Bouret Sebastien, De Seranno Sandrine, Beauvillain Jean-Claude, Prevot Vincent
Institut National de la Santé et de la Recherche Médicale Unité 422, Lille, France.
Endocrinology. 2004 Apr;145(4):1794-801. doi: 10.1210/en.2003-1468. Epub 2003 Dec 11.
In vitro studies using immortalized GT1 cells suggest that hypothalamic astrocytes employ TGFbeta(1) to directly regulate the secretion of GnRH, the neurohormone that controls sexual maturation and adult reproductive function. However, whether such astrocyte-GnRH neuron signaling occurs in vivo is not clear. In the present study, we used in situ hybridization and immunohistochemistry to determine whether astrocytes and GnRH neurons express the molecular components necessary to set in motion communication processes involving TGFbeta(1) signaling. Double-labeling experiments showed that astrocytes in the male rat preoptic region (POA) expressed TGFbeta(1) mRNA and that GnRH perikarya were often found in close association with TGFbeta(1) mRNA-expressing cells. In addition, GnRH neuronal cell bodies in the POA expressed both type II TGFbeta receptors (TGFbeta-RII), which selectively bind TGFbeta, and Smad2/3, one of the primary transducers of TGFbeta signaling, suggesting that they are fully capable of responding directly to TGFbeta(1) stimulation. Consistent with this hypothesis, incubation of POA explants with TGFbeta(1) caused a significant, dose-dependent decrease in GnRH mRNA expression in individual neurons. This effect was observed within 1 h after TGFbeta(1)-treatment and was inhibited by addition of the soluble form of TGFbeta-RII to the incubation medium. In contrast, whereas both TGFbeta(1) and TGFbeta-RII mRNAs were abundantly expressed in both glial cells and capillaries in the median eminence, the projection field of GnRH neurons, TGFbeta-RII immunoreactivity was mainly restricted to the processes of tanycytes and did not colocalize with GnRH-immunoreactive fibers. This observation supports previous in vivo studies showing that TGFbeta(1) is unable to directly modulate decapeptide release from GnRH nerve terminals. Thus, astrocyte-derived TGFbeta(1) may directly influence GnRH expression and/or secretion in vivo by acting on the perikarya, but not the terminals, of GnRH neurons.
使用永生化GT1细胞进行的体外研究表明，下丘脑星形胶质细胞利用转化生长因子β1（TGFβ(1)）直接调节促性腺激素释放激素（GnRH）的分泌，GnRH是一种控制性成熟和成年生殖功能的神经激素。然而，这种星形胶质细胞 - GnRH神经元信号传导在体内是否发生尚不清楚。在本研究中，我们使用原位杂交和免疫组织化学来确定星形胶质细胞和GnRH神经元是否表达启动涉及TGFβ(1)信号传导的通信过程所需的分子成分。双标记实验表明，雄性大鼠视前区（POA）的星形胶质细胞表达TGFβ(1) mRNA，并且经常发现GnRH核周体与表达TGFβ(1) mRNA的细胞紧密相连。此外，POA中的GnRH神经元细胞体表达II型TGFβ受体（TGFβ-RII），其选择性结合TGFβ，以及Smad2/3，TGFβ信号传导的主要转导分子之一，表明它们完全能够直接响应TGFβ(1)刺激。与此假设一致，用TGFβ(1)孵育POA外植体导致单个神经元中GnRH mRNA表达显著的剂量依赖性降低。这种效应在TGFβ(1)处理后1小时内观察到，并通过向孵育培养基中添加可溶性形式的TGFβ-RII而受到抑制。相比之下，虽然TGFβ(1)和TGFβ-RII mRNA在GnRH神经元的投射区域即正中隆起的神经胶质细胞和毛细血管中均大量表达，但TGFβ-RII免疫反应性主要局限于伸长细胞的突起，并且不与GnRH免疫反应性纤维共定位。这一观察结果支持了先前的体内研究，表明TGFβ(1)无法直接调节GnRH神经末梢的十肽释放。因此，星形胶质细胞衍生的TGFβ(1)可能通过作用于GnRH神经元的核周体而非终末，在体内直接影响GnRH的表达和/或分泌。
