Microvascular Aging and eNOS Uncoupling

心血管系统是人体氧化代谢和有氧能力的主要决定因素; 因此，成功的心血管老化对于维持老年人积极、独立的生活方式至关重要。 个体心血管系统的老化导致进行性内皮功能障碍， 患心血管疾病的风险增加，骨骼肌功能丧失。内皮 老年大鼠骨骼肌阻力动脉中存在的功能障碍主要是由一氧化氮减少引起的 然而，年龄对调节NO信号传导的细胞机制的影响仍然存在， 被确定。最近的证据表明，四氢生物蝶呤（BH 4），一种必要的辅因子， 在老年大鼠的骨骼肌阻力动脉中，NO的产生减少。不足 BH 4的可用性可导致内皮型一氧化氮合酶（eNOS）的生物化学解偶联， 此外，未偶联的eNOS产生超氧阴离子（021活性氧 这些物质可以限制NO信号传导并导致细胞损伤。本提案的总体目标 1）确定衰老是否导致骨骼肌中eNOS解偶联和生物可利用的NO减少， 肌肉阻力动脉，和2）以确定是否干预策略，包括有氧运动 训练，可以逆转与年龄相关的BH 4可用性和eNOS解偶联的缺陷，增加NO 骨骼肌阻力动脉的生物利用度。在目标1中，将直接测量NO和O2-， 确定老化是否在大鼠比目鱼肌的阻力动脉中产生eNOS的解偶联， 降低NO的生物利用度，增加细胞毒性O 2-的产生。在目标2中，内皮特异性 腺病毒基因转移将用于确定是否通过过表达BH 4来恢复BH 4的可用性。 GTP环化水解酶（GTPCH）逆转与年龄相关的eNOS解偶联，增加NO生物利用度， 减少比目鱼肌阻力动脉中的O2-。GTPCH的shRNAi敲低也将用于减少 BH 4可利用性和促进比目鱼肌阻力动脉中eNOS解偶联。目标3的目的是 确定慢性有氧运动训练是否能减少氧化应激并增加GTPCH 表达，从而增加BH 4的可用性，并逆转eNOS和NO的年龄相关解偶联 大鼠比目鱼肌阻力动脉中的生物利用度。这些研究将增加我们对 骨骼肌阻力血管中年龄相关内皮功能障碍的机制 并指出旨在改善BH 4可用性的特定干预措施是否可以改善内皮细胞 老年机能障碍

The cardiovascular system is a major determinant of the body's oxidative metabolism and aerobic capacity; thus, successful cardiovascular aging is critical to maintenance of an active, independent lifestyle in elderly individuals. Aging of the cardiovascular system results in progressive endothelial dysfunction that is associated with increased risk for cardiovascular disease and a loss of skeletal muscle performance. The endothelial dysfunction present in skeletal muscle resistance arteries of aged rats results primarily from reduced nitric oxide (NO) signaling; however, the effects of age on cellular mechanisms that regulate NO signaling remain to be determined. Recent evidence indicates that the availability of tetrahydrobiopterin (BH4), a necessary cofactor in NO production, is decreased in skeletal muscle resistance arteries of aged rats. Inadequate availability of BH4 can result in biochemical uncoupling of endothelial nitric oxide synthase (eNOS) and reduced synthesis of NO. Furthermore, uncoupled eNOS produces superoxide anion (021 a reactive oxygen species which can limit NO signaling and contribute to cellular damage. The overarching goals of this proposal are 1) to determine whether aging results in uncoupling of eNOS and reduction of bioavailable NO in skeletal muscle resistance arteries, and 2) to determine whether interventional strategies, including aerobic exercise training, can reverse age-related deficiencies in BH4 availability and uncoupling of eNOS, increasing NO bioavailability in skeletal muscle resistance arteries. In Aim 1 NO and O2- will be measured directly to determine whether aging produces uncoupling of eNOS in resistance arteries from rat soleus muscle leading to reduced NO bioavailability, and increased production of cytotoxic O2-. In Aim 2, endothelium-specific adenoviral gene transfer will be used to determine whether restoration of BH4 availability by overexpression of GTP cyclohydrolase (GTPCH) reverses age-related uncoupling of eNOS, increasing NO bioavailability and reducing O2- in soleus muscle resistance arteries. shRNAi knockdown of GTPCH will also be used to reduce BH4 availability and promote eNOS uncoupling in soleus muscle resistance arteries. The purpose of Aim 3 is to determine whether chronic aerobic exercise training reduces oxidant stress and increases GTPCH expression thereby increasing BH4 availability and reversing age-related uncoupling of eNOS and NO bioavailability in resistance arteries from rat soleus muscle. These studies will increase our understanding of mechanisms that contribute to age-related endothelial dysfunction in resistance vasculature of skeletal muscle and indicate whether specific interventions designed to improve BH4 availability can ameliorate endothelial dysfunction in old age