The p110α and p110ß isoforms of class I phosphatidylinositol 3-kinase are involved in toll-like receptor 5 signaling in epithelial cells.

BACKGROUND: Bacterial flagellin triggers inflammation in mammalian cells via Toll-like receptor (TLR) 5. Release of the chemokine IL-8 in response to flagellin involves NF-κB, p38 MAP kinase, and phosphatidylinositol 3-kinase (PI3K). However, PI3K has been reported to be either pro- or anti-inflammatory in different model systems. We hypothesized that this could be due to different activities of the p110α and ß isoforms of PI3K. RESULTS: PI3K and Akt were rapidly activated in Caco-2 colon carcinoma cells by flagellin. Using a plasmid-based shRNA delivery system and novel p110 isoform-specific inhibitors, we found that flagellin-induced IL-8 production was dependent on both p110α and p110ß. However in the mouse, inhibition of p110ß but not p110α reduced the increase of serum IL-6 levels induced by intraperitoneal injection of flagellin. CONCLUSIONS: These data demonstrate that the p110α and ß isoforms of class IA PI3K are both required for the proinflammatory response to flagellin.

Protein kinase D interaction with TLR5 is required for inflammatory signaling in response to bacterial flagellin.

Protein kinase D (PKD), also called protein kinase C (PKC)mu, is a serine-threonine kinase that is involved in diverse areas of cellular function such as lymphocyte signaling, oxidative stress, and protein secretion. After identifying a putative PKD phosphorylation site in the Toll/IL-1R domain of TLR5, we explored the role of this kinase in the interaction between human TLR5 and enteroaggregative Escherichia coli flagellin in human epithelial cell lines. We report several lines of evidence that implicate PKD in TLR5 signaling. First, PKD phosphorylated the TLR5-derived target peptide in vitro, and phosphorylation of the putative target serine 805 in HEK 293T cell-derived TLR5 was identified by mass spectrometry. Furthermore, mutation of serine 805 to alanine abrogated responses of transfected HEK 293T cells to flagellin. Second, TLR5 interacted with PKD in coimmunoprecipitation experiments, and this association was rapidly enhanced by flagellin treatment. Third, pharmacologic inhibition of PKC or PKD with Gö6976 resulted in reduced expression and secretion of IL-8 and prevented the flagellin-induced activation of p38 MAPK, but treatment with the PKC inhibitor Gö6983 had no significant effects on these phenotypes. Finally, involvement of PKD in the p38-mediated IL-8 response to flagellin was confirmed by small hairpin RNA-mediated gene silencing. Together, these results suggest that phosphorylation of TLR5 by PKD may be one of the proximal elements in the cellular response to flagellin, and that this event contributes to p38 MAPK activation and production of inflammatory cytokines in epithelial cells.

Cholesterol in Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia and affects up to 15 million people worldwide. Although no single cause of AD has been identified, recent research has suggested that several pathogenetic factors influence risk and expression. A growing amount of evidence underscores a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques. Excess brain cholesterol has been associated with increased formation and deposition of amyloid-beta peptide from amyloid precursor protein. Cholesterol-lowering statins have become a focus of research in AD. Genetic polymorphisms associated with pivotal points in cholesterol metabolism in brain tissues may contribute to the risk and pathogenesis of AD. In this review, we summarise current knowledge of the role of cholesterol metabolism in the pathogenesis of AD and examine the potential of statins in the prevention and treatment of AD.