Can one generate stable hyaline cartilage from adult mesenchymal stem cells? A developmental approach

Regulation of Oxygen Tension as a Strategy to Control Chondrocytic Phenotype for Cartilage Tissue Engineering and Regeneration

Cartilage defects and osteoarthritis are health problems which are major burdens on health care systems globally, especially in aging populations. Cartilage is a vulnerable tissue, which generally faces a progressive degenerative process when injured. This makes it the 11th most common cause of global disability. Conservative methods are used to treat the initial phases of the illness, while orthopedic management is the method used for more progressed phases. These include, for instance, arthroscopic shaving, microfracturing and mosaicplasty, and joint replacement as the final treatment. Cell-based implantation methods have also been developed. Despite reports of successful treatments, they often suffer from the non-optimal nature of chondrocyte phenotype in the repair tissue. Thus, improved strategies to control the phenotype of the regenerating cells are needed. Avascular tissue cartilage relies on diffusion for nutrients acquisition and the removal of metabolic waste products. A low oxygen content is also present in cartilage, and the chondrocytes are, in fact, well adapted to it. Therefore, this raises an idea that the regulation of oxygen tension could be a strategy to control the chondrocyte phenotype expression, important in cartilage tissue for regenerative purposes. This narrative review discusses the aspects related to oxygen tension in the metabolism and regulation of articular and growth plate chondrocytes and progenitor cell phenotypes, and the role of some microenvironmental factors as regulators of chondrocytes.

Microtissue Culture Provides Clarity on the Relative Chondrogenic and Hypertrophic Response of Bone-Marrow-Derived Stromal Cells to TGF-β1, BMP-2, and GDF-5

Chondrogenic induction of bone-marrow-derived stromal cells (BMSCs) is typically accomplished with medium supplemented with growth factors (GF) from the transforming growth factor-beta (TGF-β)/bone morphogenetic factor (BMP) superfamily. In a previous study, we demonstrated that brief (1-3 days) stimulation with TGF-β1 was sufficient to drive chondrogenesis and hypertrophy using small-diameter microtissues generated from 5000 BMSC each. This biology is obfuscated in typical large-diameter pellet cultures, which suffer radial heterogeneity. Here, we investigated if brief stimulation (2 days) of BMSC microtissues with BMP-2 (100 ng/mL) or growth/differentiation factor (GDF-5, 100 ng/mL) was also sufficient to induce chondrogenic differentiation, in a manner comparable to TGF-β1 (10 ng/mL). Like TGF-β1, BMP-2 and GDF-5 are reported to stimulate chondrogenic differentiation of BMSCs, but the effects of transient or brief use in culture have not been explored. Hypertrophy is an unwanted outcome in BMSC chondrogenic differentiation that renders engineered tissues unsuitable for use in clinical cartilage repair. Using three BMSC donors, we observed that all GFs facilitated chondrogenesis, although the efficiency and the necessary duration of stimulation differed. Microtissues treated with 2 days or 14 days of TGF-β1 were both superior at producing extracellular matrix and expression of chondrogenic gene markers compared to BMP-2 and GDF-5 with the same exposure times. Hypertrophic markers increased proportionally with chondrogenic differentiation, suggesting that these processes are intertwined for all three GFs. The rapid action, or "temporal potency", of these GFs to induce BMSC chondrogenesis was found to be as follows: TGF-β1 > BMP-2 > GDF-5. Whether briefly or continuously supplied in culture, TGF-β1 was the most potent GF for inducing chondrogenesis in BMSCs.

Angiopoietin-like 3-derivative LNA043 for cartilage regeneration in osteoarthritis: a randomized phase 1 trial

Osteoarthritis (OA) is a common, debilitating, chronic disease with no disease-modifying drug approved to date. We discovered LNA043-a derivative of angiopoietin-like 3 (ANGPTL3)-as a potent chondrogenesis inducer using a phenotypic screen with human mesenchymal stem cells. We show that LNA043 promotes chondrogenesis and cartilage matrix synthesis in vitro and regenerates hyaline articular cartilage in preclinical OA and cartilage injury models in vivo. LNA043 exerts at least part of these effects through binding to the fibronectin receptor, integrin α5β1 on mesenchymal stem cells and chondrocytes. In a first-in-human (phase 1), randomized, double-blinded, placebo-controlled, single ascending dose, single-center trial ( NCT02491281 ; sponsored by Novartis Pharmaceuticals), 28 patients with knee OA were injected intra-articularly with LNA043 or placebo (3:1 ratio) either 2 h, 7 d or 21 d before total knee replacement. LNA043 met its primary safety endpoint and showed short serum pharmacokinetics, cartilage penetration and a lack of immunogenicity (secondary endpoints). Post-hoc transcriptomics profiling of cartilage revealed that a single LNA043 injection reverses the OA transcriptome signature over at least 21 d, inducing the expression of hyaline cartilage matrix components and anabolic signaling pathways, while suppressing mediators of OA progression. LNA043 is a novel disease-modifying OA drug candidate that is currently in a phase 2b trial ( NCT04864392 ) in patients with knee OA.

Pre-culture of human mesenchymal stromal cells in spheroids facilitates chondrogenesis at a low total cell count upon embedding in biomaterials to generate cartilage microtissues

Material-assisted cartilage tissue engineering has limited application in cartilage treatment due to hypertrophic tissue formation and high cell counts required. This study aimed at investigating the potential of human mesenchymal stromal cell (hMSC) spheroids embedded in biomaterials to study the effect of biomaterial composition on cell differentiation. Pre-cultured (3 days, chondrogenic differentiation media) spheroids (250 cells/spheroid) were embedded in tyramine-modified hyaluronic acid (THA) and collagen type I (Col) composite hydrogels (four combinations of THA (12.5 vs 16.7 mg/ml) and Col (2.5 vs 1.7 mg/ml) content) at a cell density of 5 × 10⁶ cells/ml (2 × 10⁴ spheroids/ml). Macropellets derived from single hMSCs (2.5 × 10⁵ cells, ScMP) or hMSC spheroids (2.5 × 10⁵ cells, 10³ spheroids, SpMP) served as control. hMSC differentiation was analyzed using glycosaminoglycan (GAG) quantification, gene expression analysis and (immuno-)histology. Embedding of hMSC spheroids in THA-Col induced chondrogenic differentiation marked by upregulation of aggrecan (ACAN) and COL2A1, and the production of GAGs . Lower THA led to more pronounced chondrogenic phenotype compared to higher THA content. Col content had no significant influence on hMSC chondrogenesis. Pellet cultures showed an upregulation in chondrogenic-associated genes and production of GAGs with less upregulation of hypertrophic-associated genes in SpMP culture compared to ScMP group. This study presents hMSC pre-culture in spheroids as promising approach to study chondrogenic differentiation after biomaterial encapsulation at low total cell count (5 × 10⁶/ml) without compromising chondrogenic matrix production. This approach can be applied to assemble microtissues in biomaterials to generate large cartilage construct. STATEMENT OF SIGNIFICANCE: In vitro studies investigating the chondrogenic potential of biomaterials are limited due to the low cell-cell contact of encapsulated single cells. Here, we introduce the use of pre-cultured hMSC spheroids to study chondrogenesis upon encapsulation in a biomaterial. The use of spheroids takes advantage of the high cell-cell contact within each spheroid being critical in the early chondrogenesis of hMSCs. At a low seeding density of 5·10⁶ cells/ml (2 × 10⁴ spheroids/ml) we demonstrated hMSC chondrogenesis and cartilaginous matrix deposition. Our results indicate that the pre-culture might have a beneficial effect on hypertrophic gene expression without compromising chondrogenic differentiation. This approach has shown potential to assemble microtissues (here spheroids) in biomaterials to generate large cartilage constructs and to study the effect of biomaterial composition on cell alignment and migration.

Effects of Berberine on the Chondrogenic Differentiation of Embryonic Limb Skeletal Progenitors

Introduction

Berberine (BBR) is an isoquinoline plant alkaloid with demonstrated anti-inflammatory, anti-tumor and immunosuppressive pharmacological properties that functions via multiple signaling pathways and epigenetic modulators. Numerous studies have proposed BBR as a promising therapeutic agent for joint cartilage degeneration, and other connective tissue diseases.

Purpose and Methods

This work aimed to evaluate the effects of BBR on the growth and differentiation of embryonic skeletal progenitors using the limb mesoderm micromass culture assay.

Results

Our findings show that at difference of its apoptotic influence on a variety of tumor tissues, cell death was not induced in skeletal progenitors by the addition of 12 or 25 µM BBR concentration to the culture medium. Morphological and transcriptional analysis revealed dual and opposite effects of BBR treatments on chondrogenesis depending on the stage of differentiation of the cultured progenitors. At early stage of culture, BBR was a potent chondrogenic inhibitor, while chondrogenesis was intensified in treatments at advanced stages of culture. The chondrogenic promoting effect was accompanied by a moderate upregulation of gene markers of prehypertrophic cartilage, including ColXa1, alkaline phosphatase Alpl, Runx2, and Indian Hedgehog Ihh. We further observed a positive transcriptional influence of BBR in the expression of DNA methyltransferase genes, Dnmt1, Dnmt3a and Dnmt3b, suggesting a potential involvement of epigenetic factors in its effects.

Conclusion

Our study uncovers a new pharmacological influence of BBR in cartilage differentiation that must be taken into account in designing clinical protocols for its employment in the treatment of cartilage degenerative diseases.

3D printed silk-gelatin hydrogel scaffold with different porous structure and cell seeding strategy for cartilage regeneration

Hydrogel scaffolds are attractive for tissue defect repair and reorganization because of their human tissue-like characteristics. However, most hydrogels offer limited cell growth and tissue formation ability due to their submicron- or nano-sized gel networks, which restrict the supply of oxygen, nutrients and inhibit the proliferation and differentiation of encapsulated cells. In recent years, 3D printed hydrogels have shown great potential to overcome this problem by introducing macro-pores within scaffolds. In this study, we fabricated a macroporous hydrogel scaffold through horseradish peroxidase (HRP)-mediated crosslinking of silk fibroin (SF) and tyramine-substituted gelatin (GT) by extrusion-based low-temperature 3D printing. Through physicochemical characterization, we found that this hydrogel has excellent structural stability, suitable mechanical properties, and an adjustable degradation rate, thus satisfying the requirements for cartilage reconstruction. Cell suspension and aggregate seeding methods were developed to assess the inoculation efficiency of the hydrogel. Moreover, the chondrogenic differentiation of stem cells was explored. Stem cells in the hydrogel differentiated into hyaline cartilage when the cell aggregate seeding method was used and into fibrocartilage when the cell suspension was used. Finally, the effect of the hydrogel and stem cells were investigated in a rabbit cartilage defect model. After implantation for 12 and 16 weeks, histological evaluation of the sections was performed. We found that the enzymatic cross-linked and methanol treatment SF5GT15 hydrogel combined with cell aggregates promoted articular cartilage regeneration. In summary, this 3D printed macroporous SF-GT hydrogel combined with stem cell aggregates possesses excellent potential for application in cartilage tissue repair and regeneration.

ITGB1 promotes the chondrogenic differentiation of human adipose-derived mesenchymal stem cells by activating the ERK signaling

Adipose-derived mesenchymal stem cell (ADSC) with a high capacity of chondrogenic differentiation was a promising candidate for cartilage defect treatment. This study's objective is to study the roles of integrin β1 (ITGB1) in regulating ADSC chondrogenic differentiations as well as the underlying mechanisms. The identity of ADSC was confirmed by flow cytometry. ITGB1 gene was overexpressed in human ADSC (hADSC) by transfection with LV003-recombinant plasmids. Gene mRNA and protein levels were examined using quantitative RT-PCR and western blotting, respectively. Differentially expressed mRNAs and proteins were characterized by next-generation RNA sequencing and label-free quantitative proteomics, respectively. ERK signaling and AKT signaling in hADSCs were inhibited by treating with SCH772984 and GSK690693, respectively. ITGB1 gene overexpression substantially increased collagen type II alpha 1 chain (COL2A1), aggrecan (ACAN), and SRY-box transcription factor 9 (SOX9) expression but suppressed collagen type I alpha 1 chain (COL1A1) expression in hADSCs. Next-generation RNA sequencing identified a total of 246 genes differentially expressed in hADSCs by ITGB1 overexpression, such as 183 upregulated and 63 downregulated genes. Label-free proteomics characterized 34 proteins differentially expressed in ITGB1-overexpressing hADSCs. Differentially expressed genes and proteins were enriched by different biological processes such as cell adhesion and differentiation and numerous signaling pathways such as the ERK signaling pathway. ERK inhibitor treatment caused substantially enhanced chondrogenic differentiation in ITGB1-overexpressing hADSCs. ITGB1 promoted the chondrogenic differentiation of human ADSCs via the activation of the ERK signaling pathway.

In situ ornamenting poly(ε-caprolactone) electrospun fibers with different fiber diameters using chondrocyte-derived extracellular matrix for chondrogenesis of mesenchymal stem cells

Biomimetic instructive tissue engineering scaffolds are critical for achieving successful tissue regeneration. In the present study, we developed a novel scaffold via ornamenting poly(ε-caprolactone) (PCL) electrospun fibers with a chondrocyte-derived extracellular matrix (ECM)-coating, which was applied for chondrogenesis of mesenchymal stem cells (MSCs). PCL fibrous films with different fiber diameters (1282±121 nm, 549±61 nm and 285±38 nm) were first prepared via electrospinning. Rabbit articular chondrocytes (rACs) were cultured on PCL fibrous scaffolds, followed by a decellularization treatment to generate decellularized ECM (dECM)-coated PCL scaffolds (dECM/PCL). Rabbit bone marrow-derived MSCs (rMSCs) were then seeded onto these scaffolds and adhesion, proliferation and chondrogenic differentiation were evaluated. dECM/PCL scaffolds displayed distinct surface microstructural features with varying fiber diameters and fibrous mesh-like ECM with more developed collagen fibers was observed on nanofibers. On dECM/PCL scaffolds, rMSCs tended to spread more at 24 h post-seeding and proliferated better within 7 d compared to those on uncoated PCL scaffolds. Based on analysis of gene expression, rMSCs underwent the best chondrogenic differentiation on dECM/PCL scaffolds of 549-nm fibers. Collectively, such dECM/PCL composite scaffolds are very promising for cartilage tissue regeneration.

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.

Designer Stem Cells: Genome Engineering and the Next Generation of Cell-Based Therapies

Stem cells provide tremendous promise for the development of new therapeutic approaches for musculoskeletal conditions. In addition to their multipotency, certain types of stem cells exhibit immunomodulatory effects that can mitigate inflammation and enhance tissue repair. However, the translation of stem cell therapies to clinical practice has proven difficult due to challenges in intradonor and interdonor variability, engraftment, variability in recipient microenvironment and patient indications, and limited therapeutic biological activity. In this regard, the success of stem cell-based therapies may benefit from cellular engineering approaches to enhance factors such as purification, homing and cell survival, trophic effects, or immunomodulatory signaling. By combining recent advances in gene editing, synthetic biology, and tissue engineering, the potential exists to create new classes of "designer" cells that have prescribed cell-surface molecules and receptors as well as synthetic gene circuits that provide for autoregulated drug delivery or enhanced tissue repair. Published by Wiley Periodicals, Inc. J Orthop Res 37:1287-1293, 2019.

A Scaffold- and Serum-Free Method to Mimic Human Stable Cartilage Validated by Secretome

A stabilized cartilage construct without signs of hypertrophy in chondrocytes is still a challenge. Suspensions of adipose stem/stromal cells (ASCs) and cartilage progenitor cells (CPCs) were seeded into micromolded nonadhesive hydrogel to produce spheroids (scaffold- and serum-free method) characterized by size, immunohistochemistry, fusion, and biomechanical properties. After cell dissociation, they were characterized for mesenchymal cell surface markers, cell viability, and quantitative real-time polymerase chain reaction. Both targeted and nontargeted (shotgun mass spectrometry) analyses were conducted on the culture supernatants. Induced ASC spheroids (ø = 350 μm) showed high cell viability and CD73 downregulation contrasting to CD90. The transforming growth factor (TGF)-β3/TGF-β1 ratio and SOX9 increased (p < 0.05), whereas interleukin (IL)-6, IL-8, RUNX2, and ALPL decreased. Induced ASC spheroids were able to completely fuse and showed a higher force required to compression at day 14 (p < 0.0001). Strong collagen type II in situ was associated with gradual decrease of collagen type X and a lower COLXA1 gene expression at day 14 compared with day 7 (p = 0.0352). The comparison of the secretome content of induced and non-induced ASCs and CPCs identified 138 proteins directly relevant to chondrogenesis of 704 proteins in total. Although collagen X was absent, thrombospondin-1 (TSP-1), described as antiangiogenic and antihypertrophic, and cartilage oligomeric matrix protein (COMP), a biomarker of chondrogenesis, were upregulated in induced ASC spheroids. Our scaffold- and serum-free method mimics stable cartilage acting as a tool for biomarker discovery and for regenerative medicine protocols. Impact Statement Promising adult stem cell sources for cartilage regeneration include adipose stem/stromal cells (ASCs) from subcutaneous adipose tissue. Our main objective was the development of a reproducible and easy-to-handle scaffold- and serum-free method to obtain stable cartilage from induced ASC spheroids. In addition to targeted protein profiling and biomechanical analysis, we provide the first characterization of the secretome composition for ASC spheroids, providing a useful tool to monitor in vitro chondrogenesis and a noninvasive quality control of tissue-engineered constructs. Furthermore, our secretome analysis revealed a potential novel biomarker-thrombospondin-1 (TSP-1), known by its antiangiogenic properties and recently described as an antihypertrophic protein.

Re-examining osteoarthritis therapy from a developmental biologist's perspective

Osteoarthritis is the most prevalent musculoskeletal disorder and one for which there is no disease modifying therapy available at present. Our current understanding of the disease mechanism of osteoarthritis is limited owing to a lacuna of knowledge about the development and maintenance of articular cartilage that is affected during osteoarthritis. All current therapeutic strategies aim at countering inflammation which though mitigates pain but does not arrest the progressive degeneration of articular cartilage. During osteoarthritis, articular cartilage expresses markers for transient cartilage differentiation. Moreover, blocking transient cartilage differentiation is sufficient for halting the progression of experimental osteoarthritis. A developmental biology inspired approach that combines restoration of tissue microenvironment, supplementation with engineered cartilage and built in mechanism to prevent transient cartilage differentiation could be an avenue for developing a disease modifying therapy for osteoarthritis.

Efficacy of collagen and alginate hydrogels for the prevention of rat chondrocyte dedifferentiation

Dedifferentiation of chondrocytes remains a major problem in cartilage tissue engineering. The development of hydrogels that can preserve chondrogenic phenotype and prevent chondrocyte dedifferentiation is a meaningful strategy to solve dedifferentiation problem of chondrocytes. In the present study, three gels were prepared (alginate gel (Alg gel), type I collagen gel (Col gel), and their combination gel (Alg/Col gel)), and the in vitro efficacy of chondrocytes culture while preserving their phenotypes was investigated. While Col gel became substantially contracted with time, the cells encapsulated in Alg gel preserved the shape over the culture period of 14 days. The mechanical and cell-associated contraction behaviors of Alg/Col gel were similar to those of Alg. The cells in Alg and Alg/Col gels exhibited round morphology, whereas those in Col gel became elongated (i.e. fibroblast-like) during cultures. The cells proliferated with time in all gels with the highest proliferation being attained in Col gel. The expression of chondrogenic genes, including SOX9, type II collagen, and aggrecan, was significantly up-regulated in Alg/Col gel and Col gel, particularly in Col gel. However, the chondrocyte dedifferentiation markers, type I collagen and alkaline phosphatase (ALP), were also expressed at significant levels in Col gel, which being contrasted with the events in Alg and Alg/Col gels. The current results suggest the cells cultured in hydrogels can express chondrocyte dedifferentiation markers as well as chondrocyte markers, which draws attention to choose proper hydrogels for chondrocyte-based cartilage tissue engineering.

Non-contact Coculture Reveals a Comprehensive Response of Chondrocytes Induced by Mesenchymal Stem Cells Through Trophic Secretion

Coculture between mesenchymal stem cells (MSCs) and chondrocytes has significant implications in cartilage regeneration. However, a conclusive understanding remains elusive. Previously, we reported that rabbit bone marrow-derived MSCs (rbBMSCs) could downregulate the differentiated phenotype of rabbit articular chondrocytes (rbACs) in a non-contact coculture system for the first time. In the present study, a systemic investigation was performed to understand the biological characteristics of chondrocytes in coculture with MSCs. Firstly, cells (MSCs and chondrocytes) from different origins were cocultured in transwell system. Different chondrocytes, when cocultured with different MSCs respectively, consistently demonstrated stimulated proliferation, transformed morphology and declined glycosaminoglycan secretion of chondrocytes. Next, cell surface molecules and the global gene expression of rbACs were characterized. It was found that cocultured rbACs showed a distinct surface molecule profile and global gene expression compared to both dedifferentiated rbACs and rbBMSCs. In the end, cocultured rbACs were passaged and induced to undergo the chondrogenic redifferentiation. Better growth and chondrogenesis ability were confirmed compared with control cells without coculture. Together, chondrocytes display comprehensive changes in coculture with MSCs and the cocultured rbACs are beneficial for cartilage repair.

Transcriptome-Wide Analyses of Human Neonatal Articular Cartilage and Human Mesenchymal Stem Cell-Derived Cartilage Provide a New Molecular Target for Evaluating Engineered Cartilage

Cellular differentiation comprises a progressive, multistep program that drives cells to fabricate a tissue with specific and site distinctive structural and functional properties. Cartilage constitutes one of the potential differentiation lineages that mesenchymal stem cells (MSCs) can follow under the guidance of specific bioactive agents. Single agents such as transforming growth factor beta (TGF-β) and bone morphogenetic protein 2 in unchanging culture conditions have been historically used to induce in vitro chondrogenic differentiation of MSCs. Despite the expression of traditional chondrogenic biomarkers such as type II collagen and aggrecan, the resulting tissue represents a transient cartilage rather than an in vivo articular cartilage (AC), differing significantly in structure, chemical composition, cellular phenotypes, and mechanical properties. Moreover, there have been no comprehensive, multicomponent parameters to define high-quality and functional engineered hyaline AC. To address these issues, we have taken an innovative approach based on the molecular interrogation of human neonatal articular cartilage (hNAC), dissected from the knees of 1-month-old cadaveric specimens. Subsequently, we compared hNAC-specific transcriptional regulatory elements and differentially expressed genes with adult human bone marrow (hBM) MSC-derived three-dimensional cartilage structures formed in vitro. Using microarray analysis, the transcriptome of hNAC was found to be globally distinct from the transient, cartilage-like tissue formed by hBM-MSCs in vitro. Specifically, over 500 genes that are highly expressed in hNAC were not expressed at any time point during in vitro human MSC chondrogenesis. The analysis also showed that the differences were less variant during the initial stages (first 7 days) of the in vitro chondrogenic differentiation program. These observations suggest that the endochondral fate of hBM-MSC-derived cartilage may be rerouted at earlier stages of the TGF-β-stimulated chondrogenic differentiation program. Based on these analyses, several key molecular differences (transcription factors and coded cartilage-related proteins) were identified in hNAC that will be useful as molecular inductors and identifiers of the in vivo AC phenotype. Our findings provide a new gold standard of a molecularly defined AC phenotype that will serve as a platform to generate novel approaches for AC tissue engineering.

Influence of oxygen levels on chondrogenesis of porcine mesenchymal stem cells cultured in polycaprolactone scaffolds

Chondrogenesis of mesenchymal stem cells (MSCs) is known to be regulated by a number of environmental factors, including local oxygen levels. The hypothesis of this study is that the response of MSCs to hypoxia is dependent on the physical and chemical characteristics of the substrate used. The objective of this study was to explore how different modifications to polycaprolactone (PCL) scaffolds influenced the response of MSCs to hypoxia. PCL, PCL-hyaluronic acid (HA), and PCL-Bioglass^® (BG) scaffolds were seeded with MSCs derived from bone marrow and cultured for 35 days under normoxic or low oxygen conditions, and the resulting biochemical properties of the MSC laden construct were assessed. Low oxygen tension has a positive effect over cell proliferation and macromolecules biosynthesis. Furthermore, hypoxia enhanced the distribution of collagen and glycosaminoglycans (GAGs) deposition through the scaffold. On the other hand, MSCs displayed certain material dependent responses to hypoxia. Low oxygen tension had a positive effect on cell proliferation in BG and HA scaffolds, but only a positive effect on GAGs synthesis in PCL and HA scaffolds. In conclusion, hypoxia increased cell viability and expression of chondrogenic markers but the cell response was modulated by the type of scaffold used. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1684-1691, 2017.

Basic science of osteoarthritis

Osteoarthritis (OA) is a prevalent, disabling disorder of the joints that affects a large population worldwide and for which there is no definitive cure. This review provides critical insights into the basic knowledge on OA that may lead to innovative end efficient new therapeutic regimens. While degradation of the articular cartilage is the hallmark of OA, with altered interactions between chondrocytes and compounds of the extracellular matrix, the subchondral bone has been also described as a key component of the disease, involving specific pathomechanisms controlling its initiation and progression. The identification of such events (and thus of possible targets for therapy) has been made possible by the availability of a number of animal models that aim at reproducing the human pathology, in particular large models of high tibial osteotomy (HTO). From a therapeutic point of view, mesenchymal stem cells (MSCs) represent a promising option for the treatment of OA and may be used concomitantly with functional substitutes integrating scaffolds and drugs/growth factors in tissue engineering setups. Altogether, these advances in the fundamental and experimental knowledge on OA may allow for the generation of improved, adapted therapeutic regimens to treat human OA.

Chondrogenesis of embryonic limb bud cells in micromass culture progresses rapidly to hypertrophy and is modulated by hydrostatic pressure

Chondrogenesis in vivo is precisely controlled in time and space. The entire limb skeleton forms from cells at the core of the early limb bud that condense and undergo chondrogenic differentiation. Whether they form stable cartilage at the articular surface of the joint or transient cartilage that progresses to hypertrophy as endochondral bone, replacing the cartilage template of the skeletal rudiment, is spatially controlled over several days in the embryo. Here, we follow the differentiation of cells taken from the early limb bud (embryonic day 11.5), grown in high-density micromass culture and show that a self-organising pattern of evenly spaced cartilage nodules occurs spontaneously in growth medium. Although chondrogenesis is enhanced by addition of BMP6 to the medium, the spatial pattern of nodule formation is disrupted. We show rapid progression of the entire nodule to hypertrophy in culture and therefore loss of the local signals required to direct formation of stable cartilage. Dynamic hydrostatic pressure, which we have previously predicted to be a feature of the forming embryonic joint region, had a stabilising effect on chondrogenesis, reducing expression of hypertrophic marker genes. This demonstrates the use of micromass culture as a relatively simple assay to compare the effect of both biophysical and molecular signals on spatial and temporal control of chondrogenesis that could be used to examine the response of different types of progenitor cell, both adult- and embryo-derived.

Mesenchymal Stem Cells Reshape and Provoke Proliferation of Articular Chondrocytes by Paracrine Secretion

Coculture between mesenchymal stem cells (MSCs) and articular chondrocytes (ACs) represents a promising strategy for cartilage regeneration. This study aimed at elaborating how ACs were regulated by MSCs. Rabbit ACs (rACs) and rabbit MSCs (rMSCs) were seeded separately in a Transwell system to initiate non-contact coculture in growth medium without chondrogenic factors. Cell morphology, cell proliferation, production of extracellular matrix (ECM), and gene expression of rACs were characterized. Upon coculture, rACs underwent a morphological transition from a rounded or polygonal shape into a fibroblast-like one and proliferation was provoked simultaneously. Such effects were dependent on the amount of rMSCs. Along with these changes, ECM production and gene expression of rACs were also perturbed. Importantly, when a ROCK inhibitor (Y27632) was supplemented to coculture, the effects except that on cell proliferation were inhibited, suggesting the involvement of RhoA/ROCK signaling. By applying an inhibitor (BIBF1120) of VEGFR1/2/3, FGFR1/2/3 and PDGFRα/β in coculture, or supplementing FGF-1, VEGF-A and PDGFbb in monoculture, it was confirmed that the paracrine factors by rMSCs mediated the compounding effects on rACs. These findings shed light on MSCs-ACs interactions and might confer an insight view on cell-based cartilage regeneration.

Poly(ε-caprolactone)-based substrates bearing pendant small chemical groups as a platform for systemic investigation of chondrogenesis

OBJECTIVES

Physiochemical properties of biomaterials play critical roles in dictating types of cell behaviour. In this study, a series of poly(ε-caprolactone) (PCL)-derived polymers bearing different small chemical groups was employed as a platform to evaluate chondrogenesis of different cell types.

MATERIALS AND METHODS

Thin films were prepared by spin-coating PCL derivatives. Rabbit articular chondrocytes (rACs) and rabbit bone marrow-derived mesenchymal stem cells (rMSCs) were seeded on to the films, and cell adhesion, proliferation, extracellular matrix production and gene expression were evaluated.

RESULTS

The presence of hydrophilic groups (-NH2 , -COOH, -OH and -C=O) promoted adhesion and proliferation of primary rACs and rMSCs. On these polymeric films, chondrogenesis of primary rACs depended on culture time. For passaged cells, re-differentiation was induced on these films by chondrogenic induction, but less for cells of passage 5 compared to passage 3. While films with hydrophilic groups favoured chondrocytic gene expression of both types of passaged cells, production of glycosaminoglycans (GAG) was similar for those of passage 3 on all films, and PCL-CH3 film better supported GAG production for cells of passage 5. Under chondrogenic conditions, rMSCs were more efficient at GAG production on PCL and PCL-NH2 films.

CONCLUSIONS

This study demonstrates that different cells displayed distinct responses to substrate surface chemistry, implying that cell-biomaterial interactions can be developmental stage dependent. This provides a novel perspective for developing biomaterials for cartilage regeneration.

Mechanical loading inhibits hypertrophy in chondrogenically differentiating hMSCs within a biomimetic hydrogel

Three dimensional hydrogels are a promising vehicle for delivery of adult human bone-marrow derived mesenchymal stem cells (hMSCs) for cartilage tissue engineering. One of the challenges with using this cell type is the default pathway is terminal differentiation, a hypertrophic phenotype and precursor to endochondral ossification. We hypothesized that a synthetic hydrogel consisting of extracellular matrix (ECM) analogs derived from cartilage when combined with dynamic loading provides physiochemical cues for achieving a stable chondrogenic phenotype. Hydrogels were formed from crosslinked poly(ethylyene glycol) as the base chemistry and to which (meth)acrylate functionalized ECM analogs of RGD (cell adhesion peptide) and chondroitin sulfate (ChS, a negatively charged glycosaminoglycan) were introduced. Bone-marrow derived hMSCs from three donors were encapsulated in the hydrogels and cultured under free swelling conditions or under dynamic com pressive loading with 2.5 ng/ml TGF-β3. hMSC differentiation was assessed by quantitative PCR and immunohistochemistry. Nine hydrogel formulations were initially screened containing 0, 0.1 or 1mM RGD and 0, 1 or 2wt% ChS. After 21 days, the 1% ChS and 0.1 mM RGD hydrogel had the highest collagen II gene expression, but this was accompanied by high collagen X gene expression. At the protein level, collagen II was detected in all formulations with ECM analogs, but minimally detectable in the hydrogel without ECM analogs. Collagen X protein was present in all formulations. The 0.1 mM RGD and 1% ChS formulation was selected and subjected to five loading regimes: no loading, 5% strain 0.3Hz (1.5%/s), 10% strain 0.3 Hz (3%/s), 5% strain 1 Hz (5%/s), and 10% strain 1Hz (10%/s). After 21 days, ~70-90% of cells stained positive for collagen II protein regardless of the culture condition. On the contrary, only ~20-30% of cells stained positive for collagen X protein under 3 and 5%/s loading conditions, which was accompanied by minimal staining for RunX2. The other culture conditions had more cells staining positive for collagen X (40-60%) and was accompanied by positive staining for RunX2. In summary, a cartilage-like biomimetic hydrogel supports chondrogenesis of hMSCs, but dynamic loading only under select strain rates is able to inhibit hypertrophy.

Modulation of chondrogenic differentiation of human mesenchymal stem cells in jellyfish collagen scaffolds by cell density and culture medium

Studies on tissue-engineering approaches for the regeneration of traumatized cartilage focus increasingly on multipotent human mesenchymal stem cells (hMSCs) as an alternative to autologous chondrocytes. The present study applied porous scaffolds made of collagen from the jellyfish Rhopilema esculentum for the in vitro chondrogenic differentiation of hMSCs. Culture conditions in those scaffolds differ from conditions in high-density pellet cultures, making a re-examination of these data necessary. We systematically investigated the influence of seeding density, basic culture media [Dulbecco's modified Eagle's medium (DMEM), α-minimum essential medium (α-MEM)] with varying glucose content and supplementation with fetal calf serum (FCS) or bovine serum albumin (BSA) on the chondrogenic differentiation of hMSCs. Gene expression analyses of selected markers for chondrogenic differentiation and hypertrophic development were conducted. Furthermore, the production of cartilage extracellular matrix (ECM) was analysed by quantification of sulphated glycosaminoglycan and collagen type II contents. The strongest upregulation of chondrogenic markers, along with the highest ECM deposition was observed in scaffolds seeded with 2.4 × 10⁶ cells/cm³ after cultivation in high-glucose DMEM and 0.125% BSA. Lower seeding densities compared to high-density pellet cultures were sufficient to induce in vitro chondrogenic differentiation of hMSCs in collagen scaffolds, which reduces the amount of cells required for the seeding of scaffolds and thus the monolayer expansion period. Furthermore, examination of the impact of FCS and α-MEM on chondrogenic MSC differentiation is an important prerequisite for the development of an osteochondral medium for simultaneous osteogenic and chondrogenic differentiation in biphasic scaffolds for osteochondral tissue regeneration. Copyright © 2015 John Wiley & Sons, Ltd.

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

Background

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

Methods

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

Results

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

Conclusions

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

The Effects of Naproxen on Chondrogenesis of Human Mesenchymal Stem Cells

Currently, there are no established treatments to prevent, stop, or even retard the degeneration of articular cartilage in osteoarthritis (OA). Biological repair of the degenerating articular cartilage would be preferable to surgery. There is no benign site where autologous chondrocytes can be harvested and used as a cell source for cartilage repair, leaving mesenchymal stem cells (MSCs) as an attractive option. However, MSCs from OA patients have been shown to constitutively express collagen type X (COL-X), a marker of late-stage chondrocyte hypertrophy. We recently found that naproxen (Npx), but not other nonsteroidal anti-inflammatory drugs, can induce collagen type X alpha 1 (COL10A1) gene expression in bone marrow-derived MSCs from healthy and OA donors. In this study, we determined the effect of Npx on COL10A1 expression and investigated the intracellular signaling pathways that mediate such effect in normal human MSCs during chondrogenesis. MSCs were cultured in standard chondrogenic differentiation media supplemented with or without Npx. Our results show that Npx can regulate chondrogenic differentiation by affecting the gene expression of both Indian hedgehog and parathyroid hormone/parathyroid hormone-related protein signaling pathways in a time-dependent manner, suggesting a complex interaction of different signaling pathways during the process.

Cellular and Acellular Approaches for Cartilage Repair: A Philosophical Analysis

There are several choices of cells to use for cartilage repair. Cells are used as internal or external sources and sometimes in combination. In this article, an analysis of the different cell choices and their use and potential is provided. Embryonic cartilage formation is of importance when finding more about how to be able to perfect cartilage repair. Some suggestions for near future research based on up-to-date knowledge on chondrogenic cells are given to hopefully stimulate more studies on the final goal of cartilage regeneration.

Strategies to minimize hypertrophy in cartilage engineering and regeneration

Due to a blood supply shortage, articular cartilage has a limited capacity for self-healing once damaged. Articular chondrocytes, cartilage progenitor cells, embryonic stem cells, and mesenchymal stem cells are candidate cells for cartilage regeneration. Significant current attention is paid to improving chondrogenic differentiation capacity; unfortunately, the potential chondrogenic hypertrophy of differentiated cells is largely overlooked. Consequently, the engineered tissue is actually a transient cartilage rather than a permanent one. The development of hypertrophic cartilage ends with the onset of endochondral bone formation which has inferior mechanical properties. In this review, current strategies for inhibition of chondrogenic hypertrophy are comprehensively summarized; the impact of cell source options is discussed; and potential mechanisms underlying these strategies are also categorized. This paper aims to provide guidelines for the prevention of hypertrophy in the regeneration of cartilage tissue. This knowledge may also facilitate the retardation of osteophytes in the treatment of osteoarthritis.

The paracrine feedback loop between vitamin D₃ (1,25(OH)₂D₃) and PTHrP in prehypertrophic chondrocytes

The endocrine feedback loop between vitamin D₃ (1,25(OH)₂D₃) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine feedback loop between 1,25(OH)₂D₃ and PTHrP in the growth plate, in parallel with the endocrine feedback loop between 1,25(OH)₂D₃ and PTH. This was investigated in ATDC5 cells treated with 10⁻⁸ M 1,25(OH)₂D₃ or PTHrP, Col2-pd2EGFP transgenic mice, and primary Col2-pd2EGFP growth plate chondrocytes isolated by FACS, using RT-qPCR, Western blot, PTHrP ELISA, chromatin immunoprecipitation (ChIP) assay, silencing of the 1,25(OH)₂D₃ receptor (VDR), immunofluorescent staining, immunohistochemistry, and histomorphometric analysis of the growth plate. The ChIP assay confirmed functional binding of the VDR to the PTHrP promoter, but not to the PTHR1 promoter. Treatment with 1,25(OH)₂D₃ decreased PTHrP protein production, an effect which was prevented by silencing of the VDR. Treatment with PTHrP significantly induced VDR production, but did not affect 1α- and 24-hydroxylase expression. Hypertrophic differentiation was inhibited by PTHrP and 1,25(OH)₂D₃ treatment. Taken together, these findings indicate that there is a functional paracrine feedback loop between 1,25(OH)₂D₃ and PTHrP in the growth plate. 1,25(OH)₂D₃ decreases PTHrP production, while PTHrP increases chondrocyte sensitivity to 1,25(OH)₂D₃ by increasing VDR production. In light of the role of 1,25(OH)₂D₃ and PTHrP in modulating chondrocyte differentiation, 1,25(OH)₂D₃ in addition to PTHrP could potentially be used to prevent undesirable hypertrophic chondrocyte differentiation during cartilage repair or regeneration.

Human embryonic stem cell-derived neural crest cells capable of expressing markers of osteochondral or meningeal-choroid plexus differentiation

AIMS

The transcriptome and fate potential of three diverse human embryonic stem cell-derived clonal embryonic progenitor cell lines with markers of cephalic neural crest are compared when differentiated in the presence of combinations of TGFβ3, BMP4, SCF and HyStem-C matrices.

MATERIALS & METHODS

The cell lines E69 and T42 were compared with MEL2, using gene expression microarrays, immunocytochemistry and ELISA.

RESULTS

In the undifferentiated progenitor state, each line displayed unique markers of cranial neural crest including TFAP2A and CD24; however, none expressed distal HOX genes including HOXA2 or HOXB2, or the mesenchymal stem cell marker CD74. The lines also showed diverse responses when differentiated in the presence of exogenous BMP4, BMP4 and TGFβ3, SCF, and SCF and TGFβ3. The clones E69 and T42 showed a profound capacity for expression of endochondral ossification markers when differentiated in the presence of BMP4 and TGFβ3, choroid plexus markers in the presence of BMP4 alone, and leptomeningeal markers when differentiated in SCF without TGFβ3.

CONCLUSION

The clones E69 and T42 may represent a scalable source of primitive cranial neural crest cells useful in the study of cranial embryology, and potentially cell-based therapy.

Articular chondrocyte redifferentiation in 3D co-cultures with mesenchymal stem cells

In this work, we evaluated the ability of 3D co-cultures with mesenchymal stem cells (MSCs) to redifferentiate monolayer expanded articular chondrocytes (ACs) and produce cartilaginous extracellular matrix at varying stages of the dedifferentiation process and further examined the dependency of this effect on the culture medium composition. Primary bovine ACs were expanded in monolayers for up to nine population doublings to obtain seven cell stocks with gradually increasing levels of dedifferentiation. Culture expanded ACs were then seeded as monocultures and co-cultures with rabbit bone marrow-derived MSCs (30:70 ratio of ACs-to-MSCs) on porous scaffolds. Parallel cultures were established for each cell population in serum-containing growth medium and serum-free induction medium supplemented with dexamethasone and TGF-β3. After 3 weeks, all groups were analyzed for DNA content, glycosaminoglycan (GAG) and hydroxyproline (HYP) production, and chondrogenic gene expression. Significant enhancements in cellularity, GAG content and GAG/HYP ratio, and chondrogenic phenotype were observed in the induction medium compared to growth medium at all levels of AC expansion. Furthermore, primary co-cultures showed similarly enhanced chondrogenesis compared to monocultures in both culture media, whereas passaged ACs benefitted from co-culturing only in the induction medium. We conclude that co-cultures of ACs and MSCs can produce superior in vitro engineered cartilage in comparison to pure AC cultures, due to both heterotypic cellular interactions and decreased need for monolayer expansion of biopsied chondrocytes. While the initial level of AC dedifferentiation affected the quality of the engineered constructs, co-culture benefits were realized at all stages of AC expansion when suitable chondroinductive culture medium was used.

Rejuvenation of chondrogenic potential in a young stem cell microenvironment

Autologous cells suffer from limited cell number and senescence during ex vivo expansion for cartilage repair. Here we found that expansion on extracellular matrix (ECM) deposited by fetal synovium-derived stem cells (SDSCs) (FE) was superior to ECM deposited by adult SDSCs (AE) in promoting cell proliferation and chondrogenic potential. Unique proteins in FE might be responsible for the rejuvenation effect of FE while advantageous proteins in AE might contribute to differentiation more than to proliferation. Compared to AE, the lower elasticity of FE yielded expanded adult SDSCs with lower elasticity which could be responsible for the enhancement of chondrogenic and adipogenic differentiation. MAPK and noncanonical Wnt signals were actively involved in ECM-mediated adult SDSC rejuvenation.

Mechanical regulation of skeletal development

Development of the various components of a normal skeleton requires highly regulated signalling systems that co-ordinate spatial and temporal patterns of cell division, cell differentiation, and morphogenesis. Much work in recent decades has revealed cascades of molecular signalling, acting through key transcription factors to regulate, for example, organized chondrogenic and osteogenic differentiation. It is now clear that mechanical stimuli are also required for aspects of skeletogenesis but very little is known about how the mechanical signals are integrated with classic biochemical signalling. Spatially organized differentiation is vital to the production of functionally appropriate tissues contributing to precise, region specific morphologies, for example transient chondrogenesis of long bone skeletal rudiments, which prefigures osteogenic replacement of the cartilage template, compared with the production of permanent cartilage at the sites of articulation. Currently a lack of understanding of how these tissues are differentially regulated hampers efforts to specifically regenerate stable bone and cartilage. Here, we review current research revealing the influence of mechanical stimuli on specific aspects of skeletal development and refer to other developing systems to set the scene for current and future work to uncover the molecular mechanisms involved. We integrate this with a brief overview of the effects of mechanical stimulation on stem cells in culture bringing together developmental and tissue engineering aspects of mechanoregulation of cell behavior. A better understanding of the molecular mechanisms that link mechanical stimuli to transcriptional control guiding cell differentiation will lead to new ideas about how to effectively prime stem cells for tissue engineering and regenerative therapies.

Growth differentiation factor-5 enhances in vitro mesenchymal stromal cell chondrogenesis and hypertrophy

The regenerative potential for adult bone marrow-derived mesenchymal stromal cells (MSCs) has been extensively investigated in the setting of arthritic disease and focal cartilage defects. In vitro chondrogenic differentiation of MSCs is regularly accomplished by the widely used pellet culture system where MSCs are maintained in high-density pellets to mimic mesenchymal condensation during development. Supplementation of chondrogenic MSC pellet cultures with growth differentiation factor-5 (GDF-5), a highly regulated gene in the chondrogenic phase of endochondral ossification (EO), was investigated here under the hypothesis that GDF-5 will enhance the chondrogenic differentiation of MSCs, thereby supporting their entry into ossification. The supplementation of chondrogenic MSC pellets with the recombinant human GDF-5 protein significantly enhanced MSC chondrogenic differentiation, as demonstrated by enhanced collagen type II and sulfated glycosaminoglycan (GAG) incorporation into the extracellular matrix. Increased P-SMADs 1-5-8 were observed in pellets treated with GDF-5 and transforming growth factor (TGF)-β 3 when compared to the pellets treated with TGF-β 3 alone, demonstrated by immunostaining and western blot analysis of the chondrogenic pellet extract. A concurrent increase in alkaline phosphatase, collagen types I and X, and osteopontin secretion indicated a transition of these cultures to hypertrophy. Together, these data support the application of GDF-5 to enhance MSC chondrogenic differentiation and hypertrophy as a precursor to EO.

The promise and challenges of stem cell-based therapies for skeletal diseases: stem cell applications in skeletal medicine: potential, cell sources and characteristics, and challenges of clinical translation

Despite decades of research, remaining safety concerns regarding disease transmission, heterotopic tissue formation, and tumorigenicity have kept stem cell-based therapies largely outside the standard-of-care for musculoskeletal medicine. Recent insights into trophic and immune regulatory activities of mesenchymal stem cells (MSCs), although incomplete, have stimulated a plethora of new clinical trials for indications far beyond simply supplying progenitors to replenish or re-build lost/damaged tissues. Cell banks are being established and cell-based products are in active clinical trials. Moreover, significant advances have also been made in the field of pluripotent stem cells, in particular the recent development of induced pluripotent stem cells. Their indefinite proliferation potential promises to overcome the limited supply of tissue-specific cells and adult stem cells. However, substantial hurdles related to their safety must be overcome for these cells to be clinically applicable.