Myofibroblast-like cells and wound contraction in leech wound healing

This research aims to characterize the wound contraction process in the leech Hirudo medicinalis since much evidence indicates that the cells that form the pseudoblastema act in wound contraction as well as in phagocytosis and in regenerative processes. In H. medicinalis the pseudoblastema is formed by a single type of connective cell, the vasocentral cells. Electron microscopy and actin labeling with phalloidin are used to follow the behavior of vasocentral cells and actin bundles present in their cytoplasm through the healing process. During the formation and evolution of the pseudoblastema, vasocentral cells undergo several changes. When the pseudoblastema consolidates, cell junctions are formed, and the actin bundles are seen to converge with them. At this moment, the cells, and therefore the actin bundles, are lying parallel to the surface. At the time that wound contraction occurs, the cells and also the actin bundles orientate perpendicular to the wound surface, and the pseudoblastema retracts. During this stage, actin bundles become enlarged, cell-to-cell adhering junctions become more conspicuous, and the intercellular space is filled with a filamentous material. The thickening and reorganization of the actin bundles are correlated with the development of wound contraction. These findings give support to the hypothesis that tension within the wound is generated by the formation of intracellular stress fibers and transmitted by the interaction of the stress fibers with the extracellular matrix or with neighboring cells through extracellular space, analogous to the role played by myofibroblasts in vertebrate wound healing. Despite some differences, the similarity between vasocentral cells and myofibroblasts is remarkable and may reflect a requirement for contractile elements in the scar zone directed towards producing the wound contraction phenomenon. (C) 1996 Wiley-Liss, Inc.