A Mutant Variant of E2F4 Triggers Multifactorial Therapeutic Effects in 5xFAD Mice.

Alzheimer's disease (AD) has a complex etiology, which requires a multifactorial approach for an efficient treatment. We have focused on E2 factor 4 (E2F4), a transcription factor that regulates cell quiescence and tissue homeostasis, controls gene networks affected in AD, and is upregulated in the brains of Alzheimer's patients and of APPswe/PS1dE9 and 5xFAD transgenic mice. E2F4 contains an evolutionarily conserved Thr-motif that, when phosphorylated, modulates its activity, thus constituting a potential target for intervention. In this study, we generated a knock-in mouse strain with neuronal expression of a mouse E2F4 variant lacking this Thr-motif (E2F4DN), which was mated with 5xFAD mice. Here, we show that neuronal expression of E2F4DN in 5xFAD mice potentiates a transcriptional program consistent with the attenuation of the immune response and brain homeostasis. This correlates with reduced microgliosis and astrogliosis, modulation of amyloid-ß peptide proteostasis, and blocking of neuronal tetraploidization. Moreover, E2F4DN prevents cognitive impairment and body weight loss, a known somatic alteration associated with AD. We also show that our finding is significant for AD, since E2F4 is expressed in cortical neurons from Alzheimer patients in association with Thr-specific phosphorylation, as evidenced by an anti-E2F4/anti-phosphoThr proximity ligation assay. We propose E2F4DN-based gene therapy as a promising multifactorial approach against AD.

E2F4-Based Gene Therapy Mitigates the Phenotype of the Alzheimer's Disease Mouse Model 5xFAD.

After decades of unfruitful work, no effective therapies are available for Alzheimer's disease (AD), likely due to its complex etiology that requires a multifactorial therapeutic approach. We have recently shown using transgenic mice that E2 factor 4 (E2F4), a transcription factor that regulates cell quiescence and tissue homeostasis, and controls gene networks affected in AD, represents a good candidate for a multifactorial targeting of AD. Here we show that the expression of a dominant negative form of human E2F4 (hE2F4DN), unable to become phosphorylated in a Thr-conserved motif known to modulate E2F4 activity, is an effective and safe AD multifactorial therapeutic agent. Neuronal expression of hE2F4DN in homozygous 5xFAD (h5xFAD) mice after systemic administration of an AAV.PHP.B-hSyn1.hE2F4DN vector reduced the production and accumulation of Aß in the hippocampus, attenuated reactive astrocytosis and microgliosis, abolished neuronal tetraploidization, and prevented cognitive impairment evaluated by Y-maze and Morris water maze, without triggering side effects. This treatment also reversed other alterations observed in h5xFAD mice such as paw-clasping behavior and body weight loss. Our results indicate that E2F4DN-based gene therapy is a promising therapeutic approach against AD.

Neurogranin Expression Is Regulated by Synaptic Activity and Promotes Synaptogenesis in Cultured Hippocampal Neurons.

Neurogranin (Ng) is a calmodulin (CaM)-binding protein that is phosphorylated by protein kinase C (PKC) and is highly enriched in the dendrites and spines of telencephalic neurons. It is proposed to be involved in regulating CaM availability in the post-synaptic environment to modulate the efficiency of excitatory synaptic transmission. There is a close relationship between Ng and cognitive performance; its expression peaks in the forebrain coinciding with maximum synaptogenic activity, and it is reduced in several conditions of impaired cognition. We studied the expression of Ng in cultured hippocampal neurons and found that both protein and mRNA levels were about 10% of that found in the adult hippocampus. Long-term blockade of NMDA receptors substantially decreased Ng expression. On the other hand, treatments that enhanced synaptic activity such as long-term bicuculline treatment or co-culture with glial cells or cholesterol increased Ng expression. Chemical long-term potentiation (cLTP) induced an initial drop of Ng, with a minimum after 15 min followed by a slow recovery during the next 2-4 h. This effect was most evident in the synaptosome-enriched fraction, thus suggesting local synthesis in dendrites. Lentiviral expression of Ng led to increased density of both excitatory and inhibitory synapses in the second and third weeks of culture. These results indicate that Ng expression is regulated by synaptic activity and that Ng promotes the synaptogenesis process. Given its relationship with cognitive function, we propose targeting of Ng expression as a promising strategy to prevent or alleviate the cognitive deficits associated with aging and neuropathological conditions.

Activity-dependent translocation of neurogranin to neuronal nuclei.

Long-term changes of synaptic plasticity depend on protein synthesis and transcription. Ng (neurogranin) is a small protein concentrated at dendrites and spines of forebrain neurons, involved in synaptic plasticity through the regulation of CaM (calmodulin)-mediated signalling. Ng presents a central IQ motif that mediates its binding to CaM and PA (phosphatidic acid) and that can be phosphorylated by PKC (protein kinase C). In the present manuscript, we report that Ng displays a strong nuclear localization when expressed in cell lines and hippocampal neurons, either alone or fused to GFP (green fluorescent protein; GFP-Ng). Furthermore, using subcellular fractionation and immunocytochemical techniques, we were able to localize endogenous Ng in the nuclei of rat forebrain neurons. Nuclear localization of Ng depends on its IQ motif and is reduced by binding to cytoplasmic CaM. Also, PKC stimulation induces a transient nuclear translocation of Ng in acute hippocampal slices. A similar translocation is observed in the neurons of the cerebral cortex and hippocampus after the induction of generalized seizures in adult rats. In summary, the results of the present study show that a fraction of rat brain Ng is localized in the neuronal nuclei and that synaptic activity regulates its translocation from the cytoplasm. The possible involvement of Ng in the regulation of intranuclear Ca2+/CaM-dependent signalling and gene expression is discussed.