脑内皮质激素受体及其受体前代谢酶的作用

中枢神经系统的发生、分化、发育成熟和退化中均有糖皮质激素的参与。糖皮质激素对神经系统的影响是在11β－羟基类固醇脱氢酶的调节下,通过与糖皮质激素受体和盐皮质激素受体结合,调节靶基因的转录而实现的。本文介绍了脑内糖皮质激素受体和11β－羟基类固醇脱氢酶的类型、分布、功能,以及二者在糖皮质激素发挥作用中的意义。     

应激抑郁发生中糖皮质激素对BDNF信号通路的影响

脑源性神经营养因子(brain derived neurotrophic factor,BDNF)是一个关键性的神经营养因子,它既影响突触的形成和重构,又可以通过突触前和突触后机制改变突触传递的效能,从而对神经结构和功能可塑性发挥调节作用。BDNF主要通过结合TrkB受体激活细胞内信号系统来发挥它积极的生物学效应。研究表明,中枢神经系统BDNF表达或功能的变化与抑郁症的发生相关,而应激引起糖皮质激素(glucocorticoid,GC)的增加也是导致抑郁发生的重要原因之一。值得注意的是,GCs的增加会影响BDNF,一方面GCs降低BDNF的表达,另一方面GCs受体GR与BNDF受体TrkB相互作用。过多的GCs干扰了BDNF信号,使BDNF功能受到影响,导致抑郁患者脑内,尤其是海马结构的损害。就抑郁发生中糖皮质激素对BDNF功能影响的研究进展作一介绍。     

糖皮质激素受体结构与功能研究进展

糖皮质激素受体（GR）是核受体超家族中的重要成员,也是一种典型的激素依赖性转录调节因子。与激素结合后通过与靶基因糖皮质激素反应元件（GRE）相互作用。从而调节靶基因的表达。引起各种生物学效应。近年对人GR（hGR)的分子结构与生物学作用的研究有一定进展。     

糖皮质激素与miRNA关系的研究现状

糖皮质激素(glucocorticoid,GC)因具有抗炎、抑制免疫反应、调节能量代谢和细胞增殖凋亡等作用而广泛使用于临床。作为非编码RNA,内源性miRNA通过影响靶基因的表达水平在机体发育和疾病发生中发挥广泛的调控作用。目前研究发现,糖皮质激素能通过糖皮质激素受体(glucocorticoid receptor,GR)介导调节miRNA的表达,而miRNA也能通过影响糖皮质激素受体的表达水平调节细胞对糖皮质激素的反应性。在许多疾病模型中,miRNA和糖皮质激素受体之间通过密切互作关系共同影响疾病的发生发展。     

nov基因的表达与脑的种系发育分化平行相关

用地高辛标记的cRNA探针原位杂交组织化学方法研究了鲢、鸡、牛、犬和猫脑肾母细胞瘤过度表达是基因阳性神经元的比较发育。结果显示,低等脊椎动物鲢脑仅有少量nov mRNA阳性神经元,分布于延髓的迷走神经背核、三叉神经背核、丘脑前核、丘脑后核、下丘脑背侧核、下丘脑外侧核。鸡脑阳性神经元除广泛分布于脑干外,小脑、丘脑的多数核闭、下丘脑的背侧核、腹侧核和后核以及大脑纹状体等多数脑区也有一定分布。哺乳动物牛、犬和猛脑中nov mRNA阳性神经元广泛分布,在脑干、小脑、间脑和大脑都检测到强烈阳性信号。以上结果表明,在众低等脊椎动物到高等脊椎动物的进化过程中nov基因的表达也从低级中枢向高级中枢扩展,提示该基因的表达与脑的种系发育、脑功能的分化平行相关。     

大鼠海马神经元内11β-HSD1和GR的共存及其意义

本研究旨在探讨糖皮质激素代谢酶-11β-羟基类固醇脱氢酶Ⅰ型（11β-HSD1）和糖皮质激素受体（GR）在大鼠海马神经元内的共同分布及其意义。用免疫细胞化学方法研究显示,海马神经元内不仅存在11β-HSD1免疫反应物质,还存在GR免疫反应物质,而且11β-HSD1与GR共存于同一个海马神经元内,用Western印迹杂交和薄层层析（TLC）方法研究表明,地塞米松（DEX）可以促进11β-HSD1与GR共存于同一个海马神经元内,用Western印迹杂交和薄层层析（TLG）方法研究表明,地塞米松（DEX）可以促进11β-HSD1蛋白表达及其酶的活性,利用11β-HSD1基因启动子区序列构建的以CAT酶为报告基因的pBLCAT6质粒转染PC12细胞,证实DEX能够促进CAT酶的表达。以上糖皮质激素的作用均可为GR受体阻断剂RU38486所阻断,结果提示;糖皮质激素（GC）与GR结合后,可以作用于与其共存的11β-HSD1基因启动子区,使11β-HSD1表达增加,从而使更多的GC代谢产物转化为有活性的GC,此机制可能与保证GC在海马神经元内与亲和力较低的GR结合有关。     

Cd~(2+)处理后麻雀脑组织中糖皮质激素受体和盐皮质激素受体表达变化

目的检测在Cd~(2+)处理后糖皮质激素受体(GR)和盐皮质激素受体(MR)在麻雀Passer montanus脑组织中的表达变化。方法 6只麻雀随机分成2组,每组3只。处理组饮水中添加500μg·L~(-1)Cd~(2+),对照组不添加。用Clustal W2将麻雀的GR和MR氨基酸序列与其他物种氨基酸序列进行相似性比对分析。采用Real-time PCR检测基础水平下麻雀各组织中GR和MR基因的表达水平。Cd~(2+)处理后,测定GR和MR基因在脑组织中的表达变化。结果麻雀与斑胸草雀Taeniopygia guttata和原鸡Gallus gallus的GR和MR氨基酸序列的相似性大于90%;GR和MR基因在麻雀肝脏、肠、心脏、眼球、脑、肺、肌肉、肾脏和性腺9个组织中均有表达;Cd~(2+)处理后,处理组脑组织中GR和MR mRNA表达水平均上调,且显著高于对照组(P0.05)。结论 GR和MR在麻雀各组织中广泛表达;推测GR和MR基因在Cd~(2+)的应激反应中具有重要作用,具体作用还有待于进一步论证,同时该研究为野外工作提供了一定的实验依据。     

在应激低反应期新生大鼠的海马和视交叉上核核受体-MR、GR表达的变化

目的搞清新生大鼠HPA轴改变在应激低反应时期（stress hyporesponsive period、SHRP））的核受体-MR（盐皮质激素受体）和GR（糖皮质激素受体）在海马和视交叉上核（SCN）的表达变化。从而进一步了解新生大鼠发育时间对MR和GR的影响。方法本研究应用免疫荧光技术研究了生后4d（PD4）和生后12d（PD12）的新生大鼠海马和SCN的MR、GR的表达。同时采用RIA方法测定了血清中皮质类固醇的浓度水平。结果RIA结果显示在应激低反应期给予刺激,血清皮质类固醇水平没有明显改变。在海马,PD12较PD4,MR-和GR-i mmunoreactivity在CA1区表达增强;在齿状回没有明显变化;在海马门（hilus）减弱。而在海马的CA3区和SCN中,PD4 GR-ir强烈表达,在PD12却下降。同时也发现在hilus细胞出现GR和nestin（巢蛋白）阳性表达的共存,但是却没有发现MR和nestin的共存。结论新生大鼠阶段,发育时间对MR和GR的影响因区域不同影响不同。GR和nestin（巢蛋白）的共存为探讨在新生大鼠阶段GR对神经干细胞的分化有否影响提供了实验资料。本研究也为进一步研究新生大鼠应激低反应状态下海马及SCN与低活性的HPA轴的关系提供了形态学依据。     

家鸡G蛋白偶联受体78基因的克隆与组织表达图谱分析

G蛋白偶联受体(GPCR)是一大类膜受体超家族,参与了机体几乎所有的生理过程,是一类重要信号分子受体。GPR78作为GPCR超家族的成员之一,属于孤儿型受体。目前,在脊椎动物中,针对该基因结构与功能的研究极少。本研究以家鸡为动物模型,通过RT-PCR方法克隆了GPR78基因的编码区序列,并探究了该基因在家鸡各组织中的表达情况。结果显示:家鸡GPR78基因编码区全长为1020 bp,含3个外显子,可编码1个长为339个氨基酸的7次跨膜受体;该基因在家鸡脑各功能区及垂体中高表达,而在其他外周组织中均不表达。本研究为后续探究GPR78基因在家鸡中的生理功能奠定基础。     

早期社会隔离对雌性ICR小鼠焦虑水平、社会行为及神经内分泌的影响

许多证据表明早期生活应激会影响动物成年后的行为和神经化学改变,然而该过程的机制还不完全清楚。脑源性神经营养因子(BDNF)、催产素(OT)和糖皮质激素受体(GR)参与对应激的神经适应性反应。本实验将出生3 d后的雌性ICR小鼠幼仔每日隔离3 h直至出生21 d,在60日龄时检测其焦虑水平、社会行为及血清中皮质酮(CORT)和OT的水平,同时检测了中枢BDNF、OT和GR的阳性神经元表达。结果表明,与对照组相比,早期隔离组小鼠的焦虑水平增加,运动性和社会行为减少,同时血清中CORT水平上升、海马CA1和CA2/3区的BDNF及GR的阳性神经元表达下降,下丘脑室旁核和视上核的OT阳性神经元表达减少。这些结果表明,早期社会隔离下调了BDNF、OT和GR的水平,并通过调制应激系统影响雌性ICR小鼠的情绪与社会行为。     

Glial cells express both mineralocorticoid and glucocorticoid receptors.

In the brain, the action of glucocorticoid steroids is mediated via two intracellular receptors, the mineralocorticoid (MR), or type I receptor, and the glucocorticoid (GR), or type II receptor. These receptors are expressed in many types of neurons and are co-expressed in some neurons such as the hippocampal pyramidal cells. Although glucocorticoids are known to affect gliogenesis and glial cell differentiation, the expression of the GR in different types of glial cells throughout the brain has not been thoroughly studied and the expression of the MR in glia not previously reported. Here we review studies suggesting that both receptors are expressed in astrocytes and oligodendrocytes.     

Age-dependent expression of glucocorticoid- and mineralocorticoid receptors on neural precursor cell populations in the adult murine hippocampus

Steroid hormones are regulators of adult hippocampal neurogenesis and are central to hypotheses regarding adult neurogenesis in age-related and psychiatric disturbances associated with altered hippocampal plasticity--most notably dementias and major depression. Using immunohistochemistry, we examined the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors during adult hippocampal neurogenesis. In young mice only 27% of dividing cells in the subgranular zone expressed GR, whereas 4 weeks after division 87% had become positive for GR and MR. GR was expressed by 50% of the radial glia-like type-1 and type-2a progenitor cells, whereas MR was expressed only by mature calbindin-positive granule cells. Doublecortin-positive neuronal progenitor cells (type-2b) and early postmitotic calretinin-positive neurons were devoid of GR and MR expression. Fifty per cent of the intermediate type-3 cells showed GR expression, possibly reflecting cells terminating maturation. Thus, all subpopulations of dividing precursor cells showed an identical receptor profile (50% GR, no MR), except for type-2b cells, which expressed neither receptor. There was also no overlap between calretinin and GR early postnatally (P8) or after physical activity or exposure to an enriched environment, both of which are potent neurogenic stimuli. In contrast, in old age calretinin-positive young neurons became GR and MR positive, suggesting increased steroid sensitivity. Age also increased the expression of GR in type-1 and type-2a precursor cells. Other intermediates were so rare in old age that they could not be studied. This course and variability of receptor expression in aging might help to explain differential vulnerability of adult neural precursor cells to corticoid-mediated influences.     

Bombesin attenuates pre-mRNA splicing of glucocorticoid receptor by regulating the expression of serine-arginine protein p30c (SRp30c) in prostate cancer cells

Although glucocorticoids are frequently administered to patients with hormone refractory prostate cancer, their therapeutic effectiveness is limited by the development of glucocorticoid resistance. The molecular mechanisms of glucocorticoid resistance are unknown but are believed to involve neuropeptide growth factors and cytokines. We examined the functional interaction between bombesin and dexamethasone in PC-3 cells and found that bombesin could act as a survival factor by interfering with dexamethasone-mediated growth inhibition. Because glucocorticoids exert their effects through glucocorticoid receptors (GRs), we measured the expression of GR alpha and GR beta isoforms in the presence of bombesin. Western blotting and real time PCR revealed bombesin induced expression of GR beta, but not GR alpha. Because GR isoforms are generated by alternative splicing of a common GR gene, we examined the expression of serine-arginine (SR) proteins involved in alternative splicing, and found that the expression of SRp30 was induced by bombesin in PC-3 cells. To characterize the role of SRp30 in splicing of GR isoforms, siRNAs specific to various SRp30 isoforms were transfected into PC-3 cells. We found that suppression of SRp30c expression by siRNA specifically antagonized bombesin's effect on glucocorticoid-mediated inhibition of PC cells, suggesting that bombesin-induced expression of SRp30c affects GR pre-mRNA splicing, leading to increased GR beta expression and contributing to glucocorticoid resistance in PC cells.