3T3-L1脂肪细胞对MIN6胰岛素细胞中Kir6.2表达的抑制作用

3T3-L1 adipocytes reduces Kir6.2 channel expression in MIN6 insulin secreting cells in vitro

为明确脂肪细胞对胰岛素细胞中KATP通道表达的直接影响,MIN6胰岛素细胞被分为两组:一组为对照组,一组与分化的3T3-L1脂肪细胞共培养1周。运用半定量RT-PCR方法测定MIN6细胞中Katp通道蛋白Kir6.2的表达变化,Fura-2荧光方法测定MIN6细胞内钙浓度的变化,放射免疫测定方法明确MIN6细胞的胰岛素分泌功能。结果显示,与3T3-L1脂肪细胞共培养1周后,MIN6细胞中Kir6.2的表达明显减少,其表达水平降低为对照组的65.3%。对照组MIN6细胞在0.1 mmol/L甲苯磺丁脲(KATP通道关闭剂)的刺激下,表现为细胞内钙水平显著性升高和胰岛素分泌显著性增加,而共培养组MIN6细胞则失去了甲苯磺丁脲刺激所引起的细胞内钙升高及胰岛素分泌反应。以上实验结果表明,3T3-L1脂肪细胞可以通过分泌一些活性因子直接降低MIN6细胞中KATP通道蛋白的表达和合成,损害MIN6细胞的胰岛素分泌功能。实验结果提示脂肪细胞直接参与2型糖尿病中胰岛β细胞功能障碍的发生。

Dysfunction of the pancreatic β-cell is an important defect in the pathophysiological changes of type 2 diabetes, and type 2 diabetes is evidently associated with obesity. But the role of the adipocyte in the dysfunction of the pancreatic β-cell remains unknown. In the present study, we examined the direct effects of 3T3-L1 adipocytes on the expression of ATP-sensitive potassium channels (KATP channels) in MIN6 insulin-secreting cells. MIN6 cells were divided into two groups as control group, where MIN6 cells were cultured in normal culture medium, and coculture group, where MIN6 cells were cocultured with differentiated 3T3-L1 adipocytes for 1 week. Semi quantitative RT-PCR was employed to measure the expression of KAIP channel subunit Kir6.2 in MIN6 cells. Fura-2 was used to reflect changes in intracellular calcium concentration ([Ca2+]i) in MIN6 cells. The secretary function of MIN6 cells from both groups was estimated by radioimmunoassay method. The results showed that the Kir6.2 cDNA levels corrected by GAPDH cDNA levels after densitometric analysis were 0.989 ±0.035 in control group and 0.726±0.087 in coculture group. The expression of Kir6.2 was significantly decreased in MIN6 cells in the coculture group as compared with that in control. MIN6 cells cocultured with 3T3-L1 adipocytes lost the ability to increase [Ca2+]i when stimulated by tolbutamide (0.1 mmol/L), a highly selective KATP channel closer. In contrast, MIN6 cells in control group had typical responses to tolbutamide with a significant increase in [Ca2+]i. The magnitudes to basal levels of [Ca2+]i after tolbutamide stimulation were 1.520+0.203 in control and 1.114±0.097 in coculture group (P<0.05, n=6). MIN6 cells in control showed a significant increase in insulin secretion from 0.38±0.099 mU/min to 2.87±0.248 mU/min after being stimulated by tolbutamide, whereas MIN6 cells in coculture group did not increase insulin secretion when stimulated by tolbutamide (0.21±0.055 mU/min to 0.22±0.082 mU/min). It is demonstrated that 3T3-L1 adipocytes decrease the expression of KATP channels in MIN6 cells through secreting certain factors, which impair the secretary function of MIN6 cells. The present results indicate that adipocytes are directly involved in pancreatic β-cell dysfunction, which may facilitate the development of type 2 diabetes.