Malyala Anna, Zhang Chunguang, Bryant Damani N, Kelly Martin J, Rønnekleiv Oline K
Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon 97239, USA.
J Comp Neurol. 2008 Feb 20;506(6):895-911. doi: 10.1002/cne.21584.
Multiple mechanisms mediate the effects of estrogen in the central nervous system, including signal transduction pathways such as protein kinase A, protein kinase C, and phosphatidylinositol 3-kinase (PI3K) pathways. Previously we demonstrated that estrogen regulates a number of PI3K-related genes in the hypothalamus, including the PI3K p55gamma regulatory subunit. We hypothesized that PI3K activation is critical for the effects of estrogen and that the p55gamma subunit may be more prevalent than the p85alpha regulatory subunit in the hypothalamus. Therefore, in the present study, we compared the mRNA distribution of the p55gamma and p85alpha regulatory subunits by using in situ hybridization in guinea pig. Expression level of p55gamma mRNA was greater than p85alpha in most hypothalamic nuclei. Twenty-four hours of estrogen treatment increased p55gamma mRNA expression in the paraventricular, suprachiasmatic, arcuate, and ventromedial nuclei, and little or no change was observed for p85alpha mRNA. Quantitative real-time PCR confirmed the in situ hybridization results. Next, we investigated the general role of PI3K signaling in the estrogen-mediated changes of arcuate proopiomelanocortin (POMC) neuronal excitability by using whole-cell recording. One cellular mechanism by which estrogen increases neuronal excitability is to desensitize (uncouple) gamma-aminobutyric acid type B (GABA(B)) receptors from their G-protein-gated inwardly rectifying K(+) channels in hypothalamic neurons. We found that the PI3K inhibitors wortmannin and LY294002 significantly reduced the estrogen-mediated GABA(B) receptor desensitization in POMC arcuate neurons, suggesting that PI3K signaling is a critical downstream mediator of the estrogen-mediated rapid effects. Collectively, these data suggest that the interplay between estrogen and PI3K occurs at multiple levels, including transcriptional and membrane-initiated signaling events that ultimately lead to changes in homeostatic function.
多种机制介导雌激素在中枢神经系统中的作用，包括信号转导途径，如蛋白激酶A、蛋白激酶C和磷脂酰肌醇3激酶（PI3K）途径。此前我们证明，雌激素调节下丘脑中一些与PI3K相关的基因，包括PI3K p55γ调节亚基。我们推测PI3K激活对雌激素的作用至关重要，并且p55γ亚基在下丘脑中可能比p85α调节亚基更普遍。因此，在本研究中，我们通过在豚鼠中使用原位杂交比较了p55γ和p85α调节亚基的mRNA分布。在大多数下丘脑核中，p55γ mRNA的表达水平高于p85α。雌激素处理24小时增加了室旁核、视交叉上核、弓状核和腹内侧核中p55γ mRNA的表达，而p85α mRNA几乎没有变化或没有变化。定量实时PCR证实了原位杂交结果。接下来，我们通过全细胞记录研究了PI3K信号在雌激素介导的弓状核阿黑皮素原（POMC）神经元兴奋性变化中的一般作用。雌激素增加神经元兴奋性的一种细胞机制是使下丘脑神经元中的γ-氨基丁酸B型（GABA(B)）受体与其G蛋白门控内向整流钾（K(+)）通道脱敏（解偶联）。我们发现PI3K抑制剂渥曼青霉素和LY294002显著降低了雌激素介导的POMC弓状神经元中GABA(B)受体脱敏，表明PI3K信号是雌激素介导的快速作用的关键下游介质。总的来说，这些数据表明雌激素和PI3K之间的相互作用发生在多个水平，包括转录和膜起始的信号事件，最终导致稳态功能的变化。
