Age and Control of Human Skin Flow

描述（由申请人提供）：65岁以上的人对与寒冷和炎热有关的发病率和死亡率的贡献不成比例，在寒冷和炎热的天气中，各种原因导致的死亡的相对风险增加。因为即使在轻微的加热或冷却过程中（即在没有颤抖或出汗的情况下），老年人的核心温度偏差也更大，血管舒缩调节的改变是与精子年龄相关的缺陷。最近，我们研究了年龄相关的反射性皮肤血管收缩（VC）和血管舒张（VD）的机制。老化皮肤反射性血管反应性减弱是由于肾上腺素能VC和活性胆碱能VD共递质的功能丧失，以及下游血管信号的改变，包括(1)肾上腺素能脱敏，(2)一氧化氮（NO）可用性降低。这项工作的逻辑延伸，由具有争议性的初步和试点数据支持，是为了检查氧化诱导的四氢生物蝶呤（BH4）生物利用度降低在老年皮肤血管中的作用。人类衰老与氧化应激增加有关，氧化应激导致关键酶辅因子BH4的破坏。BH4在神经和血管组织中普遍存在，并已成为一种可行的分子靶点，可能是减弱反射性皮肤VC和VD机制的基础。年龄相关的BH4缺陷似乎在反射性皮肤VC减弱中起核心作用。在肾上腺素能神经末梢，BH4是儿茶酚胺的合成和包装所必需的，作为酪氨酸羟化酶的关键辅助因子，并通过维持酶的活性降低形式。在具体目标1中，我们将在单独的实验中使用生理和药物刺激来诱导交感VC，研究BH4生物利用度降低在衰老皮肤反射VC减弱中的作用。BH4也是一氧化氮合酶（NOS）亚型的重要辅助因子，这对于反射性皮肤VD的充分表达是必要的。在底物和/或氧化剂诱导的BH4缺乏过程中，NOS不偶联导致超氧化物的产生。增加NOS的底物可用性和/或提供超生理剂量的抗坏血酸增加了衰老人类皮肤中no依赖性VD。鉴于底物可用性在NOS解偶联中的作用，以及抗坏血酸作为(1)非特异性抗氧化剂、(2)精氨酸酶s -亚硝基化抑制剂和(3)BH4的化学稳定剂/再合成剂的作用机制的冗余，我们现在的目标是探索BH4缺乏在衰老人体皮肤中NOS解偶联中的作用。在具体目标2中，我们将确定BH4和底物可用性降低在NOS解耦中的作用，该解耦导致衰老皮肤中no依赖性反射性皮肤VD减弱。在Specific Aim 3中，我们将测试全身口服BH4补充策略在热应激（全身冷却和加热；在单独的实验中）下改善老年人反射性皮肤VC和VD的功效。公共卫生相关性：由于超过退休年龄的人口比例越来越大，老年人的健康问题变得普遍，需要付出高昂的情感、身体和经济代价。这项研究的结果将为老年人血管收缩和血管舒张受损导致热损伤和死亡的生理学提供新的和重要的信息。此外，这些研究的结果可能提供一种口服干预策略，从功能上改善老年人在热应激下受损的皮肤血管反应性。

DESCRIPTION (provided by applicant): Humans over the age of 65 contribute disproportionately to cold- and heat-related morbidities and mortalities and the relative risk of death from all causes increases during cold and hot weather. Because core temperature excursions during even mild heating or cooling (i.e., in the absence of shivering or sweating) are greater in the elderly, altered vasomotor regulation is the seminal age-related deficit. Recently we have examined the mechanisms of age-related attenuated reflex cutaneous vasoconstriction (VC) and vasodilation (VD). This attenuated reflex cutaneous vasoreactivity in aged skin is due to a functional loss of adrenergic VC and active cholinergic VD co-transmitter(s), and altered downstream vascular signaling including (1) adrenergic desensitization, and (2) decreased nitric oxide (NO) availability. The logical extension of that work, supported by provocative preliminary and pilot data, is to examine the role of oxidant-induced reduced tetrahydrobiopterin (BH4) bioavailability in the aged cutaneous vasculature. Human aging is associated with increased in oxidant stress leading to the destruction of the critical enzymatic cofactor BH4. BH4 is ubiquitous throughout neural and vascular tissues and has emerged as a viable molecular target that may underlie both attenuated reflex cutaneous VC and VD mechanisms. Age-related deficiencies in BH4 appear to play a central role in attenuated reflex cutaneous VC. In adrenergic nerve terminals, BH4 is required for the synthesis and packaging of catecholamines by serving as a critical cofactor for tyrosine hydroxylase and by maintaining the enzyme in its reduced active form. In Specific Aim 1 we will examine the role of reduced BH4 bioavailability in attenuated reflex VC in aged skin using physiological and pharmacological stimuli in separate experiments to induce sympathetic VC. BH4 is also an essential cofactor for the NO-synthase (NOS) isoforms which are necessary for the full expression of reflex cutaneous VD. NOS uncouples during substrate and/or oxidant-induced BH4 deficiencies resulting in superoxide production. Increasing substrate availability for NOS and/or providing supraphysiological doses of ascorbate augments NO-dependent VD in aged human skin. Because of the putative role of substrate availability in NOS uncoupling, and the redundancies in the mechanisms of action of ascorbate as (1) a non-specific antioxidant, (2) an inhibitor of S-nitrosylation of arginase, and (3) a chemical stabilizer/resynthesizer of BH4, we now aim to explore the role of BH4 deficiency in NOS uncoupling in aged human skin. In Specific Aim 2 we will determine the roles of BH4 and reduced substrate availability in the NOS uncoupling that results in attenuated NO-dependent reflex cutaneous VD in aged skin. In Specific Aim 3 we will test the efficacy of systemic oral BH4 supplementation strategies in improving reflex cutaneous VC and VD in aged human subjects during thermal stress (whole body cooling and heating; in separate experiments). PUBLIC HEALTH RELEVANCE: As a larger percent of the population surpasses retirement-age, the health issues of the elderly become pervasive exacting emotional, physical and financial costs. The results from this study will provide new and important information on the physiology governing impaired vasoconstriction and vasodilation in older humans that leads to thermal injury and death. Furthermore, results from these studies may provide an oral intervention strategy to functionally improve impaired cutaneous vasoreactivity in the aged during thermal stress.