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Bordat C, Cuerq C, Halimi C, Vairo D, Blond E, Restier L, Poinsot P, Duclaux-Loras R, Peretti N, Reboul E. Carotenoids in familial hypobetalipoproteinemia disorders: Malabsorption in Caco2 cell models and severe deficiency in patients. J Clin Lipidol 2024; 18:e105-e115. [PMID: 37989694 DOI: 10.1016/j.jacl.2023.10.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Revised: 10/17/2023] [Accepted: 10/21/2023] [Indexed: 11/23/2023]
Abstract
BACKGROUND Familial hypobetalipoproteinemias (FHBL) are rare genetic diseases characterized by lipid malabsorption. We focused on abetalipoproteinemia (FHBL-SD1) and chylomicron retention disease (FHBL-SD3), caused by mutations in microsomal triglyceride transfer protein (MTTP) and SAR1B genes, respectively. Treatments include a low-fat diet and high-dose fat-soluble vitamin supplementations. However, patients are not supplemented in carotenoids, a group of lipid-soluble pigments essential for eye health. OBJECTIVE Our aim was to evaluate carotenoid absorption and status in the context of hypobetalipoproteinemia. METHODS We first used knock-out Caco-2/TC7 cell models of FHBL-SD1 and FHBL-SD3 to evaluate carotenoid absorption. We then characterized FHBL-SD1 and FHBL-SD3 patient status in the main dietary carotenoids and compared it to that of control subjects. RESULTS In vitro results showed a significant decrease in basolateral secretion of α- and β-carotene, lutein, and zeaxanthin (-88.8 ± 2.2 % to -95.3 ± 5.8 %, -79.2 ± 4.4 % to -96.1 ± 2.6 %, -91.0 ± 4.5 % to -96.7 ± 0.3 % and -65.4 ± 3.6 % to -96.6 ± 1.9 %, respectively). Carotenoids plasma levels in patients confirmed significant deficiencies, with decreases ranging from -89 % for zeaxanthin to -98 % for α-carotene, compared to control subjects. CONCLUSION Given the continuous loss in visual function despite fat-soluble vitamin treatment in some patients, carotenoid supplementation may be of clinical utility. Future studies should assess the correlation between carotenoid status and visual function in aging patients and investigate whether carotenoid supplementation could prevent their visual impairment.
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Affiliation(s)
- Claire Bordat
- Aix-Marseille Université, INRAE, INSERM, C2VN, Marseille, France (Dr Bordat, Halimi, Drs Vairo, Reboul); Univ-Lyon, CarMeN laboratory, INSERM U1060, INRAE 1397, Université Claude Bernard Lyon-1, Pierre Benite 69495, France (Drs Bordat, Peretti)
| | - Charlotte Cuerq
- Biochemistry Department, Hospices Civils de Lyon, Pierre-Benite 69495, France (Drs Cuerq, Blond)
| | - Charlotte Halimi
- Aix-Marseille Université, INRAE, INSERM, C2VN, Marseille, France (Dr Bordat, Halimi, Drs Vairo, Reboul)
| | - Donato Vairo
- Aix-Marseille Université, INRAE, INSERM, C2VN, Marseille, France (Dr Bordat, Halimi, Drs Vairo, Reboul)
| | - Emilie Blond
- Biochemistry Department, Hospices Civils de Lyon, Pierre-Benite 69495, France (Drs Cuerq, Blond)
| | - Liora Restier
- Pediatric Hepato-Gastroenterology and Nutrition Unit, Hôpital Femme Mère Enfant de Lyon HFME, Hospices Civils de Lyon HCL, Bron 69677, France (Drs Restier, Poinsot, Duclaux-Loras, Peretti)
| | - Pierre Poinsot
- Pediatric Hepato-Gastroenterology and Nutrition Unit, Hôpital Femme Mère Enfant de Lyon HFME, Hospices Civils de Lyon HCL, Bron 69677, France (Drs Restier, Poinsot, Duclaux-Loras, Peretti)
| | - Rémi Duclaux-Loras
- Pediatric Hepato-Gastroenterology and Nutrition Unit, Hôpital Femme Mère Enfant de Lyon HFME, Hospices Civils de Lyon HCL, Bron 69677, France (Drs Restier, Poinsot, Duclaux-Loras, Peretti)
| | - Noël Peretti
- Univ-Lyon, CarMeN laboratory, INSERM U1060, INRAE 1397, Université Claude Bernard Lyon-1, Pierre Benite 69495, France (Drs Bordat, Peretti); Pediatric Hepato-Gastroenterology and Nutrition Unit, Hôpital Femme Mère Enfant de Lyon HFME, Hospices Civils de Lyon HCL, Bron 69677, France (Drs Restier, Poinsot, Duclaux-Loras, Peretti); CENS ELI-2D, 165 Chemin du Grand Revoyet, Pierre Bénite F - 69310, France (Dr Peretti)
| | - Emmanuelle Reboul
- Aix-Marseille Université, INRAE, INSERM, C2VN, Marseille, France (Dr Bordat, Halimi, Drs Vairo, Reboul).
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2
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Ikonen E, Olkkonen VM. Intracellular Cholesterol Trafficking. Cold Spring Harb Perspect Biol 2023; 15:a041404. [PMID: 37277190 PMCID: PMC10411867 DOI: 10.1101/cshperspect.a041404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Cholesterol is an essential lipid species of mammalian cells. Cells acquire it through synthesis in the endoplasmic reticulum (ER) and uptake from lipoprotein particles. Newly synthesized cholesterol is efficiently distributed from the ER to other organelles via lipid-binding/transfer proteins concentrated at membrane contact sites (MCSs) to reach the trans-Golgi network, endosomes, and plasma membrane. Lipoprotein-derived cholesterol is exported from the plasma membrane and endosomal compartments via a combination of vesicle/tubule-mediated membrane transport and transfer through MCSs. In this review, we provide an overview of intracellular cholesterol trafficking pathways, including cholesterol flux from the ER to other membranes, cholesterol uptake from lipoprotein donors and transport from the plasma membrane to the ER, cellular cholesterol efflux to lipoprotein acceptors, as well as lipoprotein cholesterol secretion from enterocytes, hepatocytes, and astrocytes. We also briefly discuss human diseases caused by defects in these processes and therapeutic strategies available in such conditions.
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Affiliation(s)
- Elina Ikonen
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, 00100 Helsinki, Finland
- Minerva Foundation Institute for Medical Research, 00290 Helsinki, Finland
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, 00290 Helsinki, Finland
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3
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Abstract
Postprandial hyperlipidaemia is an important feature of diabetic dyslipidaemia and plays an important role in the development of cardiovascular disease in individuals with type 2 diabetes. Postprandial hyperlipidaemia in type 2 diabetes is secondary to increased chylomicron production by the enterocytes and delayed catabolism of chylomicrons and chylomicron remnants. Insulin and some intestinal hormones (e.g. glucagon-like peptide-1 [GLP-1]) influence intestinal lipid metabolism. In individuals with type 2 diabetes, insulin resistance and possibly reduced GLP-1 secretion are involved in the pathophysiology of postprandial hyperlipidaemia. Several factors are involved in the overproduction of chylomicrons: (1) increased expression of microsomal triglyceride transfer protein, which is a key enzyme in chylomicron synthesis; (2) higher stability and availability of apolipoprotein B-48; and (3) increased de novo lipogenesis. Individuals with type 2 diabetes present with disorders of cholesterol metabolism in the enterocytes with reduced absorption and increased synthesis. The increased production of chylomicrons in type 2 diabetes is also associated with a reduction in their catabolism, mostly because of a reduction in activity of lipoprotein lipase. Modification of the microbiota, which is observed in type 2 diabetes, may also generate disorders of intestinal lipid metabolism, but human data remain limited. Some glucose-lowering treatments significantly influence intestinal lipid absorption and transport. Postprandial hyperlipidaemia is reduced by metformin, pioglitazone, alpha-glucosidase inhibitors, dipeptidyl peptidase 4 inhibitors and GLP-1 agonists. The most pronounced effect is observed with GLP-1 agonists, which reduce chylomicron production significantly in individuals with type 2 diabetes and have a direct effect on the intestine by reducing the expression of genes involved in intestinal lipoprotein metabolism. The effect of sodium-glucose cotransporter 2 inhibitors on intestinal lipid metabolism needs to be clarified.
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Affiliation(s)
- Bruno Vergès
- Endocrinology-Diabetology Department, University-Hospital, Dijon, France.
- Inserm UMR 1231, Medical School, University of Burgundy-Franche Comté, Dijon, France.
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4
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Markovic MA, Srikrishnaraj A, Tsang D, Brubaker PL. Requirement for the intestinal epithelial insulin-like growth factor-1 receptor in the intestinal responses to glucagon-like peptide-2 and dietary fat. FASEB J 2020; 34:6628-6640. [PMID: 32212202 DOI: 10.1096/fj.202000169r] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/28/2020] [Accepted: 03/10/2020] [Indexed: 12/13/2022]
Abstract
The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances the enterocyte chylomicron production. However, GLP-2 is known to require the intestinal-epithelial insulin-like growth factor-1 receptor (IE-IGF-1R) for its other actions to increase intestinal growth and barrier function. The role of the IE-IGF-1R in enterocyte lipid handling was thus tested in the GLP-2 signaling pathway, as well as in response to a Western diet (WD). IE-IGF-1R knockout (KO) and control mice were treated for 11 days with h(GLY2 )GLP-2 or fed a WD for 18 weeks followed by a duodenal fat tolerance test with C14 -labeled triolein. Human Caco-2BBE cells were treated with an IGF-1R antagonist or signaling inhibitors to determine triglyceride-associated protein expression. The IE-IGF-1R was required for GLP-2-induced increases in CD36 and FATP-4 in chow-fed mice, and for expression in vitro; FATP-4 also required PI3K/Akt. Although WD-fed IE-IGF-1R KO mice demonstrated normal CD36 expression, the protein was incorrectly localized 2h post-duodenal fat administration. IE-IGF-1R KO also prevented the WD-induced increase in MTP and decrease in APOC3, increased jejunal mucosal C14 -fat accumulation, and elevated plasma triglyceride and C14 -fat levels. Collectively, these studies elucidate new roles for the IE-IGF-1R in enterocyte lipid handling, under basal conditions and in response to GLP-2 and WD-feeding.
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Affiliation(s)
| | | | - Derek Tsang
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, ON, Canada.,Department of Medicine, University of Toronto, Toronto, ON, Canada
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5
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Sané A, Ahmarani L, Delvin E, Auclair N, Spahis S, Levy E. SAR1B GTPase is necessary to protect intestinal cells from disorders of lipid homeostasis, oxidative stress, and inflammation. J Lipid Res 2019; 60:1755-1764. [PMID: 31409740 PMCID: PMC6795079 DOI: 10.1194/jlr.ra119000119] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Revised: 07/29/2019] [Indexed: 12/12/2022] Open
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 β-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 β-oxidation and diminished lipogenesis in intestinal absorptive cells via the implication of PPARα and PGC1α transcription factors. Additionally, SAR1B−/−cells, which mimicked enterocytes of CM retention disease, spontaneously disclosed inflammatory and oxidative characteristics via the implication of NF-κB 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.
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Affiliation(s)
- Alain Sané
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada
| | - Lena Ahmarani
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada
| | - Edgard Delvin
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada
| | - Nikolas Auclair
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.,Departments of Pharmacology, Université de Montréal, Montreal, Quebec, Canada
| | - Schohraya Spahis
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.,Nutrition, Université de Montréal, Montreal, Quebec, Canada
| | - Emile Levy
- Research Centre, CHU-Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada .,Departments of Pharmacology, Université de Montréal, Montreal, Quebec, Canada.,Nutrition, Université de Montréal, Montreal, Quebec, Canada
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6
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Qu J, Ko CW, Tso P, Bhargava A. Apolipoprotein A-IV: A Multifunctional Protein Involved in Protection against Atherosclerosis and Diabetes. Cells 2019; 8:E319. [PMID: 30959835 PMCID: PMC6523623 DOI: 10.3390/cells8040319] [Citation(s) in RCA: 96] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Revised: 03/31/2019] [Accepted: 04/02/2019] [Indexed: 12/19/2022] Open
Abstract
Apolipoprotein A-IV (apoA-IV) is a lipid-binding protein, which is primarily synthesized in the small intestine, packaged into chylomicrons, and secreted into intestinal lymph during fat absorption. In the circulation, apoA-IV is present on chylomicron remnants, high-density lipoproteins, and also in lipid-free form. ApoA-IV is involved in a myriad of physiological processes such as lipid absorption and metabolism, anti-atherosclerosis, platelet aggregation and thrombosis, glucose homeostasis, and food intake. ApoA-IV deficiency is associated with atherosclerosis and diabetes, which renders it as a potential therapeutic target for treatment of these diseases. While much has been learned about the physiological functions of apoA-IV using rodent models, the action of apoA-IV at the cellular and molecular levels is less understood, let alone apoA-IV-interacting partners. In this review, we will summarize the findings on the molecular function of apoA-IV and apoA-IV-interacting proteins. The information will shed light on the discovery of apoA-IV receptors and the understanding of the molecular mechanism underlying its mode of action.
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Affiliation(s)
- Jie Qu
- Department of Pathology and Laboratory Medicine, Metabolic Diseases Institute, University of Cincinnati, 2180 E Galbraith Road, Cincinnati, OH 45237-0507, USA.
| | - Chih-Wei Ko
- Department of Pathology and Laboratory Medicine, Metabolic Diseases Institute, University of Cincinnati, 2180 E Galbraith Road, Cincinnati, OH 45237-0507, USA.
| | - Patrick Tso
- Department of Pathology and Laboratory Medicine, Metabolic Diseases Institute, University of Cincinnati, 2180 E Galbraith Road, Cincinnati, OH 45237-0507, USA.
| | - Aditi Bhargava
- Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, 513 Parnassus Avenue, San Francisco, CA 94143-0556, USA.
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7
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Abstract
Plasma levels of triacylglycerols and diacylglycerols, the lipoproteins that transport them, and proteins involved in their absorption from the intestinal lumen fluctuate in a circadian manner. These changes are likely controlled by clock genes expressed in the intestine that are probably synchronized by neuronal and humoral signals from the suprachiasmatic nuclei, which constitute a master clock entrained by light signals from the eyes and from the environment, e.g., food availability. Acute changes in circadian rhythms--e.g., due to nonsynchronous work schedules or a transcontinental flight--may trigger intestinal discomfort. Chronic disruptions in circadian control mechanisms may predispose the individual to irritable bowel syndrome, gastroesophageal reflux disease, and peptic ulcer disease. A more detailed understanding of the molecular mechanisms underlying temporal changes in intestinal activity might allow us to identify novel targets for developing therapeutic approaches to these disorders.
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Affiliation(s)
- M Mahmood Hussain
- Departments of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, New York 11203, and Virginia New York Harbor Healthcare System, Brooklyn, New York 11209;
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8
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Giammanco A, Cefalù AB, Noto D, Averna MR. The pathophysiology of intestinal lipoprotein production. Front Physiol 2015; 6:61. [PMID: 25852563 PMCID: PMC4367171 DOI: 10.3389/fphys.2015.00061] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 02/14/2015] [Indexed: 12/12/2022] Open
Abstract
Intestinal lipoprotein production is a multistep process, essential for the absorption of dietary fats and fat-soluble vitamins. Chylomicron assembly begins in the endoplasmic reticulum with the formation of primordial, phospholipids-rich particles that are then transported to the Golgi for secretion. Several classes of transporters play a role in the selective uptake and/or export of lipids through the villus enterocytes. Once secreted in the lymph stream, triglyceride-rich lipoproteins (TRLs) are metabolized by Lipoprotein lipase (LPL), which catalyzes the hydrolysis of triacylglycerols of very low density lipoproteins (VLDLs) and chylomicrons, thereby delivering free fatty acids to various tissues. Genetic mutations in the genes codifying for these proteins are responsible of different inherited disorders affecting chylomicron metabolism. This review focuses on the molecular pathways that modulate the uptake and the transport of lipoproteins of intestinal origin and it will highlight recent findings on TRLs assembly.
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Affiliation(s)
| | | | | | - Maurizio R. Averna
- Dipartimento Biomedico di Medicina Interna e Specialistica, Università degli Studi di PalermoPalermo, Italy
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9
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Kohan AB, Wang F, Lo CM, Liu M, Tso P. ApoA-IV: current and emerging roles in intestinal lipid metabolism, glucose homeostasis, and satiety. Am J Physiol Gastrointest Liver Physiol 2015; 308:G472-81. [PMID: 25591862 PMCID: PMC4360046 DOI: 10.1152/ajpgi.00098.2014] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Apolipoprotein A-IV (apoA-IV) is secreted by the small intestine on chylomicrons into intestinal lymph in response to fat absorption. Many physiological functions have been ascribed to apoA-IV, including a role in chylomicron assembly and lipid metabolism, a mediator of reverse-cholesterol transport, an acute satiety factor, a regulator of gastric function, and, finally, a modulator of blood glucose homeostasis. The purpose of this review is to update our current view of intestinal apoA-IV synthesis and secretion and the physiological roles of apoA-IV in lipid metabolism and energy homeostasis, and to underscore the potential for intestinal apoA-IV to serve as a therapeutic target for the treatment of diabetes and obesity-related disease.
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Affiliation(s)
- Alison B. Kohan
- 2Department of Nutritional Sciences, University of Connecticut, Storrs, Connecticut
| | - Fei Wang
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio; and
| | - Chun-Min Lo
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio; and
| | - Min Liu
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio; and
| | - Patrick Tso
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio; and
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10
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Abstract
Among all the metabolites present in the plasma, lipids, mainly triacylglycerol and diacylglycerol, show extensive circadian rhythms. These lipids are transported in the plasma as part of lipoproteins. Lipoproteins are synthesized primarily in the liver and intestine and their production exhibits circadian rhythmicity. Studies have shown that various proteins involved in lipid absorption and lipoprotein biosynthesis show circadian expression. Further, intestinal epithelial cells express circadian clock genes and these genes might control circadian expression of different proteins involved in intestinal lipid absorption. Intestinal circadian clock genes are synchronized by signals emanating from the suprachiasmatic nuclei that constitute a master clock and from signals coming from other environmental factors, such as food availability. Disruptions in central clock, as happens due to disruptions in the sleep/wake cycle, affect intestinal function. Similarly, irregularities in temporal food intake affect intestinal function. These changes predispose individuals to various metabolic disorders, such as metabolic syndrome, obesity, diabetes, and atherosclerosis. Here, we summarize how circadian rhythms regulate microsomal triglyceride transfer protein, apoAIV, and nocturnin to affect diurnal regulation of lipid absorption.
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Affiliation(s)
- M Mahmood Hussain
- Departments of Cell Biology and Pediatrics, State University of New York Downstate Medical Center, Brooklyn, NY 11203; and Veterans Affairs New York Harbor Healthcare System, Brooklyn, NY 11209
| | - Xiaoyue Pan
- Departments of Cell Biology and Pediatrics, State University of New York Downstate Medical Center, Brooklyn, NY 11203; and Veterans Affairs New York Harbor Healthcare System, Brooklyn, NY 11209
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11
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Abstract
PURPOSE OF REVIEW To summarize the evidence for the presence of two lipid absorption pathways and their regulation. RECENT FINDINGS Lipid absorption involves hydrolysis of dietary fat in the lumen of the intestine, followed by the uptake of hydrolyzed products by enterocytes. Lipids are resynthesized in the endoplasmic reticulum and are either secreted with chylomicrons and HDLs or stored as cytoplasmic lipid droplets. Lipids in the droplets are hydrolyzed and are secreted at a later time. Secretion of lipids by the chylomicron and HDL pathways are dependent on microsomal triglyceride transfer protein (MTP) and ATP-binding cassette family A protein 1, respectively, and are regulated independently. Gene-ablation studies showed that MTP function and chylomicron assembly is essential for the absorption of triglycerides. Ablation of MTP abolishes triglyceride absorption and results in massive triglyceride accumulation in enterocytes. Although the majority of phospholipid, cholesterol, and vitamin E are absorbed through the chylomicron pathway, a significant amount of these lipids are also absorbed via the HDL pathway. Chylomicron assembly and secretion is increased by the enhanced availability of fatty acids, whereas the HDL pathway is upregulated by liver X receptor agonists. SUMMARY Triglycerides are exclusively transported with chylomicrons and this process is critically dependent on MTP. In addition to chylomicrons, absorption of phospholipids, free cholesterol, retinol, and vitamin E also involves HDLs. These two pathways are complementary and are regulated independently. They may be targeted to lower lipid absorption in order to control hyperlipidemia, obesity, metabolic syndrome, steatosis, insulin resistance, atherosclerosis, and other disorders.
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Affiliation(s)
- M Mahmood Hussain
- aDepartment of Cell Biology bDepartment of Pediatrics, SUNY Downstate Medical Center cVA New York Harbor Healthcare System, Brooklyn, New York, USA
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12
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Wang F, Kohan AB, Dong HH, Yang Q, Xu M, Huesman S, Lou D, Hui DY, Tso P. Overexpression of apolipoprotein C-III decreases secretion of dietary triglyceride into lymph. Physiol Rep 2014; 2:e00247. [PMID: 24760506 PMCID: PMC4002232 DOI: 10.1002/phy2.247] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Apolipoprotein C‐III (apoC‐III) is not only predominantly synthesized by the liver but also by the small intestine. Because apoC‐III is secreted from the intestine on the chylomicron along with lipid absorption, we questioned whether apoC‐III might play a role in intestinal lipid absorption and/or transport. Using both wild‐type (WT) and apoC‐III transgenic (apoC‐III Tg) mice, we showed that apoC‐III Tg mice have decreased lymphatic lipid transport compared with WT mice in response to an intraduodenal infusion of radiolabeled lipid. This is associated with accumulation of radiolabeled lipids in the luminal compartment of the apoC‐III Tg mice, indicating delayed lipid uptake from the lumen. The total amount of radioactive lipids in the mucosal compartment did not differ between apoC‐III Tg and WT mice, but the lipid distribution analysis indicated a predominance of free fatty acids and monoacylglycerol in the mucosa of apoC‐III Tg mice, implying impaired esterification capacity. Thus, the mechanisms underlying the reduced lymphatic lipid transport in apoC‐III Tg mice involve both a delayed lipid uptake into enterocytes, as well as impaired esterification to form triglyceride in the mucosa. These data document a novel role for apoC‐III in the uptake, re‐esterification, and lymphatic transport of dietary lipids in the intestine.
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Affiliation(s)
- Fei Wang
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - Alison B. Kohan
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - H. Henry Dong
- Children's Hospital of PittsburghRangos Research CenterPittsburghPennsylvania15244
| | - Qing Yang
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - Min Xu
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - Sarah Huesman
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - Danwen Lou
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - David Y. Hui
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
| | - Patrick Tso
- Department of Pathology and Laboratory MedicineUniversity of CincinnatiCincinnatiOhio45237
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13
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Kohan AB, Wang F, Li X, Vandersall AE, Huesman S, Xu M, Yang Q, Lou D, Tso P. Is apolipoprotein A-IV rate limiting in the intestinal transport and absorption of triglyceride? Am J Physiol Gastrointest Liver Physiol 2013; 304:G1128-35. [PMID: 23599044 PMCID: PMC3680714 DOI: 10.1152/ajpgi.00409.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 04/16/2013] [Indexed: 01/31/2023]
Abstract
Apolipoprotein A-IV (apoA-IV) is synthesized by the intestine and secreted when dietary fat is absorbed and transported into lymph associated with chylomicrons. We have recently demonstrated that loss of apoA-IV increases chylomicron size and delays its clearance from the blood. There is still uncertainty, however, about the precise role of apoA-IV on the transport of dietary fat from the intestine into the lymph. ApoA-IV knockout (KO) mice do not have a gross defect in dietary lipid absorption, as measured by oral fat tolerance and fecal fat measurements. Here, using the in vivo lymph fistula mouse model, we show that the cumulative secretion of triglyceride (TG) into lymph in apoA-IV KO mice is very similar to that of wild-type (WT) mice. However, the apoA-IV KO mice do have subtle changes in TG accumulation in the intestinal mucosa during a 6-h continuous, but not bolus, infusion of lipid. There are no changes in the ratio of esterified to free fatty acids in the intestinal mucosa of the apoA-IV KO, however. When we extended these findings, by giving a higher dose of lipid (6 μmol/h) and for a longer infusion period (8 h), we found no effect of apoA-IV KO on intestinal TG absorption. This higher lipid infusion most certainly stresses the intestine, as we see a drastically lower absorption of TG (in both WT and KO mice); however, the loss of A-IV does not exacerbate this effect. This supports our hypothesis that apoA-IV is not required for TG absorption in the intestine. Our data suggest that the mechanisms by which the apoA-IV KO intestine responds to intestinal lipid may not be different from their WT counterparts. We conclude that apoA-IV is not required for normal lymphatic transport of TG.
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Affiliation(s)
- Alison B Kohan
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH 45237, USA.
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14
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Pan X, Munshi MK, Iqbal J, Queiroz J, Sirwi AA, Shah S, Younus A, Hussain MM. Circadian regulation of intestinal lipid absorption by apolipoprotein AIV involves forkhead transcription factors A2 and O1 and microsomal triglyceride transfer protein. J Biol Chem 2013; 288:20464-76. [PMID: 23729668 DOI: 10.1074/jbc.m113.473454] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We have shown previously that Clock, microsomal triglyceride transfer protein (MTP), and nocturnin are involved in the circadian regulation of intestinal lipid absorption. Here, we clarified the role of apolipoprotein AIV (apoAIV) in the diurnal regulation of plasma lipids and intestinal lipid absorption in mice. Plasma triglyceride in apoAIV(-/-) mice showed diurnal variations similar to apoAIV(+/+) mice; however, the increases in plasma triglyceride at night were significantly lower in these mice. ApoAIV(-/-) mice absorbed fewer lipids at night and showed blunted response to daytime feeding. To explain reasons for these lower responses, we measured MTP expression; intestinal MTP was low at night, and its induction after food entrainment was less in apoAIV(-/-) mice. Conversely, apoAIV overexpression increased MTP mRNA in hepatoma cells, indicating transcriptional regulation. Mechanistic studies revealed that sequences between -204/-775 bp in the MTP promoter respond to apoAIV and that apoAIV enhances expression of FoxA2 and FoxO1 transcription factors and their binding to the identified cis elements in the MTP promoter at night. Knockdown of FoxA2 and FoxO1 abolished apoAIV-mediated MTP induction. Similarly, knockdown of apoAIV in differentiated Caco-2 cells reduced MTP, FoxA2, and FoxO1 mRNA levels, cellular MTP activity, and media apoB. Moreover, FoxA2 and FoxO1 expression showed diurnal variations, and their expression was significantly lower in apoAIV(-/-) mice. These data indicate that apoAIV modulates diurnal changes in lipid absorption by regulating forkhead transcription factors and MTP and that inhibition of apoAIV expression might reduce plasma lipids.
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Affiliation(s)
- Xiaoyue Pan
- Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA.
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15
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Jaschke A, Chung B, Hesse D, Kluge R, Zahn C, Moser M, Petzke KJ, Brigelius-Flohé R, Puchkov D, Koepsell H, Heeren J, Joost HG, Schürmann A. The GTPase ARFRP1 controls the lipidation of chylomicrons in the Golgi of the intestinal epithelium. Hum Mol Genet 2012; 21:3128-42. [PMID: 22505585 PMCID: PMC3384381 DOI: 10.1093/hmg/dds140] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The uptake and processing of dietary lipids by the small intestine is a multistep process that involves several steps including vesicular and protein transport. The GTPase ADP-ribosylation factor-related protein 1 (ARFRP1) controls the ARF-like 1 (ARL1)-mediated Golgi recruitment of GRIP domain proteins which in turn bind several Rab-GTPases. Here, we describe the essential role of ARFRP1 and its interaction with Rab2 in the assembly and lipidation of chylomicrons in the intestinal epithelium. Mice lacking Arfrp1 specifically in the intestine (Arfrp1vil−/−) exhibit an early post-natal growth retardation with reduced plasma triacylglycerol and free fatty acid concentrations. Arfrp1vil−/− enterocytes as well as Arfrp1 mRNA depleted Caco-2 cells absorbed fatty acids normally but secreted chylomicrons with a markedly reduced triacylglycerol content. In addition, the release of apolipoprotein A-I (ApoA-I) was dramatically decreased, and ApoA-I accumulated in the Arfrp1vil−/− epithelium, where it predominantly co-localized with Rab2. The release of chylomicrons from Caco-2 was markedly reduced after the suppression of Rab2, ARL1 and Golgin-245. Thus, the GTPase ARFRP1 and its downstream proteins are required for the lipidation of chylomicrons and the assembly of ApoA-I to these particles in the Golgi of intestinal epithelial cells.
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Affiliation(s)
- Alexander Jaschke
- Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, D-14558 Nuthetal, Germany
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16
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Kohan AB, Wang F, Li X, Bradshaw S, Yang Q, Caldwell JL, Bullock TM, Tso P. Apolipoprotein A-IV regulates chylomicron metabolism-mechanism and function. Am J Physiol Gastrointest Liver Physiol 2012; 302:G628-36. [PMID: 22207575 PMCID: PMC3311309 DOI: 10.1152/ajpgi.00225.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Dietary fat is an important mediator of atherosclerosis and obesity. Despite its importance in mediating metabolic disease, there is still much unknown about dietary fat absorption in the intestine and especially the detailed biological roles of intestinal apolipoproteins involved in that process. We were specifically interested in determining the physiological role of the intestinal apolipoprotein A-IV (A-IV) using A-IV knockout (KO) mice. A-IV is stimulated by fat absorption in the intestine and is secreted on nascent chylomicrons into intestinal lymph. We found that A-IV KO mice had reduced plasma triglyceride (TG) and cholesterol levels and that this hypolipidemia persisted on a high-fat diet. A-IV KO did not cause abnormal intestinal lipid absorption, food intake, or adiposity. Additionally, A-IV KO did not cause abnormal liver TG and cholesterol metabolism, as assessed by measuring hepatic lipid content, lipogenic and cholesterol synthetic gene expression, and in vivo VLDL secretion. Instead, A-IV KO resulted in the secretion of larger chylomicrons from the intestine into the lymph, and those chylomicrons were cleared from the plasma more slowly than wild-type chylomicrons. These data suggest that A-IV has a previously unknown role in mediating the metabolism of chylomicrons, and therefore may be important in regulating plasma lipid metabolism.
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Affiliation(s)
- Alison B. Kohan
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Fei Wang
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Xiaoming Li
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Suzanne Bradshaw
- 2Department of Biology, University of Cincinnati, Blue Ash College, Cincinnati, Ohio
| | - Qing Yang
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Jody L. Caldwell
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Tera M. Bullock
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
| | - Patrick Tso
- 1Department of Pathology and Laboratory Medicine, University of Cincinnati; and
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17
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Weinberg RB, Gallagher JW, Fabritius MA, Shelness GS. ApoA-IV modulates the secretory trafficking of apoB and the size of triglyceride-rich lipoproteins. J Lipid Res 2012; 53:736-43. [PMID: 22257482 DOI: 10.1194/jlr.m019992] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Although the evidence linking apoA-IV expression and triglyceride (TG)-rich lipoprotein assembly and secretion is compelling, the intracellular mechanisms by which apoA-IV could modulate these processes remain poorly understood. We therefore examined the functional impact of apoA-IV expression on endogenous apoB, TG, and VLDL secretion in stably transfected McA-RH7777 rat hepatoma cells. Expression of apoA-IV modified with the endoplasmic reticulum (ER) retention signal KDEL (apoA-IV-KDEL) dramatically decreased both the rate and efficiency of endogenous apoB secretion, suggesting a presecretory interaction between apoA-IV-KDEL and apoB or apoB-containing lipoproteins. Expression of native apoA-IV using either a constitutive or tetracycline-inducible promoter delayed the initial rate of apoB secretion and reduced the final secretion efficiency by ∼40%. However, whereas apoA-IV-KDEL reduced TG secretion by 75%, expression of native apoA-IV caused a 20-35% increase in TG secretion, accompanied by a ∼55% increase in VLDL-associated apoB, an increase in the TG:phospholipid ratio of secreted d < 1.006 lipoproteins, and a 10.1 nm increase in peak VLDL(1) particle diameter. Native apoA-IV expression had a negligible impact on expression of the MTP gene. These data suggest that by interacting with apoB in the secretory pathway, apoA-IV alters the trafficking kinetics of apoB-containing TG-rich lipoproteins through cellular lipidation compartments, which in turn, enhances particle expansion and increases TG secretion.
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Affiliation(s)
- Richard B Weinberg
- Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
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18
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The chylomicron: relationship to atherosclerosis. Int J Vasc Med 2011; 2012:784536. [PMID: 22007304 PMCID: PMC3189596 DOI: 10.1155/2012/784536] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 08/08/2011] [Indexed: 12/20/2022] Open
Abstract
The B-containing lipoproteins are the transporters of cholesterol, and the evidence suggests that the apo B48-containing postprandial chylomicron particles and the triglyceride-rich very low density lipoprotein (VLDL) particles play an important part in the development of the plaque both directly and indirectly by their impact on LDL composition. The ratio of dietary to synthesised cholesterol is variable but tightly regulated: hence intervention with diet at best reduces serum cholesterol by <20% andusually <10%. Statins are the mainstay of cholesterol reduction therapy, but they increase cholesterol absorption, an example of the relationship between synthesis and absorption. Inhibition of cholesterol absorption with Ezetimibe, an inhibitor of Niemann Pick C1-like 1 (NPC1-L1), the major regulator of cholesterol absorption, increases cholesterol synthesis and hence the value of adding an inhibitor of cholesterol absorption to an inhibitor of cholesterol synthesis. Apo B48, the structural protein of the chylomicron particle, is synthesised in abundance so that the release of these particles is dependent on the amount of cholesterol and triglyceride available in the intestine. This paper will discuss cholesterol absorption and synthesis, chylomicron formation, and the effect of postprandial lipoproteins on factors involved in atherosclerosis.
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Simon T, Cook VR, Rao A, Weinberg RB. Impact of murine intestinal apolipoprotein A-IV expression on regional lipid absorption, gene expression, and growth. J Lipid Res 2011; 52:1984-94. [PMID: 21840868 DOI: 10.1194/jlr.m017418] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Apolipoprotein A-IV (apoA-IV) is synthesized by intestinal enterocytes during lipid absorption and secreted into lymph on the surface of nascent chylomicrons. A compelling body of evidence supports a central role of apoA-IV in facilitating intestinal lipid absorption and in regulating satiety, yet a longstanding conundrum is that no abnormalities in fat absorption, feeding behavior, or weight gain were observed in chow-fed apoA-IV knockout (A4KO) mice. Herein we reevaluated the impact of apoA-IV expression in C57BL6 and A4KO mice fed a high-fat diet. Fat balance and lymph cannulation studies found no effect of intestinal apoA-IV gene expression on the efficiency of fatty acid absorption, but gut sac transport studies revealed that apoA-IV differentially modulates lipid transport and the number and size of secreted triglyceride-rich lipoproteins in different anatomic regions of the small bowel. ApoA-IV gene deletion increased expression of other genes involved in chylomicron assembly, impaired the ability of A4KO mice to gain weight and increase adipose tissue mass, and increased the distal gut hormone response to a high-fat diet. Together these findings suggest that apoA-IV may play a unique role in integrating feeding behavior, intestinal lipid absorption, and energy storage.
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Affiliation(s)
- Trang Simon
- Departments of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, USA
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20
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Abstract
The absorption of dietary fat is of increasing concern given the rise of obesity not only in the United States but throughout the developed world. This review explores what happens to dietary fat within the enterocyte. Absorbed fatty acids and monoacylglycerols are required to be bound to intracellular proteins and/or to be rapidly converted to triacylglycerols to prevent cellular membrane disruption. The triacylglycerol produced at the level of the endoplasmic reticulum (ER) is either incorporated into prechylomicrons within the ER lumen or shunted to triacylglycerol storage pools. The prechylomicrons exit the ER in a specialized transport vesicle in the rate-limiting step in the intracellular transit of triacylglycerol across the enterocyte. The prechylomicrons are further processed in the Golgi and are transported to the basolateral membrane via a separate vesicular system for exocytosis into the intestinal lamina propria. Fatty acids and monoacylglycerols entering the enterocyte via the basolateral membrane are also incorporated into triacylglycerol, but the basolaterally entering lipid is much more likely to enter the triacylglycerol storage pool than the lipid entering via the apical membrane.
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Affiliation(s)
- Charles M Mansbach
- The University of Tennessee Health Science Center and the Veterans Administration Medical Center, Memphis, TN 38163, USA.
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21
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Siddiqi S, Siddiqi SA, Mansbach CM. Sec24C is required for docking the prechylomicron transport vesicle with the Golgi. J Lipid Res 2009; 51:1093-100. [PMID: 19965600 DOI: 10.1194/jlr.m002758] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rate-limiting step in the transit of dietary fat across the intestinal absorptive cell is its exit from the endoplasmic reticulum (ER) in a specialized ER-to-Golgi transport vesicle, the prechylomicron transport vesicle (PCTV). PCTV bud off from the ER membranes and have unique features; they are the largest ER-derived vesicles (average diameter 250 nm), do not require GTP and COPII proteins for their formation, and utilize VAMP7 as a v-N-ethylmaleimide sensitive factor attachment protein receptor (SNARE). However, PCTV require COPII proteins for their fusion with the Golgi, suggesting a role for them in Golgi target recognition. In support of this, PCTV contained each of the five COPII proteins when docked with the Golgi. When PCTV were fused with the Golgi, the COPII proteins were present in greatly diminished amounts, indicating they had cycled back to the cytosol. Immuno-depletion of Sec31 from the cytosol did not affect PCTV-Golgi docking, but depletion of Sec23 resulted in a 25% decrease. Immuno-depletion of Sec24C caused a nearly complete cessation of PCTV docking activity, but on the addition of recombinant Sec24C, docking activity was restored. We conclude that the COPII proteins are present at docking of PCTV with the Golgi and that Sec24C is required for this event. Sec23 plays a less important role.
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Affiliation(s)
- Shahzad Siddiqi
- Division of Gastroenterology, Department of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
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22
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Abstract
Our knowledge of the uptake and transport of dietary fat and fat-soluble vitamins has advanced considerably. Researchers have identified several new mechanisms by which lipids are taken up by enterocytes and packaged as chylomicrons for export into the lymphatic system or clarified the actions of mechanisms previously known to participate in these processes. Fatty acids are taken up by enterocytes involving protein-mediated as well as protein-independent processes. Net cholesterol uptake depends on the competing activities of NPC1L1, ABCG5, and ABCG8 present in the apical membrane. We have considerably more detailed information about the uptake of products of lipid hydrolysis, the active transport systems by which they reach the endoplasmic reticulum, the mechanisms by which they are resynthesized into neutral lipids and utilized within the endoplasmic reticulum to form lipoproteins, and the mechanisms by which lipoproteins are secreted from the basolateral side of the enterocyte. apoB and MTP are known to be central to the efficient assembly and secretion of lipoproteins. In recent studies, investigators found that cholesterol, phospholipids, and vitamin E can also be secreted from enterocytes as components of high-density apoB-free/apoAI-containing lipoproteins. Several of these advances will probably be investigated further for their potential as targets for the development of drugs that can suppress cholesterol absorption, thereby reducing the risk of hypercholesterolemia and cardiovascular disease.
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Affiliation(s)
- Jahangir Iqbal
- Dept. of Anatomy, 450 Clarkson Ave., State University of New York Downstate Medical Center, Brooklyn, NY 11203, USA.
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23
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Siddiqi SA, Mansbach CM. PKC zeta-mediated phosphorylation controls budding of the pre-chylomicron transport vesicle. J Cell Sci 2008; 121:2327-38. [PMID: 18577579 DOI: 10.1242/jcs.022780] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dietary triacylglycerols are absorbed by enterocytes and packaged in the endoplasmic reticulum (ER) in the intestinal specific lipoprotein, the chylomicron, for export into mesenteric lymph. Chylomicrons exit the ER in an ER-to-Golgi transport vesicle, the pre-chylomicron transport vesicle (PCTV), which is the rate-limiting step in the transit of chylomicrons across the cell. Here, we focus on potential mechanisms of control of the PCTV-budding step from the intestinal ER. We incubated intestinal ER with intestinal cytosol and ATP to cause PCTV budding. The budding reaction was inhibited by 60 nM of the PKC inhibitor Gö 6983, suggesting the importance of PKCzeta in the generation of PCTV. Immunodepletion of PKCzeta from the cytosol and the use of washed ER greatly inhibited the generation of PCTVs, but was restored following the addition of recombinant PKCzeta. Intestinal ER incubated with intestinal cytosol and [gamma-(32)P]ATP under conditions supporting the generation of PCTVs showed the phosphorylation of a 9-kDa band following autoradiography. The phosphorylation of this protein correlated with the generation of PCTVs but not the formation of protein vesicles and was inhibited by depletion of PKCzeta. Phosphorylation of the 9-kDa protein was restored following the addition of recombinant PKCzeta. The association of the 9-kDa protein with proteins that are important for PCTV budding was phosphorylation dependent. We conclude that PKCzeta activity is required for PCTV budding from intestinal ER, and is associated with phosphorylation of a 9-kDa protein that might regulate PCTV budding.
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Affiliation(s)
- Shadab A Siddiqi
- The Division of Gastroenterology, The University of Tennessee Health Science Center, Memphis, TN 38163, USA
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Trevaskis NL, Charman WN, Porter CJ. Lipid-based delivery systems and intestinal lymphatic drug transport: a mechanistic update. Adv Drug Deliv Rev 2008; 60:702-16. [PMID: 18155316 PMCID: PMC7103284 DOI: 10.1016/j.addr.2007.09.007] [Citation(s) in RCA: 277] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2007] [Accepted: 09/30/2007] [Indexed: 12/11/2022]
Abstract
After oral administration, the majority of drug molecules are absorbed across the small intestine and enter the systemic circulation via the portal vein and the liver. For some highly lipophilic drugs (typically log P > 5, lipid solubility > 50 mg/g), however, association with lymph lipoproteins in the enterocyte leads to transport to the systemic circulation via the intestinal lymph. The attendant delivery benefits associated with lymphatic drug transport include a reduction in first-pass metabolism and lymphatic exposure to drug concentrations orders of magnitude higher than that attained in systemic blood. In the current review we briefly describe the mechanisms by which drug molecules access the lymph and the formulation strategies that may be utilised to enhance lymphatic drug transport. Specific focus is directed toward recent advances in understanding regarding the impact of lipid source (both endogenous and exogenous) and intracellular lipid trafficking pathways on lymphatic drug transport and enterocyte-based first-pass metabolism.
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Siddiqi SA, Siddiqi S, Mahan J, Peggs K, Gorelick FS, Mansbach CM. The identification of a novel endoplasmic reticulum to Golgi SNARE complex used by the prechylomicron transport vesicle. J Biol Chem 2006; 281:20974-20982. [PMID: 16735505 PMCID: PMC2833420 DOI: 10.1074/jbc.m601401200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dietary long chain fatty acids are absorbed in the intestine, esterified to triacylglycerol, and packaged in the unique lipoprotein of the intestine, the chylomicron. The rate-limiting step in the transit of chylomicrons through the enterocyte is the exit of chylomicrons from the endoplasmic reticulum in prechylomicron transport vesicles (PCTV) that transport chylomicrons to the cis-Golgi. Because chylomicrons are 250 nm in average diameter and lipid absorption is intermittent, we postulated that a unique SNARE pairing would be utilized to fuse PCTV with their target membrane, cis-Golgi. PCTV loaded with [(3)H]triacylglycerol were incubated with cis-Golgi and were separated from the Golgi by a sucrose step gradient. PCTV-chylomicrons acquire apolipoprotein-AI (apoAI) only after fusion with the Golgi. PCTV became isodense with Golgi upon incubation and were considered fused when their cargo chylomicrons acquired apoAI but docked when they did not. PCTV, docked with cis-Golgi, were solubilized in 2% Triton X-100, and proteins were immunoprecipitated using VAMP7 or rBet1 antibodies. In both cases, a 112-kDa complex was identified in nonboiled samples that dissociated upon boiling. The constituents of the complex were VAMP7, syntaxin 5, vti1a, and rBet1. Antibodies to each SNARE component significantly inhibited fusion of PCTV with cis-Golgi. Membrin, Sec22b, and Ykt6 were not found in the 112-kDa complex. We conclude that the PCTV-cis-Golgi SNARE complex is composed of VAMP7, syntaxin 5, Bet1, and vti1a.
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Affiliation(s)
- Shadab A Siddiqi
- Division of Gastroenterology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Shahzad Siddiqi
- Division of Gastroenterology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - James Mahan
- Veterans Affairs Medical Center, Memphis, Tennessee 38104
| | - Kiffany Peggs
- Division of Gastroenterology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Fred S Gorelick
- Department of Medicine, Veterans Affairs Healthcare, New Haven, Connecticut 06516; Yale University School of Medicine, New Haven, Connecticut 06516
| | - Charles M Mansbach
- Division of Gastroenterology, University of Tennessee Health Science Center, Memphis, Tennessee 38163; Veterans Affairs Medical Center, Memphis, Tennessee 38104.
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Concha MI, López R, Villanueva J, Báez N, Amthauer R. Undetectable apolipoprotein A-I gene expression suggests an unusual mechanism of dietary lipid mobilisation in the intestine of Cyprinus carpio. ACTA ACUST UNITED AC 2005; 208:1393-9. [PMID: 15781899 DOI: 10.1242/jeb.01512] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
High density lipoprotein (HDL) has been shown to play an important role in the dietary lipid mobilisation in the carp. In spite of this, previous studies have failed to demonstrate the synthesis of the major protein component of HDL, apolipoprotein A-I (apoA-I), in the proximal intestine of the carp. Therefore, the aim of the present study was to evaluate the expression of apoA-I throughout the entire intestine. Curiously, no transcription of the apoA-I gene could be detected either by northern blot or RT-PCR assays in the intestinal mucosa, in clear contrast with the abundant cytosolic immunoreactive apoA-I detected in almost all intestinal segments, which suggests a different origin for this protein. In addition, the detection of specific, but low affinity, binding sites for apoA-I in the carp intestinal brush-border membranes (BBM), and the strong interaction with BBM, which is highly dependent on temperature, points to an important contribution of membrane lipids in apoA-I binding to the intestinal mucosa. This idea was reinforced by the ability of carp apoA-I to associate with multilamellar phospholipid vesicles.
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Affiliation(s)
- Margarita I Concha
- Instituto de Bioquímica, Facultad de Ciencias, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile
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Abstract
PURPOSE OF REVIEW The assembly of intestinal lipoproteins is critical for the transport of fat and fat-soluble vitamins. In this review we propose a nomenclature for these lipoproteins and have summarized recent data about their intracellular assembly and factors that modulate their secretion. RECENT FINDINGS The assembly and secretion of intestinal lipoproteins increases with the augmented synthesis of apoB, apoAIV and lipids. Chylomicron assembly begins with the formation of primordial, phospholipid-rich particles in the membrane, and their conversion to large chylomicrons occurs in the lumen of the smooth endoplasmic reticulum. Chylomicrons are transported from the endoplasmic reticulum via specialized vesicles to the Golgi for secretion. The identification of genetic mutations in chylomicron retention disease indicates that Sar1b may play a critical role in this process. In addition to chylomicron assembly, intestinal cells have been shown to transport dietary cholesterol via apoB-independent pathways, such as efflux. SUMMARY Understanding the mechanisms involved in the intracellular transport of chylomicrons and chylomicron-independent secretion pathways are expected to be the next frontiers in the field of intestinal lipoprotein assembly and secretion.
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Affiliation(s)
- M Mahmood Hussain
- Department of Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York, USA.
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28
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Siddiqi SA, Gorelick FS, Mahan JT, Mansbach CM. COPII proteins are required for Golgi fusion but not for endoplasmic reticulum budding of the pre-chylomicron transport vesicle. J Cell Sci 2003; 116:415-27. [PMID: 12482926 DOI: 10.1242/jcs.00215] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The budding of vesicles from endoplasmic reticulum (ER) that contains nascent proteins is regulated by COPII proteins. The mechanisms that regulate lipid-carrying pre-chylomicron transport vesicles (PCTVs) budding from the ER are unknown. To study the dependence of PCTV-ER budding on COPII proteins we examined protein and PCTV budding by using ER prepared from rat small intestinal mucosal cells prelabeled with (3)H-oleate or (14)C-oleate and (3)H-leucine. Budded (3)H-oleate-containing PCTVs were separated by sucrose density centrifugation and were revealed by electron microscopy as 142-500 nm vesicles. Our results showed the following: (1) Proteinase K treatment did not degrade the PCTV cargo protein, apolipoprotein B-48, unless Triton X-100 was added. (2) PCTV budding was dependent on cytosol and ATP. (3) The COPII proteins Sar1, Sec24 and Sec13/31 and the membrane proteins syntaxin 5 and rBet1 were associated with PCTVs. (4) Isolated PCTVs were able to fuse with intestinal Golgi. (5) Antibodies to Sar1 completely inhibited protein vesicle budding but increased the generation of PCTV; these changes were reversed by the addition of recombinant Sar1. (6) PCTVs formed in the absence of Sar1 did not contain the COPII proteins Sar1, Sec24 or Sec31 and did not fuse with the Golgi complex. Together, these findings suggest that COPII proteins may not be required for the exit of membrane-bound chylomicrons from the ER but that they or other proteins may be necessary for PCTV fusion with the Golgi.
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Affiliation(s)
- Shadab A Siddiqi
- Division of Gastroenterology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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29
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Yao Y, Eshun JK, Lu S, Berschneider HM, Black DD. Regulation of triacylglycerol and phospholipid trafficking by fatty acids in newborn swine enterocytes. Am J Physiol Gastrointest Liver Physiol 2002; 282:G817-24. [PMID: 11960778 DOI: 10.1152/ajpgi.00397.2001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We (Wang H, Berschneider HM, Du J, and Black DD. Am J Physiol Gastrointest Liver Physiol 272: G935-G942, 1997; Wang H, Lu S, Du J, Yao Y, Berschneider HM, and Black DD. Am J Physiol Gastrointest Liver Physiol 280: G1137-G1144, 2001) previously showed that different fatty acids influence synthesis and secretion of triacylglycerol (TG) and phospholipid (PL) in a newborn swine enterocyte cell line (IPEC-1). The most striking effects were produced by stearic acid (SA; 18:0), which modestly affected TG and PL synthesis but reduced TG and PL secretion, and by eicosapentaenoic acid (EPA; 20:5), which reduced TG and PL synthesis and TG secretion relative to oleic acid (OA; 18:1). To define the mechanism of these effects, differentiated IPEC-1 cells were incubated for 24 h with OA, SA, or EPA and [(3)H]glycerol. Endoplasmic reticulum (ER) and Golgi (G) content of labeled lipids and apolipoprotein (apo) B and apoAI protein were measured. Relative to OA, SA did not impair ER TG synthesis, but reduced movement of labeled TG from ER to G. EPA impaired both ER TG synthesis and movement of labeled TG from ER to G. PL followed the same pattern, except ER synthesis of PL was relatively unaffected by EPA. Carbonate treatment demonstrated decreased partitioning of labeled lipid from ER membrane to lumen in EPA-treated cells. Organelle apoB and apoAI content demonstrated opposite patterns after SA and EPA incubation. We conclude that SA and EPA adversely influence immature enterocyte ER to G lipid trafficking, compared with OA. Furthermore, EPA inhibits ER lipid synthesis and transfer of membrane lipid to luminal particles. Regulation of apoAI ER to G trafficking is independent of that of apoB.
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Affiliation(s)
- Ying Yao
- Children's Foundation Research Center at Le Bonheur Children's Medical Center, University of Tennessee Health Science Center, Memphis, Tennessee 38103, USA
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Kendrick JS, Chan L, Higgins JA. Superior role of apolipoprotein B48 over apolipoprotein B100 in chylomicron assembly and fat absorption: an investigation of apobec-1 knock-out and wild-type mice. Biochem J 2001; 356:821-7. [PMID: 11389690 PMCID: PMC1221909 DOI: 10.1042/0264-6021:3560821] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Editing of apolipoprotein (apo)-B100 mRNA to yield apo-B48 is a specific and developmentally regulated step in enterocytes of mammals. However, the functional significance of this step is not known. Since mice containing only apo-B100 have not been documented to exhibit any difference in intestinal fat absorption from wild-type mice, the evolutionary advantage of apoB mRNA editing has been questioned. In the present study, we have compared fat absorption and chylomicron assembly in apobec-1 knock-out (KO) or wild-type (WT) mice subjected to different dietary manipulations: low-fat chow, a fat-enriched 'Western' diet and overnight fasting. Experiments in vivo and in vitro revealed differences in the ability of KO and WT enterocytes to assemble and secrete chylomicrons under different dietary conditions. After overnight fasting, chylomicron secretion is reduced considerably in KO compared with WT enterocytes. This is not due to reduced synthesis of apo-B or triacylglycerol (TAG), but appears to be a result of impaired assembly of chylomicrons, so that triacylglycerol accumulates in the enterocytes. After feeding with fat, secretion of chylomicrons enriched in pre-existing TAG is stimulated in KO compared with WT mice. In the present study, we have documented for the first time that apo-B100 is considerably less efficient than apo-B48 in exerting its role in the early stage of chylomicron assembly, which is rate-limiting under conditions of low dietary fat. However, this impairment is overcome by increased TAG stores that stimulate later stages in assembly, which are rate-limiting in the fat-fed state. apo-B mRNA editing may result in more efficient fat absorption, specifically under conditions of food shortage or low-fat content, and thus provide an evolutionary advantage.
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Affiliation(s)
- J S Kendrick
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK
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Abstract
The intestine synthesizes very low density lipoproteins (VLDL) and chylomicrons (CM) to transport fat and fat-soluble vitamins into the blood. VLDL assembly occurs constitutively whereas CM assembly is a characteristic property of the enterocytes during the postprandial state. The secretion of CM is specifically inhibited by Pluronic L81. CM are very heterogeneously-sized particles that consist of a core of triglycerides (TG) and cholesterol esters and a monolayer of phospholipids (PL), cholesterol and proteins. The fatty acid composition of TG, but not PL, in CM mirrors the fatty acid composition of fat in the diet. CM assembly is deficient in abetalipoproteinemia and CM retention disease. Abetalipoproteinemia results due to mutation in the mttp gene and is characterized by the virtual absence of apoB-containing lipoproteins in the plasma. Patients suffer from neurologic disorders, visual impairment, and exhibit acanthocytosis. CM retention disease, an inherited recessive disorder, is characterized by chronic diarrhea with steatorrhea in infancy, abdominal distention and failure to thrive. It is caused by a specific defect in the secretion of intestinal lipoproteins; secretion of lipoproteins by the liver is not affected. Besides human disorders, mice that do not assemble intestinal lipoproteins have been developed. These mice are normal at birth, but defective in fat and fat-soluble vitamin absorption, and fail to thrive. Thus, fat and fat-soluble vitamin transport by the intestinal lipoproteins is essential for proper growth and development of neonates. Recently, differentiated Caco-2 cells and rabbit primary enterocytes have been described that synthesize and secrete CM. These cells can be valuable in distinguishing between the two different models proposed for the assembly of CM. In the first model, the assembly of VLDL and CM is proposed to occur by two 'independent' pathways. Second, CM assembly is proposed to be a product of 'core expansion' that results in the synthesis of lipoproteins of different sizes. According to this model, intestinal lipoprotein assembly begins with the synthesis of 'primordial' lipoprotein particles and involves release of the nascent apoB with PL derived from the endoplasmic reticulum (ER) membrane. In addition, TG-rich 'lipid droplets' of different sizes are formed independent of apoB synthesis. The fusion of lipid droplets and primordial lipoproteins results in the formation of different size lipoproteins due to the 'core expansion' of the primordial lipoproteins.
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Affiliation(s)
- M M Hussain
- Department of Biochemistry, School of Medicine, MCP Hahnemann University, Philadelphia, PA 19129, USA.
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