Isoflurane Facilitates Synaptic NMDA Receptor Endocytosis in Mice Primary Neurons
Y. Dong, X. Wu, G. Zhang, Z. Xu, Y. Zhang, V. Gautam, D.M. Kovacs, A. Wu, Y. Yue and Z. Xie
Affiliation: Geriatric Anesthesia Research Unit, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, 149 13th St., Room 4310, Charlestown, MA 02129-2060, USA.
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 isofluranefacilitated
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.
Keywords: Alzheimer’s disease, anesthesia, cognition, endocytosis, isoflurane, NMDA
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