The intramembrane COOH-terminal domain of PRRT2 regulates voltage-dependent Na+ channels

Proline-rich transmembrane protein 2 knock-in mice present dopamine-dependent motor deficits

Mutations of proline-rich transmembrane protein 2 (PRRT2) lead to dyskinetic disorders such as paroxysmal kinesigenic dyskinesia (PKD), which is characterized by attacks of involuntary movements precipitated by suddenly initiated motion, and some convulsive disorders. Although previous studies have shown that PKD might be caused by cerebellar dysfunction, PRRT2 has not been sufficiently analyzed in some motor-related regions, including the basal ganglia, where dopaminergic neurons are most abundant in the brain. Here, we generated several types of Prrt2 knock-in (KI) mice harboring mutations, such as c.672dupG, that mimics the human pathological mutation c.649dupC and investigated the contribution of Prrt2 to dopaminergic regulation. Regardless of differences in the frameshift sites, all truncating mutations abolished Prrt2 expression within the striatum and cerebral cortex, consistent with previous reports of similar Prrt2 mutant rodents, confirming the loss-of-function nature of these mutations. Importantly, administration of l-dopa, a precursor of dopamine, exacerbated rotarod performance, especially in Prrt2-KI mice. These findings suggest that dopaminergic dysfunction in the brain by the PRRT2 mutation might be implicated in a part of motor symptoms of PKD and related disorders.

Missense mutations in the membrane domain of PRRT2 affect its interaction with Nav1.2 voltage-gated sodium channels

PRRT2 is a neuronal protein that controls neuronal excitability and network stability by modulating voltage-gated Na⁺ channel (Nav). PRRT2 pathogenic variants cause pleiotropic syndromes including epilepsy, paroxysmal kinesigenic dyskinesia and episodic ataxia attributable to loss-of-function pathogenetic mechanism. Based on the evidence that the transmembrane domain of PRRT2 interacts with Nav1.2/1.6, we focused on eight missense mutations located within the domain that show expression and membrane localization similar to the wild-type protein. Molecular dynamics simulations showed that the mutants do not alter the structural stability of the PRRT2 membrane domain and preserve its conformation. Using affinity assays, we found that the A320V and V286M mutants displayed respectively decreased and increased binding to Nav1.2. Accordingly, surface biotinylation showed an increased Nav1.2 surface exposure induced by the A320V mutant. Electrophysiological analysis confirmed the lack of modulation of Nav1.2 biophysical properties by the A320V mutant with a loss-of-function phenotype, while the V286M mutant displayed a gain-of-function with respect to wild-type PRRT2 with a more pronounced left-shift of the inactivation kinetics and delayed recovery from inactivation. The data confirm the key role played by the PRRT2-Nav interaction in the pathogenesis of the PRRT2-linked disorders and suggest an involvement of the A320 and V286 residues in the interaction site. Given the similar clinical phenotype caused by the two mutations, we speculate that circuit instability and paroxysmal manifestations may arise when PRRT2 function is outside the physiological range.