Mechanical regulation of matrix metalloproteinases.

Matrix metalloproteinases can degrade and modify almost all components of the extracellular matrix hence their enzymatic activity is tightly regulated under physiological conditions. Primary modes of enzyme regulation include transcriptional control, zymogen activation and dynamic inhibition by tissue inhibitors of matrix metalloproteinases. Recent studies have demonstrated that mechanical regulation of matrix metalloproteinases largely operate through these regulatory pathways. Over the last decade a large cohort of studies have been conducted on many tissue/cell types using diverse loading parameters in vivo and in vitro suggesting that mechanical load is essential in maintaining normal tissue function via the matrix metalloproteinases. However there may be a mechanically-regulated homeostasis, with cells responding to and interpreting growth factors and other biochemical signals within the context of mechanical forces to provide a suitable cellular matrix metalloproteinase response. On the contrary, mechanical overload can result in unrestrained matrix metalloproteinase activities eventually leading to matrix degradation, mechanical dysfunction and failure of the tissue. In this chapter, the effect of mechanical load on matrix metalloproteinase expression will be reviewed, and the signal transduction pathways involved in modulating the metabolic homeostasis of various tissues including blood vessels, intervertebral disc and components of the synovial joint with emphasis on articular cartilage discussed. Both mechanically-induced stimulation and inhibition of matrix metalloproteinases will be discussed and placed into context with their potential relevance to disease.