Sar1b transgenic male mice are more susceptible to high-fat diet-induced obesity, insulin insensitivity and intestinal chylomicron overproduction (original) (raw)
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American journal of physiology. Gastrointestinal and liver physiology, 2015
The small intestine contributes to diabetic dyslipidemia through the overproduction of apolipoprotein B48 (apoB48)-containing chylomicron particles. An important regulator of chylomicron generation is dietary lipid absorption, underlining the potential involvement of intestinal lipid transporters for developing dyslipidemia. Intestinal expression of Scavenger Receptor Class B type I (SR-BI) has been found to be upregulated in animal models of insulin resistance. Here we characterized the potential importance of SR-BI in contributing to chylomicron production and postprandial hypertriglyceridemia in vivo. Postprandial triglyceride (TG)-rich lipoprotein (TRL) production was characterized in hamsters treated with the SR-BI inhibitor Block lipid transport-1 (BLT-1), under healthy conditions or conditions of diet-induced obesity and dyslipidemia. BLT-1 (1 mg/kg) or vehicle was administered acutely in chow-fed hamsters, or gavaged twice daily over 10 days during high-fructose, high-fat, h...
Journal of Lipid Research, 2019
The small intestine is the essential site for the transport of alimentary fat in the form of lipoproteins. After the digestive phase, the lipolytic products in the lumen are absorbed by enterocytes that possess the unique ability to elaborate chylomicrons (CMs), the largest triglyceride (TG)-rich lipoprotein and dietary lipid vehicle (1, 2). CM assembly within epithelial absorptive cells is a multistep pathway that includes the translocation of lipolytic products from the apical membrane to the ER by cytosolic fatty acidbinding proteins (FABPs), lipid esterification, synthesis, and the posttranslational modification of different apos, especially apoB-48, as well as the packaging of lipid and apo components into pre-CM particles (3-5). It is only under these specific conditions that CM particles move huge amounts of dietary fat into the blood circulation via the lymphatic system. Accidents of nature reveal the intracellular roles of key proteins in CM assembly and secretion (6). For example, deciphering chylomicron retention disease (CRD) afforded new insight into the crucial functions of SAR1B GTPase, the defects of which lead to severe fat malabsorption, hypocholesterolemia, extensive steatorrhea, and significant failure to thrive in children (7, 8) with developmental abnormalities in various organs (9). It is now well established that mutations in SAR1B (SARA2) gene encoding the SAR1B GTPase protein prevent the coat protein complex II (COPII) from producing mature CM-contained vesicles endowed with the ability to bud from the ER and reach the Abstract Genetic defects in SAR1B GTPase inhibit chylomicron (CM) trafficking to the Golgi and result in a huge intraenterocyte lipid accumulation with a failure to release CMs and liposoluble vitamins into the blood circulation. The central aim of this study is to test the hypothesis that SAR1B deletion (SAR1B /) disturbs enterocyte lipid homeostasis (e.g., FA -oxidation and lipogenesis) while promoting oxidative stress and inflammation. Another issue is to compare the impact of SAR1B / to that of its paralogue SAR1A / and combined SAR1A / /B /. To address these critical issues, we have generated Caco-2/15 cells with a knockout of SAR1A, SAR1B, or SAR1A/B genes. SAR1B / results in lipid homeostasis disruption, reflected by enhanced mitochondrial FA -oxidation and diminished lipogenesis in intestinal absorptive cells via the implication of PPAR and PGC1 transcription factors. Additionally, SAR1B / cells, which mimicked enterocytes of CM retention disease, spontaneously disclosed inflammatory and oxidative characteristics via the implication of NF-B and NRF2. In most conditions, SAR1A / cells showed a similar trend, albeit less dramatic, but synergetic effects were observed with the combined defects of the two SAR1 paralogues. In conclusion, SAR1B and its paralogue are needed not only for CM trafficking but also for lipid homeostasis, prooxidant/antioxidant balance, and protection against inflammatory processes.-Sane, A., L. Ahmarani, E. Delvin, N. Auclair, S. Spahis, and E. Levy. SAR1B GTPase is necessary to protect intestinal cells from disorders of lipid homeostasis, oxidative stress, and inflammation.
Journal of Lipid Research, 2021
Chylomicron retention disease (CRD) is an autosomal recessive disorder associated with biallelic Sar1b mutations leading to defects in intracellular chylomicron (CM) trafficking and secretion. To date, a direct cause-effect relationship between CRD and Sar1b mutation has not been established, but genetically modified animal models provide an opportunity to elucidate unrecognized aspects of these mutations. To examine the physiological role and molecular mechanisms of Sar1b function, we generated mice expressing either a targeted deletion or mutation of human Sar1b using the CRISPR-Cas9 system. We found that deletion or mutation of Sar1b in mice resulted in late-gestation lethality of homozygous embryos. Moreover, compared with WT mice, heterozygotes carrying a single disrupted Sar1b allele displayed lower plasma levels of triglycerides, total cholesterol, and HDL-cholesterol, along with reduced CM secretion following gastric lipid gavage. Similarly, decreased expression of apolipoprotein B and microsomal triglyceride transfer protein was observed in correlation with the accumulation of mucosal lipids. Inefficient fat absorption in heterozygotes was confirmed via an increase in fecal lipid excretion. Furthermore, genetically modified Sar1b affected intestinal lipid homeostasis as demonstrated by enhanced fatty acid β-oxidation and diminished lipogenesis through the modulation of transcription factors. This is the first reported mammalian animal model with human Sar1b genetic defects, which reproduces some of the characteristic CRD features and provides a direct cause-effect demonstration. Supplementary key words Sar1b • gene defects • embryonic lethality • chylomicron • dietary fat • lipid metabolism • CRISPR/ Cas9 • chylomicron retention disease • fatty acid β-oxidation • lipogenesis
Aims/hypotheses: To examine hepatic expression of cholesterol-trafficking proteins, mitochondrial StarD1 and endosomal StarD3, and their relationship with dyslipidaemia and steatosis in Zucker (fa/fa) genetically obese rats, and to explore their functional role in lipid metabolism in rat McArdle RH-7777 hepatoma cells. Methods: Expression of StarD1 and StarD3 in rat liver and hepatoma samples were determined by Q-PCR and/or immunoblotting; lipid mass by colorimetric assays; radiolabelled precursors were utilised to measure lipid synthesis and secretion, and lipidation of exogenous apolipoprotein A-I. Results: Hepatic expression of StarD3 protein was repressed by genetic obesity in (fa/fa) Zucker rats, compared with lean (Fa/?) controls, suggesting a link with storage or export of lipids from the liver. Overexpression of StarD1 and StarD3, and knockdown of StarD3, in rat hepatoma cells, revealed differential effects on lipid metabolism. Overexpression of StarD1 increased utilisation of exogenous (preformed) fatty acids for triacylglycerol synthesis and secretion, but impacted minimally on cholesterol homeostasis. By contrast, overexpression of StarD3 increased lipidation of exogenous apoA-I, and facilitated de novo biosynthetic pathways for neutral lipids, potentiating triacylglycerol accumulation but possibly offering protection against lipotoxicity. Finally, StarD3 overexpression altered expression of genes which impact variously on hepatic insulin resistance, inducing Ppargcla, Cyp2e1, Nr1h4, G6pc and Irs1, and repressing expression of Scl2a1, Igfbp1, Casp3 and Serpine 1. Conclusions/interpretation: Targeting StarD3 may increase circulating levels of HDL and protect the liver against lipotoxicity; loss of hepatic expression of this protein, induced by genetic obesity, may contribute to the patho-genesis of dyslipidaemia and steatosis.
Arteriosclerosis, thrombosis, and vascular biology, 2017
Understanding the specific mechanisms of rare autosomal disorders has greatly expanded insights into the complex processes regulating intestinal fat transport. Sar1B GTPase is one of the critical proteins governing chylomicron secretion by the small intestine, and its mutations lead to chylomicron retention disease, despite the presence of Sar1A paralog. The central aim of this work is to examine the cause-effect relationship between Sar1B expression and chylomicron output and to determine whether Sar1B is obligatory for normal high-density lipoprotein biogenesis. The SAR1B gene was totally silenced in Caco-2/15 cells using the zinc finger nuclease technique. SAR1B deletion resulted in significantly decreased secretion of triglycerides (≈40%), apolipoprotein B-48 (≈57%), and chylomicron (≈34.5%). The absence of expected chylomicron production collapse may be because of the compensatory SAR1A elevation observed in our experiments. Therefore, a double knockout of SAR1A and SAR1B was e...
Hepatology, 2006
Liver fatty acid-binding protein (L-Fabp) regulates murine hepatic fatty acid trafficking in response to fasting. In this study, we show that L-Fabp ؊/؊ mice fed a high-fat Western diet for up to 18 weeks are less obese and accumulate less hepatic triglyceride than C57BL/6J controls. Paradoxically, both control and L-Fabp ؊/؊ mice manifested comparable glucose intolerance and insulin resistance when fed a Western diet. Protection against obesity in Western diet-fed L-Fabp ؊/؊ mice was not due to discernable changes in food intake, fat malabsorption, or heat production, although intestinal lipid secretion kinetics were significantly slower in both chowfed and Western diet-fed L-Fabp ؊/؊ mice. By contrast, there was a significant increase in the respiratory exchange ratio in L-Fabp ؊/؊ mice, suggesting a shift in energy substrate use from fat to carbohydrate, findings supported by an approximately threefold increase in serum lactate.
Intestinal SEC16B modulates obesity by controlling dietary lipid absorption
2021
ABSTRACTGenome-wide association studies (GWAS) have identified genetic variants in SEC16 homolog B (SEC16B) locus to be associated with obesity and body mass index (BMI) in various populations. SEC16B encodes a scaffold protein located at endoplasmic reticulum (ER) exit sites that is implicated to participate in the trafficking of COPII vesicles in mammalian cells. However, the function of SEC16B in vivo, especially in lipid metabolism, has not been investigated. Here we demonstrated that intestinal SEC16B is required for dietary lipid absorption in mice. We showed that Sec16b intestinal knockout (IKO) mice, especially female mice, were protected from HFD-induced obesity. Loss of SEC16B in intestine dramatically reduced postprandial serum triglyceride output upon intragastric lipid load or during overnight fasting and high-fat diet (HFD) refeeding. Further studies showed that intestinal SEC16B deficiency impaired apoB lipidation and chylomicron secretion. These results revealed that...
Molecular and Cellular Biochemistry, 2009
Liver fatty acid binding protein (L-FABP) is highly expressed in both enterocytes and hepatocytes and binds multiple ligands, including saturated (SFA), unsaturated fatty acids (PUFA), and cholesterol. L-fabp −/− mice were protected against obesity and hepatic steatosis on a high saturated fat (SF), high cholesterol "Western" diet and manifested a similar phenotype when fed with a high SF, low cholesterol diet. There were no significant differences in fecal fat content or food consumption between the genotypes, and fatty acid (FA) oxidation was reduced, rather than increased, in SF-fed L-fabp −/− mice as evidenced by decreased heat production and serum ketones. In contrast to mice fed with a SF diet, L-fabp −/− mice fed with a high PUFA diet were not protected against obesity and hepatic steatosis. These observations together suggest that L-fabp −/− mice exhibit a specific defect in the metabolism of SFA, possibly reflecting altered kinetics of FA utilization. In support of this possibility, microarray analysis of muscle from Western diet-fed mice revealed alterations in genes regulating glucose uptake and FA synthesis. In addition, intestinal cholesterol absorption was decreased in L-fabp −/− mice. On the other hand, and in striking contrast to other reports, female L-fabp −/− mice fed with low fat, high cholesterol diets gained slightly less weight than control mice, with minor reductions in hepatic triglyceride content. Together these data indicate a role for L-FABP in intestinal trafficking of both SFA and cholesterol.
Physiological genomics, 2016
Perturbations of lipid homeostasis manifest as dyslipidemias and obesity, which are significant risk factors for atherosclerosis and diabetes. Lipoprotein receptors in the liver are key players in the regulation of lipid homeostasis, among which the hepatic lipolysis stimulated lipoprotein receptor, LSR, was recently shown to play an important role in the removal of lipoproteins from the circulation during the postprandial phase. Since heterozygous LSR+/- mice demonstrate moderate dyslipidemia and develop higher body weight gain in response to high-fat diet compared with littermate LSR+/+ controls, we questioned if LSR heterozygosity could affect genes related to hepatic lipid metabolism. A target-specific qPCR array for 84 genes related to lipid metabolism was performed on mRNA isolated from livers of 6 mo old female LSR+/- mice and LSR+/+ littermates following a 6 wk period on a standard (STD) or high-fat diet (60% kcal, HFD). Of the 84 genes studied, 32 were significantly downreg...