ERK1/2 Activation Induced by Inflammatory Cytokines Compromises Effective Host Tissue Integration of Engineered Cartilage

Abstract

Objective: Proinflammatory cytokines are known to provoke degradative signaling cascades that promote extracellular matrix disintegration in articular cartilage. Because integration of the repair tissue into the surrounding native cartilage to produce a mechanically stable interface has a profound impact on the viability and functionality of the restored joint surface, this study examined the effects of proinflammatory cytokines on the properties of tissue-engineered cartilage in the context of integration. Methods: Using an established in vitro cartilage defect model, we examined the integration of chondrocyte-laden agarose constructs into native articular cartilage and the biochemical and biomechanical alterations of these implants upon treatment with interleukin 1-β (IL1-β) and tumor necrosis factor-α (TNF-α). Additionally, we probed extracellular regulated kinase (ERK) signaling involvement in response to proinflammatory cytokines. Results: The time-dependent accumulation of extracellular matrix and concomitant increase in Young's modulus observed in the absence of cytokines was significantly decreased upon IL1-β and TNF-α treatment. Push-out test showed the highest interface strength in hybrid cultures maintained without cytokines, which was significantly lowered with IL1-β and TNF-α treatment. Histological characteristics of the interface region are consistent with the biochemical findings. Treatment with an inhibitor of ERK pathway antagonized the deleterious effects caused by both cytokines. Conclusion: This study is the first to show the functional catastrophic effects of IL1-β and TNF-α on the biochemical, structural, and integrative properties of tissue-engineered cartilage and their significant counteraction by the blockade of ERK signaling pathway. With the discovery of new potential chemical entities, ERK inhibitor may emerge as a new therapeutic approach for functional integration and mechanical integrity of an engineered cartilage to the host tissue and, therefore, enhance long-term viability and functionality of the restored joint surface.