Diabetes Enhances mRNA Levels of Proapoptotic Genes and Caspase Activity, Which Contribute to Impaired Healing

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Abstract
We previously reported that after a bacteria-induced wound in the scalp, type 2 diabetic (db/db) mice had higher levels of apoptosis of fibroblasts and bone-lining cells that are critical for healing compared with normoglycemic controls. To investigate mechanisms by which this might occur, RNA profiling and caspase activity was measured after inoculation of Porphyromonas gingivalis. Diabetes caused a more than twofold induction of 71 genes that directly or indirectly regulate apoptosis and significantly enhanced caspase-8, -9, and -3 activity. The functional significance of diabetes-induced apoptosis was studied by treating diabetic mice with a pancaspase inhibitor, z-VAD-fmk (N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone). Inhibiting apoptosis significantly improved several parameters of healing, including fibroblast density, enhanced mRNA levels of collagen I and III, and increased matrix formation. Improvements were also noted in bone, with an increase in the number of bone-lining cells and new bone formation. Thus, diabetes-enhanced apoptosis represents an important mechanism through which healing is impaired, and this can be explained, in part, by diabetes-increased expression of proapoptotic genes and caspase activity.