The ability to store fat in the form of cytoplasmic triglyceride droplets is conserved from Saccharomyces cerevisiae to humans. Although much is known regarding the composition and catabolism of lipid droplets, the molecular components necessary for the biogenesis of lipid droplets have remained obscure. Here we report the characterization of a conserved gene family important for lipid droplet formation named fat-inducing transcript (FIT). FIT1 and FIT2 are endoplasmic reticulum resident membrane proteins that induce lipid droplet accumulation in cell culture and when expressed in mouse liver. shRNA silencing of FIT2 in 3T3-LI adipocytes prevents accumulation of lipid droplets, and depletion of FIT2 in zebrafish blocks diet-induced accumulation of lipid droplets in the intestine and liver, highlighting an important role for FIT2 in lipid droplet formation in vivo. Together these studies identify and characterize a conserved gene family that is important in the fundamental process of storing fat.adipocytes ͉ diabetes ͉ FIT ͉ obesity ͉ triglyceride T he ability to store energy in the form of triglyceride (TG) is conserved from Saccharomyces cerevisiae to humans. TGs are stored in the cytoplasm surrounded by a monolayer of phospholipid in distinct structures or organelles given numerous names, such as lipid particles, oil bodies, adiposomes, eicosasomes, and, more commonly, lipid droplets (1). Under normal physiological conditions, lipid droplets are involved in maintaining energy balance at the cellular and whole-organism levels. Yet under conditions of extreme lipid droplet acquisition, as in obesity, the risk for acquiring common debilitating diseases such as type 2 diabetes and cardiovascular diseases is increased (2).Despite their central role in energy homeostasis, only recently have the composition and functions of many of the components of lipid droplets from S. cerevisiae, Drosophila, and mammalian cells been revealed. In general, lipid droplets are composed of a core of neutral lipids, primarily TGs, surrounded by a monolayer of phospholipids and lipid droplet-associated proteins (3-7). In mammalian cells, the catabolism of lipid droplets is a highly regulated process involving hormonal signals, droplet-associated proteins, and lipases (8-10). Although much has been learned about the components and catabolism of lipid droplets, the molecular mechanism of lipid droplet biogenesis has remained unknown. The prevailing view is that lipid droplets are formed at the endoplasmic reticulum (ER) because the ER is the site of TG biosynthesis, and lipid droplets are often observed in close association with the cytoplasmic face of the ER (11-13). A widely accepted model of lipid droplet biogenesis involves the formation of a core or lens of newly synthesized TG between the leaflets of the ER membrane that buds off with the cytoplasmic leaflet of the ER surrounding the neutral lipid core and acquires exchangeable cytosolic lipid droplet-associated proteins (14). However, this view was recently challenged by observatio...

Background: Animal models of non-alcoholic steatohepatitis (NASH) are important tools in preclinical research and drug discovery. Gubra-Amylin NASH (GAN) diet-induced obese (DIO) mice represent a model of fibrosing NASH. The present study directly assessed the clinical translatability of the model by head-to-head comparison of liver biopsy histological and transcriptome changes in GAN DIO-NASH mouse and human NASH patients. Methods: C57Bl/6 J mice were fed chow or the GAN diet rich in saturated fat (40%), fructose (22%) and cholesterol (2%) for ≥38 weeks. Metabolic parameters as well as plasma and liver biomarkers were assessed. Liver biopsy histology and transcriptome signatures were compared to samples from human lean individuals and patients diagnosed with NASH. Results: Liver lesions in GAN DIO-NASH mice showed similar morphological characteristics compared to the NASH patient validation set, including macrosteatosis, lobular inflammation, hepatocyte ballooning degeneration and periportal/perisinusoidal fibrosis. Histomorphometric analysis indicated comparable increases in markers of hepatic lipid accumulation, inflammation and collagen deposition in GAN DIO-NASH mice and NASH patient samples. Liver biopsies from GAN DIO-NASH mice and NASH patients showed comparable dynamics in several gene expression pathways involved in NASH pathogenesis. Consistent with the clinical features of NASH, GAN DIO-NASH mice demonstrated key components of the metabolic syndrome, including obesity and impaired glucose tolerance. Conclusions: The GAN DIO-NASH mouse model demonstrates good clinical translatability with respect to the histopathological, transcriptional and metabolic aspects of the human disease, highlighting the suitability of the GAN DIO-NASH mouse model for identifying therapeutic targets and characterizing novel drug therapies for NASH.

Background: FIT2 is an ER protein purported to be important for triglyceride lipid droplet formation. Results: FIT2 deficiency in adipose tissue results in lipodystrophy and metabolic dysfunction. Conclusion: FIT2 is required for normal triglyceride storage in adipose tissue. Significance: This study provides the first proof-of-principle mouse models indicating that FIT2 is essential for normal triglyceride storage in adipose tissue.

SUMO-modification of nuclear proteins has profound effects on gene expression. However, non-toxic chemical tools that modulate sumoylation in cells are lacking. Here, to identify small molecule sumoylation inhibitors we developed a cell-based screen that focused on the well-sumoylated substrate, human Liver Receptor Homolog-1 (hLRH-1, NR5A2). Our primary gene-expression screen assayed two SUMO-sensitive transcripts, APOC3 and MUC1, that are upregulated by SUMO-less hLRH-1 or by siUBC9 knockdown, respectively. A polyphenol, tannic acid (TA) emerged as a potent sumoylation inhibitor in vitro (IC50 = 12.8 µM) and in cells. TA also increased hLRH-1 occupancy on SUMO-sensitive transcripts. Most significantly, when tested in humanized mouse primary hepatocytes, TA inhibits hLRH-1 sumoylation and induces SUMO-sensitive genes, thereby recapitulating the effects of expressing SUMO-less hLRH-1 in mouse liver. Our findings underscore the benefits of phenotypic screening for targeting post-translational modifications, and illustrate the potential utility of TA for probing the cellular consequences of sumoylation.DOI: http://dx.doi.org/10.7554/eLife.09003.001

No abstract