Inhibition of cell-matrix adhesions prevents cartilage chondrocyte death following impact injury

Abstract

Focal adhesions are transmembrane protein complexes that attach chondrocytes to the pericellular cartilage matrix and in turn, are linked to intracellular organelles via cytoskeleton. We previously found that excessive compression of articular cartilage leads to cytoskeleton-dependent chondrocyte death. Here we tested the hypothesis that this process also requires integrin activation and signaling via focal adhesion kinase (FAK) and Src family kinase (SFK). Osteochondral explants were treated with FAK and SFK inhibitors (FAKi, SFKi, respectively) for 2 h and then subjected to a death-inducing impact load. Chondrocyte viability was assessed by confocal microscopy immediately and at 24 h post-impact. With no treatment immediate post-impact viability was 59%. Treatment with 10 μM SFKi, 10 μM, or 100 μM FAKi improved viability to 80%, 77%, and 82%, respectively (p < 0.05). After 24 h viability declined to 34% in controls, 48% with 10 μM SFKi, 45% with 10 μM FAKi, and 56% with 100 μM FAKi (p < 0.01) treatment. These results confirmed that most of the acute chondrocyte mortality was FAK- and SFK-dependent, which implicates integrin-cytoskeleton interactions in the death signaling pathway. Together with previous findings, these data support the hypothesis that the excessive tissue strains accompanying impact loading induce death via a pathway initiated by strain on cell adhesion receptors. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:448-454, 2014. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.