Efficacy of risankizumab across subgroups in patients with active psoriatic arthritis: a post hoc integrated analysis of the phase 3 KEEPsAKE 1 and KEEPsAKE 2 randomized controlled trials.

In the KEEPsAKE 1 (NCT03675308) and KEEPsAKE 2 (NCT03671148) phase 3 trials, risankizumab demonstrated greater efficacy compared with placebo in patients with active psoriatic arthritis (PsA). This post hoc integrated analysis evaluated achieving the following efficacy outcomes at weeks 24 and 52 by baseline demographics and clinical characteristics: ≥20%/50%/70% improvement in American College of Rheumatology response criteria (ACR20/50/70), ≥90% improvement in Psoriasis Area and Severity Index, minimal disease activity status, Low Disease Activity status (Disease Activity in Psoriatic Arthritis), and minimal clinically important difference in pain. Baseline demographics and clinical characteristics were similar between risankizumab (n = 707) and placebo (n = 700) groups. Numerically higher ACR20 response rates at week 24 (primary endpoint) were observed among the risankizumab (46.3%-60.1%) vs. placebo (15.5%-36.2%) cohorts, regardless of subgroups. At week 52, consistent proportions of patients randomized to risankizumab achieved ACR20 (48.6%-75.8%) while those initially randomized to placebo and switched to risankizumab experienced an improvement from week 24 (43.7%-63.9%), regardless of subgroups. Similar trends were observed for other efficacy measures assessing rigorous skin response criteria, composite measures of overall disease activity, and PsA-related symptoms. Risankizumab treatment was efficacious among patients with varying demographic and psoriatic disease characteristics through 52 weeks.

Efficacy and Safety of Risankizumab for Active Psoriatic Arthritis: 100-Week Results from the Phase 3 KEEPsAKE 1 Randomized Clinical Trial.

INTRODUCTION: Patients with psoriatic arthritis (PsA) require treatment providing durable long-term efficacy in different disease domains as well as safety. We present 100-week efficacy and safety results of risankizumab in patients with active PsA and previous inadequate response/intolerance to ≥ 1 conventional synthetic disease-modifying antirheumatic drug (csDMARD-IR). METHODS: KEEPsAKE 1 (NCT03675308) is a global phase 3 study, including a 24-week, double-blind, placebo-controlled and ongoing open-label extension periods. Patients were randomized 1:1 to receive risankizumab 150 mg or placebo at baseline and weeks 4 and 16. After week 24, all patients received open-label risankizumab every 12 weeks thereafter. Patients were evaluated through 100 weeks. Endpoints included achieving ≥ 20% reduction in American College of Rheumatology criteria for symptoms of rheumatoid arthritis (ACR20), minimal disease activity (MDA; defined as ≥ 5/7 criteria of low disease activity and extent), and other measures. RESULTS: Overall, 828/964 (85.9%) patients completed week 100. For patients receiving continuous risankizumab, 57.3%, 70.6%, and 64.3% achieved ACR20 at weeks 24, 52, and 100, respectively. For the placebo/risankizumab cohort, 33.5% achieved ACR20 at week 24 but increased after switching to active treatment at weeks 52 (63.7%) and 100 (62.1%). In ACR20 responders at week 52, 81.2% of both treatment cohorts maintained response at week 100. MDA was achieved by 25.0%, 38.3%, and 38.2% of the continuous risankizumab cohort at weeks 24, 52, and 100. In the placebo/risankizumab cohort, 10.2% achieved MDA at week 24, increasing at weeks 52 (28.0%) and 100 (35.2%). MDA response was maintained at week 100 in week 52 responders in the continuous risankizumab (75.5%) and placebo/risankizumab cohorts (78.2%). Similar trends were observed for other efficacy measures. Risankizumab was generally well tolerated through 100 weeks. CONCLUSIONS: For patients with active PsA who are csDMARD-IR, risankizumab demonstrated durable long-term efficacy and was generally well tolerated, with a consistent long-term safety profile. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT03675308.

Psoriatic arthritis (PsA) often affects individuals with the skin condition psoriasis. A biologic disease-modifying antirheumatic drug can help control inflammation and regulate the immune system to ease symptoms and slow progression of PsA. The ongoing KEEPsAKE 1 study is evaluating the efficacy and safety of risankizumab in patients with active PsA who previously have not had success with ≥ 1 conventional disease-modifying antirheumatic drug. Patients were initially treated with risankizumab 150 mg (continuous risankizumab group) or inactive drug (inactive drug/risankizumab group). After 24 weeks, all received risankizumab for the rest of the study. At week 100, 64% (continuous risankizumab group) and 62% (inactive drug/risankizumab group) of patients had ≥ 20% improvement in PsA symptoms (measured using American College of Rheumatology [ACR20] criteria). Both groups showed similar percentages at week 52 and improvement from week 24. In patients who achieved ACR20 at week 52, 81% maintained their ACR20 response at week 100. Minimal disease activity was defined as a combination of joint and skin symptoms, affected body surface area, pain, and physical functioning. At week 100, 38% of the continuous risankizumab group and 35% of the inactive drug/risankizumab group achieved minimal disease activity. Percentages were similar at week 52 and higher than week 24 in both groups. In patients who achieved minimal disease activity at week 52, 81% maintained response at week 100. All other measures of treatment responses showed similar patterns from the start of risankizumab through week 100. Risankizumab was considered generally safe by the treating physicians.

Efficacy of long-term risankizumab treatment for moderate-to-severe plaque psoriasis: Subgroup analyses by baseline characteristics and psoriatic disease manifestations through 256 weeks (LIMMitless trial).

BACKGROUND: Psoriasis is an inflammatory skin disease that impacts a heterogeneous group of patients and can have multiple clinical manifestations. Risankizumab is approved for the treatment of moderate-to-severe plaque psoriasis. OBJECTIVES: To evaluate the long-term efficacy of risankizumab according to baseline patient characteristics, and for the treatment of high-impact disease manifestations (nail, scalp and palmoplantar psoriasis), through 256 weeks of continuous treatment in the phase 3 LIMMitless study. METHODS: This subgroup analysis evaluated pooled data from patients with moderate-to-severe plaque psoriasis who were randomized to risankizumab 150 mg during two double-blind, phase 3, 52-week base studies (UltIMMa-1/2; NCT02684370/NCT02684357) and were enrolled in the phase 3 LIMMitless open-label extension study (NCT03047395). Subgroup assessments included the proportion of patients who achieved ≥90%/100% improvement in Psoriasis Area and Severity Index (PASI 90/100). Among patients with nail, scalp and/or palmoplantar psoriasis in addition to skin psoriasis, assessments included changes from baseline in and resolution of these three psoriatic manifestations. RESULTS: Overall, a numerically similar proportion of patients (N = 525) achieved PASI 90/100 through Week 256, regardless of their baseline age, sex, body mass index, weight, PASI or psoriatic arthritis status. Patients with nail, scalp and/or palmoplantar psoriasis experienced substantial improvements in manifestation-specific indices (mean improvement from baseline to Week 256 of >81%, >94% and >97%, respectively); in patients with all three manifestations (N = 121), 44.6% achieved complete clearance of these manifestations at Week 256. CONCLUSIONS: Risankizumab demonstrated generally consistent efficacy through 256 weeks across patient subgroups and showed durable long-term efficacy for psoriatic disease manifestations.

Impact of psoriasis disease severity and special area involvement on patient-reported outcomes in the real world: an analysis from the CorEvitas psoriasis registry.

BACKGROUND: The impact of psoriasis in special areas (i.e., scalp, nails, palms, soles, genitals) on patient physical functioning, health-related quality of life (HRQoL), and work abilities has not been fully characterized. We assessed associations between disease severity and special area involvement in psoriasis symptoms, HRQoL, and work/activity impairment. METHODS: Patients with psoriasis from the CorEvitas Psoriasis Registry who initiated systemic treatment between 04/2015-06/2020 were included. Outcomes were change from baseline in psoriasis symptoms, Dermatology Life Quality Index (DLQI), and work/activity impairment at 6 months stratified by baseline disease severity and special area involvement. RESULTS: Among 2620 patients, increasing disease severity was associated with worsening patient-reported outcomes. Patients with (46.0%; N = 1205) versus without (54.0%; N = 1415) psoriasis in special areas reported greater HRQoL and work/activity impairment. Over 6 months, patients with unchanged or worsening disease severity had reduced HRQoL and increased symptom severity; incremental increases in patient HRQoL and decreases in symptom severity were associated with improved disease severity. CONCLUSIONS: Higher disease severity and special area involvement was associated with worse outcomes and impaired work abilities. These data highlight the significant impact that adequate treatment of severe psoriasis and/or special area involvement may have on patient HRQoL and function.

Real-world effectiveness of risankizumab in patients with moderate-to-severe psoriasis using the CorEvitas Psoriasis Registry.

BACKGROUND: Psoriasis, an inflammatory skin disease, is often treated with biologic therapeutics. OBJECTIVE: To determine the real-world treatment effectiveness of risankizumab, an interleukin-23 inhibitor, in the treatment of moderate-to-severe plaque psoriasis. METHODS: A retrospective, observational study was conducted using the CorEvitas Psoriasis Registry for eligible adults with a diagnosis of moderate-to-severe psoriasis and persistent use of risankizumab at 12 (±3) months after initiation. Skin clearance measures and patient-reported outcomes were analyzed for the entire study population and by prior biologic treatment. RESULTS: Among 287 patients with persistent risankizumab use at 1 year, most achieved clear or clear/almost clear skin and reported significant reductions in Dermatology Life Quality Index scores, psoriasis symptoms (fatigue, skin pain, and overall itch), and work and activity impairment. LIMITATIONS: The CorEvitas Psoriasis Registry is not necessarily representative of all adults with psoriasis in the United States and Canada and does not measure patient adherence. CONCLUSION: Patients treated with risankizumab, regardless of prior treatment, achieved high levels of clear and clear/almost clear skin, Dermatology Life Quality Index scores of 0/1, and significant reductions in psoriasis symptoms (fatigue, skin pain, and overall itch) and work and activity impairment 1 year after initiation.

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

BACKGROUND: Treatment of psoriasis with risankizumab has demonstrated superior efficacy to other treatments, such as adalimumab, ustekinumab and secukinumab. OBJECTIVES: This study compared the efficacy and safety of risankizumab and apremilast in adults with moderate plaque psoriasis eligible for systemic therapy. It also evaluated the efficacy and safety of switching to risankizumab vs. continuing apremilast in patients who did not achieve ≥ 75% improvement in Psoriasis Area and Severity Index (PASI 75 nonresponders) after 16 weeks of treatment with apremilast. METHODS: This 52-week, phase IV, multicentre, randomized, open-label, efficacy assessor-blinded study (NCT04908475) enrolled patients (aged ≥ 18 years) with a diagnosis of moderate chronic plaque psoriasis (≥ 6 months) and who were candidates for systemic therapy. The enrolled patients (randomized 1 : 2) received subcutaneous risankizumab (150 mg at weeks 0 and 4) or oral apremilast (30 mg twice daily). At week 16, all patients treated with apremilast were re-randomized (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 ≥ 90% improvement in Psoriasis Area and Severity Index (PASI 90) and static Physician's Global Assessment (sPGA) 0/1 with a two-grade or better improvement from baseline. At week 52, the primary endpoint in period B was the achievement of PASI 90 in PASI 75 nonresponders 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% confidence interval (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 nonresponders 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 vs. 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 infection 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 to those treated with 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, compared with apremilast, risankizumab treatment can significantly improve clinical outcomes in systemic-eligible patients with moderate psoriasis.

Real-world dose escalation of biologics for moderate-to-severe psoriasis in the United States.

AIM: To compare real-world dose escalation of risankizumab with other US Food and Drug Administration (FDA)-approved biologic treatments for management of moderate-to-severe psoriasis (PsO) in the United States. METHODS: The Merative® MarketScan® Research Database was used to identify adults with ≥2 medical claims for PsO, ≥3 claims of the index biologic medication in the maintenance period, and ≥6 months continuous enrollment pre-induction and ≥6 months after initiation of the maintenance period. Dose escalation was defined as ≥2 dosing intervals where the average daily dose was ≥30% higher than the expected daily dose (per FDA-approved dosing). Comparisons between risankizumab and other cohorts were made using chi-square tests and logistic regression models. RESULTS: At the 30% threshold, the percentage of patients with dose escalation in the full maintenance period was significantly lower with risankizumab (2.0%) compared with other drug classes (tumor necrosis factor, interleukin (IL)-12/23, IL-17, or other IL-23 inhibitors: 17.6%, 10.0%, 18.3%, or 7.1%, respectively; p < 0.0001 for each) and individual biologics (adalimumab, ustekinumab, secukinumab, ixekizumab, and guselkumab; 17.9%, 10.0%, 15.7%, 18.0%, and 7.2%, respectively; p < 0.0001). CONCLUSION: A significantly lower proportion of risankizumab-treated patients with PsO had dose escalations compared with patients treated with other biologics.

Switching to risankizumab from ustekinumab or adalimumab in plaque psoriasis patients improves PASI and DLQI outcomes for sub-optimal responders.

BACKGROUND: Psoriasis is often treated with biologic therapies. While many patients see improvement in their symptoms with treatment, some achieve only partial success. OBJECTIVE AND METHODS: In this post-hoc analysis we assess Psoriasis Area Severity Index (PASI) and Dermatology Life Quality Index (DLQI) results from patients who switched to RZB due to suboptimal results that originally received ADA (N = 53, IMMvent NCT02694523) or UST (N = 172, UltIMMa-1 [NCT02684370], UltIMMa-2 [NCT02684357]). RESULTS: For patients originally treated with ADA, after three doses of RZB, 83.3% of PASI 50 to <75 patients improved to PASI ≥75 and for PASI 75 to <90 patients, 77.1% improved to PASI ≥90. For patients originally treated with UST, after 7 doses of RZB, 86.8% of PASI <75 patients improved to PASI ≥75 and 75.5% of PASI 75 to ≤90 patients improved to PASI ≥90. No patients demonstrated worsening from their initial PASI group after switching. There were no significant safety events associated with switching patients to RZB without a washout period. CONCLUSION: For patients with an inadequate or incomplete response to UST or ADA, switching to RZB improved PASI scores and DLQI for patients with moderate to severe plaque psoriasis with no significant safety risks.

Efficacy of Risankizumab versus Secukinumab in Patients with Moderate-to-Severe Psoriasis: Subgroup Analysis from the IMMerge Study.

INTRODUCTION: Patients with moderate-to-severe plaque psoriasis who experience poor clinical outcomes, including patients with obesity or prior treatment, need improved treatment options. Risankizumab specifically inhibits interleukin 23 and has demonstrated superior efficacy in active-comparator studies in patients with moderate-to-severe plaque psoriasis. We compared the efficacy of risankizumab with that of secukinumab across patient subgroups. METHODS: Subgroup analyses using data from the phase 3 IMMerge study (NCT03478787) were performed. Efficacy in adults with moderate-to-severe psoriasis treated with risankizumab 150 mg and secukinumab 300 mg was assessed as the proportion of patients who achieved ≥ 90% improvement in Psoriasis Area Severity Index (PASI 90) at week 52 across demographics and disease characteristics. Post hoc analyses evaluated the proportion of patients who achieved PASI 90 and the least-squares mean percent PASI improvement from baseline at week 52 by body weight and body mass index (BMI), PASI 90 by prior treatment, and clinical response [PASI 90, PASI 100, and/or static Physician's Global Assessment (sPGA) score of clear (0) or almost clear (1)] at week 16 and maintained particular response at week 52. Logistic regression analyses examined the effect of covariates (age, sex, BMI, baseline PASI, treatment) and potential interactions on PASI 90 at week 52. RESULTS: More patients who received risankizumab (n = 164) compared with secukinumab (n = 163) achieved PASI 90 at week 52, regardless of demographics and disease characteristics (BMI, prior treatment, disease duration, and maintenance of clinical response at week 52). Improvements in PASI were greater in patients taking risankizumab than those taking secukinumab, regardless of weight or BMI. Results from logistic regression analysis showed treatment type had a significant impact on PASI 90 (risankizumab versus secukinumab, p < 0.0001). CONCLUSION: Risankizumab showed consistently greater efficacy compared with secukinumab across different patient subgroups, and this was maintained through 52 weeks. TRIAL REGISTRATION: ClinicalTrials.gov identifier; NCT03478787.

Patients with moderate-to-severe plaque psoriasis are often unable to achieve treatment success with currently available biologic therapies when they have other conditions, such as obesity, or have previous biologic therapy exposure and/or failure. We studied patients in the IMMerge phase 3 clinical trial (NCT03478787) to assess the efficacy of risankizumab compared with secukinumab for the treatment of plaque psoriasis and to determine risankizumab's ability to remain effective after 52 weeks of administration. In our analysis, we looked across patient subgroups including patient body weight, body mass index, previous use of biologic therapies, length of time patients had been living with their disease, and the durability of risankizumab efficacy at 52 weeks. Results from our analysis showed that patients had greater success with risankizumab compared with secukinumab in treating their plaque psoriasis, despite their age, sex, race, and disease characteristics, and that risankizumab remained effective in treating plaque psoriasis at week 52. Previously reported safety results from the IMMerge clinical trial showed that there were no new concerns regarding side effects for either risankizumab or secukinumab. Overall, these results support the use of risankizumab to treat patients, including those who have other conditions or may not have had success with other therapies in treating their plaque psoriasis.

Dual pools of actin at presynaptic terminals.

We investigated actin's function in vesicle recycling and exocytosis at lamprey synapses and show that FM1-43 puncta and phalloidin-labeled filamentous actin (F-actin) structures are colocalized, yet recycling vesicles are not contained within F-actin clusters. Additionally, phalloidin also labels a plasma membrane-associated cortical actin. Injection of fluorescent G-actin revealed activity-independent dynamic actin incorporation into presynaptic synaptic vesicle clusters but not into cortical actin. Latrunculin-A, which sequesters G-actin, dispersed vesicle-associated actin structures and prevented subsequent labeled G-actin and phalloidin accumulation at presynaptic puncta, yet cortical phalloidin labeling persisted. Dispersal of presynaptic F-actin structures by latrunculin-A did not disrupt vesicle clustering or recycling or alter the amplitude or kinetics of excitatory postsynaptic currents (EPSCs). However, it slightly enhanced release during repetitive stimulation. While dispersal of presynaptic actin puncta with latrunculin-A failed to disperse synaptic vesicles or inhibit synaptic transmission, presynaptic phalloidin injection blocked exocytosis and reduced endocytosis measured by action potential-evoked FM1-43 staining. Furthermore, phalloidin stabilization of only cortical actin following pretreatment with latrunculin-A was sufficient to inhibit synaptic transmission. Conversely, treatment of axons with jasplakinolide, which induces F-actin accumulation but disrupts F-actin structures in vivo, resulted in increased synaptic transmission accompanied by a loss of phalloidin labeling of cortical actin but no loss of actin labeling within vesicle clusters. Marked synaptic deficits seen with phalloidin stabilization of cortical F-actin, in contrast to the minimal effects of disruption of a synaptic vesicle-associated F-actin, led us to conclude that two structurally and functionally distinct pools of actin exist at presynaptic sites.

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, whereas abnormal morphogenesis is associated with neuropsychiatric disorders. We found that activation of Epac2, a PKA-independent cAMP target and Rap guanine-nucleotide exchange factor (GEF), in cultured rat cortical neurons induced spine shrinkage, increased spine motility, removed synaptic GluR2/3-containing AMPA receptors and depressed excitatory transmission, whereas its inhibition promoted spine enlargement and stabilization. Epac2 was required for dopamine D1-like receptor-dependent spine shrinkage and GluR2 removal from spines. Epac2 interaction with neuroligin promoted its membrane recruitment and enhanced its GEF activity. Rare missense mutations in the EPAC2 (also known as RAPGEF4) gene, previously found in individuals with autism, affected basal and neuroligin-stimulated GEF activity, dendritic Rap signaling, synaptic protein distribution and spine morphology. Thus, we identify a previously unknown mechanism that promotes dynamic remodeling and depression of spiny synapses, disruption of which may contribute to some aspects of disease.

Presynaptic G-protein-coupled receptors dynamically modify vesicle fusion, synaptic cleft glutamate concentrations, and motor behavior.

Understanding how neuromodulators regulate behavior requires investigating their effects on functional neural systems, but also their underlying cellular mechanisms. Utilizing extensively characterized lamprey motor circuits, and the unique access to reticulospinal presynaptic terminals in the intact spinal cord that initiate these behaviors, we investigated effects of presynaptic G-protein-coupled receptors on locomotion from the systems level, to the molecular control of vesicle fusion. 5-HT inhibits neurotransmitter release via a Gbetagamma interaction with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that promotes kiss-and-run vesicle fusion. In the lamprey spinal cord, we demonstrate that, although presynaptic 5-HT receptors inhibit evoked neurotransmitter release from reticulospinal command neurons, their activation does not abolish locomotion but rather modulates locomotor rhythms. Liberation of presynaptic Gbetagamma causes substantial inhibition of AMPA receptor-mediated synaptic responses but leaves NMDA receptor-mediated components of neurotransmission mostly intact. Because Gbetagamma binding to the SNARE complex is displaced by Ca(2+)-synaptotagmin binding, 5-HT-mediated inhibition displays Ca(2+) sensitivity. We show that, as Ca(2+) accumulates presynaptically during physiological bouts of activity, 5-HT/Gbetagamma-mediated presynaptic inhibition is relieved, leading to a frequency-dependent increase in synaptic concentrations of glutamate. This frequency-dependent phenomenon mirrors a shift in the vesicle fusion mode and a recovery of AMPA receptor-mediated EPSCs from inhibition without a modification of NMDA receptor EPSCs. We conclude that activation of presynaptic 5-HT G-protein-coupled receptors state-dependently alters vesicle fusion properties to shift the weight of NMDA versus AMPA receptor-mediated responses at excitatory synapses. We have therefore identified a novel mechanism in which modification of vesicle fusion modes may profoundly alter locomotor behavior.

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.

Coordination of synaptic adhesion with dendritic spine remodeling by AF-6 and kalirin-7.

Remodeling of central excitatory synapses is crucial for synapse maturation and plasticity, and contributes to neurodevelopmental and psychiatric disorders. Remodeling of dendritic spines and the associated synapses has been postulated to require the coordination of adhesion with spine morphology and stability; however, the molecular mechanisms that functionally link adhesion molecules with regulators of dendritic spine morphology are mostly unknown. Here, we report that spine size and N-cadherin content are tightly coordinated. In rat mature cortical pyramidal neurons, N-cadherin-dependent adhesion modulates the morphology of existing spines by recruiting the Rac1 guanine-nucleotide exchange factor kalirin-7 to synapses through the scaffolding protein AF-6/afadin. In pyramidal neurons, N-cadherin, AF-6, and kalirin-7 colocalize at synapses and participate in the same multiprotein complexes. N-cadherin clustering promotes the reciprocal interaction and recruitment of N-cadherin, AF-6, and kalirin-7, increasing the content of Rac1 and in spines and PAK (p21-activated kinase) phosphorylation. N-cadherin-dependent spine enlargement requires AF-6 and kalirin-7 function. Conversely, disruption of N-cadherin leads to thin, long spines, with reduced Rac1 contact, caused by uncoupling of N-cadherin, AF-6, and kalirin-7 from each other. By dynamically linking N-cadherin with a regulator of spine plasticity, this pathway allows synaptic adhesion molecules to rapidly coordinate spine remodeling associated with synapse maturation and plasticity. This study hence identifies a novel mechanism whereby cadherins, a major class of synaptic adhesion molecules, signal to the actin cytoskeleton to control the morphology of dendritic spines, and outlines a mechanism that underlies the coordination of synaptic adhesion with spine morphology.

Kalirin-7 controls activity-dependent structural and functional plasticity of dendritic spines.

Activity-dependent rapid structural and functional modifications of central excitatory synapses contribute to synapse maturation, experience-dependent plasticity, and learning and memory and are associated with neurodevelopmental and psychiatric disorders. However, the signal transduction mechanisms that link glutamate receptor activation to intracellular effectors that accomplish structural and functional plasticity are not well understood. Here we report that NMDA receptor activation in pyramidal neurons causes CaMKII-dependent phosphorylation of the guanine-nucleotide exchange factor (GEF) kalirin-7 at residue threonine 95, regulating its GEF activity, leading to activation of small GTPase Rac1 and rapid enlargement of existing spines. Kalirin-7 also interacts with AMPA receptors and controls their synaptic expression. By demonstrating that kalirin expression and spine localization are required for activity-dependent spine enlargement and enhancement of AMPAR-mediated synaptic transmission, our study identifies a signaling pathway that controls structural and functional spine plasticity.

G protein betagamma-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 Gbetagamma, prevents the collapse of synaptic vesicles into the presynaptic membrane.

Location and function of vesicle clusters, active zones and Ca2+ channels in the lamprey presynaptic terminal.

Synaptic transmission requires spatial and temporal coordination of a specific sequence of events. The trigger for synaptic vesicle exocytosis is Ca(2)(+) entry into presynaptic terminals, leading to neurotransmitter release at highly specialized sites known as active zones. Ca(2)(+) channel proximity to exocytotic proteins and vesicle clusters at active zones have been inferred from biochemical, histological and ultrastructural data, but direct evidence about functional relationships between these elements in central synapses is absent. We have utilized the lamprey giant reticulospinal synapse to characterize functional colocalization of known synaptic markers in the presynaptic terminal, as well as their reliability during repeated activation. Recycling vesicle clusters, surrounding actin filaments, and physiologically relevant Ca(2)(+) influx all show identical morphological distribution. Ca(2)(+) influx is mediated by clusters of Ca(2)(+) channels that colocalize with the vesicle clusters, defined by imaged sites of vesicle recycling and actin localization. Synaptic transmission is inhibited by block of actin depolymerization, but Ca(2)(+) signalling is unaffected. Functional Ca(2)(+) channels are localized to presynaptic clusters, and Ca(2)(+) transients at these sites account for neurotransmitter release based on their spatial and temporal profiles. Ca(2)(+) transients evoked by single axonal action potentials are mediated solely by voltage-operated Ca(2)(+) channel activation, and slower Ca(2)(+) rises observed throughout the axon result from Ca(2)(+) diffusion from the synaptic regions. We conclude that at lamprey giant reticulospinal synapses, Ca(2)(+) channels and release sites colocalize, creating a close spatial relationship between active zones and Ca(2)(+) entry sites, which is necessary for site-specific, Ca(2)(+)-dependent secretion.