Negative Regulation of Innate Immune Responses through MAPK Phosphatases

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DESCRIPTION (provided by applicant): Periodontal disease initiation and progression occurs as a consequence of the host immune inflammatory response to oral pathogens. The production of inflammatory cytokines is a highly regulated process involving transcriptional and posttranscriptional mechanisms. One of the major signaling pathways activated by periopathogenic LPS in p38 MARK. Following p38 phosphorylation, inactivation of p38 MAP kinases is achieved mainly by a family of dual-specific MAP kinase phosphatases (MKP). MKP-1 is capable of negatively regulating both transcriptional and post transcriptional p38 MAP kinase activity. MKP-1 contributes towards LPS tolerance and over-expression of MKP-1 has shown to accelerate p38 inactivation resulting in diminished proinflammatory cytokine production. We have recently shown that LPS-induced IL-6 mRNA stability expression requires p38 signaling. Preliminary data for this proposal indicates that in MKP- 1 transfected cells, LPS-induced IL-6 expression is significantly attenuated. In addition, we have provided significant data showing the p38 is a major signaling pathway contributing to LPS-induced periodontal bone destruction. Based upon these data, we hypothesize that the endogenous negative regulator mechanism of p38 signaling, MKP-1, is a key component of responsible for attenuation of LPS-induced inflammatory cytokine expression in macrophages. In this proposal, the ability of TIP over-expression to decrease inflammation will be determined in vitro using gene targeted strategies in macrophages, and in vivo using experimental periodontitis models. The specific aims are 1) To determine the role of over-expressed MKP-1 on IL-6 and TNFa mRNA expression in vitro. 2) To determine the contribution of MKP-1 in ontogeny of inflammatory cytokine production and LPS-induced osteoclastogenesis in primary bone marrow macrophages and 3) To determine the impact of MKP-1 in inflammatory bone destruction in vivo using MKP mice. These studies will establish the role of LPS-induced cytokine expression and negative regulation in inflammatory bone loss through selective attenuation of p38 MAPK-induced signaling in periodontal bone destruction.