Department of Pediatrics and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA.
Neurochem Res. 2012 Nov;37(11):2613-26. doi: 10.1007/s11064-012-0901-3. Epub 2012 Oct 19.
It is well established that astrocytes can utilize many substrates to support oxidative energy metabolism; however, use of energy substrates in the presence of other substrates, as would occur in vivo, has not been systematically evaluated. Substrate competition studies were used to determine changes in the rates of (14)CO(2) production since little is known about the interaction of energy substrates in astrocytes. The rates of (14)CO(2) production from 1 mM D-[6-(14)C]glucose, L-[U-(14)C]glutamate, L-[U-(14)C]glutamine, D-3-hydroxy[3-(14)C]butyrate, L-[U-(14)C]lactate and L-[U-(14)C]malate by primary cultures of astrocytes from rat brain were determined to be 1.17 ± 0.19, 85.30 ± 12.25, 28.04 ± 2.84, 13.55 ± 4.56, 14.84 ± 2.40 and 5.20 ± 1.20 nmol/h/mg protein (mean ± SEM), respectively. The rate of (14)CO(2) production from glutamate oxidation was higher than that of the other substrates Addition of unlabeled glutamate significantly decreased the rates of (14)CO(2) production from all other substrates studied; however, glutamate oxidation was not altered by the addition of any of the other substrates. The rate of (14)CO(2) production of glutamine was decreased by glutamate, but not altered by other substrates. The rate of (14)CO(2) production from glucose was significantly decreased by the addition of unlabeled glutamate, glutamine or lactate, but not by 3-hydroxybutyrate or malate. Addition of unlabeled glucose did not significantly alter the (14)CO(2) production from any other substrate. (14)CO(2) production from lactate was decreased by the addition of unlabeled glutamine or glutamate and increased by addition of malate. The (14)CO(2) production from malate was decreased by the addition of unlabeled glutamate or lactate, but was not altered by the other substrates. The substrate utilization for oxidative energy metabolism in astrocytes is very different than the profile previously reported for synaptic terminals. These studies demonstrate the potential use of multiple substrates including glucose, glutamate, glutamine, lactate and 3-hydroxybutyrate as energy substrates for astrocytes. The data also provide evidence of interactions of substrates and multiple compartments of TCA cycle activity in cultured astrocytes.
已有充分证据表明，星形胶质细胞可以利用多种底物来支持氧化能量代谢；然而，在体内存在其他底物的情况下，对能量底物的利用情况尚未得到系统评估。我们使用底物竞争研究来确定（14）CO2产生率的变化，因为我们对星形胶质细胞中能量底物的相互作用知之甚少。通过来自大鼠大脑的原代星形胶质细胞培养物测定 1mM D-[6-（14）C]葡萄糖、L-[U-（14）C]谷氨酸、L-[U-（14）C]谷氨酰胺、D-3-羟基[3-（14）C]丁酸、L-[U-（14）C]乳酸和 L-[U-（14）C]苹果酸的（14）CO2产生率分别为 1.17±0.19、85.30±12.25、28.04±2.84、13.55±4.56、14.84±2.40 和 5.20±1.20 nmol/h/mg 蛋白（平均值±SEM）。谷氨酸氧化产生的（14）CO2产生率高于其他底物，添加未标记的谷氨酸可显著降低所有其他研究的底物的（14）CO2产生率；然而，添加其他任何底物都不会改变谷氨酸的氧化。谷氨酰胺的（14）CO2产生率被谷氨酸降低，但其他底物没有改变。添加未标记的谷氨酸、谷氨酰胺或乳酸可显著降低葡萄糖的（14）CO2产生率，但 3-羟基丁酸或苹果酸则不会。添加未标记的葡萄糖不会显著改变其他任何底物的（14）CO2产生率。添加未标记的谷氨酰胺或谷氨酸可降低乳酸的（14）CO2产生率，添加苹果酸可增加乳酸的（14）CO2产生率。添加未标记的谷氨酸或乳酸可降低苹果酸的（14）CO2产生率，但其他底物则不会改变苹果酸的（14）CO2产生率。星形胶质细胞氧化能量代谢的底物利用情况与之前报道的突触末端的谱图非常不同。这些研究表明，葡萄糖、谷氨酸、谷氨酰胺、乳酸和 3-羟基丁酸等多种底物可作为星形胶质细胞的能量底物。数据还提供了证据表明，在培养的星形胶质细胞中，底物和 TCA 循环多个隔室的活性存在相互作用。
