Enriched environment mitigates cognitive impairment in pre-adolescent mice following repeated neonatal sevoflurane exposure by reducing TTBK1 expression and Tau phosphorylation

Abstract

Enriched environment (EE) is a living setting that provides visual, olfactory, tactile, and cognitive stimulation and has demonstrated potential treatment results in neurodevelopmental diseases. We aimed to elucidate whether the neurodevelopmental toxicity of sevoflurane is linked to TTBK1 and Tau phosphorylation, as well as to evaluate the neuroprotective mechanism of EE on mice following sevoflurane exposure. Female mice were anesthetized at postnatal day 6 (P6) or P60 with 3% sevoflurane for 2 h daily for three days. P6 mice received intraperitoneal injections of the TTBK1 inhibitor WHI-180 before anesthesia. The EE exposure was 2 h daily from P9 to P29. Cognitive function was assessed using the Morris water maze and novel object recognition tests. Hippocampal and cerebral cortical tissues were collected to measure levels of TTBK1, Tau-PS422, AT8, T22, and total Tau. Co-localization of TTBK1 and Tau-PS422 was identified via immunofluorescence. The dendritic spine count and shape classification were analyzed by Golgi staining. The results indicated elevated levels of TTBK1, phosphorylated Tau-PS422, and AT8 in neonatal mice compared to adults. Sevoflurane increased the levels of TTBK1 and Tau phosphorylation, causing cognitive impairment. Both TTBK1 inhibitor and EE reversed the sevoflurane-induced increase in TTBK1 and phosphorylated Tau levels, decrease in dendritic spine density and maturity, and cognitive impairment. In conclusion, the overexpression of TTBK1 and phosphorylated Tau in neonatal mice brain contributed to cognitive dysfunction after repeated sevoflurane anesthesia. EE played a cerebro-protective role by inhibiting the TTBK1/Tau pathway and promoting the development of dendritic spines after sevoflurane anesthesia.

Keywords: Cognitive impairment; Developing brain; Enriched environment; Sevoflurane; TTBK1; Tau phosphorylation.