Constitutive Bcl-2 over-expression triggers an anabolic response in chondrocytes, with partial abatement of IL-1β catabolic effects

We are interested in engineering cartilage that is resistant to arthritic disease. We hypothesized that suppression of terminal differentiation pathways would lead to decreased chondrocyte catabolic response to inflammatory cytokines and used a Bcl-2 over-expression gene therapy approach targeting chondrocyte apoptosis. Retrovirally transduced chondrocytes were cultured in 1.25% alginate hydrogels and subjected to interleukin 1beta (IL-1beta) stimulation (5 ng/ml) over one month. In the absence of IL-1beta, Bcl-2 therapy induced a pro-chondrogenic effect, increasing anabolic gene expression and glycosaminoglycan (GAG) accumulation while decreasing injury markers. Though Bcl-2 continued to increase anabolic markers and tissue inhibitors of matrix metalloproteinases (MMPs) under IL-1beta stimulation, it did not override the overall IL-1beta suppression of cell number and anabolic markers. Bcl-2 further augmented MMP expression and total GAG loss with IL-1beta. However under long term IL-1beta stimulation, Bcl-2 abrogated the expression of hypertrophic markers such as collagen type X. Thus, elucidation of the mechanism driving the beneficial aspects of Bcl-2 over-expression and developing conditionally regulated anti-apoptotic gene therapy may prove therapeutic in engineering cartilage that is resistant to disease.