Stochastic growth and selective stabilization generate stereotyped dendritic arbors.

Stereotyped dendritic arbors are shaped by dynamic and stochastic growth during neuronal development. It remains unclear how guidance receptors and ligands coordinate branch dynamic growth, retraction, and stabilization to specify dendritic arbors. We previously showed that extracellular ligand SAX-7/LICAM dictates the shape of the PVD sensory neuron via binding to the dendritic guidance receptor DMA-1, a single transmembrane adhesion molecule. Here, we perform structure-function analyses of DMA-1 and unexpectedly find that robust, stochastic dendritic growth does not require ligand-binding. Instead, ligand-binding inhibits growth, prevents retraction, and specifies arbor shape. Furthermore, we demonstrate that dendritic growth requires a pool of ligand-free DMA-1, which is maintained by receptor endocytosis and reinsertion to the plasma membrane via recycling endosomes. Mutants defective of DMA-1 endocytosis show severely truncated dendritic arbors. We present a model in which ligand-free guidance receptor mediates intrinsic, stochastic dendritic growth, while extracellular ligands instruct dendrite shape by inhibiting growth.

The intrinsically disordered cytoplasmic tail of a dendrite branching receptor uses two distinct mechanisms to regulate the actin cytoskeleton.

Dendrite morphogenesis is essential for neural circuit formation, yet the molecular mechanisms underlying complex dendrite branching remain elusive. Previous studies on the highly branched Caenorhabditis elegans PVD sensory neuron identified a membrane co-receptor complex that links extracellular signals to intracellular actin remodeling machinery, promoting high-order dendrite branching. In this complex, the claudin-like transmembrane protein HPO-30 recruits the WAVE regulatory complex (WRC) to dendrite branching sites, stimulating the Arp2/3 complex to polymerize actin. We report here our biochemical and structural analysis of this interaction, revealing that the intracellular domain (ICD) of HPO-30 is intrinsically disordered and employs two distinct mechanisms to regulate the actin cytoskeleton. First, HPO-30 ICD binding to the WRC requires dimerization and involves the entire ICD sequence, rather than a short linear peptide motif. This interaction enhances WRC activation by the GTPase Rac1. Second, HPO-30 ICD directly binds to the sides and barbed end of actin filaments. Binding to the barbed end requires ICD dimerization and inhibits both actin polymerization and depolymerization, resembling the actin capping protein CapZ. These dual functions provide an intriguing model of how membrane proteins can integrate distinct mechanisms to fine-tune local actin dynamics.

Apremilast Long-Term Safety Up to 5 Years from 15 Pooled Randomized, Placebo-Controlled Studies of Psoriasis, Psoriatic Arthritis, and Behçet's Syndrome.

BACKGROUND: Since US FDA approval in 2014, apremilast has consistently demonstrated a favorable benefit-risk profile in 706,585 patients (557,379 patient-years of exposure) worldwide across approved indications of plaque psoriasis, psoriatic arthritis, and Behçet's syndrome; however, long-term exposure across these indications has not been reported. OBJECTIVE: The aim of this study was to conduct a pooled analysis of apremilast data from 15 clinical studies with open-label extension phases, focusing on long-term safety. METHODS: We analyzed longer-term safety and tolerability of apremilast 30 mg twice daily across three indications for up to 5 years, focusing on adverse events of special interest, including thrombotic events, malignancies, major adverse cardiac events (MACE), serious infections, and depression. Data were pooled across 15 randomized, placebo-controlled studies and divided into placebo-controlled or all-apremilast-exposure groups. Treatment-emergent adverse events (TEAEs) were assessed. RESULTS: Overall, 4183 patients were exposed to apremilast (6788 patient-years). Most TEAEs were mild to moderate in the placebo-controlled period (96.6%) and throughout all apremilast exposure (91.6%). TEAE rates of special interest were similar between treatment groups in the placebo-controlled period and remained low throughout all apremilast exposure. Exposure-adjusted incidence rates per 100 patient-years during all apremilast exposure were MACE, 0.30; thrombotic events, 0.10; malignancies, 1.0; serious infections, 1.10; serious opportunistic infections, 0.21; and depression, 1.78. Safety findings were consistent across indications and regions. No new safety signals were identified. CONCLUSIONS: The incidence of serious TEAEs and TEAEs of special interest was low despite long-term exposure, further establishing apremilast as a safe oral option for long-term use across indications with a favorable benefit-risk profile. CLINICAL TRIAL REGISTRATION: NCT00773734, NCT01194219, NCT01232283, NCT01690299, NCT01988103, NCT02425826, NCT03123471, NCT03721172, NCT01172938, NCT01212757, NCT01212770, NCT01307423, NCT01925768, NCT00866359, NCT02307513.

Dendrites use mechanosensitive channels to proofread ligand-mediated neurite extension during morphogenesis.

Ligand-receptor interactions guide axon navigation and dendrite arborization. Mechanical forces also influence guidance choices. However, the nature of such mechanical stimulations, the mechanosensor identity, and how they interact with guidance receptors are unknown. Here, we demonstrate that mechanosensitive DEG/ENaC channels are required for dendritic arbor morphogenesis in Caenorhabditis elegans. Inhibition of DEG/ENaC channels causes reduced dendritic outgrowth and branching in vivo, a phenotype that is alleviated by overexpression of the mechanosensitive channels PEZO-1/Piezo or YVC1/TrpY1. DEG/ENaCs trigger local Ca2+ transients in growing dendritic filopodia via activation of L-type voltage-gated Ca2+ channels. Anchoring of filopodia by dendrite ligand-receptor complexes is required for the mechanical activation of DEG/ENaC channels. Therefore, mechanosensitive channels serve as a checkpoint for appropriate chemoaffinity by activating Ca2+ transients required for neurite growth.

A two-step actin polymerization mechanism drives dendrite branching.

BACKGROUND: Dendrite morphogenesis plays an essential role in establishing the connectivity and receptive fields of neurons during the development of the nervous system. To generate the diverse morphologies of branched dendrites, neurons use external cues and cell surface receptors to coordinate intracellular cytoskeletal organization; however, the molecular mechanisms of how this signaling forms branched dendrites are not fully understood. METHODS: We performed in vivo time-lapse imaging of the PVD neuron in C. elegans in several mutants of actin regulatory proteins, such as the WAVE Regulatory Complex (WRC) and UNC-34 (homolog of Enabled/Vasodilator-stimulated phosphoprotein (Ena/VASP)). We examined the direct interaction between the WRC and UNC-34 and analyzed the localization of UNC-34 in vivo using transgenic worms expressing UNC-34 fused to GFP. RESULTS: We identify a stereotyped sequence of morphological events during dendrite outgrowth in the PVD neuron in C. elegans. Specifically, local increases in width ("swellings") give rise to filopodia to facilitate a "rapid growth and pause" mode of growth. In unc-34 mutants, filopodia fail to form but swellings are intact. In WRC mutants, dendrite growth is largely absent, resulting from a lack of both swelling and filopodia formation. We also found that UNC-34 can directly bind to the WRC. Disrupting this binding by deleting the UNC-34 EVH1 domain prevented UNC-34 from localizing to swellings and dendrite tips, resulting in a stunted dendritic arbor and reduced filopodia outgrowth. CONCLUSIONS: We propose that regulators of branched and linear F-actin cooperate to establish dendritic branches. By combining our work with existing literature, we propose that the dendrite guidance receptor DMA-1 recruits the WRC, which polymerizes branched F-actin to generate "swellings" on a mother dendrite. Then, WRC recruits the actin elongation factor UNC-34/Ena/VASP to initiate growth of a new dendritic branch from the swelling, with the help of the actin-binding protein UNC-115/abLIM. Extension of existing dendrites also proceeds via swelling formation at the dendrite tip followed by UNC-34-mediated outgrowth. Following dendrite initiation and extension, the stabilization of branches by guidance receptors further recruits WRC, resulting in an iterative process to build a complex dendritic arbor.

Apremilast mechanism of efficacy in systemic-naive patients with moderate plaque psoriasis: Pharmacodynamic results from the UNVEIL study.

BACKGROUND: Pharmacodynamic (PD) subanalyses of clinical trials in patients with moderate to severe psoriasis demonstrated the efficacy of apremilast correlated with reductions in cytokines involved in the pathogenesis of psoriasis. OBJECTIVE: This PD subanalysis of a phase IV, randomized, controlled trial (UNVEIL) in systemic-naive patients with moderate plaque psoriasis (psoriasis-involved body surface area [BSA] 5%-10%; static Physician's Global Assessment [sPGA] = 3) evaluated the relationship between efficacy and changes in inflammatory biomarkers with apremilast 30 mg twice daily (BID) versus placebo. METHODS: Patients were randomized (2:1) to apremilast 30 mg BID or placebo for 16 weeks. Blood samples were analyzed for interleukins (IL)-17A, -17F, -22, and -23; cardiometabolic biomarkers (leptin; adiponectin; apolipoproteins A-I, A-II, B, and E); and the number of T-helper 17 (Th17) cells, regulatory T cells, and total T cells at Weeks 0, 4, and 16. Correlations were examined between percentage change in biomarkers and efficacy (based on PGAxBSA). RESULTS: Of 221 randomized patients, 38 were included in PD analyses (placebo, n = 12; apremilast, n = 26). Median percentage reductions in plasma cytokine levels were significantly greater with apremilast versus placebo for IL-17A (P < 0.05), IL -17F (P < 0.001), and IL-22 (P < 0.01) at Week 4 and IL-22 (P < 0.05) at Week 16. At Week 16, in patients receiving apremilast, improvement in PGAxBSA significantly correlated with change in IL-17A (r = 0.45, P = 0.04). Adipokines, apolipoproteins, and T-cell population levels were largely unchanged. CONCLUSION: Clinical improvements in psoriasis correlated with apremilast-mediated decreases in IL-17A without significantly affecting systemic IL-23 levels, adipokines, or Th17 and regulatory T-cell numbers.

The Golgi Outpost Protein TPPP Nucleates Microtubules and Is Critical for Myelination.

Oligodendrocytes extend elaborate microtubule arbors that contact up to 50 axon segments per cell, then spiral around myelin sheaths, penetrating from outer to inner layers. However, how they establish this complex cytoarchitecture is unclear. Here, we show that oligodendrocytes contain Golgi outposts, an organelle that can function as an acentrosomal microtubule-organizing center (MTOC). We identify a specific marker for Golgi outposts-TPPP (tubulin polymerization promoting protein)-that we use to purify this organelle and characterize its proteome. In in vitro cell-free assays, recombinant TPPP nucleates microtubules. Primary oligodendrocytes from Tppp knockout (KO) mice have aberrant microtubule branching, mixed microtubule polarity, and shorter myelin sheaths when cultured on 3-dimensional (3D) microfibers. Tppp KO mice exhibit hypomyelination with shorter, thinner myelin sheaths and motor coordination deficits. Together, our data demonstrate that microtubule nucleation outside the cell body at Golgi outposts by TPPP is critical for elongation of the myelin sheath.

SAP102 regulates synaptic AMPAR function through a CNIH-2-dependent mechanism.

The postsynaptic density (PSD)-95-like, disk-large (DLG) membrane-associated guanylate kinase (PSD/DLG-MAGUK) family of proteins scaffold α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) complexes to the postsynaptic compartment and are postulated to orchestrate activity-dependent modulation of synaptic AMPAR functions. SAP102 is a key member of this family, present from early development, before PSD-95 and PSD-93, and throughout life. Here we investigate the role of SAP102 in synaptic transmission using a cell-restricted molecular replacement strategy, where SAP102 is expressed against the background of acute knockdown of endogenous PSD-95. We show that SAP102 rescues the decrease of AMPAR-mediated evoked excitatory postsynaptic currents (AMPAR eEPSCs) and AMPAR miniature EPSC (AMPAR mEPSC) frequency caused by acute knockdown of PSD-95. Further analysis of the mini events revealed that PSD-95-to-SAP102 replacement but not direct manipulation of PSD-95 increases the AMPAR mEPSC decay time. SAP102-mediated rescue of AMPAR eEPSCs requires AMPAR auxiliary subunit cornichon-2, whereas cornichon-2 knockdown did not affect PSD-95-mediated regulation of AMPAR eEPSC. Combining these observations, our data elucidate that PSD-95 and SAP102 differentially influence basic synaptic properties and synaptic current kinetics potentially via different AMPAR auxiliary subunits. NEW & NOTEWORTHY Synaptic scaffold proteins postsynaptic density (PSD)-95-like, disk-large (DLG) membrane-associated guanylate kinase (PSD-MAGUKs) regulate synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function. However, the functional diversity among different PSD-MAGUKs remains to be categorized. We show that distinct from PSD-95, SAP102 increase the AMPAR synaptic current decay time, and the effect of SAP102 on synaptic AMPAR function requires the AMPAR auxiliary subunit cornichon-2. Our data suggest that PSD-MAGUKs target and modulate different AMPAR complexes to exert specific experience-dependent modification of the excitatory circuit.

A Dendritic Guidance Receptor Complex Brings Together Distinct Actin Regulators to Drive Efficient F-Actin Assembly and Branching.

Proper morphogenesis of dendrites plays a fundamental role in the establishment of neural circuits. The molecular mechanism by which dendrites grow highly complex branches is not well understood. Here, using the Caenorhabditis elegans PVD neuron, we demonstrate that high-order dendritic branching requires actin polymerization driven by coordinated interactions between two membrane proteins, DMA-1 and HPO-30, with their cytoplasmic interactors, the RacGEF TIAM-1 and the actin nucleation promotion factor WAVE regulatory complex (WRC). The dendrite branching receptor DMA-1 directly binds to the PDZ domain of TIAM-1, while the claudin-like protein HPO-30 directly interacts with the WRC. On dendrites, DMA-1 and HPO-30 form a receptor-associated signaling complex to bring TIAM-1 and the WRC to close proximity, leading to elevated assembly of F-actin needed to drive high-order dendrite branching. The synergistic activation of F-actin assembly by scaffolding distinct actin regulators might represent a general mechanism in promoting complex dendrite arborization.

Shank Proteins Differentially Regulate Synaptic Transmission.

Shank proteins, one of the principal scaffolds in the postsynaptic density (PSD) of the glutamatergic synapses, have been associated with autism spectrum disorders and neuropsychiatric diseases. However, it is not known whether different Shank family proteins have distinct functions in regulating synaptic transmission, and how they differ from other scaffold proteins in this aspect. Here, we investigate the role of Shanks in regulating glutamatergic synaptic transmission at rat hippocampal SC-CA1 synapses, using lentivirus-mediated knockdown and molecular replacement combined with dual whole-cell patch clamp in hippocampal slice culture. In line with previous findings regarding PSD-MAGUK scaffold manipulation, we found that loss of scaffold proteins via knockdown of Shank1 or Shank2, but not Shank3, led to a reduction of the number but not the unitary response of AMPAR-containing synapses. Only when both Shank1 and Shank2 were knocked down, were both the number and the unitary response of active synapses reduced. This reduction was accompanied by a decrease in NMDAR-mediated synaptic response, indicating more profound deficits in synaptic transmission. Molecular replacement with Shank2 and Shank3c rescued the synaptic transmission to the basal level, and the intact sterile α-motif (SAM) of Shank proteins is required for maintaining glutamatergic synaptic transmission. We also found that altered neural activity did not influence the effect of Shank1 or Shank2 knockdown on AMPAR synaptic transmission, in direct contrast to the activity dependence of the effect of PSD-95 knockdown, revealing differential interaction between activity-dependent signaling and scaffold protein families in regulating synaptic AMPAR function.

Quality of life after laparoscopic adjustable gastric banding (LAP-BAND): APEX interim 3-year analysis.

BACKGROUND: Obesity is often associated with diminished health-related quality of life (HRQOL), but significant gains in HRQOL have been observed after bariatric surgery. Laparoscopic adjustable gastric banding has been established as a safe, effective treatment to reduce weight in patients with obesity. This report summarizes interim 3-year changes in HRQOL and body weight, as well as safety postimplantation of the LAP-BAND AP (LBAP) system. METHODS: The LAP-BAND AP EXperience (APEX) trial, an ongoing, prospective, 5-year, open-label study, assessed changes in HRQOL (Obesity and Weight-Loss Quality of Life [OWLQOL] questionnaire) and body weight, and safety after placement of LBAP. This interim analysis represents patients with evaluable OWLQOL data at baseline and at 3 years (n = 183). RESULTS: The OWLQOL total score and individual scores significantly improved within 6 months post-LBAP and continued to improve during a 3 year period (P < 0.0001, both). Total score improved from 71.0 to 34.0 (mean improvement from baseline, 52%; range, 18%-65%); mean change in individual scores was -2.2 (range, -0.7 to -3.0). Percent weight loss was maintained through 3 years (19.4%; n = 174). Improvement in OWLQOL was associated with percent weight loss at 3 years (r = -0.5407; P < 0.0001). Revisions and explants were performed in 7 (3.8%) and 20 (10.9%) out of 183 patients, respectively. CONCLUSIONS: Meaningful improvement in quality of life occurred through clinically significant weight loss after LBAP placement, extending throughout the 3 years of this analysis.

Differential requirement for NMDAR activity in SAP97ß-mediated regulation of the number and strength of glutamatergic AMPAR-containing synapses.

PSD-95-like, disc-large (DLG) family membrane-associated guanylate kinase proteins (PSD/DLG-MAGUKs) are essential for regulating synaptic AMPA receptor (AMPAR) function and activity-dependent trafficking of AMPARs. Using a molecular replacement strategy to replace endogenous PSD-95 with SAP97ß, we show that the prototypic ß-isoform of the PSD-MAGUKs, SAP97ß, has distinct NMDA receptor (NMDAR)-dependent roles in regulating basic properties of AMPAR-containing synapses. SAP97ß enhances the number of AMPAR-containing synapses in an NMDAR-dependent manner, whereas its effect on the size of unitary synaptic response is not fully dependent on NMDAR activity. These effects contrast with those of PSD-95α, which increases both the number of AMPAR-containing synapses and the size of unitary synaptic responses, with or without NMDAR activity. Our results suggest that SAP97ß regulates synaptic AMPAR content by increasing surface expression of GluA1-containing AMPARs, whereas PSD-95α enhances synaptic AMPAR content presumably by increasing the synaptic scaffold capacity for synaptic AMPARs. Our approach delineates discrete effects of different PSD-MAGUKs on principal properties of glutamatergic synaptic transmission. Our results suggest that the molecular diversity of PSD-MAGUKs can provide rich molecular substrates for differential regulation of glutamatergic synapses in the brain.

Switching from calcineurin inhibitor-based regimens to a belatacept-based regimen in renal transplant recipients: a randomized phase II study.

BACKGROUND AND OBJECTIVES: Prolonged use of calcineurin inhibitors (CNIs) in kidney transplant recipients is associated with renal and nonrenal toxicity and an increase in cardiovascular risk factors. Belatacept-based regimens may provide a treatment option for patients who switch from CNI-based maintenance immunosuppression. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This is a randomized, open-label Phase II trial in renal transplant patients with stable graft function and receiving a CNI-based regimen. Patients who were ≥6 months but ≤36 months after transplantation were randomized to either switch to belatacept or continue CNI treatment. All patients received background maintenance immunosuppression. The primary end point was the change in calculated GFR (cGFR) from baseline to month 12. RESULTS: Patients were randomized either to switch to belatacept (n=84) or to remain on a CNI-based regimen (n=89). At month 12, the mean (SD) change from baseline in cGFR was higher in the belatacept group versus the CNI group. Six patients in the belatacept group had acute rejection episodes, all within the first 6 months; all resolved with no allograft loss. By month 12, one patient in the CNI group died with a functioning graft, whereas no patients in the belatacept group had graft loss. The overall safety profile was similar between groups. CONCLUSIONS: The study identifies a potentially safe and feasible method for switching stable renal transplant patients from a cyclosporine- or tacrolimus-based regimen to a belatacept-based regimen, which may allow improved renal function in patients currently treated with CNIs.

Five-year safety and efficacy of belatacept in renal transplantation.

Belatacept is a first-in-class co-stimulation blocker in development for primary maintenance immunosuppression. A Phase II study comparing belatacept with cyclosporine (CsA) for prevention of acute rejection and protection of renal function in kidney transplant recipients demonstrated similar efficacy and significantly higher measured GFR at 1 year for belatacept, but the incidence of posttransplantation lymphoproliferative disorder was higher. Here, we present the results for the extension of this trial, which aimed to assess long-term safety and efficacy of belatacept. Seventy-eight of 102 patients who were receiving belatacept and the 16 of 26 who were receiving CsA completed the long-term extension period. GFR remained stable in patients who were receiving belatacept for 5 years, and the incidences of death/graft loss or acute rejection were low. The frequencies of serious infections were 16% for belatacept and 27% for CsA, and neoplasms occurred in 12% of each group. No patients who were treated with belatacept and one patient who was treated with CsA developed posttransplantation lymphoproliferative disorder during the follow-up period. Serious gastrointestinal disorders occurred more frequently with belatacept (12% belatacept versus 8% CsA), and serious cardiac disorders occurred more frequently with CsA (2% belatacept versus 12% CsA). Pharmacokinetic analyses showed consistent exposure to belatacept over time. CD86 receptor saturation was higher in patients who were receiving belatacept every 4 weeks (74%) compared with every 8 weeks (56%). In conclusion, this study demonstrated high patient persistence with intravenous belatacept, stable renal function, predictable pharmacokinetics, and good safety with belatacept over 5 years.