LAUSR

KCC2 expression–enhancing small molecules rescue cellular and behavior deficits in human RTT neurons and Mecp2 mutant mice. Restoring balance in Rett syndrome Rett syndrome (RTT) is a neurodevelopmental disorder causing cognitive, motor, and emotional impairments. Excitation/inhibition imbalance has been hypothesized to play a main role in RTT. The neuron-specific K+/Cl− cotransporter 2 (KCC2) is critical for maintaining the excitatory balance in the brain, and its expression is reduced in RTT. Now, Tang et al. developed a high-throughput screening to identify KCC2 expression–enhancing small molecules. The hit compounds were tested in vitro in RTT neurons and in vivo in a mouse model. The treatments rescued functional and morphological defects in neurons and ameliorated behavioral deficits in mice. Targeting KCC2 might be an effective strategy for treating RTT and possibly other disorders characterized by excitation/inhibition imbalance. Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the methyl CpG binding protein 2 (MECP2) gene. There are currently no approved treatments for RTT. The expression of K+/Cl− cotransporter 2 (KCC2), a neuron-specific protein, has been found to be reduced in human RTT neurons and in RTT mouse models, suggesting that KCC2 might play a role in the pathophysiology of RTT. To develop neuron-based high-throughput screening (HTS) assays to identify chemical compounds that enhance the expression of the KCC2 gene, we report the generation of a robust high-throughput drug screening platform that allows for the rapid assessment of KCC2 gene expression in genome-edited human reporter neurons. From an unbiased screen of more than 900 small-molecule chemicals, we have identified a group of compounds that enhance KCC2 expression termed KCC2 expression–enhancing compounds (KEECs). The identified KEECs include U.S. Food and Drug Administration–approved drugs that are inhibitors of the fms-like tyrosine kinase 3 (FLT3) or glycogen synthase kinase 3β (GSK3β) pathways and activators of the sirtuin 1 (SIRT1) and transient receptor potential cation channel subfamily V member 1 (TRPV1) pathways. Treatment with hit compounds increased KCC2 expression in human wild-type (WT) and isogenic MECP2 mutant RTT neurons, and rescued electrophysiological and morphological abnormalities of RTT neurons. Injection of KEEC KW-2449 or piperine in Mecp2 mutant mice ameliorated disease-associated respiratory and locomotion phenotypes. The small-molecule compounds described in our study may have therapeutic effects not only in RTT but also in other neurological disorders involving dysregulation of KCC2.