Dopamine dysregulation in a mouse model of paroxysmal nonkinesigenic dyskinesia

Abstract

Paroxysmal nonkinesigenic dyskinesia (PNKD) is an autosomal dominant episodic movement disorder.Patients have episodes that last 1 to 4 hours and are precipitated by alcohol, coffee, and stress. Previous research has shown that mutations in an uncharacterized gene on chromosome 2q33-q35 (which is termed PNKD) are responsible for PNKD. Here, we report the generation of antibodies specific for the PNKD protein and show that it is widely expressed in the mouse brain, exclusively in neurons. One PNKD isoform is a membrane-associated protein. Transgenic mice carrying mutations in the mouse Pnkd locus equivalent to those found in patients with PNKD recapitulated the human PNKD phenotype. Staining for c-fos demonstrated that administration of alcohol or caffeine induced neuronal activity in the basal ganglia in these mice. They also showed nigrostriatal neurotransmission deficits that were manifested by reduced extracellular dopamine levels in the striatum and a proportional increase of dopamine release in response to caffeine and ethanol treatment. These findings support the hypothesis that the PNKD protein functions to modulate striatal neurotransmitter release in response to stress and other precipitating factors. IntroductionThe paroxysmal dyskinesias consist of clinically and genetically distinct phenotypes, including paroxysmal kinesigenic dyskinesia, paroxysmal exercise-induced dyskinesia, and paroxysmal nonkinesigenic dyskinesia (PNKD) (1, 2). PNKD is a highly penetrant autosomal dominant disorder in which individuals have 1- to 4-hour attacks consisting of dystonia and choreoathetosis (3). These attacks can be induced reliably by administration of caffeine or alcohol and frequently when patients are stressed. The causative gene was mapped to chromosome 2q33-q35 (4, 5), and mutations in the PNKD gene (formerly called MR-1) were subsequently identified in PNKD families (6)(7)(8)(9)(10).The PNKD gene has at least 3 alternate splice forms, which encode proteins of 385, 361, and 142 amino acids. The long isoform of PNKD (PNKD-L) is specifically expressed in CNS, while the medium isoform (PNKD-M) and short isoform (PNKD-S) are ubiquitously expressed (7). Two missense mutations (Ala to Val) located at amino acids 7 or 9 of PNKD-L and PNKD-S were found in most patients, and a third mutation (Ala to Pro) at position 33 was reported in 1 family (11). Both PNKD-L and PNKD-M have a putative catalytic domain that is homologous to hydroxyacylglutathione hydrolase (HAGH), a member of the zinc metallo-hydrolase enzyme family, which contains β-lactamase domains. HAGH functions in a pathway to detoxify methylglyoxal, a by-product of oxidative stress (12). The normal role of PNKD in cells and the contribution of mutations to pathophysiology of PNKD are not known.Dyskinesia is seen with many genetic and acquired disorders of the brain. Theoretically, such hyperkinetic movements could have their genesis in the basal ganglia, the cerebellum, or even in the cortex. Having cloned the gene and shown by in situ hybridization that it is...

Protein mutated in paroxysmal dyskinesia interacts with the active zone protein RIM and suppresses synaptic vesicle exocytosis

“…This finding is consistent with the mutations leading to PNKD through a gain-of-function mechanism, as we have previously shown (10). Thus, the mutations are exerting an effect via a mechanism different from reducing RIM protein expression.…”

“…The use and care of animals in this study follows the guidelines of the Institutional Animal Care and Use Committee at the University of California, San Francisco. Mut-Tg and Pnkd −/− mice were generated as described previously (10). The founder mutant mice were backcrossed to C57BL/6 for 10 generations before used for experiments.…”

“…We speculate that in mut-Tg mice, neurons are more vulnerable to elevated calcium levels and thus develop hyperexcitability when challenged with coffee, alcohol, or stress. In our mutant PNKD mouse model and other generalized dystonia mouse models, dysregulated dopamine signaling has been demonstrated in the striatum (10,(33)(34)(35)(36)(37).…”

“…PNKD is interesting in that the gene encodes a novel protein with homology to human glyoxalase II, an enzyme in a stress-response pathway. Although the normal role of PNKD is unknown, we previously identified the causative gene of PNKD (9) and a mouse model of the human mutations recapitulates the phenotype and shows dopamine signaling dysregulation (10).…”

“…1D). To study the functional role of Pnkd protein in vivo, we generated a Pnkd-null mouse line (10). The homozygous Pnkd −/− mice are viable, with normal body weight and no gross morphologic abnormalities (Fig.…”