Expression of microRNA during bovine adipogenesis

Studies have recently indicated that the adipogenic process and the expression of genes involved in lipid metabolism may be regulated in part at the post-transcriptional level by a class of small RNA called microRNA (miRNA). The objectives of this study were to i) determine if miRNAs are differentially expressed, and ii) evaluate expression of known miRNA targets in bovine adipocytes. Bovine adipose samples were collected from castrated males fattened on a high concentrate diet (C) or pasture (PA) and were frozen in liquid nitrogen and stored at -80°C, or used to generate primary stromal-vascular cells (SV). SV cells were cultured to confluence (Control) or differentiated at confluence and harvested 2 (D2), 6 (D6), or 12 (D12) days post-confluence. A 3x3 microarray analysis was performed comparing Control and differentiated samples. miR-21, -221, and -222 (P less than 0.05) were differentially expressed. qRT-PCR was conducted using the in vitro samples, and all three miRNAs were down regulated on D2 (P less than 0.05). miR-221 and -222 were decreased on D6 compared to Control (P less than 0.05), but only miR-222 expression was decreased at D12 (P less than 0.05) compared to Control. miR-21 increased in expression compared to Control on D12 (P less than 0.05). In vivo, only miR-21 expression was affected and it was reduced in PA compared to C fat samples (P less than 0.05). Two targets of miR-21 are Programmed Cell Death Protein 4 (PDCD4) and Phosphatase and Tensin Homolog (PTEN), and neither messenger RNA was differentially expressed in vitro (P greater than 0.05), but both messenger RNAs were elevated for PA compared to C (P less than 0.05). These data show that miRNAs are differentially expressed in adipose cells and tissue, and that miR-21 may be involved in adipocyte function by regulating the translation of PDCD4 and PTEN