Novel Probes Establish Mas-Related G Protein-Coupled Receptor X1 Variants as Receptors with Loss or Gain of Function.

The Mas-related G protein-coupled receptor X1 (MrgprX1) is a human seven transmembrane-domain protein with a putative role in nociception and pruritus. This receptor is expressed in dorsal root ganglion neurons and is activated by a variety of endogenous peptides, including bovine adrenal medulla peptide (BAM) and γ2-melanocyte-stimulating hormone (γ2-MSH). In the present work, we study how naturally occurring missense mutations alter the activity of MrgprX1. To characterize selected receptor variants, we initially used the endogenous peptide ligand BAM8-22. In addition, we generated and characterized a panel of novel recombinant and synthetic peptide ligands. Our studies identified a mutation in the second intracellular loop of MrgprX1, R131S, that causes a decrease in both ligand-mediated and constitutive signaling. Another mutation in this region, H133R, results in a gain of function phenotype reflected by an increase in ligand-mediated signaling. Using epitope-tagged variants, we determined that the alterations in basal and ligand-mediated signaling were not explained by changes in receptor expression levels. Our results demonstrate that naturally occurring mutations can alter the pharmacology of MrgprX1. This study provides a theoretical basis for exploring whether MrgprX1 variability underlies differences in somatosensation within human populations.

Development of a membrane-anchored chemerin receptor agonist as a novel modulator of allergic airway inflammation and neuropathic pain.

The chemerin receptor (CMKLR1) is a G protein-coupled receptor found on select immune, epithelial, and dorsal root ganglion/spinal cord neuronal cells. CMKLR1 is primarily coupled to the inhibitory G protein, Gαi, and has been shown to modulate the resolution of inflammation and neuropathic pain. CMKLR1 is activated by both lipid and peptide agonists, resolvin E1 and chemerin, respectively. Notably, these ligands have short half-lives. To expedite the development of long acting, stable chemerin analogs as candidate therapeutics, we used membrane-tethered ligand technology. Membrane-tethered ligands are recombinant proteins comprised of an extracellular peptide ligand, a linker sequence, and an anchoring transmembrane domain. Using this technology, we established that a 9-amino acid-tethered chemerin fragment (amino acids 149-157) activates both mouse and human CMKLR1 with efficacy exceeding that of the full-length peptide (amino acids 21-157). To enable in vivo delivery of a corresponding soluble membrane anchored ligand, we generated lipidated analogs of the 9-amino acid fragment. Pharmacological assessment revealed high potency and wash resistance (an index of membrane anchoring). When tested in vivo, a chemerin SMAL decreased allergic airway inflammation and attenuated neuropathic pain in mice. This compound provides a prototype membrane-anchored peptide for the treatment of inflammatory disease. A parallel approach may be applied to developing therapeutics targeting other peptide hormone G protein-coupled receptors.

Naturally occurring HCA1 missense mutations result in loss of function: potential impact on lipid deposition.

The hydroxy-carboxylic acid receptor (HCA1) is a G protein-coupled receptor that is highly expressed on adipocytes and considered a potential target for the treatment of dyslipidemia. In the current study, we investigated the pharmacological properties of naturally occurring variants in this receptor (H43Q, A110V, S172L, and D253H). After transient expression of these receptors into human embryonic kidney 293 cells, basal and ligand-induced signaling were assessed using luciferase reporter gene assays. The A110V, S172L, and D253 variants showed reduced basal activity; the S172L mutant displayed a decrease in potency to the endogenous ligand L-lactate. Both the S172L and D253H variants also showed impaired cell surface expression, which may in part explain the reduced activity of these receptors. The impact of a loss in HCA1 function on lipid accumulation was investigated in the adipocyte cell line, OP9. In these cells, endogenous HCA1 transcript levels rapidly increased and reached maximal levels 3 days after the addition of differentiation media. Knockdown of HCA1 using siRNA resulted in an increase in lipid accumulation as assessed by quantification of Nile Red staining and TLC analysis. Our data suggest that lipid homeostasis may be altered in carriers of selected HCA1 missense variants.

A Non-Perturbative Molecular Grafting Strategy for Stable and Potent Therapeutic Peptide Ligands.

The gut-derived incretin hormone, glucagon-like peptide-1 (GLP1), plays an important physiological role in attenuating post-prandial blood glucose excursions in part by amplifying pancreatic insulin secretion. Native GLP1 is rapidly degraded by the serine protease, dipeptidyl peptidase-4 (DPP4); however, enzyme-resistant analogues of this 30-amino-acid peptide provide an effective therapy for type 2 diabetes (T2D) and can curb obesity via complementary functions in the brain. In addition to its medical relevance, the incretin system provides a fertile arena for exploring how to better separate agonist function at cognate receptors versus susceptibility of peptides to DPP4-induced degradation. We have discovered that novel chemical decorations can make GLP1 and its analogues completely DPP4 resistant while fully preserving GLP1 receptor activity. This strategy is also applicable to other therapeutic ligands, namely, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-2 (GLP2), targeting the secretin family of receptors. The versatility of the approach offers hundreds of active compounds based on any template that target these receptors. These observations should allow for rapid optimization of pharmacological properties and because the appendages are in a position crucial to receptor stimulation, they proffer the possibility of conferring "biased" signaling and in turn minimizing side effects.

OFF bipolar cell density varies by subtype, eccentricity, and along the dorsal ventral axis in the mouse retina.

The neural retina is organized along central-peripheral, dorsal-ventral, and laminar planes. Cellular density and distributions vary along the central-peripheral and dorsal-ventral axis in species including primates, mice, fish, and birds. Differential distribution of cell types within the retina is associated with sensitivity to different types of damage that underpin major retinal diseases, including macular degeneration and glaucoma. Normal variation in retinal distribution remains unreported for multiple cell types in widely used research models, including mouse. Here we map the distribution of all known OFF bipolar cell (BC) populations and horizontal cells. We report significant variation in the distribution of OFF BC populations and horizontal cells along the dorsal-ventral and central-peripheral axes of the retina. Distribution patterns are much more pronounced for some populations of OFF BC cells than others and may correspond to the cell type's specialized functions.

Lumacaftor/ivacaftor in people with cystic fibrosis with an A455E-CFTR mutation.

BACKGROUND: Previous in vitro organoid data showed A455E-CFTR, a rare CFTR mutation with 4.1% prevalence in the Netherlands, responds to lumacaftor/ivacaftor (LUM/IVA). We explored LUM/IVA's clinical efficacy in people with CF and ≥1 A455E-CFTR mutation. METHODS: Participants aged ≥12 years were randomized to 1 of 2 treatment sequences (LUM/IVA→placebo or placebo→LUM/IVA) with an 8-week washout period between. Primary endpoint was absolute change in ppFEV1 from study baseline through 8 weeks. Additional endpoints were change in sweat chloride concentration (SwCl) and CFQ-R respiratory domain score. Correlations between organoid-based measurements and clinical endpoints were investigated. RESULTS: Twenty participants were randomized at 2 sites in the Netherlands. Mean absolute change in ppFEV1 from study baseline through Week 8 showed a treatment difference of 0.1 percentage points (95% CI, -2.5 to 2.7; P = 0.928) between LUM/IVA (within-group mean change, 2.7) and placebo (within-group mean change, 2.6). The mean absolute change in SwCl concentration from study baseline through Week 8 showed a treatment difference of -7.8 mmol/L between LUM/IVA and placebo (P = 0.004), while the absolute change in CFQ-R respiratory domain score showed a treatment difference of 3.5 between LUM/IVA and placebo (P = 0.469). The in vitro organoid-based assay demonstrated a concentration-dependent swelling increase with LUM/IVA. Exploratory correlation analyses between organoid swelling and ppFEV1 and SwCl outcomes showed correlation coefficients of 0.49 and -0.11, respectively. CONCLUSIONS: In this exploratory study, LUM/IVA elicited an in vitro response in organoid swelling and in vivo response in SwCl in participants with CF and ≥1 A455E-CFTR mutation. The primary endpoint (ppFEV1) did not show a statistically significant difference between LUM/IVA and placebo; correlations between in vitro and in vivo responses were not established (NCT03061331).

Ivacaftor in People with Cystic Fibrosis and a 3849+10kb C→T or D1152H Residual Function Mutation.

Rationale: Ivacaftor's clinical effects in the residual function mutations 3849 + 10kb C→T and D1152H warrant further characterization.Objectives: To evaluate ivacaftor's effect in people with cystic fibrosis aged ≥6 years with 3849 + 10kb C→T or D1152H residual function mutations and to explore the correlation between ivacaftor-induced organoid-based cystic fibrosis transmembrane conductance regulator function measurements and clinical response to ivacaftor.Methods: Participants were randomized (1:1) in this placebo-controlled crossover study; each treatment sequence included two 8-week treatments with an 8-week washout period. The primary endpoint was absolute change in lung clearance index2.5 from baseline through Week 8. Additional endpoints included lung function, patient-reported outcomes, and in vitro intestinal organoid-based measurements of ivacaftor-induced cystic fibrosis transmembrane conductance regulator function.Results: Of 38 participants, 37 completed the study. The primary endpoint was met; the Bayesian posterior probability of improvement in lung clearance index2.5 with ivacaftor versus placebo was >99%. Additional endpoints improved with ivacaftor. Safety findings were consistent with ivacaftor's known safety profile. Dose-dependent swelling was observed in 23 of 25 viable organoid cultures with ivacaftor treatment. Correlations between ivacaftor-induced organoid swelling and clinical endpoints were negligible to low.Conclusions: In people with cystic fibrosis aged ≥6 years with a 3849 + 10kb C→T or D1152H mutation, ivacaftor treatment improved clinical endpoints compared with placebo; however, there was no correlation between organoid swelling and change in clinical endpoints. The organoid assay may assist in identification of ivacaftor-responsive mutations but in this study did not predict magnitude of clinical benefit for individual people with cystic fibrosis with these two mutations.Clinical trial registered with ClinicalTrials.gov (NCT03068312).

Development of an OP9 derived cell line as a robust model to rapidly study adipocyte differentiation.

One hallmark of obesity is adipocyte hypertrophy and hyperplasia. To gain novel insights into adipose biology and therapeutics, there is a pressing need for a robust, rapid, and informative cell model of adipocyte differentiation for potential RNAi and drug screens. Current models are prohibitive for drug and RNAi screens due to a slow differentiation time course and resistance to transfection. We asked if we could create a rapid, robust model of adipogenesis to potentially enable rapid functional and obesity therapeutic screens. We generated the clonal population OP9-K, which differentiates rapidly and reproducibly, and displays classic adipocyte morphology: rounded cell shape, lipid accumulation, and coalescence of lipids into a large droplet. We further validate the OP9-K cells as an adipocyte model system by microarray analysis of the differentiating transcriptome. OP9-K differentiates via known adipogenic pathways, involving the transcriptional activation and repression of common adipose markers Plin1, Gata2, C/Ebpα and C/Ebpß and biological pathways, such as lipid metabolism, PPARγ signaling, and osteogenesis. We implemented a method to quantify lipid accumulation using automated microscopy and tested the ability of our model to detect alterations in lipid accumulation by reducing levels of the known master adipogenic regulator Pparγ. We further utilized our model to query the effects of a novel obesity therapeutic target, the transcription factor SPI1. We determine that reduction in levels of Spi1 leads to an increase in lipid accumulation. We demonstrate rapid, robust differentiation and efficient transfectability of the OP9-K cell model of adipogenesis. Together with our microscopy based lipid accumulation assay, adipogenesis assays can be achieved in just four days' time. The results of this study can contribute to the development of rapid screens with the potential to deepen our understanding of adipose biology and efficiently test obesity therapeutics.

A two-step strategy to enhance activity of low potency peptides.

Novel strategies are needed to expedite the generation and optimization of peptide probes targeting G protein-coupled receptors (GPCRs). We have previously shown that membrane tethered ligands (MTLs), recombinant proteins comprised of a membrane anchor, an extracellular linker, and a peptide ligand can be used to identify targeted receptor modulators. Although MTLs provide a useful tool to identify and/or modify functionally active peptides, a major limitation of this strategy is the reliance on recombinant protein expression. We now report the generation and pharmacological characterization of prototype peptide-linker-lipid conjugates, synthetic membrane anchored ligands (SMALs), which are designed as mimics of corresponding MTLs. In this study, we systematically compare the activity of selected peptides as MTLs versus SMALs. As prototypes, we focused on the precursor proteins of mature Substance P (SubP) and Cholecystokinin 4 (CCK4), specifically non-amidated SubP (SubP-COOH) and glycine extended CCK4 (CCK4-Gly-COOH). As low affinity soluble peptides these ligands each presented a challenging test case for assessment of MTL/SMAL technology. For each ligand, MTLs and corresponding SMALs showed agonist activity and comparable subtype selectivity. In addition, our results illustrate that membrane anchoring increases ligand potency. Furthermore, both MTL and SMAL induced signaling can be blocked by specific non-peptide antagonists suggesting that the anchored constructs may be orthosteric agonists. In conclusion, MTLs offer a streamlined approach for identifying low activity peptides which can be readily converted to higher potency SMALs. The ability to recapitulate MTL activity with SMALs extends the utility of anchored peptides as probes of GPCR function.

G-protein coupled receptor 56 promotes myoblast fusion through serum response factor- and nuclear factor of activated T-cell-mediated signalling but is not essential for muscle development in vivo.

Mammalian muscle cell differentiation is a complex process of multiple steps for which many of the factors involved have not yet been defined. In a screen to identify the regulators of myogenic cell fusion, we found that the gene for G-protein coupled receptor 56 (GPR56) was transiently up-regulated during the early fusion of human myoblasts. Human mutations in the gene for GPR56 cause the disease bilateral frontoparietal polymicrogyria; however, the consequences of receptor dysfunction on muscle development have not been explored. Using knockout mice, we defined the role of GPR56 in skeletal muscle. GPR56(-/-) myoblasts have decreased fusion and smaller myotube sizes in culture. In addition, a loss of GPR56 expression in muscle cells results in decreases or delays in the expression of myogenic differentiation 1, myogenin and nuclear factor of activated T-cell (NFAT)c2. Our data suggest that these abnormalities result from decreased GPR56-mediated serum response element and NFAT signalling. Despite these changes, no overt differences in phenotype were identified in the muscle of GPR56 knockout mice, which presented only a mild but statistically significant elevation of serum creatine kinase compared to wild-type. In agreement with these findings, clinical data from 13 bilateral frontoparietal polymicrogyria patients revealed mild serum creatine kinase increase in only two patients. In summary, targeted disruption of GPR56 in mice results in myoblast abnormalities. The absence of a severe muscle phenotype in GPR56 knockout mice and human patients suggests that other factors may compensate for the lack of this G-protein coupled receptor during muscle development and that the motor delay observed in these patients is likely not a result of primary muscle abnormalities.

Serotonin 2 receptor modulation of hyperthermia, corticosterone, and hippocampal serotonin depletions following serial exposure to chronic stress and methamphetamine.

Chronic stress precipitates drug seeking behavior and alters the effects of drugs of abuse. Although it is known that chronic stress potentiates acute neurochemical and hyperthermic responses to the drug of abuse methamphetamine, no studies have investigated if and how chronic stress alters other physiological responses to methamphetamine. Therefore the objective of these studies was to determine if 10 days of chronic unpredictable stress modulates corticosterone (CORT) responses to methamphetamine and furthermore how chronic stress may modulate methamphetamine-induced increases in hyperthermia and CORT. As chronic stress potentiates hyperthermic responses to serotonin 2 (5-HT2) stimulation and 5-HT2 receptors are important in mediating both hyperthermic and CORT responses, we also investigated if 5-HT2 antagonism would block hyperthermia and CORT secretion by the serial exposure to stress and methamphetamine (stress/methamphetamine). The results of these studies illustrate that stress potentiates methamphetamine-induced increases in body temperature and CORT secretion and that these increases are blocked by the 5-HT2 antagonist ketanserin. Furthermore, the combination of stress and methamphetamine depletes 5-HT content in the hippocampus 7 days after methamphetamine administration which is blocked by the 5-HT2 antagonist ketanserin. Overall, these results indicate a pharmacological mechanism for the depletion of hippocampal 5-HT by the serial exposure to stress and methamphetamine and further illustrate the deleterious interactions between chronic stress and methamphetamine use.