Aging and Leydig Cell Function

描述（由申请人提供）：血清睾酮水平随着男性年龄的增长而下降。尽管睾酮水平下降的后果尚不完全清楚，但很明显，睾酮水平降低对骨质疏松症、认知和性欲有相关的、改变生活的影响。人们对睾丸激素下降的分子机制知之甚少。我们已经建立了棕色挪威大鼠作为研究人类生殖衰老的分子机制的合适模型，并表明与年龄相关的血清睾酮降低与间质细胞类固醇生成功能的缺陷有关。重要的是，我们发现，将老的间质细胞暴露于LH，无论是体内还是体外，都不会恢复这些细胞产生高水平（“年轻”）睾丸激素的能力，但用cAMP类似物dbcAMP孵育细胞会恢复这种能力。因此，dbcAMP实际上可以逆转Leydig细胞的衰老！这些研究强调了在与年龄相关的类固醇生成减少中至关重要的信号转导缺陷。本应用程序中提出的研究旨在解决间质细胞经历与年龄相关的功能变化导致雄激素形成减少的潜在分子机制。我们的总体假设是，衰老间质细胞信号转导级联的变化导致衰老细胞对LH的反应能力下降，从而导致cAMP降低；cAMP的减少导致胆固醇转运到线粒体和类固醇生成酶活性的降低；活性氧介导的损伤是LH信号转导级联变化的原因，最终导致睾丸激素分泌减少，这是间质细胞衰老的特征。我们将在修订后的竞争性更新申请中检查这一假设的关键组成部分，该申请有以下具体目标：确定在LH刺激下cAMP产生减少的分子基础。2. 确定cAMP使衰老的间质细胞恢复“年轻”水平的睾酮生成的机制。3. 确定活性氧介导的对老年细胞信号转导级联中特定组分的损伤是否是导致老年间质细胞睾酮分泌减少的分子变化的基础。

DESCRIPTION (provided by applicant): Serum levels of testosterone decline as men age. Although the consequences of the decline are not fully understood, it is clear that there are related, life-altering effects of reduced testosterone on osteoporosis, cognition, and libido. Little is known about the molecular mechanisms by which testosterone decline occurs. We have established the Brown Norway rat as an appropriate model with which to study the molecular mechanisms underlying reproductive aging in humans, and have shown that the age-related reductions in serum testosterone are associated with deficits in Leydig cell steroidogenic function. Importantly, we found that exposure of old Leydig cells to LH, whether in vivo or in vitro, will not restore the ability of these cells to produce testosterone at high ("young") levels, but that incubating the cells with the cAMP analog dbcAMP will do so. Thus, in effect, dbcAMP will reverse Leydig cell aging! These studies highlighted defects in signal transduction of central importance in age-related reduced steroidogenesis. The studies proposed in this application are designed to address the underlying molecular mechanisms by which Leydig cells undergo age-related functional changes that lead to reduced androgen formation. It is our overarching hypothesis that changes in the signal transduction cascade of aging Leydig cells result in the decreased ability of the aged cells to respond to LH and thus in reduced cAMP; that reduced cAMP is responsible for reductions in cholesterol transport into the mitochondria and in steroidogenic enzyme activities; and that reactive oxygen-mediated damage is responsible for changes in the LH signal transduction cascade that ultimately result in the reduced testosterone production that characterizes aging Leydig cells. We will examine critical components of this hypothesis in this revised competing renewal application, which has the following specific aims: 1. Determine the molecular basis for reduced cAMP production in response to LH stimulation. 2. Determine the mechanism by which cAMP restores "young" levels of testosterone production to aged Leydig cells. 3. Determine whether reactive oxygen-mediated damage to specific components of the signal transduction cascade in old cells is the basis of the molecular changes that lead to reduced testosterone production by aged Leydig cells.