title: Very Low Density Lipoprotein Assembly Is Required for cAMP-responsive Element-binding Protein H Processing and Hepatic Apolipoprotein A-IV Expression.
abstract: Hepatic apolipoprotein A-IV (apoA-IV) expression is correlated with hepatic triglyceride (TG) content in mouse models of chronic hepatosteatosis, and steatosis-induced hepatic apoA-IV gene expression is regulated by nuclear transcription factor cAMP-responsive element-binding protein H (CREBH) processing. To define what aspects of TG homeostasis regulate hepatic CREBH processing and apoA-IV gene expression, several mouse models of attenuated VLDL particle assembly were subjected to acute hepatosteatosis induced by an overnight fast or short term ketogenic diet feeding. Compared with chow-fed C57BL/6 mice, fasted or ketogenic diet-fed mice displayed increased hepatic TG content, which was highly correlated (r2= 0.95) with apoA-IV gene expression, and secretion of larger, TG-enriched VLDL, despite a lower rate of TG secretion and a similar or reduced rate of apoB100 secretion. When VLDL particle assembly and secretion was inhibited by hepatic shRNA-induced apoB silencing or genetic or pharmacologic reduction in microsomal triglyceride transfer protein (MTP) activity, hepatic TG content increased dramatically; however, CREBH processing and apoA-IV gene expression were attenuated compared with controls. Adenovirus-mediated reconstitution of MTP expression proportionately restored CREBH processing and apoA-IV expression in liver-specific MTP knock-out mice. These results reveal that hepatic TG content, per se, does not regulate CREBH processing. Instead, TG mobilization into the endoplasmic reticulum for nascent VLDL particle assembly activates CREBH processing and enhances apoA-IV gene expression in the setting of acute steatosis. We conclude that VLDL assembly and CREBH activation play key roles in the response to hepatic steatosis by up-regulating apoA-IV and promoting assembly and secretion of larger, more TG-enriched VLDL particles.
authors.affiliation: From the Departments of Internal Medicine-Section on Molecular Medicine.
authors.forename: Dongmei
authors.initials: D
authors.lastname: Cheng
authors.affiliation: the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, New York 10065.
authors.forename: Xu
authors.initials: X
authors.lastname: Xu
authors.affiliation: Internal Medicine-Section on Gastroenterology.
authors.forename: Trang
authors.initials: T
authors.lastname: Simon
authors.affiliation: From the Departments of Internal Medicine-Section on Molecular Medicine.
authors.forename: Elena
authors.initials: E
authors.lastname: Boudyguina
authors.affiliation: Cancer Biology, and.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Deng
authors.affiliation: From the Departments of Internal Medicine-Section on Molecular Medicine.
authors.forename: Melissa
authors.initials: M
authors.lastname: VerHague
authors.affiliation: the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, New York 10065.
authors.forename: Ann-Hwee
authors.initials: AH
authors.lastname: Lee
authors.affiliation: From the Departments of Internal Medicine-Section on Molecular Medicine.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Shelness
authors.affiliation: Internal Medicine-Section on Gastroenterology.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Weinberg
authors.affiliation: From the Departments of Internal Medicine-Section on Molecular Medicine, jparks@wakehealth.edu.|Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157 and.
authors.forename: John S
authors.initials: JS
authors.lastname: Parks
mesh_terms: D000208:Acute Disease; D000818:Animals; D001054:Apolipoproteins A / Q000235:genetics* / Q000378:metabolism; D001055:Apolipoproteins B / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D005234:Fatty Liver / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005786:Gene Expression Regulation; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D014280:Triglycerides / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D001054:Apolipoproteins A; D001055:Apolipoproteins B; D002352:Carrier Proteins; C500051:Creb3l3 protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D008079:Lipoproteins, VLDL; D014280:Triglycerides; C022205:apolipoprotein A-IV; C106092:microsomal triglyceride transfer protein; C030106:very low density lipoprotein triglyceride; D000242:Cyclic AMP
keywords: apolipoprotein; cAMP response element-binding protein (CREB); hepatosteatosis; lipoprotein; lipoprotein secretion; liver; microsomal triglyceride transfer protein; secretion; very low density lipoproteins