Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Apr 1;312(4):E244-E252.
doi: 10.1152/ajpendo.00396.2016. Epub 2017 Jan 17.

Mice With Hyperbilirubinemia Due to Gilbert's Syndrome Polymorphism Are Resistant to Hepatic Steatosis by Decreased Serine 73 Phosphorylation of PPARα

Affiliations
Free PMC article

Mice With Hyperbilirubinemia Due to Gilbert's Syndrome Polymorphism Are Resistant to Hepatic Steatosis by Decreased Serine 73 Phosphorylation of PPARα

Terry D Hinds Jr et al. Am J Physiol Endocrinol Metab. .
Free PMC article

Abstract

Gilbert's syndrome in humans is derived from a polymorphism (TA repeat) in the hepatic UGT1A1 gene that results in decreased conjugation and increased levels of unconjugated bilirubin. Recently, we have shown that bilirubin binds directly to the fat-burning nuclear peroxisome proliferator-activated receptor-α (PPARα). Additionally, we have shown that serine 73 phosphorylation [Ser(P)73] of PPARα decreases activity by reducing its protein levels and transcriptional activity. The aim of this study was to determine whether humanized mice with the Gilbert's polymorphism (HuUGT*28) have increased PPARα activation and reduced hepatic fat accumulation. To determine whether humanized mice with Gilbert's mutation (HuUGT*28) have reduced hepatic lipids, we placed them and C57BL/6J control mice on a high-fat (60%) diet for 36 wk. Body weights, fat and lean mass, and fasting blood glucose and insulin levels were measured every 6 wk throughout the investigation. At the end of the study, hepatic lipid content was measured and PPARα regulated genes as well as immunostaining of Ser(P)73 PPARα from liver sections. The HuUGT*28 mice had increased serum bilirubin, lean body mass, decreased fat mass, and hepatic lipid content as well as lower serum glucose and insulin levels. Also, the HuUGT*28 mice had reduced Ser(P)73 PPARα immunostaining in livers and increased PPARα transcriptional activity compared with controls. A chronic but mild endogenous increase in unconjugated hyperbiliubinemia protects against hepatic steatosis through a reduction in Ser(P)73 PPARα, causing an increase in PPARα transcriptional activity.

Keywords: Gilbert’s syndrome; bilirubin; fatty liver; nonalcoholic fatty liver disease; peroxisome proliferator-activated receptor-α.

Figures

Fig. 1.
Fig. 1.
Body weight, body fat, and serum bilirubin levels in HuUGT*28 and control C57 mice fed a high-fat diet. A: weekly body weight over the study. B: plasma total, conjugated, and unconjugated bilirubin levels in 30-wk-old mice. C: fat mass as measured directly at the end of the experimental protocol. D: body fat as determined by noninvasive echoMRI. E: lean mass as determined by noninvasive echoMRI. *P < 0.05 vs. control C57 mice (means ± SE; n = 4–5/group).
Fig. 2.
Fig. 2.
Food intake and indices of metabolism in HuUGT*28 and control C57 mice fed a high-fat diet. A: food intake. B: oxygen consumption (V̇o2) normalized to lean body mass. C: CO2 production (V̇co2) normalized to lean body mass. D: heat production. E: motor activity.
Fig. 3.
Fig. 3.
HuUGT*28 mice are protected against high-fat diet-induced hepatic steatosis. A: hematoxylin and eosin staining of liver sections (scale bar, 50 μm). B and C: biochemical measurements of hepatic total cholesterol and alanine aminotransferase (ALT; B) as well as albumin (ALB; C). D: Oil Red O staining of liver sections and densitometry (scale bar, 20 μm) and hepatic triglyceride levels. E: real-time PCR measurement of hepatic fatty acid synthase (FAS), sterol regulatory element-binding protein-1 (SREBP1), acetyl-CoA carboxylase (ACC), and peroxisome proliferator-activated receptor-γ2 (PPARγ2). *P < 0.05 vs. control C57 mice; (means ± SE; n = 4–5/group).
Fig. 4.
Fig. 4.
PPARα levels and target gene expression are increased in HuUGT*28 mice. A: Western blot and densitometry of hepatic protein levels of PPARα. B: immunostaining of total and serine 73 phosphorylation PPARα (pS73) in the liver. C: real-time PCR measurement of hepatic expression of fibroblast growth factor 21 (FGF21), cytochrome 450 4A10 (CYP4A10), cytochrome 450 4A12 (CYP4A12), and cytochrome 450 4A14 (CYP4A14). *P < 0.05 vs. control C57 mice (means ± SE; n = 4–5/group). WT, wild type; DRAQ5, deep red anthraquinone 5.
Fig. 5.
Fig. 5.
HuUGT*28 mice are protected against high-fat diet-induced hyperglycemia, hyperinsulinemia, and insulin resistance. A: fasting blood glucose measured at 6-wk intervals starting from week 18 on high-fat diet. B: fasting insulin measured at 6-wk intervals starting from week 18 on high-fat diet. C: intraperitoneal glucose tolerance test (GTT) measured in week 28 of the high-fat diet [area under the curve (AUC)]. *P < 0.05 vs. control C57 mice (means ± SE; n = 4–5/group).

Similar articles

See all similar articles

Cited by 19 articles

See all "Cited by" articles

Publication types

Feedback