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Although it is known that diabetes impairs oral wound healing, relatively little is known about the cellular parameters affected, particularly in connective tissue. This study investigated the hypothesis that diabetes impairs connective tissue formation in healing gingiva, and that impaired healing is associated with factors that decrease fibroblast numbers. Full-thickness wounds were created in the palatal gingiva of type 1 and type 2 diabetic and normoglycemic mice. Five days after wounding, diabetic mice had less epithelial wound coverage, less new connective tissue formation, and reduced fibroblast density (p < 0.05). This occurred with increased numbers of caspase-3- and TUNEL-positive fibroblasts, decreased fibroblast proliferation, increased nuclear translocation of the pro-apoptotic transcription factor FOXO1, and increased numbers of polymorphonuclear leukocytes, all of which were significant (p < 0.05). The results suggest that diabetes may decrease fibroblast numbers through increased apoptosis and reduced proliferation, both of which may be mediated through increased activation of FOXO1.

Porphyromonas gingivalis is an oral bacterium that causes pathology in a number of dental infections that are associated with increased fibroblast cell death. Studies presented here demonstrated that P. gingivalis stimulates cell death by apoptosis rather than necrosis. Unlike previous studies apoptosis was induced independent of proteolytic activity and was also independent of caspase activity because a pancaspase inhibitor, Z-VAD-fmk, had little effect. Moreover, P. gingivalis downregulated caspase-3 mRNA levels and caspase-3 activity. The consequence of this downregulation was a significant reduction in tumour necrosis factor-alpha-induced apoptosis, which is caspase-3-dependent. Immunofluorescence and immunoblot analysis revealed P. gingivalis-induced translocation of apoptosis-inducing factor (AIF) from the cytoplasm to the nucleus. siRNA studies were undertaken and demonstrated that P. gingivalis stimulated cell death was significantly reduced when AIF was silenced (P < 0.05). Treatment of human gingival fibroblasts with H-89, a protein kinase A inhibitor that blocks AIF activation also reduced P. gingivalis-induced apoptosis (P < 0.05). These results indicate that P. gingivalis causes fibroblast apoptosis through a pathway that involves protein kinase A and AIF, is not dependent upon bacterial proteolytic activity and is also independent of the classic apoptotic pathways involving caspase-3.

Diabetics suffer from both more frequent bacterial infections and greater consequences of infection. However, bacteria-induced tissue destruction and the subsequent response in diabetics have received relatively little attention. To investigate this issue, we inoculated the scalp of control or db/db diabetic mice, with the pathogen Porphyromonas gingivalis, which causes connective tissue destruction in humans. Both bacteria-induced cytokine expression and tissue loss were similar in diabetic and control mice. However, there was a significantly higher rate of fibroblast-specific apoptosis in the diabetic group, which was measured as cells that were double positive for the terminal deoxynucleotidyltransferase-mediated deoxy-UTP nick end labeling assay and expression of vimentin. The higher rate of fibroblast apoptosis could be explained in the diabetic group by enhanced levels of activated caspase-3. Apoptosis was evident during the peak healing period and coincided with reduced numbers of fibroblasts, diminished collagen I and III expression, and significantly reduced formation of new connective tissue matrix in diabetic mice. Thus, diabetes may impair the healing response to bacteria-induced connective tissue loss by increasing the number of caspase-3-activated fibroblasts, leading to greater apoptosis and reduced numbers of fibroblastic cells.

P. gingivalis is an important oral pathogen, which has been closely linked to periodontal disease as well as lesions of endodontic origin. Both infections are associated with a decrease in fibroblast numbers, formation of an inflammatory infiltrate, and bone resorption. The goal of this study was to investigate the role that the host response plays in the capacity of P. gingivalis to stimulate fibroblast apoptosis, PMN recruitment, and osteoclastogenesis. This was accomplished by the use of an in vivo calvarial model in mice with targeted deletion of TNF receptors p55 and p75 and matched wild-type mice. The results indicate that P. gingivalis induces fibroblast apoptosis in vivo and establish for the first time that this involves the stimulation of a host response. Moreover, bacteria-stimulated PMN recruitment and osteoclastogenesis were also dependent upon the host response. The results suggest that much of the damage caused by P. gingivalis infection, including fibroblast apoptosis, at least under some circumstances, results from stimulation of the host response rather than the direct effect of bacterial products. Furthermore, this may represent a more general mechanism by which bacterial challenge induces apoptosis of matrix-producing cells through the induction of TNF.

Using a ligature-induced model in type-2 Zucker diabetic fatty (ZDF) rat and normoglycemic littermates, we investigated whether diabetes primarily affects periodontitis by enhancing bone loss or by limiting osseous repair. Diabetes increased the intensity and duration of the inflammatory infiltrate (P < 0.05). The formation of osteoclasts and percent eroded bone after 7 days of ligature placement was similar, while four days after removal of ligatures, the type 2 diabetic group had significantly higher osteoclast numbers and activity (P < 0.05). The amount of new bone formation following resorption was 2.4- to 2.9-fold higher in normoglycemic vs. diabetic rats (P < 0.05). Diabetes also increased apoptosis and decreased the number of bone-lining cells, osteoblasts, and periodontal ligament fibroblasts (P < 0.05). Thus, diabetes caused a more persistent inflammatory response, greater loss of attachment and more alveolar bone resorption, and impaired new bone formation. The latter may be affected by increased apoptosis of bone-lining and PDL cells. [ABSTRACT FROM AUTHOR]