Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129-2060, USA.
Curr Mol Med. 2013 May;13(4):488-98. doi: 10.2174/1566524011313040003.
Inhalation anesthetic isoflurane has been reported to induce caspase activation and accumulation of β-amyloid (Aβ), however, the down-stream consequences of these effects are largely unknown. Isoflurane has also been shown to impair learning and memory, however, the up-stream mechanisms of these effects remain largely to be determined. Facilitation of synaptic NMDA receptor endocytosis can reduce synaptic function, leading to learning and memory impairment. We therefore set out to determine the effects of isoflurane on synaptic NMDA receptor endocytosis. Primary neurons from wild-type and Alzheimer's disease transgenic mice were treated with 2% isoflurane for six hours. Synaptic surface levels of NMDA receptor 2B (NR2B) and NR2B internalization were determined by surface and cleavable biotinylation assay, western blot analysis and immunofluorescence. Here we show that isoflurane can induce caspase-3 activation, increase levels of β-site amyloid precursor protein-cleaving enzyme and cause accumulation of Aβ in the primary neurons. Isoflurane facilitates synaptic NR2B endocytosis as evidenced by reducing surface NR2B levels, increasing NR2B internalization, and decreasing the ratio of synaptic surface NR2B to synapsin in mice primary neurons. Moreover, caspase activation inhibitor Z-VAD and γ-secretase inhibitor L-685,458 attenuated the isoflurane-facilitated NR2B endocytosis. These results suggest that isoflurane induces caspase activation and Aβ accumulation, leading to facilitation of synaptic NMDA receptor endocytosis, which potentially serve as the upstream mechanism of the isoflurane-induced impairment of learning and memory. These findings will encourage further studies to determine the underlying mechanism by which isoflurane and other anesthetics promote Alzheimer's disease neuropathogenesis and induce cognitive dysfunction.
吸入麻醉剂异氟醚已被报道可诱导半胱天冬酶的激活和β-淀粉样蛋白（Aβ）的积累，然而，这些影响的下游后果在很大程度上尚不清楚。异氟醚也已被证明可损害学习和记忆，然而，这些影响的上游机制在很大程度上仍有待确定。促进突触 NMDA 受体内吞作用可降低突触功能，导致学习和记忆损伤。因此，我们着手确定异氟醚对突触 NMDA 受体内吞作用的影响。用 2%异氟醚处理野生型和阿尔茨海默病转基因小鼠的原代神经元 6 小时。通过表面和可裂解生物素化测定、Western blot 分析和免疫荧光测定来确定 NMDA 受体 2B（NR2B）的突触表面水平和 NR2B 内化。在这里，我们表明异氟醚可以诱导半胱天冬酶-3 的激活，增加β-位淀粉样前体蛋白裂解酶的水平，并导致原代神经元中 Aβ的积累。异氟醚促进突触 NR2B 内吞作用，表现为减少表面 NR2B 水平、增加 NR2B 内化以及降低小鼠原代神经元中突触表面 NR2B 与突触素的比值。此外，半胱天冬酶激活抑制剂 Z-VAD 和 γ-分泌酶抑制剂 L-685,458 减弱了异氟醚促进的 NR2B 内吞作用。这些结果表明，异氟醚诱导半胱天冬酶的激活和 Aβ的积累，导致突触 NMDA 受体内吞作用的促进，这可能是异氟醚诱导学习和记忆损伤的上游机制。这些发现将鼓励进一步研究，以确定异氟醚和其他麻醉剂促进阿尔茨海默病神经病变发生和诱导认知功能障碍的潜在机制。
