Inhibition of cartilage degradation: A combined tissue engineering and gene therapy approach

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Abstract
Objective To determine if tissue‐engineered cartilage can be protected from cytokine‐induced degradation using a gene therapy approach. Methods Chemical and pantropic retroviral gene transfer methodologies were compared for their ability to introduce a luciferase reporter gene into adult bovine cartilage chondrocytes grown in monolayer. Pantropic retrovirus was then used to transduce these cells with human tissue inhibitor of metalloproteinases 1 (TIMP‐1), and the stability of expression in monolayer or pellet culture was monitored for 6 weeks. Untransduced and TIMP‐1–transduced cells were also used to tissue engineer 3‐dimensional cartilage constructs that were then challenged with interleukin‐1 (IL‐1) for 4 weeks. Conditioned media and residual cartilage were collected for analysis of matrix components, including type II collagen and proteoglycans, and for TIMP‐1 production and matrix metalloproteinase (MMP) activity. Results Chemical transfection of adult bovine chondrocytes gave rise to short‐lived reporter expression that was virtually undetectable after 4 weeks of culture. In contrast, pantropic retroviral transduction gave rise to stable expression that persisted at a high level for at least 6 weeks. Pantropic transduction of the cells with TIMP‐1 gave rise to similar long‐term expression, both in monolayer and pellet cultures. TIMP‐1–transduced tissue‐engineered cartilage also retained TIMP‐1 expression for an additional 4 weeks of culture in the presence of IL‐1. Compared with control samples, TIMP‐1–transgenic cartilage resisted the catabolic effects of IL‐1, with MMP activity reduced to basal levels and a decreased loss of type II collagen. Conclusion Pantropic retroviral transduction permits long‐term expression of potentially therapeutic transgenes in adult tissue‐engineered cartilage. While TIMP‐1 transduction could be used to prevent collagen breakdown, alternative transgenes may be necessary to protect cartilage proteoglycans.