Réponse des chondrocytes humains à la bone morphogenetic protein-2 après leur dédifférenciation in vitro : utilisation potentielle de la bone morphogenetic protein-2 pour la thérapie cellulaire du cartilage

AIMP1 downregulation restores chondrogenic characteristics of dedifferentiated/degenerated chondrocytes by enhancing TGF-β signal

Dedifferentiation and degeneration of chondrocytes critically influences the efficiency of cartilage repair. One of the causes is the defect of transforming growth factor (TGF)-β signaling that promotes chondrogenic differentiation and degeneration. In the present study, we found that aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) negatively regulates TGF-β signaling via interactions with Smad2 and Smad3 in immunoprecipitation assay and luciferase assay. In addition, we observed that the AIMP1 expression level was significantly increased in osteoarthritis (OA) patient-derived degenerated chondrocytes compared with healthy control. So, we hypothesized that downregulation of AIMP1 using small-interfering RNA (siRNA) technology in dedifferentiated (collected at passage #6) and degenerated (obtained from OA-affected areas) chondrocytes could lead to recover TGF-β signaling in both chondrocytes. Indeed, AIMP1 downregulation restored TGF-β signaling by promoting phosphorylation of Smad2 and Smad3, which shows redifferentiated characteristics in both dedifferentiated and degenerated chondrocytes. Additionally, implantation analyses using in vivo mouse model clearly showed that AIMP1 downregulation resulted in the increased chondrogenic potential as well as the enhanced cartilage tissue formation in both dedifferentiated and degenerated chondrocytes. Histological analyses clarified that AIMP1 downregulation increased expression levels of collagen type II (Col II) and aggrecan, but not Col I expression. Taken together, these data indicate that AIMP1 downregulation using siRNA is a novel tool to restore TGF-β signaling and thereby increases the chondrogenic potential of dedifferentiated/degenerated chondrocytes, which could be further developed as a therapeutic siRNA to treat OA.

Activin A/BMP2 chimera AB235 drives efficient redifferentiation of long term cultured autologous chondrocytes

Autologous chondrocyte implantation (ACI) depends on the quality and quantity of implanted cells and is hindered by the fact that chondrocytes cultured for long periods of time undergo dedifferentiation. Here we have developed a reproducible and efficient chondrogenic protocol to redifferentiate chondrocytes isolated from osteoarthritis (OA) patients. We used morphological, histological and immunological analysis together with a RT-PCR detection of collagen I and collagen II gene expression to show that chondrocytes isolated from articular cartilage biopsies of patients and subjected to long-term culture undergo dedifferentiation and that these cells can be redifferentiated following treatment with the chimeric Activin A/BMP2 ligand AB235. Examination of AB235-treated cell pellets in both in vitro and in vivo experiments revealed that redifferentiated chondrocytes synthesized a cartilage-specific extracellular matrix (ECM), primarily consisting of vertically-orientated collagen fibres and cartilage-specific proteoglycans. AB235-treated cell pellets also integrated into the surrounding subcutaneous tissue following transplantation in mice as demonstrated by their dramatic increase in size while non-treated control pellets disintegrated upon transplantation. Thus, our findings describe an effective protocol for the promotion of redifferentiation of autologous chondrocytes obtained from OA patients and the formation of a cartilage-like ECM that can integrate into the surrounding tissue in vivo.

[Reconstruction of nasal cartilage defects using a tissue engineering technique based on combination of high-density polyethylene and hydrogel]

AIM OF THE STUDY

Nasal reconstruction remains a challenge for any surgeon. The surgical indications for nasal reconstruction after oncologic resection, trauma or as part of cosmetic rhinoplasty, are steadily increasing. The current attitude for reconstruction is the use of autologous cartilage grafts of various origins (septal, ear or rib) trying to restore a physiological anatomy but their quantity is limited. Thus, in order to produce an implantable cartilaginous model, we developed a study protocol involving human nasal chondrocytes, growth factors and a composite biomaterial and studied at the molecular, cellular and tissue level the phenotype of the chondrocytes cultured in this model.

MATERIALS AND METHODS

After extraction of chondrocytes and their amplification on plastic, the cells were cultured for 15 days either in monolayer or within an agarose hydrogel or a composite biomaterial (agarose/high density polyethylene: Medpor(®)) in the presence or not of a cocktail of soluble factors (BIT): bone morphogenetic protein-2 (BMP-2), insulin and triiodothyronine (T3). The quality of the chondrocyte phenotype was analyzed by PCR, western blotting and immunohistochemistry.

RESULTS

During their amplification in monolayer, chondrocytes dedifferentiate. However, our results show that the BIT cocktail induces redifferentiation of chondrocytes cultured in agarose/Medpor with synthesis of mature chondrogenic markers. Thereby, chondrocytes associated with the agarose hydrogel will colonize Medpor and synthesize an extracellular matrix characteristic of nasal cartilage.

CONCLUSION

This nasal cartilage tissue engineering protocol provides the first interesting results for nasal reconstruction.

Cartilage Tissue Formation from Dedifferentiated Chondrocytes by Codelivery of BMP-2 and SOX-9 Genes Encoding Bicistronic Vector

Articular cartilage, when damaged by degenerative disease or trauma, has limited ability for self-repair. Recently, many trials have demonstrated that gene therapy combined with tissue engineering techniques would be a promising approach for cartilage regeneration. Bone morphogenetic protein 2 (BMP-2) is an important signal for upregulation of osteogenesis and chondrogenesis of stem cells. Sex-determining region Y box gene 9 (SOX-9) has also been reported as one of the key transcription factors for chondrogenesis. We hypothesized that codelivery of BMP-2 and SOX-9 genes would result in improved efficiency of recovery of normal chondrogenic properties in dedifferentiated chondrocytes. To this aim, we constructed a bicistronic vector encoding the BMP-2 and SOX-9 genes linked to the “self-cleaving” 2A peptide sequence. After gene delivery to dedifferentiated chondrocytes using a microporator transfection system, we confirmed over 65% delivery efficiency of the BMP-2 and SOX-9 genes. According to RT-PCR analysis and Alcian blue staining, simultaneous delivery of BMP-2/SOX-9 resulted in significantly increased expression of chondrogenesis-related markers (type II collagen and aggrecan) and GAG matrix formation compared with individual delivery of the BMP-2 or SOX-9 gene. Six weeks after in vivo transplantation, BMP-2/SOX-9 genes also showed a significant increase in cartilage formation compared with the BMP-2 or SOX-9 gene. These results demonstrate that codelivery of two chondrogenic lineage-determining genes can enhance normal chondrogenic properties of dedifferentiated chondrocytes followed by improved cartilage formation.