CDKL5 LOSS ENHANCES INHIBITORY SYNAPTIC FUNCTION AND INTERNEURON EXCITABILITY VIA NON-L-TYPE VGCCS, DRIVING AN EXCITATORY E/I SHIFT IN SOMATOSENSORY CORTEX

CDKL5 Deficiency Disorder (CDD) is a severe X-linked neurodevelopmental disorder caused by CDKL5 mutations and characterized by severe cognitive and sensorimotor impairments, communication deficits, and autistic traits. While it has been suggested that CDD is partly a channelopathy, as the voltage-gated Ca2⁺ channel (VGCC) Cav2.3 is phosphorylated by CDKL5, how this kinase regulates ion-channels function and localization in neurons remains poorly understood. To address this issue, we performed current- and voltage-clamp in-vitro recordings from cortical autaptic GABAergic interneurons, obtained from prenatal Cdkl5^+/y and Cdkl5^-/y mice.
CDKL5 loss potentiated inhibitory synaptic transmission by increasing the readily releasable pool and asynchronous GABA release. Synaptic potentiation was associated with elevated intrinsic excitability of Cdkl5^-/y interneurons, higher firing rates and altered action potential waveform. Mechanistically, increased excitability was driven by augmented Ca²⁺ influx through R-type VGCCs. Moreover, neurotransmitter release was differentially coupled to presynaptic VGCC subtypes, relying predominantly on P/Q-type in parvalbumin (PV) interneurons and on N-type in cholecystokinin interneurons. In the absence of CDKL5, both interneuron types showed that transmitter release became more dependent on such non-L-type channels. Interestingly, immunofluorescence revealed that Cdkl5^-/y interneurons exhibit an increased growth of VGAT⁺ GABAergic axon terminals showing higher density of N- or P/Q-type channels. Finally, excitatory/inhibitory balance measurements in layer 2/3 of acute somatosensory cortical slices showed a shift toward more excitation, attributable to increased inhibitory autaptic drive onto PV interneurons that alters PV inhibitory-drive and biases local somatosensory network output. Collectively, these findings disclose a novel role of VGCC-dependent inhibition mechanisms in CDD-related sensorial dysfunctions.