Characterization of human articular chondrocytes and chondroprogenitors derived from non-diseased and osteoarthritic knee joints to assess superiority for cell-based therapy

Isolation and Characterization of Meniscus Progenitor Cells From Rat, Rabbit, Goat, and Human

OBJECTIVE

Meniscus progenitor cells (MPCs) have been identified as promising candidates for meniscus regeneration, and it is crucial for us to understand meniscus injury repair mechanism at the cellular level. In this study, we investigate the biological properties of MPCs isolated from different species using the differential adhesion to fibronectin (DAF) technique. We aim to characterize MPCs in different species and evaluate the feasibility of these models for future meniscal investigation.

DESIGN

MPCs were isolated from freshly digested meniscus from rat, rabbit, goat, and human cells using DAF. Biological properties, including proliferation, colony-forming, multilineage differentiation, and migration abilities, were compared in MPCs and their corresponding mixed meniscus cell (MCs) population in each species.

RESULTS

MPCs were successfully isolated by the DAF technique in all species. Rat MPCs appeared cobblestone-like, rabbit MPCs were more polygonal, goat MPCs had a spindle-shaped morphology, human MPCs appear more fibroblast-like. Compared with MCs, isolated MPCs showed progenitor cell characteristics, including multilineage differentiation ability and MSC (mesenchymal stem cells) markers (CD166, CD90, CD44, Stro-1) expression. They also highly expressed fibronectin receptors CD49e and CD49c. MPCs also showed greater proliferation capacity and retained colony-forming ability. Except for goat MPCs showed greater migration abilities than MCs, no significant differences were found in the migration ability between MPCs and MCs in other species.

CONCLUSION

Our study shows that DAF is an effective method for isolating MPCs from rat, rabbit, goat, and human. MPCs in these species demonstrated similar characteristics, including greater proliferation ability and better chondrogenic potential.

Evaluation of ghrelin as a distinguishing marker for human articular cartilage-derived chondrocytes and chondroprogenitors

Purpose of the study

Cell-based therapeutics for articular cartilage repair primarily employed bone marrow-derived mesenchymal stem cells and chondrocytes. Research to overcome their limitation of formation of a functionally poor fibro-hyaline type of repair tissue led to the discovery of chondroprogenitors (CPCs), cartilage resident stem cells. These cells isolated by adhesion assay using fibronectin (FAA-CPs) and migration of progenitors from explants (MCPs) display higher chondrogenic and lower terminal differentiation potential. During in-vitro culture, chondrocytes tend to de-differentiate and acquire characteristics similar to stem cells, thus making it challenging to distinguish them from other cell groups. Ghrelin, a cytoplasmic growth hormone secretagogue, has been proposed to play a vital role in chondrogenesis, with reports of its higher expression in chondrocytes than BM-MSCs. The aim of this study was to compare the mRNA expression of Ghrelin between BM-MSCs, chondrocytes, FAA-CPs and MCP and the possibility of it serving as a distinguishing marker.

Methods

The four populations isolated from three human osteoarthritic knee joints were characterised by CD marker expression for positive (CD 90, CD73 and CD105) and negative (HLA-DR, CD34 and CD45) MSC markers and trilineage differentiation (adipogenic, osteogenic and chondrogenic) and subjected to qRT-PCR to assess Ghrelin's gene expression.

Results

This study showed that all groups exhibited similar expression of CD markers and multilineage potential. Though chondrocytes showed greater expression of Ghrelin, it was not statistically significant to classify it as a distinguishing marker between these cell populations.

Conclusion

Ghrelin does not serve to differentiate the subpopulations in terms of their mRNA expression. Further evaluation using their associated enzymes and receptors could provide valuable information to uncover their potential as unequivocal biomarkers.

Systematic review of articular cartilage derived chondroprogenitors for cartilage repair in animal models

Purpose of research

The potential for cartilage repair using articular cartilage derived chondroprogenitors has recently gained popularity due to promising results from in-vitro and in-vivo studies. Translation of results from in-vitro to a clinical setting requires a sufficient number of animal studies displaying significant positive outcomes. Thus, this systematic review comprehensively discusses the available literature (January 2000-March 2022) on animal models employing chondroprogenitors for cartilage regeneration, highlighting the results and limitations associated with their use.As per Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a web-based search of PubMed and SCOPUS databases was performed for the following terminologies: "chondroprogenitors", "cartilage-progenitors", and "chondrogenic-progenitors", which yielded 528 studies. A total of 12 studies met the standardized inclusion criteria, which included chondroprogenitors derived from hyaline cartilage isolated using fibronectin adhesion assay (FAA) or migratory assay from explant cultures, further analyzing the role of chondroprogenitors using in-vivo animal models.

Principal results

Analysis revealed that FAA chondroprogenitors demonstrated the ability to attenuate osteoarthritis, repair chondral defects and form stable cartilage in animal models. They displayed better outcomes than bone marrow-derived mesenchymal stem cells but were comparable to chondrocytes. Migratory chondroprogenitors also demonstrated superiority to BM-MSCs in terms of higher chondrogenesis and lower hypertrophy, although a direct comparison to FAA-CPs and other cell types is warranted.

Major conclusions

Chondroprogenitors exhibit superior properties for chondrogenic repair; however, limited data on animal studies necessitates further studies to optimize their use before clinical translation for neo-cartilage formation.

From regeneration to osteoarthritis in the knee joint: The role shift of cartilage-derived progenitor cells

A mount of growing evidence has proven that cartilage-derived progenitor cells (CPCs) harbor strong proliferation, migration, andmultiple differentiation potentials over the past 2 decades. CPCs in the stage of immature tissue play an important role in cartilage development process and injured cartilage repair in the young and active people. However, during maturation and aging, cartilage defects cannot be completely repaired by CPCs in vivo. Recently, tissue engineering has revealed that repaired cartilage defects with sufficient stem cell resources under good condition and bioactive scaffolds in vitro and in vivo. Chronic inflammation in the knee joint limit the proliferation and chondrogenesis abilities of CPCs, which further hampered cartilage healing and regeneration. Neocartilage formation was observed in the varus deformity of osteoarthritis (OA) patients treated with offloading technologies, which raises the possibility that organisms could rebuild cartilage structures spontaneously. In addition, nutritionmetabolismdysregulation, including glucose and free fatty acid dysregulation, could influence both chondrogenesis and cartilage formation. There are a few reviews about the advantages of CPCs for cartilage repair, but few focused on the reasons why CPCs could not repair the cartilage as they do in immature status. A wide spectrum of CPCs was generated by different techniques and exhibited substantial differences. We recently reported that CPCs maybe are as internal inflammation sources during cartilage inflammaging. In this review, we further streamlined the changes of CPCs from immature development to maturation and from healthy status to OA advancement. The key words including “cartilage derived stem cells”, “cartilage progenitor cells”, “chondroprogenitor cells”, “chondroprogenitors” were set for latest literature searching in PubMed and Web of Science. The articles were then screened through titles, abstracts, and the full texts in sequence. The internal environment including long-term inflammation, extendedmechanical loading, and nutritional elements intake and external deleterious factors were summarized. Taken together, these results provide a comprehensive understanding of the underlying mechanism of CPC proliferation and differentiation during development, maturation, aging, injury, and cartilage regeneration in vivo.

Stable human cartilage progenitor cell line stimulates healing of meniscal tears and attenuates post-traumatic osteoarthritis

Meniscal tearing in the knee increases the risk of post-traumatic osteoarthritis (OA) in patients. The therapeutic application of tissue-specific mesenchymal progenitor cells is currently being investigated as an emerging biologic strategy to help improve healing of musculoskeletal tissues like meniscal fibrocartilage and articular hyaline cartilage. However, many of these approaches involve isolating cells from healthy tissues, and the low yield of rare progenitor populations (< 1% of total cells residing in tissues) can make finding a readily available cell source for therapeutic use a significant logistical challenge. In the present study, we investigated the therapeutic efficacy of using expanded cartilage-derived and bone marrow-derived progenitor cell lines, which were stabilized using retroviral SV40, for repair of meniscus injury in a rodent model. Our findings indicate that these cell lines express the same cell surface marker phenotype of primary cells (CD54+, CD90+, CD105+, CD166+), and that they exhibit improved proliferative capacity that is suitable for extensive expansion. Skeletally mature male athymic rats treated with 3.2 million cartilage-derived progenitor cell line exhibited approximately 79% greater meniscal tear reintegration/healing, compared to injured animals that left untreated, and 76% greater compared to animals treated with the same number of marrow-derived stromal cells. Histological analysis of articular surfaces also showed that cartilage-derived progenitor cell line treated animals exhibited reduced post-traumatic OA associated articular cartilage degeneration. Stable cell line treatment did not cause tumor formation or off-target engraftment in animals. Taken together, we present a proof-of-concept study demonstrating, for the first time, that intra-articular injection of a stable human cartilage-derived progenitor cell line stimulates meniscus tear healing and provide chondroprotection in an animal model. These outcomes suggest that the use of stable cell lines may help overcome cell source limitations for cell-based medicine.

Supplementation of articular cartilage-derived chondroprogenitors with bone morphogenic protein-9 enhances chondrogenesis without affecting hypertrophy

INTRODUCTION

Chondroprogenitors (CPCs) have emerged as a promising cellular therapy for cartilage-related pathologies due to their inherent primed chondrogenic potential. Studies report that the addition of growth factors such as parathyroid hormone (PTH) and Bone Morphogenic Protein (BMP) enhance the chondroinducive potential in chondrocytes and mesenchymal stem cells. This study evaluated if supplementation of the standard culture medium for cell expansion with 1-34 PTH and BMP-9 would enhance the chondrogenic potential of CPCs and reduce their hypertrophic tendency.

METHODS

Human chondrocytes were isolated from patients undergoing total knee replacement for osteoarthritis (n = 3). Following fibronectin adhesion assay, passage 1 CPCs were divided and further expanded under three culture conditions (a) control, i.e., cells continued under standard culture conditions, (b) 1-34 PTH group, additional intermittent 6 h exposure with 1-34 PTH and (c) BMP-9 group, additional BMP-9 during culture expansion. All the groups were evaluated for population-doubling, cell cycle analysis, surface marker and gene expression for chondrogenesis, hypertrophy, multilineage differentiation and GAG (glycosaminoglycan)/DNA following chondrogenic differentiation.

RESULTS

Concerning growth kinetics, the BMP-9 group exhibited a significantly lower S-phase and population-doubling when compared to the other two groups. Qualitative analysis for chondrogenic potential (Alcian blue, Safranin O staining and Toluidine blue for GAG) revealed that the BMP-9 group exhibited the highest uptake. The BMP-9 group also showed significantly higher COL2A1 expression than the control group, with no change in the hypertrophy marker expression.

CONCLUSION

BMP-9 can potentially be used as an additive for CPCs expansion, to enhance their chondrogenic potential without affecting their low hypertrophic tendency. The mitigating effects of 1-34PTH on hypertrophy would benefit further investigation when used in combination with BMP-9 to enhance chondrogenesis whilst reducing hypertrophy.

Roles of Cartilage-Resident Stem/Progenitor Cells in Cartilage Physiology, Development, Repair and Osteoarthritis

Osteoarthritis (OA) is a degenerative disease that causes irreversible destruction of articular cartilage for which there is no effective treatment at present. Although articular cartilage lacks intrinsic reparative capacity, numerous studies have confirmed the existence of cartilage-resident stem/progenitor cells (CSPCs) in the superficial zone (SFZ) of articular cartilage. CSPCs are characterized by the expression of mesenchymal stromal cell (MSC)-related surface markers, multilineage differentiation ability, colony formation ability, and migration ability in response to injury. In contrast to MSCs and chondrocytes, CSPCs exhibit extensive proliferative and chondrogenic potential with no signs of hypertrophic differentiation, highlighting them as suitable cell sources for cartilage repair. In this review, we focus on the organizational distribution, markers, cytological features and roles of CSPCs in cartilage development, homeostasis and repair, and the application potential of CSPCs in cartilage repair and OA therapies.

Assessment of the inherent chondrogenic potential of human articular cartilage-derived chondroprogenitors in pellet culture using a novel whole pellet processing approach

Purpose

Cartilage-derived chondroprogenitors have been reported to possess the biological potential for cartilage repair. However, its inherent chondrogenic potential in pellet culture needs evaluation. In-vitro cartilage regeneration models based on pellet cultures have been employed to evaluate the chondrogenic potential of stem cells. Evaluation of the degree of differentiation routinely involves paraffin embedding, sectioning, and immunohistochemical staining of the pellet. However, since chondrogenic differentiation is commonly non-uniform, processing random sections could lead to inaccurate conclusions. The study aimed at assessing the inherent lineage bias of chondroprogenitors with and without chondrogenic induction, using a novel whole pellet processing technique.

Methods

Human chondroprogenitors (n=3) were evaluated for MSC markers and processed in pellet cultures either with stromal medium (uninduced) or chondrogenic differentiation medium (induced) for 28 days. The whole pellets and the conventional paraffin-embedded sectioned pellets were subjected to Collagen type II immunostaining and assessed using confocal laser microscopy. The staining intensities of the whole pellet were compared to the paraffin sections and revalidated using qRT-PCR for COL2A1 expression.

Results

Uninduced and induced pellets displayed Collagen type II in all the layers with comparable fluorescence intensities. COL2A1 expression in both pellets was comparable to confocal results. The study demonstrated that uninduced chondroprogenitors in pellet culture possess promising inherent chondrogenic potential. Confocal imaging of whole pellets displayed different degrees of chondrogenic differentiation in the entire pellet, thus its probable in-vivo behavior.

Conclusion

The novel approach presented in this study could serve as an efficient in-vitro alternative for understanding translational application for cartilage repair.

The clinical potential of articular cartilage-derived progenitor cells: a systematic review

Over the past two decades, evidence has emerged for the existence of a distinct population of endogenous progenitor cells in adult articular cartilage, predominantly referred to as articular cartilage-derived progenitor cells (ACPCs). This progenitor population can be isolated from articular cartilage of a broad range of species, including human, equine, and bovine cartilage. In vitro, ACPCs possess mesenchymal stromal cell (MSC)-like characteristics, such as colony forming potential, extensive proliferation, and multilineage potential. Contrary to bone marrow-derived MSCs, ACPCs exhibit no signs of hypertrophic differentiation and therefore hold potential for cartilage repair. As no unique cell marker or marker set has been established to specifically identify ACPCs, isolation and characterization protocols vary greatly. This systematic review summarizes the state-of-the-art research on this promising cell type for use in cartilage repair therapies. It provides an overview of the available literature on endogenous progenitor cells in adult articular cartilage and specifically compares identification of these cell populations in healthy and osteoarthritic (OA) cartilage, isolation procedures, in vitro characterization, and advantages over other cell types used for cartilage repair. The methods for the systematic review were prospectively registered in PROSPERO (CRD42020184775).

Migratory chondroprogenitors retain superior intrinsic chondrogenic potential for regenerative cartilage repair as compared to human fibronectin derived chondroprogenitors

Cell-based therapy for articular hyaline cartilage regeneration predominantly involves the use of mesenchymal stem cells and chondrocytes. However, the regenerated repair tissue is suboptimal due to the formation of mixed hyaline and fibrocartilage, resulting in inferior long-term functional outcomes. Current preclinical research points towards the potential use of cartilage-derived chondroprogenitors as a viable option for cartilage healing. Fibronectin adhesion assay-derived chondroprogenitors (FAA-CP) and migratory chondroprogenitors (MCP) exhibit features suitable for neocartilage formation but are isolated using distinct protocols. In order to assess superiority between the two cell groups, this study was the first attempt to compare human FAA-CPs with MCPs in normoxic and hypoxic culture conditions, investigating their growth characteristics, surface marker profile and trilineage potency. Their chondrogenic potential was assessed using mRNA expression for markers of chondrogenesis and hypertrophy, glycosaminoglycan content (GAG), and histological staining. MCPs displayed lower levels of hypertrophy markers (RUNX2 and COL1A1), with normoxia-MCP exhibiting significantly higher levels of chondrogenic markers (Aggrecan and COL2A1/COL1A1 ratio), thus showing superior potential towards cartilage repair. Upon chondrogenic induction, normoxia-MCPs also showed significantly higher levels of GAG/DNA with stronger staining. Focused research using MCPs is required as they can be suitable contenders for the generation of hyaline-like repair tissue.

Prospective Isolation and Characterization of Chondroprogenitors from Human Chondrocytes Based on CD166/CD34/CD146 Surface Markers

PURPOSE

Chondrocytes, isolated from articular cartilage, are routinely utilized in cell-based therapeutics for the treatment of cartilage pathologies. However, restoration of the biological tissue faces hindrance due to the formation of primarily fibrocartilaginous repair tissue. Chondroprogenitors have been reported to display superiority in terms of their chondrogenic potential and lesser proclivity for hypertrophy. In line with our recent results, comparing chondroprogenitors and chondrocytes, we undertook isolation of progenitors from the general pool of chondrocytes, based on surface marker expression, namely, CD166, CD34, and CD146, to eliminate off-target differentiation and generate cells of stronger chondrogenic potential. This study aimed to compare chondrocytes, chondroprogenitors, CD34-CD166+CD146+ sorted chondrocytes, and CD34-CD166+CD146- sorted chondrocytes.

METHODS

Chondrocytes obtained from 3 human osteoarthritic knee joints were subjected to sorting, to isolate CD166+ and CD34- subsets, and then were further sorted to obtain CD146+ and CD146- cells. Chondrocytes and fibronectin adhesion-derived chondroprogenitors served as controls. Assessment parameters included reverse transcriptase polymerase chain reaction for markers of chondrogenesis and hypertrophy, trilineage differentiation, and total GAG/DNA content.

RESULTS

Based on gene expression analysis, CD34-CD166+CD146+ sorted chondrocytes and chondroprogenitors displayed comparability and significantly higher chondrogenesis with a lower tendency for hypertrophy when compared to chondrocytes and CD34-CD166+CD146- sorted chondrocytes. The findings were also reiterated in multilineage potential differentiation with the 146+ subset and chondroprogenitors displaying lower calcification and chondroprogenitors displaying higher total GAG/DNA content compared to chondrocytes and 146- cells.

CONCLUSION

This unique progenitor-like population based on CD34-CD166+CD146+ sorting from chondrocytes exhibits efficient potential for cartilage repair and merits further evaluation for its therapeutic application.

Selection of Highly Proliferative and Multipotent Meniscus Progenitors through Differential Adhesion to Fibronectin: A Novel Approach in Meniscus Tissue Engineering

Meniscus injuries can be highly debilitating and lead to knee osteoarthritis. Progenitor cells from the meniscus could be a superior cell type for meniscus repair and tissue-engineering. The purpose of this study is to characterize meniscus progenitor cells isolated by differential adhesion to fibronectin (FN-prog). Human osteoarthritic menisci were digested, and FN-prog were selected by differential adhesion to fibronectin. Multilineage differentiation, population doubling time, colony formation, and MSC surface markers were assessed in the FN-prog and the total meniscus population (Men). Colony formation was compared between outer and inner zone meniscus digest. Chondrogenic pellet cultures were performed for redifferentiation. FN-prog demonstrated multipotency. The outer zone FN-prog formed more colonies than the inner zone FN-prog. FN-prog displayed more colony formation and a higher proliferation rate than Men. FN-prog redifferentiated in pellet culture and mostly adhered to the MSC surface marker profile, except for HLA-DR receptor expression. This is the first study that demonstrates differential adhesion to fibronectin for the isolation of a progenitor-like population from the meniscus. The high proliferation rates and ability to form meniscus extracellular matrix upon redifferentiation, together with the broad availability of osteoarthritis meniscus tissue, make FN-prog a promising cell type for clinical translation in meniscus tissue-engineering.

Comparative analysis of human bone marrow mesenchymal stem cells, articular cartilage derived chondroprogenitors and chondrocytes to determine cell superiority for cartilage regeneration

INTRODUCTION

Chondroprogenitors, a promising therapeutic modality in cell-based therapy, are routinely isolated from articular cartilage by fibronectin differential adhesion assay. However, there is paucity of information regarding their biological profile and the lack of a marker that can reliably distinguish them from cultured chondrocytes due to possible dedifferentiation. Since chondroprogenitors have been classified as mesenchymal stem cells(MSCs), the aim of our study was to compare bone marrow-MSCs, chondroprogenitors and chondrocytes, and assess superiority for cartilage repair. An additional objective was to also compare CD49b as a differentiating marker for isolating chondroprogenitors as a recent report demonstrated significantly high expression in the surfaceome of migratory articular chondroprogenitors.

METHODS

Bone marrow aspirate and articular cartilage was obtained from three osteoarthritic knee joints. Study arms included a) bone marrow-MSCs, b) chondroprogenitors, c) cultured chondrocytes, d) chondrocytes cultured with additional growth factors and e) CD49b + sorted chondroprogenitors. Assessment parameters included population doubling, surface expression for positive, negative MSC markers and potential markers of chondrogenesis (CD29, CD49e, CD49b, CD166 and CD146), RT-PCR for markers of chondrogenesis and hypertrophy and trilineage differentiation.

RESULTS AND CONCLUSION

Chondroprogenitors exhibited efficient chondrogenesis (SOX-9 and COL2A1) and significantly lower tendency for hypertrophy (RUNX2), which was also reflected in trilineage differentiation where progenitors displayed minimal calcified matrix, efficient glycosaminoglycan deposition and high collagen type II uptake. CD49b did not serve as a marker for isolation as sorted chondroprogenitors performed significantly poorer when compared to fibronectin assay derived cells. Emphasis on preclinical studies utilizing progenitors of higher purity is the future direction.

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.