R2 Subunit Research Articles

Reelin signaling modulates GABAB receptor function in the neocortex.

Reelin is a protein that is best known for its role in controlling neuronal layer formation in the developing cortex. Here, we studied its role for post-natal cortical network function, which is poorly explored. To preclude early cortical migration defects caused by Reelin deficiency, we used a conditional Reelin knock-out (RelncKO ) mouse, and induced Reelin deficiency post-natally. Induced Reelin deficiency caused hyperexcitability of the neocortical network in vitro and ex vivo. Blocking Reelin binding to its receptors ApoER2 and VLDLR resulted in a similar effect. Hyperexcitability in RelncKO organotypic slice cultures could be rescued by co-culture with wild-type organotypic slice cultures. Moreover, the GABAB receptor (GABAB R) agonist baclofen failed to activate and the antagonist CGP35348 failed to block GABAB Rs in RelncKO mice. Immunolabeling of RelncKO cortical slices revealed a reduction in GABAB R1 and GABAB R2 surface expression at the plasma membrane and western blot of RelncKO cortical tissue revealed decreased phosphorylation of the GABAB R2 subunit at serine 892 and increased phosphorylation at serine 783, reflecting receptor deactivation and proteolysis. These data show a role of Reelin in controlling early network activity, by modulating GABAB R function. Cover Image for this issue: https://doi.org/10.1111/jnc.15054.

Hipscs Derived Cardiomyocytes Overexpressing Deoxy ATP to Restore Cardiac Function

Reduced contractility, caused either by dysfunction or loss of cardiomyocytes, is the leading cause of systolic heart failure (HF). We have demonstrated that deoxy-ATP (dATP) improves systolic cardiac contractility by activating myosin without affecting the diastolic function, suggesting a promising candidate to mitigate cardiac dysfunction. Endogenously, Ribonucleotide Reductase (RNR), a rate-limiting enzyme for de novo synthesis of deoxynucleotides, produces dATP. The goal is to overexpress RNR in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to create cells with elevated dATP levels for use as a novel therapeutic strategy to improve contractility and regeneration in hearts following myocardial infarct. We used CRISPR-Cas9 gene editing to integrate an RNR expression cassette at the AAVS1 locus in hiPSCs WTC11 cell line (#GM25256, Coriell Institute). A double mutant form (RNR-DM) was generated by site-directed mutagenesis to limit proteolytic degradation of RNR in post-mitotic CMs. RNR subunits—R1 and R2-DM—intervened by a self-cleavage peptide P2A were expressed under a strong constitutively expressed CAG promoter. The integration of RNR cassette at the AAVS1 locus in hiRNR clones were confirmed by PCR genotyping, sequencing, transgene transcript, and protein expression. The stability and function of RNR-DM transgene were assessed in hiRNR-CMs, differentiated from the hiRNR clone. hiRNR-CMs expressed elevated levels of R1 and R2 subunits as compared to control WTC11-CMs (N=3, where N is an independent run of cardiac differentiation) by immunoblotting. This resulted in an elevation of dATP/ATP ratio (3.4±1.9 fold) (N=2) for hiRNR-CMs vs. WTC11-CMs, as detected by Mass Spectrometry. Cardiomyocyte shortening measurements by video-based IonOptix were increased (2.03±0.7 fold) in hiRNR CMs as compared to WTC11-CMs (N=2). Currently, we are characterizing the hiRNR-CMs, including DNA stability, apoptosis, cell division, calcium cycling, hypertrophy, and structural maturation for future studies of transplantation into models of HF.

Sociability development in mice with cell-specific deletion of the NMDA receptor NR1 subunit gene.

Social affiliative behavior is an important component of everyday life in many species and is likely to be disrupted in disabling ways in various neurodevelopmental and neuropsychiatric disorders. Therefore, determining the mechanisms involved in these processes is crucial. A link between N-methyl-d-aspartate (NMDA) receptor function and social behaviors has been clearly established. The cell types in which NMDA receptors are critical for social affiliative behavior, however, remain unclear. Here, we use mice carrying a conditional allele of the NMDA R1 subunit to address this question. Mice bearing a floxed NMDAR1 (NR1) allele were crossed with transgenic calcium/calmodulin-dependent kinase IIα (CaMKIIα)-Cre mice or parvalbumin (PV)-Cre mice targeting postnatal excitatory forebrain or PV-expressing interneurons, respectively, and assessed using the three-chambered Social Approach Test. We found that deletion of NR1 in PV-positive interneurons had no effect on social sniffing, but deletion of NR1 in glutamatergic pyramidal cells resulted in a significant increase in social approach behavior, regardless of age or sex. Therefore, forebrain excitatory neurons expressing NR1 play an important role in regulating social affiliative behavior.

The Absence of Tryptase Mcpt6 Causes Elevated Cellular Stress in Response to Modulation of the Histone Acetylation Status in Mast Cells.

Mast cells contain large amounts of proteases stored within their secretory granules. Previously we showed that one of these proteases, tryptase, in addition to its location within granules, can also be found within the mast cell nucleus, where it has the capacity to affect the acetylation profile of nucleosomal core histones in aging cells. Based on this notion, and on the known sensitivity of mast cells to modulation of histone acetylation, we here asked whether tryptase could impact on the responses against cellular stress caused by disturbed histone acetylation status. To address this, wild-type and tryptase-deficient (Mcpt6−/−) mast cells were subjected to cell stress caused by trichostatin A (TSA), a histone deacetylase inhibitor. Wild-type and Mcpt6−/− mast cells were equally sensitive to TSA at an early stage of culture (~8 weeks). However, in aging mast cells (>50 weeks), tryptase-deficiency led to increased sensitivity to cell death. To address the underlying mechanism, we assessed effects of tryptase deficiency on the expression of markers for proliferation and cell stress. These analyses revealed aberrant regulation of thioredoxin, thioredoxin reductase, glutaredoxin, and glutathione reductase, as well as blunted upregulation of ribonucleotide reductase subunit R2 in response to TSA in aging cells. Moreover, the absence of tryptase led to increased expression of Psme4/PA200, a proteasome variant involved in the processing of acetylated core histones. Altogether, this study identifies a novel role for tryptase in regulating the manifestations of cell stress in aging mast cells.

Redox-induced structural changes in the di-iron and di-manganese forms of Bacillus anthracis ribonucleotide reductase subunit NrdF suggest a mechanism for gating of radical access

Class Ib ribonucleotide reductases (RNR) utilize a di-nuclear manganese or iron cofactor for reduction of superoxide or molecular oxygen, respectively. This generates a stable tyrosyl radical (Y·) in the R2 subunit (NrdF), which is further used for ribonucleotide reduction in the R1 subunit of RNR. Here, we report high-resolution crystal structures of Bacillus anthracis NrdF in the metal-free form (1.51 Å) and in complex with manganese (MnII/MnII, 1.30 Å). We also report three structures of the protein in complex with iron, either prepared anaerobically (FeII/FeII form, 1.32 Å), or prepared aerobically in the photo-reduced FeII/FeII form (1.63 Å) and with the partially oxidized metallo-cofactor (1.46 Å). The structures reveal significant conformational dynamics, likely to be associated with the generation, stabilization, and transfer of the radical to the R1 subunit. Based on observed redox-dependent structural changes, we propose that the passage for the superoxide, linking the FMN cofactor of NrdI and the metal site in NrdF, is closed upon metal oxidation, blocking access to the metal and radical sites. In addition, we describe the structural mechanics likely to be involved in this process.

The combination of ascorbate and menadione causes cancer cell death by oxidative stress and replicative stress

The combination of ascorbate and menadione (VC:VK3 = 100:1) is an investigational treatment for cancer under clinical trials. Dehydroascorbic acid (DHA), the oxidized form of ascorbate, can be taken up by cells via glucose transporters, over-expressed in many cancer cells. It has been known that the combination of VC/VK3 kills cancer cells by inducing hydrogen peroxide (H2O2) via a redox cycling reaction. However, the mechanism has not been fully understood yet. Intracellularly, DHA is reduced to ascorbate by NADPH via GSH and glutaredoxin as well as by thioredoxin (Trx) and the selenoenzyme thioredoxin reductase (TrxR). These two systems are also critical as electron donors for ribonucleotide reductase (RNR), which produces deoxyribonucleotides de novo for DNA replication and DNA repair and is highly expressed in tumor cells. We found that RNR was highly sensitive to VC/VK3 in vitro with similar effects as observed with H2O2. In cancer cells, VC/VK3 inhibited RNR mainly by targeting its R2 subunit. More importantly, both the Trx and GSH systems were oxidized by the combination, which resulted in the loss of GSH, increased protein glutathionylation, and highly oxidized Trx1. The mechanism of cell death induced by VC/VK3 was also elucidated. We found that VC/VK3 inhibited glutathione peroxidase activity and led to an elevated level of lipid peroxidation, which triggered apoptosis-inducing factor (AIF) mediated cell death pathway. Therefore, the combination not only induced replicative stress by inhibiting RNR, but also oxidative stress by targeting anti-oxidant systems and triggered AIF-mediated cancer cell death.

Diversity of structure and function of GABAB receptors: a complexity of GABAB-mediated signaling.

γ-aminobutyric acid type B (GABAB) receptors are broadly expressed in the nervous system and play an important role in neuronal excitability. GABAB receptors are G protein-coupled receptors that mediate slow and prolonged inhibitory action, via activation of Gαi/o-type proteins. GABAB receptors mediate their inhibitory action through activating inwardly rectifying K+ channels, inactivating voltage-gated Ca2+ channels, and inhibiting adenylate cyclase. Functional GABAB receptors are obligate heterodimers formed by the co-assembly of R1 and R2 subunits. It is well established that GABAB receptors interact not only with G proteins and effectors but also with various proteins. This review summarizes the structure, subunit isoforms, and function of GABAB receptors, and discusses the complexity of GABAB receptors, including how receptors are localized in specific subcellular compartments, the mechanism regulating cell surface expression and mobility of the receptors, and the diversity of receptor signaling through receptor crosstalk and interacting proteins.

Structure, subunit organization and behavior of the asymmetric Type IIT restriction endonuclease BbvCI.

BbvCI, a Type IIT restriction endonuclease, recognizes and cleaves the seven base pair sequence 5′-CCTCAGC-3′, generating 3-base, 5′-overhangs. BbvCI is composed of two protein subunits, each containing one catalytic site. Either site can be inactivated by mutation resulting in enzyme variants that nick DNA in a strand-specific manner. Here we demonstrate that the holoenzyme is labile, with the R1 subunit dissociating at low pH. Crystallization of the R2 subunit under such conditions revealed an elongated dimer with the two catalytic sites located on opposite sides. Subsequent crystallization at physiological pH revealed a tetramer comprising two copies of each subunit, with a pair of deep clefts each containing two catalytic sites appropriately positioned and oriented for DNA cleavage. This domain organization was further validated with single-chain protein constructs in which the two enzyme subunits were tethered via peptide linkers of variable length. We were unable to crystallize a DNA-bound complex; however, structural similarity to previously crystallized restriction endonucleases facilitated creation of an energy-minimized model bound to DNA, and identification of candidate residues responsible for target recognition. Mutation of residues predicted to recognize the central C:G base pair resulted in an altered enzyme that recognizes and cleaves CCTNAGC (N = any base).

Genome-scale identification of cellular pathways required for cell surface recognition

Interactions mediated by cell surface receptors initiate important instructive signaling cues but can be difficult to detect in biochemical assays because they are often highly transient and membrane-embedded receptors are difficult to solubilize in their native conformation. Here, we address these biochemical challenges by using a genome-scale, cell-based genetic screening approach using CRISPR gene knockout technology to identify cellular pathways required for specific cell surface recognition events. By using high-affinity monoclonal antibodies and low-affinity ligands, we determined the necessary screening parameters, including the importance of establishing binding contributions from the glycocalyx, that permitted the unequivocal identification of genes encoding directly interacting membrane-embedded receptors with high statistical confidence. Importantly, we show that this genome-wide screening approach additionally identified receptor-specific pathways that are required for functional display of receptors on the cell surface that included chaperones, enzymes that add post-translational modifications, trafficking proteins, and transcription factors. Finally, we demonstrate the utility of the approach by identifying IGF2R (insulin like growth factor 2 receptor) as a binding partner for the R2 subunit of GABAB receptors. We show that this interaction is direct and is critically dependent on mannose-6-phosphate, providing a mechanism for the internalization and regulation of GABAB receptor signaling. We conclude that this single approach can reveal both the molecular nature and the genetic pathways required for functional cell surface display of receptors recognized by antibodies, secreted proteins, and membrane-embedded ligands without the need to make any prior assumptions regarding their biochemical properties.

Structure-Guided Synthesis and Mechanistic Studies Reveal Sweetspots on Naphthyl Salicyl Hydrazone Scaffold as Non-Nucleosidic Competitive, Reversible Inhibitors of Human Ribonucleotide Reductase.

Ribonucleotide reductase (RR), an established cancer target, is usually inhibited by antimetabolites, which display multiple cross-reactive effects. Recently, we discovered a naphthyl salicyl acyl hydrazone-based inhibitor (NSAH or E-3a) of human RR (hRR) binding at the catalytic site (C-site) and inhibiting hRR reversibly. We herein report the synthesis and biochemical characterization of 25 distinct analogs. We designed each analog through docking to the C-site of hRR based on our 2.7 Å X-ray crystal structure (PDB ID: 5TUS). Broad tolerance to minor structural variations preserving inhibitory potency is observed. E-3f (82% yield) displayed an in vitro IC50 of 5.3 ± 1.8 μM against hRR, making it the most potent in this series. Kinetic assays reveal that E-3a, E-3c, E-3t, and E-3w bind and inhibit hRR through a reversible and competitive mode. Target selectivity toward the R1 subunit of hRR is established, providing a novel way of inhibition of this crucial enzyme.

GABAA and GABAB receptor subunit localization on neurochemically identified neurons of the human subthalamic nucleus.

The subthalamic nucleus (STN) is a critical excitatory signaling center within the basal ganglia circuitry. The activity of subthalamic neurons is tightly controlled by upstream inhibitory signaling centers in the basal ganglia. In this study, we used immunohistochemical techniques to firstly, visualize and quantify the STN neurochemical organization based on neuronal markers including parvalbumin (PV), calretinin (CR), SMI-32, and GAD65/67 . Secondly, we characterized the detailed regional, cellular and subcellular expression of GABAA (α1 , α2 , α3 , β2/3 , and γ2 ) and GABAB (R1 and R2) receptor subunits within the normal human STN. Overall, we found seven neurochemically distinct populations of principal neurons in the human STN. The three main populations detected were: (a) triple-labeled PV+ /CR+ /SMI32+ ; (b) double-labeled PV+ /CR+ ; and (c) single-labeled CR+ neurons. Subthalamic principal neurons were found to express GABAA receptor subunits α1 , α3 , β2/3 , γ2 , and GABAB receptor subunits R1 and R2. However, no expression of GABAA receptor α2 subunit was detected. We also found a trend of increasing regional staining intensity for all positive GABAA receptor subunits from the dorsolateral pole to ventromedial extremities. The GAD+ interneurons showed relatively low expression of GABAA receptor subunits. These results provide the morphological basis of GABAergic transmission within the normal human subthalamic nucleus and evidence of GABA innervation through both GABAA and GABAB receptors on subthalamic principal neurons.

Protein Kinase A Distribution Differentiates Human Glioblastoma from Brain Tissue.

Brain tumor glioblastoma has no clear molecular signature and there is no effective therapy. In rodents, the intracellular distribution of the cyclic AMP (cAMP)-dependent protein kinase (Protein kinase A, PKA) R2Alpha subunit was previously shown to differentiate tumor cells from healthy brain cells. Now, we aim to validate this observation in human tumors. The distribution of regulatory (R1 and R2) and catalytic subunits of PKA was examined via immunohistochemistry and Western blot in primary cell cultures and biopsies from 11 glioblastoma patients. Data were compared with information obtained from 17 other different tumor samples. The R1 subunit was clearly detectable only in some samples. The catalytic subunit was variably distributed in the different tumors. Similar to rodent tumors, all human glioblastoma specimens showed perinuclear R2 distribution in the Golgi area, while it was undetectable outside the tumor. To test the effect of targeting PKA as a therapeutic strategy, the intracellular cyclic AMP concentration was modulated with different agents in four human glioblastoma cell lines. A significant increase in cell death was detected after increasing cAMP levels or modulating PKA activity. These data raise the possibility of targeting the PKA intracellular pathway for the development of diagnostic and/or therapeutic tools for human glioblastoma.

Nuclear inelastic scattering at the diiron center of ribonucleotide reductase from Escherichia coli

The enzyme ribonucleotide reductase R2 catalyzes an important step in the synthesis of the building blocks of DNA, and harbors a dinuclear iron center required for activity. Not only the iron valence states but also the protonation of the iron ligands govern the enzymatic activity of the enzyme. We have performed Nuclear Inelastic Scattering (NIS) experiments on the 57Fe reconstituted ribonucleotide reductase R2 subunit from Escherichia coli (Ec R2a). Accompanying Mossbauer spectroscopic investigations show that the partial density of vibrational states (pDOS) of the 57Fe reconstituted Ec R2a sample contained contributions from both 57Fe-Ec R2a protein as well as unspecifically bound 57Fe. Subtraction of a featureless pDOS as obtained from protein-coated iron oxide particles allowed modeling of the contribution of non-specifically bound iron and thus the pDOS of 57Fe-Ec R2a could be obtained. Quantum-mechanics/molecular-mechanics (QM/MM) calculations of the whole 57Fe-Ec R2a protein with variations of the cofactor protonation were performed in order to assign characteristic bands to their corresponding molecular vibrational modes.

Thiosemicarbazone derivatives, thiazolyl hydrazones, effectively inhibit leukemic tumor cell growth: Down-regulation of ribonucleotide reductase activity and synergism with arabinofuranosylcytosine

Cellular growth inhibition exerted by thiosemicarbazones is mainly attributed to down-regulation of ribonucleotide reductase (RNR) activity, with RNR being responsible for the rate-limiting step of de novo DNA synthesis. In this study, we investigated the antineoplastic effects of three newly synthesized thiosemicarbazone derivatives, thiazolyl hydrazones, in human HL-60 promyelocytic leukemia cells.The cytotoxicity of compounds alone and in combination with arabinofuranosylcytosine (AraC) was determined by growth inhibition assays. Effects on deoxyribonucleoside triphosphate (dNTP) concentrations were quantified by HPLC, and the incorporation of radio-labeled 14C-cytidine into nascent DNA was measured using a beta counter. Cell cycle distribution was analyzed by FACS, and protein levels of RNR subunits and checkpoint kinases were evaluated by Western blotting.VG12, VG19, and VG22 dose-dependently decreased intracellular dNTP concentrations, impaired cell cycle progression and, consequently, inhibited the growth of HL-60 cells. VG19 also lowered the protein levels of RNR subunits R1 and R2 and significantly diminished the incorporation of radio-labeled 14C-cytidine, being equivalent to an inhibition of DNA synthesis. Combination of thiazolyl hydrazones with AraC synergistically potentiated the antiproliferative effects seen with each drug alone and might therefore improve conventional chemotherapeutic regimens for the treatment of human malignancies such as acute promyelocytic or chronic myelogenous leukemia.

Toxoplasma gondii: Manipulation of host cell machinery in the journey from intestine to brain

QuestionFrom previous work, this group had discovered that infection of dendritic cells (DC) caused by the intracellular parasite (Toxoplasma gondii) induced a hyper-migratory state in DC which was a possible mechanism of the protozoan dissemination. For this study, their question was whether ϒ-aminobutyric acid (GABA) signaling was the possible mechanism underlying the control to the migratory properties of the infected DC. MethodsTo affirm the hypothesis, a series of complimentary experiments were conducted using both animal and human DC, also in vitro and in vivo. Main resultsThe main results of the experiments were as follows:First, murine and human DC produced GABA upon T. gondii infection. By quantitatively measuring GABA in the supernatant by enzyme-linked immunosorbent assay (ELISA), they found that live Toxoplasma infection of mouse DC, from the three predominant genotypes, increased GABA and the secretion occurred rapidly following infection. In addition, the fluorescence-activated cell sorting (FACS) of infected DC populations demonstrated that GABA production happened mainly in green fluorescent protein (GFP)+DC.Second, functional GABAA receptors were expressed in mouse and human DC. The GABAA receptors of a3, ß3, and r1 subunit expression was determined with quantitative reverse transcription polymerase reaction (RT-qPCR). Subsequent immune-cytochemical stainings indicated expression of the ß3 subunit in both infected and non infected DC. These receptors were proved to be functional in the electrophysiology tests as membrane currents were induced in T. gondii-infected DC.Third, transmigration of infected DC in vitro was reduced by targeting GABA synthesis and transport. Addition of inhibitors of GABA system such as glutamic acid decarboxylase (GAD) inhibitor (SC) and gamma-aminobutyric acid transporter 4 (GAT4) inhibitor (SNAP) to the infected DC had significantly decreased the secretion of GABA and also the transmigration of infected DC.Fourth, the motility and chemotaxis of infected DC in vitro was modulated by GABAergic signaling in vitro. In a chemotaxis chamber system which consisted of chemokine CCL19 concentration gradient, Toxoplasma-infected DC demonstrated an increased random directional motility and velocity even in absence of chemokine compared to non-infected DC.Finally, up-regulation of CCR7 in human and mouse DC were observed upon T. gondii infection in vitro. Furthermore, the dissemination of T. gondii in vivo was reduced by GABAergic inhibition in adoptively transferred infected DC as shown in the bioluminescence imaging (BLI) studies. Photonic emissions were also observed ex vivo in different organs, and the authors noted significant differences in the emissions on days 1–2 in the brain parenchyma. ConclusionThe authors concluded that GABAergic signaling modulated the transmigration of DC and that the intracellular pathogen Toxoplasma gondii seizes the GABAergic signaling of DC like a trojan horse mechanism to assure dissemination.

Deficits in the activity of presynaptic γ-aminobutyric acid type B receptors contribute to altered neuronal excitability in fragile X syndrome

The behavioral and anatomical deficits seen in fragile X syndrome (FXS) are widely believed to result from imbalances in the relative strengths of excitatory and inhibitory neurotransmission. Although modified neuronal excitability is thought to be of significance, the contribution that alterations in GABAergic inhibition play in the pathophysiology of FXS are ill defined. Slow sustained neuronal inhibition is mediated by γ-aminobutyric acid type B (GABAB) receptors, which are heterodimeric G-protein-coupled receptors constructed from R1a and R2 or R1b and R2 subunits. Via the activation of Gi/o, they limit cAMP accumulation, diminish neurotransmitter release, and induce neuronal hyperpolarization. Here we reveal that selective deficits in R1a subunit expression are seen in Fmr1 knock-out mice (KO) mice, a widely used animal model of FXS, but the levels of the respective mRNAs were unaffected. Similar trends of R1a expression were seen in a subset of FXS patients. GABAB receptors (GABABRs) exert powerful pre- and postsynaptic inhibitory effects on neurotransmission. R1a-containing GABABRs are believed to mediate presynaptic inhibition in principal neurons. In accordance with this result, deficits in the ability of GABABRs to suppress glutamate release were seen in Fmr1-KO mice. In contrast, the ability of GABABRs to suppress GABA release and induce postsynaptic hyperpolarization was unaffected. Significantly, this deficit contributes to the pathophysiology of FXS as the GABABR agonist (R)-baclofen rescued the imbalances between excitatory and inhibitory neurotransmission evident in Fmr1-KO mice. Collectively, our results provided evidence that selective deficits in the activity of presynaptic GABABRs contribute to the pathophysiology of FXS.

Investigating Metallocofactor Assembly and Enzymatic Capability in the Novel Mn/Fe Lipid‐Binding Oxidases

Recently, the discovery of a novel Mn/Fe protein in a number of pathogens and extremophiles has led to the establishment of a new group of proteins, dubbed R2lox (R2‐like ligand‐binding oxidase). Originally flagged for being highly upregulated in the virulent strain of Mycobacterium tuberculosis, R2lox was initially identified as a sequence homolog for the R2 subunit in class 1 ribonucleotide reductase (RNR); however, a lack of RNR activity combined with x‐ray crystallography data indicate significant differences between R2lox and the typical RNRs. Despite conventional inorganic wisdom and the presence of identical ligands, R2lox has been shown in vitro to bind MnII in the presence of FeII and spontaneously self‐assembles with a site‐differentiated Mn/Fe cofactor. In the absence of MnII, a canonical Fe/Fe cofactor assembles. More interestingly, upon O2 exposure, both cofactors oxidize a nearby valine residue, forming an unprecedented tyrosine‐valine crosslink via C‐H bond activation. However, work in our lab has indicated the mechanisms by which these two cofactors perform this chemistry is thoroughly distinct. It is our goal to utilize the R2lox system as a model to further explore factors governing metallocofactor formation, as well as investigate the potential of these cofactors to perform challenging substrate oxidation reactions using divergent pathways. Utilizing aerobic UV/vis, stopped‐flow, and EPR spectroscopies, the kinetics of metal binding, cofactor assembly, and characterization of discrete intermediates were studied in both Mn/Fe and Fe/Fe R2lox. Through this work, a number of distinctions between the mechanisms for Mn/Fe and Fe/Fe cofactor maturation were identified, and models for the assembly processes have been developed. The implications of these findings are further discussed in the context of potential relevance of R2lox towards therapeutic development and biocatalysis.Support or Funding InformationThe Ohio State University, Pelotonia Fellowship Program, and NIH Cellular, Molecular, and Biochemical Sciences Training Grant

Long-term HIV-1 infection induces an antiviral state in primary macrophages

HIV-1 infection is thought to impair type I interferon (IFN-I) production in macrophages, a cell type that is also relatively resistant to HIV-1 cytotoxic effects. Here, we show that monocyte differentiation into macrophages by M-CSF led to cell proliferation and susceptibility to HIV-1 infection that induced cell cycle arrest and increased cell death. Established HIV-1 infection of monocyte-derived macrophages induced the upregulation of the pattern recognition receptors MDA5 and Rig-I that serve as virus sensors; production of interferon-β, and transcription of interferon-stimulated genes including CXCL10. Infected macrophages showed increased expression of p21 and subsequent inactivation of cyclin-CDK2 activity leading to a hypo-phosphorylated active retinoblastoma protein (pRb) and deactivation of E2F1-dependent transcription and CDK1 downregulation. Additionally, HIV-1 infection limited deoxynucleotide pool by downregulation of the ribonucleotide reductase subunit R2 (RNR2) and reactivation of the HIV-1 restriction factor SAMHD1 together with increased cell death. In conclusion, HIV-1 induced an innate antiviral mechanism associated to IFN-I production, interferon stimulated gene activation, and p21-mediated G2/M arrest leading to elevated levels of cell death in monocyte derived macrophages. Upregulation of MDA5 and Rig-I may serve as targets for the development of antiviral strategies leading to the elimination of HIV-1 infected cells.

Activation of GABAA receptors controls mesiotemporal lobe epilepsy despite changes in chloride transporters expression: In vivo and in silico approach

Mesiotemporal lobe Epilepsy (MTLE), the most frequent form of focal epilepsy, is often drug-resistant. Enriching the epileptic focus with GABA-releasing engineered cells has been proposed as a strategy to prevent seizures. However, ex vivo data from animal models and MTLE patients suggest that, due to changes in chloride homeostasis, GABAA receptor activation is depolarizing and partly responsible for focal interictal discharges and seizure initiation. To understand how these two contradictory aspects of GABAergic neurotransmission coexist in MTLE, we used an established mouse model of MTLE presenting hippocampal sclerosis and recurrent hippocampal paroxysmal discharges (HPDs) 30–40days after a unilateral injection of kainate in the dorsal hippocampus. We first showed that injections of GABAA receptor agonists either systemically or directly into hippocampus suppressed HPDs. Western-blotting and immunostaining revealed that levels of α1, α3 and γ2 GABAA receptor subunits were increased in epileptic mice, compared to saline controls, while levels of R1 and R2 GABAB receptor subunits but also NR1, NR2A and NR2B NMDA receptor subunits and GluR1 and GluR2 AMPA receptor subunits were decreased. In addition, we showed that the expression of the transporter NKCC1, which load neurons with chloride, was increased, whereas KCC2, a chloride extruder, was decreased and that HPDs were suppressed by injection of blockers of NKCC1. These different changes were integrated in a numerical model, and in silico simulations supported the notion that chloride imbalance impair local inhibitory control of pyramidal neurons' activity in this model of MTLE. However, our numerical model also suggested that lasting activation of these receptors restore physiological intracellular chloride concentrations and suppress HPDs. Overall, our study suggests that activation of GABAA receptor remains an effective antiepileptic strategy to suppress focal seizures in MTLE, and demonstrates that modeling and simulation studies provide new insights about the cellular and synaptic mechanisms of this disease.

Transcriptional Activity of Gene Encoding Subunits R1 and R2 of Interferon Gamma Receptor in Peripheral Blood Mononuclear Cells in Patients with Slow Coronary Flow.

SummaryBackgroundSlow coronary flow (SCF) is a coronary artery disorder characterized with delayed opacification of epicardial coronary arteries without obstructive coronary disease. The pathophysiological mechanisms of SCF remain unclear. One of the possible mechanisms that may participate in the pathology of SCF is endothelial dysfunction related to the inflammatory process. Interferon gamma (IFN-γ) is an inflammatory cytokine that acts through its specific receptor composed of two subunits, IFN-γR1 and IFN-γR2. Transcriptional activity of the gene encoding these subunits influences IFN-γ activity. This study aimed to investigate the gene expression of IFN-γ receptor subunits in peripheral blood mononuclear cells (PBMC) from patients with SCF.MethodsThe study was performed with 30 patients (22 male/8 female) aged 35–76 (52.8±11.7 years) with SCF and 15 sex- (11 male/4 female), Body Max Index (BMI)- and age-matched (54.73±9.42 years) healthy subjects. Total mRNA was extracted from PBMC and was determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). The relative expression values (2-ΔΔCt) between control and case groups were determined and the Mann-Whitney U test was used for statistical analysis.ResultsThere was a significant increase in the gene expression of IFN-γR1 in PBMC from SCF patients vs. controls (P< 0.0001); but the differences in IFN-γR2 gene expression were statistically insignificant between patient and control groups (P= 0.853).ConclusionsIt can be concluded that IFN-γ gene expression may influence the function of microvasculature and thereby contribute to the pathophysiology of SCF.