Stem cells and cartilage development: complexities of a simple tissue

Cartilage regeneration using transforming growth factor-beta 3-loaded injectable crosslinked hyaluronic acid hydrogel

Cartilage defects can be difficult to heal, potentially leading to complications such as osteoarthritis. Recently, a tissue engineering approach that uses scaffolds and growth factors has been proposed to regenerate new cartilage tissues. Herein, we investigated the application of hyaluronic acid (HA) gel loaded with transforming growth factor-beta 3 (TGF-β3) for enhanced cartilage regeneration. We assessed the clinical conditions required to efficiently enhance the ability of the modified HA gel to repair defective cartilage. Based on our findings, the prepared HA gel exhibited good physicochemical and mechanical properties and was non-toxic and non-inflammatory. Moreover, HA gel-loaded TGF-β3 (HAT) had improved biocompatibility and promoted the synthesis of cartilage-specific matrix and collagen, further improving its ability to repair defects. The application of HAT resulted in an initial burst release of HA, which degraded slowly in vivo. Finally, HAT combined with microfracture-inducing bone marrow stem cells could significantly improve the cartilage microenvironment and regeneration of cartilage defects. Our results indicate that HA is a suitable material for developing growth factor carriers, whereas HAT is a promising candidate for cartilage regeneration. Furthermore, this differentiated strategy provides a rapid and effective clinical approach for next-generation cartilage regeneration.

Novel Osteochondral Biotemplate Improves Long-term Cartilage Repair Compared With Microfracture in an Ovine Model

BACKGROUND

Current cartilage repair therapies do not re-create the complex mechanical interface between cartilage and bone, which is critical for long-term repair durability. New biomaterial designs that include hard tissue-soft tissue interface structures offer promise to improve clinical outcomes.

PURPOSE/HYPOTHESIS

The purpose of this study was to evaluate the efficacy and safety of a naturally derived osteochondral biotemplate with a novel contiguous hard tissue-soft tissue interface in an ovine model as a regenerative solution for articular cartilage defects. It was hypothesized that the osteochondral biotemplate would produce structurally superior repair tissue compared with microfracture over a 13-month period.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral biotemplates were manufactured from porcine cancellous bone. Skeletally mature sheep (N = 30) were randomly allocated to 3 groups: early healing stage (euthanasia at 4 months), 6-month treatment, and 13-month treatment. In the early healing stage group, an 8 mm-diameter by 5 mm-deep osteochondral defect was created on the medial femoral condyle and treated at the time of iatrogenic injury with an osteochondral biotemplate. The contralateral limb received the same treatment 2 months later. In the 6- and 13-month treatment groups, 1 limb received the same osteochondral procedure as the early healing stage group. In the contralateral limb, an 8 mm-diameter, full-thickness cartilage defect (1-2 mm deep) was created and treated with microfracture. Cartilage repair and integration were quantitatively and qualitatively assessed with gross inspection, histological evaluation, and magnetic resonance imaging (MRI). Wilcoxon signed-rank and McNemar tests were used to compare the treatments.

RESULTS

At 6 and 13 months after treatment, the biotemplate was not present histologically. At 13 months, the biotemplate treatment demonstrated statistically higher histological scores than microfracture for integration with surrounding cartilage (biotemplate: 74 ± 31; microfracture: 28 ± 39; P = .03), type 2 collagen (biotemplate: 72 ± 33; microfracture: 40 ± 38; P = .02), total cartilage (biotemplate: 71 ± 9; microfracture: 59 ± 9; P = .01), and total integration (biotemplate: 85 ± 15; microfracture: 66 ± 20; P = .04). The osteochondral biotemplate treatment produced a notable transient nonneutrophilic inflammatory response that appeared to approach resolution at 13 months. MRI results were not statistically different between the 2 treatments.

CONCLUSION

Even with the inflammatory response, after 13 months, the osteochondral biotemplate outperformed microfracture in cartilage regeneration and demonstrated superiority in integration between the repair tissue and host tissue as well as integration between the newly formed cartilage and the underlying bone.

CLINICAL RELEVANCE

This work has demonstrated the clinical potential of a novel biomaterial template to regenerate the complex mechanical interface between cartilage and the subchondral bone.

Cell surface markers for mesenchymal stem cells related to the skeletal system: A scoping review

Multipotent mesenchymal stromal cells (MSCs) have been described as bone marrow stromal cells, which can form cartilage, bone or hematopoietic supportive stroma. In 2006, the International Society for Cell Therapy (ISCT) established a set of minimal characteristics to define MSCs. According to their criteria, these cells must express CD73, CD90 and CD105 surface markers; however, it is now known they do not represent true stemness epitopes. The objective of the present work was to determine the surface markers for human MSCs associated with skeletal tissue reported in the literature (1994-2021). To this end, we performed a scoping review for hMSCs in axial and appendicular skeleton. Our findings determined the most widely used markers were CD105 (82.9%), CD90 (75.0%) and CD73 (52.0%) for studies performed in vitro as proposed by the ISCT, followed by CD44 (42.1%), CD166 (30.9%), CD29 (27.6%), STRO-1 (17.7%), CD146 (15.1%) and CD271 (7.9%) in bone marrow and cartilage. On the other hand, only 4% of the articles evaluated in situ cell surface markers. Even though most studies use the ISCT criteria, most publications in adult tissues don't evaluate the characteristics that establish a stem cell (self-renewal and differentiation), which will be necessary to distinguish between a stem cell and progenitor populations. Collectively, MSCs require further understanding of their characteristics if they are intended for clinical use.

Progress in Composite Hydrogels and Scaffolds Enriched with Icariin for Osteochondral Defect Healing

Osteochondral structure reconstruction by tissue engineering, a challenge in regenerative medicine, requires a scaffold that ensures both articular cartilage and subchondral bone remodeling. Functional hydrogels and scaffolds present a strategy for the controlled delivery of signaling molecules (growth factors and therapeutic drugs) and are considered a promising therapeutic approach. Icariin is a pharmacologically-active small molecule of prenylated flavonol glycoside and the main bioactive flavonoid isolated from Epimedium spp. The in vitro and in vivo testing of icariin showed chondrogenic and ostseoinductive effects, comparable to bone morphogenetic proteins, and suggested its use as an alternative to growth factors, representing a low-cost, promising approach for osteochondral regeneration. This paper reviews the complex structure of the osteochondral tissue, underlining the main aspects of osteochondral defects and those specifically occurring in osteoarthritis. The significance of icariin's structure and the extraction methods were emphasized. Studies revealing the valuable chondrogenic and osteogenic effects of icariin for osteochondral restoration were also reviewed. The review highlighted th recent state-of-the-art related to hydrogels and scaffolds enriched with icariin developed as biocompatible materials for osteochondral regeneration strategies.

Creating an Optimal In Vivo Environment to Enhance Outcomes Using Cell Therapy to Repair/Regenerate Injured Tissues of the Musculoskeletal System

Following most injuries to a musculoskeletal tissue which function in unique mechanical environments, an inflammatory response occurs to facilitate endogenous repair. This is a process that usually yields functionally inferior scar tissue. In the case of such injuries occurring in adults, the injury environment no longer expresses the anabolic processes that contributed to growth and maturation. An injury can also contribute to the development of a degenerative process, such as osteoarthritis. Over the past several years, researchers have attempted to use cellular therapies to enhance the repair and regeneration of injured tissues, including Platelet-rich Plasma and mesenchymal stem/medicinal signaling cells (MSC) from a variety of tissue sources, either as free MSC or incorporated into tissue engineered constructs, to facilitate regeneration of such damaged tissues. The use of free MSC can sometimes affect pain symptoms associated with conditions such as OA, but regeneration of damaged tissues has been challenging, particularly as some of these tissues have very complex structures. Therefore, implanting MSC or engineered constructs into an inflammatory environment in an adult may compromise the potential of the cells to facilitate regeneration, and neutralizing the inflammatory environment and enhancing the anabolic environment may be required for MSC-based interventions to fulfill their potential. Thus, success may depend on first eliminating negative influences (e.g., inflammation) in an environment, and secondly, implanting optimally cultured MSC or tissue engineered constructs into an anabolic environment to achieve the best outcomes. Furthermore, such interventions should be considered early rather than later on in a disease process, at a time when sufficient endogenous cells remain to serve as a template for repair and regeneration. This review discusses how the interface between inflammation and cell-based regeneration of damaged tissues may be at odds, and outlines approaches to improve outcomes. In addition, other variables that could contribute to the success of cell therapies are discussed. Thus, there may be a need to adopt a Precision Medicine approach to optimize tissue repair and regeneration following injury to these important tissues.

Effects of rAAV-mediated overexpression of bone morphogenetic protein 3 (BMP-3) on the chondrogenic fate of human bone marrow-derived mesenchymal stromal cells

Implantation of genetically modified chondrogenically competent human bone marrow-derived mesenchymal stromal cells (hMSCs) is an attractive strategy to improve cartilage repair. The goal of this study was to examine the potential benefits of transferring a sequence coding for the bone morphogenetic protein 3 (BMP-3) that modulates bone and cartilage formation, using recombinant adeno-associated virus (rAAV) vectors on the chondroreparative activities of hMSCs. Undifferentiated and chondrogenically induced primary human MSCs were treated with an rAAV-hBMP-3 construct to evaluate its effects on the proliferative, metabolic, and chondrogenic activities of the cells compared with control (reporter rAAV-lacZ vector) condition. Effective BMP-3 expression was noted both in undifferentiated and chondrogenically differentiated cells in the presence of rAAV-hBMP-3 relative to rAAV-lacZ, stimulating cell proliferation and extracellular matrix (proteoglycans, type-II collagen) deposition together with higher levels of chondrogenic SOX9 expression. rAAV-hBMP-3 also advantageously decreased terminal differentiation, hypertrophy, and osteogenesis (type-I/-X collagen and alkaline phosphatase expression), with reduced levels of osteoblast-related RUNX-2 transcription factor and β-catenin (osteodifferentiation mediator) and enhanced PTHrP expression (inhibitor of hypertrophic maturation, calcification, and bone formation). This study shows the advantage of modifying hMSCs with rAAV-hBMP-3 to trigger adapted chondroreparative activities as a source of improved cells for transplantation protocols in cartilage defects.

Role of lncRNAs into Mesenchymal Stromal Cell Differentiation

Currently, findings support that 75% of the human genome is actively transcribed, but only 2% is translated into a protein, according to databases such as ENCODE (Encyclopedia of DNA Elements) [1]. The development of high-throughput sequencing technologies, computational methods for genome assembly and biological models have led to the realization of the importance of the previously unconsidered non-coding fraction of the genome. Along with this, noncoding RNAs have been shown to be epigenetic, transcriptional and post-transcriptional regulators in a large number of cellular processes [2]. Within the group of non-coding RNAs, lncRNAs represent a fascinating field of study, given the functional versatility in their mode of action on their molecular targets. In recent years, there has been an interest in learning about lncRNAs in MSC differentiation. The aim of this review is to address the signaling mechanisms where lncRNAs are involved, emphasizing their role in either stimulating or inhibiting the transition to differentiated cell. Specifically, the main types of MSC differentiation are discussed: myogenesis, osteogenesis, adipogenesis and chondrogenesis. The description of increasingly new lncRNAs reinforces their role as players in the well-studied field of MSC differentiation, allowing a step towards a better understanding of their biology and their potential application in the clinic.

Recent Advances in Injectable Dual Crosslinking Hydrogels for Biomedical Applications

Injectable dual crosslinking hydrogels hold great promise to improve therapeutic efficacy in minimally invasive surgery. Compared with prefabricated hydrogels, injectable hydrogels can be implanted more accurately into deeply enclosed sites and repair irregularly shaped lesions, showing great applicable potential. Here, the current fabrication considerations of injectable dual crosslinking hydrogels are reviewed. Besides, the progress of the hydrogels used in corresponding applications and emerging challenges are discussed, with detailed emphasis in the fields of bone and cartilage regeneration, wound dressings, sensors and other less mentioned applications for their more hopeful employments in clinic. It is envisioned that the further development of the injectable dual crosslinking hydrogels will catalyze their innovation and transformation in the biomedical field.

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

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

lncRNA-CRNDE regulates BMSC chondrogenic differentiation and promotes cartilage repair in osteoarthritis through SIRT1/SOX9

Osteoarthritis (OA) is the most common chronic and degenerative joint disease. Although traditional OA medications can partially relieve pain, these medications cannot completely cure OA. Therefore, it is particularly important to find an effective treatment for OA. This study explored the function of long non-coding RNA (lncRNA)-colorectal neoplasia differentially expressed gene (CRNDE) in the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the underlying molecular mechanism, aiming to develop a new treatment method for osteoarthritis. BMSCs were isolated from rat bone marrow using the gradient centrifugation method. And BMSC chondrogenic differentiation was induced with chondrogenic medium. The expression of lncRNA-CRNDE was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Silent information regulator factor 2-related enzyme 1 (SIRT1) and cartilage marker genes Aggrecan and collagen 2 (α1) protein expression were researched using western blot. Alcian blue staining was employed to examine the content of cartilage matrix proteoglycan glycosaminoglycan (GAG). The interaction between lncRNA-CRNDE and SIRT1 was detected by RNA pull-down and RNA immunoprecipitation (RIP) assay. Ubiquitination experiments were performed to measure the ubiquitination level of SIRT1. The combination between SMAD ubiquitination regulatory factor 2 (SMURF2) and SIRT1, as well as SRY-related high-mobility-group box 9 (SOX9) and collagen 2 (α1) promoter, was detected by Co-immunoprecipitation or ChIP. With the prolongation of induction time, the expression of lncRNA-CRNDE, SIRT1, cartilage marker genes Aggrecan and collagen 2 (α1) in BMSC osteogenic differentiation was gradually increased. Also, the content of cartilage matrix proteoglycan GAG was gradually elevated with the extension of the induction time. Further increase in the expression of SIRT1, cartilage marker genes Aggrecan and collagen 2 (α1) by overexpression of lncRNA-CRNDE also indicated elevated GAG content. RNA pull-down and RIP assay confirmed the binding between lncRNA-CRNDE and SIRT1. qRT-PCR and western blot showed that interference with lncRNA-CRNDE significantly inhibited the protein expression of SIRT1. BMSCs transfected with si-CRNDE increased ubiquitination levels of SIRT1 mediated by the E3 ligase SMURF2, leading to the reduced protein stability of SIRT1. However, overexpression of lncRNA-CRNDE increased the binding ability of SOX9 and collagen 2 (α1) promoter, which was reversed by the simultaneous transfection of CRNDE overexpression (pcDNA-CRNDE) and SIRT1 small interfering RNA (si-SIRT1). lncRNA-CRNDE regulates BMSC chondrogenic differentiation to promote cartilage repair in osteoarthritis through SIRT1/SOX9.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Dual functional construct containing kartogenin releasing microtissues and curcumin for cartilage regeneration

BACKGROUND

Regeneration of articular cartilage poses a tremendous challenge due to its limited self-repair capability and inflammation at the damaged site. To generate the desired structures that mimic the structure of native tissue, microtissues with repeated functional units such as cell aggregates have been developed. Multicellular aggregates of mesenchymal stem cells (MSCs) can be used as microscale building blocks of cartilage due to their potential for cell-cell contact, cell proliferation, and differentiation.

METHODS

Chondrogenic microtissues were developed through incorporation of kartogenin-releasing poly (lactic-co-glycolic acid) (PLGA) microparticles (KGN-MP) within the MSC aggregates. The chondrogenic potential of KGN-MP treated MSC aggregates was proven in vitro by studying the chondrogenic markers at the RNA level and histological analysis. In order to address the inflammatory responses at the defect site, the microtissues were delivered in vivo via an injectable, anti-inflammatory hydrogel that contained gelatin methacryloyl (GelMA) loaded with curcumin (Cur).

RESULTS

The KGN-MPs were fabricated to support MSCs during cartilage differentiation. According to real-time RT-PCR analysis, the presence of KGN in the aggregates led to the expression of cartilage markers by the MSCs. Both toluidine blue (TB) and safranin O (SO) staining demonstrated homogeneous glycosaminoglycan production throughout the KGN-MP incorporated MSC aggregates. The curcumin treatment efficiently reduced the expressions of hypertrophy markers by MSCs in vitro. The in vivo results showed that implantation of chondrogenic microtissues (KGN-MP incorporated MSC aggregates) using the curcumin loaded GelMA hydrogel resulted in cartilage tissue regeneration that had characteristic features close to the natural hyaline cartilage according to observational and histological results.

CONCLUSIONS

The use of this novel construct that contained chondrogenic cell blocks and curcumin is highly desired for cartilage regeneration.

Bioprintable tough hydrogels for tissue engineering applications

Bioprinting is an advanced fabrication approach to engineer complex living structures as the conventional fabrication methods are incapable of integrating structural and biological complexities. It offers the versatility of printing different cell incorporated hydrogels (bioink) layer by layer; offering control over spatial resolution and cell distribution to mimic native tissue architectures. However, the bioprinting of tough hydrogels involve additional complexities, such as employing complex crosslinking or reinforcing mechanisms during printing and pre/post printing cellular activities. Solving this complexity requires attention from engineering, material science and cell biology perspectives. In this review, we discuss different types of bioprinting techniques with focus on current state-of-the-art in bioink formulations and pivotal characteristics of bioinks for tough hydrogel printing. We discuss the scope of transition from 3D to 4D bioprinting and some of the advanced characterization techniques for in-depth understanding of the 3D printing process from the microstructural perspective, along with few specific applications and conclude with the future perspectives in biofabrication of hydrogels for tissue engineering applications.

Injectable in situ forming kartogenin-loaded chitosan hydrogel with tunable rheological properties for cartilage tissue engineering

Limited regeneration capacity of cartilage can be addressed by tissue engineering approaches including localized delivery of bioactive agents using biomaterials. Although chitosan hydrogels have been considered as appropriate candidates for these purposes, however, their poor mechanical properties limit their real applications. Here, we develop in situ forming chitosan hydrogels with enhanced shear modulus by chemical modification of chitosan using N-(β-maleimidopropyloxy) succinimide ester (BMPS). Moreover, we utilize β-Glycerophosphate (β-GP) in the hydrogels for achieving thermosensitivity. We investigate the effects of BMPS, β-GP and chitosan concentration on rheological and swelling properties of the hydrogels. Accordingly, we generate significant statistical models by response surface method to predict these properties. These models provide us beneficial tools to tune the hydrogel properties depending on the cartilage defect location and properties. Finally, we incorporate a recently discovered small biomolecule, kartogenin (KGN), for promoting chondrogenesis of stem cells into the optimized hydrogel. The hydrogel's shear modulus is 78 ± 5 kPa which covers a wide range of human articular cartilage shear modulus (50-250 kPa). It can be injected to the defects non-invasively at room temperature which gels at 37 °C within minutes. Additionally, it provides a sustained KGN release for ∼40 days that may eliminate the need of multiple injections. In vitro chondrogenic results confirm enhanced chondrogenic differentiation of human adipose mesenchymal stem cells (hAMSCs) treated with KGN-loaded hydrogel, compared to pure KGN. Based on the enhanced hydrogel shear modulus, injectability, gelation behavior, long-term drug release and in vitro results, this thermosensitive hydrogel looks promising for cartilage tissue engineering.

A novel bovine serum albumin and sodium alginate hydrogel scaffold doped with hydroxyapatite nanowires for cartilage defects repair

Cartilage tissue engineering has become the trend of cartilage defect repair owing to the engineered biomimetic tissue that can mimic the structural, biological and functional characteristics of natural cartilage. Biomaterials with high biocompatibility and regeneration capacity are expected to be used in cartilage tissue engineering. Herein, in this study, a dual-network bovine serum albumin/sodium alginate with hydroxyapatite nanowires composite (B-S-H) hydrogel scaffold has been prepared for cartilage repair. The obtained B-S-H hydrogel scaffold exhibits ideal physical properties, such as excellent mechanical strength, high porosity and swelling ratio, as well as the excellent biological activity to promote the human bone marrow derived mesenchymal stem cells (hBMSCs) proliferation and differentiation. The in vivo study further shows that the B-S -H hydrogel scaffold can obviously promote the generation of new cartilage that integrates well with surrounding tissues and is similar to adjacent cartilage in terms of thickness. It is considered that the B-S-H hydrogel scaffold has great potential in the application of cartilage defects repair.

A novel elastic and controlled-release poly(ether-ester-urethane)urea scaffold for cartilage regeneration

In the tissue engineering of cartilage, scaffolds with appropriate elasticity and controlled-release properties are essential. Herein, we synthesized a poly(ether-ester-urethane)urea scaffold with a pendant amino group (PEEUUN) through a de-protection process from PEEUU-Boc polymers and grafted kartogenin (KGN) onto the PEEUUN scaffolds (PEEUUN-KGN). Characterization, performance tests, scaffold biocompatibility analysis, and chondrogenesis evaluation both in vitro and in vivo were conducted. The results revealed that the PEEUUN-KGN scaffolds were degradable and three-dimensional (3D) with interconnected pores, and possessed good elasticity, as well as excellent cytocompatibility. Meanwhile, KGN on the PEEUUN-KGN scaffolds underwent stable sustained release for a long time and promoted human umbilical cord mesenchymal stem cells (HUCMSCs) to differentiate into chondrocytes in vitro, thus enhancing cartilage regeneration in vivo. In conclusion, the present PEEUUN-KGN scaffolds would have application potential for cartilage tissue engineering.

Bio-ink development for three-dimensional bioprinting of hetero-cellular cartilage constructs

Bioprinting is a promising tool to fabricate organized cartilage. This study aimed to investigate the printability of gelatin-methacryloyl/gellan gum (gelMA/gellan) hydrogels with and without methacrylated hyaluronic acid (HAMA), and to explore (zone-specific) chondrogenesis of chondrocytes, articular cartilage progenitor cells (ACPCs), and multipotent mesenchymal stromal cells (MSCs) embedded in these bio-inks.The incorporating of HAMA in gelMA/gellan bio-ink increased filament stability, as measured using a filament collapse assay, but did not influence (zone-specific) chondrogenesis of any of the cell types. Highest chondrogenic potential was observed for MSCs, followed by ACPCs, which displayed relatively high proteoglycan IV mRNA levels. Therefore, two-zone constructs were printed with gelMA/gellan/HAMA containing ACPCs in the superficial region and MSCs in the middle/deep region. Chondrogenic differentiation was confirmed, however, printing influence cellular differentiation.ACPC- and MSC-laden gelMA/gellan/HAMA hydrogels are of interest for the fabrication of cartilage constructs. Nevertheless, this study underscores the need for careful evaluation of the effects of printing on cellular differentiation.

BMSCs-assisted injectable Col I hydrogel-regenerated cartilage defect by reconstructing superficial and calcified cartilage

The self-healing capacity of cartilage was limited due to absence of vascular, nervous and lymphatic systems. Although many clinical treatments have been used in cartilage defect repair and shown a promising repair result in short term, however, regeneration of complete zonal structure with physiological function, reconstruction cartilage homeostasis and maintaining long-term repair was still an unbridgeable chasm. Cartilage has complex zonal structure and multiple physiological functions, especially, superficial and calcified cartilage played an important role in keeping homeostasis. To address this hurdle of regenerating superficial and calcified cartilage, injectable tissue-induced type I collagen (Col I) hydrogel-encapsulated BMSCs was chosen to repair cartilage damage. After 1 month implantation, the results demonstrated that Col I gel was able to induce BMSCs differentiation into chondrocytes, and formed hyaline-like cartilage and the superficial layer with lubrication function. After 3 months post-surgery, chondrocytes at the bottom of the cartilage layer would undergo hypertrophy and promote the regeneration of calcified cartilage. Six months later, a continuous anatomical tidemark and complete calcified interface were restored. The regeneration of neo-hyaline cartilage was similar with adjacent normal tissue on the thickness of the cartilage, matrix secretion, collagen type and arrangement. Complete multilayer zonal structure with physiological function remodeling indicated that BMSCs-assisted injectable Col I hydrogel could reconstruct cartilage homeostasis and maintain long-term therapeutic effect.

N-methyl-D-aspartate (NMDA) receptor expression and function is required for early chondrogenesis

Background

In vitro chondrogenesis depends on the concerted action of numerous signalling pathways, many of which are sensitive to the changes of intracellular Ca²⁺ concentration. N-methyl-D-aspartate (NMDA) glutamate receptor is a cation channel with high permeability for Ca²⁺. Whilst there is now accumulating evidence for the expression and function of NMDA receptors in non-neural tissues including mature cartilage and bone, the contribution of glutamate signalling to the regulation of chondrogenesis is yet to be elucidated.

Methods

We studied the role of glutamatergic signalling during the course of in vitro chondrogenesis in high density chondrifying cell cultures using single cell fluorescent calcium imaging, patch clamp, transient gene silencing, and western blotting.

Results

Here we show that key components of the glutamatergic signalling pathways are functional during in vitro chondrogenesis in a primary chicken chondrogenic model system. We also present the full glutamate receptor subunit mRNA and protein expression profile of these cultures. This is the first study to report that NMDA-mediated signalling may act as a key factor in embryonic limb bud-derived chondrogenic cultures as it evokes intracellular Ca²⁺ transients, which are abolished by the GluN2B subunit-specific inhibitor ifenprodil. The function of NMDARs is essential for chondrogenesis as their functional knock-down using either ifenprodil or GRIN1 siRNA temporarily blocks the differentiation of chondroprogenitor cells. Cartilage formation was fully restored with the re-expression of the GluN1 protein.

Conclusions

We propose a key role for NMDARs during the transition of chondroprogenitor cells to cartilage matrix-producing chondroblasts.

lncRNAs: function and mechanism in cartilage development, degeneration, and regeneration

With the increasing incidence of cartilage-related diseases such as osteoarthritis (OA) and intervertebral disc degeneration (IDD), heavier financial and social burdens need to be faced. Unfortunately, there is no satisfactory clinical method to target the pathophysiology of cartilage-related diseases. Many gene expressions, signaling pathways, and biomechanical dysregulations were involved in cartilage development, degeneration, and regeneration. However, the underlying mechanism was not clearly understood. Recently, lots of long non-coding RNAs (lncRNAs) were identified in the biological processes, including cartilage development, degeneration, and regeneration. It is clear that lncRNAs were important in regulating gene expression and maintaining chondrocyte phenotypes and homeostasis. In this review, we summarize the recent researches studying lncRNAs’ expression and function in cartilage development, degeneration, and regeneration and illustrate the potential mechanism of how they act in the pathologic process. With continued efforts, regulating lncRNA expression in the cartilage regeneration may be a promising biological treatment approach.

Effects of Stromal Cell-Derived Factor-1α Secreted in Degenerative Intervertebral Disc on Activation and Recruitment of Nucleus Pulposus-Derived Stem Cells

Stromal cell-derived factor-1α (SDF-1α) plays a significant role in mobilizing and recruiting mesenchymal stem cells (MSCs) to the sites of injury. This study investigated the potential of SDF-1α released in the degenerative intervertebral disc (IVD) to activate and recruit endogenous nucleus pulposus-derived stem cells (NPSCs) for regeneration in situ. We found SDF-1α was highly expressed and secreted by the native disc cells when cultured in the proinflammatory mediators in vitro mimicking the degenerative settings. Immunohistochemical staining also showed that the expression level of SDF-1α was significantly higher in the degenerative group compared to that in the normal group. In addition to enhancement of viability, SDF-1α significantly increased the number of NPSCs migrating into the center of the nucleotomized bovine IVD ex vivo. After the systemic delivery of exogenous PKH26-labelled NPSCs into the rats in vivo, there was a significant difference in the distribution of the migrated cells between the normal and the degenerative IVDs, which might be caused by the different expression levels of SDF-1α. However, blocking CXC chemokine receptor 4 (CXCR4) with AMD3100 effectively abrogated SDF-1α-stimulated proliferation and migration. Taken together, SDF-1α may be a key chemoattractant that is highly produced in response to the degenerative changes, which can be used to enhance the proliferation and recruitment of endogenous stem cells into the IVDs. These findings may be of importance for understanding IVD regenerative mechanisms and development of regenerative strategies in situ for IVD degeneration.

A novel construct with biomechanical flexibility for articular cartilage regeneration

BACKGROUND

Although tissue-engineered cartilage has been broadly studied, complete integration of regenerated cartilage with residual cartilage is still difficult for the inferior mechanical and biochemical feature of neocartilage. Chondrogenesis of mesenchymal stem cells can be induced by biophysical and biochemical factors.

METHODS

In this study, autologous platelet-rich fibrin (PRF) membrane was used as a growth factor-rich scaffold that may facilitate differentiation of the transplanted bone marrow mesenchymal stem cells (BMSCs). At the same time, hydrostatic pressure was adopted for pre-adjustment of the seed cells before transplantation that may promote the mechanical flexibility of neocartilage.

RESULTS

An in vitro study showed that the feasible hydrostatic pressure stimulation substantially promoted the chondrogenic potential of in vitro-cultured BMSC/PRF construct. In vivo results revealed that at every time point, the newborn tissues were the most favorable in the pressure-pretreated BMSC/PRF transplant group. Besides, the transplantation of feasible hydrostatic pressure-pretreated construct by BMSC sheet fragments and PRF granules could obviously improve the integration between the regenerated cartilage and host cartilage milieu, and thereby achieve boundaryless repair between the neocartilage and residual host cartilage tissue in rabbit temporomandibular joints. It could be concluded that feasible hydrostatic pressure may effectively promote the proliferation and chondrogenic differentiation of BMSCs in a BMSC/PRF construct.

CONCLUSION

This newly formed construct with biomechanical flexibility showed a superior capacity for cartilage regeneration by promoting the mechanical properties and integration of neocartilage.

Biomimicry in Bio-Manufacturing: Developments in Melt Electrospinning Writing Technology Towards Hybrid Biomanufacturing

Melt electrospinning writing has been emerged as a promising technique in the field of tissue engineering, with the capability of fabricating controllable and highly ordered complex three-dimensional geometries from a wide range of polymers. This three-dimensional (3D) printing method can be used to fabricate scaffolds biomimicking extracellular matrix of replaced tissue with the required mechanical properties. However, controlled and homogeneous cell attachment on melt electrospun fibers is a challenge. The combination of melt electrospinning writing with other tissue engineering approaches, called hybrid biomanufacturing, has introduced new perspectives and increased its potential applications in tissue engineering. In this review, principles and key parameters, challenges, and opportunities of melt electrospinning writing, and particularly, recent approaches and materials in this field are introduced. Subsequently, hybrid biomanufacturing strategies are presented for improved biological and mechanical properties of the manufactured porous structures. An overview of the possible hybrid setups and applications, future perspective of hybrid processes, guidelines, and opportunities in different areas of tissue/organ engineering are also highlighted.

Gelatin-Based Microribbon Hydrogels Accelerate Cartilage Formation by Mesenchymal Stem Cells in Three Dimensions

Hydrogels (HGs) are attractive matrices for cell-based cartilage tissue regeneration given their injectability and ability to fill defects with irregular shapes. However, most HGs developed to date often lack cell scale macroporosity, which restrains the encapsulated cells, leading to delayed new extracellular matrix deposition restricted to pericellular regions. Furthermore, tissue-engineered cartilage using conventional HGs generally suffers from poor mechanical property and fails to restore the load-bearing property of articular cartilage. The goal of this study was to evaluate the potential of macroporous gelatin-based microribbon (μRB) HGs as novel 3D matrices for accelerating chondrogenesis and new cartilage formation by human mesenchymal stem cells (MSCs) in 3D with improved mechanical properties. Unlike conventional HGs, these μRB HGs are inherently macroporous and exhibit cartilage-mimicking shock-absorbing mechanical property. After 21 days of culture, MSC-seeded μRB scaffolds exhibit a 20-fold increase in compressive modulus to 225 kPa, a range that is approaching the level of native cartilage. In contrast, HGs only resulted in a modest increase in compressive modulus of 65 kPa. Compared with conventional HGs, macroporous μRB scaffolds significantly increased the total amount of neocartilage produced by MSCs in 3D, with improved interconnectivity and mechanical strength. Altogether, these results validate gelatin-based μRBs as promising scaffolds for enhancing and accelerating MSC-based cartilage regeneration and may be used to enhance cartilage regeneration using other cell types as well.

Characterization of articular cartilage homeostasis and the mechanism of superior cartilage regeneration of MRL/MpJ mice

This study investigated articular cartilage (AC) homeostasis and different signaling pathways involved in the superior cartilage regeneration of Murphy Roths large (MRL/MpJ) mice previously reported. We collected uninjured and destabilized medial meniscus (DMM)-injured knees from 8-wk-old C57BL/6J and MRL/MpJ mice. We used micro-computed tomography (microCT), histology, and immunohistochemistry to evaluate AC homeostasis and repair. We used the ear punch model to investigate the role of angiogenesis and inflammation in the superior healing of MRL/MpJ mice. We found fewer β-catenin and more pSMAD5 positive cells in the uninjured AC of MRL/MpJ mice than that from C57BL/6J mice. MRL/MpJ mice exhibited better AC repair in DMM-induced OA, as indicated by microCT results, Alcian blue, and Safranin O staining. Mechanistically, fewer β-catenin, pSMAD2-, pSMAD3-, a disintegrin and metalloproteinase with thrombospondin motifs 4-, matrix metalloproteinase (MMP) 9-, and MMP13-positive cells and more proliferating cell nuclear antigen- and pSMAD5-positive cells were found in the DMM-injured AC in MRL/MpJ mice than in normal mice. The accelerated ear wound healing of MRL/MpJ mice correlated with enhanced angiogenesis and macrophage polarization toward the M2a phenotype through elevated IL-10 and IL-4 expressing cells. Collectively, our study revealed that down-regulation of pSMAD2/3, β-catenin, and MMPs and up-regulation of pSMAD5 and M2a macrophage polarization contribute to the enhanced cartilage repair observed in MRL/MpJ mice.-Deng, Z., Gao, X., Sun, X., Amra, S., Lu, A., Cui, Y., Eltzschig, H. K., Lei, G., Huard, J. Characterization of articular cartilage homeostasis and the mechanism of superior cartilage regeneration of MRL/MpJ mice.

Xenotransplantation of human dental pulp stem cells in platelet-rich plasma for the treatment of full-thickness articular cartilage defects in a rabbit model

Stem cells in platelet-rich plasma (PRP) scaffolds may be a promising treatment for cartilage repair. Human dental pulp stem cell (hDPSC) subpopulations have been identified to have substantial angiogenic, neurogenic and regenerative potential when compared with other stem cell sources. The present study evaluated the potential of hDPSCs in a PRP scaffold to regenerate full-thickness cartilage defects in rabbits. Full-thickness articular cartilage defects were created in the patellar groove of the femur of 30 rabbits allocated into three experimental groups: Those with an untreated critical defect (CTL), those treated with PRP (PRP) and those treated with stem cells in a PRP scaffold (PRP+SC). The patellar grooves of the femurs from the experimental groups were evaluated macroscopically and histologically at 6 and 12 weeks post-surgery. The synovial membranes were also collected and evaluated for histopathological analysis. The synovial lining cell layer was enlarged in the CTL group compared with the PRP group at 6 weeks (P=0.037) but not with the PRP+SC group. All groups exhibited low-grade synovitis at 6 weeks and no synovitis at 12 weeks. Notably, macroscopic grades for the area of articular cartilage repair for the PRP+SC group were significantly improved compared with those in the CTL (P=0.001) and PRP (P=0.049) groups at 12 weeks. Furthermore, histological scores (modified O'Driscoll scoring system) of the patellar groove articular cartilage in the PRP+SC and PRP groups, in which the articular cartilage was primarily hyaline-like, were significantly higher compared with those in the CTL group at 12 weeks (P=0.002 and P=0.007, respectively). The present results support the therapeutic use of hDPSCs for the treatment of full-thickness articular cartilage defects.

Combination of kartogenin and transforming growth factor-β3 supports synovial fluid-derived mesenchymal stem cell-based cartilage regeneration

Synovial fluid-derived mesenchymal stem cells (SF-MSCs) represent a superior source of stem cells and have great potential for autologous transplantation for cartilage regeneration. Transforming growth factor-β3 (TGF-β3) has been demonstrated to stimulate the chondrogenic differentiation of MSCs. Recently, the small molecule kartogenin (KGN) was reported to enhance chondrogenic differentiation and cartilage regeneration. The effects of KGN and TGF-β3 on the in vitro chondrogenic differentiation of rabbit SF-MSCs were studied. The monolayer and pellet cultures of rabbit SF-MSCs were stimulated in vitro using either KGN or TGF-β3 alone or in combination for 21 days. The in vivo therapeutic effects of KGN combined with TGF-β3 were studied using an intra-articular delivery of autologous rabbit SF-MSCs to cartilage defects in a rabbit model. Compared to a single treatment, the in vitro results demonstrated that the combination of KGN and TGF-β3 resulted in significantly increased protein expression levels of type II collagen (COL II) and SRY-box 9 (SOX9) and decreased the expression level of type X collagen (COL X). Compared with the regenerated cartilage in the single treatment groups, the intra-articular injection of rabbit SF-MSCs mixed with TGF-β3 and KGN exhibited substantial amounts of regenerated cartilage in the defective areas in the medial femoral condyles. We noted that the thicker, hyaline-like cartilaginous tissue contained abundant levels of extracellular matrix, which is characteristic of cartilage. This study demonstrated that TGF-β3 and KGN exhibit synergistic effects for the promotion of the chondrogenesis of rabbit SF-MSCs and can effectively repair cartilage defects through the regeneration of hyaline cartilage.

Simultaneous Micropatterning of Fibrous Meshes and Bioinks for the Fabrication of Living Tissue Constructs

Fabrication of biomimetic tissues holds much promise for the regeneration of cells or organs that are lost or damaged due to injury or disease. To enable the generation of complex, multicellular tissues on demand, the ability to design and incorporate different materials and cell types needs to be improved. Two techniques are combined: extrusion-based bioprinting, which enables printing of cell-encapsulated hydrogels; and melt electrowriting (MEW), which enables fabrication of aligned (sub)-micrometer fibers into a single-step biofabrication process. Composite structures generated by infusion of MEW fiber structures with hydrogels have resulted in mechanically and biologically competent constructs; however, their preparation involves a two-step fabrication procedure that limits freedom of design of microfiber architectures and the use of multiple materials and cell types. How convergence of MEW and extrusion-based bioprinting allows fabrication of mechanically stable constructs with the spatial distributions of different cell types without compromising cell viability and chondrogenic differentiation of mesenchymal stromal cells is demonstrated for the first time. Moreover, this converged printing approach improves freedom of design of the MEW fibers, enabling 3D fiber deposition. This is an important step toward biofabrication of voluminous and complex hierarchical structures that can better resemble the characteristics of functional biological tissues.

StarPEG/heparin-hydrogel based in vivo engineering of stable bizonal cartilage with a calcified bottom layer

Repaired cartilage tissue lacks the typical zonal structure of healthy native cartilage needed for appropriate function. Current grafts for treatment of full thickness cartilage defects focus primarily on a nonzonal design and this may be a reason why inferior nonzonal regeneration tissue developed in vivo. No biomaterial-based solutions have been developed so far to induce a proper zonal architecture into a non-mineralized and a calcified cartilage layer. The objective was to grow bizonal cartilage with a calcified cartilage bottom zone wherein main tissue development is occurring in vivo. We hypothesized that starPEG/heparin-hydrogel owing to the glycosaminoglycan heparin contained as a building-block would prevent mineralization of the upper cartilage zone and be beneficial in inhibiting long-term progression of calcified cartilage into bone. MSCs were pre-cultured as self-assembling non-mineralized cell discs before a chondrocyte-seeded fibrin- or starPEG/heparin-hydrogel layer was cast on top directly before ectopic implantation. Bizonal cartilage with a calcified bottom-layer developed in vivo showing stronger mineralization compared to in vitro samples, but the hydrogel strongly determined outcome. Zonal fibrin-constructs lost volume and allowed non-organized expansion of collagen type X, ALP-activity and mineralization from the bottom-layer into upper regions, whereas zonal starPEG/heparin-constructs were of stable architecture. While non-zonal MSCs-derived discs formed bone over 12 weeks, the starPEG/heparin-chondrocyte layer prevented further progression of calcified cartilage into bone tissue. Conclusively, starPEG/heparin-hydrogel-controlled and cell-type mediated spatiotemporal regulation allowed in vivo growth of bizonal cartilage with a stable calcified cartilage layer. Altogether our work is an important milestone encouraging direct in vivo growth of organized cartilage after biofabrication.

Biofabrication of human articular cartilage: a path towards the development of a clinical treatment

Cartilage injuries cause pain and loss of function, and if severe may result in osteoarthritis (OA). 3D bioprinting is now a tangible option for the delivery of bioscaffolds capable of regenerating the deficient cartilage tissue. Our team has developed a handheld device, the Biopen, to allow in situ additive manufacturing during surgery. Given its ability to extrude in a core/shell manner, the Biopen can preserve cell viability during the biofabrication process, and it is currently the only biofabrication tool tested as a surgical instrument in a sheep model using homologous stem cells. As a necessary step toward the development of a clinically relevant protocol, we aimed to demonstrate that our handheld extrusion device can successfully be used for the biofabrication of human cartilage. Therefore, this study is a required step for the development of a surgical treatment in human patients. In this work we specifically used human adipose derived mesenchymal stem cells (hADSCs), harvested from the infra-patellar fat pad of donor patients affected by OA, to also prove that they can be utilized as the source of cells for the future clinical application. With the Biopen, we generated bioscaffolds made of hADSCs laden in gelatin methacrylate, hyaluronic acid methacrylate and cultured in the presence of chondrogenic stimuli for eight weeks in vitro. A comprehensive characterisation including gene and protein expression analyses, immunohistology, confocal microscopy, second harmonic generation, light sheet imaging, atomic force mycroscopy and mechanical unconfined compression demonstrated that our strategy resulted in human hyaline-like cartilage formation. Our in situ biofabrication approach represents an innovation with important implications for customizing cartilage repair in patients with cartilage injuries and OA.

Melatonin-mediated miR-526b-3p and miR-590-5p upregulation promotes chondrogenic differentiation of human mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (BMSCs), with inherent chondrogenic differentiation potential appear to be ideally suited for therapeutic use in cartilage regeneration. Accumulating evidence has demonstrated that melatonin can promote chondrogenic differentiation in human BMSCs. However, little is known about the mechanism. MicroRNAs (miRNAs) have been shown to regulate the differentiation of BMSCs, but their roles in melatonin-promoted chondrogenic differentiation have not been characterized. Here, we demonstrate that melatonin promoted chondrogenic differentiation of human BMSCs via upregulation of miR-526b-3p and miR-590-5p. Mechanistically, the elevated miR-526b-3p and miR-590-5p enhanced SMAD1 phosphorylation by targeting SMAD7. Additionally, administration of miR-526b-3p mimics or miR-590-5p mimics successfully promoted the chondrogenic differentiation of human BMSCs. Collectively, our study suggests that modification of BMSCs using melatonin or miRNA transduction could be an effective therapy for cartilage damage and degeneration.

Adipose-Derived Mesenchymal Stem Cells in the Use of Cartilage Tissue Engineering: The Need for a Rapid Isolation Procedure

Mesenchymal stem cells (MSCs) have shown much promise with respect to their use in cartilage tissue engineering. MSCs can be obtained from many different tissue sources. Among these, adipose tissue can provide an abundant source of adipose-derived mesenchymal stem cells (ADMSCs). The infrapatellar fat pad (IFP) is a promising source of ADMSCs with respect to producing a cartilage lineage. Cell isolation protocols to date are time-consuming and follow conservative approaches that rely on a long incubation period of 24–48 hours. The different types of ADMSC isolation techniques used for cartilage repair will be reviewed and compared with the view of developing a rapid one-step isolation protocol that can be applied in the context of a surgical procedure.

Biodiversity of CS–proteoglycan sulphation motifs: chemical messenger recognition modules with roles in information transfer, control of cellular behaviour and tissue morphogenesis

Chondroitin sulphate (CS) glycosaminoglycan chains on cell and extracellular matrix proteoglycans (PGs) can no longer be regarded as merely hydrodynamic space fillers. Overwhelming evidence over recent years indicates that sulphation motif sequences within the CS chain structure are a source of significant biological information to cells and their surrounding environment. CS sulphation motifs have been shown to interact with a wide variety of bioactive molecules, e.g. cytokines, growth factors, chemokines, morphogenetic proteins, enzymes and enzyme inhibitors, as well as structural components within the extracellular milieu. They are therefore capable of modulating a panoply of signalling pathways, thus controlling diverse cellular behaviours including proliferation, differentiation, migration and matrix synthesis. Consequently, through these motifs, CS PGs play significant roles in the maintenance of tissue homeostasis, morphogenesis, development, growth and disease. Here, we review (i) the biodiversity of CS PGs and their sulphation motif sequences and (ii) the current understanding of the signalling roles they play in regulating cellular behaviour during tissue development, growth, disease and repair.

Three-Dimensional Bioprinting and Its Potential in the Field of Articular Cartilage Regeneration

Three-dimensional (3D) bioprinting techniques can be used for the fabrication of personalized, regenerative constructs for tissue repair. The current article provides insight into the potential and opportunities of 3D bioprinting for the fabrication of cartilage regenerative constructs. Although 3D printing is already used in the orthopedic clinic, the shift toward 3D bioprinting has not yet occurred. We believe that this shift will provide an important step forward in the field of cartilage regeneration. Three-dimensional bioprinting techniques allow incorporation of cells and biological cues during the manufacturing process, to generate biologically active implants. The outer shape of the construct can be personalized based on clinical images of the patient's defect. Additionally, by printing with multiple bio-inks, osteochondral or zonally organized constructs can be generated. Relevant mechanical properties can be obtained by hybrid printing with thermoplastic polymers and hydrogels, as well as by the incorporation of electrospun meshes in hydrogels. Finally, bioprinting techniques contribute to the automation of the implant production process, reducing the infection risk. To prompt the shift from nonliving implants toward living 3D bioprinted cartilage constructs in the clinic, some challenges need to be addressed. The bio-inks and required cartilage construct architecture need to be further optimized. The bio-ink and printing process need to meet the sterility requirements for implantation. Finally, standards are essential to ensure a reproducible quality of the 3D printed constructs. Once these challenges are addressed, 3D bioprinted living articular cartilage implants may find their way into daily clinical practice.

Electrospun Nanofibrous Meshes Cultured With Wharton's Jelly Stem Cell: An Alternative for Cartilage Regeneration, Without the Need of Growth Factors

Many efforts are being directed worldwide to the treatment of OA-focal lesions. The majority of those efforts comprise either the refinement of surgical techniques or combinations of biomaterials with various autologous cells. Herein, we tested electrospun polycaprolactone (PCL) nanofibrous meshes for cartilage tissue engineering. For that, articular chondrocytes (hACs) isolated from human osteoarthritic joints and Wharton's Jelly Stem Cells (hWJSCs) are cultured on electrospun nanofiber meshes, without adding external growth factors. We observed higher glycosaminoglycans production and higher over-expression of cartilage-related genes from hWJSCs cultured with basal medium, when compared to hACs isolated from osteoarthritic joints. Moreover, the presence of sulfated proteoglycans and collagen type II is observed on both types of cell cultures. We believe that this effect is due to either the electrospun nanofibers topography or the intrinsic chondrogenic differentiation potential of hWJSCs. Therefore, we propose the electrospun nanofibrous scaffolds in combination with hWJSCs as a viable alternative to the commercial membranes used in autologous chondrogenic regeneration approaches.

Combination of bone marrow mesenchymal stem cells and cartilage fragments contribute to enhanced repair of osteochondral defects

Cartilage tissue engineering using stem cells and biomaterials is considered a promising approach despite poor outcomes. We hypothesise that articular cartilage fragments provides native environmental cues to enhance stem cell differentiation. As such we evaluated the chondrogenic differentiation and repair of critical size defect in a human explant osteochondral model (OD) using bone marrow derived mesenchymal stem cells (BM-MSCs) and homogenised cartilage. BM-MSCs were established from the bone-marrow plugs of patients undergoing total knee arthroplasty and characterized. Osteochondral tissue was trimmed and a central drill defect (∼2mm) was made. Chondrogenic repair was evaluated by filling the OD defect area with either BM-MSCs (Group II), homogenized cartilage (Group III) or a combination of both BM-MSCs and homogenized cartilage (Group IV). OD with no added cell or tissue served as control (Group I). Samples were maintained in chondrogenic differentiation medium for 28 days. Microscopic images showed maximal OD closure in Group IV. Partial OD closure was observed in Group II and to a lesser extent in Group III. Haematoxylin-eosin staining revealed immature cartilaginous matrix in Group II and more mature matrix in Group IV. Sircol™ Assay showed increased collagen deposition in both Group II and Group IV. Immunostaining for both groups revealed positive staining for type II collagen. Combining BM-MSCs and homogenised cartilage demonstrated enhanced cartilage formation and defect filling in a human ex-vivo osteochondral model.

Fast fabrication of stable cartilage-like tissue using collagen hydrogel microsphere culture

Fabrication of cartilage-like tissue by mimicking chondrogenesis of MSCs in collagen hydrogel microsphere (CHM) culture.

Bilayer Implants: Electromechanical Assessment of Regenerated Articular Cartilage in a Sheep Model

OBJECTIVE

To compare the regenerative capacity of 2 distinct bilayer implants for the restoration of osteochondral defects in a preliminary sheep model.

METHODS

Critical sized osteochondral defects were treated with a novel biomimetic poly-ε-caprolactone (PCL) implant (Treatment No. 2; n = 6) or a combination of Chondro-Gide and Orthoss (Treatment No. 1; n = 6). At 19 months postoperation, repair tissue (n = 5 each) was analyzed for histology and biochemistry. Electromechanical mappings (Arthro-BST) were performed ex vivo.

RESULTS

Histological scores, electromechanical quantitative parameter values, dsDNA and sGAG contents measured at the repair sites were statistically lower than those obtained from the contralateral surfaces. Electromechanical mappings and higher dsDNA and sGAG/weight levels indicated better regeneration for Treatment No. 1. However, these differences were not significant. For both treatments, Arthro-BST revealed early signs of degeneration of the cartilage surrounding the repair site. The International Cartilage Repair Society II histological scores of the repair tissue were significantly higher for Treatment No. 1 (10.3 ± 0.38 SE) compared to Treatment No. 2 (8.7 ± 0.45 SE). The parameters cell morphology and vascularization scored highest whereas tidemark formation scored the lowest.

CONCLUSION

There was cell infiltration and regeneration of bone and cartilage. However, repair was incomplete and fibrocartilaginous. There were no significant differences in the quality of regeneration between the treatments except in some histological scoring categories. The results from Arthro-BST measurements were comparable to traditional invasive/destructive methods of measuring quality of cartilage repair.

Angiogenic Potential of Human Bone Marrow-Derived Mesenchymal Stem Cells in Chondrocyte Brick-Enriched Constructs Promoted Stable Regeneration of Craniofacial Cartilage

Craniofacial deformities caused by congenital defects or trauma remain challenges for clinicians, whereas current surgical interventions present limited therapeutic outcomes. Injection of bone marrow‐derived mesenchymal stem cells (BMSCs) into the defect is highly desirable because such a procedure is microinvasive and grafts are more flexible to fill the lesions. However, preventing hypertrophic transition and morphological contraction remain significant challenges. We have developed an “all host derived” cell transplantation system composed of chondrocyte brick (CB)‐enriched platelet‐rich plasma (P) gel and BMSCs (B). Without exogenous biomaterials or growth factors, such grafts regenerate cartilage efficiently and present great clinical promise. In immunodeficient mice, we compared performance of BMSCs and BMSCs lacking angiogenic potential in CB‐B‐P constructs and followed the cartilage maturation process by histology, immunostaining, micro‐computed tomography, and protein analysis. We determined that angiogenesis occurred quickly inside rudimentary cartilage derived from CB‐B‐P constructs after implantation, which improved tissue survival, tissue growth, and production of chondrogenic signals from chondrocytes. In contrast, silencing angiogenic potential of BMSCs led to poor chondrogenesis accompanied by necrosis. Chondrocyte bricks merged rapidly with angiogenesis, which constituted an enclosed chondrogenic niche and effectively inhibited runt‐related transcription factor‐2‐dependent hypertrophic transition of BMSCs as well as endochondral ossification; progressive chondrogenic differentiation of BMSCs resulted in vascularization regression, thus favoring persistent chondrogenesis and effectively augmenting nasal cartilage. In conclusion, these findings provided a novel, efficient approach to regenerating cartilage tissues in vivo. Chondrocyte bricks mixed with P provide transient vascularization and a persistently chondrogenic microenvironment for BMSCs; this provides a mini‐invasive approach for craniofacial cartilage reconstruction. Stem Cells Translational Medicine2017;6:601–612

The CS Sulfation Motifs 4C3, 7D4, 3B3[-]; and Perlecan Identify Stem Cell Populations and Their Niches, Activated Progenitor Cells and Transitional Areas of Tissue Development in the Fetal Human Elbow

We compared the immunohistochemical distribution of (1) the novel chondroitin sulfate (CS) sulfation motifs 7D4, 4C3, and 3B3[-], (2) native heparan sulfate (HS) and Δ-HS "stubs" generated by heparitinase III digestion and (3) the HS-proteoglycan (PG), perlecan, in the fetal human elbow joint. Putative stem cell populations associated with hair bulbs, humeral perichondrium, humeral and ulnar rudiment stromal/perivascular tissues expressed the CS motifs 4C3, 7D4, and 3B3[-] along with perlecan in close association but not colocalized. Chondrocytes in the presumptive articular cartilage of the fetal elbow expressed the 4C3 and 7D4 CS sulfation motifs consistent with earlier studies on the expression of these motifs in knee cartilage following joint cavitation. This study also indicated that hair bulbs, skin, perichondrium, and rudiment stroma were all perlecan-rich progenitor cell niches that contributed to the organization and development of the human fetal elbow joint and associated connective tissues. One of the difficulties in determining the precise role of stem cells in tissue development and repair processes is their short engraftment period and the lack of specific markers, which differentiate the activated stem cell lineages from the resident cells. The CS sulfation motifs 7D4, 4C3, and 3B3[-] decorate cell surface PGs on activated stem/progenitor cells and thus can be used to identify these cells in transitional areas of tissue development and in repair tissues and may be applicable to determining a more precise mode of action of stem cells in these processes. Isolation of perlecan from 12 to 14 week gestational age fetal knee rudiments demonstrated that perlecan in these fetal tissues was a HS-CS hybrid PG further supporting roles for CS in tissue development.

MicroRNA-30a promotes chondrogenic differentiation of mesenchymal stem cells through inhibiting Delta-like 4 expression

AIMS

MicroRNAs (miRNAs) play important roles in chondrogenic differentiation of mesenchymal stem cells (MSCs). However, the regulation of miR-30a during such process has not yet been well understood. The aim of the study was to investigate the effects of miR-30a on chondrogenic differentiation of MSCs and explore the underlying mechanisms.

MATERIALS AND METHODS

MSCs were isolated from rat bone marrow, and their immunophenotypes and multilineage differentiation potentials were identified. MiR-30a mimics or inhibitor were transfected into rat MSCs and SW1353 cells, respectively, and then the effects of miR-30a on chondrogenic differentiation were detected. The predicted target gene Delta-like 4 (DLL4, a ligand of the Notch signaling family) was verified by luciferase reporter assay, quantitative real time PCR and western blot.

KEY FINDINGS

MiR-30a was significantly up-regulated during chondrogenic differentiation of rat MSCs. Additionally, transfection of miR-30a mimics remarkably promoted the differentiation of rat MSCs into chondrocytes as evidence by the notably increased mRNA and protein expression levels of chondrogenic markers Collagen II and aggrecan as well as the enhanced alcian blue staining intensity, whereas inhibition of miR-30a obviously suppressed such process. Furthermore, during chondrogenesis, DLL4 expression was found to significantly decrease at both mRNA and protein levels, which was negatively regulated by miR-30a through directly targeting the 3'UTR of DLL4.

SIGNIFICANCE

Our results indicate that miR-30a acts as a key promoter for chondrogenic differentiation of MSCs by down-regulating DLL4 expression, and provide a novel insight on miRNA-mediated MSC therapy for cartilage-related disorders including osteoarthritis.

Photo-Cross-Linked Scaffold with Kartogenin-Encapsulated Nanoparticles for Cartilage Regeneration

The regeneration of cartilage, an aneural and avascular tissue, is often compromised by its lack of innate abilities to mount a sufficient healing response. Kartogenin (KGN), a small molecular compound, can induce bone marrow-derived mesenchymal stem cells (BMSCs) into chondrocytes. The previous in vitro study showed that kartogenin also had a chondrogenesis effect on synovium derived mesenchymal stem cells (SMSCs). Herein, we present the effect of an ultraviolet-reactive, rapidly cross-linkable scaffold integrated with kartogenin-loaded nanoparticles using an innovational one-step technology. In vivo studies showed its potential role for cell homing, especially for recruiting the host's endogenous cells, including BMSCs and SMSCs, without cell transplantation. Of note, the regenerated tissues were close to the natural hyaline cartilage based on the histological tests, specific markers analysis, and biomechanical tests. This innovative KGN release system makes the chondrogenesis efficient and persistent.