Mechanism of action for small-molecule inhibitors of triacylglycerol synthesis.

Inhibitors of triacylglycerol (TG) synthesis have been developed to treat metabolism-related diseases, but we know little about their mechanisms of action. Here, we report cryo-EM structures of the TG-synthesis enzyme acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a membrane bound O-acyltransferase (MBOAT), in complex with two different inhibitors, T863 and DGAT1IN1. Each inhibitor binds DGAT1's fatty acyl-CoA substrate binding tunnel that opens to the cytoplasmic side of the ER. T863 blocks access to the tunnel entrance, whereas DGAT1IN1 extends further into the enzyme, with an amide group interacting with more deeply buried catalytic residues. A survey of DGAT1 inhibitors revealed that this amide group may serve as a common pharmacophore for inhibition of MBOATs. The inhibitors were minimally active against the related MBOAT acyl-CoA:cholesterol acyltransferase 1 (ACAT1), yet a single-residue mutation sensitized ACAT1 for inhibition. Collectively, our studies provide a structural foundation for developing DGAT1 and other MBOAT inhibitors.

Low vitamin A levels are associated with liver-related mortality: a nationally representative cohort study.

INTRODUCTION: Vitamin A, a fat-soluble vitamin that includes retinol and carotenoids, is implicated in liver fibrosis, whereas its deficiency has been associated with various liver diseases and higher overall mortality. This study aims to determine the relationship between levels of vitamin A species and liver fibrosis, as well as liver-related mortality in the population of the US. METHODS: A total of 12,299 participants from the National Health and Nutrition Examination Survey III (NHANES III) were analyzed to provide nationally representative estimates of the relationship between the levels of vitamin A species and liver fibrosis measured by Fibrosis-4 (FIB-4) index and liver-related mortality. RESULTS: A low blood level of retinol, but not other retinoid derivatives, was associated with significant liver fibrosis after adjustment for demographics, anthropometric measurements, medical history, retinol, and carotene intakes. Compared with vitamin D and E, retinol deficiency demonstrated much stronger associations with a high FIB-4 score. Individuals with known risks of chronic liver disease (CLD) and the lowest pentile of retinol levels had ORs of 3.12 (95% CI, 1.64-5.91) for possible fibrosis and 19.7 (95% CI, 5.71-67.7) for likely fibrosis, and an HR of 7.76 (95% CI, 1.19-50.5) for liver-related mortality compared with those in the highest retinol-level pentile. These relationships were more pronounced among individuals with known risks of chronic liver disease than without. CONCLUSIONS: A low circulating retinol level is associated with liver fibrosis and liver-related mortality in chronic liver disease. This relationship is potentially driven by a mechanistic link rather than the malabsorption of fat-soluble vitamins and may be leveraged for disease prognostication and have therapeutic implications.

Identification of two pathways mediating protein targeting from ER to lipid droplets.

Pathways localizing proteins to their sites of action are essential for eukaryotic cell organization and function. Although mechanisms of protein targeting to many organelles have been defined, how proteins, such as metabolic enzymes, target from the endoplasmic reticulum (ER) to cellular lipid droplets (LDs) is poorly understood. Here we identify two distinct pathways for ER-to-LD protein targeting: early targeting at LD formation sites during formation, and late targeting to mature LDs after their formation. Using systematic, unbiased approaches in Drosophila cells, we identified specific membrane-fusion machinery, including regulators, a tether and SNARE proteins, that are required for the late targeting pathway. Components of this fusion machinery localize to LD-ER interfaces and organize at ER exit sites. We identified multiple cargoes for early and late ER-to-LD targeting pathways. Our findings provide a model for how proteins target to LDs from the ER either during LD formation or by protein-catalysed formation of membrane bridges.

The Lipid Droplet Knowledge Portal: A resource for systematic analyses of lipid droplet biology.

Lipid droplets (LDs) are organelles of cellular lipid storage with fundamental roles in energy metabolism and cell membrane homeostasis. There has been an explosion of research into the biology of LDs, in part due to their relevance in diseases of lipid storage, such as atherosclerosis, obesity, type 2 diabetes, and hepatic steatosis. Consequently, there is an increasing need for a resource that combines datasets from systematic analyses of LD biology. Here, we integrate high-confidence, systematically generated human, mouse, and fly data from studies on LDs in the framework of an online platform named the "Lipid Droplet Knowledge Portal" (https://lipiddroplet.org/). This scalable and interactive portal includes comprehensive datasets, across a variety of cell types, for LD biology, including transcriptional profiles of induced lipid storage, organellar proteomics, genome-wide screen phenotypes, and ties to human genetics. This resource is a powerful platform that can be utilized to identify determinants of lipid storage.

Deletion of p22phox-dependent oxidative stress in the hypothalamus protects against obesity by modulating ß3-adrenergic mechanisms.

A role for oxidative stress in the brain has been suggested in the pathogenesis of diet-induced obesity (DIO), although the underlying neural regions and mechanisms remain incompletely defined. We tested the hypothesis that NADPH oxidase-dependent oxidative stress in the paraventricular nucleus (PVN), a hypothalamic energy homeostasis center, contributes to the development of DIO. Cre/LoxP technology was coupled with selective PVN adenoviral microinjection to ablate p22phox , the obligatory subunit for NADPH oxidase activity, in mice harboring a conditional p22phox allele. Selective deletion of p22phox in the PVN protected mice from high-fat DIO independent of changes in food intake or locomotor activity. This was accompanied by ß3-adrenoceptor-dependent increases in energy expenditure, elevations in brown adipose tissue thermogenesis, and browning of white adipose tissue. These data reveal a potentially novel role for brain oxidative stress in the development of DIO by modulating ß3-adrenoceptor mechanisms and point to the PVN as an underlying neural site.

Adverse metabolic phenotype of female offspring exposed to preeclampsia in utero: a characterization of the BPH/5 mouse in postnatal life.

Preeclampsia (PE) is a devastating disorder of pregnancy that classically presents with maternal hypertension and proteinuria after 20 wk of gestation. In addition to being a leading cause of maternal and fetal morbidity/mortality, epidemiological and prospective studies have revealed long-term consequences for both the mother and baby of preeclamptic pregnancies, including chronic hypertension as well as other cardiovascular diseases and metabolic derangements. To better understand the effect of in utero exposure of PE on offspring, we utilized the BPH/5 mouse, a spontaneous model of the maternal and fetal PE syndrome. We hypothesized that young BPH/5 offspring would have altered metabolic and cardiovascular phenotypes. Indeed, BPH/5 growth-restricted offspring showed excess catch-up growth by early adulthood due to hyperphagia and increased white adipose tissue (WAT) accumulation, with inflammation markers isolated to the reproductive WAT depot only. Both excessive WAT accumulation and the inflammatory WAT phenotype were corrected by pair-feeding young BPH/5 female mice. We also found that young BPH/5 female mice showed evidence of leptin resistance. Indeed, chronic hyperleptinemia has been shown to characterize other rodent models of PE; however, the maternal metabolic profile before pregnancy has not been fully understood. Furthermore, we found that these mice show signs of cardiovascular anomalies (hypertension and cardiomegaly) and altered signaling within the reproductive axis in early life. Future studies will involve challenging the physiological metabolic state of BPH/5 mice through pair-feeding to reduce WAT before pregnancy and determining its causal role in adverse pregnancy outcomes.