PRRT2 controls neuronal excitability by negatively modulating Na+ channel 1.2/1.6 activity

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Proline-rich transmembrane protein 2 (PRRT2) gene mutations are linked to familial paroxysmal neurological disorders like infantile seizures and dyskinesia.
• The common c.649dupC mutation results in a loss-of-function and haploinsufficiency, leading to premature stop codons.
• Understanding PRRT2's physiological role is crucial for modeling these disorders.

Purpose of the Study:

• To investigate the physiological function of PRRT2 in neuronal excitability.
• To elucidate the molecular mechanisms underlying PRRT2-associated neurological disorders.
• To model PRRT2 loss-of-function using patient-derived induced pluripotent stem cells (iPSCs) and knockout mouse models.

Main Methods:

• Differentiation of iPSCs from heterozygous and homozygous PRRT2 mutation carriers.
• Single-cell patch-clamp electrophysiology on iPSC-derived neurons and primary mouse neurons.
• Multi-electrode array (MEA) electrophysiology for network activity analysis.
• HEK-293 cell-based assays to study PRRT2 interaction with Nav channel subtypes.
• Co-immunoprecipitation assays in brain tissue.

Main Results:

• Homozygous PRRT2-deficient neurons exhibited increased Na+ currents, longer axon initial segments, and augmented neuronal firing and bursting activity.
• PRRT2 expression was found to decrease membrane exposure and Na+ current of Nav1.2 and Nav1.6 channels, but not Nav1.1.
• PRRT2 directly interacts with Nav1.2/Nav1.6 channels, negatively shifting voltage-dependence of inactivation and slowing recovery from inactivation.

Conclusions:

• Loss of PRRT2 function leads to hyperactivity of voltage-dependent Na+ channels (Nav1.2/Nav1.6) in human and mouse neurons.
• PRRT2 acts as a critical negative modulator of Nav1.2 and Nav1.6 channels, in addition to its known synaptic functions.
• Dysregulation of cellular excitability due to impaired Na+ channel modulation by PRRT2 is a key pathogenetic mechanism in PRRT2-linked diseases.