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.