Apoptosis of endothelial cells in diabetes type 2 and atherosclerosis eventually results in loss of integrity of the endothelial lining with the consequences described above (Fig. 3). Until recently it was accepted that repair of these defects could only be accomplished by local endothelial cells. Recently published observations, however, indicate that certain subpopulations of bone marrow stem cells, circulatory endothelial progenitor cells (CPCs), can be mobilized in response to various stimuli, such as exercise and growth factors (28). After leaving the bone marrow they home in to vessels with defective endothelial lining; they attach to these defective areas and become competent and functional endothelial cells. Their concentration in the peripheral circulation can be increased by regular physical exercise; moreover, their functional capabilities as reflected by their migratory capacity are improved, and their concentration has been associated with future cardiovascular events. However, their survival and functional integrity in the peripheral circulation is greatly diminished by hyperglycemic states (28, 29).
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