No abstract

Beta-amyloid (Abeta) peptides are key proteins in the pathophysiology of Alzheimer's disease (AD). While Abeta42 aggregates very rapidly to form early diffuse plaques, supplemental Abeta40 deposition is required to form mature neuritic plaques. We here investigated the role of nuclear factor-kappaB (NF-kappaB) pathway in Abeta40-mediated neuronal damage and amyloid pathology. In rat primary neurons and human postmitotic neuronal cells, the Abeta peptide induced a dose-dependent neuronal death, reduced the levels of the anti-apoptotic protein Bcl-XL, enhanced the cytosolic release of cytochrome c, and elicited the intracellular accumulation and secretion of Abeta42 oligomers. Moreover, Abeta40 activated the NF-kappaB pathway by selectively inducing the nuclear translocation of p65 and p50 subunits, and promoted an apoptotic profile of gene expression. As inhibitors of the NF-kappaB pathway, we tested the capability of a double-stranded kappaB decoy oligonucleotide, the anti-inflammatory drug aspirin and the selective IkappaB kinase 2 inhibitor, AS602868, to modify the Abeta40-mediated effects. These treatments, transiently applied before Abeta exposure, completely inhibited p50/p65 nuclear translocation and neuronal damage. The kappaB decoy also inhibited the Abeta-induced release of cytochrome c, restored the levels of Bcl-XL, and prevented intraneuronal accumulation and secretion of Abeta42. These results open up interesting perspectives on the development of novel strategies targeting out NF-kappaB p50/p65 dimers for pharmacological intervention in AD.

We examined the effects of the adipose hormone leptin on the development of mouse cortical neurons. Treatment of neonatal and adult mice with intraperitoneal leptin (5 mg/kg) induced extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in pyriform and entorhinal cortex neurons. Stimulation of cultured embryonic cortical neurons with leptin evoked Janus kinase 2 and ERK1/2 phosphorylation and activated the downstream effector 90-kDa ribosomal protein S6 kinase. Moreover, leptin elicited the phosphorylation of the phosphatidylinositol 3-kinase effector Akt and evoked Ser-9 phosphorylation of glycogen synthase kinase-3␤ (GSK3␤), an event inactivating this kinase. Leptin-mediated GSK3␤ phosphorylation was prevented by the MEK/ERK inhibitor PD98059, the phosphatidylinositol 3-kinase inhibitor LY294002, or the protein kinase C inhibitor GF109203X. Exposure of cortical neurons to leptin also induced Ser-41 phosphorylation of the neuronal growth-associated protein GAP-43, an effect prevented by LY294002 and GF109203X but not by PD98059. Ser-41-GAP-43 phosphorylation is usually high in expanding axonal growth cones. Neurons exposed to 100 ng/ml leptin for 72 h displayed reduced rate of growth cone collapse, a shift of growth cone size distribution toward higher values, and a 4-fold increase in mean growth cone surface area compared with control cultures. The leptin-induced growth cone spreading was hampered in cortical neurons from Lepr db/db mice lacking functional leptin receptors; it was associated with localized Ser-9-GSK3␤ phosphorylation and mimicked by the GSK3␤ inhibitor SB216763. At concentrations preventing GSK3␤ phosphorylation, PD98059, LY294002, or GF109203X reversed the leptin-induced growth cone surface enlargement. We concluded that the leptinmediated regulation of growth cone morphogenesis in cortical neurons relies on upstream regulators of GSK3␤ activity.The adipocyte-derived hormone leptin acts as satiety signal in hypothalamic nuclei to regulate energy homeostasis (1, 2). Mice lacking leptin (Lep ob/ob mice) display obesity and several associated abnormalities (1). Excluding very rare cases of humans with genetic obesity, obese human subjects have high circulating leptin levels and hypothalamic insensitivity to leptin (1).Five leptin receptors (LEPRs) 2 in the mouse have been identified, including long (LEPRb) and short isoforms (LEPRa and LEPRc-e). LEPRb, which is ineffective in Lepr db/db mice, phosphorylates Janus kinase 2 (JAK2), which in turn phosphorylates LEPRb tyrosine residues to mediate downstream signaling (3, 4). Recruitment of the signal transducer and activator of transcription-3 (STAT3) is broadly considered a molecular signature of hypothalamic leptin signaling and drives subsequent induction of genes, including that of the feedback inhibitor, suppressor of cytokine signaling-3 (SOCS3). LEPRb stimulation can also activate the extracellular signal-regulated kinase (ERK) signaling in the mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol 3-kinase (PI...

The two major porins of Escherichia coli K-12 strains, OmpC and OmpF, are inversely regulated with respect to one another. The expression of OmpC and OmpF has been shown to be influenced by the leucine-responsive regulatory protein (Lrp): two-dimensional gel electrophoresis of proteins from strains with and strains without a functional Lrp protein revealed that OmpC expression is increased in an lrp strain, while OmpF expression is decreased. In agreement with these findings, we now present evidence that transcriptional (operon) fusions of lacZ ؉ to ompC and micF are negatively regulated by Lrp. Lrp binds specifically to the intergenic region between micF and ompC, as indicated by mobility shift assays and by DNase I footprinting. The expression of an ompF -lacZ ؉ gene (translational) fusion is increased 3.7-fold in an lrp ؉ background compared with an lrp background, but expression of an ompF-lacZ ؉ operon fusion is not. Studies of in vivo expression of the outer membrane porins during growth on glucose minimal medium showed that the OmpF/OmpC ratio is higher in lrp ؉ strains than it is in isogenic lrp strains. The effect of Lrp was not seen in a strain containing a deletion of micF. Our studies suggest that the positive effect of Lrp on OmpF expression stems from a negative effect of Lrp on the expression of micF, an antisense RNA that inhibits ompF translation.