Altered Gene Expression in Gingival Tissues and Enhanced Bone Loss in Rats With Diabetes With Experimental Periodontitis

• Autores: Toshihide Noguchi, Kyoko Soboku, Takeshi Kikuchi, Sachiko Fujita
• Localización: Journal of periodontology, ISSN 0022-3492, Nº. 3, 2014, págs. 455-464
• Idioma: inglés
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• Resumen

  • Background: Systemic hyperglycemia is clearly related to severity of periodontitis, meaning that periodontitis can be exacerbated by diabetes mellitus (DM). However, the biologic mechanisms responsible for this relationship remain unclear. Thus, in this study, the global gene expression in gingival tissue with periodontitis is profiled in Zucker diabetic fatty (ZDF) rats compared with Zucker normoglycemic littermates (Lean).

    Methods: At age 8 weeks, ZDF and Lean rats received ligature placement around the maxillary right second molar. At 0, 14, 28, 42, and 56 days after ligature placement, the maxilla around the molar was analyzed using microcomputed tomography. Two and 7 days after ligature placement, total RNA in the gingival tissue was isolated, and gene expression analysis was conducted using a rat oligo array. To validate the microarray findings, the selected genes were analyzed using real-time quantitative polymerase chain reaction assays.

    Results: There was a significant difference regarding the average amount of bone resorption between ZDF and Lean rats from days 14 to 56. On day 2, it was found that 113 genes were regulated (20 upregulated, 93 downregulated) in the presence of DM. Lipopolysaccharide binding protein (LBP) messenger RNA (mRNA) expression was significantly higher in gingival tissue with periodontitis from ZDF rats compared with that from Lean rats. On day 7, interleukin (IL)-10 and IL-24 mRNA levels were significantly lower, whereas IL-2 level was significantly elevated.

    Conclusion: The results of this study indicate that the role of DM in modulating bone breakdown related to periodontitis may involve an increased level of LBP and reduced levels of T-helper 2 cytokines.

    Periodontal disease has been identified as a complication of diabetes mellitus (DM), and previous studies have found that individuals with diabetes have a two- to three-fold greater risk for both severe periodontitis and periodontal disease progression.1 A diabetic condition increases periodontal tissue breakdown as a result of abnormal immune response, altered fibroblast function and levels of collagen, and microvascular dysfunction. It has been reported that patients with DM have an oral bacterial flora similar to that found in healthy individuals,2 although their response to infection is not the same.3,4 In addition, patients with DM have been shown to have markers of systemic inflammation, and it has been postulated that such an inflammatory state can lead to increased breakdown of chronically infected periodontium.1,5 Because these patients have increased levels of systemic proinflammatory mediators, the local environment of the periodontium is also affected by higher levels of inflammation.

    Bacterial byproducts from periodontal infections, such as lipopolysaccharide (LPS), act through distinct pathways to increase inflammation.6 Furthermore, the synergistic effects of impaired fibroblasts and neutrophils and decreased levels of collagen and hyper-responsive inflammatory cells, coupled with the effects of advanced glycation end products (AGEs) and LPS, function through distinct pathways to increase inflammation.7,8 Wound healing is also impaired in the periodontium under a diabetic condition; thus, these defects promote its breakdown.9 Zucker diabetic fatty (ZDF) rats, a well-characterized model of obesity and type 2 DM, have a point mutation in the leptin receptor that leads to impairment of the signaling capabilities of this receptor. The ZDF rat develops an age-dependent diabetic phenotype, with onset of obesity at 5 to 7 weeks of age accompanied by a metabolic state of early diabetes with hyperinsulinemia and insulin resistance but with euglycemia.10 The pathogenetic features of DM manifested in this animal model are in many ways reminiscent of the pathogenesis of type 2 DM in humans.11 Therefore, the ZDF animal model is useful for identifying molecules contributing to insulin resistance related to obesity and elucidating the molecular pathogenesis of type 2 DM.

    Despite findings showing that DM increases the risk of periodontal disease,12 relatively little is known about how type 2 DM alters inflammatory response in the periodontium. Thus, it was hypothesized that the biologic changes associated with type 2 DM may modulate the expression of proinflammatory and anti-inflammatory genes and proresorptive and antiresorptive agents in sites with periodontitis. In the present study, complementary DNA (cDNA) microarray analysis is used to examine global gene expressions in gingival tissue with periodontitis in 8-week-old ZDF rats, and the present findings were compared with those of age- and sex-matched Zucker normoglycemic littermate (Lean) control rats.