Gβγ and the C Terminus of SNAP-25 Are Necessary for Long-Term Depression of Transmitter Release

Short-term presynaptic inhibition mediated by G protein-coupled receptors involves a direct interaction between G proteins and the vesicle release machinery. Recent studies implicate the C terminus of the vesicle-associated protein SNAP-25 as a molecular binding target of Gβγ that transiently reduces vesicular release. However, it is not known whether SNAP-25 is a target for molecular modifications expressing long-term changes in transmitter release probability.This study utilized two-photon laser scanning microscopy for real-time imaging of action potential-evoked [Ca(2+)] increases, in single Schaffer collateral presynaptic release sites in in vitro hippocampal slices, plus simultaneous recording of Schaffer collateral-evoked synaptic potentials. We used electroporation to infuse small peptides through CA3 cell bodies into presynaptic Schaffer collateral terminals to selectively study the presynaptic effect of scavenging the G-protein Gβγ. We demonstrate here that the C terminus of SNAP-25 is necessary for expression of LTD, but not long-term potentiation (LTP), of synaptic strength. Using type A botulinum toxin (BoNT/A) to enzymatically cleave the 9 amino acid C-terminus of SNAP-25 eliminated the ability of low frequency synaptic stimulation to induce LTD, but not LTP, even if release probability was restored to pre-BoNT/A levels by elevating extracellular [Ca(2+)]. Presynaptic electroporation infusion of the 14-amino acid C-terminus of SNAP-25 (Ct-SNAP-25), to scavenge Gβγ, reduced both the transient presynaptic inhibition produced by the group II metabotropic glutamate receptor stimulation, and LTD. Furthermore, presynaptic infusion of mSIRK, a second, structurally distinct Gβγ scavenging peptide, also blocked the induction of LTD. While Gβγ binds directly to and inhibit voltage-dependent Ca(2+) channels, imaging of presynaptic [Ca(2+)] with Mg-Green revealed that low-frequency stimulation only transiently reduced presynaptic Ca(2+) influx, an effect not altered by infusion of Ct-SNAP-25.The C-terminus of SNAP-25, which links synaptotagmin I to the SNARE complex, is a binding target for Gβγ necessary for both transient transmitter-mediated presynaptic inhibition, and the induction of presynaptic LTD

Efficacy of risankizumab in patients with moderate-to-severe plaque psoriasis by baseline demographics, disease characteristics and prior biologic therapy: an integrated analysis of the phase III UltIMMa-1 and UltIMMa-2 studies.

BACKGROUND: Risankizumab is a humanized IgG monoclonal antibody that selectively inhibits interleukin-23 through binding the p19 subunit. In Phase 3 trials, risankizumab demonstrated superior efficacy compared with adalimumab and ustekinumab in patients with moderate-to-severe plaque psoriasis. Here, we evaluated the impact of baseline characteristics on efficacy of risankizumab compared with ustekinumab in patients with moderate-to-severe plaque psoriasis. METHODS: This analysis included all patients initially randomized to risankizumab or ustekinumab from the replicate, double-blinded, randomized, placebo-controlled phase 3 trials, UltIMMa-1 (NCT02684370) and UltIMMa-2 (NCT02684357). Patients received either risankizumab (150 mg) or ustekinumab (weight-based; 45 or 90 mg per label) at weeks 0, 4, 16, 28 and 40. Efficacy was assessed as the proportion of patients achieving ≥90% improvement in Psoriasis Area and Severity Index (PASI 90) at weeks 16 and 52 by baseline patient demographics, disease characteristics and prior biologic exposure. Mean per cent improvement in PASI was calculated by body weight and body mass index at week 52. Missing efficacy data were imputed as non-responders for categorical variables and last observation carried forward for continuous variables. Logistic regression analyses assessed for interactions between treatment and five independent variables (age, sex, weight, baseline PASI score and presence of psoriatic arthritis) at both weeks 16 and 52. RESULTS: Baseline patient demographics, disease characteristics and prior biologic exposure were similar between patients randomized to risankizumab (n = 598) and ustekinumab (n = 199). At weeks 16 and 52, risankizumab demonstrated superior efficacy compared with ustekinumab across these patient characteristics (P < 0.01). Logistic regression analyses demonstrated that risankizumab was superior to ustekinumab at weeks 16 and 52 in all models tested (P < 0.0001 for all). CONCLUSIONS: Risankizumab demonstrated consistent and superior efficacy compared with ustekinumab regardless of patient demographics, disease characteristics or prior biologic exposure

Comparison of risankizumab and apremilast for the treatment of adult patients with moderate plaque psoriasis eligible for systemic therapy: results from a randomised, open-label, assessor-blinded phase IV (IMMpulse) study

BACKGROUND: Treatment with risankizumab has demonstrated superior efficacy to other psoriasis treatments, such as adalimumab, ustekinumab, and secukinumab. OBJECTIVES: This study compared the efficacy and safety of risankizumab and apremilast among adult patients with moderate plaque psoriasis eligible for systemic therapy. It also evaluated the efficacy and safety of switching to risankizumab versus continuing apremilast among patients who did not achieve ≥ 75% improvement in Psoriasis Area and Severity Index (PASI 75 non-responders) after 16 weeks of treatment with apremilast. METHODS: This 52-week, phase 4, multicenter, randomised, open-label, efficacy assessor-blinded study (NCT04908475) enrolled patients (≥ 18 years) with a diagnosis of moderate chronic plaque psoriasis (≥ 6 months) and were candidates for systemic therapy. The enrolled patients (1:2) received subcutaneous risankizumab (150 mg, week 0, 4) or oral apremilast (30 mg twice daily). At week 16, all apremilast-treated patients were re-randomised (1:1) to risankizumab or apremilast, stratified by week 16 PASI 75 response. The co-primary outcomes in Period A at week 16 were the achievement of PASI 90 and static Physician\u27s Global Assessment (sPGA) 0/1 with ≥ 2-grade improvement from baseline. At week 52, the primary endpoint in Period B was the achievement of PASI 90 in PASI 75 non-responders with apremilast at week 16. Safety was monitored throughout the study. All patients who received one dose of treatment were included in the efficacy and safety analysis. RESULTS: At baseline, 118 and 234 patients were assigned to receive risankizumab and apremilast, respectively. At week 16, PASI 90 was achieved by 55.9% (95% CI, 47.0%, 64.9%) and 5.1% (95% CI, 2.3%, 8.0%), and sPGA 0/1 by 75.4% (95% CI, 67.7%, 83.2%) and 18.4% (95% CI, 13.4%, 23.3%), respectively. In Period B, among PASI 75 non-responders with apremilast at week 16, 83 switched to risankizumab, and 78 continued apremilast. At week 52, 72.3% (95% CI, 62.7%, 81.9%) who switched to risankizumab achieved PASI 90 versus 2.6% (95% CI, 0.0%, 6.1%) who continued apremilast. The most frequent adverse events (reported in ≥ 5%) in risankizumab-treated patients were COVID-19 and nasopharyngitis. Diarrhoea, nausea, and headache were most frequent among apremilast-treated patients. CONCLUSIONS: For patients with moderate psoriasis, treatment with risankizumab demonstrated superior efficacy compared to apremilast, including those who did not benefit from prior treatment with apremilast. The safety profile of risankizumab was similar to prior studies, and no new safety signals were identified. These results show that risankizumab treatment can significantly improve clinical outcomes in systemic-eligible patients with moderate psoriasis compared to apremilast

G protein βγ-subunits activated by serotonin mediate presynaptic inhibition by regulating vesicle fusion properties

Neurotransmitters are thought to be released as quanta, where synaptic vesicles deliver packets of neurotransmitter to the synaptic cleft by fusion with the plasma membrane. However, synaptic vesicles may undergo incomplete fusion. We provide evidence that G protein-coupled receptors inhibit release by causing such incomplete fusion. 5-hydroxytryptamine (5-HT) receptor signaling potently inhibits excitatory postsynaptic currents (EPSCs) between lamprey reticulospinal axons and their postsynaptic targets by a direct action on the vesicle fusion machinery. We show that 5-HT receptor-mediated presynaptic inhibition, at this synapse, involves a reduction in EPSC quantal size. Quantal size was measured directly by comparing unitary quantal amplitudes of paired EPSCs before and during 5-HT application and indirectly by determining the effect of 5-HT on the relationship between mean-evoked EPSC amplitude and variance. Results from FM dye-labeling experiments indicate that 5-HT prevents full fusion of vesicles. 5-HT reduces FM1-43 staining of vesicles with a similar efficacy to its effect on the EPSC. However, destaining of FM1-43-labeled vesicles is abolished by lower concentrations of 5-HT that leave a substantial EPSC. The use of a water-soluble membrane impermeant quenching agent in the extracellular space reduced FM1-43 fluorescence during stimulation in 5-HT. Thus vesicles contact the extracellular space during inhibition of synaptic transmission by 5-HT. We conclude that 5-HT, via free Gβγ, prevents the collapse of synaptic vesicles into the presynaptic membrane

Kalirin regulates cortical spine morphogenesis and disease-related behavioral phenotypes

Dendritic spine morphogenesis contributes to brain function, cognition, and behavior, and is altered in psychiatric disorders. Kalirin is a brain-specific guanine-nucleotide exchange factor (GEF) for Rac-like GTPases and is a key regulator of spine morphogenesis. Here, we show that KALRN-knockout mice have specific reductions in cortical, but not hippocampal, Rac1 signaling and spine density, and exhibit reduced cortical glutamatergic transmission. These mice exhibit robust deficits in working memory, sociability, and prepulse inhibition, paralleled by locomotor hyperactivity reversible by clozapine in a kalirin-dependent manner. Several of these deficits are delayed and age-dependent. Our study thus links spine morphogenic signaling with age-dependent, delayed, disease-related phenotypes, including cognitive dysfunction

Epac2 induces synapse remodeling and depression and its disease-associated forms alter spines

Dynamic remodeling of spiny synapses is crucial for cortical circuit development, refinement, and plasticity, while abnormal morphogenesis is associated with neuropsychiatric disorders. Here we show in cultured rat cortical neurons that activation of Epac2, a PKA-independent cAMP target and Rap guanine-nucleotide exchange factor (GEF), induces spine shrinkage, increases spine motility, removes synaptic GluR2/3-containing AMPA receptors, and depresses excitatory transmission, while its inhibition promotes spine enlargement and stabilization. Epac2 is required for dopamine D1-like receptor-dependent spine shrinkage and GluR2 removal from spines. Epac2 interaction with neuroligin promotes its membrane recruitment and enhances its GEF activity. Rare missense mutations in the EPAC2 gene, previously found in individuals with autism, affect basal and neuroligin-stimulated GEF activity, dendritic Rap signaling, synaptic protein distribution, and spine morphology. Thus, we identify a novel mechanism that promotes dynamic remodeling and depression of spiny synapses, whose mutations may contribute to some aspects of disease

Cannabinoids and epilepsy

Cannabis has been used for centuries to treat seizures. Recent anecdotal reports, accumulating animal model data, and mechanistic insights have raised interest in cannabis-based antiepileptic therapies. In this study, we review current understanding of the endocannabinoid system, characterize the pro- and anticonvulsive effects of cannabinoids [e.g., Δ9-tetrahydrocannabinol and cannabidiol (CBD)], and high-light scientific evidence from pre-clinical and clinical trials of cannabinoids in epilepsy. These studies suggest that CBD avoids the psychoactive effects of the endocannabinoid system to provide a well-tolerated, promising therapeutic for the treatment of seizures, while whole-plant cannabis can both contribute to and reduce seizures. Finally, we discuss results from a new multicenter, open-label study using CBD in a population with treatment-resistant epilepsy. In all, we seek to evaluate our current understanding of cannabinoids in epilepsy and guide future basic science and clinical studies