Hyperglycemia In Vitro Up-Regulates Growth-Related Cell Cycle Proteins of Adult Mouse Pancreatic Islets

To study effects of glucose on growth-related proteins of adult islets, we cultured mice islets in medium containing either 5.5 mmol/L (LG) or 20 mmol/L (HG) glucose. Total islet proteins were processed for sodium dodecyl sulfate polyacrylamide gel and Western blotting using antibodies against β-actin (housekeeping), p27kip1 (G1/G0 checkpoint), cyclin D1 (G1/S), cyclin B1 (G2/M), and FoxM1. At day 1, protein levels p27, B1, D1, and FoxM1 of islets on LG and HG were 0.48- and 0.63-fold; 7.09- and 11.58-fold; 1.25- and 1.38-fold; and 1.75- and 1.75-folds, the value of day 0, determinations respectively. At day 3, the proteins of p27, B1, D1, and FoxM1 of islets in LG and HG were 0.84- and 0.84-fold; 3.08- and 17.17-fold; 1.41- and 1.54-fold; and 0.83- and 1.17-fold of those on day 0, respectively. On day 7 the values were 1.19- and 1.09-fold; 3.15- and 14.81-fold; 0.86- and 1.44-fold; and 2.75- and 3.42-fold that of day 0, respectively. At day 1, the ratios of protein in islets after HG verse LG were 1.25, 2.38, 0.94, and 1.00 for p27, B1, D1, and FoxM1, respectively. At days 3 and 7, the protein ratios of HG/LG were 0.81 and 0.82, 5.47 and 2.64, 0.81 and 1.51, and 1.11 and 1.24 for p27, B1, D1, and FoxM1, respectively. In conclusion, adult mouse islets rapidly respond to cultivation by reducing p27 and increasing B1; HG attenuates p27 elevation but enhances B1 and D1 elevations, which favor islet entry into the cell cycle.