Regulation of de novo hepatic lipogenesis by insulin infusion in rainbow trout fed a high-carbohydrate diet

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Dietary medium chain fatty acids from coconut oil have little effects on postprandial plasma metabolite profiles in rainbow trout (Oncorhynchus mykiss)

International audienceThis study examined the effect of dietary medium-chain triglycerides supplied by coconut oil on postprandial plasma metabolite profiles in rainbow trout. The fish (initial body weight 71.3 ± 0.3 g, 17 °C) were fed one of four practical diets containing either 5% fish oil (FO low-fat, FL), 15% fish oil (FO high-fat, FH), 5% coconut oil (CO low-fat, CL) or 15% coconut oil (CO high-fat, CH) for 3 weeks. At the end of the trial, the fish were weighed and plasma sampled to determine glucose, non-esterified fatty acids (NEFA), triglyceride (TG), cholesterol, high density lipoprotein-cholesterol (HDL-cholesterol), and myeloperoxidase (MPO) at 3, 6, 9, 12, 15 and 24 h after the last meal. Plasma total ketone bodies (KB) were determined at 6, 12 and 24 h after meal. Blood nitroblue tetrazolium (NBT) tests were also performed in samples withdrawn at 24 h after meal. Plasma glucose was higher in fish fed the low fat level diet than those fed high fat level, and peaked at postprandial 9–12 h. Fish fed CH showed higher plasma TG than CL at 3 h after meal, and there was no significant difference in plasma TG at the other time points. The peak of TG appeared 12 h after the meal. No clear pattern was found for cholesterol and HDL-cholesterol (HDL-C) in any of the groups. However, fish fed diet FH had the highest postprandial plasma HDL-cholesterol level and HDL-C/cholesterol ratio. The peak of NEFA was observed at 12–15 h after meal and plasma NEFA of fish fed CH was the highest. Plasma total KB decreased with postprandial time, and fish of FH groups had higher KB than that of CL group at 6 h. Besides, NBT in fish fed FH was significantly higher than that of CH, but there were no differences in MPO between groups. In summary, time-course changes in plasma profiles related to dietary fat level were as expected whereas those related to dietary fat source were relatively small

Insulin stimulates lipogenesis and attenuates beta-oxidation in white adipose tissue of fed rainbow trout

International audienceAs lipid deposition tissue in fish, the white adipose tissue (WAT) has important functions related to reproduction and the challenges of long-term fasting. In the study reported here, we infused fish fed a high-carbohydrate diet with two doses of insulin for 5 days in order to explore the effects of this hormone on lipogenesis and beta-oxidation-related enzymes. We demonstrated the presence of some of the main lipogenic enzymes at molecular, protein and activity levels (ATP-citrate lyase and fatty acid synthase). However, while ATP-citrate lyase was unexpectedly down-regulated, fatty acid synthase was up-regulated (at protein and activity levels) in an insulin dose-dependent manner. The main enzymes acting as NADPH donors for lipogenesis were also characterized at biochemical and molecular levels, although there was no evidence of their regulation by insulin. On the other hand, lipid oxidation potential was found in this tissue through the measurement of gene expression of enzymes involved in beta-oxidation, highlighting two carnitine palmitoyltransferase isoforms, both down-regulated by insulin infusion. We found that insulin acts as an important regulator of trout WAT lipid metabolism, inducing the final stage of lipogenesis at molecular, protein and enzyme activity levels and suppressing beta-oxidation at least at a molecular level. These results suggest that WAT in fish may have a role that is important not only as a lipid deposition tissue but also as a lipogenic organ (with possible involvement in glucose homeostasis) that could also be able to utilize the lipids stored as a local energy source

Synthesis, Assembly, and Processing of the Env ERVWE1/Syncytin Human Endogenous Retroviral Envelope

Syncytin is a fusogenic protein involved in the formation of the placental syncytiotrophoblast layer. This protein is encoded by the envelope gene of the ERVWE1 proviral locus belonging to the human endogenous retrovirus W (HERV-W) family. The HERV-W infectious ancestor entered the primate lineage 25 to 40 million years ago. Although the syncytin fusion property has been clearly demonstrated, little is known about this cellular protein maturation process with respect to classical infectious retrovirus envelope proteins. Here we show that the cellular syncytin protein is synthesized as a glycosylated gPr73 precursor cleaved into two mature proteins, a gp50 surface subunit (SU) and a gp24 transmembrane subunit (TM). These SU and TM subunits are found associated as homotrimers. The intracytoplasmic tail is critical to the fusogenic phenotype, although its cleavage requirements seem to have diverged from those of classical retroviral maturation

Naturalised populations of mesorhizobia in chickpea (Cicer arietinum L.) cropping soils: effects on nodule occupancy and productivity of commercial chickpea

Background and aims: Chickpea rhizobia did not occur naturally in Australian cropping soils, necessitating inoculation at sowing. Now, after more than 30 years of chickpea cultivation using a single inoculant strain, CC1192, it is likely that chickpea rhizobia are established in 1.0-1.5 Mha cropping land. The aims of this study were to examine effects of the naturalised chickpea rhizobia on nodulation and productivity (total crop N, crop N fixed and grain yield) of commercial chickpea. Methods: Soil was sampled from 26 fields to estimate chickpea rhizobial numbers, relate numbers to edaphic factors and years since previous chickpea crop, determine the proportions of CC1192 and novel strains using RAPD-PCR and subject a subset of novel strains from one site to 16S rRNA analysis. Nodules were harvested from 15 inoculated, commercial chickpea crops to determine occupancy by CC1192. The symbiotic effectiveness of a second subset of novel strains was assessed. Results: The mean number of rhizobia in the soils varied from log 0.08 to log 5.16 rhizobia g soil⁻¹ with population size positively correlated with soil moisture content and negatively correlated with salt concentration (ECe). RAPD-PCR analysis of 570 strains of chickpea rhizobia isolated from the soils indicated only 14 % with molecular fingerprints similar to CC1192. Occupancy by CC1192 of nodules harvested from commercial crops ranged 0-100 %, with an average of 53 %. Occupancy by CC1192 declined by an average 17 % with each log unit increase in numbers of novel chickpea rhizobia. Conclusions: We found no evidence that the novel mesorhizobia in the chickpea soils compromised N₂ fixation or productivity of commercial chickpea crops, even though individual strains had generally reduced symbiotic effectiveness relative to CC1192