Mechanical Loading Modulates Gene Expression in Chondrocyte-Seeded Agarose Hydrogels

Abstract

A successful tissue engineered articular cartilage construct needs to possess mechanical, biochemical, and histological features similar to that of native cartilage in order to serve its load-bearing function. Agarose is a suitable scaffold material for chondrocyte cultures (1,2), allowing long-term maintenance of cell phenotype and the elaboration of a functional cartilage-like matrix. This culture system facilitates further elucidation of the roles of matrix and cell-matrix interactions in the regulation of chondrocyte response to mechanical loads. We have previously shown (3) that mechanical loading at a physiologic frequency can increase the rate of matrix deposition, increasing mechanical properties of the tissue engineered constructs (∼21 fold increases in HA over day 0 with loading vs. ∼4 fold increases for free swelling controls). We have also shown that dynamic loading of transiently transfected chondrocytes in agarose hydrogels for 1 hour at 10% strain increased aggrecan promoter activity by ∼1.5 fold (4). In this study we sought to further characterize the short term response of chondrocytes to static load (by measuring aggrecan promoter activity) and the effects of dynamic compression on aggrecan gene expression over a longer (3 day) culture period (by monitoring mRNA levels). Monitoring matrix gene expression during early times of culture, when there is little matrix accumulation and the cells deform directly with the matrix (5), may provide insights into cellular responses to strain and allow for the optimization of cartilage bioreactor conditions.