Boudarine Mikhail, Yegorov Oleg, Sterling-Dubrovsky Anna, Devi Lakshmi A, Berman Yemiliya
Department of Pharmacology, New York University School of Medicine, New York, New York 10016, USA.
J Pharmacol Exp Ther. 2002 Dec;303(3):1317-24. doi: 10.1124/jpet.102.037663.
Carboxypeptidase E (CPE) is involved in the biosynthesis of a number of neuropeptides including opioid peptides. A point mutation in this gene results in a loss of enzyme activity, decrease in mature neuroendocrine peptides, and development of late onset obesity as seen in Cpe(fat)/Cpe(fat) mice. In this study, we examined the processing of peptides derived from prodynorphin and proenkephalin in various brain regions of these mice during development. At 6 to 8 weeks, an age prior to the onset of obesity, levels of dynorphin peptides are decreased in all brain regions, whereas levels of ir-Met-enkephalin are differentially altered. There is an accumulation of C-terminally extended forms of all three opioid peptides in Cpe(fat)/Cpe(fat) mice, consistent with a lack of CPE activity. Thus, it appears that there is no direct correlation between the level of mature opioid peptides and the development of obesity in these mice. Since altered levels of peptides can influence the opioid receptor system, we examined the functional activity of mu and kappa opioid receptors using [35S]guanosine-5'-O-(gamma-thio)-triphosphate binding assays. We find no differences in kappa receptor activity in Cpe(fat)/Cpe(fat) compared with control littermate mice. In contrast, the mu receptor activity is differentially altered in select regions of Cpe(fat)/Cpe(fat) mice in response to a mu-specific ligand. Taken together, these results suggest that the lack of CPE activity leads to alterations in the level of opioid peptides during development and that changes in peptide levels differentially affect opioid receptor activity in vivo.
羧肽酶E（CPE）参与包括阿片肽在内的多种神经肽的生物合成。该基因的一个点突变导致酶活性丧失、成熟神经内分泌肽减少，并出现如Cpe(fat)/Cpe(fat)小鼠中所见的晚发性肥胖。在本研究中，我们检测了这些小鼠发育过程中不同脑区源自前强啡肽原和前脑啡肽原的肽段加工情况。在6至8周龄，即肥胖开始之前的年龄，所有脑区中强啡肽肽段水平均降低，而免疫反应性甲硫氨酸脑啡肽水平则有不同程度的改变。在Cpe(fat)/Cpe(fat)小鼠中，所有三种阿片肽的C末端延伸形式均有积累，这与CPE活性缺乏一致。因此，在这些小鼠中，成熟阿片肽水平与肥胖的发生之间似乎没有直接关联。由于肽段水平的改变会影响阿片受体系统，我们使用[35S]鸟苷-5'-O-(γ-硫代)-三磷酸结合试验检测了μ和κ阿片受体的功能活性。我们发现，与对照同窝小鼠相比，Cpe(fat)/Cpe(fat)小鼠的κ受体活性没有差异。相反，在Cpe(fat)/Cpe(fat)小鼠的特定脑区，μ受体活性在μ特异性配体作用下有不同程度的改变。综上所述，这些结果表明，CPE活性的缺乏导致发育过程中阿片肽水平的改变，且肽段水平的变化在体内对阿片受体活性有不同程度的影响。
