Neuron‐Targeted Caveolin‐1 Gene Therapy Preserves Cognitive Function and Synaptic Plasticity in a Mouse Model of Alzheimer's Disease (AD)

Abstract

Introduction Alzheimer's disease (AD) is a devastating neurodegenerative condition. AD patients develop severe cognitive deficits, which are closely correlated with loss of synapses and decreased plasticity. Caveolin-1 (Cav-1), a scaffolding protein within the microdomains of membrane/lipid rafts (MLRs), organizes signaling complexes that promote functional neuronal and synaptic plasticity. Previously we showed that neuron-targeted overexpression of Cav-1 using a synapsin promoter (SynCav1) promotes neuroplasticity, increases synaptic plasticity, and improves memory in aged mice. The current study investigated the impact of SynCav-1 on markers of synaptic plasticity and cognitive function in an APPSwePS1d9 mouse model of AD. Methods AAV9-SynRFP (red fluorescent protein) or AAV9-SynCav1 was delivered into the hippocampus of wild type (WT) or AD mice at 2.5 months of age. At 9 months, open field and fear conditioning test were used to evaluate learning and memory performance. After behavior tests, animal were sacrificed for immunoblot (IB) and immunofluorence microscopy (IF). Electron microscopy (EM) was used to observe the ultrastructure morphology. Results AD-SynRFP mice exhibited significant decreased fear learning (day 1) compared to WT-SynRFP mice and AD-SynCav1 mice. In contrast, AD-SynCav1 mice showed preserved fear learning (day 1), and improved contextual and cued memory recall (day 2 & 3). Both IB and IF showed decreased Cav-1 expression in 9 month-old AD-SynRFP mice. AD-SynCav1 mice showed preserved Cav-1 levels and increased expression of neuroplasticity markers (TrkB, MAP2) compared to AD-SynRFP mice. IB analysis of MLR (buoyant fractions 4 & 5) demonstrate decreased MLR-localization of TrkB, Cav-1, CT-B, synaptophysin, TrkA, PSD95, LRP in AD-SynRFP mice. In contrast, AD-SynCav1 exhibited preserved MLR-localization of TrkB, Cav-1, CT-B, synaptophysin, TrkA, PSD95 and LRP1. IF showed preserved markers of dendritic integrity (MAP2) in AD-SynCav1 mice. EM analysis of the hippocampus revealed that AD-SynRFP mice had fewer type I excitatory synapses and decreased number of presynaptic vesicles per axonal bouton, and altered spine morphology (reduced spine length and increased spine neck diameter) in CA1 apical dendrites within the stratum radiatum, which were not exhibited by AD-SynCav1 mice. Additional analysis revealed preserved myelinated Schaffer collateral axons in AD-SynCav1 mice compared to AD-SynRFP. Conclusion SynCav1 gene delivery to the hippocampus of pre-symptomatic adult AD mice (2.5 m) preserves fear learning, improves memory, and preserves ultrastructural indicators of synaptic plasticity and myelination in mild symptomatic AD mice (9 months), therefore may serve as a novel gene therapy to restore synaptic and neuroplasticity and improve brain function in individuals afflicted with Alzheimer's disease. Support or Funding Information Veterans Affairs Merit Award from the Department of Veterans Affairs BX003671 (B. P. Head), National Institutes of Health, Bethesda, MD, U.S.A., NS073653 (B. P. Head); GM085179 (P. M. Patel). (A) AD - SynRFP at 2.5 months of age exhibited learning deficits on acquisition Day 1 training compared to both WT -SynRFP and AD -SynCav1 at 9 months of age. There was no significant difference between WT - SynRFP versus AD-SynCav1. SynCav1 delivery to AD mice significantly improved hippocampal-dependent contextual memory recall on Day 2 (B) and hippocampal-independent cued memory recall on Day 3 (C). Data are presented as mean ± SEM. Significance was assumed when p < 0.05. IF microscopy revealed that, in 9 month-old age, AD-SynRFP exhibited decreased in hippocampal Cav-1 expression compared to WT-SynRFP, while SynCav1 gene delivery preserved Cav-1 expression. Scale bar = 50 mm. IB analysis of MLR fractions (buoyant fractions 4 & 5) demonstrates decreased MLR-localization of full length TrkB, Cav-1, CT-B, synaptophysin, TrkA, LRP1 in AD-SynRFP mice; while SynCav1 treatment preserve MLR-localized synaptic proteins. CA1 distal apical dendrites in the stratum radiatum were examined for ultrastructure changes of type I asymmetric synapses and presynaptic vesicles (PSVs)/axonal bouton. SynCav1 preserves total number of synapses and PSVs in the hippocampus of 9 month old AD mice. CA1 distal apical dendrites in the stratum radiatum were examined for alterations in dendritic spine morphology, i.e., spine length (mm), spine neck diameter (mm), and spine area (mm2). SynCav1 preserves dendritic spine morphology in the hippocampus of 9 month old APPSwePS1d9 mice. G ratio analysis (axon lumen diameter (Di)/fiber (axon lumen + myelin) diameter (Do)) was used to measure changes in axonal myelin fiber content of CA3 Schaffer collaterals innervating the CA1 apical dendritic arbor. SynCav1 preserves axonal myelin fiber content of hippocampal CA3 Schaffer collaterals in 9 month old APPSwePS1d9 mice. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.