Endogenus chondrocytes immobilized by G-CSF in nanoporous gels enable repair of critical-size osteochondral defects

Injured articular cartilage is a leading cause for osteoarthritis. We recently discovered that endogenous stem/progenitor cells not only reside in the superficial zone of mouse articular cartilage, but also regenerated heterotopic bone and cartilage in vivo. However, whether critical-size osteochondral defects can be repaired by pure induced chemotatic cell homing of these endogenous stem/progenitor cells remains elusive. Here, we first found that cells in the superficial zone of articular cartilage surrounding surgically created 3 × 1 mm defects in explant culture of adult goat and rabbit knee joints migrated into defect-filled fibrin/hylaro1nate gel, and this migration was significantly more robust upon delivery of exogenous granulocyte-colony stimulating factor (G-CSF). Remarkably, G-CSF-recruited chondrogenic progenitor cells (CPCs) showed significantly stronger migration ability than donor-matched chondrocytes and osteoblasts. G-CSF-recruited CPCs robustly differentiated into chondrocytes, modestly into osteoblasts, and barely into adipocytes. In vivo, critical-size osteochondral defects were repaired by G-CSF-recruited endogenous cells postoperatively at 6 and 12 weeks in comparison to poor healing by gel-only group or defect-only group. ICRS and O'Driscoll scores of articular cartilage were significantly higher for both 6- and 12-week G-CSF samples than corresponding gel-only and defect-only groups. Thus, endogenous stem/progenitor cells may be activated by G-CSF, a Food and Drug Administration (FDA)-cleared bone-marrow stimulating factor, to repair osteochondral defects.

Defect-adaptive Stem-cell-microcarrier Construct Promotes Tissue Repair in Rabbits with Knee Cartilage Defects

Although various reconstruction techniques are available for cartilage defects, the repair effects and conveniences remain to be further improved due to the limited regenerative capacity of cartilaginous tissues and difficulties in seamlessly fulfilling irregularly shaped defects. In the current study, we explored the repair efficacy of stem cell microcarrier construct (microcarriers loaded with human chondrogenic progenitor cells or bone marrow mesenchymal stem cells) in cartilage defect models. A total of 39 healthy New Zealand white rabbits were included, and femoral trochlear cartilage defect models were established (n = 33). Stem cell microcarrier constructs were implanted into cartilage defects (n = 6), the maintenance conditions of the implanted constructs were observed on days 4, 8, and 30 post implantation (n = 3). Gross observation and pathological analysis were performed to assay the reconstitution of cartilage defects at 12 weeks post-cartilage defect repair(n = 6). The microcarriers could fill the defect model with good plasticity to integrate well with the boundary native normal cartilage. At 3 months after implantation, the defects were filled with fibrous cartilage tissues in the microcarrier without stem cells group. In the microcarrier loaded with BMSCs group, newly formed tissue with a similar appearance of boundary cartilage fulfilled the defects, but the surface was not completely smooth. Promisingly, the defects were almost completely filled with newly regenerated cartilaginous tissues, which had a smooth appearance similar to that of normal cartilage in the microcarrier loaded with CPCs group. These results suggest the feasibility of stem cell microcarrier construct in repairing cartilage defects, indicating promising clinical application prospects.

Senescent chondrogenic progenitor cells derived from articular cartilage of knee osteoarthritis patients contributes to senescence-associated secretory phenotype via release of IL-6 and IL-8

OBJECTIVES

Despite the presence of chondrogenic progenitor cells (CPCs) in knee osteoarthritis patients they are unable to repair the damaged cartilage. This study aimed to evaluate the oxidative stress, cellular senescence, and senescence-associated secretory phenotype (SASP) in the CPCs derived from osteoarthritic cartilage and compare with the CPCs of healthy articular cartilage.

METHODS

Isolated CPCs were characterized based on phenotypic expression of stem cell markers, clonogenicity, and tri-lineage differentiation assay. Production of ROS was measured using DCFDA assay. Cellular senescence in CPCs was assessed by senescence-associated beta-galactosidase assay and expression of senescence markers at the gene level using real-time PCR. Morphological features associated with senescent OA-CPCs were studied using scanning electron microscopy. To study SASP, the production of inflammatory cytokines was assessed in the culture supernatant using a flow-cytometer based cytometric bead array.

RESULTS

OA-CPCs exhibited elevated ROS levels along with a relatively high percentage of senescent cells compared to non-OA CPCs, and a positive correlation exists between ROS production and senescence. The morphological assessment of senescent CPCs revealed increased cell size and multiple nuclei in senescent OA-CPCs. These results were further validated by elevated expression of senescence genes p16, p21, and p53. Additionally, culture supernatant of senescent OA-CPCs expressed IL-6 and IL-8 cytokines indicative of SASP.

CONCLUSIONS

Despite exhibiting similar expression of stem cell markers and clonogenicity, CPCs undergo oxidative stress in diseased knee joint leading to increased production of intracellular ROS in chondrogenic progenitor cells that support cellular senescence. Further, senescence in OA-CPCs is mediated via the release of pro-inflammatory cytokines, IL-6 and IL-8.

Intra-articular delivery of extracellular vesicles secreted by chondrogenic progenitor cells from MRL/MpJ superhealer mice enhances articular cartilage repair in a mouse injury model

Background

Chondrogenic progenitor cells (CPCs) have high self-renewal capacity and chondrogenic potential. Intra-articular delivery of purified mesenchymal stem cells (MSCs) from MRL/MpJ “superhealer” mice increased bone volume during repair and prevents post-traumatic arthritis. Recently, although extracellular vesicles released from MSCs have been used widely for treating OA, the application of extracellular vesicles secreted by CPCs from MRL/MpJ mice in OA therapy has never been reported. In this study, we evaluated the effects of extracellular vesicles secreted by CPCs from control CBA (CBA-EVs) and MRL/MpJ mice (MRL-EVs) on proliferation and migration of murine chondrocytes. We also determined here if weekly intra-articular injections of CBA-EVs and MRL-EVs would repair and regenerate surgically induced model in mice.

Methods

CPC surface markers were detected by flow cytometry. CBA-EVs and MRL-EVs were isolated using an ultrafiltration method. Nanoparticle tracking analysis, transmission electron microscopy, and western blots were used to identify extracellular vesicles. CBA-EVs and MRL-EVs were injected intra-articularly in a mouse model of surgical destabilization of the medial meniscus (DMM)-induced OA, and histological and immunohistochemistry analyses were used to assess the efficacy of exosome injections. We used miRNA-seq analysis to analyze the expression profiles of exosomal miRNAs derived from CBA-EVs as well as MRL-EVs. Cell-counting and scratch assays were used to evaluate the effects of CBA-EVs and MRL-EVs on proliferation and migration of murine chondrocytes, respectively. Meanwhile, a specific RNA inhibitor assesses the roles of the candidate miRNAs in CPC-EV-induced regulation of function of chondrocytes.

Results

Both CBA-EVs and MRL-EVs stimulated chondrocyte proliferation and migration, but MRL-EVs exerted a stronger effect than CBA-EVs. The similar result was also observed in in vivo study, which indicated that injecting either CBA-EVs or MRL-EVs attenuated OA, but MRL-EVs showed a superior therapeutic effect in comparison with CBA-EVs. The results of bioinformatics analyses revealed that the differentially expressed exosomal miRNAs participated in multiple biological processes. We identified 80 significantly upregulated and 100 downregulated miRNAs. Moreover, we found that the top 20 differentially expressed exosomal miRNAs connected OA repair to processes such as AMPK signaling, regulation of autophagy, and insulin signaling. Notably, miRNA 221-3p were highly enriched in MRL-Exos and treatment with miR 221-3p inhibitor markedly decreased chondrocyte proliferation and migration induced by CBA-EVs or MRL-EVs in vitro.

Conclusions

This is the first study to demonstrate MRL-EVs had a greater therapeutic effect on the treatment of OA than CBA-EVs. This study will hopefully provide new insight into the pathogenesis, prevention, and treatment of OA.

Adenosine production in mesenchymal stromal cells in relation to their developmental status

BACKGROUND

Mesenchymal stromal cells (MSC) are multipotent progenitor cells found in the tumor microenvironment. They have an innate and regulatory immune activity, and they are able to produce immunosuppressive adenosine (ADO) via their ectonucleotidases CD39 and CD73. The present study explores ADO metabolism of MSC in relation to their developmental status.

METHODS

We analyzed MSC (n = 6), chondrogenic progenitor cells (CPC, n = 8), and chondrocytes (n = 8) for surface markers by flow cytometry. The ability to hydrolyze ATP and to produce ADO was tested by luminescence assays and mass spectrometry.

RESULTS

Significant differences in the surface marker expression of MSC, CPC, and chondrocytes were seen. While the expression of CD73 was observed to be the same on all cell types, the expression of the ectonucleotidase CD39 was significantly increased on MSC. Consequently, production of ADO was most abundant in MSC as compared with chondrocytes and CPC.

CONCLUSION

Mesenchymal stromal cells are potent producers of ADO and are, therefore, able to increase immunosuppression. As MSC differentiate into chondrocytes, they lose this ability and may take on other functions.

Enhanced phagocytic capacity endows chondrogenic progenitor cells with a novel scavenger function within injured cartilage

OBJECTIVE

Articular cartilage harbors chondrogenic progenitor cells (CPCs), a population that responds chemotactically to cell death. Because this behavior is reminiscent of macrophages, we hypothesized that CPCs have macrophage-like capabilities for scavenging cell and tissue debris through phagocytosis.

DESIGN

CPCs, chondrocytes, synoviocytes, and macrophages were cultured with fluorophore-labeled chondrocyte debris for 3, 6, 12, or 24 h. Debris internalization was quantified by confocal microscopy and flow cytometry. Confocal microscopy was also used to test CPCs and chondrocytes for uptake of fluorophore-labeled fibronectin fragments (Fn-fs), a form of extracellular matrix debris. Lysosome activity and mass in CPCs and chondrocytes were measured using fluorescent probes. The relative expression of phagocytosis-related genes and proteins was evaluated by polymerase chain reaction (PCR) and immunoblotting, respectively. Pulse-chase experiments were performed to determine if the debris internalized by CPCs and chondrocytes was cleared, and if clearance was affected by a cathepsin B inhibitor.

RESULTS

More macrophages, synoviocytes, and CPCs internalized cell debris than chondrocytes at all time points. While uptake remained flat in chondrocytes at ∼10%, in the other cell types it peaked at more than 60% after 12-24 h. Relative to chondrocytes, CPCs showed significantly higher rates of Fn-fs engulfment, greater lysosome activity and mass, and over-expressed phagocytosis-related genes and proteins. Pulse-chase experiments revealed time- and cathepsin B-dependent clearance of cell debris in CPCs, but not in chondrocytes.

CONCLUSIONS

CPCs phagocytized cell and matrix debris much more efficiently than chondrocytes, supporting the hypothesis that they play a macrophage-like role in injured cartilage.

Characterization of a migrative subpopulation of adult human nasoseptal chondrocytes with progenitor cell features and their potential for in vivo cartilage regeneration strategies

Background

Progenitor cells display interesting features for tissue repair and reconstruction. In the last years, such cells have been identified in different cartilage types. In this study, we isolated a migrative subpopulation of adult human nasoseptal chondrocytes with progenitor cell features by outgrowth from human nasal septum cartilage. These putative progenitor cells were comparatively characterized with mesenchymal stem cells (MSC) and human nasal septum chondrocytes with respect to their cellular characteristics as well as surface marker profile using flow cytometric analyses. Differentiation capacity was evaluated on protein and gene expression levels.

Results

The migrative subpopulation differentiated into osteogenic and chondrogenic lineages with distinct differences to chondrocytes and MSC. Cells of the migrative subpopulation showed an intermediate surface marker profile positioned between MSC and chondrocytes. Significant differences were found for CD9, CD29, CD44, CD90, CD105 and CD106. The cells possessed a high migratory ability in a Boyden chamber assay and responded to chemotactic stimulation. To evaluate their potential use in tissue engineering applications, a decellularized septal cartilage matrix was either seeded with cells from the migrative subpopulation or chondrocytes. Matrix production was demonstrated immunohistochemically and verified on gene expression level. Along with secretion of matrix metalloproteinases, cells of the migrative subpopulation migrated faster into the collagen matrix than chondrocytes, while synthesis of cartilage specific matrix was comparable.

Conclusions

Cells of the migrative subpopulation, due to their migratory characteristics, are a potential cell source for in vivo regeneration of nasal cartilage. The in vivo mobilization of nasal cartilage progenitor cells is envisioned to be the basis for in situ tissue engineering procedures, aiming at the use of unseeded biomaterials which are able to recruit local progenitor cells for cartilage regeneration.