University of Rouen

About: University of Rouen is a education organization based out in Rouen, France. It is known for research contribution in the topics: Population & Receptor. The organization has 7299 authors who have published 13209 publications receiving 313477 citations.

Amyloid precursor protein controls cholesterol turnover needed for neuronal activity

Abstract: Perturbation of lipid metabolism favours progression of Alzheimer disease, in which processing of Amyloid Precursor Protein (APP) has important implications. APP cleavage is tightly regulated by cholesterol and APP fragments regulate lipid homeostasis. Here, we investigated whether up or down regulation of full-length APP expression affected neuronal lipid metabolism. Expression of APP decreased HMG-CoA reductase (HMGCR)-mediated cholesterol biosynthesis and SREBP mRNA levels, while its down regulation had opposite effects. APP and SREBP1 co-immunoprecipitated and co-localized in the Golgi. This interaction prevented Site-2 protease-mediated processing of SREBP1, leading to inhibition of transcription of its target genes. A GXXXG motif in APP sequence was critical for regulation of HMGCR expression. In astrocytes, APP and SREBP1 did not interact nor did APP affect cholesterol biosynthesis. Neuronal expression of APP decreased both HMGCR and cholesterol 24-hydroxylase mRNA levels and consequently cholesterol turnover, leading to inhibition of neuronal activity, which was rescued by geranylgeraniol, generated in the mevalonate pathway, in both APP expressing and mevastatin treated neurons. We conclude that APP controls cholesterol turnover needed for neuronal activity.

Detection and localization of pectin methylesterase isoforms in pollen tubes of Nicotiana tabacum L.

Abstract: Pectin methylesterases (PMEs) were detected in tobacco (Nicotiana tabacum) pollen tubes grown in vitro. Seven PME isoforms exhibiting a wide isoelectric-point (pI) range (5.3–9.1) were found in crude extracts of pollen tubes. These isoforms were mainly retrieved in supernatants after low- and high-speed separation of the crude extract. Two isoforms, with pIs 5.5 and 7.3 and molecular weight about 158 kDa, were detected by immunoblotting with anti-flax PME antiserum. Localization of pectins and PME isoforms in pollen tubes was investigated by immunogold labelling with JIM5 monoclonal antibodies and anti-flax PME antiserum, respectively. In germinated pollen grains, two PME isoforms were mainly detected in the exine, Golgi apparatus and secretory vesicles. In pollen tubes the same two PME isoforms were distributed along the outer face of the plasma membrane in the vicinity of the inner layer of the cell wall, in the Golgi and around secretory vesicles. In pollen grains, PME isoforms were, in some cases, mixed with acidic pectins in proximity to the outer surface of the plasma membrane. In pollen tubes the presence of PMEs inside secretory vesicles carrying esterified pectins supports the hypothesis that, during pollen tube growth, PMEs could be transferred by secretory vesicles in a precursor form and be activated at the tip where exocytosis takes place.

Roles of Corticotropin‐Releasing Factor, Neuropeptide Y and Corticosterone in the Regulation of Food Intake In Xenopus laevis

Abstract: In mammals, hypothalamic control of food intake involves counterregulation of appetite by an orexigenic peptides such as corticotropin-releasing factor (CRF), and orexigenic peptides such as neuropeptide Y (NPY). Glucocorticoids also stimulate food intake by inhibiting CRF while facilitating NPY actions. To gain a better understanding of the diversity and evolution of neuroendocrine feeding controls in vertebrates, we analysed the effects of CRF, NPY and glucocorticoids on food intake in juvenile Xenopus laevis. We also analysed brain CRF and NPY mRNA content and plasma corticosterone concentrations in relation to nutritional state. Intracerebroventricular (i.c.v.) injection of ovine CRF suppressed food intake while CRF receptor antagonist alpha helical CRF(9-41) significantly increased food intake relative to uninjected and placebo controls. By contrast, i.c.v. injection of frog NPY and short-term corticosterone treatment increased food intake. Semi-quantitative reverse transcription-polymerase chain reaction analyses showed that CRF and NPY mRNA fluctuated with food intake in the brain region containing the mid-posterior hypothalamus, pretectum, and optic tectum: CRF mRNA decreased 6 h after a meal and remained low through 31 days of food deprivation; NPY mRNA content also decreased 6 h after a meal, but increased to prefeeding levels by 24 h. Plasma corticosterone concentration increased 6 h after a meal, returned to prefeeding levels by 24 h, and did not change with prolonged food deprivation. This postprandial increase in plasma corticosterone may be related to the subsequent increase in plasma glucose and body water content that occurs 24 h postfeeding. Overall, our data support the conclusion that, similar to other vertebrates, CRF is anorexigenic while NPY is orexigenic in X. laevis, and CRF secretion modulates food intake in the absence of stress by exerting an inhibitory tone on appetite. Furthermore, the stress axis is activated in response to food intake, but in contrast to mammals and birds is not activated during periods of food deprivation.

Hydrodynamics of suspended particulate matter in the tidal freshwater zone of a macrotidal estuary (the Seine Estuary, France)

Abstract: The effects of fortnightly, semidiurnal, and quaterdiurnal lunar tidal cycles on suspended particle concentrations in the tidal freshwater zone of the Seine macrotidal estuary were studied during periods of medium to low freshwater flow. Long-term records of turbidity show semidiurnal and spring-neap erosion-sedimentation cycles. During spring tide, the rise in low tide levels in the upper estuary leads to storage of water in the upper estuary. This increases residence time of water and suspended particulate matter (SPM). During spring tide periods, significant tidal pumping, measured by flux calculations, prevents SPM transit to the middle estuary which is characterized by the turbidity maximum zone. On a long-term basis, this tidal pumping allows marine particles to move upstream for several tens of kilometers into the upper estuary. At the end of the spring tide period, when the concentrations of suspended particulate matter are at their peak values and the low-tide level drops, the transport of suspended particulate matter to the middle estuary reaches its highest point. This period of maximum turbidity is of short duration because a significant amount of the SPM settles during neap tide. The particles, which settle under these conditions, are trapped in the upper estuary and cannot be moved to the zone of maximum turbidity until the next spring tide. From the upper estuary to the zone of maximum turbidity, particulate transport is generated by pulses at the start of the spring-neap tide transition period.