Abstract
Objectives
This study was designed to investigate whether unconventional prefoldin RPB5 interactor (URI)-1 mediates hepatic accumulation of triglyceride (TG) in response to a diet with trans-10,cis-12 conjugated linoleic acid (t10,c12 CLA) in lean or genetically obese mice. URI-1 belongs to the prefoldin family of proteins that have been shown to coordinate nutrient availablility by transcriptional regulation of genes involved in glucose and lipid metabolism. Thus, it was hypothesized that URI-1 in liver is involved in increased fatty acid uptake and accumulation leading to fatty liver.
Methods
C57BL/6 and db/db mice were randomly assigned to two diet groups, control (CTL) and t10,c12 CLA (0.4% w/w). After 4 weeks, the mice were weighed and euthanized. Livers were dissected, weighed and stored at –80°C. Liver lysates were prepared from the tissue for Western blotting to measure hepatic protein levels of URI-1 and FABP1. The amount of lipid in the livers was determined using the LabAssay™ Triglyceride kit, a colorimetric TG assay.
Results
The liver to body weight ratio of db/db and C57BL/6 mice fed t10,c12 CLA increased by 90% and 52%, respectively, compared to their counterparts fed the CTL diet. Likewise, the hepatic TG concentration (mg TG/mg protein) was increased 38% and 5-fold, respectively, in CLA-fed db/db and C57BL/6 mice compared to CTL db/db and C57BL/6 mice. Western blotting showed that FABP1 levels were approximately 2-fold greater in the db/db t10,c12 CLA group relative to the db/db CTL group, and may contribute to increased fatty acid uptake. Furthermore, URI-1 protein levels were elevated 4-fold in db/db and C57BL6 mice fed t10,c12 CLA compared to their respective CTL groups. Lastly, correlation analysis revealed that URI-1 levels were significantly correlated with hepatic TG concentrations (r = 0.61) and liver/body weight ratio (r = 0.64).
Conclusions
This study revealed a relationship between hepatic TG accumulation and URI-1, a protein associated with hepatocellular carcinoma (HCC) and cirrhosis. This study provides a basis for in vitro experiments exploring the causative role of URI-1 in propagating hepatic TG accumulation, and ultimately the progression of fatty liver disease to HCC and cirrhosis.
Funding Sources
University Collaborative Research Project, NSERC Discovery, and University of Manitoba Graduate Enhancement of Tri-Council Stipends.
FATTY ACID UPTAKE BY THE BRAIN. V. INCORPORATION OF LINOLENIC ACID 1- $sup 14$C INTO ADULT RAT BRAIN