Chondrogenesis by bone marrow‐derived mesenchymal stem cells grown in chondrocyte‐conditioned medium for auricular reconstruction

The role of plasma-induced surface chemistry on polycaprolactone nanofibers to direct chondrogenic differentiation of human mesenchymal stem cells

Bone marrow-derived mesenchymal stromal cells (BMSCs) are extensively being utilized for cartilage regeneration owing to their excellent differentiation potential and availability. However, controlled differentiation of BMSCs towards cartilaginous phenotypes to heal full-thickness cartilage defects remains challenging. This study investigates how different surface properties induced by either coating deposition or biomolecules immobilization onto nanofibers (NFs) could affect BMSCs chondro-inductive behavior. Accordingly, electrospun poly(ε-caprolactone) (PCL) NFs were exposed to two surface modification strategies based on medium-pressure plasma technology. The first strategy is plasma polymerization, in which cyclopropylamine (CPA) or acrylic acid (AcAc) monomers were plasma polymerized to obtain amine- or carboxylic acid-rich NFs, respectively. The second strategy uses a combination of CPA plasma polymerization and a post-chemical technique to immobilize chondroitin sulfate (CS) onto the NFs. These modifications could affect surface roughness, hydrophilicity, and chemical composition while preserving the NFs' nano-morphology. The results of long-term BMSCs culture in both basic and chondrogenic media proved that the surface modifications modulated BMSCs chondrogenic differentiation. Indeed, the incorporation of polar groups by different modification strategies had a positive impact on the cell proliferation rate, production of the glycosaminoglycan matrix, and expression of extracellular matrix proteins (collagen I and collagen II). The chondro-inductive behavior of the samples was highly dependent on the nature of the introduced polar functional groups. Among all samples, carboxylic acid-rich NFs promoted chondrogenesis by higher expression of aggrecan, Sox9, and collagen II with downregulation of hypertrophic markers. Hence, this approach showed an intrinsic potential to have a non-hypertrophic chondrogenic cell phenotype.

The application and progress of stem cells in auricular cartilage regeneration: a systematic review

Background: The treatment of microtia or acquired ear deformities by surgery is a significant challenge for plastic and ENT surgeons; one of the most difficult points is constructing the scaffold for auricular reconstruction. As a type of cell with multiple differentiation potentials, stem cells play an essential role in the construction of cartilage scaffolds, and therefore have received widespread attention in ear reconstructive research. Methods: A literature search was conducted for peer-reviewed articles between 2005 and 2023 with the following keywords: stem cells; auricular cartilage; ear cartilage; conchal cartilage; auricular reconstruction, regeneration, and reparation of chondrocytes; tissue engineering in the following databases: PubMed, MEDLINE, Cochrane, and Ovid. Results: Thirty-three research articles were finally selected and their main characteristics were summarized. Adipose-derived stem cells (ADSCs), bone marrow mesenchymal stem cells (BMMSCs), perichondrial stem/progenitor cells (PPCs), and cartilage stem/progenitor cells (CSPCs) were mainly used in chondrocyte regeneration. Injecting the stem cells into the cartilage niche directly, co-culturing the stem cells with the auricular cartilage cells, and inducing the cells in the chondrogenic medium in vitro were the main methods that have been demonstrated in the studies. The chondrogenic ability of these cells was observed in vitro, and they also maintained good elasticity and morphology after implantation in vivo for a period of time. Conclusion: ADSC, BMMSC, PPC, and CSPC were the main stem cells that have been researched in craniofacial cartilage reconstruction, the regenerative cartilage performed highly similar to normal cartilage, and the test of AGA and type II collagen content also proved the cartilage property of the neo-cartilage. However, stem cell reconstruction of the auricle is still in the initial stage of animal experiments, transplantation with such scaffolds in large animals is still lacking, and there is still a long way to go.

Mesenchymal Stromal Cells in Osteoarthritis: Evidence for Structural Benefit and Cartilage Repair

Osteoarthritis (OA) presents a major clinical challenge to rheumatologists and orthopedists due to the lack of available drugs reducing structural degradation. Mesenchymal stromal cells (MSCs) may represent new therapeutic approaches in cartilage regeneration. In this review, we highlight the latest knowledge on the biological properties of MSC, such as their chondrogenic and immunomodulatory potential, and we give a brief overview of the effects of MSCs in preclinical and clinical studies of OA treatment and also compare different MSC sources, with the adipose tissue-derived MSCs being promising. Then, we focus on their structural benefit in treating OA and summarize the current evidence for the assessment of cartilage in OA according to magnetic resonance imaging (MRI) and second-look arthroscopy after MSC therapy. Finally, this review provides a brief perspective on enhancing the activity of MSCs.

Effect of passage number of genetically modified TGF-β3 expressing primary chondrocytes on the chondrogenesis of ATDC5 cells in a 3D coculture system

Due to the lack of blood vessels, nerves and lymphatics, articular cartilage is difficult to repair once damaged. Tissue engineering is considered to be a potential strategy for cartilage regeneration. Successful tissue engineering strategies depend on the effective combination of biomaterials, seed cells and biological factors. In our previous study, a genetically modified coculture system with chondrocytes and ATDC5 cells in an alginate hydrogel has exhibited a superior ability to enhance chondrogenesis. In this study, we further evaluated the influence of chondrocytes at various passages on chondrogenesis in the coculture system. The results demonstrated that transfection efficiency was hardly influenced by the passage of chondrocytes. The coculture system with passage 5 (P5) chondrocytes had a better effect on chondrogenesis of ATDC 5 cells, while chondrocytes in this coculture system presented higher levels of dedifferentiation than other groups with P1 or P3 chondrocytes. Therefore, P5 chondrocytes were shown to be more suitable for the coculture system, as they accumulated in sufficient cell numbers with more passages and had a higher level of dedifferentiation, which was prone to form a favorable niche for chondrogenesis of ATDC5 cells. This study may provide fresh insights for future cartilage tissue engineering strategies with a combination of a coculture system and advanced biomaterials.

Static Magnetic Fields Enhance the Chondrogenesis of Mandibular Bone Marrow Mesenchymal Stem Cells in Coculture Systems

Objectives

Combining the advantages of static magnetic fields (SMF) and coculture systems, we investigated the effect of moderate-intensity SMF on the chondrogenesis and proliferation of mandibular bone marrow mesenchymal stem cells (MBMSCs) in the MBMSC/mandibular condylar chondrocyte (MCC) coculture system. The main aim of the present study was to provide an experimental basis for obtaining better cartilage tissue engineering seed cells for the effective repair of condylar cartilage defects in clinical practice.

Methods

MBMSCs and MCCs were isolated from SD (Sprague Dawley) rats. Flow cytometry, three-lineage differentiation, colony-forming assays, immunocytochemistry, and toluidine blue staining were used for the identification of MBMSCs and MCCs. MBMSCs and MCCs were seeded into the lower and upper Transwell chambers, respectively, at a ratio of 1 : 2, and exposed to a 280 mT SMF. MBMSCs were harvested after 3, 7, or 14 days for analysis. CCK-8 was used to detect cell proliferation, Alcian blue staining was utilized to evaluate glycosaminoglycan (GAG), and western blotting and real-time quantitative polymerase chain reaction (RT-qPCR) detected protein and gene expression levels of SOX9, Col2A1 (Collagen Type II Alpha 1), and Aggrecan (ACAN).

Results

The proliferation of MBMSCs was significantly enhanced in the experimental group with MBMSCs cocultured with MCCs under SMF stimulation relative to controls (P < 0.05). GAG content was increased, and SOX9, Col2A1, and ACAN were also increased at the mRNA and protein levels (P < 0.05).

Conclusions

Moderate-intensity SMF improved the chondrogenesis and proliferation of MBMSCs in the coculture system, and it might be a promising approach to repair condylar cartilage defects in the clinical setting.

Chondrogenic Characteristics of Auricular Chondrocytes Cocultured With Adipose-Derived Stem Cells are Superior to Stromal Vascular Fraction of Adipose Tissue

ABSTRACT

Reconstruction of craniofacial cartilage defects is among the most challenging operations in facial plastic surgery. The co-culture system of partial replacement of chondrocytes by stem cells has been confirmed effective in the repair of cartilaginous defects. The aim of this study is to compare chondrogenic properties of expanded adipose-derived stem cells (ADSCs) and stromal vascular fraction (SVF), including ADSCs/SVF monoculture and coculture with rabbit auricular chondrocytes (ACs). Analysis of morphology, histology, real-time polymerase chain reaction and glycosaminoglycans (GAG) quantification were performed to characterize the chondrogenesis of pellets. The triple differentiation potential of ADSCs had been confirmed. Further, using flow cytometry, the authors demonstrated that ADSCs and SVF have different characteristics in cell surface markers, and ADSCs are more enriched in cells from the mesenchymal lineage than SVF. GAG production of ADSCs is significantly higher than that of SVF in pellet monoculture, and pellet coculture of ADSCs and ACs are better in depositing cartilage matrix than the mixture of SVF and ACs. Our study suggests that ADSCs may be more suitable seed cells for craniofacial cartilage defect or deformity repair.

Cell Sources for Cartilage Repair-Biological and Clinical Perspective

Cell-based therapy represents a promising treatment strategy for cartilage defects. Alone or in combination with scaffolds/biological signals, these strategies open many new avenues for cartilage tissue engineering. However, the choice of the optimal cell source is not that straightforward. Currently, various types of differentiated cells (articular and nasal chondrocytes) and stem cells (mesenchymal stem cells, induced pluripotent stem cells) are being researched to objectively assess their merits and disadvantages with respect to the ability to repair damaged articular cartilage. In this paper, we focus on the different cell types used in cartilage treatment, first from a biological scientist’s perspective and then from a clinician’s standpoint. We compare and analyze the advantages and disadvantages of these cell types and offer a potential outlook for future research and clinical application.

Effect of human articular chondroprogenitor derived conditioned media on chondrogenic potential of bone marrow derived mesenchymal stromal cells

Background:

Current research in cartilage repair is focusing on the use of soluble factors released by cells during expansion, either as stand-alone therapy or as conditioned media (CM) supplements to optimize cellular phenotype for in-vivo transplantation. The present study aimed at utilizing spent media from cultured human articular cartilage derived chondroprogenitors and assessing their influence on bone marrow mesenchymal stem cell (BM-MSC) growth and phenotype.

Methodology:

CM was collected from passage 2 chondroprogenitors and evaluated for latent TGFβ1 levels. Passage 3 BM-MSCs were divided into two groups and cultured with either a) standard expansion medium (EM-group) or b) EM supplemented with 50% CM (CCM-group). At sub-confluence both groups were assessed for population doubling, migration assay, cell surface markers, gene expression for chondrogenic and hypertrophy markers. Additionally, pellet cultures were subjected to chondrogenic differentiation and analyzed by Alcian blue stain.

Results:

On analysis of proliferation and migration, CCM-group showed comparable results to EM in terms of population doubling and cell movement toward scratched area. Similarly, use of spent medium did not affect the surface protein or gene expression profile of BM-MSCs with similar flow cytometric and mRNA results seen in both groups. Glycosaminoglycan deposition (Alcian blue) was seen in the CCM-group, comparable to the EM-group.

Conclusion:

This preliminary report provided valuable information on the influence of unfractionated CCM on BM-MSC characteristics which may be further optimized for cartilage regeneration by the use of purified components such as exosomes, micro-vesicles, and concentrated trophic factors in future.

Biofabrication of a shape-stable auricular structure for the reconstruction of ear deformities

Bioengineering of the human auricle remains a significant challenge, where the complex and unique shape, the generation of high-quality neocartilage, and shape preservation are key factors. Future regenerative medicine–based approaches for auricular cartilage reconstruction will benefit from a smart combination of various strategies. Our approach to fabrication of an ear-shaped construct uses hybrid bioprinting techniques, a recently identified progenitor cell population, previously validated biomaterials, and a smart scaffold design. Specifically, we generated a 3D-printed polycaprolactone (PCL) scaffold via fused deposition modeling, photocrosslinked a human auricular cartilage progenitor cell–laden gelatin methacryloyl (gelMA) hydrogel within the scaffold, and cultured the bioengineered structure in vitro in chondrogenic media for 30 days. Our results show that the fabrication process maintains the viability and chondrogenic phenotype of the cells, that the compressive properties of the combined PCL and gelMA hybrid auricular constructs are similar to native auricular cartilage, and that biofabricated hybrid auricular structures exhibit excellent shape fidelity compared with the 3D digital model along with deposition of cartilage-like matrix in both peripheral and central areas of the auricular structure. Our strategy affords an anatomically enhanced auricular structure with appropriate mechanical properties, ensures adequate preservation of the auricular shape during a dynamic in vitro culture period, and enables chondrogenically potent progenitor cells to produce abundant cartilage-like matrix throughout the auricular construct. The combination of smart scaffold design with 3D bioprinting and cartilage progenitor cells holds promise for the development of clinically translatable regenerative medicine strategies for auricular reconstruction.

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First application of human auricular cartilage progenitor cells for bioprinting.

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Dual-printing of hybrid ear-shaped constructs with excellent shape fidelity over time.

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Strategy and design ensured adequate deposition of cartilage-like matrix throughout large auricular constructs.

Cartilage Repair by Mesenchymal Stem Cell-Derived Exosomes: Preclinical and Clinical Trial Update and Perspectives

Osteoarthritis (OA) and other degenerative joint diseases are characterized by articular cartilage destruction, synovial inflammation, sclerosis of subchondral bone, and loss of extracellular matrix (ECM). Worldwide, these diseases are major causes of disability. Cell therapies have been considered to be the best therapeutic strategies for long-term treatment of articular cartilage diseases. It has been suggested that the mechanism of stem cell-based therapy is related to paracrine secretion of extracellular vesicles (EVs), which are recognized as the main secretion factors of stem cells. EVs, and in particular the subclass exosomes (Exos), are novel therapeutic approaches for treatment of cartilage lesions and OA. The results of recent studies have shown that EVs isolated from mesenchymal stem cells (MSCs) could inhibit OA progression. EVs isolated from various stem cell sources, such as MSCs, may contribute to tissue regeneration of the limbs, skin, heart, and other tissues. Here, we summarize recent findings of preclinical and clinical studies on different MSC-derived EVs and their effectiveness as a treatment for damaged cartilage. The Exos isolation techniques in OA treatment are also highlighted.

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

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

Tissue engineering applications in otolaryngology-The state of translation

While tissue engineering holds significant potential to address current limitations in reconstructive surgery of the head and neck, few constructs have made their way into routine clinical use. In this review, we aim to appraise the state of head and neck tissue engineering over the past five years, with a specific focus on otologic, nasal, craniofacial bone, and laryngotracheal applications. A comprehensive scoping search of the PubMed database was performed and over 2000 article hits were returned with 290 articles included in the final review. These publications have addressed the hallmark characteristics of tissue engineering (cellular source, scaffold, and growth signaling) for head and neck anatomical sites. While there have been promising reports of effective tissue engineered interventions in small groups of human patients, the majority of research remains constrained to in vitro and in vivo studies aimed at furthering the understanding of the biological processes involved in tissue engineering. Further, differences in functional and cosmetic properties of the ear, nose, airway, and craniofacial bone affect the emphasis of investigation at each site. While otolaryngologists currently play a role in tissue engineering translational research, continued multidisciplinary efforts will likely be required to push the state of translation towards tissue-engineered constructs available for routine clinical use.

LEVEL OF EVIDENCE

NA.

Enhanced chondrogenesis in a coculture system with genetically manipulated dedifferentiated chondrocytes and ATDC5 cells

Articular cartilage repair after injury is a great challenge worldwide due to its nerveless and avascular features. Tissue engineering is proposed as a promising alternative for cartilage regeneration. In this study, an adenoviral vector carrying the transforming growth factor-β3 (TGF-β3) gene was constructed and introduced into dedifferentiated chondrocytes, which were then cocultured with ATDC5 cells in an alginate hydrogel system. The results showed that the experimental groups exhibited better cell viability and higher levels of cartilage-related genes than the control groups. In this coculture system, the chondrogenic differentiation of ATDC5 cells was effectively induced by TGF-β3 and other latent cytokines that were produced by the transfected chondrocytes. Thus, this method can avoid the degradation of exogenous TGF-β3, and it can protect ATDC5 cells during virus transfection to maintain cell viability and chondrogenic differentiation capability. Taken together, this study provides fresh insights for applying this genetically manipulated coculture system to cartilage repair in the future.

Human chondrocyte-conditioned medium promotes chondrogenesis of bone marrow stem cells

Background

Cell-based therapy for osteoarthritis requires culturing of good quality cells, especially with a chondrogenic lineage, for implantation.

Objective

To investigate the ability of chondrocyte-conditioned medium (CCM) to induced chondrogenesis.

Methods

Bone marrow mesenchymal stem cells (BMSCs) were subjected to chondrogenic induction using CCM and chondrocyte induction medium (CIM). The optimal condition for the collection of CCM was evaluated by quantifying the concentration of secreted proteins. The chondrogenic efficiency of BMSCs induced by CCM (iCCM) was evaluated using immunocytochemical analysis, Safranin-O staining, and gene expression.

Results

Protein quantification revealed that CCM obtained from cells at passage 3 at the 72 h collection point had the greatest amount of protein. Supplementation of CCM results in the aggregation of BMSCs; however, no clumping was visible as in iCIM. The expression of collagen type 2 was detected as early as day 7 for all groups except for non-induced BMSCs; however, the level of expression decreased with culture time. Similarly, all tested groups showed positive staining for Safranin-O as early as day 7. The induction of BMSCs by CCM caused the down-regulation of collagen type 1, along with the up-regulation of the collagen type 2, ACP and SOX9 genes.

Conclusion

The optimum CCM to induce BMSC into chondrocytes was collected at passage 3 after 72 h and was used in a 50:50 ratio of CCM to fresh medium.

Transplantation of a 3D-printed tracheal graft combined with iPS cell-derived MSCs and chondrocytes

For successful tracheal reconstruction, tissue-engineered artificial trachea should meet several requirements, such as biocompatible constructs comparable to natural trachea, coverage with ciliated respiratory mucosa, and adequate cartilage remodeling to support a cylindrical structure. Here, we designed an artificial trachea with mechanical properties similar to the native trachea that can enhance the regeneration of tracheal mucosa and cartilage through the optimal combination of a two-layered tubular scaffold and human induced pluripotent stem cell (iPSC)-derived cells. The framework of the artificial trachea was fabricated with electrospun polycaprolactone (PCL) nanofibers (inner) and 3D-printed PCL microfibers (outer). Also, human bronchial epithelial cells (hBECs), iPSC-derived mesenchymal stem cells (iPSC-MSCs), and iPSC-derived chondrocytes (iPSC-Chds) were used to maximize the regeneration of tracheal mucosa and cartilage in vivo. After 2 days of cultivation using a bioreactor system, tissue-engineered artificial tracheas were transplanted into a segmental trachea defect (1.5-cm length) rabbit model. Endoscopy did not reveal granulation ingrowth into tracheal lumen. Alcian blue staining clearly showed the formation of ciliated columnar epithelium in iPSC-MSC groups. In addition, micro-CT analysis showed that iPSC-Chd groups were effective in forming neocartilage at defect sites. Therefore, this study describes a promising approach for long-term functional reconstruction of a segmental tracheal defect.

Chondrocytes-derived exosomal miR-8485 regulated the Wnt/β-catenin pathways to promote chondrogenic differentiation of BMSCs

In indirect co-culture system, chondrocytes can induce differentiation of bone marrow mesenchymal stem cells (BMSCs) to chondrocytes without additional inducer. The participation of microRNAs (miRNAs) may take part in the chondrogenic differentiation. Present study aimed to investigate the effect and mechanism of chondrocytes-derived exosomal miRNA in BMSCs chondrogenic differentiation. Our data showed that miR-8485 was the exosomal miRNA derived from chondrocytes and transmitted to BMSCs. Functionally, miR-8485 silence in chondrocytes impaired exosome-induced chondrogenic differentiation of BMSCs. Mechanistically, exosomal miR-8485 targeted GSK3B to repress GSK-3β expression and targeted DACT1 to induce p-GSK-3β (Ser9), activating Wnt/β-catenin pathways. Our study firstly showed that chondrocytes-derived exosomal miR-8485 regulated the Wnt/β-catenin pathways to promote chondrogenic differentiation of BMSCs, providing innovative thoughts for cartilage reconstruction.

Effect of cyclic compression on bone marrow mesenchymal stromal cells in tissue engineered cartilage scaffold

In this current study, a novel multilayer porous composite scaffold was fabricated with chitosan (CS), silk fibrin (SF) and nano-hydroxyapatite (n-HA). Scanning electron microscope was utilized to detect the characteristics of the composed scaffold. Rat bone marrow stromal cells (rBMSC) were loaded onto the CS/SF/n-HA scaffold and cultured in a bioreactor under an on-off dynamic compression (10% compressive strain, 0.5 Hz, [2 h action + 4 h pause]/cycle, 4 cycles/day). Metabolism of the loaded rBMSC was assessed through CCK-8 test. Qualitative polymerase chain reaction and western blot were applied to assess the chondrogenic differentiation of the seeded cells. Compressive modulus of the cell/scaffold constructs was analyzed. Additionally, a pig model was employed to evaluate the effect of the tissue-engineered cartilage on repairing of cartilage defect. Results showed that the four layers within the scaffold were tightly connected without gaps between porous interfaces of the layers. Scaffold porosity was 92.20% ± 1.30%. The cyclic compression upregulated chondrogenesis markers (Aggrecan, Sox-9, and collagen II). Increased compressive modulus of the cell/scaffold complex was detected after dynamic compression. The pig bone marrow stromal cells/scaffold complex exposed to cyclic compression presented most favorable reparative effect on the mini pig femoral condyle cartilage defects. Our study suggested that the on-off dynamic compression might be a promising approach to fabricate tissue-engineered cartilage in vitro. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1294-1302, 2019.

Exosomes derived from mature chondrocytes facilitate subcutaneous stable ectopic chondrogenesis of cartilage progenitor cells

BACKGROUND

Developing cartilage constructed with the appropriate matrix composition and persistent chondrogenesis remains an enduring challenge in cartilage defects. Cartilage progenitor cell (CPC)-based tissue engineering has attracted recent attention because of its strong chondrogenic differentiation capacity. However, due to the lack of a suitable chondrogenic niche, the clinical application of CPC-regenerated cartilage in the subcutaneous environment remains a challenge. In this study, exosomes derived from chondrocytes (CC-Exos) were used to provide the CPC constructs with a cartilage signal in subcutaneous environments for efficient ectopic cartilage regeneration.

METHODS

Rabbit CPC-alginate constructs were prepared and implanted subcutaneously in nude mice. CC-Exos were injected into the constructs at the same dose (30 μg exosomes per 100 μL injection) after surgery and thereafter weekly for a period of 12 weeks. Exosomes derived from bone mesenchymal stem cells (BMSC-Exos) were used as the positive control. The mice in the negative control were administered with the same volume of PBS. At 4 and 12 weeks after implantation, the potential of CC-Exos and BMSC-Exos to promote chondrogenesis and stability of cartilage tissue in a subcutaneous environment were analyzed by histology, immunostaining, and protein analysis. The influences of BMSC-Exos and CC-Exos on chondrogenesis and angiogenic characteristics in vitro were assessed via coculturing with CPCs and human umbilical vein endothelial cells.

RESULTS

The CC-Exos injection increased collagen deposition and minimized vascular ingrowth in engineered constructs, which efficiently and reproducibly developed into cartilage. The generated cartilage was phenotypically stable with minimal hypertrophy and vessel ingrowth up to 12 weeks, while the cartilage formed with BMSC-Exos was characterized by hypertrophic differentiation accompanied by vascular ingrowth. In vitro experiments indicated that CC-Exos stimulated CPCs proliferation and increased expression of chondrogenesis markers while inhibiting angiogenesis.

CONCLUSIONS

These findings suggest that the novel CC-Exos provides the preferable niche in directing stable ectopic chondrogenesis of CPCs. The use of CC-Exos may represent an off-the-shelf and cell-free therapeutic approach for promoting cartilage regeneration in the subcutaneous environment.

Progress of co-culture systems in cartilage regeneration

INTRODUCTION

Cartilage tissue engineering has rapidly developed in recent decades, exhibiting promising potential to regenerate and repair cartilage. However, the origin of a large amount of a suitable seed cell source is the major bottleneck for the further clinical application of cartilage tissue engineering. The use of a monoculture of passaged chondrocytes or mesenchymal stem cells results in undesired outcomes, such as fibrocartilage formation and hypertrophy. In the last two decades, co-cultures of chondrocytes and a variety of mesenchymal stem cells have been intensively investigated in vitro and in vivo, shedding light on the perspective of co-culture in cartilage tissue engineering.

AREAS COVERED

We summarize the recent literature on the application of heterologous cell co-culture systems in cartilage tissue engineering and compare the differences between direct and indirect co-culture systems as well as discuss the underlying mechanisms.

EXPERT OPINION

Co-culture system is proven to address many issues encountered by monocultures in cartilage tissue engineering, including reducing the number of chondrocytes needed and alleviating the dedifferentiation of chondrocytes. With the further development and knowledge of biomaterials, cartilage tissue engineering that combines the co-culture system and advanced biomaterials is expected to solve the difficult problem regarding the regeneration of functional cartilage.

Ghrelin accelerates the cartilagic differentiation of rabbit mesenchymal stem cells through the ERK1/2 pathway

Mesenchymal stem cells (MSCs) can differentiate into chondroblasts, adipocytes, or cartilage under appropriate stimulation. Identifying a mechanism triggering the differentiation of MSCs into cartilage may help develop novel therapeutic approaches for treating heterotopic ossification, the pathological formation of lamellar bone in soft tissue outside the skeleton that can lead to debilitating immobility. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, stimulates growth hormone secretion, and has both orexigenic and adipogenic effects. This study sought to understand the potential involvement of the ERK1/2 signaling pathway in the ghrelin-induced growth of rat MSCs (rMSCs). We applied various concentrations of ghrelin to cultured rMSCs by observing the changes in the phosphorylation state of ERK1/2, p38, JNK as well as the type II collagen expression levels by western blot. The highest expression level for both type II collagen was obtained with 600 ng/mL ghrelin at 24 h. We found that the ghrelin-induced differentiation of rMSCs into cartilage was promoted primarily by the ERK1/2 pathway. Our study suggests that ghrelin induced differentiation of rMSCs into cartilage primarily through the ERK1/2 pathway.

Implantation of Bone Marrow Stromal Cell Sheets Derived from Old Donors Supports Bone Tissue Formation

The purpose of this study was to evaluate the osteogenesis ability of osteogenic matrix cell sheets (OMCS) derived from old donor cells. Bone marrow stromal cells (BMSC) were obtained from young (7-week-old) and old (1-year-old) Fischer344 rats donors and cultured with modified Eagle's medium (MEM group) alone or containing dexamethasone (Dex; 10 nM) and ascorbic acid phosphate (AscP; 0.28 mM) (Dex/AscP group). We prepared four in vitro experimental groups: (1) young MEM, (2) young Dex/AscP, (3) old MEM and (4) old Dex/AscP. Cell proliferation and osteogenic marker mRNA expression levels were evaluated in vitro. To assess bone formation in vivo, the cells of each group were combined with beta tricalcium phosphate (TCP) disks followed by implantation in recipient rats. The in vitro study showed significant differences in the mRNA expression of osteocalcin, ALP, and BMP2 between MEM and Dex/AscP groups. Bone formation following implantation was observed upon histological analyses of all groups. TCP combined with OMCS (OMCS/TCP group) resulted in enhanced bone formation compared to that following combination with BMSC (BMSC/TCP). The osteocalcin content of the OMCS/TCP group 4 weeks after implantation was significantly higher than that in the BMSC/TCP construct for both young and old donors. The present study clearly indicated that OMCS could be generated from BMSCs of old as well as young donors using a mechanical retrieval method. Thus, through its usage of OMCS, this method may represent a potentially effective therapeutic option for cell-based therapy in elderly patients.