“Adding new Molecular Insights to a given Endophenotype: the Relevance of Epigenetics in Environmental Stress Response”

Molecular psychiatry research needs a deeper characterization of emotional and cognitive neural underpinnings, along with a broader recognition of trauma-related circuitries and their involvement in shared pathological endophenotypes. One such endophenotype is unbalanced approach avoidance conflict (AAC), a highly recurrent trait of psychopathology. A translationally validated rodent model of AAC is the elevated plus maze (EPM) test, recently shown to be pharmacologically controlled in human and rodents via homologous neural substrates. Thanks to this test, we identified the involvement of the epigenetic enzyme LSD1 as a molecular restrainer of anxiety. We identified LSD1 aberrant regulation within the hippocampus of suicidal victims, suggesting its broad functional involvement in maladaptive behaviors. Interestingly, thanks to the parallel employment of rodent models, we evaluated a stress-related LSD1 homeostatic regulation that transiently limits memory formation-instrumental gene expression in the hippocampus upon trauma. Our work shed new light on epigenetic processes devoted to trauma resiliency through a negative regulation of anxiety plasticity.

LSD1 is an environmental stress-sensitive negative modulator of the glutamatergic synapse

Along with neuronal mechanisms devoted to memory consolidation –including long term potentiation of synaptic strength as prominent electrophysiological correlate, and inherent dendritic spines stabilization as structural counterpart– negative control of memory formation and synaptic plasticity has been described at the molecular and behavioral level. Within this work, we report a role for the epigenetic corepressor Lysine Specific Demethylase 1 (LSD1) as a negative neuroplastic factor whose stress-enhanced activity may participate in coping with adverse experiences. Constitutively increasing LSD1 activity via knocking out its dominant negative splicing isoform neuroLSD1 (neuroLSD1^KO mice), we observed extensive structural, functional and behavioral signs of excitatory decay, including disrupted memory consolidation. A similar LSD1 increase, obtained with acute antisense oligonucleotide-mediated neuroLSD1 splicing knock down in primary neuronal cultures, dampens spontaneous glutamatergic transmission, reducing mEPSCs. Remarkably, LSD1 physiological increase occurs in response to psychosocial stress-induced glutamatergic signaling. Since this mechanism entails neuroLSD1 splicing downregulation, we conclude that LSD1/neuroLSD1 ratio modulation in the hippocampus is instrumental to a negative homeostatic feedback, restraining glutamatergic neuroplasticity in response to glutamate. The active process of forgetting provides memories with salience. With our work, we propose that softening memory traces of adversities could further represent a stress-coping process in which LSD1/neuroLSD1 ratio modulation may help preserving healthy emotional references.