Sanz Carmen, Roncero Isabel, Vázquez Patricia, Navas M Angeles, Blázquez Enrique
Department of Biochemistry and Molecular Biology, Faculty of Medicine, Complutense University, Madrid, Spain.
J Endocrinol. 2007 May;193(2):259-67. doi: 10.1677/JOE-06-0146.
In an attempt to study the role of glucokinase (GK) and the effects of glucose and peptides on GK gene expression and on the activity of this enzyme in the hypothalamus, we used two kinds of biological models: hypothalamic GT1-7 cells and rat hypothalamic slices. The expression of the GK gene in GT1-7 cells was reduced by insulin (INS) and was not modified by different glucose concentrations, while GK enzyme activities were significantly reduced by the different peptides. Interestingly, a distinctive pattern of GK activities between the ventromedial hypothalamus (VMH) and lateral hypothalamus (LH) were found, with higher enzyme activities in the VMH as the glucose concentrations rose, while LH enzyme activities decreased at 2.8 and 20 mM glucose, the latter effect being prevented by incubation with INS. These effects were produced only by d-glucose and the modifications found were due to GK, but not to other hexokinases. In addition, GK activities in the VMH and the LH were reduced by glucagon-like peptide 1, leptin, orexin B, INS, and neuropeptide Y (NPY), but this effect was only statistically significant for NPY in LH. Our results indicate that the effects of both glucose and peptides occur on GK enzyme activities rather than on GK gene transcription. Moreover, the effects of glucose and INS on GK activity suggest that in the brain GK behaves in a manner opposite to that in the liver, which might facilitate its role in glucose sensing. Finally, hypothalamic slices seem to offer a good physiological model to discriminate the effects between different areas.
为了研究葡萄糖激酶（GK）的作用以及葡萄糖和肽对下丘脑GK基因表达和该酶活性的影响，我们使用了两种生物学模型：下丘脑GT1-7细胞和大鼠下丘脑切片。GT1-7细胞中GK基因的表达受胰岛素（INS）抑制，不受不同葡萄糖浓度的影响，而不同的肽可显著降低GK酶活性。有趣的是，发现腹内侧下丘脑（VMH）和外侧下丘脑（LH）之间的GK活性存在独特模式，随着葡萄糖浓度升高，VMH中的酶活性升高，而在2.8和20 mM葡萄糖时LH酶活性降低，INS孵育可防止后一种效应。这些效应仅由d-葡萄糖产生，发现的变化是由于GK，而非其他己糖激酶。此外，胰高血糖素样肽1、瘦素、食欲素B、INS和神经肽Y（NPY）可降低VMH和LH中的GK活性，但这种效应仅在LH中对NPY具有统计学意义。我们的结果表明，葡萄糖和肽的作用均发生在GK酶活性上，而非GK基因转录上。此外，葡萄糖和INS对GK活性的影响表明，在脑中GK的行为方式与肝脏相反，这可能有助于其在葡萄糖感知中的作用。最后，下丘脑切片似乎提供了一个很好的生理学模型来区分不同区域之间的影响。
