Apoptosis during wound healing, fibrocontractive diseases and vascular wall injury

Following injury, tissue repair involves inflammation, granulation tissue formation and scar constitution. Granulation tissue develops from the connective tissue surrounding the damaged or missing area and contains mainly small vessels, inflammatory cells, fibroblasts and myofibroblasts. As the wound closes and evolves into a scar, there is a striking decrease in cellularity, including disappearance of typical myofibroblasts. The question arises as to what process is responsible for granulation tissue cell disappearance. Our results (in cutaneous wounds) and results of other laboratories (particularly in lungs and kidney) suggest that apoptosis is the mechanism responsible for the evolution of granulation tissue into a scar. During excessive scarring (hypertrophic scar or fibrosis), it is conceivable that the process of apoptosis cannot take place. After experimental endothelial injury in an artery, accumulation of smooth muscle cells participates in the formation of intimal thickening. Apoptotic features have been observed in cells of intimal thickening and also within human atherosclerotic plaques. In the case of atherosclerosis, apoptosis could be detrimental: since smooth muscle cells participate in plaque stability, apoptosis could lead to weakening and rupture of the plaque. These results underline the fact that both increased cell survival or excessive cell death can be associated with pathological disorders. Specific therapies devised to enhance or decrease the susceptibility of individual cell types to apoptosis development could modify the evolution of a variety of human diseases.