The Dlg4 gene encodes for post-synaptic density protein 95 (PSD95), a major synaptic protein that clusters glutamate receptors and is critical for plasticity. PSD95 levels are diminished in ageing and neurodegenerative disorders, including Alzheimer’s disease and Huntington’s disease. The epigenetic mechanisms that (dys)regulate transcription of Dlg4/PSD95, or other plasticity genes, are largely unknown, limiting the development of targeted epigenome therapy. We analysed the Dlg4/PSD95 epigenetic landscape in hippocampal tissue and designed a Dlg4/PSD95 gene-targeting strategy: a Dlg4/PSD95 zinc finger DNA-binding domain was engineered and fused to effector domains to either repress (G9a, Suvdel76, SKD) or activate (VP64) transcription, generating artificial transcription factors or epigenetic editors (methylating H3K9). These epi-editors altered critical histone marks and subsequently Dlg4/PSD95 expression, which, importantly, impacted several hippocampal neuron plasticity processes. Intriguingly, transduction of the artificial transcription factor PSD95-VP64 rescued memory deficits in aged and Alzheimer’s disease mice. Conclusively, this work validates PSD95 as a key player in memory and establishes epigenetic editing as a potential therapy to treat human neurological disorders.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease in which pathogenesis and death of motor neurons are triggered by non-cell-autonomous mechanisms. We showed earlier that exposing primary rat spinal cord cultures to conditioned media derived from primary mouse astrocytes (ACM) that express human SOD1G93A (ACM-hSOD1G93A) quickly enhances Nav channel-mediated excitability and calcium influx, generates intracellular reactive oxygen species (ROS), and leads to death of motoneurons within days. Here we examined the role of mitochondrial dysfunction and of the activation of c-Abl, a tyrosine kinase that induces apoptosis. We show that ACM-hSOD1G93A, but not ACM-hSOD1WT, increases c-Abl activity in motoneurons, interneurons and glial cells, starting at 60 min; the c-Abl inhibitor STI571 (imatinib) prevents this ACM-hSOD1G93A-mediated motoneuron death. Interestingly, similar results were obtained with ACM derived from astrocytes expressing SOD1G86R or TDP43A315T. We further find that co-application of ACM-SOD1G93A with blockers of Nav channels (spermidine, mexiletine, or riluzole) or anti-oxidants (Trolox, esculetin, or tiron) effectively prevent c-Abl activation and motoneuron death. In addition, ACM-SOD1G93A induces alterations in the morphology of neuronal mitochondria that are related with their membrane depolarization. Finally, we find that blocking the opening of the mitochondrial permeability transition pore (mPTP) with cyclosporine A, or inhibiting mitochondrial calcium uptake with Ru360, reduces ROS production and c-Abl activation. Together, our data point to a sequence of events in which a toxic factor(s) released by ALS-expressing astrocytes rapidly induces hyper-excitability, which in turn increases calcium influx and affects mitochondrial structure and physiology. ROS production, mediated at least in part through mitochondrial alterations, trigger c-Abl signaling and lead to motoneuron death.

Objective: To assess whether autoantibodies against ribosomal P (anti‐P), which are possibly pathogenic in neuropsychiatric systemic lupus erythematosus (NPSLE), alter glutamatergic synaptic transmission and to what extent the cross‐reacting neuronal surface P antigen (NSPA) is involved.Methods: We analyzed glutamatergic transmission and long‐term potentiation (LTP) mediated by AMPA receptor (AMPAR) and N‐methyl‐d‐aspartate receptor (NMDAR) by field excitatory postsynaptic potential (EPSP) at the CA3–CA1 synapse. AMPAR activation by patch‐clamp recordings in primary ventral spinal cord neurons was analyzed. In primary hippocampal neurons, NSPA distribution was assessed by double immunofluorescence, and intracellular calcium changes were evaluated using Fura‐2 AM. NSPA‐LacZ reporter–knockin mice expressing a truncated NSPA were used to assess NSPA expression pattern and function in the brain using β‐galactosidase staining and comparative electrophysiology, calcium responses, and water maze memory tests.Results: NSPA was expressed in the brain in hippocampal CA1, dentate gyrus and ventral, but not dorsal, CA3 regions, encompassing postsynaptic regions and partial colocalization with NMDAR. Notably, NSPA‐LacZ reporter–knockin mice showed impaired memory, and decreased NMDAR activity and LTP, with neurons insensitive to anti‐P autoantibodies. Anti‐P autoantibodies enhanced CA1 postsynaptic transmission, increasing AMPAR and NMDAR activity and leading to LTP abrogation after prolonged (20‐minute) incubation.Conclusion: Our findings indicate that the neuronal cell surface target of anti‐P, NSPA, is involved in glutamatergic synaptic transmission and plasticity related to memory in the hippocampus, and mediates the deleterious effects of anti‐P on these processes. Cognitive impairment, as well as other diffuse NPSLE manifestations, may develop when anti‐P autoantibodies have access to brain regions coexpressing NSPA, AMPAR, and NMDAR.

Antidepressant drugs are usually administered for several weeks for the treatment of major depressive disorder. However, they are also prescribed in several additional psychiatric conditions as well as during long-term maintenance treatments. Antidepressants induce adaptive changes in several forebrain structures which include modifications at glutamatergic synapses. We recently found that repetitive administration of the selective serotonin reuptake inhibitor (SSRI) fluoxetine to naïve adult male rats induced an increase of mature, mushroom-type dendritic spines in several forebrain regions. This was associated with an increase of GluA2-containing α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors (AMPA-Rs) in telencephalic postsynaptic densities. To unravel the functional significance of such a synaptic re-arrangement, we focused on glutamate neurotransmission in the hippocampus. We evaluated the effect of four weeks of 0.7 mg/kg fluoxetine on long-term potentiation (LTP) and long-term depression (LTD) in the CA1 hippocampal subfield. Recordings in hippocampal slices revealed profound deficits in LTP and LTD at Schaffer collateral-CA1 synapses associated to increased spine density and enhanced presence of mushroom-type spines, as revealed by Golgi staining. However, the same treatment had neither an effect on spine morphology, nor on LTP and LTD at perforant path-CA1 synapses. Cobalt staining and immunohistochemical experiments revealed decreased AMPA-R Ca²⁺ permeability in the stratum radiatum (s.r.) together with increased GluA2-containing Ca²⁺ impermeable AMPA-Rs. Therefore, 4 weeks of fluoxetine treatment promoted structural and functional adaptations in CA1 neurons in a pathway-specific manner that were selectively associated with impairment of activity-dependent plasticity at Schaffer collateral-CA1 synapses.