Human auricular chondrocytes with high proliferation rate show high production of cartilage matrix

Superior stemness of a rapidly growing subgroup of isolated human auricular chondrocytes and the potential for use in cartilage regenerative therapy

Introduction

In cartilage regenerative medicine, transplanted chondrocytes contain a mixture of populations, that complicates the regeneration of uniform cartilage tissue. Our group previously reported that chondrocytes with higher chondrogenic ability could be enriched by selection of rapidly growing cells. In this study, the detailed properties of rapidly growing chondrocytes were examined and compared to slowly growing cells.

Methods

Human auricular chondrocytes were fluorescently labeled with carboxyfluorescein succinimidyl ester (CFSE) and analyzed using flow cytometry, focusing on division rates as indicated by fluorescence intensity and cell morphology according to the forward scatter and side scatter. Rapid and slow growing cell groups were harvested on days 2 and 4 after CFSE labeling, and their ability to produce cartilage matrix in vitro was examined. To compare the chondrogenic ability in vivo, the cells were seeded on poly-l-lactic acid scaffolds and transplanted into nude mice. Gene expression differences between the rapid and slow cell groups were investigated by microarray analysis.

Results

On day 2 after CFSE labeling, the rapidly growing cell group showed the highest proliferation rate. The results of pellet culture showed that the rapid cell group produced more glycosaminoglycans per cell than the slow cell group. The amount of glycosaminoglycan production was highest in the rapid cell group on day 2 after CFSE labeling, indicating high chondrogenic ability. Furthermore, microarray, gene ontology, and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed upregulation of genes that promote cell division such as origin recognition complex subunit 1 and downregulation of genes that inhibit cell division such as cyclin dependent kinase inhibitor 1A. Besides cell cycle-related genes, chondrocyte-related genes such as serpin family B member 2, clusterin, bone morphogenetic protein 2, and matrix metalloproteinase 3 were downregulated, while fibroblast growth factor 5 which is involved in stem cell maintenance, and coiled-coil and C2 domain containing 2A, which is required for cilia formation, were upregulated.

Conclusion

The results showed that the rapid cell group proliferated well and had more undifferentiated properties, suggesting a higher stemness. The present findings provide a basis for the use of the rapid cell group in cartilage regeneration.

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Highly-chondrogenic chondrocytes can be enriched based on their high division rate.

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Rapidly dividing cells are smaller and have less granularity.

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Cell cycle-related genes are upregulated in rapidly dividing cells.

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Chondrocyte-related genes are downregulated in rapidly dividing cells.

Understanding factors affecting human chondrocyte culturing: an experimental study

Over the years, surgical strategies have been developed in hope of full regeneration of the injured cartilage. In our study, we aimed to develop an optimized chondrocyte culture isolation technique as an active ingredient of a standardized autologous chondrocte implantation product, which is able to maintain the phenotype along with the molecular features of the cartilage. We compared different enzymes, which suggested optimal performance with collagenase type II at 5 mg/ml concentration. Thereafter, we observed that COL2 and GAG expression is substantially reduced with passaging. There was a need to omit passaging to reach the optimal isolation method. We then tested various growth factors and media in order to maintain the natural character of chondrocytes. Our study also suggested the highest COL2 and GAG expressions with the highest recovery in the presence of Advanced DMEM. Autologous chondrocyte implantation manufacturing approval was recently received from the national competent authority, making it possible to utilize the process engineering protocol developed with this study at our Tissue and Cell Manufacturing Center as a part of the autologous chondrocyte implantation manufacturing standard operation procedure (SOP).

RSK-3 promotes cartilage regeneration via interacting with rpS6 in cartilage stem/progenitor cells

Rationale: Cartilage stem/progenitor cells (CSPC) are a promising cellular source to promote endogenous cartilage regeneration in osteoarthritis (OA). Our previous work indicates that ribosomal s6 kinase 3 (RSK-3) is a target of 4-aminobiphenyl, a chemical enhancing CSPC-mediated cartilage repair in OA. However, the primary function and mechanism of RSK-3 in CSPC-mediated cartilage pathobiology remain undefined.

Methods: We systematically assessed the association of RSK-3 with OA in three mouse strains with varying susceptibility to OA (MRL/MpJ>CBA>STR/Ort), and also RSK-3^-/- mice. Bioinformatic analysis was used to identify the possible mechanism of RSK-3 affecting CSPC, which was further verified in OA mice and CSPC with varying RSK-3 expression induced by chemicals or gene modification.

Results: We demonstrated that the level of RSK-3 in cartilage was positively correlated with cartilage repair capacities in three mouse strains (MRL/MpJ>CBA>STR/Ort). Enhanced RSK-3 expression by 4-aminobiphenyl markedly attenuated cartilage injury in OA mice and inhibition or deficiency of RSK-3 expression, on the other hand, significantly aggravated cartilage damage. Transcriptional profiling of CSPC from mice suggested the potential role of RSK-3 in modulating cell proliferation. It was further shown that the in vivo and in vitro manipulation of the RSK-3 expression indeed affected the CSPC proliferation. Mechanistically, ribosomal protein S6 (rpS6) was activated by RSK-3 to accelerate CSPC growth.

Conclusion: RSK-3 is identified as a key regulator to enhance cartilage repair, at least partly by regulating the functionality of the cartilage-resident stem/progenitor cells.

Where is human-based cellular pharmaceutical R&D taking us in cartilage regeneration?

Lately, cellular-based cartilage joint therapies have gradually gained more attention, which leads to next generation bioengineering approaches in the development of cell-based medicinal products for human use in cartilage repair. The greatest hurdles of chondrocyte-based cartilage bioengineering are: (i) preferring the cell source; (ii) differentiation and expansion processes; (iii) the time necessary for chondrocyte expansion pre-implantation; and (iv) fixing the chondrocyte count in accordance with the lesion surface area of the patient in question. The chondrocyte presents itself to be the focal starting material for research and development of bioengineered cartilage-based medicinal products which promise the regeneration and restoration of non-orthopedic cartilage joint defects. Even though chondrocytes seem to be the first choice, inevitable complications related to proliferation, dedifferentation and redifferentiation are probable. Detailed studies are a necessity to fully investigate detailed culturing conditions, the chondrogenic strains of well-defined phenotypes and evaluation of the methods to be used in biomaterial production. Despite a majority of the current methods which aid amelioration of joint functionality, they are insufficient in fully restoring the natural structure and composition of the joint cartilage. Hence current studies have trended towards gene therapy, mesenchymal stem cells and tissue engineering practices. There are many studies addressing the outcomes of chondrocytes in the clinical scene, and many vital biomaterials have been developed for structuring the bioengineered cartilage. This study aims to convey to the audience the practical significance of chondrocyte-based clinical applications.

Optimising platelet secretomes to deliver robust tissue-specific regeneration

Promoting cell proliferation is the cornerstone of most tissue regeneration therapies. As platelet-based applications promote cell division and can be customised for tissue-specific efficacy, this makes them strong candidates for developing novel regenerative therapies. Therefore, the aim of this study was to determine if platelet releasate could be optimised to promote cellular proliferation and differentiation of specific tissues. Growth factors in platelet releasate were profiled for physiological and supraphysiological platelet concentrations. We analysed the effect of physiological and supraphysiological releasate on C2C12 skeletal myoblasts, H9C2 rat cardiomyocytes, human dermal fibroblasts (HDF), HaCaT keratinocytes, and chondrocytes. Cellular proliferation and differentiation were assessed through proliferation assays, mRNA, and protein expression. We show that supraphysiological releasate is not simply a concentrated version of physiological releasate. Physiological releasate promoted C2C12, HDF, and chondrocyte proliferation with no effect on H9C2 or HaCaT cells. Supraphysiological releasate induced stronger proliferation in C2C12 and HDF cells compared with physiological releasate. Importantly, supraphysiological releasate induced proliferation of H9C2 cells. The proliferative effects of skeletal and cardiac muscle cells were in part driven by vascular endothelial growth factor alpha. Furthermore, supraphysiological releasate induced differentiation of H9C2 and C2C12, HDF, and keratinocytes. This study provides insights into the ability of releasate to promote muscle, heart, skin, and cartilage cell proliferation and differentiation and highlights the importance of optimising releasate composition for tissue-specific regeneration.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.