Recombinant Rodent Research Articles

A Novel Potentially Recombinant Rodent Coronavirus with a Polybasic Cleavage Site in the Spike Protein.

ABSTRACTThe emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has reignited global interest in animal coronaviruses and their potential for human transmission. While bats are thought to be the wildlife reservoir of SARS-CoV and SARS-CoV-2, the widespread human coronavirus OC43 is thought to have originated in rodents. Here, we sampled 297 rodents and shrews, representing eight species, from three municipalities of southern China. We report coronavirus prevalences of 23.3% and 0.7% in Guangzhou and Guilin, respectively, with samples from urban areas having significantly higher coronavirus prevalences than those from rural areas. We obtained three coronavirus genome sequences from Rattus norvegicus, including a Betacoronavirus (rat coronavirus [RCoV] GCCDC3), an Alphacoronavirus (RCoV-GCCDC5), and a novel Betacoronavirus (RCoV-GCCDC4). Recombination analysis suggests that there was a potential recombination event involving RCoV-GCCDC4, murine hepatitis virus (MHV), and Longquan Rl rat coronavirus (LRLV). Furthermore, we uncovered a polybasic cleavage site, RARR, in the spike (S) protein of RCoV-GCCDC4, which is dominant in RCoV. These findings provide further information on the potential for interspecies transmission of coronaviruses and demonstrate the value of a One Health approach to virus discovery.IMPORTANCE Surveillance of viruses among rodents in rural and urban areas of South China identified three rodent coronaviruses, RCoV-GCCDC3, RCoV-GCCDC4, and RCoV-GCCDC5, one of which was identified as a novel potentially recombinant coronavirus with a polybasic cleavage site in the spike (S) protein. Through reverse transcription-PCR (RT-PCR) screening of coronaviruses, we found that coronavirus prevalence in urban areas is much higher than that in rural areas. Subsequently, we obtained three coronavirus genome sequences by deep sequencing. After different method-based analyses, we found that RCoV-GCCDC4 was a novel potentially recombinant coronavirus with a polybasic cleavage site in the S protein, dominant in RCoV. This newly identified coronavirus RCoV-GCCDC4 with its potentially recombinant genome and polybasic cleavage site provides a new insight into the evolution of coronaviruses. Furthermore, our results provide further information on the potential for interspecies transmission of coronaviruses and demonstrate the necessity of a One Health approach for zoonotic disease surveillance.

Molecular mechanisms underlying pimaric acid-induced modulation of voltage-gated K+ channels

Voltage-gated K+ (KV) channels, which control firing and shape of action potentials in excitable cells, are supposed to be potential therapeutic targets in many types of diseases. Pimaric acid (PiMA) is a unique opener of large conductance Ca2+-activated K+ channel. Here, we report that PiMA modulates recombinant rodent KV channel activity. The enhancement was significant at low potentials (<0 mV) but not at more positive potentials. Application of PiMA significantly shifted the voltage-activation relationships (V1/2) of rodent KV1.1, 1.2, 1.3, 1.4, 1.6 and 2.1 channels (KV1.1–KV2.1) but KV4.3 to lower potentials and prolonged their half-decay times of the deactivation (T1/2D). The amino acid sequence which is responsible for the difference in response to PiMA was examined between KV1.1–KV2.1 and KV4.3 by site-directed mutagenesis of residues in S5 and S6 segments of Kv1.1. The point mutation of Phe332 into Tyr mimics the effects of PiMA on V1/2 and T1/2D and also abolished the further change by addition of PiMA. The results indicate that PiMA enhances voltage sensitivity of KV1.1–KV2.1 channels and suggest that the lipophilic residues including Phe332 in S5 of KV1.1–KV2.1 channels may be critical for the effects of PiMA, providing beneficial information for drug development of KV channel openers.

A highly infectious Plasmodium yoelii parasite, bearing Plasmodium falciparum circumsporozoite protein.

BackgroundPlasmodium circumsporozoite protein (CSP) is a major surface antigen present in the sporozoite (Spz) stage of a malaria parasite. RTS, S vaccine, the most clinically advanced malaria vaccine, consists of a large portion of Plasmodium falciparum CSP (PfCSP). A highly infectious, recombinant rodent malaria, Plasmodium yoelii parasite bearing a full-length PfCSP, PfCSP/Py Spz, was needed as a tool to evaluate the role of PfCSP in mediating, protective, anti-malaria immunity in a mouse model.MethodsA transgenic parasite, PfCSP/Py Spz, was generated by inserting a construct expressing the PfCSP at the locus of the P. yoelii CSP gene by double cross-over homologous recombination. Then the biological and protective properties of PfCSP/Py Spz were determined.ResultsThis PfCSP/Py parasite produced up to 30,000 Spz in mosquito salivary glands, which is equal or even higher than the number of Spz produced by wild-type P. yoelii parasites. Five bites of PfCSP/Py-infected mosquitoes could induce blood infection in BALB/c mice.ConclusionsThe current study has demonstrated a successful establishment of a transgenic P. yoelii parasite clone that is able to express a full-length PfCSP, PfCSP/Py parasite. Importantly, this PfCSP/Py parasite can be as infectious as the wild-type P. yoelii parasite both in mosquito vector and in mouse, a mammalian host. A new transgenic parasite that expresses a full-length PfCSP may become a useful tool for researchers to investigate immunity against PfCSP in a mouse model.

Agonist- and antagonist-induced up-regulation of surface 5-HT3 A receptors.

The 5-HT3 receptor is a member of the pentameric ligand-gated ion channel family and is pharmacologically targeted to treat irritable bowel syndrome and nausea/emesis. Furthermore, many antidepressants elevate extracellular concentrations of 5-HT. This study investigates the functional consequences of exposure of recombinant 5-HT3 A receptors to agonists and antagonists. We used HEK cells stably expressing recombinant 5-HT3 A receptors and the ND7/23 (mouse neuroblastoma/dorsal root ganglion hybrid) cell line, which expresses endogenous 5-HT3 receptors. Surface expression of recombinant 5-HT3 A receptors, modified to contain the bungarotoxin (BTX) binding sequence, was quantified using fluorescence microscopy to image BTX-conjugated fluorophores. Whole cell voltage-clamp electrophysiology was used to measure the density of current mediated by 5-HT3 A receptors. 5-HT3 A receptors were up-regulated by the prolonged presence of agonists (5-HT and m-chlorophenylbiguanide) and antagonists (MDL-72222 and morphine). The up-regulation of 5-HT3 A receptors by 5-HT and MDL-72222 was time- and concentration-dependent but was independent of newly translated receptors. The phenomenon was observed for recombinant rodent and human 5-HT3 A receptors and for endogenous 5-HT3 receptors in neuronal ND7/23 cells. Up-regulation of 5-HT3 A receptors, following exposure to either agonists or antagonists suggests that this phenomenon may occur in response to different therapeutic agents. Medications that elevate 5-HT levels, such as the antidepressant inhibitors of 5-HT reuptake and antiemetic inhibitors of 5-HT3 receptor function, may both raise receptor expression. However, this will require further investigation in vivo.

Activation of TRPA1 by Membrane Permeable Local Anesthetics

BackgroundLow concentrations of local anesthetics (LAs) suppress cellular excitability by inhibiting voltage-gated Na+ channels. In contrast, LAs at high concentrations can be excitatory and neurotoxic. We recently demonstrated that LA-evoked activation of sensory neurons is mediated by the capsaicin receptor TRPV1, and, to a lesser extent by the irritant receptor TRPA1. LA-induced activation and sensitization of TRPV1 involves a domain that is similar, but not identical to the vanilloid-binding domain. Additionally, activation of TRPV1 by LAs involves PLC and PI(4,5)P2-signalling. In the present study we aimed to characterize essential structural determinants for LA-evoked activation of TRPA1.ResultsRecombinant rodent and human TRPA1 were expressed in HEK293t cells and investigated by means of whole-cell patch clamp recordings. The LA lidocaine activates TRPA1 in a concentration-dependent manner. The membrane impermeable lidocaine-derivative QX-314 is inactive when applied extracellularly. Lidocaine-activated TRPA1-currents are blocked by the TRPA1-antagonist HC-030031. Lidocaine is also an inhibitor of TRPA1, an effect that is more obvious in rodent than in human TRPA1. This species-specific difference is linked to the pore region (transmembrane domain 5 and 6) as described for activation of TRPA1 by menthol. Unlike menthol-sensitivity however, lidocaine-sensitivity is not similarly determined by serine- and threonine-residues within TM5. Instead, intracellular cysteine residues known to be covalently bound by reactive TRPA1-agonists seem to mediate activation of TRPA1 by LAs.ConclusionsThe structural determinants involved in activation of TRPA1 by LAs are disparate from those involved in activation by menthol or those involved in activation of TRPV1 by LAs.

Novel adenovirus-based helper system to support production of recombinant parvovirus

Preclinical studies using various cell culture and animal systems highlight the potential of recombinant rodent parvoviruses (recPVs) for cancer therapy. Production of these viruses is, however, not efficient and this hampers the clinical applications of these agents. In this study, we show that the adenovirus genes E2a, E4(orf6) and VA RNA increase the production of recPVs by more than 10-fold and reduce the time of production from 3 to 2 days in HEK293T cells. The helper effects of these genes can be observed with different recPVs, regardless of the nature and size of the inserted transgene. Furthermore, we generated a recombinant Adenovirus 5 carrying the parvovirus VP transcription unit. This helper, named Ad-VP, allows recPVs to be efficiently produced through a protocol based only on cell infection, making possible to use cell lines, such as NB324K, which are good producers of parvoviruses but are hardly transfectable. Hence, we could further improve viral titers and reduce time and costs of production. This Ad-VP helper-based protocol could be scaled up to a bioreactor format for the generation of the large amounts of recPVs needed for future clinical applications.

Direct Selection of Monoclonal Phosphospecific Antibodies without Prior Phosphoamino Acid Mapping

In the current post-genomic era, large scale efforts are underway to functionally explore the proteome by assembling large antibody libraries. However, because many proteins are modified post-translationally to regulate their function, collections of modification-specific sensors are also needed. Here we applied a novel approach to select monoclonal phosphospecific antibodies directly from the full-length protein and without up-front phosphoamino acid identification. We chose as antigen GRASP65, a well studied Golgi phosphoprotein. Bacterially produced full-length protein was first incubated with mitotic cytosol, thus allowing modification by naturally occurring kinases, and then used directly for affinity-based antibody selection using a single chain variable fragment phagemid library. In less than 1 week, three distinct and highly functional monoclonal phosphospecific antibodies against two GRASP65 epitopes were obtained and subsequently characterized. The presented approach is carried out fully in vitro, requires no prior knowledge of the phosphoamino acid identity, and is fast and inexpensive. It therefore has great potential to be an attractive alternative to classic animal-based protocols for the selection of post-translation modification sensors and thus to become an invaluable tool in our quest to understand the proteome in all its complexity.

Targeting different isoforms of HMGB1 leads to different beneficial effects in preclinical models of sepsis and inflammatory arthritis (100.6)

Abstract HMGB1 is a multifunctional protein that exerts diverse proinflammatory effects when released into the extracellular milieu. Because several HMGB1 isoforms may be generated depending on the activation state of a cell, these isoforms may play distinct roles in different inflammatory disorders. To examine this, we generated a panel of fully human anti-HMGB1 monoclonal antibodies using a phage display approach. The two most potent mAbs, IA-4 and IA-6, displayed comparable binding affinity to HMGB1 (KD=30 and 39nM) and blockade of HMGB1/RAGE binding (IC50=0.9 and 1.2nM). However, only IA-4 but not IA-6 could detect HMGB1 actively secreted from LPS-treated cells. IA-4 and IA-6 were then tested in rodent models of inflammatory arthritis (rat AIA) and sepsis (mouse CLP). IA-4 reduced paw swelling in the rat AIA model (32% inhibition @ 10mg/kg, p&amp;lt;0.05 vs. isotype control, n=32) while IA-6 had little effect. In contrast, only IA-6 but not IA-4 prolonged survival in the mouse CLP model (@ 8mg/kg , p&amp;lt;0.05 vs. isotype control, n=72). IA-4 and IA-6 displayed similar pharmacokinetics and recognized recombinant rodent HMGB1 with equal affinity. In summary, these results suggest that different isoforms of HMGB1 may have distinct in vivo roles and that HMGB1 mAbs targeting these isoforms may provide tailored therapeutics.

Indiplon Is a High-Affinity Positive Allosteric Modulator with Selectivity for α1 Subunit-Containing GABAAReceptors

Indiplon (NBI 34060) is a novel pyrazolopyrimidine currently in development for the treatment of insomnia. We have previously shown that indiplon exhibits high-affinity binding to native GABA(A) receptors from rat brain and acts as a positive allosteric modulator of GABA(A) receptor currents in cultured rat neurons (Sullivan et al., 2004). In this study, we examined the GABA(A) receptor alpha subunit selectivity of indiplon using electrophysiological techniques to record GABA-activated chloride currents from recombinant rodent GABA(A) receptors expressed in human embryonic kidney 293 cells. Indiplon potentiated the GABA-activated chloride current in recombinant GABA(A) receptors in a dose-dependent and reversible manner and was approximately 10-fold selective for alpha1 subunit-containing receptors over GABA(A) receptors containing alpha2, alpha3, or alpha5 subunits. The EC(50) values were 2.6, 24, 60, and 77 nM for alpha1beta2gamma2, alpha2beta2gamma2, alpha3beta3gamma2, and alpha5beta2gamma2 receptors, respectively. Indiplon was approximately 10 times more potent than zolpidem and zopiclone and >100 times more potent than zaleplon. Moreover, indiplon, up to 1 microM, did not potentiate GABA(A) receptors composed of alpha4beta2gamma2 and alpha6beta2gamma2 subunits. This mechanism of action is proposed to underlie the sedative-hypnotic effects of indiplon in animals and humans.

Iodo-resiniferatoxin, a new potent vanilloid receptor antagonist.

The highly potent vanilloid receptor (VR) agonist resiniferatoxin has been radiolabeled with 125I, and the pharmacology to the cloned rodent VR, VR1, and the endogenous VR in rat spinal cord membranes has been characterized. [125I]RTX binding to human embryonic kidney 293 cells expressing VR1 was reversible and with high affinity (Kd = 4.3 nM) in an apparent monophasic manner. In rat spinal cord membranes, [125I]RTX bound with a similar high affinity (Kd = 4.2 nM) to a limited number of binding sites (Bmax = 51 +/- 8 fmol/mg of protein). The pharmacology of recombinant rodent VR1 and the endogenous rat VR1 was indistinguishable when measuring displacement of [125I]RTX binding (i.e., the following rank order of affinity was observed: RTX > I-RTX > olvanil > capsaicin > capsazepine). Capsaicin and RTX induced large nondesensitizing currents in Xenopus laevis oocytes expressing VR1 (EC50 values were 1300 nM and 0.2 nM, respectively), whereas I-RTX induced no current per se at concentrations up to 10 microM. However, I-RTX completely blocked capsaicin-induced currents (IC50 = 3.9 nM). In vivo, I-RTX effectively blocked the pain responses elicited by capsaicin (ED50 = 16 ng/mouse, intrathecally). The present study showed that I-RTX is at least 40-fold more potent than the previously known VR antagonist, capsazepine. Thus, I-RTX as well as its radiolabeled form, should be highly useful for further exploring the physiological roles of VRs in the brain and periphery.

Subunit-dependent inhibition of recombinant rodent N-methyl- d-aspartate receptors by a HIV-1 glycoprotein 120 derived peptide

Considerable evidence suggests that low (picomolar) concentrations of the HIV-1 envelope glycoprotein gp120 induce neuronal cell death by stimulating the release of microglial toxins, which in turn activate N-methyl- d-aspartate (NMDA) receptors. Conversely, high (micromolar) concentrations of gp120 have been reported to directly inhibit NMDA receptor-mediated currents and do not induce neurotoxicity. Here we show that micromolar concentrations of a synthetic peptide corresponding to the V3-loop of gp120 (V3-pep) inhibited agonist responses of recombinant heteromeric rodent NMDA receptors expressed in Xenopus laevis oocytes by decreasing their apparent glycine affinity. Different combinations of NMDA receptor subunits displayed differential sensitivities to inhibition by V3-pep, with a potency rank order of NR1/2B>NR1/2D>NR1/2C≥NR1/2A. Our observations may provide an explanation for the reduced neurotoxicity of high doses of gp120 in cell cultures and may be useful for the pharmacological discrimination of NMDA receptor subtypes.

Bacterial Expression and Purification of RecombinantPlasmodium yoeliiCircumsporozoite Protein

We report the expression and purification of recombinant rodent malarialPlasmodium yoeliicircumsporozoite surface protein (PyCSP) inEscherichia coli.To facilitate purification of the recombinant protein, the PyCSP was expressed as an amino-terminal fusion protein to glutathioneS-transferase and as a carboxy-terminal fusion protein to a hexahistidyl tag. The expression of the fusion protein was controlled by the inducibletacpromoter. Under optimal conditions the immunoreactive PyCSP represented approximately 0.04% of the total cell lysate. Western blot analysis probing with an anti-PyCSP antibody revealed a wide array of immunoreactive bands. Material isolated by affinity purification on glutathione–Sepharose 4B resin also contained multiple bands indicative of premature termination or carboxyl-terminal degradation. Analysis of protein retained on a nickel nitrilotriacetic acid resin revealed evidence of amino-terminal deleted material. Combining the two mild affinity purifications resulted in isolation of a single immunoreactive protein of approximate molecular weight of 96 kDa. We anticipate that the approach described in this study will facilitate the production of highly purified recombinant proteins.

Susceptibility of Rickettsia tsutsugamushi Gilliam to gamma interferon in cultured mouse cells

Recombinant rodent gamma interferon (IFN-gamma) inhibited the infection of cultured BALB/3T3 mouse fibroblasts by Rickettsia tsutsugamushi Gilliam, apparently mainly by clearance of intracellular rickettsiae. No significant effect on rickettsial entry into the cells was noted; IFN-gamma was toxic to infected cells, as measured by the capacity of treated, infected cells to attach to the surfaces of culture vessels. In a small proportion of IFN-gamma-treated cells, rickettsial replication appeared to persist at normal levels. A fraction (28%) of rickettsiae clonally isolated from cultures treated with IFN-gamma was resistant to IFN-gamma-mediated inhibition, but four serial passages of these resistant clones in the absence of additional IFN-gamma resulted in the loss of resistance. In several respects, therefore, the IFN-gamma-mediated inhibition of scrub typhus rickettsiae in cultured fibroblasts was similar to that reported for Rickettsia prowazekii.