Diabetes enhances mRNA levels of proapoptotic genes and caspase activity, which contribute to impaired healing
Date
2007
DOI
Authors
Al-Mashat, Hesham Abdulatif
Version
OA Version
Citation
Abstract
Diabetes has been identified as an important risk factor for periodontal disease. After bacterial insult, inflammation induces a net loss of both connective tissue attachment and bone. Under normal conditions this bacteria-stimulated injury is healed by the action of matrix producing ce11s. It is widely known that diabetes can affect fibroblasts proliferation. Other mechanisms for the loss of matrix-producing cells through apoptosis may be implicated but have not yet been well studied. To investigate a potential mechanism by which this might occur, Porphyromonas gingivalis were inoculated into the scalp of type 2 diabetic (db/db) and control mice. Mice were euthanized at the early phase of infection (8 and 21 hours) or during the repair of the bacteria-induced wound (5 and 8 days). At 8 hours the activity of caspase-8 and -9 was significantly higher in diabetic mice (P[less than]0.05). At 21 hours, the rate of fibroblast apoptosis along with the activity of caspase-3 and -8 were all significantly higher in diabetic mice (P[less than]0.05). Treatment with pan caspase inhibitors Z-VAD-fmk N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone) or more specific caspase-3 inhibitor Z-DEVD-FMK (Z-Asp (OMe)-Glu (OMe)-Val-Asp (OMe)-fluoromethylketone) equally and significantly reduced the rate of fibroblast apoptosis. We investigated the repair of bacteria-induced tissue loss in diabetic mice. The results indicate that during the peak healing period there was a significantly higher rate of fibroblast apoptosis and bone-1ining cells in the diabetic group (P[less than]0.05). This coincided with a significantly diminished collagen I and III expression and significantly reduced formation of new connective tissue matrix and bone in diabetic mice. RNA profiling and caspase activity were measured. Diabetes caused a more than two fold 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 pan caspase inhibitor. 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. Therefore, the results signifying that most of the damage caused by P. gingivalis infection, including fibroblast apoptosis, at least under some circumstances, occur from the host response stimulation rather than the direct effect of bacterial products. Furthermore, diabetes-enhanced apoptosis represents an important mechanism through which healing is impaired. This can be explained, in part, by diabetes-increased expression of proapoptotic genes and caspase activity.
Description
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.
Thesis (D.Sc.)--Boston University, Henry M. Goldman School of Dental Medicine, 2007 (Oral Biology).
Includes bibliography: leaves 102-124.
Thesis (D.Sc.)--Boston University, Henry M. Goldman School of Dental Medicine, 2007 (Oral Biology).
Includes bibliography: leaves 102-124.
License
This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.