University of Waterloo, Kitchener, ON, Canada.
Diabetologia. 2011 Jan;54(1):135-45. doi: 10.1007/s00125-010-1923-5. Epub 2010 Oct 15.
AIMS/HYPOTHESIS: We have previously described a strong correlation between pyruvate cycling and insulin secretion. We have also demonstrated a particularly important role for a pyruvate-isocitrate cycling pathway involving the mitochondrial citrate/isocitrate carrier (CIC) and cytosolic NADP-dependent isocitrate dehydrogenase. CIC requires cytosolic malate as a counter-substrate during citrate and isocitrate export. Thus, considering that the mitochondrial dicarboxylate carrier (DIC) provides an important source of cytosolic malate, we investigated the potential role of DIC in control of glucose-stimulated insulin secretion (GSIS).
We used pharmacological and small interfering RNA (siRNA) tools to assess the role of DIC in insulin release in clonal insulin-secreting 832/13 cells and isolated rat islets.
Butylmalonate, an inhibitor of malate transport, reduced cytosolic malate and citrate levels, and inhibited GSIS in a dose-dependent manner in 832/13 cells. Suppression of DIC expression resulted in inhibition of GSIS by 5% to 69%, the extent of inhibition of insulin secretion being proportional to the level of Dic (also known as Slc25a10) gene knockdown. The most effective siRNA duplex against Dic did not affect glucose utilisation, glucose oxidation or ATP/ADP ratio, but did suppress glucose-induced increments of the NADPH/NADP(+) ratio. Confirmation of our results in primary cultures of isolated rat islets showed that butylmalonate and an adenovirus expressing an siRNA against Dic-inhibited GSIS.
CONCLUSIONS/INTERPRETATION: Malate transport by DIC may play an important role in GSIS, possibly by providing cytosolic malate as a counter-substrate for citrate and/or isocitrate export by CIC. These studies also suggest that malate transport by DIC is (1) a critical component of NADPH production mediated by pyruvate-cycling and (2) regulates GSIS.
目的/假设：我们之前描述了丙酮酸循环与胰岛素分泌之间的强相关性。我们还证明了涉及线粒体柠檬酸/异柠檬酸载体（CIC）和细胞质 NADP 依赖性异柠檬酸脱氢酶的丙酮酸-异柠檬酸循环途径起着特别重要的作用。CIC 在柠檬酸和异柠檬酸输出时需要细胞质苹果酸作为反底物。因此，考虑到线粒体二羧酸载体（DIC）提供细胞质苹果酸的重要来源，我们研究了 DIC 在控制葡萄糖刺激的胰岛素分泌（GSIS）中的潜在作用。
我们使用药理学和小干扰 RNA（siRNA）工具来评估 DIC 在克隆胰岛素分泌细胞 832/13 和分离的大鼠胰岛中的胰岛素释放中的作用。
丁烯二酸单酰，一种苹果酸转运抑制剂，以剂量依赖的方式降低 832/13 细胞中的细胞质苹果酸和柠檬酸水平，并抑制 GSIS。DIC 表达的抑制导致胰岛素分泌的抑制率为 5%至 69%，胰岛素分泌的抑制程度与 Dic（也称为 Slc25a10）基因敲低的水平成正比。针对 Dic 的最有效的 siRNA 双链体不影响葡萄糖利用、葡萄糖氧化或 ATP/ADP 比，但确实抑制了葡萄糖诱导的 NADPH/NADP(+) 比的增加。在分离的大鼠胰岛原代培养物中证实了我们的结果，表明丁烯二酸单酰和表达针对 Dic 的 siRNA 的腺病毒抑制了 GSIS。
结论/解释：DIC 的苹果酸转运可能在 GSIS 中发挥重要作用，可能通过为 CIC 的柠檬酸和/或异柠檬酸输出提供细胞质苹果酸作为反底物。这些研究还表明，DIC 的苹果酸转运是（1）丙酮酸循环介导的 NADPH 产生的关键组成部分，（2）调节 GSIS。
