Chapter category: Cell Metabolism

External Lysosomes The Osteoclast and its Unique Capacities to Degrade Mineralised Tissues

This chapter appears in the following book:

Lysosomes

Edited by: Paul Saftig
ISBN: 0-387-25562-1
» Get more information about this book at landesbioscience.com «

Chapter authors:
Vincent Everts, Wouter Beertsen

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Lysosomes contain the enzymatic machinery to digest a host of organic substances. This degrading activity occurs primarily inside the living cell where the lysosomes reside. Yet, some cells use lysosomal enzymes in the extracellular space to digest proteins in their direct vicinity. Secretion of these enzymes by neutrophils is an essential step in the digestion/ killing of (parts of ) bacteria in the defence of an organism.1-4 Macrophages also may secrete lysosomal enzymes.2,5-7 Some observations even suggest that fibroblasts have the capacity to secrete such enzymes into the extracellular space.8,9 Since the majority of lysosomal enzymes are active at a low pH, an effective use of the enzymes extracellular can occur only if a low pH is created and maintained for some time. This is possible if the cell has the capacity to seclude a restricted area from its surrounding environment. The latter situation is highly effective during degradation of mineralised matrices, like bone and calcified cartilage. The cell primarily involved in this process is the multinucleated osteoclast.10,11 In the present paper some of the unique properties of this cell will be discussed, in particular its ability to create an extracellular lysosomal compartment, the prime site where resorption of mineralised tissue occurs.

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Chapter category: Cell Metabolism

External Lysosomes The Osteoclast and its Unique Capacities to Degrade Mineralised Tissues

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