Matrix metalloproteinases and their specific tissue inhibitors in menstruation.

The timely breakdown of extracellular matrix is essential for menstruation. Matrix metalloproteinases, which are able to degrade virtually all components of the extracellular matrix, are spatiotemporally expressed in the cyclic endometrium. The expression of most matrix metalloproteinases is regulated transcriptionally and their proteolytic activities are precisely controlled. The balance between matrix metalloproteinases and their specific tissue inhibitors is believed to be crucial for menstruation. This review focuses on the roles of matrix metalloproteinases and their tissue inhibitors in the initiation of menstruation and on the regulation of matrix metalloproteinase expression and activation. For example, the function of matrix metalloproteinases and their tissue inhibitors in endometrial re-epithelialization and angiogenesis during endometrial regeneration, when cell migration is facilitated to ensure endometrial repair, is discussed. This and other processes, although not fully resolved, serve to illustrate the involvement of matrix metalloproteinases and their tissue inhibitors in the process of menstruation.