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Additional file 1. Fig. S1. Induction of synaptic IR in primary neurons. Fig. S2. Proteasomal degradation of IRS2 is not affected by neddylation. Fig. S3. CUL7 KD does not alter insulin signaling and A��3(pE) application exacerbates IR. Fig. S4. MetS induces neuronal cell loss, astroglial and microglial activation in the hippocampal CA1 region of heterozygous TBA2.1 mice. Fig. S5. Baseline recordings of fEPSP in hippocampal acute slices from WT and heterozygous TBA2.1 mice fed with a RD or HFD. Fig. S6. Characterization of the effects of MLN-4924 on basic metabolic parameters, basal fEPSP slope and LTD-dependent learning and memory in WT and heterozygous TBA2.1 mice fed with a RD or HFD. Table S1. Expression constructs and antibodies used in this study.

Oligomeric amyloid‐v (Av) 1‐42 disrupts synaptic function at an early stage of Alzheimer's disease (AD). Multiple posttranslational modifications of Av have been identified, among which N‐terminally truncated forms are the most abundant. It is not clear, however, whether modified species can induce synaptic dysfunction on their own and how altered biochemical properties can contribute to the synaptotoxic mechanisms. Here, we show that a prominent isoform, pyroglutamated Av3(pE)‐42, induces synaptic dysfunction to a similar extent like Av1‐42 but by clearly different mechanisms. In contrast to Av1‐42, Av3(pE)‐42 does not directly associate with synaptic membranes or the prion protein but is instead taken up by astrocytes and potently induces glial release of the proinflammatory cytokine TNFa. Moreover, Av3(pE)‐42‐induced synaptic dysfunction is not related to NMDAR signalling and Av3(pE)‐42‐induced impairment of synaptic plasticity cannot be rescued by D1‐agonists. Collectively, the data point to a scenario where neuroinflammatory processes together with direct synaptotoxic effects are caused by posttranslational modification of soluble oligomeric Av and contribute synergistically to the onset of synaptic dysfunction in AD.

Jacob, the protein encoded by the Nsmf gene, is involved in synapto-nuclear signaling and docks an N-Methyl-D-Aspartate receptor (NMDAR)-derived signalosome to nuclear target sites like the transcription factor cAMP-response-element-binding protein (CREB). Several reports indicate that mutations in NSMF are related to Kallmann syndrome (KS), a neurodevelopmental disorder characterized by idiopathic hypogonadotropic hypogonadism (IHH) associated with anosmia or hyposmia. It has also been reported that a protein knockdown results in migration deficits of Gonadotropin-releasing hormone (GnRH) positive neurons from the olfactory bulb to the hypothalamus during early neuronal development. Here we show that mice that are constitutively deficient for the Nsmf gene do not present phenotypic characteristics related to KS. Instead, these mice exhibit hippocampal dysplasia with a reduced number of synapses and simplification of dendrites, reduced hippocampal long-term potentiation (LTP) at CA1 synapses and deficits in hippocampus-dependent learning. Brain-derived neurotrophic factor (BDNF) activation of CREB-activated gene expression plays a documented role in hippocampal CA1 synapse and dendrite formation. We found that BDNF induces the nuclear translocation of Jacob in an NMDAR-dependent manner in early development, which results in increased phosphorylation of CREB and enhanced CREB-dependent Bdnf gene transcription. Nsmf knockout (ko) mice show reduced hippocampal Bdnf mRNA and protein levels as well as reduced pCREB levels during dendritogenesis. Moreover, BDNF application can rescue the morphological deficits in hippocampal pyramidal neurons devoid of Jacob. Taken together, the data suggest that the absence of Jacob in early development interrupts a positive feedback loop between BDNF signaling, subsequent nuclear import of Jacob, activation of CREB and enhanced Bdnf gene transcription, ultimately leading to hippocampal dysplasia., Author Summary Kallmann syndrome (KS) is a neurodevelopmental disorder that is characterized by a migration deficit of GnRH neurons that fail to migrate into the hypothalamus during embryonic development. The affected patients suffer from idiopathic hypogonadotropic hypogonadism associated with anosmia or hyposmia. Mutations in NSMF (NMDA Receptor Synaptonuclear Signaling And Neuronal Migration Factor) have been associated with KS. In previous work we could show that Jacob, the protein encoded by the Nsmf gene, is involved in NMDA receptor synaptonuclear signaling. Jacob operates as a mobile hub that docks NMDA receptor-derived signalosomes to nuclear target sites and thereby plays a role in activity-dependent gene transcription. We found that mice that are deficient for the Nsmf gene do not present phenotypic characteristics related to KS. Instead, these mice exhibit hippocampal dysplasia with a reduced number of synapses and simplification of dendrites, reduced plasticity at CA1 synapses and deficits in hippocampus dependent learning. Brain-derived neurotrophic factor (BDNF) induces the nuclear translocation of Jacob in an NMDAR-dependent manner in early development, which results in increased phosphorylation of CREB and enhanced CREB-dependent Bdnf gene transcription. Nsmf knockout mice show reduced hippocampal Bdnf mRNA and protein levels as well as reduced pCREB levels during dendritogenesis. Moreover, BDNF application can rescue the morphological deficits in hippocampal pyramidal neurons devoid of Jacob. Taken together, the data suggest that the absence of Jacob in early development interrupts a positive feedback loop between BDNF signaling, subsequent nuclear import of Jacob, activation of CREB and enhanced Bdnf gene transcription, ultimately leading to hippocampal dysplasia.

DNA methylation is a crucial epigenetic mark for activity-dependent gene expression in neurons. Very little is known about how synaptic signals impact promoter methylation in neuronal nuclei. In this study we show that protein levels of the principal de novo DNA-methyltransferase in neurons, DNMT3A1, are tightly controlled by activation of N-methyl-D-aspartate receptors (NMDAR) containing the GluN2A subunit. Interestingly, synaptic NMDARs drive degradation of the methyltransferase in a neddylation-dependent manner. Inhibition of neddylation, the conjugation of the small ubiquitin-like protein NEDD8 to lysine residues, interrupts degradation of DNMT3A1. This results in deficits in promoter methylation of activity-dependent genes, as well as synaptic plasticity and memory formation. In turn, the underlying molecular pathway is triggered by the induction of synaptic plasticity and in response to object location learning. Collectively, the data show that plasticity-relevant signals from GluN2A-containing NMDARs control activity-dependent DNA-methylation involved in memory formation.