Tau/DDX6 interaction increases microRNA activity.

Tauopathies, such as Alzheimer's disease, are characterized by intracellular aggregates of insoluble Tau proteins. Originally described as a microtubule binding protein, recent studies demonstrated additional physiological roles for Tau. The fact that a single protein can regulate multiple cellular functions has posed challenge in terms of understanding mechanistic cues behind the pathology. Here, we used tandem-affinity purification methodology coupled to mass spectrometry to identify novel interaction partners. We found that Tau interacts with DDX6, a DEAD box RNA helicase involved in translation repression and mRNA decay as well as in the miRNA pathway. Our results demonstrate that Tau increases the silencing activity of the miRNA let-7a, miR-21 and miR-124 through DDX6. Importantly, Tau mutations (P301S, P301L) found in the inherited tauopathies, frontotemporal dementia and parkinsonism linked to chromosome 17, disrupt Tau/DDX6 interaction and impair gene silencing by let-7a. Altogether, these data demonstrated a new unexpected role for Tau in regulating miRNA activity.

Deficient hippocampal insulin signaling and augmented Tau phosphorylation is related to obesity- and age-induced peripheral insulin resistance: a study in Zucker rats.

BACKGROUND: Insulin signaling and Tau protein phosphorylation in the hippocampi of young and old obese Zucker fa/fa rats and their lean controls were assessed to determine whether obesity-induced peripheral insulin resistance and aging are risk factors for central insulin resistance and whether central insulin resistance is related to the pathologic phosphorylation of the Tau protein. RESULTS: Aging and obesity significantly attenuated the phosphorylation of the insulin cascade kinases Akt (protein kinase B, PKB) and GSK-3ß (glycogen synthase kinase 3ß) in the hippocampi of the fa/fa rats. Furthermore, the hyperphosphorylation of Tau Ser396 alone and both Tau Ser396 and Thr231 was significantly augmented by aging and obesity, respectively, in the hippocampi of these rats. CONCLUSIONS: Both age-induced and obesity-induced peripheral insulin resistance are associated with central insulin resistance that is linked to hyperTau phosphorylation. Peripheral hyperinsulinemia, rather than hyperglycemia, appears to promote central insulin resistance and the Tau pathology in fa/fa rats.

Hypooxytocinaemia in obese Zucker rats relates to oxytocin degradation in liver and adipose tissue.

The metabolic action of oxytocin has recently been intensively studied to assess the ability of the peptide to regulate energy homeostasis. Despite the obvious weight-reducing effect of oxytocin observed in experimental studies, plasma oxytocin levels were found to be unchanged or even elevated in human obesity. The aim of our study was to evaluate the changes in the oxytocin system in Zucker rats, an animal model closely mirroring morbid obesity in humans. Plasma oxytocin levels were measured in obese Zucker rats and lean controls by enzyme immunoassay after plasma extraction. The expression of oxytocin and oxytocin receptor (OXTR) was assessed at the mRNA and protein levels by quantitative real-time PCR and immunoblotting respectively. Plasma and tissue activity of oxytocinase, the main enzyme involved in oxytocin degradation, were measured by fluorometric assay using an arylamide derivate as the substrate. Obese Zucker rats displayed a marked reduction in plasma oxytocin levels. Elevated liver and adipose tissue oxytocinase activity was noticed in obese Zucker rats. Hypothalamic oxytocin gene expression was not altered by the obese phenotype. OXTR mRNA and protein levels were upregulated in the adipose tissue of obese animals in contrast to the reduced OXTR protein levels in skeletal muscle. Our results show that obesity is associated with reduced plasma oxytocin due to increased peptide degradation by liver and adipose tissue rather than changes in hormone synthesis. This study highlights the importance of the oxytocin system in the pathogenesis of obesity and suggests oxytocinase inhibition as a candidate approach in the therapy of obesity.

Neuropeptide FF analog RF9 is not an antagonist of NPFF receptor and decreases food intake in mice after its central and peripheral administration.

Neuropeptide FF (NPFF) belongs to the RF-amide family of peptides bearing the identical C-terminal amino acid sequence (R-F-NH2). In addition to NPFF, prolactin-releasing peptide (PrRP), another RF-amide, binds to NPFF receptors with high affinity. A selective antagonist of PrRP has not yet been identified, but a selective antagonist of NPFF, 1-adamantanecarbonyl-RF-NH2 (RF9), was recently reported to antagonize the hyperalgesic effect of NPFF after central administration to mice. In the present study, RF9 competed with NPFF analog D-Y-L-(N-Me)-F-Q-P-Q-R-F-NH2 (1DMe) in binding to CHO-K1 cell membranes transfected with the human NPFF2 receptor. In rat pituitary RC-4B/C cells, where the expression of the NPFF2 receptor was proved by immunodetection, RF9 did not reverse the phosphorylation of MAPK/ERK1/2 induced by [Tyr(1)]NPFF. In vivo experiments with fasted mice confirmed that centrally injected [Tyr(1)]NPFF significantly lowered food intake. However, RF9, a putative NPFF2 antagonist, did not reverse the anorectic effect of [Tyr(1)]NPFF. Paradoxically, RF9 itself exhibited an anorectic effect in fasted mice not only after intracerebroventricular but also after subcutaneous administration. This finding casts doubt on claims that RF9 is an NPFF antagonist.

Biological properties of prolactin-releasing peptide analogs with a modified aromatic ring of a C-terminal phenylalanine amide.

Prolactin-releasing peptide (PrRP)-induced secretion of prolactin is not currently considered a primary function of PrRP, but the development of late-onset obesity in both PrRP and PrRP receptor knock-out mice indicates the unique anorexigenic properties of PrRP. In our recent study, we showed comparable potencies of peptides PrRP31 and PrRP20 in binding, intracellular signaling and prolactin release in pituitary RC-4B/C cells, and anorexigenic effect after central administration in fasted mice. In the present study, eight analogs of PrRP20 with C-terminal Phe amide modified with a bulky side chain or a halogenated aromatic ring revealed high binding potency, activation of mitogen-activated protein kinase/extracellular-regulated kinase (MAPK/ERK1/2) and cAMP response element-binding protein (CREB) and prolactin release in RC-4B/C cells. In particular, [PheNO(2)(31)]PrRP20, [1-Nal(31)]PrRP20, [2-Nal(31)]PrRP20 and [Tyr(31)]PrRP20 showed not only in vitro effects comparable or higher than those of PrRP20, but also a very significant and long-lasting anorexigenic effect after central administration in fasted mice. The design of potent and long-lasting PrRP analogs with selective anorexigenic properties promises to contribute to the study of food intake disorders.

Characterization of prolactin-releasing peptide: binding, signaling and hormone secretion in rodent pituitary cell lines endogenously expressing its receptor.

The recently discovered prolactin-releasing peptide (PrRP) binds to the PrRP receptor and is involved in endocrine regulation and energy metabolism. However, its main physiological role is currently unknown. Two biologically active isoforms of PrRP exist: the 31 (PrRP31) and the 20 (PrRP20) amino acid forms, which both contain a C-terminal Phe amide sequence. In the present study, the PrRP receptor was immunodetected in three rodent tumor pituitary cell lines: GH3, AtT20 and RC-4B/C cells. The saturation binding of radioiodinated PrRP31 to intact cells demonstrated a K(d) in the 10(-9)M range and a B(max) in the range of tens of thousands binding sites per cell. For binding to RC-4B/C cells, both PrRP31 and PrRP20 competed with (125)I-PrRP31 with a similar K(i). The C-terminal analog PrRP13 showed lower binding potency compared to PrRP31 and PrRP20. All PrRP analogs increased the phosphorylation of MAPK/ERK1/2 (mitogen-activated phosphorylase/extracellular-regulated kinase) and CREB (cAMP response element-binding protein) in RC-4B/C cells. Additionally, prolactin release was induced by the PrRP analogs in a dose-dependent manner in RC-4B/C cells. Finally, food intake after intracerebroventricular administration of PrRP analogs in fasted mice was followed. Both PrRP31 and PrRP20 decreased food intake, but PrRP13 did not show significant effect. Studies on pituitary cell lines expressing the PrRP receptor are more physiologically relevant than those on cells transfected with the receptor. This cell type can be used as a model system for pharmacological studies searching for PrRP antagonists and stable effective PrRP agonists, as these drugs may have potential as anti-obesity agents.