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相同的性质。它在大脑中具有不均匀的区域分布，是一个神经元生物合成途径，在去极化时依赖Ca++释放，并由神经元l -脯氨酸转运体PROT介导的高亲和力摄取，有望控制l -脯氨酸的细胞外水平。然而，没有证据表明中枢神经系统中存在特异性的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，我们产生了一个PROT敲除小鼠系。这些小鼠在焦虑样、运动活动和感觉运动门控范式方面表现出行为差异。此外，还发现了谷氨酸能神经传递突触成分表达水平的改变，从而表明l -脯氨酸和PROT在大脑中都具有重要的神经调节功能。本研究项目的目标是进一步了解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的影响分析；(2)评估PROT−/−小鼠的新行为差异；(3)通过电生理分析证实PROT在谷氨酸能神经传递中的神经调节作用；(4)表征神经元中PROT的细胞定位、转运和功能调节。

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.