CNC-Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal.
IIIU-Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal.
Int J Mol Sci. 2021 Dec 15;22(24):13470. doi: 10.3390/ijms222413470.
Diabetes is a chronic metabolic disease that seriously compromises human well-being. Various studies highlight the importance of maintaining a sufficient glucose supply to the brain and subsequently safeguarding cerebral glucose metabolism. The goal of the present work is to clarify and disclose the metabolic alterations induced by recurrent hypoglycemia in the context of long-term hyperglycemia to further comprehend the effects beyond brain harm. To this end, chemically induced diabetic rats underwent a protocol of repeatedly insulin-induced hypoglycemic episodes. The activity of key enzymes of glycolysis, the pentose phosphate pathway and the Krebs cycle was measured by spectrophotometry in extracts or isolated mitochondria from brain cortical tissue. Western blot analysis was used to determine the protein content of glucose and monocarboxylate transporters, players in the insulin signaling pathway and mitochondrial biogenesis and dynamics. We observed that recurrent hypoglycemia up-regulates the activity of mitochondrial hexokinase and Krebs cycle enzymes (namely, pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and succinate dehydrogenase) and the protein levels of mitochondrial transcription factor A (TFAM). Both insults increased the nuclear factor erythroid 2-related factor 2 (NRF2) protein content and induced divergent effects in mitochondrial dynamics. Insulin-signaling downstream pathways were found to be down-regulated, and glycogen synthase kinase 3 beta (GSK3β) was found to be activated through both decreased phosphorylation at Ser9 and increased phosphorylation at Y216. Interestingly, no changes in the levels of cAMP response element-binding protein (CREB), which plays a key role in neuronal plasticity and memory, were caused by hypoglycemia and/or hyperglycemia. These findings provide experimental evidence that recurrent hypoglycemia, in the context of chronic hyperglycemia, has the capacity to evoke coordinated adaptive responses in the brain cortex that will ultimately contribute to sustaining brain cell health.
糖尿病是一种慢性代谢疾病，严重影响人类健康。各种研究强调了维持大脑葡萄糖供应充足以及随后保护大脑葡萄糖代谢的重要性。本工作的目的是阐明和揭示长期高血糖背景下反复低血糖引起的代谢变化，以进一步了解除了对大脑损害以外的影响。为此，化学诱导的糖尿病大鼠接受了胰岛素诱导的反复低血糖发作方案。通过分光光度法测量脑皮质组织提取物或分离的线粒体中糖酵解、戊糖磷酸途径和三羧酸循环的关键酶的活性。使用 Western blot 分析来确定葡萄糖和单羧酸转运蛋白的蛋白质含量，这些蛋白在胰岛素信号通路和线粒体生物发生和动力学中发挥作用。我们观察到，反复低血糖会上调线粒体己糖激酶和三羧酸循环酶（即丙酮酸脱氢酶、α-酮戊二酸脱氢酶和琥珀酸脱氢酶）的活性以及线粒体转录因子 A（TFAM）的蛋白质水平。两种损伤都增加了核红细胞 2 相关因子 2（NRF2）的蛋白质含量，并在线粒体动力学中诱导了不同的效应。胰岛素信号下游途径被发现被下调，并且糖原合酶激酶 3β（GSK3β）通过 Ser9 磷酸化减少和 Y216 磷酸化增加被激活。有趣的是，低血糖和/或高血糖并没有引起 cAMP 反应元件结合蛋白（CREB）水平的变化，CREB 在神经元可塑性和记忆中起着关键作用。这些发现为实验证据提供了支持，即反复低血糖在慢性高血糖背景下，有能力在大脑皮层中引发协调的适应性反应，最终有助于维持脑细胞健康。
