Roles for miRNA-378/378* in adipocyte gene expression and lipogenesis

Abstract

In this study, we explored the roles of microRNAs in adipocyte differentiation and metabolism. We first knocked down Argonaute2 (Ago2), a key enzyme in the processing of micro-RNAs (miRNAs), to investigate a potential role for miRNAs in adipocyte differentiation and/or metabolism. Although we did not observe dramatic differences in adipogenesis between Ago2 knock-down and control 3T3-L1 cells, incorporation of [(14)C]glucose or acetate into triacylglycerol, and steady-state levels of triacyglycerol were all reduced, suggesting a role for miRNAs in adipocyte metabolism. To study roles of specific miRNAs in adipocyte biology, we screened for miRNAs that are differentially expressed between preadipocytes and adipocytes for the 3T3-L1 and ST2 cell lines. Distinct subsets of miRNAs decline or increase during adipocyte conversion, whereas most miRNAs are not regulated. One locus encoding two miRNAs, 378/378*, contained within the intron of PGC-1beta is highly induced during adipogenesis. When overexpressed in ST2 mesenchymal precursor cells, miRNA378/378* increases the size of lipid droplets and incorporation of [(14)C]acetate into triacylglycerol. Although protein and mRNA expression levels of C/EBPalpha, C/EBPbeta, C/EBPdelta, and PPARgamma1 are unchanged, microarray and quantitative RT-PCR analyses indicate that a set of lipogenic genes are upregulated, perhaps due to increased expression of PPARgamma2. Knock-down of miRNA378 and/or miRNA378* decreases accumulation of triacylglycerol. Interestingly, we made the unexpected finding that miRNA378/378* specifically increases transcriptional activity of C/EBPalpha and C/EBPbeta on adipocyte gene promoters.

Control of mitochondrial metabolism and systemic energy homeostasis by microRNAs 378 and 378*

“…We found that mice lacking miR-378 and miR-378* are protected against diet-induced obesity. Previous studies have identified numerous metabolic regulatory proteins as targets for repression by miR-378 and miR-378* (10,(26)(27)(28). In addition, we found that carnitine O-acetyltransferase (CRAT), a mitochondrial enzyme involved in fatty acid metabolism (29,30), and MED13 are repressed by miR-378 and miR-378*, respectively.…”

“…In addition, we noted a reduction of adipocyte size in mice lacking miR-378/378*, raising the possibility that these miRNAs are required for efficient hypertrophy and lipid uptake in white adipocytes. In this regard, overexpression of miR-378/378* in mesenchymal precursor cells has been shown to increase lipogenesis (26). The modulation of fatty acid metabolism by miR-378/378* is crucial not only in the context of adipogenesis, but also in the maintenance of cardiac function, given that the adult heart depends primarily on fatty acids as an energy source (47).…”

MicroRNAs in farm animals

“…Jin et al compared the expression of 89 bovine miRNAs in adipose tissues between three crossbreeds differing in backfat thickness, and found that 42 miRNAs were differentially expressed, of which miR-378 was most differentiated (Jin et al, 2010). miR-378 has been shown to play a role in lipogenesis in mice (Gerin et al, 2010). Thus, miR-378 might participate in the control of subcutaneous growth in cattle.…”

Inauhzin(c) Inactivates c-Myc Independently of p53

“…As shown in Figure 4B, the induction of miR-24 and miR-34a by INZ(c) was abrogated by Ago2 knockdown, which is consistent with literature showing that knocking down RISC complex could affect the level of mature miRNAs. 31,32 Interestingly, Ago2 knockdown impaired the targeting of c-Myc by INZ(c) as shown in Figure 4C, suggesting INZ(c) regulates c-Myc expression via the miRNA pathway.…”