The Alzheimer multifactorial therapeutic agent E2F4DN prevents long‐term potentiation and cognitive loss and improves neuronal survival in homozygous 5xFAD mice

Abstract

AbstractBackgroundDespite many decades of work, we still lack effective therapies against Alzheimer’s disease (AD), likely due to its complex etiology, which requires a multifactorial therapeutic approach. Among the variety of proposed etiological factors, synaptic failure has proof to be an early hallmarks of AD (Nat. Neurosci. 2016;19:443‐453), which precedes neuronal‐death (J. Neurosci. 2006;26:10129‐10140). We have recently shown, using both transgenic mice and gene therapy, that E2F4 is a multifactorial therapeutic target against AD (Neurotherapeutics 2021;18:2484‐2503, Mol. Neurobiol. 2022;59:3016‐3039), likely due to its homeostatic function (Int. J. Mol. Sci. 2022;23:12093). The phosphorylation of two conserved Thr residues of E2F4 is necessary to induce cognitive loss in AD (Neurotherapeutics 2021;18:2484‐2503). Therefore, we have developed a novel therapy consisting in neuronal expression of a dominant negative form of E2F4 (E2F4DN), which cannot be phosphorylated in the conserved Thr residues (Neurotherapeutics 2021;18:2484‐2503, Mol. Neurobiol. 2022;59:3016‐3039). In this work we wanted to verify whether the expression of E2F4DN could correct AD‐associated synaptic dysfunction and neuronal loss in 5xFAD mice, a known mouse model of AD.MethodWe expressed E2F4DN (intravenous administration of AAV‐E2F4DN) in 6 weeks old control and homozygous 5xFAD mice, and stereological, electrophysiological and behavioral studies were performed at 6 months. Cell counting was achieved by unbiased stereology in the CA1 hippocampal region. Cognition was analyzed through novel‐object location and contextual fear conditioning test. Synaptic function (basal synaptic transmission, presynaptic function and long‐term potentiation (LTP)) were measured by electrophysiological recordings of field excitatory postsynaptic potentials in hippocampal CA3‐CA1 synapses. Afterwards, the mechanism underlying memory recovery was evaluated analyzing protein levels of different subunits of the synaptic receptors AMPA and NMDA.ResultE2F4DN expression in neurons prevents neuronal death in the hippocampus (CA1) of homozygous 5xFAD mice, reaching similar values of cell number and CA1 volume to those observed in control mice. Moreover, E2F4DN prevents LTP loss leading to cognitive improvement, as 5xFAD mice treated with our therapy present a noticeable improvement hippocampal‐dependent memory. This effect correlates with the increase of key LTP regulators.ConclusionE2F4‐Based Gene Therapy improves neuronal survival, LTP and cognition, being a safe multifactorial approach for AD treatment.