Regulation of matrix metalloproteinase activity during tissue remodelling

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Tissues are comprised of cells and a complex matrix of proteins cells secrete and adhere to. This extracellular matrix (ECM) is constantly remodeled, most obviously during the dramatic growth and cellular rearrangements of embryonic development, but also during wound healing and as part of the process of ageing. Cells remodel the ECM using a complex family of enzymes called matrix metalloproteinases (MMPs). Because MMPs digest all of the ECM proteins, their activity must be carefully regulated or tissues would disintegrate. Not surprisingly, defects in MMP regulation are causes and/or effects of a variety of diseases, including arthritis, heart disease and cancer. But surprisingly little is known about the regulation of MMP activity in living tissues; most of what we have learned comes from experiments done on isolated cells in petri dishes, and biochemical experiments with purified proteins.Zebrafish are an excellent model organism for biomedical research and we have identified all of the MMPs and their known regulators in the zebrafish genome. Because the zebrafish embryo is transparent, and develops externally and rapidly, we can observe the effects of manipulating MMP activity relatively easily. Furthermore, we have developed techniques that take advantage of the transparency of the fish embryo to visualize MMP activity, and to detect the biochemical events that regulate these ECM-remodeling proteases in the intact embryo. We have developed a novel transgenic line of zebrafish that expresses an engineered protein, which reports on the activation of one of these MMPs. Using these embryos we will generate the first ever map' of when and where this MMP becomes activated during development. Furthermore, using these embryos we can find out if the biochemical mechanisms that are thought to regulate this MMP are actually occurring in the living animal.Invasive cells use MMPs to degrade the boundaries between tissues, allowing them to migrate through the body. This is essential for normal embryonic development, wound healing, and the immune response, but it is also how tumour cells metastasize. We would therefore like to better understand how MMPs are regulated at the interface between normally and pathologically invasive cell types. We can transplant human tumour cells into zebrafish embryos and observe them as they proliferate and spread through the embryo. Using our transgenic line and other tools, we can test hypotheses about how invasive cells use their own MMPs and/or the MMPs present in the surrounding tissues to degrade the ECM, allowing them to invade and move through the embryo. This will not only help us understand how embryos build themselves and how tissues maintain and regenerate their structure after injury, but also how MMPs become activated under pathological conditions that cause damage to tissues, and allow tumors to spread throughout the body.