SummaryVirulence of Pseudomonas aeruginosa involves the co-ordinate expression of a range of factors including type IV pili (tfp), the type III secretion system (TTSS) and quorum sensing. Tfp are required for twitching motility, efficient biofilm formation, and for adhesion and type III secretion (TTS)-mediated damage to mammalian cells. We describe a novel gene ( fimL ) that is required for tfp biogenesis and function, for TTS and for normal biofilm development in P. aeruginosa . The predicted product of fimL is homologous to the Nterminal domain of ChpA, except that its putative histidine and threonine phosphotransfer sites have been replaced with glutamine. fimL mutants resemble vfr mutants in many aspects including increased autolysis, reduced levels of surface-assembled tfp and diminished production of type III secreted effectors. Expression of vfr in trans can complement fimL mutants. vfr transcription and production is reduced in fimL mutants whereas cAMP levels are unaffected. Deletion and insertion mutants of fimL frequently revert to wild-type phenotypes suggesting that an extragenic suppressor mutation is able to overcome the loss of fimL . vfr transcription and production, as well as cAMP levels, are elevated in these revertants, while Pseudomonas quinolone signal (PQS) production is reduced. These results suggest that the site(s) of spontaneous mutation is in a gene(s) which lies upstream of vfr transcription, cAMP, production, and PQS synthesis. Our studies indicate that Vfr and FimL are components of intersecting pathways that control twitching motility, TTSS and autolysis in P. aeruginosa .

Type IV pili of the opportunistic pathogen Pseudomonas aeruginosa mediate twitching motility and act as receptors for bacteriophage infection. They are also important bacterial adhesins, and nonpiliated mutants of P. aeruginosa have been shown to cause less epithelial cell damage in vitro and have decreased virulence in animal models. This finding raises the question as to whether the reduction in cytotoxicity and virulence of nonpiliated P. aeruginosa mutants are primarily due to defects in cell adhesion or loss of twitching motility, or both. This work describes the role of PilT and PilU, putative nucleotide-binding proteins involved in pili function, in mediating epithelial cell injury in vitro and virulence in vivo. Mutants of pilT and pilU retain surface pili but have lost twitching motility. In three different epithelial cell lines, pilT or pilU mutants of the strain PAK caused less cytotoxicity than the wild-type strain but more than isogenic, nonpiliated pilA or rpoN mutants. ThepilT and pilU mutants also showed reduced association with these same epithelial cell lines compared both to the wild type, and surprisingly, to a pilA mutant. In a mouse model of acute pneumonia, the pilT and pilUmutants showed decreased colonization of the liver but not of the lung relative to the parental strain, though they exhibited no change in the ability to cause mortality. These results demonstrate that pilus function mediated by PilT and PilU is required for in vitro adherence and cytotoxicity toward epithelial cells and is important in virulence in vivo.

PPARgamma ligands repress VEGF gene expression via a PPARgamma-responsive element (PPRE) in the VEGF gene promoter. Agonists of this nuclear receptor might be exploited pharmacologically to inhibit pathological vascularization in complications of pregnancy, endometriosis and endometrial adenocarcinoma.

We previously described activators of peroxisome proliferator-activated receptor gamma (PPAR gamma) in the serum of pregnant women. We have also characterized this activating component by using a hexane-extracted serum fraction to examine PPAR activator levels in normal and preeclamptic (PE) pregnancies. In this study we report that the pregnancy PPAR activator is present in similar concentrations in serum and plasma. We also found that the activating fractions from pregnancy sera stimulate not only PPAR gamma, but also PPAR alpha, and are capable of inhibiting the production of inflammatory cytokines, consistent with known PPAR ligands. In experiments comparing extracts from normal and PE patients, we found that extracts from women with severe PE showed a reduced level of PPAR activation compared with extracts from normal pregnant women. This reduction was more pronounced for PPAR gamma than PPAR alpha activation. Finally, this reduction in circulating PPAR activator was observed weeks and sometimes months before the clinical diagnosis of PE. Based on these results, we conclude that PPAR activation is reduced in preeclamptic pregnancy before the onset of maternal symptoms. We speculate that endogenous regulators of PPAR play a role in maternal metabolism and immune function in normal and pathological pregnancies.