A Sendai virus recombinant vaccine expressing a gene for truncated human metapneumovirus (hMPV) fusion protein protects cotton rats from hMPV challenge

Human metapneumovirus (hMPV) infections pose a serious health risk to young children, particularly in cases of premature birth. No licensed vaccine exists and there is no standard treatment for hMPV infections apart from supportive hospital care. We describe the production of a Sendai virus (SeV) recombinant that carries a gene for a truncated hMPV fusion (F) protein (SeV-MPV-Ft). The vaccine induces binding and neutralizing antibody responses toward hMPV and protection against challenge with hMPV in a cotton rat system. Results encourage advanced development of SeV-MPV-Ft to prevent the morbidity and mortality caused by hMPV infections in young children.

Quantum dot ex vivo labeling of neuromuscular synapses

Nicotinic receptors (nAchRs) are responsible for fast excitatory signaling by the neurotransmitter acetylcholine (Ach). They are present on the postsynaptic membrane at neuromuscular junctions (NMJs) and also at brain synapses. Alpha-bungarotoxin (alpha-BTX), a high-affinity nAchR antagonist, inhibits Ach binding and neurotransmission. Here we demonstrate biotinylated alpha-BTX, bound to native mouse diaphragm nAchRs, can be quantified and visualized ex vivo using streptavidin-conjugated quantum dots. This approach provides a novel methodology for the direct assessment of the presence and mobility of neurotransmitter receptors in native tissue.

Synthesis and characterization of a pegylated derivative of 3-(1,2,3,6-tetrahydro-pyridin-4yl)-1H-indole (IDT199): a high affinity SERT ligand for conjugation to quantum dots

Quantum dots consisting of a cadmium selenide core encapsulated in a shell of cadmium doped zinc sulfide have the potential to revolutionize fluorescent imaging of live cell cultures. In order to utilize these fluorescent probes it is necessary to functionalize them with biologically active ligands. In this paper we report the design and synthesis of a ligand that has a high affinity for the serotonin transporter (SERT) that may be conjugated to quantum dots.

Desvenlafaxine Succinate Identifies Novel Antagonist Binding Determinants in the Human Norepinephrine Transporter

Desvenlafaxine succinate (DVS) is a recently introduced antagonist of the human norepinephrine and serotonin transporters (hNET and hSERT, respectively), currently in clinical development for use in the treatment of major depressive disorder and vasomotor symptoms associated with menopause. Initial evaluation of the pharmacological properties of DVS (J Pharmacol Exp Ther 318:657-665, 2006) revealed significantly reduced potency for the hNET expressed in membranes compared with whole cells when competing for [(3)H]nisoxetine (NIS) binding. Using hNET in transfected human embryonic kidney-293 cells, this difference in potency for DVS at sites labeled by [(3)H]NIS was found to distinguish DVS, the DVS analog rac-(1-[1-(3-chloro-phenyl)-2-(4-methylpiperazin-1-yl)-ethyl]cyclohexanol (WY-46824), methylphenidate, and the cocaine analog 3beta-(4-iodophenyl)tropane-2beta-carboxylic acid methyl ester (RTI-55) from other hNET antagonists, such as NIS, mazindol, tricyclic antidepressants, and cocaine. These differences seem not to arise from preparation-specific perturbations of ligand intrinsic affinity or antagonist-specific surface trafficking but rather from protein conformational alterations that perturb the relationships between distinct hNET binding sites. In an initial search for molecular features that differentially define antagonist binding determinants, we document that Val148 in hNET transmembrane domain 3 selectively disrupts NIS binding but not that of DVS.

High affinity inhibitors of the dopamine transporter (DAT): novel biotinylated ligands for conjugation to quantum dots

Compounds capable of inhibiting the dopamine transporter protein (DAT) that can be conjugated to cadmium selenide/zinc sulfide/core shell nanocrystals may be used to image the location and distribution of the DAT in neuronal cell membranes. This letter describes the synthesis of biotinylated analogs of the DAT antagonists GBR 12909 and GBR 12935 that can be attached to streptavidin coated cadmium selenide/zinc sulfide/core shell nanocrystals.

Inhibitors of the serotonin transporter protein (SERT): the design and synthesis of biotinylated derivatives of 3-(1,2,3,6-tetrahydro-pyridin-4-yl)-1H-indoles. High-affinity serotonergic ligands for conjugation with quantum dots

There is a growing demand for compounds with specificity for the serotonin transporter protein (SERT) that can be conjugated to cadmium selenide/zinc sulfide core shell nanocrystals. This letter describes the design and synthesis of two different biotinylated SERT antagonists that can be attached to streptavidin-coated cadmium selenide/zinc sulfide core shell nanocrystals.

Labeling cell-surface proteins via antibody quantum dot streptavidin conjugates

The quantum dot is a novel fluorescent platform that has the potential to become an alternative to conventional organic dyes used to label biological probes such as antibodies or ligands. Compared to typical fluorescent organic dyes, cadmium selenide/zinc sulfide core-shell nanocrystals, or quantum dots, have greater photostability, resist metabolic and chemical degradation, are nontoxic, and display broad emission and narrow excitation bands. When conjugated to generic adaptor molecules such as streptavidin, quantum dots can be used to label different biotinylated antibodies or ligands without having to customize the quantum dot surface chemistry for each antibody or ligand. In this chapter, we outline the methodology for using streptavidin quantum dots to label biotinylated antibodies that target cell-surface ectodomain proteins on both living and fixed cells.

Peptide-conjugated quantum dots: imaging the angiotensin type 1 receptor in living cells

Peptide-quantum dot conjugates have been prepared by attaching angiotensin II (Ang II) to cadmium selenide/zinc sulfide core-shell nanocrystals using an 1-[3-(Dimethyamino)propyl]-3-ethylcarbo diimide hydrochloride (EDC) coupling. These conjugates have been used to image angiotensin I-expressing Chinese hamster ovary (CHO) cells in vitro. When CHO cells were incubated with Ang II before incubating with Ang II-conjugated quantum dots, we were able to block the binding of the dots. The Ang II-quantum dot conjugates did not bind to parental cells and showed similar staining patterns when compared with a commercially available Ang II Alexa 488 conjugate.

Novel fluorescence-based approaches for the study of biogenic amine transporter localization, activity, and regulation

Pre-synaptic norepinephrine (NE) and dopamine (DA) transporters (NET and DAT) terminate catecholamine synaptic transmission through reuptake of released neurotransmitter. Recent studies reveal that NET and DAT are tightly regulated by receptor and second messenger-linked signaling pathways. Common approaches for studying these transporters involve use of radiolabeled substrates or antagonists, methods possessing limited spatial resolution and that bear limited opportunities for repeated monitoring of living preparations. To circumvent these issues, we have explored two novel assay platforms that permit temporally resolved quantitation of transport activity and transporter protein localization. To monitor the binding and transport function of NET and DAT in real-time, we have investigated the uptake of the fluorescent organic compound 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (ASP+). We have extended our previous single cell level application of this substrate to monitor transport activity via high-throughput assay platforms. Compared to radiotracer uptake methods, acquisition of ASP+ fluorescence is non-isotopic and allows for continuous, repeated transport measurements on both transfected and native preparations. Secondly, we have extended our application of small-molecule-conjugated fluorescent CdSe/ZnS nanocrystals, or quantum dots (Qdots), to utilize antibody and peptide ligands that can identify surface expressed transporters, receptors and other membrane proteins in living cell systems. Unlike typical organic fluorophores, Qdots are highly resistant to bleaching and can be conjugated to multiple ligands. They can also be illuminated by conventional light sources, yet produce narrow, gaussian emission spectra compatible with multiple target visualization (multiplexing). Together, these approaches offer novel opportunities to investigate changes in transporter function and distribution in real-time with superior spatial and temporal resolution.

Regulation of dopamine D(1) receptor trafficking by protein kinase A-dependent phosphorylation

The aim of this study was to use pharmacological inhibition of protein kinase A and mutation of potential protein kinase A phosphorylation sites to determine the role of protein kinase A-catalyzed phosphorylation of the dopamine D(1) receptor in agonist-stimulated desensitization and internalization of the receptor. To facilitate purification and imaging of the D(1) receptor, we attached a polyhistidine tag to the amino terminus and enhanced green fluorescent protein to the carboxyl terminus of the receptor (D(1)-EGFP). D(1)-EGFP was similar to the untagged D(1) receptor in terms of affinity for agonist and antagonist ligands, coupling to G proteins, and stimulation of cyclic AMP accumulation. D(1)-EGFP and two mutants in which either Thr268 or Ser380 was replaced with Ala were stably expressed in NS20Y neuroblastoma cells. Pretreatment with the protein kinase A inhibitor H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) or substitution of Ala for Thr268 reduced agonist-stimulated phosphorylation of the receptor and resulted in diminished trafficking of the receptor to the perinuclear region of the cell. Substitution of Ala for Thr268 had no effect, however, on agonist-induced receptor sequestration or desensitization of cyclic AMP accumulation. Substitution of Ala for Ser380 had no effect on D(1) receptor phosphorylation, sequestration, desensitization, or trafficking to the perinuclear region. We conclude that protein kinase A-dependent phosphorylation of the D(1) receptor on Thr268 regulates a late step in the sorting of the receptor to the perinuclear region of the cell, but that phosphorylation of Thr268 is not required for receptor sequestration or maximal desensitization of cyclic AMP accumulation.

NMDA receptor subunit mRNA and protein expression in ethanol-withdrawal seizure-prone and -resistant mice

BACKGROUND

Ethanol withdrawal seizure-prone (WSP) and -resistant (WSR) mice have been genetically selected for differences in handling-induced convulsion severity during withdrawal from chronic ethanol administration. Importantly, drug-naïve mice from these selected lines also differ in handling-induced convulsion severity. Different N-methyl-D-aspartate (NMDA) receptor subunit and splice variant associations confer varying sensitivities to ethanol, and may play a role in the different behavioral responses of the WSP and WSR mice.

METHODS

In situ hybridization of riboprobes was used to characterize NMDA receptor subunit and splice variant mRNA expression in cortex and hippocampus from WSP and WSR mice. In addition, immunoblotting and immunohistochemistry were used to examine the expression of specific NMDA receptor subunits and splice variants in hippocampus and cortex from the selected mouse lines.

RESULTS

In situ hybridization of riboprobes indicated that, in brain sections from both WSP and WSR mice, there was a differential regional distribution of mRNA for the mouse NR1, NR2A, NR2B, and NR2C NMDA receptor subunits. However, there were no differences between the selected lines in the hybridization of riboprobes to hippocampal subfields or cortical layers. In addition, hybridization of the probe for a 63-base N1-terminal cassette of ethanol-sensitive NR1 splice variants labeled both cortex and hippocampus. The level of hybridization did not differ across subfields of the hippocampus. Results from Western blot and immunohistochemical experiments also indicated that there were no differences between selected lines in NMDA receptor subunit protein expression. However, there was a correlation between mRNA and protein expression in hippocampus and cortex for each NMDA receptor subunit that was examined.

CONCLUSIONS

The data suggest that at the level of both mRNA and protein, NMDA receptor subunit and splice variant expression can be uncoupled from convulsion severity in mice that have been selectively bred for symptoms of ethanol withdrawal.

Metabolism of catecholamines by catechol-O-methyltransferase in cells expressing recombinant catecholamine transporters

To determine if catechol-O-methyltransferase (COMT) metabolizes catecholamines within cell lines used for heterologous expression of plasmalemmal transporters and alters the measured characteristics of 3H-substrate transport, the uptake of monoamine transporter substrates was assessed in three cell lines (C6 glioma, L-M fibroblast, and HEK293 cells) that had been transfected with the recombinant human transporters. Uptake and cellular retention of 3H-catecholamines was increased by up to fourfold by two COMT inhibitors, tropolone and Ro 41-0960, with potencies similar to those for inhibition of COMT activity, whereas the uptake of two transporter substrates that are not substrates for COMT, [3H]serotonin and [3H]MPP+, was unaffected. Direct measurement of monoamine substrates by HPLC confirmed that tropolone (1 mM) increased the retention of the catecholamines dopamine and norepinephrine, but not the retention of serotonin in HEK293 cells. Saturation analysis of the uptake of [3H]dopamine by C6 cells expressing the dopamine transporter demonstrated that tropolone (1 mM) decreased the apparent Km of transport from 0.61 microM to 0.34 microM without significantly altering the maximal velocity of transport. These data suggest that endogenous COMT activity in mammalian cells may alter neurotransmitter deposition and thus the apparent kinetic characteristics of transport.

Effects of subchronic clozapine and haloperidol on striatal glutamatergic synapses

Subchronic treatment with haloperidol increases the number of asymmetric glutamate synapses associated with a perforated postsynaptic density in the striatum. To characterize these synaptic changes further, the effects of subchronic (28 days) administration of an atypical antipsychotic, clozapine (30 mg/kg, s.c.), or a typical antipsychotic, haloperidol (0.5 mg/kg, s.c.), on the binding of [3H] MK-801 to the NMDA receptor-linked ion channel complex and on the in situ hybridization of riboprobes for NMDAR2A and 2B subunits and splice variants of the NMDAR1 subunit were examined in striatal preparations from rats. The density of striatal glutamate immunogold labeling associated with nerve terminals of all asymmetric synapses and the immunoreactivity of those asymmetric synapses associated with a perforated postsynaptic density were also examined by electron microscopy. Subchronic neuroleptic administration had no effect on [3H] MK-801 binding to striatal membrane preparations. Both drugs increased glutamate immunogold labeling in nerve terminals of all asymmetric synapses, but only haloperidol increased the density of glutamate immunoreactivity within nerve terminals of asymmetric synapses containing a perforated postsynaptic density. Whereas subchronic administration of clozapine, but not haloperidol, resulted in a significant increase in the hybridization of a riboprobe that labels all splice variants of the NMDAR1 subunit, both drugs significantly decreased the abundance of NMDAR1 subunit mRNA containing a 63-base insert. Neither drug altered mRNA for the 2A subunit, but clozapine significantly increased hybridization of a probe for the 2B subunit. The data suggest that some neuroleptic effects may be mediated by glutamatergic systems and that typical and atypical antipsychotics can have varying effects on the density of glutamate in presynaptic terminals and on the expression of specific NMDA receptor splice variant mRNAs. Alternatively, NMDAR1 subunit splice variants may differentially respond to interactions with glutamate.