E2F4DN‐based gene therapy recovers long‐term potentiation and hippocampal‐dependent memory in homozygous 5xFAD mice

Abstract

AbstractBackgroundNeuronal cell‐cycle reentry, followed by DNA duplication (tetraploidization), precedes and recapitulates Alzheimer´s disease (AD) neuropathological hallmarks (Arendt et al., 2010; López‐Sánchez et al., 2017). E2F4 is expressed by neurons and becomes phosphorylated in APP/PS1 mice and in Alzheimer patients. We have demonstrated that the phosphorylation of two conserved Thr residues of E2F4 is necessary to induce neuronal tetraploidization and cognitive loss in AD (Lopez‐Sanchez and Frade, 2017; López‐Sánchez et al., 2017). Thus, it was developed a therapy consisting in neuronal expression of a dominant negative form of E2F4 (E2F4DN), not phosphorylatable. This therapy has been patented (US9567384B2, EP2783696B1, JP6100276B2), and is licensed by Tetraneuron. Initial stages of AD are proposed to be linked to alterations in synapse function, responsible for the cognitive deficits observed in AD (Knafo et al., 2016). Thus, we hypothesized that viral expression of E2F4DN could correct the synaptic dysfunction associated to AD.MethodHippocampal primary cultures were prepared and neurons were transduced with a viral vector containing E2F4DN. Through whole‐cell recordings spontaneous synaptic activity (sEPSC) was analyzed (control n=15, E2F4DN n=21). Afterwards E2F4DN was expressed in vivo (AAV‐E2F4DN intravenous administration) in six‐week old homozygous 5xFAD and WT mice and behavior and electrophysiology was achieved (6‐months‐old). Cognition was analyzed in not injected (n=7) and injected WT (n=5) and not injected (n=19) and injected 5xFAD (n=5) mice through novel‐object location and contextual fear conditioning test. Synaptic function was evaluated by electrophysiological recordings of field excitatory postsynaptic potential (fEPSPs) in CA3‐CA1 synapses in acute slices from WT (not injected n=10, injected n=7) and 5xFAD mice (not injected n=11, injected n=8), both basal transmission and LTP (3xTBS) was examined.ResultWe demonstrated that E2F4DN does not alter basal properties of hippocampal neurons in culture. Intravenous administration of AAV‐E2F4DN improves basal synaptic transmission and reverts LTP inhibition, observed in not injected 5xFAD mice. Furthermore, this LTP recovery leads to cognitive improvement. 5xFAD mice treated with our therapy present a notably improvement in two hippocampal‐dependent memory tasks compared to not injected 5xFAD mice.ConclusionE2F4DN‐based gene therapy represents a promising approach for AD treatment with capacity to prevent cognitive decline associated to the disease.