Regulation of plasma LDL and HDL by microRNA-541-3p

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High LDL and low HDL levels are risk factors for cardiovascular disease. Our long-term goal is to identify and explain mechanisms through which microRNAs (miRs) regulate plasma lipoprotein levels. Here, we report the identification of a novel miR-541-3p that decreases ApoB secretion and increases ApoA1 secretion in human hepatoma cells. Furthermore, we show that miR-541-3p regulates the zinc finger (Znf) transcription factors (TFs) zinc finger 101 (Znf101) and castor zinc finger protein 1 (Casz1), thereby modulating the expression of ApoB and ApoA1, respectively. On the basis of these novel findings, the following aims focus on elucidating how miR- 541-3p regulates the expression of these TFs, and how these TFs regulate ApoB and ApoA1 expression. Furthermore, we plan to establish the roles of these TFs in the control of plasma lipoproteins and atherosclerosis. Aim 1. Establish that miR-541-3p enhances post-transcriptional degradation of Znf101 and Casz1 mRNA by interacting with 3´-untranslated region (UTR) sequences. We propose to establish that RNA-RNA interactions between miR-541-3p and Znf101/Casz1 mRNAs are necessary for the regulation of mRNA levels and show that miR-541-3p interacts with target sequences in the 3´-UTR, thereby enhancing mRNA degradation. Aim 2. Explain the mechanism of regulation of ApoB and ApoA1 expression by Znf101 and Casz1 in human and mouse liver cells. We plan to elucidate how Znf101 and Casz1 regulate transcription of the APOB and APOA1 genes. We propose to show that Znf101 is an enhancer of APOB gene transcription, and Casz1 is a repressor of APOA1 gene transcription. Furthermore, we plan to clarify the roles of mouse orthologs of these TFs in the transcriptional regulation of mouse Apob and Apoa1 genes. These studies should reveal the molecular underpinnings of the regulation of ApoB and ApoA1 by miR-541-3p. Aim 3. Elucidate the roles of Zfp961 (mouse ortholog of human Znf101) and Casz1 in the regulation of plasma LDL, HDL, and atherosclerosis in mice. In these in vivo studies, we will investigate the physiological roles of ApoB and ApoA1 regulation by the TFs identified and characterized in the earlier aims. We will interrogate whether regulation of ApoB and ApoA1 by these TFs decreases LDL levels, increases HDL levels, and diminishes atherosclerosis. These studies should demonstrate that transcriptional regulation of ApoB and ApoA1 leads to an anti-atherogenic profile in mice. This proposal is based on our discovery of a novel miR-541-3p that regulates the expression of ApoB and ApoA1 in opposite directions through two newly identified TFs. After completion of the proposed studies, we expect to: (1) elucidate how miR-541-3p regulates various TFs; (2) explain the molecular mechanisms through which these TFs regulate APOB and APOA1 transcription; and (3) establish the physiological importance of the identified molecules and mechanisms in the regulation of plasma lipoproteins and atherosclerosis. These genes and mechanisms may serve as new therapeutic targets to prevent and treat cardiovascular disease.