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2004
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tom 51
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nr 1
253-262
EN
We have previously reported on the identification and characterization of the Porphyromonas gingivalis A7436 strain outer membrane receptor HmuR, which is involved in the acquisition of hemin and hemoglobin. We demonstrated that HmuR interacts with the lysine- (Kgp) and arginine- (HRgpA) specific proteases (gingipains) and that Kgp and HRgpA can bind and degrade hemoglobin. Here, we report on the physiological significance of the HmuR-Kgp complex in heme utilization in P. gingivalis through the construction and characterization of a defined kgp mutant and a hmuR kgp double mutant in P. gingivalis A7436. The P. gingivalis kgp mutant exhibited a decreased ability to bind both hemin and hemoglobin. Growth of this strain with hemoglobin was delayed and its ability to utilize hemin as a sole iron source was diminished as compared to the wild type strain. Inactivation of both the hmuR and kgp genes resulted in further decreased ability of P. gingivalis to bind hemoglobin and hemin, as well as diminished ability to utilize either hemin or hemoglobin as a sole iron source. Collectively, these in vivo results further confirmed that both HmuR and Kgp are involved in the utilization of hemin and hemoglobin in P. gingivalis A7436.
EN
Peroxisome proliferator-activated receptor (PPAR), a member of the superfamily of nuclear receptor transcription factors, plays a critical role in the regulation of the expression of genes associated with inflammation. Using mucous acinar cells of sublingual salivary gland, we investigated the effect of PPAR activation on the disturbances in salivary mucin synthesis evoked by lipopolysaccharide (LPS) of periodontopathic bacterium, P. gingivalis. Exposure of the acinar cells to the LPS led to a dose-dependent decrease (up to 58.4%) in mucin synthesis, accompanied by a massive enhancement in apoptosis and NO production, and an induction in inducible nitric oxide synthase (NOS-2) activity. Activation of PPAR with a specific synthetic agonist, ciglitazone, prevented in a dose-dependent fashion the LPS-induced reduction in mucin synthesis, and the effect was reflected in a marked decrease in apoptosis, NO generation, and the expression of NOS-2 activity. The impedance by ciglitazone of the LPS-induced changes in mucin synthesis was blocked by PD98059, an inhibitor of extracellular signal regulated kinase (ERK), as well as wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K). Moreover, both agents caused further enhancement in the LPS-induced nitric oxide generation and countered the inhibitory effect of ciglitazone on the LPS-induced upregulation in NOS-2. The findings suggest that the impedance of P. gingivalis LPS inhibition of salivary mucin synthesis by PPAR agonist, ciglitazone, involves activation of ERK pathway by PI3K.
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