Poster Sessions

PHARM -9

Jessica Bonzo

J. A. Bonzo, Y. Shah, F. J. Gonzalez

A microRNA-mediated mechanism of lipid homeostasis by PPAR-alpha

The peroxisome proliferator activated receptors (PPARs) play key roles in the management of lipid homeostasis. Clinically, activators of PPAR-alpha known as fibrates are used in the treatment of dyslipidemia to lower plasma triglyceride levels and increase HDL-cholesterol. A previous study identified a panel of 27 microRNAs (miRNAs) that were significantly regulated in mouse liver following treatment with the PPAR-alpha agonist Wy-14643. Mir-103 and mir-107 expression levels were upregulated 2.00 and 2.25 fold, respectively, in this study. A recent review suggested a role for mir-103 and mir-107 in complementation to the direct effects of ligand-activated PPAR-alpha by affecting translation of genes involved in fatty acid synthesis and storage. Mir-103 and mir-107 sequences differ by a single nucleotide, thus, to more accurately quantitate miRNA expression levels, the Taqman miRNA assay was used. Mir-103 was induced 1.7 fold and mir-107 was induced 4.5 fold suggesting that mir-107 is the principle contributor to the induction previously observed in microarray and Northern blot analysis. Time course analysis revealed that mir-107 expression achieved significance after 3 days of Wy-14643 treatment while mir-103 was not induced until 5 days of treatment. This correlates with the induction pattern of the genes within which they are encoded. Mir-103 and mir-107 are encoded within the Pank3 and Pank1 genes, respectively. Pank1 mRNA is induced 2.5 fold within 24 hr treatment, reaching a 6-fold induction after two weeks of treatment. Pank3 mRNA does not reach a 2-fold induction until 5 days of Wy-14643 treatment. A PPAR-alpha binding site was identified within the Pank1 promoter by ChIP-on-Chip analysis and confirmed by direct ChIP and luciferase assay. In silico databases predict that mir-103 and mir-107 will target specific mRNAs involve in lipid and pyruvate metabolism. To assess the functional impact of increased expression of these miRNAs, isolated primary hepatocytes from wild type mice were transfected with pre-mir-103 or pre-mir-107 to increase expression of the mature miRNA. Microarray analysis revealed the regulation of many genes involved in the transport, synthesis, and storage of lipids. The maintenance of lipid homeostasis through PPAR-alpha mediated miRNAs has the potential to explain species-specific responses to fibrate treatments as well as provide additional pharmacological targets for the treatment of dyslipidemia disorders.