Radiosynthesis and in vivo evaluation of a fluorine-18 labeled pyrazine based radioligand for PET imaging of the adenosine A2B receptor

On the basis of a pyrazine core structure, three new adenosine A_2B receptor ligands (7a–c) were synthesized containing a 2-fluoropyridine moiety suitable for ¹⁸F-labeling. Compound 7a was docked into a homology model of the A_2B receptor based on X-ray structures of the related A_2A receptor, and its interactions with the adenosine binding site were rationalized. Binding affinity data were determined at the four human adenosine receptor subtypes. Despite a rather low selectivity regarding the A₁ receptor, 7a was radiolabeled as the most suitable candidate (K_i(A_2B)?=?4.24?nM) in order to perform in vivo studies in mice with the aim to estimate fundamental pharmacokinetic characteristics of the compound class. Organ distribution studies and a single PET study demonstrated brain uptake of [¹⁸F]7a with a standardized uptake value (SUV) of ≈1 at 5?min post injection followed by a fast wash out. Metabolism studies of [¹⁸F]7a in mice revealed the formation of a blood–brain barrier penetrable radiometabolite, which could be structurally identified. The results of this study provide an important basis for the design of new derivatives with improved binding properties and metabolic stability in vivo.     

Functional defect of peripheral neutrophils in mice with induced deletion of CXCR2

Type 2 CXC chemokine receptor CXCR2 plays roles in development, tumorigenesis, and inflammation. CXCR2 also promotes demyelination and decreases remyelination by actions toward hematopoietic cells and nonhematopoietic cells. Germline CXCR2 deficient (Cxcr2^‐/‐) mice reported in 1994 revealed the complexity of CXCR2 function and its differential expression in varied cell‐types. Here, we describe Cxcr2^fl/fl mice for which the targeting construct was generated by recombineering based on homologous recombination in E. coli. Without recombination Cxcr2^fl/fl mice have CXCR2 expression on neutrophils in peripheral blood, bone marrow and spleen. Cxcr2^fl/fl mice were crossed to Mx‐Cre mice in which Cre recombinase is induced by Type I interferons, elicited by injection with polyinosinic‐polycytidylic acid (poly(I:C)). CXCR2‐deficient neutrophils were observed in poly(I:C) treated Cxcr2^fl/fl::Mx‐Cre⁺ (Cxcr2‐CKO) mice, but not in poly(I:C) treated Cxcr2^f//+::Mx‐Cre⁺ mice. CXCR2 deletion was mainly observed peripherally but not in the CNS. Cxcr2‐CKO mice showed impaired neutrophil migration in sterile peritonitis. Cxcr2‐CKO mice reported here will provide a genetic reagent to dissect roles of CXCR2 in the neutrophil granulocyte lineage. Furthermore Cxcr2^fl/fl mice will provide useful genetic models to evaluate CXCR2 function in varied cell populations. genesis 51:587–595. © 2013 Wiley Periodicals, Inc.     

DR5 as a reporter system to study auxin response in Populus

Key message

Auxin responsive promoter DR5 reporter system is functional in Populus to monitor auxin response in tissues including leaves, roots, and stems.

Abstract

We described the behavior of the DR5::GUS reporter system in stably transformed Populus plants. We found several similarities with Arabidopsis, including sensitivity to native and synthetic auxins, rapid induction after treatment in a variety of tissues, and maximal responses in root tissues. There were also several important differences from Arabidopsis, including slower time to maximum response and lower induction amplitude. Young leaves and stem sections below the apex showed much higher DR5 activity than did older leaves and stems undergoing secondary growth. DR5 activity was highest in cortex, suggesting high levels of auxin concentration and/or sensitivity in this tissue. Our study shows that the DR5 reporter system is a sensitive and facile system for monitoring auxin responses and distribution at cellular resolution in poplar.     

Restoration of SMN to Emx-1 expressing cortical neurons is not sufficient to provide benefit to a severe mouse model of Spinal Muscular Atrophy

Spinal Muscular Atrophy (SMA), an autosomal recessive neuromuscular disorder, is a leading genetic cause of infant mortality. SMA is caused by the homozygous loss of Survival Motor Neuron-1 (SMN1). However, low, but essential, levels of SMN protein are produced by a nearly identical copy gene called SMN2. Detailed analysis of neuromuscular junctions in SMA mice has revealed a selective vulnerability in a subset of muscle targets, suggesting that while SMN is reduced uniformly, the functional deficits manifest sporadically. Additionally, in severe SMA models, it is becoming increasing apparent that SMA is not restricted solely to motor neurons. Rather, additional tissues including the heart, vasculature, and the pancreas contribute to the complete SMA-associated pathology. Recently, transgenic models have been utilized to examine the tissue-specific requirements of SMN, including selective depletion and restoration of SMN in motor neurons. To determine whether the cortical neuronal populations expressing the Emx-1 promoter are involved in SMA pathology, we generated a novel SMA mouse model in which SMN expression was specifically induced in Emx-1 expressing cortical neurons utilizing an Emx-1-Cre transgene. While SMN expression was robust in the central nervous system as expected, SMA mice did not live longer. Weight and time-to-right motor function were not significantly improved.     

Adenovirus RIDα uncovers a novel pathway requiring ORP1L for lipid droplet formation independent of NPC1

Niemann–Pick disease type C (NPC) is caused by mutations in NPC1 or NPC2, which coordinate egress of low-density-lipoprotein (LDL)-cholesterol from late endosomes. We previously reported that the adenovirus-encoded protein RIDα rescues the cholesterol storage phenotype in NPC1-mutant fibroblasts. We show here that RIDα reconstitutes deficient endosome-to-endoplasmic reticulum (ER) transport, allowing excess LDL-cholesterol to be esterified by acyl-CoA:cholesterol acyltransferase and stored in lipid droplets (LDs) in NPC1-deficient cells. Furthermore, the RIDα pathway is regulated by the oxysterol-binding protein ORP1L. Studies have classified ORP1L as a sterol sensor involved in LE positioning downstream of GTP-Rab7. Our data, however, suggest that ORP1L may play a role in transport of LDL-cholesterol to a specific ER pool designated for LD formation. In contrast to NPC1, which is dispensable, the RIDα/ORP1L-dependent route requires functional NPC2. Although NPC1/NPC2 constitutes the major pathway, therapies that amplify minor egress routes for LDL-cholesterol could significantly improve clinical management of patients with loss-of-function NPC1 mutations. The molecular identity of putative alternative pathways, however, is poorly characterized. We propose RIDα as a model system for understanding physiological egress routes that use ORP1L to activate ER feedback responses involved in LD formation.     

Window Area and Development Drive Spatial Variation in Bird-Window Collisions in an Urban Landscape

Collisions with windows are an important human-related threat to birds in urban landscapes. However, the proximate drivers of collisions are not well understood, and no study has examined spatial variation in mortality in an urban setting. We hypothesized that the number of fatalities at buildings varies with window area and habitat features that influence avian community structure. In 2010 we documented bird-window collisions (BWCs) and characterized avian community structure at 20 buildings in an urban landscape in northwestern Illinois, USA. For each building and season, we conducted 21 daily surveys for carcasses and nine point count surveys to estimate relative abundance, richness, and diversity. Our sampling design was informed by experimentally estimated carcass persistence times and detection probabilities. We used linear and generalized linear mixed models to evaluate how habitat features influenced community structure and how mortality was affected by window area and factors that correlated with community structure. The most-supported model was consistent for all community indices and included effects of season, development, and distance to vegetated lots. BWCs were related positively to window area and negatively to development. We documented mortalities for 16/72 (22%) species (34 total carcasses) recorded at buildings, and BWCs were greater for juveniles than adults. Based on the most-supported model of BWCs, the median number of annual predicted fatalities at study buildings was 3 (range = 0–52). These results suggest that patchily distributed environmental resources and levels of window area in buildings create spatial variation in BWCs within and among urban areas. Current mortality estimates place little emphasis on spatial variation, which precludes a fundamental understanding of the issue. To focus conservation efforts, we illustrate how knowledge of the structural and environmental factors that influence bird-window collisions can be used to predict fatalities in the broader landscape.     

Phospho-dependent functional modulation of GABA(B) receptors by the metabolic sensor AMP-dependent protein kinase

GABA(B) receptors are heterodimeric G protein-coupled receptors composed of R1 and R2 subunits that mediate slow synaptic inhibition in the brain by activating inwardly rectifying K(+) channels (GIRKs) and inhibiting Ca(2+) channels. We demonstrate here that GABA(B) receptors are intimately associated with 5'AMP-dependent protein kinase (AMPK). AMPK acts as a metabolic sensor that is potently activated by increases in 5'AMP concentration that are caused by enhanced metabolic activity, anoxia, or ischemia. AMPK binds the R1 subunit and directly phosphorylates S783 in the R2 subunit to enhance GABA(B) receptor activation of GIRKs. Phosphorylation of S783 is evident in many brain regions, and is increased dramatically after ischemic injury. Finally, we also reveal that S783 plays a critical role in enhancing neuronal survival after ischemia. Together our results provide evidence of a neuroprotective mechanism, which, under conditions of metabolic stress or after ischemia, increases GABA(B) receptor function to reduce excitotoxicity and thereby promotes neuronal survival.     

PKCtheta is a key player in the development of insulin resistance

Activation of PKCtheta is associated with lipid-induced insulin resistance and PKCtheta knockout mice are protected from the lipid-induced defects. However, the exact mechanism by which PKCtheta contributes to insulin resistance is not known. To investigate whether an increase in PKCtheta expression leads to insulin resistance, C2C12 skeletal muscle cells were transfected with PKCtheta DNA and treated with different concentrations of insulin for 10 min. PKCtheta overexpression induced reduction of IRS-1 protein levels with a decrease in insulin-induced p85 binding to IRS-1, phosphorylation of PKB and its substrates, p70 and GSK3. Pretreatment of these cells with GF-109203X (a non-specific PKC inhibitor, IC50 for PKCtheta = 10 nM) recovered insulin signaling. PKCtheta was found to be expressed in liver and treatment of human hepatoma cells (HepG2) with high insulin and glucose resulted in an increase in PKCtheta expression that correlated with a decrease in IRS-1 protein levels and the development of insulin resistance. Reduction of PKCtheta expression using RNAi technology significantly inhibited the degradation of IRS-1 and enhanced insulin-induced IRS-1 tyrosine phosphorylation, p85 association to IRS-1 and PKB phosphorylation. In conclusion, by overexpressing PKCtheta or using RNAi technology to downregulate PKCtheta, we have demonstrated that PKCtheta has a key role in the development of insulin resistance. These findings suggest that PKCtheta mediates not only insulin resistance in muscle but also in liver, which may contribute to the development of whole body insulin resistance and diabetes.     

Zinc-secreting Paneth cells studied by ZP fluorescence.

We have used a new family of zinc-specific-responsive fluorescent dyes (ZPs) to study the sequestration and secretion of zinc from Paneth cells, which are located in the bases of the crypts of Lieberkühn within the rat small intestine. Vivid ZP fluorescence zinc staining of Paneth cell secretory granules is seen in both cryostat sections and isolated crypts, providing firm evidence for a pool of labile (rapidly exchangeable) zinc within these cells. We further demonstrate that this ionic zinc pool is secreted under physiological conditions. In vivo stimulation of the small intestine by IP injection of the secretagogue pilocarpine results in discrete zinc staining within the lumens of subsequently isolated crypts, concomitant with a decrease in the zinc staining of Paneth cell granules located within the same crypts. In contrast, the secretion of zinc into the lumens of isolated crypts stimulated in vitro with either carbachol or LPS (lipopolysaccharide) is not observed. However, a distinct change in Paneth cell morphology, suggesting attempted secretion, is seen in response to the direct application of cholinergics but not LPS. These findings suggest that zinc is coreleased with other Paneth cell anti-microbials, and that the intact intestine is necessary for secretion into the crypt lumen.