral disc (IVD) regeneration. DCs and hMSC pellets (approx.. 200,000 cells) were cultured and stimulated with hMSC-derived CM or CTGF and TGF-β over 28 days. The effects of CM and CTGF on DCs and hMSCs were assessed via cell viability, proteoglycan production, the expression of ECM proteins, and chondrogenesis in 3D pellet culture. To identify the constituents of CM, CM was analyzed with tandem mass spectrometry. The findings indicate that CM enhanced the cellular viability and ECM production of DCs while CTGF and the control exhibited nonsignificant differences. The same was observed in the hMSC group. Mass spectrometry analysis of CM identified >700 peptides, 129 of which showed a relative abundance of ≥2 (CTGF among them). The results suggest that CM holds potential to counter the progression of disc degeneration, likely resulting from the combination of all the substances released by the hMSCs. The soluble factors released belong to different peptide families. The precise mechanism underlying the regenerative effect needs to be investigated further, prior to incorporating peptides in the development of new treatment strategies for low back pain that is potentially caused by IVD degeneration.

Carosella E, Benkirane-Jessel N, Moreau P, Rouas-Freiss N, Bensoussan D, Huselstein C. Are the Immune Properties of Mesenchymal Stem Cells from Wharton's Jelly Maintained during Chondrogenic Differentiation?

Background: Umbilical mesenchymal stem/stromal cells (MSCs), and especially those derived from Wharton’s jelly (WJ), are a promising engineering tool for tissue repair in an allogeneic context. This is due to their differentiation capacity and immunological properties, like their immunomodulatory potential and paracrine activity. Hence, these cells may be considered an Advanced Therapy Medicinal Product (ATMP). The purpose of this work was to differentiate MSCs from WJ (WJ-MSCs) into chondrocytes using a scaffold and to evaluate, in vitro, the immunomodulatory capacities of WJ-MSCs in an allogeneic and inflammatory context, mimicked by IFN-γ and TNF-α priming during the chondrogenic differentiation. Methods: Scaffolds were made from hydrogel composed by alginate enriched in hyaluronic acid (Alg/HA). Chondrogenic differentiation, immunological function, phenotype expression, but also secreted soluble factors were the different parameters followed during 28 days of culture. Results: During chondrocyte differentiation, even in an allogeneic context, WJ-MSCs remained unable to establish the immunological synapse or to induce T cell alloproliferation. Moreover, interestingly, paracrine activity and functional immunomodulation were maintained during cell differentiation. Conclusion: These results show that WJ-MSCs remained hypoimmunogenic and retained immunomodulatory properties even when they had undergone chondrocyte differentiation.

Pulsed electromagnetic fields potentiate the paracrine function of mesenchymal stem cells for cartilage regeneration

Background

The mesenchymal stem cell (MSC) secretome, via the combined actions of its plethora of biologically active factors, is capable of orchestrating the regenerative responses of numerous tissues by both eliciting and amplifying biological responses within recipient cells. MSCs are “environmentally responsive” to local micro-environmental cues and biophysical perturbations, influencing their differentiation as well as secretion of bioactive factors. We have previously shown that exposures of MSCs to pulsed electromagnetic fields (PEMFs) enhanced MSC chondrogenesis. Here, we investigate the influence of PEMF exposure over the paracrine activity of MSCs and its significance to cartilage regeneration.

Methods

Conditioned medium (CM) was generated from MSCs subjected to either 3D or 2D culturing platforms, with or without PEMF exposure. The paracrine effects of CM over chondrocytes and MSC chondrogenesis, migration and proliferation, as well as the inflammatory status and induced apoptosis in chondrocytes and MSCs was assessed.

Results

We show that benefits of magnetic field stimulation over MSC-derived chondrogenesis can be partly ascribed to its ability to modulate the MSC secretome. MSCs cultured on either 2D or 3D platforms displayed distinct magnetic sensitivities, whereby MSCs grown in 2D or 3D platforms responded most favorably to PEMF exposure at 2 mT and 3 mT amplitudes, respectively. Ten minutes of PEMF exposure was sufficient to substantially augment the chondrogenic potential of MSC-derived CM generated from either platform. Furthermore, PEMF-induced CM was capable of enhancing the migration of chondrocytes and MSCs as well as mitigating cellular inflammation and apoptosis.

Conclusions

The findings reported here demonstrate that PEMF stimulation is capable of modulating the paracrine function of MSCs for the enhancement and re-establishment of cartilage regeneration in states of cellular stress. The PEMF-induced modulation of the MSC-derived paracrine function for directed biological responses in recipient cells or tissues has broad clinical and practical ramifications with high translational value across numerous clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-020-1566-5) contains supplementary material, which is available to authorized users.

Impact of Prevalence Ratios of Chondroitin Sulfate (CS)- 4 and -6 Isomers Derived from Marine Sources in Cell Proliferation and Chondrogenic Differentiation Processes

Osteoarthritis is the most prevalent rheumatic disease. During disease progression, differences have been described in the prevalence of chondroitin sulfate (CS) isomers. Marine derived-CS present a higher proportion of the 6S isomer, offering therapeutic potential. Accordingly, we evaluated the effect of exogenous supplementation of CS, derived from the small spotted catshark (Scyliorhinus canicula), blue shark (Prionace glauca), thornback skate (Raja clavata) and bovine CS (reference), on the proliferation of osteochondral cell lines (MG-63 and T/C-28a2) and the chondrogenic differentiation of mesenchymal stromal cells (MSCs). MG-G3 proliferation was comparable between R. clavata (CS-6 intermediate ratio) and bovine CS (CS-4 enrichment), for concentrations below 0.5 mg/mL, defined as a toxicity threshold. T/C-28a2 proliferation was significantly improved by intermediate ratios of CS-6 and -4 isomers (S. canicula and R. clavata). A dose-dependent response was observed for S. canicula (200 µg/mL vs 50 and 10 µg/mL) and bovine CS (200 and 100 µg/mL vs 10 µg/mL). CS sulfation patterns discretely affected MSCs chondrogenesis; even though S. canicula and R. clavata CS up-regulated chondrogenic markers expression (aggrecan and collagen type II) these were not statistically significant. We demonstrate that intermediate values of CS-4 and -6 isomers improve cell proliferation and offer potential for chondrogenic promotion, although more studies are needed to elucidate its mechanism of action.

Muscle Spindle Density of Lateral Rotators of the Thigh in Japanese Macaques and a Gibbon

We examined the six small lateral rotators of the hip joint, which is one of the most flexible joints and allows kinematically complex motions of the hindlimb, to elucidate the functional differentiation among these muscles and to test the hypothesis that species-specific characteristics in hindlimb use during locomotion are reflected in the muscle spindle density and in other parameters of the deep small hip joint rotators. For these purposes, we estimated the number of muscle spindles of the superior gemellus muscle (SG), inferior gemellus muscle, quadratus femoris muscle, obturator internus muscle (OI), obturator externus muscle, and piriformis muscle in three Japanese macaques and a gibbon, using 30-µm-thick serial sections throughout each muscle length after azan staining. The numbers of muscle spindles per 10,000 muscle fibers were determined to compare inter-muscle variation. The spindle density was highest in the SG and lowest in the OI in the Japanese macaques, suggesting that the SG, which is attached to the tendon of the OI, functions as a kinesiological monitor of the OI. On the other hand, SG the was missing in the gibbon, and the OI in the gibbon contained more spindles than that in the Japanese macaques. This suggests that the SG and the OI fused into one muscle in the gibbon. We postulate that the relative importance of the deep small hip rotator muscles differs between the Japanese macaques and gibbon and that the gibbon's muscles are less differentiated in terms of the spindle density, probably because this brachiating species uses its hindlimbs less frequently.

Mesenchymal stem cells for cartilage regeneration

Cartilage injuries are typically caused by trauma, chronic overload, and autoimmune diseases. Owing to the avascular structure and low metabolic activities of chondrocytes, cartilage generally does not self-repair following an injury. Currently, clinical interventions for cartilage injuries include chondrocyte implantation, microfracture, and osteochondral transplantation. However, rather than restoring cartilage integrity, these methods only postpone further cartilage deterioration. Stem cell therapies, especially mesenchymal stem cell (MSCs) therapies, were found to be a feasible strategy in the treatment of cartilage injuries. MSCs can easily be isolated from mesenchymal tissue and be differentiated into chondrocytes with the support of chondrogenic factors or scaffolds to repair damaged cartilage tissue. In this review, we highlighted the full success of cartilage repair using MSCs, or MSCs in combination with chondrogenic factors and scaffolds, and predicted their pros and cons for prospective translation to clinical practice.

Osteogenic and Chondrogenic Potential of the Supramolecular Aggregate T-LysYal®

Hard tissue regeneration represents a challenge for the Regenerative Medicine and Mesenchymal stem cells (MSCs) could be a successful therapeutic strategy. T-LysYal® (T-Lys), a new derivative of Hyaluronic Acid (HA) possessing a superior stability, has already been proved efficient in repairing corneal epithelial cells damaged by dry conditions in vitro. We investigated the regenerative potential of T-Lys in the hard tissues bone and cartilage. We have previously demonstrated that cells isolated from the tooth germ, Dental Bud Stem Cells (DBSCs), differentiate into osteoblast-like cells, representing a promising source of MSCs for bone regeneration. Herewith, we show that T-Lys treatment stimulates the expression of typical osteoblastic markers, such as Runx-2, Collagen I (Col1) and Alkaline Phosphatase (ALP), determining a higher production of mineralized matrix nodules. In addition, we found that T-Lys treatment positively affects α_Vβ₃ integrin expression, key integrin in the osteoblastic commitment, leading to the formation of focal adhesions (FAs). The efficacy of T-Lys was also tested on chondrogenic differentiation starting from human articular chondrocytes (HACs) resulting in an increase of differentiation markers and cell number.

Usefulness of Mesenchymal Cell Lines for Bone and Cartilage Regeneration Research

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