Pro-cognitive restoration of experience-dependent parvalbumin inhibitory neuron plasticity in neurodevelopmental disorders.

The hippocampus forms memories of our experiences by registering processed sensory information in coactive populations of excitatory principal cells or ensembles(1-3). Fast-spiking parvalbumin-expressing inhibitory neurons (PV INs) in the dentate gyrus (DG)-CA3/CA2 circuit contribute to memory encoding by exerting precise temporal control of excitatory principal cell activity through mossy fiber-dependent feed-forward inhibition(4-13). PV INs respond to input-specific information by coordinating changes in their intrinsic excitability, input-output synaptic-connectivity, synaptic-physiology and synaptic-plasticity(9,13-17), referred to here as experience-dependent PV IN plasticity, to influence hippocampal functions. PV IN impairments in early life, when neural circuitry is highly sensitive to experience-dependent refinement, are thought to result in imbalanced excitation and inhibition, impaired cognition, network hyperexcitability and seizures: hallmarks of neurodevelopmental disorders (NDDs) such as Autism Spectrum Disorder and epilepsy(18-20). Discovery of transcriptional regulators of experience-dependent PV IN plasticity in the adult hippocampus may permit reversal of these developmental impairments. Here, in a screen designed to capture the PV IN intrinsic program induced by increased mossy fiber inputs, a trigger for experience-dependent PV IN plasticity, we identify the homeobox gene Meis2 (21) as a regulator of experience-dependent PV IN plasticity gene (XPG) in the adult DG-CA3/CA2 circuit. We found that a significant number of upregulated XPGs also exhibit haploinsufficiency in ASDs, epilepsies, and schizophrenia. We demonstrate that virally-mediated rescue of experience-dependent Meis2 upregulation in CA3/CA2 PV INs in a NDD risk mouse model in adulthood is sufficient to restore experience-dependent PV IN plasticity, spatial and social memory, ensemble specificity, suppression of network hyperexcitability and seizures. Together, these findings suggest that experience-dependent PV IN plasticity is a convergent mechanism for NDD risk genes that can be re-instated in adulthood to reverse developmental deficits in circuitry, network excitability and cognition.