Elevated miR-24 reduces cell viability and impairs β-cell function. A: Pre–miR-24 mimetics or pre-Neg at different concentrations (2, 10, or 50 nmol/L) were transfected into MIN6 cells for 48
h, when TaqMan qRT-PCR was carried out. Transfection caused an effective increase in miR-24 abundance in MIN6 cells. B: Overexpression of miR-24 for 48 h caused a decrease of cell viability in MIN6 cells, measured by the WST-1 assay. Transfection of 10 nmol/L miR-24 led to a decrease of cell number in the S phase (C) and to an increase in the G2 phase (D). The same results were detected with transfection of miR-24 at 50 nmol/L but not at 2 nmol/L, which was insufficient to induce cell cycle arrest. E and F: BrdU labeling was used to confirm the reduced DNA synthesis accompanying the elevation of miR-24. E: Representative images show BrdU and Hoechst stained cells, and at least 800 cells were counted. F: The BrdU labeling index is defined as the ratio of the number of BrdU+ nuclei to the total number of nuclei within the fields. G: Decreased cell proliferation was also detected in primary islets isolated from ICR mice. GSIS and KSIS assays were performed
on MIN6 cells overexpressing miR-24 for 48 h, and the GSIS index (H) and KSIS index (I) were calculated. The results were similar to those in palmitate-treated cells. **P < 0.01 vs. pre-Neg.