FcγRIIB controls antibody-mediated target cell depletion by ITIM-independent mechanisms

Many therapeutic antibodies deplete target cells and elicit immunotherapy by engaging activating Fc gamma receptors (FcγRs) on host effector cells. These antibodies are negatively regulated by the inhibitory FcγRIIB (CD32B). Dogma suggests inhibition is mediated through the FcγRIIB immunoreceptor tyrosine-based inhibition motif (ITIM), negatively regulating immunoreceptor tyrosine-based activation motif (ITAM)-mediated signaling from activating FcγR. To assess this, we generated experimental models expressing human (h)FcγRIIB on targets or effectors, lacking or retaining ITIM signaling capacity. We demonstrate that signaling through the hFcγRIIB ITIM is dispensable for impairing monoclonal antibody (mAb)-mediated depletion of normal and malignant murine target cells through three therapeutically relevant surface receptors (CD20, CD25, and OX40) affecting immunotherapy. We demonstrate that hFcγRIIB competition with activating FcγRs for antibody Fc, rather than ITIM signaling, is sufficient to impair activating FcγR engagement, inhibiting effector function and immunotherapy.

Activation of GABA(A) receptors inhibits T cell proliferation

BACKGROUND

The major sites for fast synaptic inhibition in the central nervous system (CNS) are ion channels activated by γ-aminobutyric acid (GABA). These receptors are referred as GABA(A) receptors (GABA(A)R). Recent evidence indicates a role of GABA(A)R in modulating the immune response. This work aimed to discern the role of GABA and GABA(A)Rs in human and mouse T cell activity.

METHODS

Mouse splenocytes or human peripheral blood mononuclear cells (PBMCs) were activated with anti-CD3 antibodies and the proliferation of both CD8+ and CD4+ T cells assessed through flow cytometry. Subsequently, the effects on T cell proliferation of either GABA(A)R modulation by diazepam that is also capable of activating mitochondrial based translocator protein (TSPO), alprazolam and allopregnanolone or inhibition by bicucculine methiodide (BMI) and (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) were assessed.

RESULTS

Positive modulation of GABA(A)Rs either by benzodiazepines or the neurosteroid allopregnanolone inhibits both mouse and human T cell proliferation. GABAergic inhibition of T cell proliferation by benzodiazepines could be rescued by GABA(A)R blocking. Our data suggest that benzodiazepines influence T cell proliferation through both TSPO and GABA(A)Rs activation.

CONCLUSIONS

We conclude that activation of GABA(A)Rs provides immunosuppression by inhibiting T cell proliferation.

Tools for analysis and conditional deletion of subsets of sensory neurons

Background: Somatosensation depends on primary sensory neurons of the trigeminal and dorsal root ganglia (DRG). Transcriptional profiling of mouse DRG sensory neurons has defined at least 18 distinct neuronal cell types. Using an advillin promoter, we have generated a transgenic mouse line that only expresses diphtheria toxin A (DTA) in sensory neurons in the presence of Cre recombinase. This has allowed us to ablate specific neuronal subsets within the DRG using a range of established and novel Cre lines that encompass all sets of sensory neurons.    Methods: A floxed-tdTomato-stop-DTA bacterial artificial chromosome (BAC) transgenic reporter line (AdvDTA) under the control of the mouse advillin DRG promoter was generated. The line was first validated using a Na _v1.8 ^Cre and then crossed to CGRP ^CreER (Calca), Th ^CreERT2, Tmem45b ^Cre, Tmem233 ^Cre, Ntng1 ^Cre and TrkB ^CreER (Ntrk2) lines. Pain behavioural assays included Hargreaves', hot plate, Randall-Selitto, cold plantar, partial sciatic nerve ligation and formalin tests. Results: Motor activity, as assessed by the rotarod test, was normal for all lines tested. Noxious mechanosensation was significantly reduced when either Na _v1.8 positive neurons or Tmem45b positive neurons were ablated whilst acute heat pain was unaffected. In contrast, noxious mechanosensation was normal following ablation of CGRP-positive neurons but acute heat pain thresholds were significantly elevated and a reduction in nocifensive responses was observed in the second phase of the formalin test. Ablation of TrkB-positive neurons led to significant deficits in mechanical hypersensitivity in the partial sciatic nerve ligation neuropathic pain model. Conclusions: Ablation of specific DRG neuronal subsets using the AdvDTA line will be a useful resource for further functional characterization of somatosensory processing, neuro-immune interactions and chronic pain disorders.

A novel human pain insensitivity disorder caused by a point mutation in ZFHX2

Chronic pain is a major global public health issue causing a severe impact on both the quality of life for sufferers and the wider economy. Despite the significant clinical burden, little progress has been made in terms of therapeutic development. A unique approach to identifying new human-validated analgesic drug targets is to study rare families with inherited pain insensitivity. Here we have analysed an otherwise normal family where six affected individuals display a pain insensitive phenotype that is characterized by hyposensitivity to noxious heat and painless bone fractures. This autosomal dominant disorder is found in three generations and is not associated with a peripheral neuropathy. A novel point mutation in ZFHX2, encoding a putative transcription factor expressed in small diameter sensory neurons, was identified by whole exome sequencing that segregates with the pain insensitivity. The mutation is predicted to change an evolutionarily highly conserved arginine residue 1913 to a lysine within a homeodomain. Bacterial artificial chromosome (BAC) transgenic mice bearing the orthologous murine p.R1907K mutation, as well as Zfhx2 null mutant mice, have significant deficits in pain sensitivity. Gene expression analyses in dorsal root ganglia from mutant and wild-type mice show altered expression of genes implicated in peripheral pain mechanisms. The ZFHX2 variant and downstream regulated genes associated with a human pain-insensitive phenotype are therefore potential novel targets for the development of new analgesic drugs.awx326media15680039660001.

Endogenous opioids contribute to insensitivity to pain in humans and mice lacking sodium channel Nav1.7

Loss-of-function mutations in the SCN9A gene encoding voltage-gated sodium channel Nav1.7 cause congenital insensitivity to pain in humans and mice. Surprisingly, many potent selective antagonists of Nav1.7 are weak analgesics. We investigated whether Nav1.7, as well as contributing to electrical signalling, may have additional functions. Here we report that Nav1.7 deletion has profound effects on gene expression, leading to an upregulation of enkephalin precursor Penk mRNA and met-enkephalin protein in sensory neurons. In contrast, Nav1.8-null mutant sensory neurons show no upregulated Penk mRNA expression. Application of the opioid antagonist naloxone potentiates noxious peripheral input into the spinal cord and dramatically reduces analgesia in both female and male Nav1.7-null mutant mice, as well as in a human Nav1.7-null mutant. These data suggest that Nav1.7 channel blockers alone may not replicate the analgesic phenotype of null mutant humans and mice, but may be potentiated with exogenous opioids.

Pain without nociceptors? Nav1.7-independent pain mechanisms

Nav1.7, a peripheral neuron voltage-gated sodium channel, is essential for pain and olfaction in mice and humans. We examined the role of Nav1.7 as well as Nav1.3, Nav1.8, and Nav1.9 in different mouse models of chronic pain. Constriction-injury-dependent neuropathic pain is abolished when Nav1.7 is deleted in sensory neurons, unlike nerve-transection-related pain, which requires the deletion of Nav1.7 in sensory and sympathetic neurons for pain relief. Sympathetic sprouting that develops in parallel with nerve-transection pain depends on the presence of Nav1.7 in sympathetic neurons. Mechanical and cold allodynia required distinct sets of neurons and different repertoires of sodium channels depending on the nerve injury model. Surprisingly, pain induced by the chemotherapeutic agent oxaliplatin and cancer-induced bone pain do not require the presence of Nav1.7 sodium channels or Nav1.8-positive nociceptors. Thus, similar pain phenotypes arise through distinct cellular and molecular mechanisms. Therefore, rational analgesic drug therapy requires patient stratification in terms of mechanisms and not just phenotype.

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Phenotypically identical pain models have different underlying molecular mechanisms

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Nav1.7 expression is required for sympathetic sprouting after neuronal damage

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Oxaliplatin and cancer-induced bone pain are both Nav1.7-independent

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Deleting Nav1.7 in adult mice reverses nerve damage-induced neuropathic pain

Temporal control of gene deletion in sensory ganglia using a tamoxifen-inducible Advillin-Cre-ERT2 recombinase mouse

Background

Tissue-specific gene deletion has proved informative in the analysis of pain pathways. Advillin has been shown to be a pan-neuronal marker of spinal and cranial sensory ganglia. We generated BAC transgenic mice using the Advillin promoter to drive a tamoxifen-inducible CreERT2 recombinase construct in order to be able to delete genes in adult animals. We used a floxed stop ROSA26LacZ reporter mouse to examine functional Cre expression, and analysed the behaviour of mice expressing Cre recombinase.

Results

We used recombineering to introduce a CreERT2 cassette in place of exon 2 of the Advillin gene into a BAC clone (RPCI23-424F19) containing the 5' region of the Advillin gene. Transgenic mice were generated using pronuclear injection. The resulting AvCreERT2 transgenic mice showed a highly specific expression pattern of Cre activity after tamoxifen induction. Recombinase activity was confined to sensory neurons and no expression was found in other organs. Less than 1% of neurons showed Cre expression in the absence of tamoxifen treatment. Five-day intraperitoneal treatment with tamoxifen (2 mg per day) induced Cre recombination events in ≈90% of neurons in dorsal root and cranial ganglia. Cell counts of dorsal root ganglia (DRG) from transgenic animals with or without tamoxifen treatment showed no neuronal cell loss. Sensory neurons in culture showed ≈70% induction after 3 days treatment with tamoxifen. Behavioural tests showed no differences between wildtype, AvCreERT2 and tamoxifen-treated animals in terms of motor function, responses to light touch and noxious pressure, thermal thresholds as well as responses to inflammatory agents.

Conclusions

Our results suggest that the inducible pan-DRG AvCreERT2 deleter mouse strain is a useful tool for studying the role of individual genes in adult sensory neuron function. The pain phenotype of the Cre-induced animal is normal; therefore any alterations in pain processing can be unambiguously attributed to loss of the targeted gene.

Gephyrin regulates the cell surface dynamics of synaptic GABAA receptors

The efficacy of fast synaptic inhibition is critically dependent on the accumulation of GABAA receptors at inhibitory synapses, a process that remains poorly understood. Here, we examined the dynamics of cell surface GABAA receptors using receptor subunits modified with N-terminal extracellular ecliptic pHluorin reporters. In hippocampal neurons, GABAA receptors incorporating pHluorin-tagged subunits were found to be clustered at synaptic sites and also expressed as diffuse extrasynaptic staining. By combining FRAP (fluorescence recovery after photobleaching) measurements with live imaging of FM4-64-labeled active presynaptic terminals, it was evident that clustered synaptic receptors exhibit significantly lower rates of mobility at the cell surface compared with their extrasynaptic counterparts. To examine the basis of this confinement, we used RNAi to inhibit the expression of gephyrin, a protein shown to regulate the accumulation of GABAA receptors at synaptic sites. However, whether gephyrin acts to control the actual formation of receptor clusters, their stability, or is simply a global regulator of receptor cell surface number remains unknown. Inhibiting gephyrin expression did not modify the total number of GABAA receptors expressed on the neuronal cell surface but significantly decreased the number of receptor clusters. Live imaging revealed that clusters that formed in the absence of gephyrin were significantly more mobile compared with those in control neurons. Together, our results demonstrate that synaptic GABAA receptors have lower levels of lateral mobility compared with their extrasynaptic counterparts, and suggest a specific role for gephyrin in reducing the diffusion of GABAA receptors, facilitating their accumulation at inhibitory synapses.

Putative neuropeptides and an EF-hand motif region are encoded by a novel gene expressed in the four giant interneurons of the terrestrial snail

Nine giant interneurons located in the pleural and parietal ganglia of the terrestrial snail Helix lucorum L. were reported to be a key element in the network controlling withdrawal behaviour of the animal. Using a combination of complementary DNA subtraction cloning and differential screening approaches we have isolated a novel gene named HCS2 which is expressed predominantly in a subset of these interneurons. The predicted amino acid sequence of the HCS2 protein contains at the N-terminus a hydrophobic leader sequence and four putative neuropeptides, and at the C-terminus a perfect match to the consensus motif of the EF-hand family of the Ca2+-binding proteins. All four predicted neuropeptides bear a C-terminal signature sequence Tyr-Pro-Arg-X (where X is Ile, Leu, Val or Pro), and three of them are likely to be amidated. Physiological action of three synthetic peptides corresponding to the predicted mature HCS2 peptides mimics fairly well the described action of parietal interneurons on follower motoneurons controlling pneumostome closure. In situ hybridization experiments demonstrated that the HCS2 gene is selectively expressed in the four parietal giant interneurons, as well as in several small unidentified neurons. The onset of the HCS2 transcription during embryogenesis coincides temporally with the time-point when the first withdrawal responses of the embryo to tactile stimulation appear. We propose that the HCS2 gene encodes a hybrid precursor protein whose processed products act as neuromodulators or neurotransmitters mediating the withdrawal reactions of the snail, and in addition may participate in the calcium regulatory pathways or calcium homeostasis in command neurons.

Molecular cloning and characterization of rat P2Y4 nucleotide receptor

An intronless open reading frame encoding a protein (361aa in length) was isolated from a rat genomic library probed with a DNA fragment from rat heart. This protein showed 83% sequence identity with the human P2Y4 (hP2Y4) receptor and represents a homologue of the human pyrimidinoceptor. However, the rP2Y4 receptor is not selective for uridine nucleotides and, instead, shows an agonist potency order of ITP = ATP = ADP(pure) = UTP = ATPgammaS = 2-MeSATP = Ap4A > UDP(pure). ADP, ATPgammaS, 2-MeSATP and UDP are partial agonists. Thus, in terms of agonist profile, rP2Y4 is more like the P2U receptor subtype. The rP2Y4 receptor was reversibly antagonized by Reactive blue 2 but not by suramin which, otherwise, inhibits the hP2Y2 receptor (a known P2U receptor). Thus, rP2Y4 and the P2Y2 subtype appear to be structurally distinct forms of the P2U receptor (where ATP and UTP are equi-active) but can be distinguished as suramin-insensitive and suramin-sensitive P2U receptors, respectively.

Early expression of a novel nucleotide receptor in the neural plate of Xenopus embryos

Extracellular ATP functions as a neurotransmitter and neuromodulator in the adult nervous system, and a signaling molecule in non-neural tissue, acting either via ligand-gated ion channels (P2X) or G-protein-coupled receptors (P2Y). ATP can cause an increase in intracellular Ca2+ (Ca2+i) in embryonic cells and so regulate cell proliferation, migration, and differentiation. We have isolated a Xenopus cDNA encoding a novel P2Y receptor, XlP2Y, which is expressed abundantly in developing embryos. Recombinant XlP2Y responds equally to all five naturally occurring nucleoside triphosphates (ATP, UTP, CTP, GTP, and ITP), which elicit a biphasic Ca2+-dependent Cl- current (ICl,Ca) where the second phase persists for up to 60 min. XlP2Y also causes a continuous release of Ca2+i and a low level persistent activation of ICl,Ca in Xenopus oocytes through the spontaneous efflux of ATP. mRNAs for XlP2Y are expressed transiently in the neural plate and tailbud during Xenopus development, coincident with neurogenesis. This restricted pattern of expression and novel pharmacological features confer unique properties to XlP2Y, which may play a key role in the early development of neural tissue.

Novel gene HCS1 is specifically expressed in the giant interneurones of the terrestrial snail

The terrestrial snail Helix lucorum is a promising model for molecular neurobiology since its central nervous system (CNS) is simple and contains many morphologically and functionally identified large neurones. Among these, the giant interneurones located in pleural and parietal ganglia are especially interesting because they trigger the withdrawal behaviour of the snail and participate in aversive conditioning. Here we describe the identification and characterization of a gene named HCS1 which is preferentially expressed in these interneurones. It encodes a putative protein 100 amino acids long containing an N-terminal hydrophobic leader peptide. No sequences with significant homology to HCS1 were found in the protein (Swiss-Prot) and nucleotide (EMBLbank) data libraries. We suppose that the product of this gene is a secreted protein, presumably a neuropeptide or a growth factor.

Differential splicing creates a diversity of transcripts from a neurospecific developmentally regulated gene encoding a protein with new zinc-finger motifs

We have cloned a novel neurospecific gene, named neuro-d4, by differential screening a rat cerebral cortex cDNA library. Northern blot hybridization showed that neuro-d4 expression is restricted to neuronal tissues both in newborn and adult animals. The level of neuro-d4 mRNA in the rat central nervous system is high during the later stages of embryonic development and gradually decreases during the postnatal period. In situ hybridization suggests that the gene transcripts are localized in neuronal cell bodies. Nucleotide sequences of overlapped cDNA clones and all 12 exons in genomic clone were determined. The deduced protein has consensus sequences for a nuclear localization signal, a Krüppel-type zinc-finger and a new type of cysteine/histidine-rich motif resembling zinc-fingers. Several differential splicing variants were found, each of which influences the structure of the encoded protein.