Pazarlar Burcu Azak, Egilmez Cansu Bilister, Oyar Eser Öz, Mikkelsen Jens D
Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.
Neurobiology Research Unit, University Hospital Copenhagen, Rigshospitalet, Copenhagen, Denmark.
Synapse. 2025 May;79(3):e70018. doi: 10.1002/syn.70018.
AIM/HYPOTHESIS: Diabetes mellitus has been reported to be a risk factor for cognitive dysfunction, depression, stroke, and seizures. Diabetic pathology is believed to interfere with synaptic plasticity. Synaptic vesicle glycoprotein 2A (SV2A) is a presynaptic vesicular protein and a popular synaptic density imaging marker. We investigated the effect of chronic hyperglycemia on the expression of SV2A in the cerebral cortex and hippocampus of rats and compared it to other presynaptic markers, such as GAP43, Synaptotagmin-1, and SNAP25.
A single dose of streptozotocin (STZ, 45 mg/kg, i.p.) was administered to adult male rats, resulting in sustained hyperglycemia and reduced plasma insulin levels. Controls were injected with saline, and another STZ group was treated with insulin. Fasting blood glucose (FBG) and fasting plasma insulin (FPI) levels were monitored throughout the observation period, and the level of SV2A was determined by radioligand, [H]UCB-J, binding capacity using in-vitro autoradiography and by ELISA. Similarly, the tissue concentration of other synaptic proteins GAP43, SNAP25, and SYN1 was measured using ELISA. Quantitative RT-qPCR was performed to measure Sv2a, Sv2b, and Sv2c transcripts. Finally, hippocampal and cortical glutamate levels were measured in all tissues.
[H]UCB-J binding, SV2A (pg/mg protein) and Sv2a mRNA levels were significantly higher in hyperglycemic rats. The SV2A concentration detected by ELISA and [H]UCB-J binding showed, as expected, a positive correlation with each other. The same positive and significant correlation was seen between SV2A, FBG, and glutamate l levels across animals (p ≤ 0.001). Notably, there was no difference and no linearity between FBG and other presynaptic markers such as GAP43, Synaptotagmin-1, and SNAP25.
Unlike other synaptic markers (e.g., SNAP25, SYN-1), SV2A levels rise independently of synaptic density, correlating with elevated glutamate and metabolic activity. These findings raise doubt about SV2A's role as a pure synaptic density marker.
目的/假设：据报道，糖尿病是认知功能障碍、抑郁症、中风和癫痫发作的一个风险因素。糖尿病病理被认为会干扰突触可塑性。突触囊泡糖蛋白2A（SV2A）是一种突触前囊泡蛋白，也是一种常用的突触密度成像标志物。我们研究了慢性高血糖对大鼠大脑皮层和海马体中SV2A表达的影响，并将其与其他突触前标志物（如GAP43、突触结合蛋白-1和SNAP25）进行比较。
给成年雄性大鼠单次腹腔注射链脲佐菌素（STZ，45mg/kg），导致持续性高血糖和血浆胰岛素水平降低。对照组注射生理盐水，另一个STZ组用胰岛素治疗。在整个观察期内监测空腹血糖（FBG）和空腹血浆胰岛素（FPI）水平，并通过放射性配体[H]UCB-J结合能力，采用体外放射自显影和酶联免疫吸附测定法（ELISA）测定SV2A水平。同样，使用ELISA测量其他突触蛋白GAP43、SNAP25和SYN1的组织浓度。进行定量逆转录-定量聚合酶链反应（RT-qPCR）以测量Sv2a、Sv2b和Sv2c转录本。最后，测量所有组织中海马体和皮层的谷氨酸水平。
高血糖大鼠的[H]UCB-J结合、SV2A（pg/mg蛋白）和Sv2a mRNA水平显著更高。如预期的那样，ELISA检测到的SV2A浓度与[H]UCB-J结合呈正相关。在所有动物中，SV2A、FBG和谷氨酸水平之间也呈现相同的正相关且具有显著性（p≤0.001）。值得注意的是，FBG与其他突触前标志物（如GAP43、突触结合蛋白-1和SNAP25）之间没有差异，也不存在线性关系。
与其他突触标志物（如SNAP25、SYN-1）不同，SV2A水平的升高与突触密度无关，而是与谷氨酸水平升高和代谢活性相关。这些发现对SV2A作为一种纯粹的突触密度标志物的作用提出了质疑。
