Early Activation of Experience-Independent Dendritic Spine Turnover in a Mouse Model of Alzheimer's Disease.

Synaptic loss is critical in Alzheimer's disease (AD), but the dynamics of synapse turnover are poorly defined. We imaged dendritic spines in transgenic APPswe/PSen1∆E9 (APP/PS1) cerebral cortex. Dendritic spine turnover is increased far from plaque in aged APP/PS1 mice, and in young APP/PS1 mice prior to plaque formation. Dysregulation occurs in the presence of soluble Aβ oligomer and requires cellular prion protein (PrPC). APP/PS1 mice lack responsiveness of spine turnover to sensory stimulation. Critically, enhanced spine turnover is coupled with the loss of persistent spines starting early and continuing with age. To evaluate mechanisms of experience-independent supranormal spine turnover, we analyzed the transcriptome of young APP/PS1 mouse brain when turnover is altered but synapse density and memory are normal, and plaque and inflammation are absent. Early PrPC-dependent expression changes occur in synaptic and lipid-metabolizing genes. Thus, pathologic synaptic dysregulation underlying AD begins at a young age prior to Aβ plaque.