Estrogen and High-Affinity Choline Transport

女性患阿尔茨海默病（AD）的风险比男性高2-3倍。有证据表明，雌激素替代疗法可以降低这种风险。然而，没有生物学机制证明这种保护作用。在AD中，基底前脑中含乙酰胆碱的神经元退化。因此，假设雌激素的作用机制之一是刺激基底前脑胆碱能神经元。更具体地说，雌激素刺激高亲和力胆碱转运蛋白的活性，该转运蛋白进行乙酰胆碱合成的关键步骤。 为了检验这一假设，将从胚胎大鼠的基底前脑制备原代神经元培养物。这些培养物将富含胆碱能神经元，并优化其存活条件。将检测培养物的高亲和力胆碱转运蛋白活性。将用雌激素处理细胞，并测量该处理对高亲和力胆碱转运蛋白活性的影响。高亲和力胆碱转运将与胆碱能神经元的数量和胆碱能功能的其他标志物（包括乙酰胆碱含量、胆碱乙酰转移酶活性和高亲和力胆碱转运蛋白mRNA水平）相关。如果雌激素增加了转运蛋白的活性，这一假说将得到证实。还预期 雌激素会提高这些神经元的存活率。这些实验将扩展到解决植物雌激素，植物来源的雌激素样化合物，对胆碱能存活和功能的影响。由于几个原因，确定雌激素在AD中具有保护作用的机制是重要的。首先，它为绝经后妇女的雌激素替代治疗提供了生物学依据。其次，它提供了深入了解AD的病理生理过程，因此确定了治疗AD的新靶点。最后，雌激素的作用机制的知识允许设计药物，模仿其治疗效果，但没有其不良副作用。

Women have a 2-3-fold greater risk of developing Alzheimer's disease (AD) than men. There is evidence that estrogen replacement therapy reduces this risk. However, no biological mechanism is proven for this protective effect. In AD, acetylcholine-containing neurons in the basal forebrain degenerate. Thus, it is hypothesized that one mechanism for estrogen's effect is to stimulate basal forebrain cholinergic neurons. More specifically, estrogen stimulates the activity of the high affinity choline transporter, which carries out the critical step in the synthesis of acetylcholine. To test this hypothesis, primary neuronal cultures will be prepared from basal forebrain of embryonic rats. These cultures will be enriched for cholinergic neurons and conditions optimized for their surivival. Cultures will be tested for high affinity choline transporter activity. Cells will be treated with estrogen and the effect of this treatment on the activity of the high affinity choline transporter will be measured. High affinity choline transport will be correlated with the number of cholinergic neurons and other markers of cholinergic function including acetylcholine content, choline acetyltransferase activity and high affinity choline transporter mRNA level. The hypothesis will be proven if estrogen increases the activity of the transporter. It is also expected that estrogen will enhance the survival of these neurons in culture. These experiments will be extended to address the effects that phytoestrogens, plant-derived estrogen-like compounds, have on cholinergic survival and function. Identifying the mechanism(s) by which estrogen is protective in AD is important for several reasons. First, it provides a biological rationale for estrogen replacement therapy in postmenopausal women. Second, it provides insights into the pathophysiological processes underlying AD and therefore identifies new targets for the treatment of AD. Lastly, knowledge of estrogen's mechanism of action allows design of drugs that mimic its therapeutic effects, but lack its undesirable side effects.