Shen Hong, Smith David E, Keep Richard F, Xiang Jianming, Brosius Frank C
Department of Pharmaceutical Sciences, College of Pharmacy, the University of Michigan, Ann Arbor, Michigan 48109, USA.
J Biol Chem. 2003 Feb 14;278(7):4786-91. doi: 10.1074/jbc.M207397200. Epub 2002 Dec 6.
The presence of multiple oligopeptide transporters in brain has generated considerable interest as to their physiological role in neuropeptide homeostasis, pharmacologic importance, and potential as a target for drug delivery through the blood-brain and blood-cerebrospinal fluid barriers. To understand further the purpose of specific peptide transporters in brain, we have generated PEPT2-deficient mice by targeted gene disruption. Homozygous PepT2 null mice lacked expression of PEPT2 mRNA and protein in choroid plexus and kidney, tissues in which PepT2 is normally expressed, whereas heterozygous mice displayed PepT2 expression levels that were intermediate between those of wild-type and homozygous null animals. Mutant PepT2 null mice were found to be viable, grew to normal size and weight, and were without obvious kidney or brain abnormalities. Notwithstanding the lack of apparent biological effects, the proton-stimulated uptake of 1.9 microm glycylsarcosine (a model, hydrolysis-resistant dipeptide) in isolated choroid plexus was essentially ablated (i.e. residual activity of 10.9 and 3.9% at 5 and 30 min, respectively). These novel findings provide strong evidence that, under the experimental conditions of this study, PEPT2 is the primary member of the peptide transporter family responsible for dipeptide uptake in choroid plexus tissue.
大脑中多种寡肽转运体的存在引发了人们对其在神经肽稳态中的生理作用、药理学重要性以及作为通过血脑屏障和血脑脊液屏障进行药物递送靶点的潜力的浓厚兴趣。为了进一步了解大脑中特定肽转运体的作用，我们通过靶向基因敲除构建了PEPT2基因缺陷小鼠。纯合子PepT2基因敲除小鼠在脉络丛和肾脏（正常表达PepT2的组织）中缺乏PEPT2 mRNA和蛋白质的表达，而杂合子小鼠的PepT2表达水平介于野生型和纯合子基因敲除动物之间。发现突变的PepT2基因敲除小鼠能够存活，生长至正常大小和体重，且无明显的肾脏或脑部异常。尽管缺乏明显的生物学效应，但在分离的脉络丛中，1.9微摩尔甘氨酰肌氨酸（一种耐水解的二肽模型）的质子刺激摄取基本被消除（即分别在5分钟和30分钟时残留活性为10.9%和3.9%）。这些新发现提供了强有力的证据，即在本研究的实验条件下，PEPT2是肽转运体家族中负责脉络丛组织中二肽摄取的主要成员。
