Kramer Bianca M R, Cruijsen Peter M J M, Ouwens Debbie T W M, Coolen Marcel W, Martens Gerard J M, Roubos Eric W, Jenks Bruce G
Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences, University of Nijmegen, Nijmegen 6525 ED, The Netherlands.
Endocrinology. 2002 Apr;143(4):1337-45. doi: 10.1210/endo.143.4.8721.
We have investigated the physiological regulation and functional significance of brain-derived neurotrophic factor (BDNF) in the endocrine melanotrope cells of the pituitary pars intermedia of the amphibian Xenopus laevis, which can adapt its skin color to the light intensity of its environment. In black-adapted animals, melanotrope cells produce and release alpha-melanophore-stimulating hormone (alpha-MSH). In white-adapted animals, the activity of melanotrope cells is inhibited by neuronal input. Using Western blotting and immunocytochemistry at the light and electron microscopical level, we have detected both the BDNF precursor and the mature BDNF protein in Xenopus melanotrope cells. In situ hybridization and RT-PCR revealed the presence of BDNF mRNA in the pituitary pars intermedia, indicating that BDNF is synthesized in the melanotropes. Real-time quantitative RT-PCR showed that levels of BDNF mRNA in melanotrope cells are about 25 times higher in black- than in white-adapted animals. Although there is no difference in the amount of stored mature BDNF, the amount of BDNF precursor protein is 3.5 times higher in melanotropes of black-adapted animals than in those of white-adapted animals. These data indicate that BDNF mRNA expression and BDNF biosynthesis are up-regulated in active melanotrope cells. Because immunoelectron microscopy showed that BDNF is located in melanotrope secretory granules, BDNF is probably coreleased with alpha-MSH via the regulated secretory pathway. Superfusion and (3)H-amino acid incorporation studies demonstrated that BDNF stimulates the release of alpha-MSH and the biosynthesis of its precursor protein, POMC. Our results provide evidence that BDNF regulates the activity of Xenopus melanotrope cells in an autocrine fashion.
我们研究了脑源性神经营养因子（BDNF）在非洲爪蟾垂体中间叶内分泌黑素细胞中的生理调节及其功能意义，非洲爪蟾能够使其皮肤颜色适应环境的光照强度。在适应黑色环境的动物中，黑素细胞产生并释放α-促黑素细胞激素（α-MSH）。在适应白色环境的动物中，黑素细胞的活性受到神经输入的抑制。我们利用蛋白质免疫印迹法以及光镜和电镜水平的免疫细胞化学方法，在爪蟾黑素细胞中检测到了BDNF前体和成熟的BDNF蛋白。原位杂交和逆转录-聚合酶链反应（RT-PCR）显示垂体中间叶存在BDNF信使核糖核酸（mRNA），表明BDNF是在黑素细胞中合成的。实时定量RT-PCR结果显示，适应黑色环境的动物黑素细胞中BDNF mRNA水平比适应白色环境的动物高约25倍。虽然储存的成熟BDNF量没有差异，但适应黑色环境的动物黑素细胞中BDNF前体蛋白的量比适应白色环境的动物高3.5倍。这些数据表明，在活跃的黑素细胞中BDNF mRNA表达和BDNF生物合成上调。因为免疫电镜显示BDNF位于黑素细胞分泌颗粒中，BDNF可能通过调节性分泌途径与α-MSH共同释放。灌流和（3）H-氨基酸掺入研究表明，BDNF刺激α-MSH的释放及其前体蛋白阿黑皮素原（POMC）的生物合成。我们的结果提供了证据，证明BDNF以自分泌方式调节爪蟾黑素细胞的活性。
