The receptor protein tyrosine phosphatase CLR-1 is required for synaptic partner recognition.

During neural circuit formation, most axons are guided to complex environments, coming into contact with multiple potential synaptic partners. However, it is critical that they recognize specific neurons with which to form synapses. Here, we utilize the split GFP-based marker Neuroligin-1 GFP Reconstitution Across Synaptic Partners (NLG-1 GRASP) to visualize specific synapses in live animals, and a circuit-specific behavioral assay to probe circuit function. We demonstrate that the receptor protein tyrosine phosphatase (RPTP) clr-1 is necessary for synaptic partner recognition (SPR) between the PHB sensory neurons and the AVA interneurons in C. elegans. Mutations in clr-1/RPTP result in reduced NLG-1 GRASP fluorescence and impaired behavioral output of the PHB circuit. Temperature-shift experiments demonstrate that clr-1/RPTP acts early in development, consistent with a role in SPR. Expression and cell-specific rescue experiments indicate that clr-1/RPTP functions in postsynaptic AVA neurons, and overexpression of clr-1/RPTP in AVA neurons is sufficient to direct additional PHB-AVA synaptogenesis. Genetic analysis reveals that clr-1/RPTP acts in the same pathway as the unc-6/Netrin ligand and the unc-40/DCC receptor, which act in AVA and PHB neurons, respectively. This study defines a new mechanism by which SPR is governed, and demonstrates that these three conserved families of molecules, with roles in neurological disorders and cancer, can act together to regulate communication between cells.

A novel clock-face method for characterizing peridevice leaks after left atrial appendage occlusion.

OBJECTIVES: To propose a novel method for mapping leak location and frequency to a clock-face representation of the left atrial appendage (LAA) ostium. BACKGROUND: LAA occlusion with the Watchman device (WD) is an established therapy to reduce thromboembolic events in patients with atrial fibrillation (AF) and intolerance to long-term oral anticoagulation. Postimplantation leaks are known sequelae, but leak locations and characteristics are poorly described. METHODS: We retrospectively reviewed 101 consecutive WD implants from April 2015 to February 2018. Leak locations from 6-week post-implant transesophageal echocardiograms were mapped to a clock-face representation of the LAA ostium: 12:00 as cranial near the limbus, 3:00 as anterior toward the pulmonary artery, 6:00 as caudal near the mitral annulus, and 9:00 as posterior. Patient demographics, LAA dimensions, and procedural characteristics were also collected. RESULTS: Thirty-four patients had ≥1 leak totaling 45 leaks at 6-week follow-up. Baseline patient demographics showed a mean age 77, CHA2 DS2 VASc 4.69, and 64% of patients with permanent AF. No patient had a detectable leak at the time of implant. At 6 weeks, mean leak size was 2.67 ± 0.89 mm with no leak over 5 mm (largest 4.60 mm). Most leaks occurred along the posterior 6:00-12:00 segment (39/45) and the 6:00-9:00 quadrant (16/45). CONCLUSION: Six-week post-WD implant leaks localize to the posterior LAA ostium. This could result from the elliptical LAA orifice, differential LAA tissue composition, or implantation technique. This study provides a novel method for describing the location of post-implant leaks and serves as the basis for further investigations.

Intraprocedural direct left atrial and wedge pressure correlation during transcatheter mitral valve repair: Results from a single center registry.

OBJECTIVES: This study investigates the correlation of occlusive wedge pressure (WP) with direct left atrial (LA) pressure in patients with severe mitral regurgitation (MR) undergoing transcatheter mitral valve repair (TMVr) with MitraClip. BACKGROUND: There is interest in acquiring objective hemodynamic parameters for intraprocedural guidance in patients undergoing MitraClip. METHODS: The study included 94 patients with severe MR at prohibitive surgical risk who underwent MitraClip at the University of California Davis Medical Center between 2014 and 2016. RESULTS: An average of 1.8 ± 0.7 clips were used to achieve MR grade of 2+ or less in 99% of patients. Correlation analysis of all (n = 236) pre-clip, inter-clip, and final-clip WP and LA pressures yielded a Pearson's R (r) of 0.85 and 0.79 for mean WP vs mean LA and WP V vs LA V, respectively. Median LA V to mean LA ratio (LAV:mLA) was 1.75 (IQR 1.5-1.9). 79% (n = 74) of patients had LAV:mLA ratio ≥ 1.5 with associated WP V vs LA V correlation (r) of 0.83. In patients with LAV:mLA ratio < 1.5, the correlation (r) was 0.69. Baseline characteristics were not significantly different between patients with LAV:mLA ratio ≥ 1.5 and patients with LAV:mLA ratio < 1.5. Post-procedure, median LA V: mean LA ratio decreased from 1.75 to 1.4, P = 0.0001. CONCLUSIONS: Correlation between WP and direct LA pressure in patients with severe MR undergoing Mitraclip is modest. Caution is advised when using WP to approximate LA pressure intraprocedurally, especially in patients with baseline low LAV:mLA ratios.

"Cool Knees" as a Measure of Systemic Vascular Resistance in Cardiac Patients.

INTRODUCTION: Clinical assessment of cardiac output (CO) and systemic vascular resistance (SVR) in cardiac patients is often inaccurate. Since the genicular arteries form a watershed zone accessible to physical examination, we hypothesized that "cool knees" would reflect abnormalities in central hemodynamics. METHODS: Nineteen patients with cardiac diagnoses, but without distributive shock, had a measurement of skin temperature over the thigh, knee, and foot in parallel with central hemodynamics derived from invasive monitoring. RESULTS: The temperature gradient from thigh to knee (DTK) reflected increased SVR, and was significantly correlated with SVR, cardiac index (CI), and CO. Cool feet (DTF) were significantly correlated only with systemic hypotension, but not central hemodynamics. CONCLUSION: Cool knees reflect increased SVR in cardiac patients and may be an important physical exam finding in their assessment and management.

Watchman Occlusion in Long-Standing Persistent Atrial Fibrillation: Larger Left Atrial Appendages With Greater Residual Leak.

OBJECTIVES: This study sought to compare patients with and without long-standing persistent atrial fibrillation (LSPAF) undergoing Watchman left atrial appendage (LAA) occlusion. BACKGROUND: An increased burden of atrial fibrillation is associated with progressive left atrial remodeling and enlargement. METHODS: Transesophageal echocardiography (TEE) measures of LAA ostial diameter and depth, device compression, and residual leak were evaluated in 101 consecutive Watchman cases. The patients were categorized into LSPAF (n = 48) or non-LSPAF (n = 53) groups and compared. RESULTS: The average LAA ostial diameter for LSPAF versus non-LSPAF by TEE omniplane at 0° was 21.1 ± 4.1 mm versus 18.2 ± 3.6 mm (p = 0.0002); at 45° was 18.7 ± 3.4 mm versus 16.3 ± 3.1 mm (p = 0.0004); at 90° was 19.6 ± 3.8 mm versus 16.2 ± 3.4 mm (p = 0.00001); and at 135° was 21.0 ± 4.1 mm versus 18.0 ± 4.1 mm (p = 0.0005). The average LAA depth for LSPAF versus non-LSPAF by TEE at 0° was 28.1 ± 6.4 mm versus 25.2 ± 4.9 mm (p = 0.02); at 45° was 27.9 ± 5.8 mm versus 25.1 ± 4.3 mm (p = 0.007); at 90° was 27.2 ± 5.2 mm versus 22.8 ± 3.7 mm (p = 0.0001); and at 135° was 25.6 ± 5.4 mm versus 21.5 ± 3.8 mm (p = 0.0001). In successfully treated patients, 77% of the LSPAF group received larger device (27, 30, or 33 mm) implants versus only 46% in the non-LSPAF group (p = 0.003). While both groups had similar rates of moderate (3 to 5 mm) leaks at implant (2% vs. 0%; p = 0.14), 27% of the LSPAF vs. 4% of the non-LSPAF group had moderate leaks (p = 0.04) on 6-week follow-up TEE. CONCLUSIONS: Patients with LSPAF have significantly larger LAA sizes, require larger devices, and have more residual leak on follow-up TEE. LSPAF may represent a higher risk group that warrants more stringent long-term follow-up.

Proteinuria, Hypoalbuminemia, and Chronic Lymphocytic Leukemia: An Unusual Trio.

Chronic lymphocytic leukemia (CLL) is a chronic, progressive lymphoproliferative disorder characterized by a monoclonal population of functionally incompetent lymphocytes. Renal involvement is rare and poorly described. A 57-year-old male with no prior medical history was diagnosed with CLL and followed with a watch and wait approach. He was referred to our institution several months later due to concern for Richter's transformation to diffuse large B-cell lymphoma. A positron emission tomography/computed tomography scan showed no evidence of diffuse large B-cell lymphoma; however, the patient was noted to have hypoalbuminemia, nephrotic range proteinuria, an acute left renal vein thrombus, and a right pulmonary embolus. A nephrotic syndrome workup including autoimmunity and infection was unremarkable, and a kidney biopsy was deferred due to concern for renal compromise in the setting of a renal vein thrombus. The patient was treated with 6 cycles of reduced-dose fludarabine, cyclophosphamide, and rituximab for a presumed CLL-associated nephrotic syndrome and anticoagulation for his venous thromboemboli. At 6-month follow-up, the patient achieved complete remission of his CLL with normalization of all cell lines and resolution of his nephrotic range proteinuria. Repeat computed tomography scans showed no evidence of recurrent venous thromboemboli. This case demonstrates a potential role of empiric chemotherapy in cases of CLL-associated nephrotic syndrome given its potentially life-threatening sequelae and response to treatment.

A conserved juxtacrine signal regulates synaptic partner recognition in Caenorhabditis elegans.

BACKGROUND: An essential stage of neural development involves the assembly of neural circuits via formation of inter-neuronal connections. Early steps in neural circuit formation, including cell migration, axon guidance, and the localization of synaptic components, are well described. However, upon reaching their target region, most neurites still contact many potential partners. In order to assemble functional circuits, it is critical that within this group of cells, neurons identify and form connections only with their appropriate partners, a process we call synaptic partner recognition (SPR). To understand how SPR is mediated, we previously developed a genetically encoded fluorescent trans-synaptic marker called NLG-1 GRASP, which labels synaptic contacts between individual neurons of interest in dense cellular environments in the genetic model organism Caenorhabditis elegans. RESULTS: Here, we describe the first use of NLG-1 GRASP technology, to identify SPR genes that function in this critical process. The NLG-1 GRASP system allows us to assess synaptogenesis between PHB sensory neurons and AVA interneurons instantly in live animals, making genetic analysis feasible. Additionally, we employ a behavioral assay to specifically test PHB sensory circuit function. Utilizing this approach, we reveal a new role for the secreted UNC-6/Netrin ligand and its transmembrane receptor UNC-40/Deleted in colorectal cancer (DCC) in SPR. Synapses between PHB and AVA are severely reduced in unc-6 and unc-40 animals despite normal axon guidance and subcellular localization of synaptic components. Additionally, behavioral defects indicate a complete disruption of PHB circuit function in unc-40 mutants. Our data indicate that UNC-40 and UNC-6 function in PHB and AVA, respectively, to specify SPR. Strikingly, overexpression of UNC-6 in postsynaptic neurons is sufficient to promote increased PHB-AVA synaptogenesis and to potentiate the behavioral response beyond wild-type levels. Furthermore, an artificially membrane-tethered UNC-6 expressed in the postsynaptic neurons promotes SPR, consistent with a short-range signal between adjacent synaptic partners. CONCLUSIONS: These results indicate that the conserved UNC-6/Netrin-UNC-40/DCC ligand-receptor pair has a previously unknown function, acting in a juxtacrine manner to specify recognition of individual postsynaptic neurons. Furthermore, they illustrate the potential of this new approach, combining NLG-1 GRASP and behavioral analysis, in gene discovery and characterization.