KCC2 activation during postnatal development alleviates long-term deficits in CDKL5-deficient mice

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a severe developmental and epileptic encephalopathy characterized by early onset drug-resistant seizures and later cognitive and social impairments. Existing therapies primarily involve antiseizure medications, which have sedative side effects and lack effective treatments for behavioral impairments. Potassium chloride cotransporter (KCC2) activity is regulated by phosphorylation and is a crucial component of the GABAergic inhibitory system. However, KCC2 dysfunction in CDD remains poorly understood. Here, to investigate potential KCC2 dysfunction, we used a constitutive Cdkl5 knockout mouse model of CDD. We used liquid chromatography coupled with tandem mass spectrometry and quantitative analysis to examine the unbiased phosphorylation of KCC2. We observed aberrant KCC2 phosphorylation and reduced expression, suggesting reduced KCC2 activity. Examining developmental KCC2 changes revealed significant alterations in key phosphorylation residues and decreased expression between postnatal days 14 and 21. Treatment with the KCC2 activator (OV350) between p10 and p21 saw a significant reduction in infantile spasms compared to vehicle-treated Cdkl5 knockout mice. Remarkably, when these mice were adults, the mice that received OV350 as pups had reduced seizure susceptibility and their cognitive and behavioral deficits were alleviated. These findings indicate that enhancing KCC2 function during a critical developmental window may be a promising therapeutic strategy for CDD and other developmental and epileptic encephalopathies.