Long-Term Consequences of Early-in-Life Genetic and Pharmacological Interventions In Down Syndrome Mice

Down syndrome (DS) is the leading cause of genetically-defined intellectual disability. Additionally, DS individuals often present with increased susceptibility to epileptic seizures and hyperactivity. Recently, several studies identified altered GABAergic activity through chloride-permeable GABAA receptors as one of the main contributors to impaired cognitive performance in the Ts65Dn mouse model of DS. Data from adult Ts65Dn mice and DS individuals showed an increased expression of the chloride importer NKCC1. As a result, intracellular chloride concentration is higher in Ts65Dn mice and GABAergic responses are depolarizing (vs hyperpolarizing and inhibitory). Accordingly, treatment with the FDA-approved diuretic and NKCC1 inhibitor bumetanide during adulthood rescues inhibitory GABAergic transmission and cognitive deficits in DS mice, although the beneficial effect of the treatment is rapidly lost upon drug withdrawal. However, hyperactivity and susceptibility to seizures are not rescued by bumetanide treatment in adulthood. Here, we investigated the long-term effects of early-in-life genetic and pharmacological interventions targeting NKCC1 by neuron-specific AAV9-mediated NKCC1 knockdown and bumetanide treatment during the first 2 weeks of development, respectively. We found a rescue in long-term memory in two different memory tasks in adult Ts65Dn animals after both interventions. Additionally, early NKCC1 downregulation rescued short-term memory, susceptibility to seizures and hyperactivity phenotype in Ts65Dn mice in adulthood. Notably, both early-in-life genetic and pharmacological interventions rescued the increased GABA-mediated spiking events in acute brain slices from adult trisomic animals. Finally, since bumetanide treatment of human infants can lead to deafness, we assessed ototoxicity in adult WT and Ts65Dn mice treated early in development and found no significant deficits in acoustic startle-response. Our results suggest that time-specific interventions possibly impacting on the trajectories of the developing brain could rescue cognitive performance and deficits that are not rescued by treatment in adulthood, avoiding the adverse diuretic effects of the required chronic adult treatment with bumetanide.