L-proline and glutamatergic neurotransmission: clarifying the modulatory role of neuronal proline transporter in cognition.

L-脯氨酸与神经递质有几种共同的特性。它在脑内具有异质性的区域分布，是神经元的生物合成途径，在去极化时依赖于钙离子的释放，并由神经元L-Pro转运体Prot介导的高亲和力摄取，有望控制细胞外L-Pro的水平。然而，目前还没有证据表明中枢神经系统存在特定的L-脯氨酸受体。因此，L-脯氨酸和Prot在神经传递中的作用尚不清楚。为了确定Prot在体内的作用，我们建立了一个Prot基因敲除的小鼠系。这些小鼠在类焦虑、运动活动和感觉运动门控范例上表现出不同的行为。此外，谷氨酸能神经传递的突触成分的表达水平也发生了变化，这表明L在脑内具有重要的神经调节功能--Pro和Prot。这项研究的目的是更深入地了解Prot在中枢神经系统中的具体功能作用，以及调节其表达和功能的机制。为此，我们将：(1)扩展Prot基因缺失对突触蛋白表达影响的分析；(2)评估Prot−/−小鼠新的行为差异；(3)通过电生理学分析确认Prot在谷氨酸能神经传递中的神经调节作用；(4)表征Prot在神经元中的细胞定位、运输和功能调节。

L-proline shares several properties with neurotransmitters. It has heterogeneous regional distribution in brain, a neuronal biosynthetic pathway, Ca++ dependent release upon depolarization, and high-affinity uptake mediated by the neuronal L-proline transporter PROT, which is expected to control extracellular levels of L-proline. However, no evidence exists for specific L-proline receptors in the CNS. Hence, the roles of L-proline and PROT in neurotransmission remain unknown. To determine the in vivo role of PROT, we have generated a PROT knock-out mouse line. These mice show behavioral differences in anxiety-like, locomotor activity and sensorimotor gating paradigms. In addition, alterations in expression levels of synaptic components of glutamatergic neurotransmission have been also identified, thus suggesting an important neuromodulator function in brain both for L-proline and PROT. The goal of this research project is to gain more insight into the specific functional roles of PROT in the CNS and into mechanisms that regulate its expression and functionality. Toward this goal, we will: (1) extend the analysis on the effects of PROT gene deletion on synaptic protein expression; (2) assess new behavioral differences in PROT−/− mice; (3) confirm the neuromodulator role of PROT in glutamatergic neurotransmission by electrophysiological analysis; (4) characterize the cellular localization, trafficking and function modulation of PROT in neurons.