Fine-tuned photochromic sulfonylureas for optical control of beta cell Ca2+ fluxes

We previously developed, synthesized and tested light-activated sulfonylureas for optical control of KATP channels and pancreatic beta cell activity in vitro and in vivo. Such technology relies on installation of azobenzene photoswitches onto the sulfonylurea backbone, affording light-dependent isomerization, alteration in ligand affinity for SUR1 and hence KATP channel conductance. Inspired by molecular dynamics simulations and to further improve photoswitching characteristics, we set out to develop a novel push-pull closed ring azobenzene unit, before installing this on the sulfonylurea glimepiride as a small molecule recipient. Three fine-tuned, light-activated sulfonylureas were synthesized, encompassing azetidine, pyrrolidine and piperidine closed rings. Azetidine-, pyrrolidine- and piperidine-based sulfonylureas all increased beta cell Ca2+ -spiking activity upon continuous blue light illumination, similarly to first generation JB253. Notably, the pyrrolidine-based sulfonylurea showed superior switch OFF performance to JB253. As such, third generation sulfonylureas afford more precise optical control over primary pancreatic beta cells, and showcase the potential of pyrrolidine-azobenzenes as chemical photoswitches across drug classes.

Hypothalamic and brainstem glucose-dependent insulinotropic polypeptide receptor neurons employ distinct mechanisms to affect feeding

Central glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) signaling is critical in GIP-based therapeutics' ability to lower body weight, but pathways leveraged by GIPR pharmacology in the brain remain incompletely understood. We explored the role of Gipr neurons in the hypothalamus and dorsal vagal complex (DVC) - brain regions critical to the control of energy balance. Hypothalamic Gipr expression was not necessary for the synergistic effect of GIPR/GLP-1R coagonism on body weight. While chemogenetic stimulation of both hypothalamic and DVC Gipr neurons suppressed food intake, activation of DVC Gipr neurons reduced ambulatory activity and induced conditioned taste avoidance, while there was no effect of a short-acting GIPR agonist (GIPRA). Within the DVC, Gipr neurons of the nucleus tractus solitarius (NTS), but not the area postrema (AP), projected to distal brain regions and were transcriptomically distinct. Peripherally dosed fluorescent GIPRAs revealed that access was restricted to circumventricular organs in the CNS. These data demonstrate that Gipr neurons in the hypothalamus, AP, and NTS differ in their connectivity, transcriptomic profile, peripheral accessibility, and appetite-controlling mechanisms. These results highlight the heterogeneity of the central GIPR signaling axis and suggest that studies into the effects of GIP pharmacology on feeding behavior should consider the interplay of multiple regulatory pathways.

GC-Globulin/Vitamin D-Binding Protein Is Required for Pancreatic α-Cell Adaptation to Metabolic Stress

GC-globulin (GC), or vitamin D-binding protein, is a multifunctional protein involved in the transport of circulating vitamin 25(OH)D and fatty acids, as well as actin scavenging. In the pancreatic islets, the gene encoding GC, GC/Gc, is highly localized to glucagon-secreting α-cells. Despite this, the role of GC in α-cell function is poorly understood. We previously showed that GC is essential for α-cell morphology, electrical activity, and glucagon secretion. We now show that loss of GC exacerbates α-cell failure during metabolic stress. High-fat diet-fed GC-/- mice have basal hyperglucagonemia, which is associated with decreased α-cell size, impaired glucagon secretion and Ca2+ fluxes, and changes in glucose-dependent F-actin remodelling. Impairments in glucagon secretion can be rescued using exogenous GC to replenish α-cell GC levels, increase glucagon granule area, and restore the F-actin cytoskeleton. Lastly, GC levels decrease in α-cells of donors with type 2 diabetes, which is associated with changes in α-cell mass, morphology, and glucagon expression. Together, these data demonstrate an important role for GC in α-cell adaptation to metabolic stress.

Enzyme self-label-bound ATTO700 in single-molecule and super-resolution microscopy

Herein, we evaluate near-infrared ATTO700 as an acceptor in SNAP- and Halo-tag protein labelling for Förster Resonance Energy Transfer (FRET) by ensemble and single molecule measurements. Microscopy of cell surface proteins in live cells is perfomed including super-resolution stimulated emission by depletion (STED) nanoscopy.

Two Pex5 Proteins With Different Cargo Specificity Are Critical for Peroxisome Function in Ustilago maydis

Peroxisomes are dynamic multipurpose organelles with a major function in fatty acid oxidation and breakdown of hydrogen peroxide. Many proteins destined for the peroxisomal matrix contain a C-terminal peroxisomal targeting signal type 1 (PTS1), which is recognized by tetratricopeptide repeat (TPR) proteins of the Pex5 family. Various species express at least two different Pex5 proteins, but how this contributes to protein import and organelle function is not fully understood. Here, we analyzed truncated and chimeric variants of two Pex5 proteins, Pex5a and Pex5b, from the fungus Ustilago maydis. Both proteins are required for optimal growth on oleic acid-containing medium. The N-terminal domain (NTD) of Pex5b is critical for import of all investigated peroxisomal matrix proteins including PTS2 proteins and at least one protein without a canonical PTS. In contrast, the NTD of Pex5a is not sufficient for translocation of peroxisomal matrix proteins. In the presence of Pex5b, however, specific cargo can be imported via this domain of Pex5a. The TPR domains of Pex5a and Pex5b differ in their affinity to variations of the PTS1 motif and thus can mediate import of different subsets of matrix proteins. Together, our data reveal that U. maydis employs versatile targeting modules to control peroxisome function. These findings will promote our understanding of peroxisomal protein import also in other biological systems.

Expanded LUXendin Color Palette for GLP1R Detection and Visualization In Vitro and In Vivo

The glucagon-like peptide-1 receptor (GLP1R) is expressed in peripheral tissues and the brain, where it exerts pleiotropic actions on metabolic and inflammatory processes. Detection and visualization of GLP1R remains challenging, partly due to a lack of validated reagents. Previously, we generated LUXendins, antagonistic red and far-red fluorescent probes for specific labeling of GLP1R in live and fixed cells/tissues. We now extend this concept to the green and near-infrared color ranges by synthesizing and testing LUXendin492, LUXendin551, LUXendin615, and LUXendin762. All four probes brightly and specifically label GLP1R in cells and pancreatic islets. Further, LUXendin551 acts as a chemical beta cell reporter in preclinical rodent models, while LUXendin762 allows noninvasive imaging, highlighting differentially accessible GLP1R populations. We thus expand the color palette of LUXendins to seven different spectra, opening up a range of experiments using wide-field microscopy available in most labs through super-resolution imaging and whole animal imaging. With this, we expect that LUXendins will continue to generate novel and specific insights into GLP1R biology.

14-3-3ζ constrains insulin secretion by regulating mitochondrial function in pancreatic β-cells

While critical for neurotransmitter synthesis, 14-3-3 proteins are often assumed to have redundant functions due to their ubiquitous expression, but despite this assumption, various 14-3-3 isoforms have been implicated in regulating metabolism. We previously reported contributions of 14-3-3ζ in β cell function, but these studies were performed in tumor-derived MIN6 cells and systemic KO mice. To further characterize the regulatory roles of 14-3-3ζ in β cell function, we generated β cell–specific 14-3-3ζ–KO mice. Although no effects on β cell mass were detected, potentiated glucose-stimulated insulin secretion (GSIS), mitochondrial function, and ATP synthesis were observed. Deletion of 14-3-3ζ also altered the β cell transcriptome, as genes associated with mitochondrial respiration and oxidative phosphorylation were upregulated. Acute 14-3-3 protein inhibition in mouse and human islets recapitulated the enhancements in GSIS and mitochondrial function, suggesting that 14-3-3ζ is the critical isoform in β cells. In dysfunctional db/db islets and human islets from type 2 diabetic donors, expression of Ywhaz/YWHAZ, the gene encoding 14-3-3ζ, was inversely associated with insulin secretion, and pan–14-3-3 protein inhibition led to enhanced GSIS and mitochondrial function. Taken together, this study demonstrates important regulatory functions of 14-3-3ζ in the regulation of β cell function and provides a deeper understanding of how insulin secretion is controlled in β cells.

GLP1R Attenuates Sympathetic Response to High Glucose via Carotid Body Inhibition

Supplemental Digital Content is available in the text.

Aberrant sympathetic nerve activity exacerbates cardiovascular risk in hypertension and diabetes, which are common comorbidities, yet clinically sympathetic nerve activity remains poorly controlled. The hypertensive diabetic state is associated with increased reflex sensitivity and tonic drive from the peripheral chemoreceptors, the cause of which is unknown. We have previously shown hypertension to be critically dependent on the carotid body (CB) input in spontaneously hypertensive rat, a model that also exhibits a number of diabetic traits. CB overstimulation by insulin and leptin has been similarly implicated in the development of increased sympathetic nerve activity in metabolic syndrome and obesity. Thus, we hypothesized that in hypertensive diabetic state (spontaneously hypertensive rat), the CB is sensitized by altered metabolic signaling causing excessive sympathetic activity levels and dysfunctional reflex regulation.

Sulfonated red and far-red rhodamines to visualize SNAP- and Halo-tagged cell surface proteins

The (in)ability to permeate membranes is a key feature of chemical biology probes that defines their suitability for specific applications. Here we report sulfonated rhodamines that endow xanthene dyes with cellular impermeability for analysis of surface proteins. We fuse charged sulfonates to red and far-red dyes to obtain Sulfo549 and Sulfo646, respectively, and further link these to benzylguanine and choloralkane substrates for SNAP-tag and Halo-tag labelling. Sulfonated rhodamine-conjugated fluorophores maintain desirable photophysical properties, such as brightness and photostability. While transfected cells with a nuclear localized SNAP-tag remain unlabelled, extracellular exposed tags can be cleanly visualized. By multiplexing with a permeable rhodamine, we are able to differentiate extra- and intracellular SNAP- and Halo-tags, including those installed on the glucagon-like peptide-1 receptor, a prototypical class B G protein-coupled receptor. Sulfo549 and Sulfo646 also labelled transfected neurons derived from induced pluripotent stem cells (iPSCs), allowing STED nanoscopy of the axonal membrane. Together, this work provides a new avenue for rendering dyes impermeable for exclusive extracellular visualization via self-labelling protein tags. We anticipate that Sulfo549, Sulfo646 and their congeners will be useful for a number of cell biology applications where labelling of intracellular sites interferes with accurate surface protein analysis.

Sulfonated rhodamine dyes allow SNAP- and Halo-tag labelling of cell surface protein fusions. A far-red version can be used for STED nanoscopy.

Reagents and models for detecting endogenous GLP1R and GIPR

Glucagon-like peptide-1 receptor (GLP1R) agonists target the GLP1R, whereas dual GLP1R/ gastric inhibitory polypeptide receptor (GIPR) agonists target both the GLP1R and GIPR. Despite the importance of these drug classes for the treatment of diabetes and obesity, still very little is known about the localization of GLP1R and GIPR themselves. Complicating matters is the low abundance of GLP1R and GIPR mRNA/protein, as well as a lack of specific and validated reagents for their detection. Without knowing where GLP1R and GIPR are located, it is difficult to propose mechanisms of action in the various target organs, and whether this is indirect or direct. In the current review, we will explain the steps needed to properly validate reagents for endogenous GLP1R/GIPR detection, describe the available approaches to visualize GLP1R/GIPR, and provide an update on the state-of-art. The overall aim is to provide a reference resource for researchers interested in GLP1R and GIPR signaling.

SNAP-tag-enabled super-resolution imaging reveals constitutive and agonist-dependent trafficking of GPR56 in pancreatic β-cells

Objective

Members of the adhesion G protein-coupled receptor (aGPCR) subfamily are important actors in metabolic processes, with GPR56 (ADGRG1) emerging as a possible target for type 2 diabetes therapy. GPR56 can be activated by collagen III, its endogenous ligand, and by a synthetic seven amino-acid peptide (TYFAVLM; P7) contained within the GPR56 Stachel sequence. However, the mechanisms regulating GPR56 trafficking dynamics and agonist activities are not yet clear.

Methods

Here, we introduced SNAPf-tag into the N-terminal segment of GPR56 to monitor GPR56 cellular activity in situ. Confocal and super-resolution microscopy were used to investigate the trafficking pattern of GPR56 in native MIN6 β-cells and in MIN6 β-cells where GPR56 had been deleted by CRISPR-Cas9 gene editing. Insulin secretion, changes in intracellular calcium, and β-cell apoptosis were determined by radioimmunoassay, single-cell calcium microfluorimetry, and measuring caspase 3/7 activities, respectively, in MIN6 β-cells and human islets.

Results

SNAP-tag labelling indicated that GPR56 predominantly underwent constitutive internalisation in the absence of an exogenous agonist, unlike GLP-1R. Collagen III further stimulated GPR56 internalisation, whereas P7 was without significant effect. The overexpression of GPR56 in MIN6 β-cells did not affect insulin secretion. However, it was associated with reduced β-cell apoptosis, while the deletion of GPR56 made MIN6 β-cells more susceptible to cytokine-induced apoptosis. P7 induced a rapid increase in the intracellular calcium in MIN6 β-cells (in a GPR56-dependent manner) and human islets, and it also caused a sustained and reversible increase in insulin secretion from human islets. Collagen III protected human islets from cytokine-induced apoptosis, while P7 was without significant effect.

Conclusions

These data indicate that GPR56 exhibits both agonist-dependent and -independent trafficking in β-cells and suggest that while GPR56 undergoes constitutive signalling, it can also respond to its ligands when required. We have also identified that constitutive and agonist-dependent GPR56 activation is coupled to protect β-cells against apoptosis, offering a potential therapeutic target to maintain β-cell mass in type 2 diabetes.

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GPR56 predominantly underwent constitutive internalisation in β-cells in the absence of exogenous agonist.

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The GPR56 agonists, collagen III and P7, showed differential effects on GPR56 trafficking and islet functions.

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Constitutive and agonist-dependent GPR56 activation is coupled to protection of β-cells against apoptosis.

Author Correction: Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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 labelling sites. Here we describe a novel approach to improve extracellular labelling by functionalizing the SNAP-tag substrate benzyl guanine ("BG") with a charged sulfonate ("SBG"). This chemical manipulation can be applied to any SNAP-tag substrate, 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 superresolution 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.

Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics

The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in metabolism. Presently, its visualization is limited to genetic manipulation, antibody detection or the use of probes that stimulate receptor activation. Herein, we present LUXendin645, a far-red fluorescent GLP1R antagonistic peptide label. LUXendin645 produces intense and specific membrane labeling throughout live and fixed tissue. GLP1R signaling can additionally be evoked when the receptor is allosterically modulated in the presence of LUXendin645. Using LUXendin645 and LUXendin651, we describe islet, brain and hESC-derived β-like cell GLP1R expression patterns, reveal higher-order GLP1R organization including membrane nanodomains, and track single receptor subpopulations. We furthermore show that the LUXendin backbone can be optimized for intravital two-photon imaging by installing a red fluorophore. Thus, our super-resolution compatible labeling probes allow visualization of endogenous GLP1R, and provide insight into class B GPCR distribution and dynamics both in vitro and in vivo.

Glucagon-like peptide-1 receptor is an important regulator of appetite and glucose homeostasis. Here the authors describe super-resolution microscopy and in vivo imaging compatible fluorescent probes, which reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics in islets and brain.

Conditional and Reversible Activation of Class A and B G Protein-Coupled Receptors Using Tethered Pharmacology

Understanding the activation and internalization of G protein-coupled receptors (GPCRs) using conditional approaches is paramount to developing new therapeutic strategies. Here, we describe the design, synthesis, and testing of ExONatide, a benzylguanine-linked peptide agonist of the glucagon-like peptide-1 receptor (GLP-1R), a class B GPCR required for maintenance of glucose levels in humans. ExONatide covalently binds to SNAP-tagged GLP-1R-expressing cells, leading to prolonged cAMP generation, Ca²⁺ rises, and intracellular retention of the receptor. These effects were readily switched OFF following cleavage of the introduced disulfide bridge using the cell-permeable reducing agent beta-mercaptoethanol (BME). A similar approach could be extended to a class A GPCR using GhrelON, a benzylguanine-linked peptide agonist of the growth hormone secretagogue receptor 1a (GHS-R1a), which is involved in food intake and growth. Thus, ExONatide and GhrelON allow SNAP-tag-directed activation of class A and B GPCRs involved in gut hormone signaling in a reversible manner. This tactic, termed reductively cleavable agONist (RECON), may be useful for understanding GLP-1R and GHS-R1a function both in vitro and in vivo, with applicability across GPCRs.

Optical control of a receptor-linked guanylyl cyclase using a photoswitchable peptidic hormone

The optical control over biological function with small photoswitchable molecules has gathered significant attention in the last decade. Herein, we describe the design and synthesis of a small library of photoswitchable peptidomimetics based upon human atrial natriuretic peptide (ANP), in which the photochromic amino acid [3-(3-aminomethyl)phenylazo]phenylacetic acid (AMPP) is incorporated into the peptide backbone. The endogeneous hormone ANP signals via the natriuretic peptide receptor A (NPR-A) through raising intracellular cGMP concentrations, and is involved in blood pressure regulation and sodium homeostasis, as well as lipid metabolism and pancreatic function. The cis- and trans-isomers of one of our peptidomimetics, termed TOP271, exhibit a four-fold difference in NPR-A mediated cGMP synthesis in vitro. Despite this seemingly small difference, TOP271 enables large, optically-induced conformational changes ex vivo and transforms the NPR-A into an endogenous photoswitch. Thus, application of TOP271 allows the reversible generation of cGMP using light and remote control can be afforded over vasoactivity in explanted murine aortic rings, as well as pancreatic beta cell function in islets of Langerhans. This study demonstrates the broad applicability of TOP271 to enzyme-dependent signalling processes, extends the toolbox of photoswitchable molecules to all classes of transmembrane receptors and utilizes photopharmacology to deduce receptor activation on a molecular level.

Non-human primate and rodent embryonic stem cells are differentially sensitive to embryotoxic compounds

Many industrial chemicals and their respective by-products need to be comprehensively evaluated for toxicity using reliable and efficient assays. In terms of teratogenicity evaluations, the murine-based embryonic stem cell test (EST) offers a promising solution to screen for multiple tissue endpoints. However, use of a mouse model in the EST can yield only a limited understanding of human development, anatomy, and physiology. Non-human primate or human in vitro models have been suggested to be a pharmacologically and pathophysiologically desirable alternative to murine in vitro models. Here, we comparatively evaluated the sensitivity of embryonic stem cells (ESCs) of a non-human primate to skeletal teratogens with mouse ESCs hypothesizing that inclusion of non-human primate cells in in vitro tests would increase the reliability of safety predictions for humans.

First, osteogenic capacity was compared between ESCs from the mouse and a New World monkey, the common marmoset. Then, cells were treated with compounds that have been previously reported to induce bone teratogenicity. Calcification and MTT assays evaluated effects on osteogenesis and cell viability, respectively. Our data indicated that marmoset ESCs responded differently than mouse ESCs in such embryotoxicity screens with no obvious dependency on chemical or compound classes and thus suggest that embryotoxicity screening results could be affected by species-driven response variation. In addition, ESCs derived from rhesus monkey, an Old World monkey, and phylogenetically closer to humans than the marmoset, were observed to respond differently to test compounds than marmoset ESCs. Together these results indicate that there are significant differences in the responses of non-human primate and mouse ESC to embryotoxic agents.

Ribosomal readthrough at a short UGA stop codon context triggers dual localization of metabolic enzymes in Fungi and animals

Translation of mRNA into a polypeptide chain is a highly accurate process. Many prokaryotic and eukaryotic viruses, however, use leaky termination of translation to optimize their coding capacity. Although growing evidence indicates the occurrence of ribosomal readthrough also in higher organisms, a biological function for the resulting extended proteins has been elucidated only in very few cases. Here, we report that in human cells programmed stop codon readthrough is used to generate peroxisomal isoforms of cytosolic enzymes. We could show for NAD-dependent lactate dehydrogenase B (LDHB) and NAD-dependent malate dehydrogenase 1 (MDH1) that translational readthrough results in C-terminally extended protein variants containing a peroxisomal targeting signal 1 (PTS1). Efficient readthrough occurs at a short sequence motif consisting of a UGA termination codon followed by the dinucleotide CU. Leaky termination at this stop codon context was observed in fungi and mammals. Comparative genome analysis allowed us to identify further readthrough-derived peroxisomal isoforms of metabolic enzymes in diverse model organisms. Overall, our study highlights that a defined stop codon context can trigger efficient ribosomal readthrough to generate dually targeted protein isoforms. We speculate that beyond peroxisomal targeting stop codon readthrough may have also other important biological functions, which remain to be elucidated.

Eukaryotic organisms use various strategies to generate protein isoforms with different function or intracellular localization from a single gene. While differential splicing of mRNA is the most common mechanism to expand the number of encoded proteins, translational readthrough of stop codons is an alternative strategy to create protein variants with C-terminally extended proteins. Recently, it has been shown that fungi use both alternative splicing and translational readthrough to specify peroxisomal isoforms of glycolytic enzymes. Here we show that stop codon readthrough is also used in the animal kingdom to target important metabolic enzymes to peroxisomes. Interestingly, several of these enzymes have a function in peroxisomal redox homeostasis and energy metabolism. It has been described that termination fidelity is modulated by oxidation of specific ribosomal proteins. This suggests that dual targeting via translational readthrough allows adaptation of peroxisomal metabolism to the oxidative status of the cell.

Fungal peroxisomes as biosynthetic organelles

Peroxisomes are nearly ubiquitous single-membrane organelles harboring multiple metabolic pathways beside their prominent role in the β-oxidation of fatty acids. Here we review the diverse metabolic functions of peroxisomes in fungi. A variety of fungal metabolites are at least partially synthesized inside peroxisomes. These include the essential co-factor biotin but also different types of secondary metabolites. Peroxisomal metabolites are often derived from acyl-CoA esters for example β-oxidation intermediates. In several ascomycetes a subtype of peroxisomes has been identified that is metabolically inactive but is required to plug the septal pores of wounded hyphae. Thus, peroxisomes are versatile organelles that can adapt their function to the life style of an organism. This remarkable variability suggests that the full extent of the biosynthetic capacity of peroxisomes is still elusive. Moreover, in fungi peroxisomes are non-essential under laboratory conditions making them attractive organelles for biotechnological approaches and the design of novel metabolic pathways in customized peroxisomes.

Dual targeting of peroxisomal proteins

Cellular compartmentalization into organelles serves to separate biological processes within the environment of a single cell. While some metabolic reactions are specific to a single organelle, others occur in more than one cellular compartment. Specific targeting of proteins to compartments inside of eukaryotic cells is mediated by defined sequence motifs. To achieve multiple targeting to different compartments cells use a variety of strategies. Here, we focus on mechanisms leading to dual targeting of peroxisomal proteins. In many instances, isoforms of peroxisomal proteins with distinct intracellular localization are encoded by separate genes. But also single genes can give rise to differentially localized proteins. Different isoforms can be generated by use of alternative transcriptional start sites, by differential splicing or ribosomal read-through of stop codons. In all these cases different peptide variants are produced, of which only one carries a peroxisomal targeting signal. Alternatively, peroxisomal proteins contain additional signals that compete for intracellular targeting. Dual localization of proteins residing in both the cytoplasm and in peroxisomes may also result from use of inefficient targeting signals. The recent observation that some bona fide cytoplasmic enzymes were also found in peroxisomes indicates that dual targeting of proteins to both the cytoplasm and the peroxisome might be more widespread. Although current knowledge of proteins exhibiting only partial peroxisomal targeting is far from being complete, we speculate that the metabolic capacity of peroxisomes might be larger than previously assumed.

Crosstalk between the unfolded protein response and pathways that regulate pathogenic development in Ustilago maydis

The unfolded protein response (UPR) is a conserved eukaryotic signaling pathway regulating endoplasmic reticulum (ER) homeostasis during ER stress, which results, for example, from an increased demand for protein secretion. Here, we characterize the homologs of the central UPR regulatory proteins Hac1 (for Homologous to ATF/CREB1) and Inositol Requiring Enzyme1 in the plant pathogenic fungus Ustilago maydis and demonstrate that the UPR is tightly interlinked with the b mating-type-dependent signaling pathway that regulates pathogenic development. Exact timing of UPR is required for virulence, since premature activation interferes with the b-dependent switch from budding to filamentous growth. In addition, we found crosstalk between UPR and the b target Clampless1 (Clp1), which is essential for cell cycle release and proliferation in planta. The unusual C-terminal extension of the U. maydis Hac1 homolog, Cib1 (for Clp1 interacting bZIP1), mediates direct interaction with Clp1. The interaction between Clp1 and Cib1 promotes stabilization of Clp1, resulting in enhanced ER stress tolerance that prevents deleterious UPR hyperactivation. Thus, the interaction between Cib1 and Clp1 constitutes a checkpoint to time developmental progression and increased secretion of effector proteins at the onset of biotrophic development. Crosstalk between UPR and the b mating-type regulated developmental program adapts ER homeostasis to the changing demands during biotrophy.

Oral L-arginine supplementation in patients with mild arterial hypertension and its effect on plasma level of asymmetric dimethylarginine, L-citruline, L-arginine and antioxidant status

BACKGROUND

Potential role of L-arginine supplementation as a new effective strategy of improving endothelial function in patients with hypertension is recently under consideration.

OBJECTIVE

To evaluate influence of 28-day oral supplementation of L-arginine on plasma level of asymmetric dimethylarginine (ADMA), L-citrulline, L-arginine and total antioxidant status (TAS), in patients with mild arterial hypertension.

SUBJECTS AND METHODS

54 participants (24 women and 30 men) were studied. Ambulatory blood pressure monitoring (ABPM) was used for allotting patients to either healthy control group (19 subjects) or hypertensive treatment group (35 patients). Patients were later randomized to either L-arginine (2 g tid or 4 g tid) or placebo. During 28 days of study on 5 consecutive visits TAS, plasma level of ADMA, L-citrulline, and L-arginine were measured.

RESULTS

In patients with mild hypertension treated with L-arginine significant increase in TAS and plasma level of arginine and citrulline was observed. Additionally plasma ADMA concentrations after 28 days of L-arginine supplementation significantly exceeded initial concentrations.

CONCLUSIONS

L-arginine supplementation increases plasma arginine, citrulline and TAS in patients with mild arterial hypertension. It confirms the thesis that augmented concentrations of L-arginine stimulate NO biosynthesis which leads to reduction of oxidative stress. Increase of ADMA plasma level after L-arginine supplementation confirms correlation between ADMA and L-arginine.

Supplementation with L-arginine does not influence arterial blood pressure in healthy people: a randomized, double blind, trial

BACKGROUND AND OBJECTIVES

It cannot be excluded that supplementation with L-arginine, by improving function of endothelium and hypotensive effect, can be advantegeous in prevention of cardiovascular diseases in healthy people. However, reports about hypotensive effect of L-arginine in healthy people are unclear. Moreover, no research including ambulatory blood pressure measurement (ABPM) has been conducted so far. Therefore, the aim of our study was to show if 4-week supplementation of healthy people with L-arginine influences blood pressure measured with ABPM.

MATERIALS AND METHODS

The study was carried out on 19 healthy people randomized to 6 g/24-hour, 12 g/24-hours of L-arginine or placebo. ABPM was carried out 4 times: before randomization, after 2 and 4 weeks of supplementation and 2 weeks after finishing supplementation.

RESULTS

It was found that 4 weeks of supplementation of healthy people with L-arginine (6 or 12 g/24-hour) led to nonsignificant decrease of systolic and diastolic blood pressure; the decrease was greater during night.

CONCLUSION

These findings showed that supplementation with L-arginine is not necessarily advantageous in healthy people.

Need for treatment of gonorrhea to be effective against Chlamydia trachomatis

Men and women with gonorrhea or contact to gonorrhea are frequently co-infected with Chlamydia trachomatis. To assess the importance of using treatment regimens active against both Neisseria gonorrhoeae and C trachomatis, tetracycline 500 mg orally four times daily for five days, with activity against both organisms, was compared with ceftriaxone, 250 mg once intramuscularly, with activity against only N gonorrhoeae. N gonorrhoeae microbiological failure occurred in six of 148 patients (4%) on tetracycline and zero of 85 on ceftriaxone. Microbiological failure for C trachomatis occurred in zero of 27 on tetracycline and 10 of 12 (83%) on ceftriaxone (P<0.001). In addition, 14 others on ceftriaxone had C trachomatis first isolated after treatment. When all types of microbiologialc and clinical failures are included, outcome was significantly better on tetracycline (P<0.001). Optimal treatment of patients with gonorrhea must include regimens with activity against both C trachomatis and N gonorrhoeae.