Autophagy controls the hippocampal postsynaptic organization and affects cognition in a mouse model of Fragile X syndrome

Dysregulated spine morphology is a common feature in the pathology of many neurodevelopmental and neuropsychiatric disorders. Overabundant immature dendritic spines in the hippocampus are causally related to cognitive deficits of Fragile X syndrome (FXS), the most common form of heritable intellectual disability. Recent findings from us and others indicate autophagy plays important roles in synaptic stability and morphology, and autophagy is downregulated in FXS neurons. However, the mechanism remains unclear. In this study, we identified that activated autophagy degrades the eukaryotic initiation factor 4G1 (eIF4G1) and postsynaptic density protein-95 (PSD-95) in hippocampal neurons of Fmr1 KO mice and FXS neurons from patients, which subsequently corrected the dysregulated postsynaptic organization and actin assembly, the critical processes determining synaptic maturation and density. Centrally activating autophagy in hippocampus degrades eIF4G1 and PSD-95, restores actin dynamics, and improves cognition of Fmr1 KO mice. In human neurons derived from patients diagnosed with both FXS and intellectual disability, activating autophagy corrected the aberrant actin assembly. Thus, our findings revealed a previously unappreciated mechanism through which autophagy affects actin assembly and synaptic organization, suggesting a critical role of autophagy in regulating structural synaptic plasticity in healthy and diseased conditions.