Reducing GABAAR over-inhibition via KCC2 modulation restores cognition and benzodiazepine sensitivity in elderly mice

Aging leads to progressive accumulation of cellular and molecular damage across multiple organs including the brain. This results in cognitive and memory deficits, dementia, and sleep disturbances. Additionally, some elderly individuals experience increased sensitivity to GABAergic agonists such as benzodiazepines. Prior research indicate GABA as fundamental in memory formation and potentially involved in age-related cognitive decline. Two key players in maintaining the correct balance between neuronal excitation and inhibition through GABAA-receptor signaling are the chloride exporter KCC2 and the chloride importer NKCC1. Given the projected increase in the ageing population, here, we examined elderly C57BL/6J mice aged 24–25 months, which closely reflects the latest stages of human aging. We specifically investigated how GABAergic signaling and in particular the chloride co-transporters KCC2 and NKCC1 relates to the cognitive impairment of ageing in wild type mice. We found increased KCC2 expression in the hippocampus of elderly mice (24-month old) compared to adult controls (i.e., 2 months old mice). Moreover, we observed increased phosphorylation of KCC2 at serine 940, accompanied by elevated levels of APP and SNAP23, all known to stabilize KCC2 at the plasma membrane. Accordingly, our in vivo calcium imaging and behavioral experiments revealed that elderly mice exhibited an increased neuronal inhibition and heightened benzodiazepines-induced sedation, consistent with age-related symptoms reported in elderly people. Pharmacological treatment of elderly mice with two different KCC2 inhibitors rescued the age-associated cognitive impairment in long-term and short-term memory, which we observed in behavioral studies. Furthermore, we showed that virus-mediated KCC2 overexpression in the hippocampus impaired cognition in adult mice, supporting its role in age-related cognitive decline. Importantly, analysis of post-mortem hippocampal tissue from elderly (>75) individuals confirmed increased KCC2 expression and function, further supporting the translational relevance of our findings. Together, our findings highlight new mechanisms of brain aging and suggest that inhibiting KCC2 activity could represent a novel strategy to preserve cognitive health and quality of life in elderliness.