The brain-specific kinase LMTK3 regulates neuronal excitability by decreasing KCC2-dependent neuronal Cl extrusion.

LMTK3 is a brain-specific transmembrane serine/threonine protein kinase that acts as a scaffold for protein phosphatase-1 (PP1). Although LMKT3 has been identified as a risk factor for autism and epilepsy, its physiological significance is unknown. Here, we demonstrate that LMTK3 copurifies and binds to KCC2, a neuron-specific K/Cl transporter.

Spectrin-beta 2 facilitates the selective accumulation of GABA receptors at somatodendritic synapses.

Fast synaptic inhibition is dependent on targeting specific GABAR subtypes to dendritic and axon initial segment (AIS) synapses. Synaptic GABARs are typically assembled from α1-3, β and γ subunits. Here, we isolate distinct GABARs from the brain and interrogate their composition using quantitative proteomics.

Analyzing the mechanisms that facilitate the subtype-specific assembly of -aminobutyric acid type A receptors.

Impaired inhibitory signaling underlies the pathophysiology of many neuropsychiatric and neurodevelopmental disorders including autism spectrum disorders and epilepsy. Neuronal inhibition is regulated by synaptic and extrasynaptic -aminobutyric acid type A receptors (GABA Rs), which mediate phasic and tonic inhibition, respectively. These two GABA R subtypes differ in their function, ligand sensitivity, and physiological properties.

KCC2 is required for the survival of mature neurons but not for their development.

The K/Cl cotransporter KCC2 (SLC12A5) allows mature neurons in the CNS to maintain low intracellular Cl levels that are critical in mediating fast hyperpolarizing synaptic inhibition via type A γ-aminobutyric acid receptors (GABARs). In accordance with this, compromised KCC2 activity results in seizures, but whether such deficits directly contribute to the subsequent changes in neuronal structure and viability that lead to epileptogenesis remains to be assessed. Canonical hyperpolarizing GABAR currents develop postnatally, which reflect a progressive increase in KCC2 expression levels and activity.

Isolation and Characterization of Multi-Protein Complexes Enriched in the K-Cl Co-transporter 2 From Brain Plasma Membranes.

Kcc2 plays a critical role in determining the efficacy of synaptic inhibition, however, the cellular mechanisms neurons use to regulate its membrane trafficking, stability and activity are ill-defined. To address these issues, we used affinity purification to isolate stable multi-protein complexes of K-Cl Co-transporter 2 (Kcc2) from the plasma membrane of murine forebrain. We resolved these using blue-native polyacrylamide gel electrophoresis (BN-PAGE) coupled to LC-MS/MS and label-free quantification.