Liu P, Smith P F, Appleton I, Darlington C L, Bilkey D K
Department of Pharmacology and Toxicology, School of Medical Sciences, University of Otago, Dunedin, New Zealand.
Neuroscience. 2003;119(3):679-87. doi: 10.1016/s0306-4522(03)00210-0.
L-arginine can be metabolised by nitric oxide synthase (NOS) with the formation of L-citrulline and nitric oxide (NO), or arginase with the production of L-ornithine and urea. In contrast to studies showing a potential involvement of NOS/NO in the aging process, the role of arginase has not been well documented. The present study investigates for the first time the regional variations and age-related changes in both NOS and arginase in sub-regions of the hippocampus. In young adult rats, although the total NOS activity was not significantly different across the hippocampal CA1, CA2/3 and the dentate gyrus (DG) sub-regions, the total arginase activity showed a clear regional variation with the highest level in DG. Western blotting revealed that the highest levels of neuronal NOS (nNOS) and endothelial NOS (eNOS) proteins were located in CA1. Arginase I is expressed at a very low level in the brain (the whole hippocampus) as compared with the liver. By contrast, arginase II protein shows an extremely high expression in the brain with little or no expression in the liver. There was no regional variation in arginase I or arginase II protein expression across the sub-regions of the hippocampus. When a comparison was made between young (4-month-old) and aged (24-month-old) rats, a significant increase in total NOS activity was found in DG and significant decreases in arginase activity were observed in the CA1 and CA2/3 regions in the aged animals. Western blotting further revealed a dramatic decrease in eNOS protein expression in aged CA2/3 with no age-associated changes in nNOS, arginase I and II protein expression in any region examined. Interestingly, evidence of activity or protein expression of the inducible isoform of NOS (iNOS) was not detected in any tissue from either group. The present results, in conjunction with previous findings, support the contribution of NOS/NO to aging but question the involvement of iNOS in the normal aging process. Region-specific changes in arginase suggest that this enzyme may also contribute to aging.
L-精氨酸可被一氧化氮合酶（NOS）代谢生成L-瓜氨酸和一氧化氮（NO），或被精氨酸酶代谢生成L-鸟氨酸和尿素。与显示NOS/NO可能参与衰老过程的研究不同，精氨酸酶的作用尚未得到充分记录。本研究首次调查了海马体各亚区域中NOS和精氨酸酶的区域差异及与年龄相关的变化。在年轻成年大鼠中，虽然海马体CA1、CA2/3和齿状回（DG）亚区域的总NOS活性无显著差异，但总精氨酸酶活性呈现明显的区域差异，在DG中水平最高。蛋白质印迹法显示，神经元型NOS（nNOS）和内皮型NOS（eNOS）蛋白的最高水平位于CA1。与肝脏相比，精氨酸酶I在脑（整个海马体）中的表达水平非常低。相比之下，精氨酸酶II蛋白在脑中表达极高，而在肝脏中几乎不表达或不表达。海马体各亚区域中精氨酸酶I或精氨酸酶II蛋白表达无区域差异。当对年轻（4个月大）和老年（24个月大）大鼠进行比较时，发现老年动物的DG中总NOS活性显著增加，而CA1和CA2/3区域的精氨酸酶活性显著降低。蛋白质印迹法进一步显示，老年CA2/3中eNOS蛋白表达显著下降，而在所检查的任何区域中，nNOS、精氨酸酶I和II蛋白表达均无与年龄相关的变化。有趣的是，在两组的任何组织中均未检测到诱导型NOS（iNOS）的活性或蛋白表达证据。本研究结果与先前的发现一致，支持NOS/NO对衰老的作用，但质疑iNOS参与正常衰老过程。精氨酸酶的区域特异性变化表明该酶也可能参与衰老过程。
