We have recently described an A350V mutation in IQSEC2 associated with intellectual disability, autism and epilepsy. We sought to understand the molecular pathophysiology of this mutation with the goal of developing targets for drug intervention. We demonstrate here that the A350V mutation results in interference with the binding of apocalmodulin to the IQ domain of IQSEC2. We further demonstrate that this mutation results in constitutive activation of the guanine nucleotide exchange factor (GEF) activity of IQSEC2 resulting in increased production of the active form of Arf6. In a CRISPR generated mouse model of the A350V IQSEC2 mutation, we demonstrate that the surface expression of GluA2 AMPA receptors in mouse hippocampal tissue was significantly reduced in A350V IQSEC2 mutant mice compared to wild type IQSEC2 mice and that there is a significant reduction in basal synaptic transmission in the hippocampus of A350V IQSEC2 mice compared to wild type IQSEC2 mice. Finally, the A350V IQSEC2 mice demonstrated increased activity, abnormal social behavior and learning as compared to wild type IQSEC2 mice. These findings suggest a model of how the A350V mutation in IQSEC2 may mediate disease with implications for targets for drug therapy. These studies provide a paradigm for a personalized approach to precision therapy for a disease that heretofore has no therapy.

The dopamine D5 receptor (D5R) is a Gα s-coupled dopamine receptor belonging to the dopamine D1-like receptor family. Together with the dopamine D2 receptor it is highly expressed in striatal cholinergic interneurons and therefore is poised to be a positive regulator of cholinergic activity in response to L-DOPA in the dopamine-depleted parkinsonian brain. Tonically active cholinergic interneurons become dysregulated during chronic L-DOPA administration and participate in the expression of L-DOPA induced dyskinesia. The molecular mechanisms involved in this process have not been elucidated, however a correlation between dyskinesia severity and pERK expression in cholinergic cells has been described. To better understand the function of the D5 receptor and how it affects cholinergic interneurons in L-DOPA induced dyskinesia, we used D5R knockout mice that were rendered parkinsonian by unilateral 6-OHDA injection. In the KO mice, expression of pERK was strongly reduced indicating that activation of these cells is at least in part driven by the D5 receptor. Similarly, pS6, another marker for the activity status of cholinergic interneurons was also reduced. However, mice lacking D5R exhibited slightly worsened locomotor performance in response to L-DOPA and enhanced LID scores. Our findings suggest that D5R can modulate L-DOPA induced dyskinesia and is a critical activator of CINs via pERK and pS6. Parkinson's disease (PD) is the second most prevalent neurodegenerative disease, it affects up to 4% of people aged 65 years or more 1. Hallmarks of the disorder are motor symptoms such as tremor, rigidity, bradykinesia and gait disturbances 2 , which are a result of the selective degeneration of dopaminergic neurons within the substantia nigra pars compacta and thus not by but of dopamine depletion 3. Up to today, L-DOPA treatment remains the gold standard treatment for PD. In the majority of patients, the efficacy of L-DOPA is reduced and debilitating involuntary movements, termed L-DOPA-induced dyskinesia (LID), develop during chronic L-DOPA treatment over several years 4. Various pharmacological tools are currently investigated with the aim to mitigate these complications. The striatum is comprised mainly by two types of GABAergic projection neurons (SPNs) that are categorized based on their predominant expression of either D1-or D2 receptors, together making up over 95% of all striatal neurons 5. The spiny neurons that project directly to the basal ganglia output nuclei are termed 'direct pathway' or dSPNs and express D1 receptor (D1R), that signals via the G proteins Gα s /Gα olf to PKA and enhances cAMP production. The other class of projection neurons is termed 'indirect pathway' or iSPNs, and they express the inhibitory, Gα i/o-coupled D2 receptor (D2R) 6 , leading to less cAMP being produced. The balance between the two pathways is crucial for voluntary movement control and is disturbed in PD. In addition, cholinergic interneurons (CINs), which represent 1-3% of striatal neurons but are extensively arborized, gat...

We have previously shown that casein kinase 2 (CK2) negatively regulates dopamine D1 and adenosine A receptor signaling in the striatum. Ablation of CK2 in D1 receptor-positive striatal neurons caused enhanced locomotion and exploration at baseline, whereas CK2 ablation in D2 receptor-positive neurons caused increased locomotion after treatment with A antagonist, caffeine. Because both, D1 and A receptors, play major roles in the cellular responses to l-DOPA in the striatum, these findings prompted us to examine the impact of CK2 ablation on the effects of l-DOPA treatment in the unilateral 6-OHDA lesioned mouse model of Parkinson's disease. We report here that knock-out of CK2 in striatonigral neurons reduces the severity of l-DOPA-induced dyskinesia (LID), a finding that correlates with lowered pERK but unchanged pPKA substrate levels in D1 medium spiny neurons as well as in cholinergic interneurons. In contrast, lack of CK2 in striatopallidal neurons enhances LID and ERK phosphorylation. Coadministration of caffeine with a low dose of l-DOPA reduces dyskinesia in animals with striatopallidal knock-out to wild-type levels, suggesting a dependence on adenosine receptor activity. We also detect reduced G levels in the striatonigral but not in the striatopallidal knock-out in response to l-DOPA treatment.Our work shows, in a rodent model of PD, that treatment-induced dyskinesia and striatal ERK activation are bidirectionally modulated by ablating CK2 in D1- or D2-positive projection neurons, in male and female mice. The results reveal that CK2 regulates signaling events critical to LID in each of the two main populations of striatal neurons. To date, l-DOPA is the most effective treatment for PD. Over time, however, its efficacy decreases, and side effects including l-DOPA-induced dyskinesia (LID) increase, affecting up to 78% of patients within 10 years of therapy (Hauser et al., 2007). It is understood that supersensitivity of the striatonigral pathway underlies LID, however, D2 agonists were also shown to induce LID (Bezard et al., 2001; Delfino et al., 2004). Our work implicates a novel player in the expression of LID, the kinase CK2: knock-out of CK2 in striatonigral and striatopallidal neurons has opposing effects on LID. The bidirectional modulation of dyskinesia reveals a central role for CK2 in striatal physiology and indicates that both pathways contribute to LID.

SUMMARY The regulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking affects multiple brain functions, such as learning and memory. We have previously shown that Thorase plays an important role in the internalization of AMPARs from the synaptic membrane. Here, we show that N -methyl- d -aspartate receptor (NMDAR) activation leads to increased S -nitrosylation of Thorase and N-ethylmaleimide-sensitive factor (NSF). S -nitrosylation of Thorase stabilizes Thorase-AMPAR complexes and enhances the internalization of AMPAR and interaction with protein-interacting C kinase 1 (PICK1). S -nitrosylated NSF is dependent on the S -nitrosylation of Thorase via trans-nitrosylation, which modulates the surface insertion of AMPARs. In the presence of the S -nitrosylation-deficient C137L Thorase mutant, AMPAR trafficking, long-term potentiation, and long-term depression are impaired. Overall, our data suggest that both S -nitrosylation and interactions of Thorase and NSF/PICK1 are required to modulate AMPAR-mediated synaptic plasticity. This study provides critical information that elucidates the mechanism underlying Thorase and NSF-mediated trafficking of AMPAR complexes.