How do epidermal matrix metalloproteinases support re-epithelialization during skin healing?

Epithelialization of normal wounds occurs by an orderly series of events whereby keratinocytes migrate, proliferate, and differentiate to restore the epidermal barrier function. Keratinocyte migration is one of the earliest and crucial events determining the efficiency of the overall wound repair process. In response to various stimuli including that of growth factors, cytokines and the extracellular matrix, activated keratinocytes at the edges of the wound undergo dramatic morphological changes according to their migratory behaviour through development of protrusive adhesion contacts and cytoskeleton rearrangements. These phenotypic changes are accompanied by the upregulated expression of a new set of genes, among which are adhesion receptors and specific matrix degrading enzymes named matrix metalloproteinases (MMPs). The tightly regulated spatial and temporal MMP expression is crucial for proper re-epithelialization. These multi-domain zinc-containing endopeptidases are necessary for the proper completion of multiple features of epidermal regeneration. They play a key role in the migration process by controlling the repeated cycles of keratinocyte attachment and retraction. In the meantime, they process, degrade or remodel the extracellular matrix often producing cleavages in a gain-of-function manner.