Biology subjects

Levitz, J.

Publications and source records attributed to Levitz, J..

At least 19 recordsLinked to original sources

bioRxiv2025

MRAP2 potentiates GPCR signaling by conserved mechanisms that are disrupted by obesity-associated genetic variants

Accessory proteins such as members of the melanocortin-2 receptor accessory protein family (MRAP) have been described to interact with and regulate the signaling of diverse G protein-coupled receptors (GPCRs), however, surprisingly little is known about the mechanisms by which they mediate these effects. MRAP2 modifies signaling of three distinct GPCRs, melanocortin receptor 4 (MC4R), MC3R and the ghrelin receptor (GHSR), which each play essential roles in appetite regulation. Human mutations in MRAP2 cause obesity with hyperglycaemia and hypertension, suggesting that its regulation of GPCRs is critical for maintaining metabolic homeostasis. However, the nature of MRAP2/GPCR complexes and whether there are shared mechanisms for complex assembly, critical structural regions or consistent effects on receptor signaling and trafficking remains unknown. Here we showed all three GPCRs preferentially interact with MRAP2 as 1:1 complexes and that MRAP2 binding disrupts GPCR homodimerization. MRAP2 interacts with the same receptor transmembrane regions to promote GPCR signaling, and the accessory protein impairs {beta}-arrestin-2 recruitment to prolong signaling and delay internalization. Deletion of the cytoplasmic region of MRAP2 impairs GPCR signaling by modulating receptor constitutive activity. Genetic variants in MRAP2 associated with overweight or obesity modulate the constitutive activity of all three GPCRs. Thus, MRAP2 regulates GPCR function using shared molecular mechanisms and these studies provide further evidence of the importance of GHSR constitutive activity.

molecular biology↗

bioRxiv2025

Structural Diversity of Metabotropic Glutamate Receptor/Beta-Arrestin Coupling

Beta-arrestins ({beta}-arrs) are cytosolic proteins which mediate G protein-coupled receptor (GPCR) desensitization, endocytosis, and signaling. Despite the widespread physiological roles of {beta}-arr coupling, the molecular basis of GPCR/{beta}-arr interaction has been studied primarily in monomeric family A GPCRs. Here we take an integrative biophysical and structural approach to uncover molecular diversity in {beta}-arr coupling to the neuromodulatory metabotropic glutamate receptors (mGluRs), prototypical, dimeric family C GPCRs. We find, using a new single molecule pulldown assay, that mGluRs couple to {beta}-arrs with a 2:1 or 2:2 stoichiometry via a combination of "tail" and "core" interactions. Using single molecule FRET analysis, we also find that {beta}-arr1 stabilizes active conformations of mGluR8. Cryo-EM structures of mGluR8 alone or with either G proteins or {beta}-arr1 reveal transducer-specific mGluR8 active states and, in combination with molecular dynamics simulations, define the positioning of mGluR8-bound {beta}-arr1, supporting a steric mechanism of mGluR desensitization involving interactions with both subunits and the lipid bilayer. Finally, combinatorial mutagenesis enables the identification of a landscape of homo- and hetero-dimeric mGluR/{beta}-arr complexes, including mGluR/{beta}-arr1/{beta}-arr2 megacomplexes, providing a framework for family C GPCR/{beta}-arr coupling and expanding the known range of GPCR/transducer coupling modes.

biophysics↗

bioRxiv2024

An opioid efficacy switch for reversible optical control of peripheral analgesia

The mu-opioid receptor (MOR) is a major target for the treatment of pain. However, opioids are prone to side effects which limit their effectiveness as analgesics and can lead to opioid use disorders or, even, lethal overdose. The systemic administration of opioid agonists makes it both very difficult to decipher their underlying circuit mechanisms of action and to limit drug action to specific receptor subpopulations to isolate therapeutic effects from adverse side effects. Here we design, synthesize, and characterize a reversibly photoswitchable morphinan agonist termed "azo-morphine-3" (AM-3) which interconverts from low to high efficacy in response to different wavelengths of light to enable optical control of MOR signaling. Cryo-EM structures of the low efficacy "trans" and high efficacy "cis" states of AM-3 bound to the MOR reveal distinct binding modes of the photoswitchable azobenzene moiety, each inducing unique structural dynamics, providing insight into the molecular basis of agonist efficacy. In mice, AM-3 drives reversible and repeatable optical control of anti-nociception with a reduced side effect profile owing to its restriction to the periphery and its ability to be locally activated at the site of pain.

pharmacology and toxicology↗

bioRxiv2024

The MRAP2 accessory protein directly interacts with melanocortin-3 receptor to enhance signaling

The central melanocortin system links nutrition to energy expenditure, with melanocortin-4 receptor (MC4R) controlling appetite and food intake, and MC3R regulating timing of sexual maturation, rate of linear growth and lean mass accumulation. Melanocortin-2 receptor accessory protein-2 (MRAP2) is a single transmembrane protein that interacts with MC4R to potentiate its signalling, and human mutations in MRAP2 cause obesity. Previous studies have been unable to consistently show whether MRAP2 affects MC3R activity. Here we used single-molecule pull-down (SiMPull) to confirm that MC3R and MRAP2 interact in HEK293 cells. Analysis of fluorescent photobleaching steps showed that MC3R and MRAP2 readily form heterodimers most commonly with a 1:1 stoichiometry. Human single-nucleus and spatial transcriptomics show MRAP2 is co-expressed with MC3R in hypothalamic neurons with important roles in energy homeostasis and appetite control. Functional analyses showed MRAP2 enhances MC3R cAMP signalling, impairs {beta}-arrestin recruitment, and reduces internalization in HEK293 cells. Structural homology models revealed putative interactions between the two proteins and alanine mutagenesis of five MRAP2 and three MC3R transmembrane residues significantly reduced MRAP2 effects on MC3R signalling. Finally, we showed genetic variants in MRAP2 that have been identified in individuals that are overweight or obese prevent MRAP2s enhancement of MC3R-driven signalling. Thus, these studies reveal MRAP2 as an important regulator of MC3R function and provide further evidence for the crucial role of MRAP2 in energy homeostasis.

molecular biology↗

bioRxiv2024

A one-step protocol to generate impermeable fluorescent HaloTag substrates for in situ live cell application and super-resolution imaging

Communication between cells is largely orchestrated by proteins on the cell surface, which allow information transfer across the cell membrane. Super-resolution and single-molecule visualization of these proteins can be achieved by genetically grafting HTP (HaloTag Protein) into the protein of interest followed by brief incubation of cells with a dye-HTL (dye-linked HaloTag Ligand). This approach allows for use of cutting-edge fluorophores optimized for specific optical techniques or a cell-impermeable dye-HTL to selectively label surface proteins without labeling intracellular copies. However, these two goals often conflict, as many high-performing dyes exhibit membrane permeability. Traditional methods to eliminate cell permeability face synthetic bottlenecks and risk altering photophysical properties. Here we report that dye-HTL reagents can be made cell-impermeable by inserting a charged sulfonate directly into the HTL, leaving the dye moiety unperturbed. This simple, one-step method requires no purification and is compatible with both the original HTL and second-generation HTL.2, the latter offering accelerated labeling. We validate such compounds, termed dye-SHTL ( dye shuttle) conjugates, in live cells via widefield microscopy, demonstrating exclusive membrane staining of extracellular HTP fusion proteins. In transduced primary hippocampal neurons, we label mGluR2, a neuromodulatory G protein-coupled receptor (GPCR), with dyes optimized for stimulated emission by depletion (STED) super-resolution microscopy, allowing unprecedented accuracy in distinguishing surface and receptors from those in internal compartments of the presynaptic terminal, important in neural communication. This approach offers broad utility for surface-specific protein labelling.

pharmacology and toxicology↗

bioRxiv2024

Elevating levels of the endocannabinoid 2-arachidonoylglycerol blunts opioid reward but not analgesia

Converging findings have established that the endocannabinoid (eCB) system serves as a possible target for the development of new treatments for pain as a complement to opioid-based treatments. Here we show in male and female mice that enhancing levels of the eCB, 2-arachidonoylglycerol (2-AG), through pharmacological inhibition of its catabolic enzyme, monoacylglycerol lipase (MAGL), either systemically or in the ventral tegmental area (VTA) with JZL184, leads to a substantial attenuation of the rewarding effects of opioids in male and female mice using conditioned place preference and self-administration paradigms, without altering their analgesic properties. These effects are driven by CB1 receptors (CB1Rs) within the VTA as VTA CB1R conditional knockout, counteracts JZL184s effects. Conversely, pharmacologically enhancing the levels of the other eCB, anandamide (AEA), by inhibition of fatty acid amide hydrolase (FAAH) has no effect on opioid reward or analgesia. Using fiber photometry with fluorescent sensors for calcium and dopamine (DA), we find that enhancing 2-AG levels diminishes opioid reward-related nucleus accumbens (NAc) activity and DA neurotransmission. Together these findings reveal that 2-AG counteracts the rewarding properties of opioids and provides a potential adjunctive therapeutic strategy for opioid-related analgesic treatments.

neuroscience↗

bioRxiv2024

Projection-Targeted Photopharmacology Reveals Distinct Anxiolytic Roles for Presynaptic mGluR2 in Prefrontal- and Insula-Amygdala Synapses

Dissecting how membrane receptors regulate neural circuit function is critical for deciphering basic principles of neuromodulation and mechanisms of therapeutic drug action. Classical pharmacological and genetic approaches are not well-equipped to untangle the roles of specific receptor populations, especially in long-range projections which coordinate communication between brain regions. Here we use viral tracing, electrophysiological, optogenetic, and photopharmacological approaches to determine how presynaptic metabotropic glutamate receptor 2 (mGluR2) activation in the basolateral amygdala (BLA) alters anxiety-related behavior. We find that mGluR2-expressing neurons from the ventromedial prefrontal cortex (vmPFC) and posterior insular cortex (pIC) preferentially target distinct cell types and subregions of the BLA to regulate different forms of avoidant behavior. Using projection-specific photopharmacological activation, we find that mGluR2-mediated presynaptic inhibition of vmPFC-BLA, but not pIC-BLA, connections can produce long-lasting decreases in spatial avoidance. In contrast, presynaptic inhibition of pIC-BLA connections decreased social avoidance, novelty-induced hypophagia, and increased exploratory behavior without impairing working memory, establishing this projection as a novel target for the treatment of anxiety disorders. Overall, this work reveals new aspects of BLA neuromodulation with therapeutic implications while establishing a powerful approach for optical mapping of drug action via photopharmacology. Highlights- Basolateral amygdala is a key site for anxiolytic action of mGluR2 agonism - BLA receives dense Grm2+ inputs from ventromedial prefrontal cortex and posterior insular cortex - Photoactivation of mGluR2 has distinct anxiolytic effects in vmPFC-BLA and pIC-BLA synapses - Grm2+ vmPFC and pIC projections target medial and lateral BLA subregions, respectively

neuroscience↗

bioRxiv2023

A cholesterol switch controls phospholipid scrambling by G protein-coupled receptors

Class A G protein-coupled receptors (GPCRs), a superfamily of cell membrane signaling receptors, moonlight as constitutively active phospholipid scramblases. The plasma membrane of metazoan cells is replete with GPCRs, yet has a strong resting trans-bilayer phospholipid asymmetry, with the signaling lipid phosphatidylserine confined to the cytoplasmic leaflet. To account for the persistence of this lipid asymmetry in the presence of GPCR scramblases, we hypothesized that GPCR-mediated lipid scrambling is regulated by cholesterol, a major constituent of the plasma membrane. We now present a technique whereby synthetic vesicles reconstituted with GPCRs can be supplemented with cholesterol to a level similar to that of the plasma membrane and show that the scramblase activity of two prototypical GPCRs, opsin and the {beta}1-adrenergic receptor, is impaired upon cholesterol loading. Our data suggest that cholesterol acts as a switch, inhibiting scrambling above a receptor-specific threshold concentration to disable GPCR scramblases at the plasma membrane.

biochemistry↗

bioRxiv2023

Deuteration provides a general strategy to enhance azobenzene-based photopharmacology

Herein, we present deuterated azobenzene photoswitches as a general means of enhancing photopharmacological molecules. Deuteration can improve azobenzene performance in terms of light sensitivity, photoswitch efficiency, and photoswitch kinetics with minimal alteration to the underlying structure of the photopharmacological ligand. We report synthesized deuterated azobenzene-based ligands for the optimized optical control of ion channel and G protein-coupled receptor function in live cells, setting the stage for the straightforward, widespread adoption of this approach.

biochemistry↗

bioRxiv2023

Synaptic plasticity via receptor tyrosine kinase / G protein-coupled receptor crosstalk

Cellular signaling involves a large repertoire of membrane receptors operating in overlapping spatiotemporal regimes and targeting many common intracellular effectors. However, both the molecular mechanisms and physiological roles of crosstalk between receptors, especially those from different superfamilies, are poorly understood. We find that the receptor tyrosine kinase (RTK), TrkB, and the G protein-coupled receptor (GPCR), metabotropic glutamate receptor 5 (mGluR5), together mediate a novel form of hippocampal synaptic plasticity in response to brain-derived neurotrophic factor (BDNF). Activated TrkB enhances constitutive mGluR5 activity to initiate a mode-switch that drives BDNF-dependent sustained, oscillatory Ca2+ signaling and enhanced MAP kinase activation. This crosstalk is mediated, in part, by synergy between G{beta}{gamma}, released by TrkB, and Gq-GTP, released by mGluR5, to enable a previously unidentified form of physiologically relevant RTK/GPCR crosstalk.

cell biology↗

bioRxiv2023

Control of G protein-coupled receptor function via membrane-interacting intrinsically disordered C-terminal domains

G protein-coupled receptors (GPCRs) control intracellular signaling cascades via agonist-dependent coupling to intracellular transducers including heterotrimeric G proteins, GPCR kinases (GRKs), and arrestins. In addition to their critical interactions with the transmembrane core of active GPCRs, all three classes of transducers have also been reported to interact with receptor C-terminal domains (CTDs). An underexplored aspect of GPCR CTDs is their possible role as lipid sensors given their proximity to the membrane. CTD-membrane interactions have the potential to control the accessibility of key regulatory CTD residues to downstream effectors and transducers. Here we report that the CTDs of two closely related family C GPCRs, metabotropic glutamate receptor 2 (mGluR2) and mGluR3, bind to membranes and that this interaction can regulate receptor function. We first characterize CTD structure with NMR spectroscopy, revealing lipid composition-dependent modes of membrane binding. Using molecular dynamics simulations and structure-guided mutagenesis, we then identify key conserved residues and cancer-associated mutations that modulate CTD-membrane binding. Finally, we provide evidence that mGluR3 transducer coupling is controlled by CTD-membrane interactions in live cells, which may be subject to regulation by CTD phosphorylation and changes in membrane composition. This work reveals a novel mechanism of GPCR modulation, suggesting that CTD-membrane binding may be a general regulatory mode throughout the broad GPCR superfamily. Significance StatementG protein-coupled receptors (GPCRs) allow cells to sense and respond to their environment and constitute the largest class of targets for approved therapeutic drugs. Temporally precise GPCR signaling is achieved by coupling the binding of extracellular ligands to the binding of intracellular signal transducers (e.g. heterotrimeric G proteins) and regulators (e.g. {beta}-arrestins). The C-terminal domains (CTDs) of GPCRs are targets of various post-translational modifications and play a critical role in transducer and regulator recruitment. Here we report novel interactions of the CTDs of two GPCRs of the metabotropic glutamate receptor family with cellular membranes. These interactions serve to regulate CTD accessibility and thus, mGluR coupling to transducers and regulators. We propose that dynamic CTD-membrane interaction constitutes a general mechanism for regulating GPCR function.

biophysics↗

bioRxiv2023

Structural basis of allosteric modulation ofmetabotropic glutamate receptor activation and desensitization

The metabotropic glutamate receptors (mGluRs) are neuromodulatory family C G protein coupled receptors which assemble as dimers and allosterically couple extracellular ligand binding domains (LBDs) to transmembrane domains (TMDs) to drive intracellular signaling. Pharmacologically, mGluRs can be targeted either at the LBDs by glutamate and synthetic orthosteric compounds or at the TMDs by allosteric modulators. Despite the potential of allosteric TMD-targeting compounds as therapeutics, an understanding of the functional and structural basis of their effects on mGluRs is limited. Here we use a battery of approaches to dissect the distinct functional and structural effects of orthosteric versus allosteric ligands. We find using electrophysiological and live cell imaging assays that both agonists and positive allosteric modulators (PAMs) can drive activation and desensitization of mGluRs. The effects of PAMs are pleiotropic, including both the ability to boost the maximal response to orthosteric agonists and to serve independently as desensitization-biased agonists across mGluR subtypes. Conformational sensors reveal PAM-driven inter-subunit re-arrangements at both the LBD and TMD. Motivated by this, we determine cryo-electron microscopy structures of mGluR3 in the presence of either an agonist or antagonist alone or in combination with a PAM. These structures reveal PAM-driven re-shaping of intra- and inter-subunit conformations and provide evidence for a rolling TMD dimer interface activation pathway that controls G protein and beta-arrestin coupling. Highlights-Agonists and PAMs drive mGluR activation, desensitization, and endocytosis -PAMs are desensitization-biased and synergistic with agonists -Four combinatorial ligand conditions reveal an ensemble of full-length mGluR structures with novel interfaces -Activation and desensitization involve rolling TMD interfaces which are re-shaped by PAM

biophysics↗

bioRxiv2022

Combined small molecule treatment accelerates timing of maturation in human pluripotent stem cell-derived neurons

The maturation of human pluripotent stem cell (hPSC)-derived neurons mimics the protracted timing of human brain development, extending over months and years to reach adult-like function. Prolonged in vitro maturation presents a major challenge to stem cell-based applications in modeling and treating neurological disease. We designed a high-content imaging assay based on morphological and functional readouts in hPSC-derived cortical neurons to reveal underlying pathways and to identify chemicals capable of accelerating neuronal maturation. Probing a library of 2688 bioactive drugs, we identified multiple compounds that drive neuronal maturation including inhibitors of LSD1 and DOT1L and activators of calcium-dependent transcription. A cocktail of 4 factors GSK-2879552, EPZ-5676, NMDA and Bay K 8644, which we collectively termed GENtoniK, triggered maturation across all assays tested including measures of synaptic density, electrophysiology and transcriptomics. Remarkably, GENtoniK was similarly effective in enhancing neuronal maturation in 3D cortical organoids and in spinal motoneurons, and improved aspects of cell maturation in non-neural lineages such as melanocytes and pancreatic beta cells. These results demonstrate that the maturation of multiple hPSC-derived cell types can be enhanced by simple pharmacological intervention and suggests that some of the mechanisms controlling the timing of human maturation are shared across lineages.

neuroscience↗

bioRxiv2022

Profiling the diversity of agonist-selective effects on the proximal proteome environment of G protein-coupled receptors

The mu opioid receptor (OR), a prototypic member of the large G protein-coupled receptor (GPCR) family, represents an important target of therapeutic and abused drugs. To date, most of our understanding of OR activity has focused on signal transducers and regulatory molecules including G proteins, GPCR kinases, and beta-arrestins. Yet it is clear that signaling through the OR is coordinated by additional proteins recruited into the proximal interaction network of the activated receptor, which have largely remained invisible given the lack of technologies to interrogate these networks systematically. Here, we implement a quantitative proteomics pipeline leveraging the chemical diversity of OR agonists and APEX-based proximity labeling to investigate the protein networks that underlie OR signaling. We leverage a novel computational framework to extract subcellular location, trafficking, and functional partners of GPCR activity from the proximity labeling datasets. Applying this unbiased, systematic approach to the OR, we demonstrate that opioid agonists exert differences in the OR proximal proteome mediated by endocytosis and subsequent endosomal sorting, exemplified by VPS35 and COMMD3. Moreover, we identify two novel OR network components, EYA4 and KCTD12, that are recruited into the receptor proximal network irrespective of the activating ligand and independent of receptor trafficking but based on receptor-triggered G protein activation. We provide functional evidence that these network components form a previously unrecognized buffering system for G protein activity which broadly modulates cellular GPCR signaling.

systems biology↗

bioRxiv2021

Differences in interactions between transmembrane domains tune the activation of metabotropic glutamate receptors

The metabotropic glutamate receptors (mGluRs) form a family of neuromodulatory G protein-coupled receptors that contain both a seven-helix transmembrane domain (TMD) and a large extracellular ligand-binding domain (LBD) which enables stable dimerization. While numerous studies have revealed variability across subtypes in the initial activation steps at the level of LBD dimers, an understanding of inter-TMD interaction and rearrangement remains limited. Here we use a combination of single molecule fluorescence, molecular dynamics, functional assays, and conformational sensors to reveal that distinct TMD assembly properties drive differences between mGluR subtypes. We uncover a variable region within transmembrane helix 4 (TM4) that contributes to homo- and heterodimerization in a subtype-specific manner and tunes orthosteric, allosteric and basal activation. We also confirm a critical role for a conserved inter-TM6 interface in stabilizing the active state during orthosteric or allosteric activation. Together this study informs a working model of inter-TMD rearrangement that drives mGluR function.

neuroscience↗

bioRxiv2020

Unusual mode of dimerization of retinitis pigmentosa-associated F220C rhodopsin

Mutations in the G protein-coupled receptor (GPCR) rhodopsin are a common cause of autosomal dominant retinitis pigmentosa, a blinding disease. Rhodopsin self-associates in the membrane, and the purified monomeric apo-protein opsin dimerizes in vitro as it transitions from detergent micelles to reconstitute into a lipid bilayer. We previously reported that the retinitis pigmentosa-linked F220C opsin mutant fails to dimerize in vitro, reconstituting as a monomer. Using fluorescence-based assays and molecular dynamics simulations we now report that whereas wildtype and F220C opsin display distinct dimerization propensities in vitro as previously shown, they both dimerize in the plasma membrane of HEK293 cells. Unexpectedly, molecular dynamics simulations show that F220C opsin forms an energetically favored dimer in the membrane when compared with the wild-type protein. The conformation of the F220C dimer is unique, with transmembrane helices 5 and 6 splayed apart, promoting widening of the intracellular vestibule of each protomer and influx of water into the protein interior. FRET experiments with SNAP-tagged wild-type and F220C opsin expressed in HEK293 cells are consistent with this conformational difference. We speculate that the unusual mode of dimerization of F220C opsin in the membrane may have physiological consequences.

biophysics↗

bioRxiv2020

Interrogating surface versus intracellular transmembrane receptor populations using cell-impermeable SNAP-tag substrates

Employing self-labelling protein tags for the attachment of fluorescent dyes has become a routine and powerful technique in optical microscopy to visualize and track fused proteins. However, membrane permeability of the dyes and the associated background signals can interfere with the analysis of extracellular labeling sites. Here we describe a novel approach to improve extracellular labeling by functionalizing the SNAP-tag substrate benzyl guanine ("BG") with a charged sulfonate ("SBG"). This chemical manipulation improves solubility, reduces non-specific staining and renders the bioconjugation handle impermeable while leaving its cargo untouched. We report SBG-conjugated fluorophores across the visible spectrum, which cleanly label SNAP-fused proteins in the plasma membrane of living cells. We demonstrate the utility of SBG-conjugated fluorophores to interrogate class A, B and C G protein-coupled receptors (GPCRs) using a range of imaging approaches including nanoscopic super-resolution imaging, analysis of GPCR trafficking from intra- and extracellular pools, in vivo labelling in mouse brain and analysis of receptor stoichiometry using single molecule pull down.

physiology↗

bioRxiv2019

Branched photoswitchable tethered ligands enable ultra-efficient optical control and detection of class C G protein-coupled receptors

The limitations of classical, soluble drugs in terms of subtype-specificity, spatiotemporal precision, and genetic targeting have spurred the development of advanced pharmacological techniques, including the use of covalently-tethered photoswitchable ligands. However, a major shortcoming of tethered photopharmacology is the inability to obtain optical control with a comparable efficacy to the native ligand. To overcome the limitations of photoisomerization efficiency and tethered ligand affinity, we have developed a family of branched photoswitchable compounds to target G protein-coupled metabotropic glutamate receptors (mGluRs). These compounds permit photo-agonism of Gi/o-coupled group II mGluRs with near-complete efficiency relative to saturating glutamate when attached to receptors via a range of orthogonal, multiplexable modalities including SNAP-, CLIP-, and Halo-tags, as well as via receptor-targeting nanobodies. Through a chimeric approach, branched ligands also allow efficient optical control of Gq-coupled mGluR5 with precise, dynamic subcellular targeting. Finally, branched ligands enabled the development of dual photoswitch-fluorophore compounds that allow simultaneous imaging and manipulation of receptors via the same attachment point. Together this work provides a new design framework for photoswitchable ligands and demonstrates a toolset suitable for quantitative, mechanistic study of neuromodulatory receptors at the molecular, cellular and circuit levels.

bioengineering↗