MondoA regulates gene expression in cholesterol biosynthesis-associated pathways required for zebrafish epiboly

The glucose-sensing Mondo pathway regulates expression of metabolic genes in mammals. Here, we characterized its function in the zebrafish and revealed an unexpected role of this pathway in vertebrate embryonic development. We showed that knockdown of mondoa impaired the early morphogenetic movement of epiboly in zebrafish embryos and caused microtubule defects. Expression of genes in the terpenoid backbone and sterol biosynthesis pathways upstream of pregnenolone synthesis was coordinately downregulated in these embryos, including the most downregulated gene nsdhl. Loss of Nsdhl function likewise impaired epiboly, similar to MondoA loss of function. Both epiboly and microtubule defects were partially restored by pregnenolone treatment. Maternal-zygotic mutants of mondoa showed perturbed epiboly with low penetrance and compensatory changes in the expression of terpenoid/sterol/steroid metabolism genes. Collectively, our results show a novel role for MondoA in the regulation of early vertebrate development, connecting glucose, cholesterol and steroid hormone metabolism with early embryonic cell movements.

Effects of hypolipidemic drugs on the expression of genes involved in high density lipoprotein metabolism in the rat

Johan Auwerx

Since plasma high density lipoprotein (HDL) concentrations are inversely related to the development of atherosclerosis, induction of HDL after pharmacological treatment is considered of benefit. To study whether currently used hypolipidemic drugs affect HDL metabolism by modulating the expression of genes involved in HDL metabolism, liver and intestinal apolipoprotein (apo) AI, apo-AII and apo-AIV gene expression was evaluated in rats treated with different classes of hypolipidemic drugs, and correlated to the changes in plasma lipid and apolipoprotein concentrations. In rats, the most pronounced hypolipidemic effects were observed after treatment with the fibrates clofibrate and fenofibrate, which lowered plasma lipid, apo-AI and apo-AIV concentrations. This decrease was accompanied by lowered liver apo-AI, apo-AII and apo-AIV mRNA levels. None of the other compounds tested affected plasma cholesterol, whereas probucol and simvastatin decreased plasma triglyceride concentrations. Apo-AI and apo-AII mRNA remained constant after nicotinic acid and probucol, whereas liver apo-AIV mRNA levels decreased. Cholestyramine increased hepatic apo-AI and apo-AII, but not apo-AIV mRNA levels. Simvastatin treatment increased apo-AI mRNA nearly threefold, whereas apo-AII and apo-AIV decreased by more than 50%. Similarly as after cholestyramine, the alteration in hepatic apo-AI mRNA levels did not result in changed plasma apo-AI concentrations. Remarkably, none of the drugs tested significantly affected intestinal apolipoprotein mRNA levels. These results indicate that hypolipidemic drugs may act on plasma lipoprotein metabolism by regulating apolipoprotein gene expression. Further studies in humans and primates are therefore warranted.

1996

Consequences of Exchanging Carbohydrates for Proteins in the Cholesterol Metabolism of Mice Fed a High-fat Diet

Martin Kussmann, Sylviane Métairon, Mireille Moser

Consumption of low-carbohydrate, high-protein, high-fat diets lead to rapid weight loss but the cardioprotective effects of these diets have been questioned. We examined the impact of high-protein and high-fat diets on cholesterol metabolism by comparing the plasma cholesterol and the expression of cholesterol biosynthesis genes in the liver of mice fed a high-fat (HF) diet that has a high (H) or a low (L) protein-to-carbohydrate (P/C) ratio. H-P/C-HF feeding, compared with L-P/C-HF feeding, decreased plasma total cholesterol and increased HDL cholesterol concentrations at 4-wk. Interestingly, the expression of genes involved in hepatic steroid biosynthesis responded to an increased dietary P/C ratio by first down-regulation (2-d) followed by later up-regulation at 4-wk, and the temporal gene expression patterns were connected to the putative activity of SREBF1 and 2. In contrast, Cyp7a1, the gene responsible for the conversion of cholesterol to bile acids, was consistently up-regulated in the H-P/C-HF liver regardless of feeding duration. Over expression of Cyp7a1 after 2-d and 4-wk H-P/C-HF feeding was connected to two unique sets of transcription regulators. At both time points, up-regulation of the Cyp7a1 gene could be explained by enhanced activations and reduced suppressions of multiple transcription regulators. In conclusion, we demonstrated that the hypocholesterolemic effect of H-P/C-HF feeding coincided with orchestrated changes of gene expressions in lipid metabolic pathways in the liver of mice. Based on these results, we hypothesize that the cholesterol lowering effect of high-protein feeding is associated with enhanced bile acid production but clinical validation is warranted. (246 words)

Public Library of Science2012

Learning-Induced Gene Expression in the Hippocampus Reveals a Role of Neuron-Astrocyte Metabolic Coupling in Long Term Memory

Igor Allaman, Gabriele Grenningloh, Sylvain Eric Lengacher, Pierre Magistretti, Monika Tadi

We examined the expression of genes related to brain energy metabolism and particularly those encoding glia (astrocyte)-specific functions in the dorsal hippocampus subsequent to learning. Context-dependent avoidance behavior was tested in mice using the step-through Inhibitory Avoidance (IA) paradigm. Animals were sacrificed 3, 9, 24, or 72 hours after training or 3 hours after retention testing. The quantitative determination of mRNA levels revealed learning-induced changes in the expression of genes thought to be involved in astrocyte-neuron metabolic coupling in a time dependent manner. Twenty four hours following IA training, an enhanced gene expression was seen, particularly for genes encoding monocarboxylate transporters 1 and 4 (MCT1, MCT4), alpha2 subunit of the Na/K-ATPase and glucose transporter type 1. To assess the functional role for one of these genes in learning, we studied MCT1 deficient mice and found that they exhibit impaired memory in the inhibitory avoidance task. Together, these observations indicate that neuron-glia metabolic coupling undergoes metabolic adaptations following learning as indicated by the change in expression of key metabolic genes.

Public Library of Science2015