Our results showed that the low-level Er:YAG laser irradiation stimulates the proliferation of cultured gingival fibroblasts. The optimal stimulative energy density was found to be 3.37 J/cm(2). This result suggests that Er:YAG laser irradiation may be of therapeutic benefit for wound healing.

Prostaglandin E2 (PGE2) exerts its biological actions via EP receptors (EP1, EP2, EP3, and EP4). In the present study, we investigated whether PGE2 regulated interleukin (IL)-1beta-induced matrix metalloproteinase (MMP)-3 production in human gingival fibroblasts (HGF) derived from periodontally healthy subjects and diseased patients. In HGF from healthy gingiva, PGE2 down-regulated IL-1beta-induced MMP-3 production, whereas in HGF from periodontitis patients, PGE2 enhanced it. Butaprost (an EP2 agonist) and ONO-AE1-329 (an EP4 agonist) suppressed IL-1beta-induced MMP-3 production, and 17-phenyl-omega-trinor PGE2 (an EP1 agonist) mimicked the PGE(2) effect in HGF from healthy and periodontally diseased tissues, respectively. Analysis of these data suggests that, in HGF from healthy tissue, IL-1beta-induced MMP-3 production is down-regulated by PGE2 via EP2 and EP4 receptors, whereas in cells from periodontally diseased tissue, IL-1beta-induced MMP-3 production is up-regulated via EP1 receptors. Different regulation of IL-1beta-induced MMP-3 production by PGE2 between healthy and periodontally diseased tissues may be involved in the pathogenesis of periodontal disease.

Our results showed that Er:YAG laser irradiation appears to exert its stimulative action on gingival fibroblasts proliferation through the production of PGE2 via the expression of COX-2. This should be considered as one of the important regulatory pathways to accelerate wound healing after Er:YAG laser irradiation.

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We suggest that PGE2 downregulates IL-1alpha-induced IL-6 production via EP2/EP4 receptors in human PDL cells.