Sevoflurane-induced disruption of critical period Arc signaling drives aberrant microglial synaptic pruning and cognitive deficits.

Early-life sevoflurane exposure is associated with long-term cognitive deficits. Given that hippocampal development relies on precise critical windows, disruption of developmental processes during these periods is likely the origin of these impairments. However, the molecular mechanisms underlying sevoflurane-induced perturbations during critical development periods and their progression to lasting cognitive dysfunction remain elusive. Here, we determined that the first three postnatal weeks are a critical window of vulnerability to early-life sevoflurane exposure. Mechanistically, sevoflurane exposure suppressed the physiological upregulation of activity-regulated cytoskeleton-associated protein (Arc; also known as Arg3.1) during the critical period of hippocampal development, a process driven by glycogen synthase kinase-3 beta (GSK3β)-mediated protein degradation. We demonstrated that transient suppression of Arc via hippocampal injection of Arc antisense oligonucleotide (ASO) during the third postnatal week was sufficient to recapitulate the sevoflurane-induced phenotype, impairing microglial synaptic pruning and causing initial synaptic redundancy. This early pathology subsequently evolved into aberrant microglial phagocytic activation in adolescence and adulthood, resulting in excessive synaptic loss and cognitive deficits. Crucially, restoration of Arc expression specifically during this critical period using a doxycycline (Dox)-inducible Tet-On system successfully reversed this pathological pruning trajectory and prevented long-term cognitive impairment. Our findings highlight that Arc upregulation during this critical period is essential for microglial function and synaptic homeostasis, establishing Arc as a time-sensitive therapeutic target for preventing the developmental neurotoxicity associated with pediatric anesthesia. This diagram illustrates the role of the Arc protein in microglial synaptic pruning and cognitive development under physiological conditions (upper panel, blue; Arc is highly expressed during the critical period) and sevoflurane exposure (lower panel, red; Arc expression during the critical period is downregulated). Under normal conditions, Arc is expressed during the critical period and is localized to synapses, where it facilitates the tagging of redundant synapses for elimination. Synaptic pruning peaks during the critical period, followed by further refinement during adolescence, leading to mature cognitive function in adulthood. Neonatal sevoflurane exposure leads to aberrant activation of GSK3β during the critical period. This promotes Arc degradation, thereby disrupting its synaptic localization. This leads to microglial dysfunction in terms of synaptic engulfment. In adolescence, this disruption leads to excessive microglial phagocytosis and significant synaptic loss, ultimately resulting in cognitive deficits. Graphical elements: GSK3β, green circles; Arc, orange circles; phosphorylation site, pale yellow circle containing the letter "P"; C1q, yellow umbrella shapes.