REGULATION OF EXPRESSION OF NO SYNTHASE

一氧化氮（NO）是哺乳动物体内重要的生理和病理过程，其中许多过程都涉及血管系统。 NO的许多生理作用是由环GMP介导的，并且NO和环GMP都具有相对短的作用持续时间。 NO是不稳定的，不能通过常规机制储存、释放或失活。NO与活性氧以及含铁和硫的分子的反应性导致NO的快速失活。由于特定磷酸二酯酶的水解，环GMP也不稳定。 因此，NO被自然发生的化学过程快速灭活，而环GMP被细胞中的磷酸二酯酶快速灭活，产生的半衰期均小于1秒。 因此，NO的作用高度依赖于NO合酶（NOS）从L-精氨酸合成NO。 因此，NO的生物合成的调节或调制是最重要的过程，指示NO的药效学。拟议的研究的主要目的是阐明几个潜在的新机制，NO的生物合成可以控制。 这些靶向机制涉及NOS mRNA表达、NOS蛋白表达和稳定性、精氨酸酶表达和催化活性、精氨酸底物可用性以及NOS产生活性氧的变化。 要测试的中心假设是，细胞NO的产生是密切调节的各种内源性因素影响NOS亚型的转录，翻译和翻译后表达。本研究拟从三个方面探讨NO下调诱导型一氧化氮合酶（iNOS）和内皮型一氧化氮合酶（eNOS）表达的分子机制;探讨NOS激活酶上调诱导型一氧化氮合酶（iNOS）和内皮型一氧化氮合酶（eNOS）表达的分子机制;探讨NOS激活酶调节诱导型一氧化氮合酶（iNOS）和内皮型一氧化氮合酶（eNOS）产生超氧阴离子和过氧化氢的分子机制。 拟议的研究代表了一个持续的长期努力，以阐明影响血管和NO在健康和疾病的相关行动的生物因素。

Nitric oxide (NO) is a key molecule mediating physiological and pathophysiological processes in mammals, many of which involve the vascular system. Many physiological actions of NO are mediated by cyclic GMP, and both NO and cyclic GMP have relatively short durations of action. NO is labile and is not stored, released, or inactivated by conventional mechanisms. Reactivity of NO with reactive oxygen species and with iron and sulfur containing molecules causes rapid inactivation of NO. Cyclic GMP is also unstable due to hydrolysis by specific phosphodiesterases. Thus, NO is rapidly inactivated by naturally-occurring chemical processes and cyclic GMP is rapidly inactivated by phosphodiesterases in cells, yielding half lives for each of less than 1-second. Therefore, the actions of NO are highly dependent on its biosynthesis from L-arginine by NO synthase (NOS). Accordingly, the regulation or modulation of NO biosynthesis is the most important process dictating the pharmacodynamics of NO. The principal objective of the proposed studies is to elucidate several potentially novel mechanisms by which NO biosynthesis may be controlled. These targeted mechanisms involve changes in NOS mRNA expression, NOS protein expression and stability, arginase expression and catalytic activity, arginine substrate availability, and the production of reactive oxygen species by NOS. The central hypothesis to be tested is that cellular NO production is tightly regulated by various endogenous factors affecting transcriptional, translational and posttranslational expression of NOS isoforms. Three Specific Aims are proposed to achieve this objective: (1) to elucidate the molecular mechanisms by which NO downregulates the expression of inducible NOS (iNOS) and endothelial NOS (eNOS); (2) to elucidate the mechanisms by which arginase upregulates the expression of iNOS and eNOS; and (3) to elucidate the role of arginase in modulating the production of superoxide anion and hydrogen peroxide by iNOS and eNOS. The proposed research represents a continuing long-term effort to elucidate the biological factors influencing the vascular and related actions of NO in health and disease.