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XI European Meeting on Glial Cell Function in Health and Disease

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July 3, 2013 - Room 3 3:15pm - 5:15pm
Symposium 3: Glial Cells and Chronic Pain

Organizer:
Marzia Malcangio (London)

3:15pm
S03-01

TRPV1-dependent and -independent alterations in the limbic cortex of neuropathic mouse: impact on glial caspases and pain perception.

*Sabatino Maione 1
1 Second University of Naples, , Naples, Italy
Abstract text :

Neuropathic pain induces morpho-functional changes in the limbic cortex. We investigated the role of TRPV1 channel and non neuronal cell-derived mediators in the mouse pre-limbic and infra-limbic (PL-IL) cortex in spared nerve injury (SNI) model of neuropathic pain. Reverse transcriptase-polymerase chain reaction, western blots, and immunfluorescence showed caspases activation in the PL-IL cortex of SNI mice. We observed up-regulation of IL-1 receptor and TRPV1 in VGluT1 positive profiles and cleaved caspase-3 and AMPA receptor up-regulation in different non-neural cells; moreover, caspase-1 activation and IL-1β increase in astrocytes was found. A pan-caspase inhibitor, injected into the PL-IL cortex, reduced mechanical allodynia, this effect being reduced, but not abolished, in Trpv1(-/-) mice. Single-unit extracellular recordings in vivo following electrical stimulation of basolateral amygdala or application of noxious paw pressure, showed increased excitatory pyramidal neuron activity in the SNI PL-IL cortex. Intriguingly, intra-PL-IL cortex injection of mGluR5 and NMDA receptor antagonists or AMPA exacerbated, whereas TRPV1 and AMPA receptor antagonists and a CB1 agonist inhibited allodynia. We observed that SNI triggers both TRPV1-dependent and independent glutamate- and caspase-mediated cross-talk among neurons and glia in the cortex, which either facilitates or counteracts pain. We suggest that, even though microglia are not activated in the cortex by peripheral neuropathy, those cells may be involved in anomalous neural plasticity in neuropathic pain.



3:45pm
S03-02

Mechanisms for neuron-microglia communication after peripheral insult

*Marzia Malcangio 1
1 King's College London, , London, United Kingdom
Abstract text :

The chronic pain which results from peripheral nerve or tissue damage is the result of neuronal malfunction and glial cell-mediated neuronal sensitization. Specifically, in the dorsal horn of the spinal cord microglial cells responds to remote damage in the periphery and to the resulting increase in primary afferent input to dorsal horn neurons at the first pain synapse. The microglial response which is triggered by neuronal activity is characterised by an increase in cell numbers, change in cell morphology and release pro-nociceptive factors which sensitize neurons. An intense series of studies has devoted attention to the mechanisms and pathways involved in microglia-neuron communication at the first pain synapse in order to identify novel targets for chronic pain therapy (Beggs et al., 2012).


We have recently described a novel circuit in spinal integration of pain signalling whereby the lysosomal cysteine protease cathepsin S (CatS) released by microglia liberates soluble FKN which then activates CX3CR1 receptor exclusively expressed by microglia.


The release of CatS from microglia occurs following activation of P2X7 receptor by high concentrations of ATP (Clark et al., 2010). CatS contributes to chronic pain via liberation of the neuronal chemokine fractalkine which further activates microglial mechanisms via activation of CX3CR1 receptor and intracellular p38 MAPK thereby establishing a positive feedback which contributes to nociceptive signalling (Clark and Malcangio, 2012). Indeed, mice lacking the CX3CR1 receptor do not develop hypersensitivity in models of inflammatory and neuropathic pain.  Furthermore, intrathecal administration of CatS inhibitors reverses neuropathic and inflammatory allodynia and hyperalgesia.


Our studies suggest that centrally active CX3CR1 antagonists and CatS inhibitors constitute new therapeutic agents for chronic pain.


MM research is supported by the Wellcome Trust, Arthritis Research UK and BBSRC PhD studentships


 References


Beggs S,Trang T, Salter MW. P2X4R microglia drive neuropathic pain. Nat Neurosci. 15: 1068-1073, 2012


Clark AK, Wodarski R, Guida F, Sasso O, Malcangio M. Cathepsin S release from primary cultured microglia is regulated by the P2X7 receptor. Glia, 58: 1710-1726, 2010


Clark AK, Malcangio M.Microglial signalling mechanisms: Cathepsin S and Fractalkine.Exp. Neurol. 234: 283-292, 2012


 


 


 



4:15pm
S03-03

What links peripheral nerve injury to spinal cord microglial reactivity?

*Marc Suter 1
1 CHUV-Lausanne University Hospital Center, , Lausanne, Switzerland
Abstract text :

Microglia is known to actively participate in chronic pain. A peripheral insult, inflammation or nerve injury, can trigger the globally called “microglial activation” phenomenon in the CNS. This reactivity is somatotopically distributed in the territory where the injured nerve enters the spinal cord. The trigger must therefore be transmitted along the nerve through two types of signals: injury-induced discharge of axon potential and/or axonal transport.
Electrical stimulation of the sciatic nerve induces the expression of Iba1 marker in the spinal cord. In neuropathic models consisting of section or ligation of different nerves, a burst of electrical activity starts at the time of injury, followed byongoing spontaneous discharges arising from the injury site, the axon or the dorsal root ganglion. These discharges can come from myelinated, unmyelinated, injured or adjacent non-injured fibers and participate in the process of central sensitization. A complete block of that activity with local anesthetics reduces microglial reactivity with a decreased activation p38 mitogen-activating protein kinase (MAPK) and microglial proliferation. Interestingly blocking only the nociceptive fibers is not as effective in reducing microglial reactivity. This could partly explain why current clinical practice of blocking nociceptive input in patients does not prevent the development of chronic pain after surgery. The blockade of motor and proprioceptive function is not feasible over a long period clinically but maybe systemically administered sodium channel blockers might be more efficient. The hypothesis of axonal transport includes 2 aspects: First the interruption of trophic factors from the target (negative injury signals) and second activation of signal from the injury site (positive injury signals). We observed a reduction in the expression of the microglial marker Iba1 after nerve injury with an axonal transport blockade using colchicine. The behavioral response was also changed with a slight reduction of mechanical allodynia. Specific interventions to assess positive and negative factors have to be done.



4:45pm
S03-04

Role of spinal glia and toll-like receptor 4 in inflammation-induced pain

*Camilla Svensson 1 , Christina  Christianson 2 , Nilesh  Agalave 1 , Jie Su 1 , Helena Harris 1 , Ulf Andersson 1 , Tony Yaksh 2
1 Karolinska Institutet, , Stockholm, Sweden
2 University of California, San Diego, , La Jolla, United States
Abstract text :

Rheumatoid arthritis (RA) is chronic disease evident as joint inflammation and progressive joint destruction. Of importance, pain is one of the most bothersome symptoms reported by RA patients. Autoantibodies to type II collagen and glucose-6-phosphate isomerase (GPI) are detected in serum of RA patients. Systemic injection of these antibodies to mice induces arthritis-like symptoms that last for 3-4 weeks. While collagen antibody-induced arthritis (CAIA) and K/BxN serum transfer (GPI antibody-mediated) are commonly used in the rheumatology field, they have just recently been evaluated as models of arthritis-induced pain. Pain-like behaviors such as mechanical and cold hypersensitivity and reduced locomotor activity are pronounced. Interestingly, both microglia and astrocyte reactivity is elevated in the spinal cord after induction of arthritis, and spinal injection of glia inhibitors attenuate pain-like behavior in these models, pointing to a functional contribution of spinal glia to pain signaling. Spinal toll-like receptor (TLR) 4 expressed on microglia and astrocytes has been implicated as a potential therapeutic target in neuropathic and other pain models. We compared the relative courses of arthritis-induced hypersensitivity in wild type (WT) and Tlr4(-/-) mice. Unlike WT mice, Tlr4(-/-) mice displayed a significant reversal in mechanical hypersensitivity and diminished appearance of glial activation markers. Spinal delivery of LPS-RS, a TLR4 antagonist, abrogated the arthritis-induced persistent mechanical hypersensitivity. We assessed gene expression of different endogenous TLR4 ligands and found that high mobility box protein 1 (HMGB1) was elevated in the spinal cord subsequent to induction of arthritis, which was also confirmed on protein level. Spinal injection of HMGB1 neutralizing antibodies reversed arthritis-induced hypersensitivity. Further, spinal injection of HMGB1 to naïve mice induced long-lasting hypersensitivity, an effect that was abolished in TLR4-/- mice. Taken together, our data suggest that spinal endogenous TLR4 ligands such as HMGB1 regulate persistent pain states initiated by joint inflammation trough modulation of microglia and astrocyte activity.