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BackgroundReduction of adult hippocampal neurogenesis is an early critical event in Alzheimer's disease (AD), contributing to progressive memory loss and cognitive decline. Reduced levels of the nucleoporin 153 (Nup153), a key epigenetic regulator of NSC stemness, characterize the neural stem cells isolated from a mouse model of AD (3xTg) (AD-NSCs) and determine their altered plasticity and gene expression.MethodsNup153-regulated mechanisms contributing to NSC function were investigated: (1) in cultured NSCs isolated from AD and wild type (WT) mice by proteomics; (2) in vivo by lentiviral-mediated delivery of Nup153 or GFP in the hippocampus of AD and control mice analyzing neurogenesis and cognitive function; (3) in human iPSC-derived brain organoids obtained from AD patients and control subjects as a model of neurodevelopment.ResultsProteomic approach identified Nup153 interactors in WT- and AD-NSCs potentially implicated in neurogenesis regulation. Gene ontology (GO) analysis showed that Nup153-bound proteins in WT-NSCs were involved in RNA metabolism, nuclear import and epigenetic mechanisms. Nup153-bound proteins in AD-NSCs were involved in pathways of neurodegeneration, mitochondrial dysfunction, proteasomal processing and RNA degradation. Furthermore, recovery of Nup153 levels in AD-NSCs reduced the levels of oxidative stress markers and recovered proteasomal activity. Lentiviral-mediated delivery of Nup153 in the hippocampal niche of AD mice increased the proliferation of early progenitors, marked by BrdU/DCX and BrdU/PSANCAM positivity and, later, the integration of differentiating neurons in the cell granule layer (BrdU/NeuN+ cells) compared with GFP-injected AD mice. Consistently, Nup153-injected AD mice showed an improvement of cognitive performance in comparison to AD-GFP mice at 1 month after virus delivery assessed by Morris Water Maze. To validate the role of Nup153 in neurogenesis we took advantage of brain organoids derived from AD-iPSCs characteri

It has been recently established that GPR158, a class C orphan G protein-coupled receptor, serves as a metabotropic glycine receptor. GPR158 is highly expressed in the nucleus accumbens (NAc), a major input structure of the basal ganglia that integrates information from cortical and subcortical structures to mediate goal-directed behaviors. However, whether glycine modulates neuronal activity in the NAc through GPR158 activation has not been investigated yet. Using whole-cell patch-clamp recordings, we found that glycine-dependent activation of GPR158 increased the firing rate of NAc medium spiny neurons (MSNs) while it failed to significantly affect the excitability of cholinergic interneurons (CIN). In MSNs GPR158 activation reduced the latency to fire, increased the action potential half-width, and reduced action potential afterhyperpolarization, effects that are all consistent with negative modulation of potassium M-currents, that in the central nervous system are mainly carried out by Kv7/KCNQ-channels. Indeed, we found that the GPR158-induced increase in MSN excitability was associated with decreased M-current amplitude, and selective pharmacological inhibition of the M-current mimicked and occluded the effects of GPR158 activation. In addition, when the protein kinase A (PKA) or extracellular signal-regulated kinase (ERK) signaling was pharmacologically blocked, modulation of MSN excitability by GPR158 activation was suppressed. Moreover, GPR158 activation increased the phosphorylation of ERK and Kv7.2 serine residues. Collectively, our findings suggest that GPR158/PKA/ERK signaling controls MSN excitability via Kv7.2 modulation. Glycine-dependent activation of GPR158 may significantly affect MSN firing in vivo, thus potentially mediating specific aspects of goal-induced behaviors.

Dopamine D3 receptors (D3Rs) modulate neuronal activity in several brain regions including the hippocampus. Although previous studies reported that blocking D3Rs exerts pro-cognitive effects, their involvement in hippocampal synaptic function and memory in the healthy and aged brain has not been thoroughly investigated. We demonstrated that in adult wild type (WT) mice, D3R pharmacological blockade or genetic deletion as in D3 knock out (KO) mice, converted the weak form of long-term potentiation (LTP1) into the stronger long-lasting LTP (LTP2) via the cAMP/PKA pathway, and allowed the formation of long-term memory. D3R effects were mainly mediated by post-synaptic mechanisms as their blockade enhanced basal synaptic transmission (BST), AMPAR-mediated currents, mEPSC amplitude, and the expression of the post-synaptic proteins PSD-95, phospho(p)GluA1 and p-CREB. Consistently, electron microscopy revealed a prevalent expression of D3Rs in post-synaptic dendrites. Interestingly, with age, D3Rs decreased in axon terminals while maintaining their levels in post-synaptic dendrites. Indeed, in aged WT mice, blocking D3Rs reversed the impairment of LTP, BST, memory, post-synaptic protein expression, and PSD length. Notably, aged D3-KO mice did not exhibit synaptic and memory deficits. In conclusion, we demonstrated the fundamental role of D3Rs in hippocampal synaptic function and memory, and their potential as a therapeutic target to counteract the age-related hippocampal cognitive decline.

Several studies including ours reported the detrimental effects of extracellular tau oligomers (ex-oTau) on glutamatergic synaptic transmission and plasticity. Astrocytes greatly internalize ex-oTau whose intracellular accumulation alters neuro/gliotransmitter handling thereby negatively affecting synaptic function. Both amyloid precursor protein (APP) and heparan sulfate proteoglycans (HSPGs) are required for oTau internalization in astrocytes but the molecular mechanisms underlying this phenomenon have not been clearly identified yet. Here we found that a specific antibody anti-glypican 4 (GPC4), a receptor belonging to the HSPG family, significantly reduced oTau uploading from astrocytes and prevented oTau-induced alterations of Ca2+-dependent gliotransmitter release. As such, anti-GPC4 spared neurons co-cultured with astrocytes from the astrocyte-mediated synaptotoxic action of ex-oTau, thus preserving synaptic vesicular release, synaptic protein expression and hippocampal LTP at CA3-CA1 synapses. Of note, the expression of GPC4 depended on APP and, in particular, on its C-terminal domain, AICD, that we found to bind Gpc4 promoter. Accordingly, GPC4 expression was significantly reduced in mice in which either APP was knocked-out or it contained the non-phosphorylatable amino acid alanine replacing threonine 688, thus becoming unable to produce AICD. Collectively, our data indicate that GPC4 expression is APP/AICD-dependent, it mediates oTau accumulation in astrocytes and the resulting synaptotoxic effects.

Aims Early dysfunction in Alzheimer's disease (AD) is characterised by alterations of synapse structure and function leading to dysmorphic neurites, decreased spine density, impaired synaptic plasticity and cognitive deficits. The class II member HDAC4, which recently emerged as a crucial factor in shaping synaptic plasticity and memory, was found to be altered in AD. We investigated how the modulation of HDAC4 may contribute to counteracting AD pathogenesis. Methods Using a cytoplasmic HDAC4 mutant (HDAC4(SD)), we studied the recovery of synaptic function in hippocampal tissue and primary neurons from the triple-transgenic mouse model of AD (3xTg-AD). Results Here, we report that in wild-type mice, HDAC4 is localised at synapses and interacts with postsynaptic proteins, whereas in the 3xTg-AD, it undergoes nuclear import, reducing its interaction with synaptic proteins. Of note, HDAC4 delocalisation was induced by both amyloid-beta and tau accumulation. Overexpression of the HDAC4(SD) mutant in CA1 pyramidal neurons of organotypic hippocampal slices obtained from 3xTg-AD mice increased dendritic length and promoted the enrichment of N-cadherin, GluA1, PSD95 and CaMKII proteins at the synaptic level compared with AD neurons transfected with the empty vector. Moreover, HDAC4 overexpression recovered the level of SUMO2/3ylation of PSD95 in AD hippocampal tissue, and in AD organotypic hippocampal slices, the HDAC4(SD) rescued spine density and synaptic transmission. Conclusions These results highlight a new role of cytoplasmic HDAC4 in providing a structural and enzymatic regulation of postsynaptic proteins. Our findings suggest that controlling HDAC4 localisation may represent a promising strategy to rescue synaptic function in AD, potentially leading to memory improvement.

Down syndrome (DS) is the most frequent genetic cause of intellectual disability and is strongly associated with Alzheimer’s disease (AD). Brain insulin resistance greatly contributes to AD development in the general population and previous studies from our group showed an early accumulation of insulin resistance markers in DS brain, already in childhood, and even before AD onset. Here we tested the effects promoted in Ts2Cje mice by the intranasal administration of the KYCCSRK peptide known to foster insulin signaling activation by directly interacting and activating the insulin receptor (IR) and the AKT protein. Therefore, the KYCCSRK peptide might represent a promising molecule to overcome insulin resistance. Our results show that KYCCSRK rescued insulin signaling activation, increased mitochondrial complexes levels (OXPHOS) and reduced oxidative stress levels in the brain of Ts2Cje mice. Moreover, we uncovered novel characteristics of the KYCCSRK peptide, including its efficacy in reducing DYRK1A (triplicated in DS) and BACE1 protein levels, which resulted in reduced AD-like neuropathology in Ts2Cje mice. Finally, the peptide elicited neuroprotective effects by ameliorating synaptic plasticity mechanisms that are altered in DS due to the imbalance between inhibitory vs. excitatory currents. Overall, our results represent a step forward in searching for new molecules useful to reduce intellectual disability and counteract AD development in DS

Histamine, a monoamine implicated in stress-related arousal states, is synthesized in neurons exclusively located in the hypothalamic tuberomammillary nucleus (TMN) from where they diffusely innervate striatal and mesolimbic networks including the nucleus accumbens (NAc), a vital node in the limbic loop. Since histaminecontaining TMN neuron output increases during stress, we hypothesized that exposure of mice to acute restrain stress (ARS) recruits endogenous histamine type 2 receptor (H2R) signaling in the NAc, whose activation increases medium spiny neurons (MSNs) intrinsic excitability via downregulation of A-type K+ currents. We employed an ARS paradigm in which mice were restrained for 120 min, followed by a 20-min recovery period, after which brain slices were prepared for ex vivo electrophysiology. Using whole-cell patch-clamp recordings, we found that pharmacological activation of H2R failed to affect MSN excitability and A-type K+ currents in mice that underwent ARS. Interestingly, in mice treated with H2R-antagonist prior to ARS paradigm, H2R activation increased evoked firing and decreased A-type K+ currents similarly to what observed in control mice. Furthermore, H2R-antagonist treatment ameliorated anxiety-like behavior in ARS mice. Together, our findings indicate that ARS paradigm recruits endogenous H2R signaling in MSNs and suggest the involvement of H2R signaling in stress-related motivational states.