PPAR-DELTA: EXPRESSION PATTERN AND ITS ROLE IN THE PATHOGENESIS OF HIGH FAT DIET INDUCED NON ALCOHOLIC FATTY LIVER DISEASE

Abstract

Background: PPAR-δ has an important role in the regulation of fatty acid burning capacities of skeletal muscle and adipose tissue. The aim of our study was to define the role of PPAR δin the pathogenesis of high fat diet induced nonalcoholic fatty liver disease mouse model.

Materials and Methods: Sixteen C57BL/J6 mice were divided into 2 groups; Gr. I mice fed control diet for 8 weeks, Gr. II mice fed high fat diet for 8 weeks. Liver sections were stained with hematoxylin and eosin (H&E) and were scored for steatosis and necroinflammation by a liver pathologist. Protein expression of p-AKT, p-GSK 3β, p-PTEN, and PPAR-α,-γ,-δ were quantified after immunoprecipitation. mRNA expression of Long chain acyl-CoAdehydrogenase(LCAD), uncoupling protein 3(UCP3), carnitinepalmitoyl transferase (CPT) I, and PPAR-α,-γ,-δ were quantified by Real Time RT-PCR. Protein-DNA interaction was analyzed using electrophoretic mobility shift assay (EMSA) with DNA probe of peroxisome proliferator response element (PPRE) and nuclear extract. The terminal transferase dUTP end-labeling(TUNEL) assay was used to detect apoptosis.

Results: Gr. II mice gave rise to diffuse microvesicular steatosis, portalinflammation, and mild fibrotic stage compared to Gr. I. In Gr.II PPAR-α protein expression was not different, but PPAR-γ protein expression was elevated compared with Gr. I. mRNA expression of PPAR-α and –γ were reduced in Gr. II compared with Gr.I(p=0.002, p=0.000). PPAR-δ, important regulator of fatty acid burning, protein expression and mRNA were decreased in Gr. II compared with Gr.I(p=0.040, p=0.022). mRNA expression of GLUT4, CPT, LCAD, UCP3, PTEN in Gr. II was 130%, 157%, 80%, 65%, 100% out of Gr. I, respectively. Protein expression of p-GSK 3β was significantly elevated in Gr. II. EMSA revealed reduced PPRE-nuclear protein interaction in Gr. II. In TUNEL assay, there were no evidences of apoptosis in all groups.

Conclusion: Reduced expression of PPAR-δ protein and mRNA and reduced nuclear interaction with PPRE are important factors for the development of nonalcoholic fatty liver disease.