Project description:A population genetic study identified that the asialoglycoprotein receptor 1 (ASGR1) mutation carriers had significantly lower non-HDL-c levels and reduced risks of cardiovascular diseases. However, the mechanism behind this phenomenon remained unclear. Here, we established Asgr1 knockout mice that represented a plasma lipid profile with significantly lower non-HDL-c and triglyceride caused by decreased secretion and increased uptake of VLDL/LDL. These two phenotypes were linked with the decreased expression of microsomal triglyceride transfer protein (MTTP) and proprotein convertase subtilisin/kexin type 9 (PCSK9), two key target genes of the sterol regulatory element-binding proteins (SREBPs). Furthermore, there were less nSREBPs on account of more SREBPs being trapped in endoplasmic reticulum, which was caused by an increased expression of insulin-induced gene 1 (INSIG1), an anchor of SREBPs. Logically, two rescue experiments were conducted in ASGR1 deficient condition. Both INSIG1 knockdown and ASGR1 rescue independently reversed the ASGR1-mutated phenotypes, restoring the SREBP signaling manifested by improved APOB secretion and reduced LDL uptake. Our observation demonstrated a novel axis of ASGR1-INSIG1-SREBPs regulating lipid hemostasis, and hypomorphic manipulation of ASGR1 leads to significant reduction of lipid content via less nSREBPs. It provides multiple potential targets, including ASGR, for lipid-lowering drug development.
Project description:Lipid composition can differ widely among organelles and even between leaflets of a membrane. Lipid homeostasis is critical because disequilibrium can have disease outcomes. Despite their importance, mechanisms maintaining lipid homeostasis remain poorly understood. Here, we establish a model system to study the global effects of lipid imbalance. Quantitative lipid profiling was integral to monitor changes to lipid composition and for system validation. Applying global transcriptional and proteomic analyses, a dramatically altered biochemical landscape was revealed from adaptive cells. The resulting composite regulation we term the ?membrane stress response? (MSR) confers compensation, not through restoration of lipid composition, but by remodeling the protein homeostasis network. To validate its physiological significance, we analyzed the unfolded protein response (UPR), one facet of the MSR and a key regulator of protein homeostasis. We demonstrate that the UPR maintains protein biogenesis, quality control, and membrane integrity?functions otherwise lethally compromised in lipid dysregulated cells. Genes expression from early log phase of CHO2, OPI3, and PAH1 knockout cell and untreated and DTT-treated WT cells. RNA was prepared from independent triplicate samples. Array sets performed and collected on different dates are as follows: Array 1, Day 1: WT_rep1 pah1_rep1 cho2_rep1 opi3_rep1 Array 2, Day 2: WT_rep2 WT_rep3 WT_Tm_rep1 WT_DTT_rep1 Array 3, Day 2: WT_DTT_rep2 WT_DTT_rep3 cho2_rep2 cho2_rep3 Array 4, Day 2: pah1_rep2 pah1_rep3 opi3_rep2 opi3_rep3
Project description:The Wnt pathway, which controls crucial steps of the development and differentiation programs, has been proposed to influence lipid storage and homeostasis. In this paper, using an unbiased strategy based on high content genome-wide RNAi screens that monitored lipid distribution and amounts, we find that Wnt3a regulates cellular cholesterol. We show that Wnt3a stimulates the production of lipid droplets, and that this stimulation strictly depends on endocytosed, LDL-derived cholesterol and on functional early and late endosomes. We also show that Wnt signaling itself controls cholesterol endocytosis and flux along the endosomal pathway, which in turn modulates cellular lipid homeostasis. These results underscore the importance of endosome functions for LD formation and reveal a previously unknown cellular program controlling lipid storage and endosome transport under the control of Wnt signaling.
Project description:Lipid composition can differ widely among organelles and even between leaflets of a membrane. Lipid homeostasis is critical because disequilibrium can have disease outcomes. Despite their importance, mechanisms maintaining lipid homeostasis remain poorly understood. Here, we establish a model system to study the global effects of lipid imbalance. Quantitative lipid profiling was integral to monitor changes to lipid composition and for system validation. Applying global transcriptional and proteomic analyses, a dramatically altered biochemical landscape was revealed from adaptive cells. The resulting composite regulation we term the ?membrane stress response? (MSR) confers compensation, not through restoration of lipid composition, but by remodeling the protein homeostasis network. To validate its physiological significance, we analyzed the unfolded protein response (UPR), one facet of the MSR and a key regulator of protein homeostasis. We demonstrate that the UPR maintains protein biogenesis, quality control, and membrane integrity?functions otherwise lethally compromised in lipid dysregulated cells.
Project description:Maintaining metabolic homeostasis in response to fluctuating nutrient intake requires intricate coordination between tissues of multicellular animals. The insulin/glucagon axis is well known to hormonally coordinate organism-wide carbohydrate metabolism. The ChREBP/Mondo-Mlx transcription factors regulate glycolytic and lipogenic genes locally in hepatocytes and adipocytes, but its role in systemic metabolic homeostasis has remained poorly understood. We demonstrate that Mondo-Mlx controls gene activity in several peripheral tissues of Drosophila melanogaster, where it regulates nutrient digestion and transport as well as carbohydrate, amino acid and lipid metabolism. In addition to directly regulating metabolic genes Mondo-Mlx controls a regulatory network composed of the Activin ligand Dawdle and GLI similar transcription factor Sugarbabe. Dawdle and Sugarbabe contribute to the regulation of a subset of Mondo-Mlx-dependent processes, including sugar-induced de novo synthesis of serine and fatty acids. In summary, our study establishes Mondo-Mlx sugar sensor as a master regulator of organismal metabolic homeostasis upon sugar feeding.
Project description:Maintaining metabolic homeostasis in response to fluctuating nutrient intake requires intricate coordination between tissues of multicellular animals. The insulin/glucagon axis is well known to hormonally coordinate organism-wide carbohydrate metabolism. The ChREBP/Mondo-Mlx transcription factors regulate glycolytic and lipogenic genes locally in hepatocytes and adipocytes, but its role in systemic metabolic homeostasis has remained poorly understood. We demonstrate that Mondo-Mlx controls gene activity in several peripheral tissues of Drosophila melanogaster, where it regulates nutrient digestion and transport as well as carbohydrate, amino acid and lipid metabolism. In addition to directly regulating metabolic genes Mondo-Mlx controls a regulatory network composed of the Activin ligand Dawdle and GLI similar transcription factor Sugarbabe. Dawdle and Sugarbabe contribute to the regulation of a subset of Mondo-Mlx-dependent processes, including sugar-induced de novo synthesis of serine and fatty acids. In summary, our study establishes Mondo-Mlx sugar sensor as a master regulator of organismal metabolic homeostasis upon sugar feeding.
Project description:ANGPTL4 regulates plasma lipids, making it an attractive target for correcting dyslipidemia. However, ANGPTL4 inactivation in mice fed a high fat diet causes chylous ascites, an acute-phase response, and mesenteric lymphadenopathy. Here, we studied the role of ANGPTL4 in lipid uptake in macrophages and in the above-mentioned pathologies using Angptl4-hypomorphic and Angptl4-/- mice. Angptl4 expression in peritoneal and bone marrow-derived macrophages was highly induced by lipids. Recombinant ANGPTL4 decreased lipid uptake in macrophages, whereas deficiency of ANGPTL4 increased lipid uptake, upregulated lipid-induced genes, and increased respiration. ANGPTL4 deficiency did not alter LPL protein levels in macrophages. Angptl4-hypomorphic mice with partial expression of a truncated N-terminal ANGPTL4 exhibited reduced fasting plasma triglyceride, cholesterol, and non-esterified fatty acid levels, strongly resembling Angptl4-/- mice. However, during high fat feeding, Angptl4-hypomorphic mice showed markedly delayed and attenuated elevation in plasma serum amyloid A and much milder chylous ascites than Angptl4-/- mice, despite similar abundance of lipid-laden giant cells in mesenteric lymph nodes. In conclusion, ANGPTL4 deficiency increases lipid uptake and respiration in macrophages without affecting LPL protein levels. Compared with the absence of ANGPTL4, low levels of N-terminal ANGPTL4 mitigate the development of chylous ascites and an acute-phase response in mice.
Project description:The cleavage of sphingoid base phosphates by sphingosine-1-phosphate (S1P) lyase to produce phosphoethanolamine and a fatty aldehyde is the final degradative step in the sphingolipid metabolic pathway. We have studied mice with an inactive S1P lyase gene and have found that, in addition to the expected increase of sphingoid base phosphates, other sphingolipids (including sphingosine, ceramide, and sphingomyelin) were substantially elevated in the serum and /or liver of these mice. This latter increase is consistent with a reutilization of the sphingosine backbone for sphingolipid synthesis due to its inability to exit the sphingolipid metabolic pathway. Furthermore, the S1P lyase deficiency resulted in changes in the levels of serum and liver lipids not directly within the sphingolipid pathway, including phospholipids, triacyglycerol, diacylglycerol, and cholesterol. Even though lipids in serum and lipid storage were elevated in liver, adiposity was reduced in the S1P lyase-deficient mice. Microarray analysis of lipid metabolism genes in liver showed that the S1P lyase deficiency caused widespread changes in their expression pattern. These results demonstrate that S1P lyase is a key regulator of the levels of multiple sphingolipid substrates and reveal functional links between the sphingolipid metabolic pathway and other lipid metabolic pathways that may be mediated by shared lipid substrates and changes in gene expression programs. The disturbance of lipid homeostasis by altered sphingolipid levels may be relevant to metabolic diseases. Experiment Overall Design: RNA samples from liver for three sphingosine-1-phosphate lyase knock-out and three WT mice.