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Alpha-Tocopherol Reduces VLDL Secretion Through Modulation of the VLDL Transport Vesicle

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Date Issued:
2019
Abstract/Description:
The liver distributes serum triacylglycerol (TAG) via the very low-density lipoprotein (VLDL), and an increase in VLDL production may result in hyperlipidemia. VLDL synthesis consists of lipidation of Apolipoprotein B100 (ApoB) as it is co- translationally translocated across the endoplasmic reticulum (ER) membrane, and this nascent VLDL particle must undergo subsequent maturation and post-translational modification in the Golgi. The ER-to-Golgi trafficking of VLDL represents the rate-limiting step in VLDL secretion and is mediated by the VLDL Transport Vesicle (VTV). Many in vivo studies have indicated that vitamin E (alpha-tocopherol) supplementation protects against atherosclerosis and can reduce hepatic steatosis in nonalcoholic fatty liver disease (NAFLD), but its effects at the molecular level on hepatic lipid metabolism are poorly understood. To investigate the effects of alpha-tocopherol on hepatic VLDL secretion and cellular lipid retention, we performed several experiments in HepG2 (human) and McARH- 7777 (rat) hepatoma cell lines including pulse-chase experiments using 3H-oleic acid (3H- OA), confocal microscopy with BODIPY lipid droplet staining, and an in vitro VTV budding assay. Our results demonstrate a significant reduction of 3H-TAG secretion and ApoB media expression in response to 100 uM alpha-tocopherol, with a corresponding decrease in markers of VTV biogenesis in western blots of whole cell lysates (WCL) and retention of ApoB within the cell, indicating disruption of an early step in VLDL biogenesis. Further evidence indicates an increase in size and lipidation of the VTV and VLDL particle. BODIPY staining as well as 3H-TAG retention in WCLs was also sharply reduced. Overall, these results indicate that alpha-tocopherol reduces VLDL secretion, partially disrupts hepatic VLDL synthesis and VTV biogenesis, increases the lipidation of remaining VLDL particles, and diminishes overall cellular lipid droplet retention.
Title: Alpha-Tocopherol Reduces VLDL Secretion Through Modulation of the VLDL Transport Vesicle.
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Name(s): Clay, Ryan, Author
Siddiqi, Shadab, Committee Chair
Altomare, Deborah, Committee Member
Masternak, Michal, Committee Member
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2019
Publisher: University of Central Florida
Language(s): English
Abstract/Description: The liver distributes serum triacylglycerol (TAG) via the very low-density lipoprotein (VLDL), and an increase in VLDL production may result in hyperlipidemia. VLDL synthesis consists of lipidation of Apolipoprotein B100 (ApoB) as it is co- translationally translocated across the endoplasmic reticulum (ER) membrane, and this nascent VLDL particle must undergo subsequent maturation and post-translational modification in the Golgi. The ER-to-Golgi trafficking of VLDL represents the rate-limiting step in VLDL secretion and is mediated by the VLDL Transport Vesicle (VTV). Many in vivo studies have indicated that vitamin E (alpha-tocopherol) supplementation protects against atherosclerosis and can reduce hepatic steatosis in nonalcoholic fatty liver disease (NAFLD), but its effects at the molecular level on hepatic lipid metabolism are poorly understood. To investigate the effects of alpha-tocopherol on hepatic VLDL secretion and cellular lipid retention, we performed several experiments in HepG2 (human) and McARH- 7777 (rat) hepatoma cell lines including pulse-chase experiments using 3H-oleic acid (3H- OA), confocal microscopy with BODIPY lipid droplet staining, and an in vitro VTV budding assay. Our results demonstrate a significant reduction of 3H-TAG secretion and ApoB media expression in response to 100 uM alpha-tocopherol, with a corresponding decrease in markers of VTV biogenesis in western blots of whole cell lysates (WCL) and retention of ApoB within the cell, indicating disruption of an early step in VLDL biogenesis. Further evidence indicates an increase in size and lipidation of the VTV and VLDL particle. BODIPY staining as well as 3H-TAG retention in WCLs was also sharply reduced. Overall, these results indicate that alpha-tocopherol reduces VLDL secretion, partially disrupts hepatic VLDL synthesis and VTV biogenesis, increases the lipidation of remaining VLDL particles, and diminishes overall cellular lipid droplet retention.
Identifier: CFE0007617 (IID), ucf:52538 (fedora)
Note(s): 2019-08-01
M.S.
Medicine, Biomedical Sciences
Masters
This record was generated from author submitted information.
Subject(s): VLDL -- very low-density lipoprotein -- alpha-tocopherol -- vitamin E -- ApoB -- VLDL Transport Vesicle -- VTV -- nonalcoholic fatty liver disease -- NAFLD -- nonalcoholic steatohepatitis -- NASH -- lipid trafficking -- VLDL secretion -- lipid droplet -- steatosis -- lipid retention Sar1b -- SVIP
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0007617
Restrictions on Access: campus 2024-08-15
Host Institution: UCF

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