D-Serine and Serine Racemase Are Associated with PSD-95 and Glutamatergic Synapse Stability.
D-Serine and Serine Racemase Are Associated with PSD-95 and Glutamatergic Synapse Stability.
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DOI：
10.3389/fncel.2016.00034
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发表时间：
2016
影响因子：
5.3
通讯作者：
Lynch DR
中科院分区：
文献类型：
--
作者：
Lin H;Jacobi AA;Anderson SA;Lynch DR
D-丝氨酸是突触 NMDA 受体 (NMDAR) 甘氨酸位点的内源性共激动剂，由丝氨酸消旋酶 (SR) 通过 L-丝氨酸转化合成。它对于突触可塑性至关重要，并与精神分裂症有关。我们之前的研究表明，缺乏 α7 烟碱乙酰胆碱受体的皮质神经元中 SR、D-丝氨酸反应性突触 NMDAR 和谷氨酸突触发生特异性缺失，从而促进发育过程中谷氨酸突触的形成和成熟。因此，我们假设 D-丝氨酸和 SR (D-丝氨酸/SR) 与谷氨酸能突触发育有关。通过对皮质神经元培养物的形态学和分子研究，我们证明 D-丝氨酸/SR 与突触后神经元中的 PSD-95 和 NMDAR 以及突触发育过程中的谷氨酸突触稳定性相关。在培养的皮质神经元的谷氨酸能突触中，内源性 D-丝氨酸和 SR 与 PSD-95 共定位，但不与突触前囊泡谷氨酸转运蛋白 1 (VGLUT1) 共定位。皮质神经元培养物中的低密度星形胶质细胞缺乏 SR 表达，但在大囊泡样结构中含有丰富的 D-丝氨酸，表明 D-丝氨酸可能在突触后神经元中合成并储存在星形胶质细胞中。更有趣的是，在突触发育早期和晚期，内源性 D-丝氨酸和 SR 与 PSD-95 共定位于谷氨酸能突触的突触后末端，这表明 D-丝氨酸/SR 参与谷氨酸能突触发育。外源性应用 D-丝氨酸增强 SR 与 PSD-95 和 NR1 的相互作用，并增加 VGLUT1 和 PSD-95 阳性谷氨酸突触的数量，表明外源性 D-丝氨酸增强突触后 SR/PSD-95 信号传导并稳定皮质突触发育过程中的谷氨酸突触。这一过程被 NMDAR 拮抗剂 2-氨基-5-膦酰戊酸 (AP5) 和 7-氯犬尿酸 (7-CK)（NMDAR 甘氨酸位点的特异性拮抗剂）阻断，表明 D-丝氨酸效应是通过突触后 NMDAR 介导的。相反，外源性应用甘氨酸则没有这样的作用，这表明调节突触后事件的是 D-丝氨酸，而不是甘氨酸。总而言之，我们的研究结果表明，D-丝氨酸/SR 与突触后神经元中的 PSD-95 和 NMDAR 以及突触发育过程中的谷氨酸突触稳定性相关，表明 D-丝氨酸/SR 作为皮质突触和回路发育的调节剂。
D-serine is an endogenous coagonist at the glycine site of synaptic NMDA receptors (NMDARs), synthesized by serine racemase (SR) through conversion of L-serine. It is crucial for synaptic plasticity and is implicated in schizophrenia. Our previous studies demonstrated specific loss of SR, D-serine-responsive synaptic NMDARs, and glutamatergic synapses in cortical neurons lacking α7 nicotinic acetylcholine receptors, which promotes glutamatergic synapse formation and maturation during development. We thus hypothesize that D-serine and SR (D-serine/SR) are associated with glutamatergic synaptic development. Using morphological and molecular studies in cortical neuronal cultures, we demonstrate that D-serine/SR are associated with PSD-95 and NMDARs in postsynaptic neurons and with glutamatergic synapse stability during synaptic development. Endogenous D-serine and SR colocalize with PSD-95, but not presynaptic vesicular glutamate transporter 1 (VGLUT1), in glutamatergic synapses of cultured cortical neurons. Low-density astrocytes in cortical neuronal cultures lack SR expression but contain enriched D-serine in large vesicle-like structures, suggesting possible synthesis of D-serine in postsynaptic neurons and storage in astrocytes. More interestingly, endogenous D-serine and SR colocalize with PSD-95 in the postsynaptic terminals of glutamatergic synapses during early and late synaptic development, implicating involvement of D-serine/SR in glutamatergic synaptic development. Exogenous application of D-serine enhances the interactions of SR with PSD-95 and NR1, and increases the number of VGLUT1- and PSD-95-positive glutamatergic synapses, suggesting that exogenous D-serine enhances postsynaptic SR/PSD-95 signaling and stabilizes glutamatergic synapses during cortical synaptic development. This is blocked by NMDAR antagonist 2-amino-5-phosphonopentanoic acid (AP5) and 7-chlorokynurenic acid (7-CK), a specific antagonist at the glycine site of NMDARs, demonstrating that D-serine effects are mediated through postsynaptic NMDARs. Conversely, exogenous application of glycine has no such effects, suggesting D-serine, rather than glycine, modulates postsynaptic events. Taken together, our findings demonstrate that D-serine/SR are associated with PSD-95 and NMDARs in postsynaptic neurons and with glutamatergic synapse stability during synaptic development, implicating D-serine/SR as regulators of cortical synaptic and circuit development.