The immortalized chondrocyte: art without sacrifice

High-efficiency non-viral transfection of primary chondrocytes and perichondrial cells for ex-vivo gene therapy to repair articular cartilage defects

BACKGROUND

Primary perichondrial cells and chondrocytes have been used to repair articular cartilage defects in tissue engineering studies involving various animal models. Transfection of these cells with a gene that induces chondrocytic phenotype may form an ideal method to affect tissue engineering of articular cartilage.

DESIGN

A protocol for high-efficiency transfection of primary perichondrial and cartilage cells was optimized. Plasmids carrying the marker beta-galactosidase (beta-gal), PTHrP and TGF-beta1 genes driven by a strong mammalian promoter were transfected into primary perichondrial cells and chondrocytes. A three-step method was used to achieve high efficiency of transfection: (1) permeabilization of primary cells using a mild detergent, (2) association of plasmid DNAs with a polycationic (poly-l-lysine) core covalently linked to a receptor ligand (transferrin), (3) introduction of cationic liposomes to form the quaternary complex. For in-vivo assessment, polylactic acid (PLA) scaffolds seeded with beta-gal transfected perichondrial cells were implanted into experimentally created osteochondral defects in rabbit knees for 1 week.

RESULTS

The efficiency of transfection was determined to be over 70%in vitro. The transformed cells continued to express beta-gal, in vivo for the entire test period of 7 days. Furthermore, primary perichondrial cells transfected with TGF-beta1 and PTHrP over-expressed their cognate gene products.

CONCLUSION

The ability to transfect autologous primary perichondrial cells and chondrocytes with high efficiency using a non-viral system may form a first step towards tissue engineering with these transformed cells to repair articular cartilage defects.

Differential mechanisms of inorganic pyrophosphate production by plasma cell membrane glycoprotein-1 and B10 in chondrocytes

OBJECTIVE

Increased nucleoside triphosphate pyrophosphohydrolase (NTPPPH) activity in chondrocytes is associated with cartilage matrix inorganic pyrophosphate (PPi) supersaturation in chondrocalcinosis. This study compared the roles of the transforming growth factor beta (TGFbeta)-inducible plasma cell membrane glycoprotein-1 (PC-1) and the closely related B10 NTPPPH activities in chondrocyte PPi metabolism.

METHODS

NTPPPH expression was studied using reverse transcriptase-polymerase chain reaction and Western blotting. Transmembrane PC-1 (tmPC-1), water-soluble secretory PC-1 (secPC-1), and transmembrane B10 were expressed by adenoviral gene transfer or plasmid transfection, and expression of PPi was assessed in cultured articular chondrocytes and immortalized NTPPPH-deficient costal chondrocytes (TC28 cells).

RESULTS

PC-1 and B10 messenger RNA were demonstrated in articular cartilages in situ, in untreated cultured normal articular chondrocytes, and in TC28 cells. Expression of tmPC-1 and secPC-1, but not B10, rendered the NTPPPH-deficient TC28 cells able to increase expression of extracellular PPi, with or without addition of TGFbeta (10 ng/ml) to the media. More plasma membrane NTPPPH activity was detected in cells transfected with tmPC-1 than in cells transfected with B10. Furthermore, confocal microscopy with immunofluorescent staining of articular chondrocytes confirmed preferential plasma membrane localization of PC-1, relative to B10. Finally, both PC-1 and B10 increased the levels of intracellular PPi, but PC-1 and B10 appeared to act principally in different intracellular compartments (Golgi and post-Golgi versus pre-Golgi, respectively).

CONCLUSION

PC-1 and B10 NTPPPH activities were not redundant in chondrocytes. Although increased PC-1 and B10 expression caused elevations in intracellular PPi, the major effects of PC-1 and B10 were exerted in distinct subcellular compartments. Moreover, PC-1 (transmembrane and secreted), but not B10, increased the levels of extracellular PPi. Differential expression of PC-1 and B10 could modulate cartilage mineralization in degenerative joint diseases.