PD1 pathway in immune-mediated myopathies: Pathogenesis of dysfunctional T cells revisited

Objective

To investigate the relevance of dysfunctional T cells in immune-mediated myopathies. We analyzed T-cell exhaustion and senescence, in the context of programmed cell death protein 1 (PD1)-related immunity in skeletal muscle biopsies from patients with immune-mediated necrotizing myopathy (IMNM), sporadic inclusion body myositis (sIBM), and myositis induced by immune checkpoint inhibitors (irMyositis).

Methods

Skeletal muscle biopsies from 12 patients with IMNM, 7 patients with sIBM, and 8 patients with irMyositis were analyzed by immunostaining and immunofluorescence as well as by quantitative PCR. Eight biopsies from nondisease participants served as controls.

Results

CD3⁺CD8⁺ T cells in biopsies from IMNM, sIBM, and irMyositis were largely PD1-positive, while CD68⁺ macrophages were sparsely positive to the ligand of programmed cell death protein 1 (PD-L1). The sarcolemma of myofibers was PD-L2⁺ and was colocalized with major histocompatibility complex (MHC) class I. CD68⁺ macrophages were colocalized with PD-L2. Senescent T cells were strongly enriched in skeletal muscle of sIBM, revealing a distinct immunologic signature. Biopsies from patients with irMyositis showed mild signs of senescence and exhaustion.

Conclusion

Persistent exposure to antigens in IMNMs and sIBM may lead to T-cell exhaustion, a process controlled by the PD1 receptor and its cognate ligands PD-L1/PD-L2. To our knowledge, these data are the first evidence of presence of dysfunctional T cells and relevance of the PD1 pathway in IMNM, sIBM, and irMyositis. These findings may guide the way to a novel understanding of the immune pathogenesis of immune-mediated myopathies.

Characterization of Naïve and Vitamin C-Treated Mouse Schwann Cell Line MSC80: Induction of the Antioxidative Thioredoxin Related Transmembrane Protein 1

Schwann cells (SCs) are essential in the production of the axon-wrapping myelin sheath and provide trophic function and repair mechanisms in the peripheral nerves. Consequently, well-characterized SC in vitro models are needed to perform preclinical studies including the investigation of the complex biochemical adaptations occurring in the peripheral nervous system (PNS) under different (patho)physiological conditions. MSC80 cells represent a murine SC line used as an in vitro system for neuropathological studies. Here, we introduce the most abundant 9532 proteins identified via mass spectrometry-based protein analytics, and thus provide the most comprehensive SC protein catalogue published thus far. We cover proteins causative for inherited neuropathies and demonstrate that in addition to cytoplasmic, nuclear and mitochondrial proteins and others belonging to the protein processing machinery are very well covered. Moreover, we address the suitability of MSC80 to examine the molecular effect of a drug-treatment by analyzing the proteomic signature of Vitamin C-treated cells. Proteomic findings, immunocytochemistry, immunoblotting and functional experiments support the concept of a beneficial role of Vitamin C on oxidative stress and identified TMX1 as an oxidative stress protective factor, which might represent a promising avenue for therapeutic intervention of PNS-disorders with oxidative stress burden such as diabetic neuropathy.

The adenosine generating enzymes CD39/CD73 control microglial processes ramification in the mouse brain

Microglial cells invade the brain as amoeboid precursors and acquire a highly ramified morphology in the postnatal brain. Microglia express all essential purinergic elements such as receptors, nucleoside transporters and ecto-enzymes, including CD39 (NTPDase1) and CD73 (5'-nucleotidase), which sequentially degrade extracellular ATP to adenosine. Here, we show that constitutive deletion of CD39 and CD73 or both caused an inhibition of the microglia ramified phenotype in the brain with a reduction in the length of processes, branching frequency and number of intersections with Sholl spheres. In vitro, unlike wild-type microglia, cd39^-/- and cd73^-/- microglial cells were less complex and did not respond to ATP with the transformation into a more ramified phenotype. In acute brain slices, wild-type microglia retracted approximately 50% of their processes within 15 min after slicing of the brain, and this phenomenon was augmented in cd39^-/- mice; moreover, the elongation of microglial processes towards the source of ATP or towards a laser lesion was observed only in wild-type but not in cd39^-/- microglia. An elevation of extracellular adenosine 1) by the inhibition of adenosine transport with dipyridamole, 2) by application of exogenous adenosine or 3) by degradation of endogenous ATP/ADP with apyrase enhanced spontaneous and ATP-induced ramification of cd39^-/- microglia in acute brain slices and facilitated the transformation of cd39^-/- and cd73^-/- microglia into a ramified process-bearing phenotype in vitro. These data indicate that under normal physiological conditions, CD39 and CD73 nucleotidases together with equilibrative nucleoside transporter 1 (ENT1) control the fate of extracellular adenosine and thereby the ramification of microglial processes.

Spontaneous Ca2+ transients in mouse microglia

Microglia are the resident immune cells in the central nervous system and many of their physiological functions are known to be linked to intracellular calcium (Ca²⁺) signaling. Here we show that isolated and purified mouse microglia-either freshly or cultured-display spontaneous and transient Ca²⁺ elevations lasting for around ten to twenty seconds and occurring at frequencies of around five to ten events per hour and cell. The events were absent after depletion of internal Ca²⁺ stores, by phospholipase C (PLC) inhibition or blockade of inositol-1,4,5-trisphosphate receptors (IP₃Rs), but not by removal of extracellular Ca²⁺, indicating that Ca²⁺ is released from endoplasmic reticulum intracellular stores. We furthermore provide evidence that autocrine ATP release and subsequent activation of purinergic P2Y receptors is not the trigger for these events. Spontaneous Ca²⁺ transients did also occur after stimulation with Lipopolysaccharide (LPS) and in glioma-associated microglia, but their kinetics differed from control conditions. We hypothesize that spontaneous Ca²⁺ transients reflect aspects of cellular homeostasis that are linked to regular and patho-physiological functions of microglia.

The subpopulation of microglia expressing functional muscarinic acetylcholine receptors expands in stroke and Alzheimer's disease

Microglia undergo a process of activation in pathology which is controlled by many factors including neurotransmitters. We found that a subpopulation (11 %) of freshly isolated adult microglia respond to the muscarinic acetylcholine receptor agonist carbachol with a Ca(2+) increase and a subpopulation of similar size (16 %) was observed by FACS analysis using an antibody against the M3 receptor subtype. The carbachol-sensitive population increased in microglia/brain macrophages isolated from tissue of mouse models for stroke (60 %) and Alzheimer's disease (25 %), but not for glioma and multiple sclerosis. Microglia cultured from adult and neonatal brain contained a carbachol-sensitive subpopulation (8 and 9 %), which was increased by treatment with interferon-γ to around 60 %. This increase was sensitive to blockers of protein synthesis and correlated with an upregulation of the M3 receptor subtype and with an increased expression of MHC-I and MHC-II. Carbachol was a chemoattractant for microglia and decreased their phagocytic activity.

The subpopulation of microglia sensitive to neurotransmitters/neurohormones is modulated by stimulation with LPS, interferon-γ, and IL-4

Recently, neurotransmitters/neurohormones have been identified as factors controlling the function of microglia, the immune competent cells of the central nervous system. In this study, we compared the responsiveness of microglia to neurotransmitters/neurohormones. We freshly isolated microglia from healthy adult C57Bl/6 mice and found that only a small fraction (1-20%) responded to the application of endothelin, histamine, substance P, serotonin, galanin, somatostatin, angiotensin II, vasopressin, neurotensin, dopamine, or nicotine. In cultured microglia from neonatal and adult mice, a similarly small population of cells responded to these neurotransmitters/neurohormones. To induce a proinflammatory phenotype, we applied lipopolysaccaride (LPS) or interferon-gamma (IFN-γ) to the cultures for 24 h. Several of the responding populations increased; however, there was no uniform pattern when comparing adult with neonatal microglia or LPS with IFN-γ treatment. IL-4 as an anti-inflammatory substance increased the histamine-, substance P-, and somatostatin-sensitive populations only in microglia from adult, but not in neonatal cells. We also found that the expression of different receptors was not strongly correlated, indicating that there are many different populations of microglia with a distinct set of receptors. Our results demonstrate that microglial cells are a heterogeneous population with respect to their sensitivity to neurotransmitters/neurohormones and that they are more responsive in defined activation states.

Minocycline protects the immature white matter against hyperoxia

Poor neurological outcome in preterm infants is associated with periventricular white matter damage and hypomyelination, often caused by perinatal inflammation, hypoxia-ischemia, and hyperoxia. Minocycline has been demonstrated in animal models to protect the immature brain against inflammation and hypoxia-ischemia by microglial inhibition. Here we studied the effect of minocycline on white matter damage caused by hyperoxia. To mimic the 3- to 4-fold increase of oxygen tension caused by preterm birth, we have used the hyperoxia model in neonatal rats providing 24h exposure to 4-fold increased oxygen concentration (80% instead of 21% O2) from P6 to P7. We analyzed whether minocycline prevents activation of microglia and damage of oligodendroglial precursor cell development, and whether acute treatment of hyperoxia-exposed rats with minocycline improves long term white matter integrity. Minocycline administration during exposure to hyperoxia resulted in decreased apoptotic cell death and in improved proliferation and maturation of oligodendroglial precursor cells (OPC). Minocycline blocked changes in microglial morphology and IL-1β release induced by hyperoxia. In primary microglial cell cultures, minocycline inhibited cytokine release while in mono-cultures of OPCs, it improved survival and proliferation. Long term impairment of white matter diffusivity in MRI/DTI in P30 and P60 animals after neonatal hyperoxia was attenuated by minocycline. Minocycline protects white matter development against oxygen toxicity through direct protection of oligodendroglia and by microglial inhibition. This study moreover demonstrates long term benefits of minocycline on white matter integrity.

Abstract 215: Neural precursor cells induce cell death of high-grade astrocytomas through stimulation of TRPV1

Primary astrocytomas of grade 3 or 4 according to the classification system of the World Health Organization (high-grade astrocytomas or HGAs) are preponderant among adults and are almost invariably fatal despite the use of multimodal therapy. Here we show that the juvenile brain has an endogenous defense mechanism against HGAs. Neural precursor cells (NPCs) migrate to HGAs, reduce glioma expansion and prolong survival time by releasing endovanilloids that activate the vanilloid receptor (transient receptor potential vanilloid subfamily member-1 or TRPV1) on HGA cells. TRPV1 is highly expressed in tumor and weakly expressed in tumor-free brain. TRPV1 stimulation triggers tumor cell death through the branch of the endoplasmic reticulum stress pathway that is controlled by activating transcription factor-3 (ATF3). The antitumorigenic response of NPCs is lost with aging. NPC-mediated tumor suppression can be mimicked in the adult brain by systemic administration of the synthetic vanilloid arvanil, suggesting that TRPV1 agonists have potential as new HGA therapeutics.

Citation Format: Michael Synowitz, Kristin Stock, Jitender Kumar, Stefania Petrosino, Roberta Imperatore, Ewan St J Smith, Peter Wend, Bettina Purfürst, Ulrike A Nuber, Ulf Gurok, Vitali Matyash, Joo-Hee Wälzlein, Sridhar R Chirasani, Gunnar Dittmar, Benjamin F Cravatt, Stefan Momma, Gary R Lewin, Alessia Ligresti, Luciano De Petrocellis, Luigia Cristino, Joerg Christian Tonn, Vincenzo Di Marzo, Helmut Kettenmann, Rainer Glass. Neural precursor cells induce cell death of high-grade astrocytomas through stimulation of TRPV1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 215. doi:10.1158/1538-7445.AM2013-215

Functional impairment of microglia coincides with Beta-amyloid deposition in mice with Alzheimer-like pathology

Microglial cells closely interact with senile plaques in Alzheimer’s disease and acquire the morphological appearance of an activated phenotype. The significance of this microglial phenotype and the impact of microglia for disease progression have remained controversial. To uncover and characterize putative changes in the functionality of microglia during Alzheimer’s disease, we directly assessed microglial behavior in two mouse models of Alzheimer’s disease. Using in vivo two-photon microscopy and acute brain slice preparations, we found that important microglial functions - directed process motility and phagocytic activity - were strongly impaired in mice with Alzheimer’s disease-like pathology compared to age-matched non-transgenic animals. Notably, impairment of microglial function temporally and spatially correlated with Aβ plaque deposition, and phagocytic capacity of microglia could be restored by interventionally decreasing amyloid burden by Aβ vaccination. These data suggest that major microglial functions progressively decline in Alzheimer’s disease with the appearance of Aβ plaques, and that this functional impairment is reversible by lowering Aβ burden, e.g. by means of Aβ vaccination.

GDNF mediates glioblastoma-induced microglia attraction but not astrogliosis

High-grade gliomas are the most common primary brain tumors. Their malignancy is promoted by the complex crosstalk between different cell types in the central nervous system. Microglia/brain macrophages infiltrate high-grade gliomas and contribute to their progression. To identify factors that mediate the attraction of microglia/macrophages to malignant brain tumors, we established a glioma cell encapsulation model that was applied in vivo. Mouse GL261 glioma cell line and human high-grade glioma cells were seeded into hollow fibers (HF) that allow the passage of soluble molecules but not cells. The glioma cell containing HF were implanted into one brain hemisphere and simultaneously HF with non-transformed fibroblasts (controls) were introduced into the contralateral hemisphere. Implanted mouse and human glioma- but not fibroblast-containing HF attracted microglia and up-regulated immunoreactivity for GFAP, which is a marker of astrogliosis. In this study, we identified GDNF as an important factor for microglial attraction: (1) GL261 and human glioma cells secret GDNF, (2) reduced GDNF production by siRNA in GL261 in mouse glioma cells diminished attraction of microglia, (3) over-expression of GDNF in fibroblasts promoted microglia attraction in our HF assay. In vitro migration assays also showed that GDNF is a strong chemoattractant for microglia. While GDNF release from human or mouse glioma had a profound effect on microglial attraction, the glioma-induced astrogliosis was not affected. Finally, we could show that injection of GL261 mouse glioma cells with GDNF knockdown by shRNA into mouse brains resulted in reduced tumor expansion and improved survival as compared to injection of control cells.

Astrocytes control GABAergic inhibition of neurons in the mouse barrel cortex

Astrocytes in the barrel cortex respond with a transient Ca2+ increase to neuronal stimulation and this response is restricted to the stimulated barrel field. In the present study we suppressed the astrocyte response by dialysing these cells with the Ca2+ chelator BAPTA. Electrical stimulation triggered a depolarization in stellate or pyramidal ‘regular spiking' neurons from cortex layer 4 and 2/3 and this response was augmented in amplitude and duration after astrocytes were dialysed with BAPTA. Combined blockade of GABAA and GABAB receptors mimicked the effect of BAPTA dialysis, while glutamate receptor blockers had no effect. Moreover, the frequency of spontaneous postsynaptic currents was increased after BAPTA dialysis. Outside the range of BAPTA dialysis astrocytes responded with a Ca2+ increase, but in contrast to control, the response was no longer restricted to one barrel field. Our findings indicate that astrocytes control neuronal inhibition in the barrel cortex.

LET-767 is required for the production of branched chain and long chain fatty acids in Caenorhabditis elegans

LET-767 from Caenorhabditis elegans belongs to a family of short chain dehydrogenases/reductases and is homologous to 17beta-hydroxysterol dehydrogenases of type 3 and 3-ketoacyl-CoA reductases. Worms subjected to RNA interference (RNAi) of let-767 displayed multiple growth and developmental defects in the first generation and arrested in the second generation as L1 larvae. To determine the function of LET-767 in vivo, we exploited a biochemical complementation approach, in which let-767 (RNAi)-arrested larvae were rescued by feeding with compounds isolated from wild type worms. The arrest was only rescued by the addition of triacylglycerides extracted from worms but not from various natural sources, such as animal fats and plant oils. The mass spectrometric analyses showed alterations in the fatty acid content of triacylglycerides. Essential for the rescue were odd-numbered fatty acids with monomethyl branched chains. The rescue was improved when worms were additionally supplemented with long chain even-numbered fatty acids. Remarkably, let-767 completely rescued the yeast 3-ketoacyl-CoA reductase mutant (ybr159Delta). Because worm ceramides exclusively contain a monomethyl branched chain sphingoid base, we also investigated ceramides in let-767 (RNAi). Indeed, the amount of ceramides was greatly reduced, and unusual sphingoid bases were observed. Taken together, we conclude that LET-767 is a major 3-ketoacyl-CoA reductase in C. elegans required for the bulk production of monomethyl branched and long chain fatty acids, and the developmental arrest in let-767 (RNAi) worms is caused by the deficiency of the former.

Lipid extraction by methyl-tert-butyl ether for high-throughput lipidomics

Accurate profiling of lipidomes relies upon the quantitative and unbiased recovery of lipid species from analyzed cells, fluids, or tissues and is usually achieved by two-phase extraction with chloroform. We demonstrated that methyl-tert-butyl ether (MTBE) extraction allows faster and cleaner lipid recovery and is well suited for automated shotgun profiling. Because of MTBE's low density, lipid-containing organic phase forms the upper layer during phase separation, which simplifies its collection and minimizes dripping losses. Nonextractable matrix forms a dense pellet at the bottom of the extraction tube and is easily removed by centrifugation. Rigorous testing demonstrated that the MTBE protocol delivers similar or better recoveries of species of most all major lipid classes compared with the "gold-standard" Folch or Bligh and Dyer recipes.

Sterol-derived hormone(s) controls entry into diapause in Caenorhabditis elegans by consecutive activation of DAF-12 and DAF-16

Upon starvation or overcrowding, Caenorhabditis elegans interrupts its reproductive cycle and forms a specialised larva called dauer (enduring). This process is regulated by TGF-β and insulin-signalling pathways and is connected with the control of life span through the insulin pathway components DAF-2 and DAF-16. We found that replacing cholesterol with its methylated metabolite lophenol induced worms to form dauer larvae in the presence of food and low population density. Our data indicate that methylated sterols do not actively induce the dauer formation but rather that the reproductive growth requires a cholesterol-derived hormone that cannot be produced from methylated sterols. Using the effect of lophenol on growth, we have partially purified activity, named gamravali, which promotes the reproduction. In addition, the effect of lophenol allowed us to determine the role of sterols during dauer larva formation and longevity. In the absence of gamravali, the nuclear hormone receptor DAF-12 is activated and thereby initiates the dauer formation program. Active DAF-12 triggers in neurons the nuclear import of DAF-16, a forkhead domain transcription factor that contributes to dauer differentiation. This hormonal control of DAF-16 activation is, however, independent of insulin signalling and has no influence on life span.

A sterol-derived activity is partially purified and shown to support reproductive growth under sterol-free conditions that normally induce dauer larva formation in nematodes

Requirement of functional ryanodine receptor type 3 for astrocyte migration

Astrocyte motility plays an important role in the response of the brain to injury and during regeneration. We used two in vitro assays, a wound-healing model and a chemotaxis assay, to study mechanisms that control astrocyte motility. Ryanodine receptors (RyR), intracellular calcium-release channels, modulate intracellular Ca2+ levels, and also motility: 1) blocking RyR with antagonizing concentration of ryanodine (200 microM) strongly attenuated motility and 2) motility of astrocytes cultured from homozygous RyR type 3 knockout mice was impaired strongly compared with wild-type. In contrast, MIP-1a-induced chemotaxis was neither impaired in the presence of ryanodine nor in the cells from the knockout animals. Reverse transcription-polymerase chain reaction (RT-PCR) analysis combined with Western blotting and immunocytochemistry confirmed the expression of RyR type 3, but not type 1 or 2 in cultured and acutely isolated astrocytes. RyR in astrocytes are linked to Ca2+ signaling because the RyR agonist 4-chloro-m-cresol induced a release of Ca2+ from intracellular stores. These results indicate that astrocytes express only RyR type 3 and that this receptor is important for controlling astrocyte motility.

Nitric oxide signals parallel fiber activity to Bergmann glial cells in the mouse cerebellar slice

Stimulation of parallel fibers in the cerebellar cortex triggers a transient calcium increase in Bergmann glial cells, a special form of astrocytes. Using patch-clamping and imaging techniques we have found that this form of neuron-glia interaction is mediated by nitric oxide (NO) since the response is blocked by the NO-synthase inhibitor N omega-nitro-l-arginine and mimicked by NO donors. None of the neurotransmitter receptors of Bergmann glia identified so far participates in or interferes with this signaling cascade. The NO-triggered increases in [Ca(2+)](i), as studied in Bergmann glial cells in the slice or in cultured astrocytes, are due to Ca(2+) influx and not to release from cytoplasmic stores. Thus, NO released from parallel fibers serves as a signaling substance to the neighboring glial elements.

Distribution and transport of cholesterol in Caenorhabditis elegans

Cholesterol transport is an essential process in all multicellular organisms. In this study we applied two recently developed approaches to investigate the distribution and molecular mechanisms of cholesterol transport in Caenorhabditis elegans. The distribution of cholesterol in living worms was studied by imaging its fluorescent analog, dehydroergosterol, which we applied to the animals by feeding. Dehydroergosterol accumulates primarily in the pharynx, nerve ring, excretory gland cell, and gut of L1-L3 larvae. Later, the bulk of dehydroergosterol accumulates in oocytes and spermatozoa. Males display exceptionally strong labeling of spermatids, which suggests a possible role for cholesterol in sperm development. In a complementary approach, we used a photoactivatable cholesterol analog to identify cholesterol-binding proteins in C. elegans. Three major and several minor proteins were found specifically cross-linked to photocholesterol after UV irradiation. The major proteins were identified as vitellogenins. rme-2 mutants, which lack the vitellogenin receptor, fail to accumulate dehydroergosterol in oocytes and embryos and instead accumulate dehydroergosterol in the body cavity along with vitellogenin. Thus, uptake of cholesterol by C. elegans oocytes occurs via an endocytotic pathway involving yolk proteins. The pathway is a likely evolutionary ancestor of mammalian cholesterol transport.

Glutamate-triggered calcium signalling in mouse bergmann glial cells in situ: role of inositol-1,4,5-trisphosphate-mediated intracellular calcium release

The mechanisms of glutamate-induced changes in intracellular free calcium concentration in Bergmann glial cells in mouse cerebellar slices were investigated by Fura-2-based microfluorimetry. Extracellular applications of glutamate, quisqualate and kainate triggered an increase in cytoplasmic calcium concentration, whereas N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate were ineffective. The calcium elevation triggered by kainate was completely blocked by removal of calcium ions from the external solutions or by slice incubation with 6-cyano-7-nitroquinoxaline-2,3-dione. Conversely, both glutamate- and quisqualate-induced intracellular calcium transients were only slightly attenuated by slice incubation with either 6-cyano-7-nitroquinoxaline-2,3-dione or calcium-free solution, suggesting the intracellular origin for calcium ions. The glutamate-triggered cytosolic calcium increases were inhibited by slice incubation with thapsigargin, the inhibitor of intracellular calcium pumps, or by intracellular perfusion of Bergmann glial cells with heparin, the antagonist of inositol-1,4,5-trisphosphate-gated calcium release channels. Therefore the calcium release from inositol-1,4,5-trisphosphate-sensitive intracellular stores plays the major role in glutamate-induced calcium signalling. We concluded that Bergmann glial cells express calcium permeable ionotropic glutamate receptors, which might be important for generation of fast calcium signals. However, slow glutamate-evoked calcium signals are mostly determined by inositol-1,4,5-trisphosphate-dependent intracellular signalling chain.

Microdomains for neuron-glia interaction: parallel fiber signaling to Bergmann glial cells

Astrocytes are considered a reticulate network of cells, through which calcium signals can spread easily. In Bergmann glia, astrocytic cells of the cerebellum, we identified subcellular compartments termed 'glial microdomains'. These elements have a complex surface consisting of thin membrane sheets, contain few mitochondria and wrap around synapses. To test for neuronal interaction with these structures, we electrically stimulated parallel fibers. This stimulation increased intracellular calcium concentration ([Ca2+]i) in small compartments within Bergmann glial cell processes similar in size to glial microdomains. Thus, a Bergmann glial cell may consist of hundreds of independent compartments capable of autonomous interactions with the particular group of synapses that they ensheath.