129 microRNA-183~96~182 CLUSTER PROMOTE BOVINE GRANULOSA CELL PROLIFERATION THROUGH COORDINATED REGULATION OF FOXO1

Abstract

Among other microRNA clusters, we previously showed that the miR-183~96~182 cluster (miR-183, miR-96, and miR-182) is abundantly expressed in bovine granulosa cells (bGC) of preovulatory dominant follicles obtained at the follicular phase of the bovine oestrous cycle. Moreover, this miRNA cluster are validated to coordinately target the Fork head O1 (FOXO1), a subfamily of transcription factors that regulate genes involved in cell proliferation, apoptosis, cell cycle arrest, and metabolism. However, the functional involvement of miR-183~96~182 cluster in bGC function by regulation of FOXO1 is not yet determined. Here, we aimed to investigate the function of miR-183~96~182 cluster in bGC using in vitro cell culture model. For this, bGC were aspirated from ovarian follicles (Ø 3–5 mm) obtained from local abattoir. Cells were plated in 24-well plate (2.5 × 10⁵ cells well^–1) in DMEM/F-12 (Sigma, Germany) supplemented with 10% FBS (GIBCO, Grand Island, NY) and 1% penicillin/streptomycin (GIBCO) and incubated at 37°C in 5% CO₂. Transfection of bGC with miRNA mimics, inhibitors, FOXO1-siRNA, and appropriate controls (Exiqon, Vedbæk, Denmark) was performed using Lipofectamine 2000 (Invitrogen, Carlsbad, CA, USA). Cell proliferation was determined using Cell Counting Kit-8 (CCK-8; Dojindo Molecular Technology, Kumamoto, Japan). Cell cycle distribution was determined with flow cytometric analysis. Total RNA was isolated using miRNeasy mini kit (Qiagen, Hilden, Germany), quantification of target gene was performed using qPCR, and data were analysed using ΔΔC_T method. Differences in the mean expression values between treatments were analysed with two-tailed Student’s t-test and statistical significance was defined at P ≤ 0.05. Results showed that a sponge effect was observed upon inhibition in individual miRNA of the cluster, which could be attributed to the partial sequence similarity among cluster members. Both FOXO1 mRNA and protein expression were significantly reduced upon transfection of bGC with miR-183~96~182 cluster mimics, while miR-183~96~182 cluster inhibition increased both FOXO1 mRNA and protein expression. Transfection of bGC with miR-183~96~182 mimics promoted cell proliferation, while inhibition tends to slow down proliferation. Furthermore, the proportion of bGC under G0/G1 arrest markedly declined (P < 0.05), while the S and G2/M phases increased in response to miR-183~96~182 mimicking. Selective knockdown of FOXO1 with FOXO1-siRNA significantly reduced FOXO1 mRNA and protein expression. Interestingly, knockdown of FOXO1 showed similar phenotypic effects such as that of miR-183~96~182 mimics transfection, which resulted in elevated bGC proliferation and reduction in the proportion of cells under G0/G1 arrest. In conclusion, overexpression of miR-183~96~182 cluster promote bGC proliferation and G0/G1 to S and G2/M cell cycle transition through coordinated regulation of genes in the FOXO1 signaling axis.