Antiribosomal-P autoantibodies from psychiatric lupus target a novel neuronal surface protein causing calcium influx and apoptosis.
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ABSTRACT:
SUBMITTER: Matus S
PROVIDER: S-EPMC2150977 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The mitochondrion supplies energy to the cell and regulates apoptosis. Unlike other mammalian organelles, mitochondria are formed by binary fission and cannot be directly produced by the cell. They contain numerous copies of a compact circular genome that encodes RNA molecules and proteins involved in mitochondrial oxidative phosphorylation. Whereas, mitochondrial DNA (mtDNA) activates the innate immune system if present in the cytosol or the extracellular milieu, it is also the target of circulating autoantibodies in systemic lupus erythematosus (SLE). However, it is not known whether mitochondrial RNA is also recognized by autoantibodies in SLE. In the present study, we evaluated the presence of autoantibodies targeting mitochondrial RNA (AmtRNA) in SLE. We quantified AmtRNA in an inducible model of murine SLE. The AmtRNA were also determined in SLE patients and healthy volunteers. AmtRNA titers were measured in both our induced model of murine SLE and in human SLE, and biostatistical analyses were performed to determine whether the presence and/or levels of AmtRNA were associated with clinical features expressed by SLE patients. Both IgG and IgM classes of AmtRNA were increased in SLE patients (n = 86) compared to healthy controls (n = 30) (p < 0.0001 and p = 0.0493, respectively). AmtRNA IgG levels correlated with anti-mtDNA-IgG titers (r s = 0.54, p < 0.0001) as well as with both IgG and IgM against β-2-glycoprotein I (anti-β2GPI; r s = 0.22, p = 0.05), and AmtRNA-IgG antibodies were present at higher levels when patients were positive for autoantibodies to double-stranded-genomic DNA (p < 0.0001). AmtRNA-IgG were able to specifically discriminate SLE patients from healthy controls, and were negatively associated with plaque formation (p = 0.04) and lupus nephritis (p = 0.03). Conversely, AmtRNA-IgM titers correlated with those of anti-β2GPI-IgM (r s = 0.48, p < 0.0001). AmtRNA-IgM were higher when patients were positive for anticardiolipin antibodies (aCL-IgG: p = 0.01; aCL-IgM: p = 0.002), but AmtRNA-IgM were not associated with any of the clinical manifestations assessed. These findings identify mtRNA as a novel mitochondrial antigen target in SLE, and support the concept that mitochondria may provide an important source of circulating autoantigens in SLE.
| S-EPMC6524553 | biostudies-literature
Project description: Not available
| S-EPMC6611989 | biostudies-literature
Project description:IMPORTANCE:High titers of autoantibodies to glutamic acid decarboxylase (GAD) are well documented in association with stiff person syndrome (SPS). Glutamic acid decarboxylase is the rate-limiting enzyme in the synthesis of ?-aminobutyric acid (GABA), and impaired function of GABAergic neurons has been implicated in the pathogenesis of SPS. Autoantibodies to GAD might be the causative agent or a disease marker. OBJECTIVE:To investigate the characteristics and potential pathogenicity of GAD autoantibodies in patients with SPS and related disorders. DESIGN:Retrospective cohort study and laboratory investigation. SETTING:Weatherall Institute of Molecular Medicine, University of Oxford. PARTICIPANTS:Twenty-five patients with SPS and related conditions identified from the Neuroimmunology Service. EXPOSURES:Neurological examination, serological characterization and experimental studies. MAIN OUTCOMES AND MEASURES:Characterization of serum GAD antibodies from patients with SPS and evidence for potential pathogenicity. RESULTS:We detected GAD autoantibodies at a very high titer (median, 7500 U/mL) in 19 patients (76%), including all 12 patients with classic SPS. The GAD autoantibodies were high affinity (antibody dissociation constant, 0.06-0.78 nmol) and predominantly IgG1 subclass. The patients’ autoantibodies co-localized with GAD on immunohistochemistry and in permeabilized cultured cerebellar GABAergic neurons, as expected, but they also bound to the cell surface of unpermeabilized GABAergic neurons. Adsorption of the highest titer (700 000 U/mL) serum with recombinant GAD indicated that these neuronal surface antibodies were not directed against GAD itself. Although intraperitoneal injection of IgG purified from the 2 available GAD autoantibody–ositive purified IgG preparations did not produce clinical or pathological evidence of disease, SPS and control IgG were detected in specific regions of the mouse central nervous system, particularly around the lateral and fourth ventricles. CONCLUSIONS AND RELEVANCE:Autoantibodies to GAD are associated with antibodies that bind to the surface of GABAergic neurons and that could be pathogenic. Moreover, in mice, human IgG from the periphery gained access to relevant areas in the hippocampus and brainstem. Identification of the target of the non-GAD antibodies and peripheral and intrathecal transfer protocols, combined with adsorption studies, should be used to demonstrate the role of the non-GAD IgG in SPS.
| S-EPMC6055982 | biostudies-literature
Project description:Neuronal surface autoantibodies (NSAbs) against various antigens cause autoimmune encephalitis. Some of these antigens are also involved in the pathology of depression and anxiety. To study whether NSAbs are more common in plasma of individuals with depression and anxiety than in controls, and to investigate if NSAbs correlate with disease status, plasma samples of 819 individuals with a current diagnosis of depression and/or anxiety, 920 in remission and 492 individuals without these disorders were included in this study. Samples were tested by a combination of immunohistochemistry (IHC), staining on live rat hippocampus neurons and cell-based assay (CBA). By IHC, 50 (2.2%) samples showed immunoreactivity to rat brain tissue, with no significant differences between the aforementioned groups (22/819 vs 18/920 vs 11/492, P > 0.99). In addition, eight IHC positive samples were positive for NSAbs on live neurons (7/819 vs 0/920 vs 1/492, P = 0.006). The IHC-staining patterns of these eight samples were atypical for autoimmune encephalitis and accordingly, they tested negative for known NSAbs by CBA. No obvious difference in the clinical characteristics between individuals with or without NSAbs was observed. In conclusion, novel NSAbs were rare but predominately found in patients with current anxiety or depression indicating they might affect mental health in a small group of patients.
| S-EPMC7683539 | biostudies-literature
Project description:The hyperpolarization-activated cation channels (I(h)) play a distinct role in rhythmic activities in a variety of tissues, including neurons and cardiac cells. In the present study, we investigated whether Ca(2+) can permeate through the hyperpolarization-activated pacemaker channels (HCN) expressed in HEK293 cells and I(h) channels in dorsal root ganglion (DRG) neurons. Using combined measurements of whole-cell currents and fura-2 Ca(2+) imaging, we found that there is a Ca(2+) influx in proportion to I(h) induced by hyperpolarization in HEK293 cells. The I(h) channel blockers Cs(+) and ZD7288 inhibit both HCN current and Ca(2+) influx. Measurements of the fractional Ca(2+) current showed that it constitutes 0.60 +/- 0.02% of the net inward current through HCN4 at -120 mV. This fractional current is similar to that of the low Ca(2+)-permeable AMPA-R (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) channels in Purkinje neurons. In DRG neurons, activation of I(h) for 30 s also resulted in a Ca(2+) influx and an elevated action potential-induced secretion, as assayed by the increase in membrane capacitance. These results suggest a functional significance for I(h) channels in modulating neuronal secretion by permitting Ca(2+) influx at negative membrane potentials.
| S-EPMC327149 | biostudies-literature
Project description:Local delivery of amyloid beta oligomers from the tip of a nanopipette, controlled over the cell surface, has been used to deliver physiological picomolar oligomer concentrations to primary astrocytes or neurons. Calcium influx was observed when as few as 2000 oligomers were delivered to the cell surface. When the dosing of oligomers was stopped the intracellular calcium returned to basal levels or below. Calcium influx was prevented by the presence in the pipette of the extracellular chaperone clusterin, which is known to selectively bind oligomers, and by the presence a specific nanobody to amyloid beta. These data are consistent with individual oligomers larger than trimers inducing calcium entry as they cross the cell membrane, a result supported by imaging experiments in bilayers, and suggest that the initial molecular event that leads to neuronal damage does not involve any cellular receptors, in contrast to work performed at much higher oligomer concentrations.
| S-EPMC4995397 | biostudies-literature
Project description:Lymphocytes mediate cytotoxicity by polarized release of the contents of cytotoxic granules toward their target cells. Here, we have studied the role of the calcium release-activated calcium channel ORAI1 in human lymphocyte cytotoxicity. Natural killer (NK) cells obtained from an ORAI1-deficient patient displayed defective store-operated Ca(2+) entry (SOCE) and severely defective cytotoxic granule exocytosis leading to impaired target cell lysis. Similar findings were obtained using NK cells from a stromal interaction molecule 1-deficient patient. The defect occurred at a late stage of the signaling process, because activation of leukocyte functional antigen (LFA)-1 and cytotoxic granule polarization were not impaired. Moreover, pharmacological inhibition of SOCE interfered with degranulation and target cell lysis by freshly isolated NK cells and CD8(+) effector T cells from healthy donors. In addition to effects on lymphocyte cytotoxicity, synthesis of the chemokine macrophage inflammatory protein-1? and the cytokines TNF-? and IFN-? on target cell recognition was impaired in ORAI1-deficient NK cells, as previously described for T cells. By contrast, NK cell cytokine production induced by combinations of IL-12, IL-15, and IL-18 was not impaired by ORAI1 deficiency. Taken together, these results identify a critical role for ORAI1-mediated Ca(2+) influx in granule exocytosis for lymphocyte cytotoxicity as well as for cytokine production induced by target cell recognition.
| S-EPMC3044412 | biostudies-literature
Project description:ObjectiveSystemic lupus erythematosus (SLE) T cells display a hyperactive calcineurin/NF-AT pathway. The aim of this study was to determine whether this pathway is responsible for the aberrant SLE T cell function and to test the effectiveness of the recently recognized calcineurin inhibitor dipyridamole in limiting SLE-related pathology.MethodsT cells and mononuclear cells were isolated from the peripheral blood of SLE patients and healthy individuals. Murine cells were isolated from the spleens and lymph nodes of lupus-prone MRL/lpr mice and control MRL/MpJ mice. Cells were treated in vitro with tacrolimus, dipyridamole, or control. MRL/lpr mice were injected intraperitoneally with 50 mg/kg of dipyridamole 3 times a week for 3 weeks.ResultsMRL/lpr T cells, especially CD3+CD4-CD8- cells, displayed a robust calcium influx upon activation and increased levels of NF-ATc1. MRL/lpr T cells (both CD4+ and CD3+CD4-CD8- cells) provided help to B cells to produce immunoglobulin in a calcineurin-dependent manner. Dipyridamole treatment of SLE T cells significantly inhibited CD154 expression, interferon-γ, interleukin-17 (IL-17), and IL-6 production, and T cell-dependent B cell immunoglobulin secretion. Treatment of MRL/lpr mice with dipyridamole alleviated lupus nephritis and prevented the appearance of skin ulcers.ConclusionNF-AT activation is a key step in the activation of SLE T cells and the production of immunoglobulin. Dipyridamole inhibits SLE T cell function and improves pathologic changes of the disease in lupus-prone mice. We propose that dipyridamole can be used in treatment regimens for patients with SLE.
| S-EPMC3128171 | biostudies-literature
Project description:UNLABELLED:The process of capacitative or store-operated Ca(2+) entry has been extensively investigated, and recently two major molecular players in this process have been described. Stromal interacting molecule (STIM) 1 acts as a sensor for the level of Ca(2+) stored in the endoplasmic reticulum, and Orai proteins constitute pore-forming subunits of the store-operated channels. Store-operated Ca(2+) entry is readily demonstrated with protocols that provide extensive Ca(2+) store depletion; however, the role of store-operated entry with modest and more physiological cell stimuli is less certain. Recent studies have addressed this question in cell lines; however, the role of store-operated entry during physiological activation of primary cells has not been extensively investigated, and there is little or no information on the roles of STIM and Orai proteins in primary cells. Also, the nature of the Ca(2+) influx mechanism with hormone activation of hepatocytes is controversial. Hepatocytes respond to physiological levels of glycogenolytic hormones with well-characterized intracellular Ca(2+) oscillations. In the current study, we have used both pharmacological tools and RNA interference (RNAi)-based techniques to investigate the role of store-operated channels in the maintenance of hormone-induced Ca(2+) oscillations in rat hepatocytes. Pharmacological inhibitors of store-operated channels blocked thapsigargin-induced Ca(2+) entry but only partially reduced the frequency of Ca(2+) oscillations. Similarly, RNAi knockdown of STIM1 or Orai1 substantially reduced thapsigargin-induced calcium entry, and more modestly diminished the frequency of vasopressin-induced oscillations. CONCLUSION:Our findings establish that store-operated Ca(2+) entry plays a role in the maintenance of agonist-induced oscillations in primary rat hepatocytes but indicate that other agonist-induced entry mechanisms must be involved to a significant extent.
| S-EPMC2808042 | biostudies-literature
Project description:To investigate the autoantibody repertoire associated with SLE, we have created phage display IgG Fab libraries from two clinically active SLE patients and from the healthy identical twin of one of these patients. The libraries from the lupus discordant twins were found to both include unusually large representations of the V(H)5 gene family. By panning with DNA, the SLE libraries each yielded IgG anti-double-stranded (ds) DNA autoantibodies, which are characteristic of lupus disease. These included a V(H)5 autoantibody from the affected twin, that has a targeted cluster of mutations that potentially improves binding affinity. The recovered IgG anti-dsDNA autoantibodies expressed the same idiotypes associated with the in vivo IgG anti-dsDNA response of the respective SLE donor. Heavy-light chain shuffling experiments demonstrated a case in which the in vitro creation of anti-dsDNA binding activity required restrictive pairing of a heavy chain with Vlambda light chains similar to those in circulating anti-dsDNA autoantibodies. By contrast, IgG anti-ds autoantibodies could not be recovered from the library from the healthy twin, or from shuffled libraries with heavy chains from the healthy twin. These repertoire analyses illustrate how inheritance and somatic processes interplay to produce lupus-associated IgG autoantibodies.
| S-EPMC507750 | biostudies-other