Background: There are only a few studies concerning the cellular,
biochemical, and genetic processes that occur during the remodeling of graft
tissue after autologous chondrocyte transplantation. The purpose of the
present study was to quantify the expression of genes encoding extracellular
matrix proteins and regulatory factors that are essential for cell
differentiation in cartilage biopsy specimens from patients who had this
treatment two years previously.
Methods: Two cartilage biopsy specimens from each of four patients
who had been treated with autologous chondrocyte transplantation and from two
multiorgan donors were used. Real-time reverse transcriptase-polymerase chain
reaction analysis was performed to evaluate the expression of types I, II, and
X collagen; aggrecan; cathepsin B; and early growth response protein-1 (Egr-1)
and Sry-type high-mobility-group box transcription factor-9 (Sox-9) mRNAs.
Immunohistochemical analysis for matrix proteins and regulatory proteins was
carried out on paraffin-embedded sections.
Results: Type-I collagen mRNA was expressed in all of the samples
evaluated. Type-II collagen was present in autologous chondrocyte
transplantation samples but at lower levels than in the controls. Type-X
collagen messenger was undetectable. Aggrecan mRNA was present in all of the
samples at lower levels than in the controls, while cathepsin-B messenger
levels were higher and Egr-1 and Sox-9 mRNAs were expressed at lower levels.
The immunohistochemical analysis showed slight positivity for type-I collagen
in all of the sections. Type-II collagen was found in all of the samples with
positivity confined inside the cells, while the controls displayed a
positivity that was diffuse in the extracellular matrix. Cathepsin B was
slightly positive in all of the samples, while the controls were negative.
Egr-1 protein was particularly evident in the areas negative for type-II
collagen. Sox-9 was positive in all samples, with evident localization in the
superficial and middle layers.
Conclusions: In biopsy specimens from autologous chondrocyte
transplantation tissue at two years, there is evidence of the formation of new
tissue, which displays varying degrees of organization with some fibrous and
fibrocartilaginous features. Long-term follow-up investigations are needed to
verify whether, once all of the remodeling processes are completed, the newly
formed tissue will acquire the more typical features of articular
Clinical Relevance: Our data provide important further information
about the nature of the new cartilage tissue formed two years after autologous
chondrocyte transplantation, allowing a better interpretation of the clinical
and histological findings.