title: Fish oil and fenofibrate prevented phosphorylation-dependent hepatic sortilin 1 degradation in Western diet-fed mice.
abstract: Obesity and diabetes are associated with hepatic triglyceride overproduction and hypertriglyceridemia. Recent studies have found that the cellular trafficking receptor sortilin 1 (Sort1) inhibits hepatic apolipoprotein B secretion and reduces plasma lipid levels in mice, and its hepatic expression was negatively associated with plasma lipids in humans. This study investigated the regulation of hepatic Sort1 under diabetic conditions and by lipid-lowering fish oil and fenofibrate. Results showed that hepatic Sort1 protein, but not mRNA, was markedly lower in Western diet-fed mice. Knockdown of hepatic Sort1 increased plasma triglyceride in mice. Feeding mice a fish oil-enriched diet completely restored hepatic Sort1 levels in Western diet-fed mice. Fenofibrate also restored hepatic Sort1 protein levels in Western diet-fed wild type mice, but not in peroxisome proliferator-activated receptor α (PPARα) knock-out mice. PPARα ligands did not induce Sort1 in hepatocytes in vitro. Instead, fish oil and fenofibrate reduced circulating and hepatic fatty acids in mice, and n-3 polyunsaturated fatty acids prevented palmitate inhibition of Sort1 protein in HepG2 cells. LC/MS/MS analysis revealed that Sort1 phosphorylation at serine 793 was increased in obese mice and in palmitate-treated HepG2 cells. Mutations that abolished phosphorylation at Ser-793 increased Sort1 stability and prevented palmitate inhibition of Sort1 ubiquitination and degradation in HepG2 cells. In summary, therapeutic strategies that prevent posttranslational hepatic Sort1 down-regulation in obesity and diabetes may be beneficial in improving dyslipidemia.
authors.affiliation: From the Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160.
authors.forename: Jibiao
authors.initials: J
authors.lastname: Li
authors.affiliation: From the Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160.
authors.forename: Lipeng
authors.initials: L
authors.lastname: Bi
authors.affiliation: From the Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160.
authors.forename: Michelle
authors.initials: M
authors.lastname: Hulke
authors.affiliation: From the Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160 tli@kumc.edu.
authors.forename: Tiangang
authors.initials: T
authors.lastname: Li
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism / Q000628:therapy; D066273:Diet, Western / Q000009:adverse effects*; D011345:Fenofibrate / Q000008:administration & dosage*; D005395:Fish Oils / Q000008:administration & dosage*; D055785:Gene Knockdown Techniques; D056945:Hep G2 Cells; D006801:Humans; D000960:Hypolipidemic Agents / Q000008:administration & dosage; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008820:Mice, Obese; D009765:Obesity / Q000235:genetics / Q000378:metabolism / Q000628:therapy; D047493:PPAR alpha / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D055550:Protein Stability; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D000099183:Sortilin
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D011345:Fenofibrate; D005395:Fish Oils; D000960:Hypolipidemic Agents; D047493:PPAR alpha; D012333:RNA, Messenger; D012694:Serine; D000099183:Sortilin
keywords: ApoB; Cholesterol; Diabetes; Fish Oil; Lipid Metabolism; Peroxisome Proliferator-activated Receptor (PPAR); Triglyceride