Apoptosis is increased in a model of diabetes-impaired wound healing in genetically diabetic mice

Impaired wound healing is a common complication of diabetes mellitus. The underlying pathophysiology of diabetes-impaired healing is poorly understood. In the present study we have compared cell proliferation rates, apoptosis (programmed cell death), the myofibroblast marker alpha-smooth muscle actin and procollagen I mRNA expression, between diabetic and control mice. Full-thickness skin wounds were made in non-obese diabetic (NOD) mice and C57B6 controls. NOD mice showed a marked retardation of wound healing at both 7 and 14 days after wounding. Comparison of cell proliferation rates 7 days after wounding, using 5-bromo-2'-deoxy-Uridine incorporation, showed higher rates of cell proliferation in controls (88.1 +/- 12.8) than in NOD wounds (52.1 +/- 9.9, p < 0.02, n = 4). Immunohistochemical detection of alpha-smooth muscle actin, showed a later onset in diabetic wounds, suggesting that wound contraction may be delayed in the diabetic animals. In situ hybridisation for alpha 1 (I) procollagen mRNA expression, showed reduced procollagen I expression in the diabetic wounds when compared with controls. Lastly, there appeared to be higher levels of apoptosis in diabetic wounds, shown by the terminal transferase mediated UTP nick end-labelling technique. Apoptotic cells were rare in control wounds confirming previous studies, which showed that apoptosis occurs late in normal wound healing as the wound matures into scar tissue. In conclusion, we hypothesize that reduced cell proliferation, retarded onset of the myofibroblast phenotype, reduced procollagen I mRNA expression and aberrant control of apoptotic cell death may contribute to impaired wound healing seen in this diabetic model.