Chemokine CXCL8 modulates GluR1 phosphorylation

Kaixin-San improves Aβ-induced synaptic plasticity inhibition by affecting the expression of regulation proteins associated with postsynaptic AMPAR expression

Objective: To explore the mechanism underlying Kaixin-San (KXS) regulation of postsynaptic AMPA receptor (AMPAR) expression to mitigate toxic effects of the amyloid-β protein (Aβ). Methods: An animal model was established via intracerebroventricular injection of Aβ1-42. The Morris water maze test was conducted to evaluate learning and memory, while electrophysiological recording was conducted to assess the hippocampal long-term potentiation (LTP). Western blotting was used to detect expression levels of the hippocampal postsynaptic AMPAR and its accessory proteins. Results: The time spent to find the platform was significantly prolonged, the number of mice crossing the target site was significantly reduced, and the maintenance of LTP was inhibited in the Aβ group than in the control group. In the Aβ/KXS group, the time taken to find the platform was significantly shortened and the number of mice crossing the target site was significantly increased than in the Aβ group; furthermore, the inhibition of LTP induced by Aβ was reversed. The expression of GluR1, GluR2, ABP, GRIP1, NSF, and pGluR1-Ser845 was upregulated, while that of pGluR2-Ser880 and PKC δ was downregulated in the Aβ/KXS group. Conclusion: The increased expression of ABP, GRIP1, NSF, and pGluR1-Ser845 and the decreased expression of pGluR2-Ser880 and PKC δ under the influence of KXS, followed by the upregulation of postsynaptic GluR1 and GluR2, alleviated the inhibition of LTP induced by Aβ. Ultimately, the memory function of model animals was improved by KXS. Our study provides novel insights into the mechanism underlying KXS mitigation of Aβ-induced synaptic plasticity inhibition and memory impairment by altering the levels of accessory proteins associated with AMPAR expression.

Role of interleukin 8 in depression and other psychiatric disorders

Low grade neuroinflammation has been suggested as one of the underlying mechanisms of many psychiatric diseases as well as cognitive disorders. Interleukin 8 (IL-8), a proinflammatory cytokine produced by many cell types including macrophage and microglia, mainly functions as a neutrophil chemoattractant in the bloodstream. IL-8 is also found in the brain, where it is released from microglia in response to proinflammatory stimuli. In this review, we highlight studies focusing on the role of IL-8 in psychiatric diseases such as major depression, bipolar disorder, schizophrenia, sleep disorder, autism spectrum disorder, anxiety disorders and dementia. Increased peripheral IL-8 levels have been reported in these diseases, particularly in schizophrenic disorder, bipolar disorder, obstructive sleep apnea and autism spectrum disorder. The literature on IL-8 and major depression is inconsistent. IL-8 has been found to be a factor associated with schizophrenic prognosis and therapeutic response, and may affect a wide range of symptomatology. Considering that the exact role of immune alterations is still under research, the success of immune-based therapies in psychiatric diseases is limited for the time being.

A guide to chemokines and their receptors

The chemokines (or chemotactic cytokines) are a large family of small, secreted proteins that signal through cell surface G protein-coupled heptahelical chemokine receptors. They are best known for their ability to stimulate the migration of cells, most notably white blood cells (leukocytes). Consequently, chemokines play a central role in the development and homeostasis of the immune system, and are involved in all protective or destructive immune and inflammatory responses. Classically viewed as inducers of directed chemotactic migration, it is now clear that chemokines can stimulate a variety of other types of directed and undirected migratory behavior, such as haptotaxis, chemokinesis, and haptokinesis, in addition to inducing cell arrest or adhesion. However, chemokine receptors on leukocytes can do more than just direct migration, and these molecules can also be expressed on, and regulate the biology of, many nonleukocytic cell types. Chemokines are profoundly affected by post-translational modification, by interaction with the extracellular matrix (ECM), and by binding to heptahelical 'atypical' chemokine receptors that regulate chemokine localization and abundance. This guide gives a broad overview of the chemokine and chemokine receptor families; summarizes the complex physical interactions that occur in the chemokine network; and, using specific examples, discusses general principles of chemokine function, focusing particularly on their ability to direct leukocyte migration.

Role of microglia in mechanical allodynia in the anterior cingulate cortex

Plastic changes that increase nociceptive transmission are observed in several brain regions under conditions of chronic pain. Synaptic plasticity in the anterior cingulate cortex (ACC) is particularly associated with neuropathic pain. Glial cells are considered candidates for the modulation of neural plastic changes in the central nervous system. In this study, we aimed to investigate the role of ACC glial cells in the development of neuropathic pain. First, we examined the expression of glial cells in the ACC of nerve-ligated mice. The expression of astrocytes and microglia was increased in the ACC of nerve-ligated mice, which was reversed by intracerebroventricular (i.c.v) treatment with the microglia inhibitor minocycline. Then, we examined the effect of minocycline on mechanical allodynia in nerve-ligated mice. I.c.v. and intra-ACC treatment with minocycline partially inhibited mechanical allodynia in the nerve-ligated mice. The expression of phosphorylated alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluR1 subunit at Ser831, but not at Ser845, was increased in the ACC of the nerve-ligated mice compared to sham-operated mice, which was attenuated by minocycline administration. These results suggest that the activation of microglia in the ACC is involved in the development of hyperalgesia in mice with neuropathic pain.

CXCL1/CXCR2 signaling in pathological pain: Role in peripheral and central sensitization

Pathological pain conditions can be triggered after peripheral nerve injury and/or inflammation. It is associated with plasticity of nociceptive pathway in which pain is prolonged even after healing of the injured tissue. Generally combinations of analgesic drugs are not sufficient to achieve selective palliation from chronic pain, besides causing a greater number of side effects. In order to identify novel alternatives for more effective treatments, it is necessary to clarify the underlying mechanisms of pathological pain. It is well established that there are two main components in pathological pain development and maintenance: (i) primary sensory neuron sensitization (peripheral sensitization), and (ii) central sensitization. In both components cytokines and chemokines act as key mediators in pain modulation. CXCL1 is a chemokine that promote both nociceptor and central sensitization via its main receptor CXCR2, which is a promising target for novel analgesic drugs. Here, we reviewed and discussed the role of the CXCL1/CXCR2 signaling axis in pathological pain conditions triggered by either peripheral inflammation or nerve injury.

Inflammation-induced GluA1 trafficking and membrane insertion of Ca2+ permeable AMPA receptors in dorsal horn neurons is dependent on spinal tumor necrosis factor, PI3 kinase and protein kinase A

Peripheral inflammation induces sensitization of nociceptive spinal cord neurons. Both spinal tumor necrosis factor (TNF) and neuronal membrane insertion of Ca²⁺ permeable AMPA receptor (AMPAr) contribute to spinal sensitization and resultant pain behavior, molecular mechanisms connecting these two events have not been studied in detail. Intrathecal (i.t.) injection of TNF-blockers attenuated paw carrageenan-induced mechanical and thermal hypersensitivity. Levels of GluA1 and GluA4 from dorsal spinal membrane fractions increased in carrageenan-injected rats compared to controls. In the same tissue, GluA2 levels were not altered. Inflammation-induced increases in membrane GluA1 were prevented by i.t. pre-treatment with antagonists to TNF, PI3K, PKA and NMDA. Interestingly, administration of TNF or PI3K inhibitors followed by carrageenan caused a marked reduction in plasma membrane GluA2 levels, despite the fact that membrane GluA2 levels were stable following inhibitor administration in the absence of carrageenan. TNF pre-incubation induced increased numbers of Co²⁺ labeled dorsal horn neurons, indicating more neurons with Ca²⁺ permeable AMPAr. In parallel to Western blot results, this increase was blocked by antagonism of PI3K and PKA. In addition, spinal slices from GluA1 transgenic mice, which had a single alanine replacement at GluA1 ser 845 or ser 831 that prevented phosphorylation, were resistant to TNF-induced increases in Co²⁺ labeling. However, behavioral responses following intraplantar carrageenan and formalin in the mutant mice were no different from littermate controls, suggesting a more complex regulation of nociception. Co-localization of GluA1, GluA2 and GluA4 with synaptophysin on identified spinoparabrachial neurons and their relative ratios were used to assess inflammation-induced trafficking of AMPAr to synapses. Inflammation induced an increase in synaptic GluA1, but not GluA2. Although total GluA4 also increased with inflammation, co-localization of GluA4 with synaptophysin, fell short of significance. Taken together these data suggest that peripheral inflammation induces a PI3K and PKA dependent TNFR1 activated pathway that culminates with trafficking of calcium permeable AMPAr into synapses of nociceptive dorsal horn projection neurons.

Chemokine receptor oligomerization and allostery

Oligomerization of chemokine receptors has been reported to influence many aspects of receptor function through allosteric communication between receptor protomers. Allosteric interactions within chemokine receptor hetero-oligomers have been shown to cause negative cooperativity in the binding of chemokines and to inhibit receptor activation in the case of some receptor pairs. Other receptor pairs can cause enhanced signaling and even activate entirely new, hetero-oligomer-specific signaling complexes and responses downstream of receptor activation. Many mechanisms contribute to these effects including direct allosteric coupling between the receptors, G protein-mediated allostery, G protein stealing, ligand sequestration, and recruitment of new intracellular proteins by exposing unique binding interfaces on the oligomerized receptors. These effects present both challenges as well as exciting opportunities for drug discovery. One of the most difficult challenges will involve determining if and when hetero-oligomers versus homomeric receptors are involved in specific disease states.

Serum cytokines in a clinical trial of hypothermia for neonatal hypoxic-ischemic encephalopathy

Inflammatory cytokines may mediate hypoxic-ischemic (HI) injury and offer insights into the severity of injury and the timing of recovery. In our randomized, multicenter trial of hypothermia, we analyzed the temporal relationship of serum cytokine levels in neonates with hypoxic-ischemic encephalopathy (HIE) with neurodevelopmental outcome at 12 months. Serum cytokines were measured every 12 hours for 4 days in 28 hypothermic (H) and 22 normothermic (N) neonates with HIE. Monocyte chemotactic protein-1 (MCP-1) and interleukins (IL)-6, IL-8, and IL-10 were significantly higher in the H group. Elevated IL-6 and MCP-1 within 9 hours after birth and low macrophage inflammatory protein 1a (MIP-1a) at 60 to 70 hours of age were associated with death or severely abnormal neurodevelopment at 12 months of age. However, IL-6, IL-8, and MCP-1 showed a biphasic pattern in the H group, with early and delayed peaks. In H neonates with better outcomes, uniform down modulation of IL-6, IL-8, and IL-10 from their peak levels at 24 hours to their nadir at 36 hours was observed. Modulation of serum cytokines after HI injury may be another mechanism of improved outcomes in neonates treated with induced hypothermia.

Peripheral inflammation induces tumor necrosis factor dependent AMPA receptor trafficking and Akt phosphorylation in spinal cord in addition to pain behavior

In the present study, intraplantar carrageenan induced increased mechanical allodynia, phosphorylation of PKB/Akt and GluR1 ser 845 (PKA site) as well as GluR1, but not GluR2 movement into neuronal membranes. This change in membrane GluR1/GluR2 ratio is indicative of Ca(2+) permeable AMPA receptor insertion. Pain behavior was reduced and biochemical changes blocked by spinal pretreatment, but not post-treatment, with a tumor necrosis factor (TNF) antagonist, Etanercept (100microg). Pain behavior was also reduced by spinal inhibition of phosphatidylinositol 3-kinase (PI-3K) (wortmannin; 1 and 5microg) and LY294002; 50 and 100microg) and Akt (Akt inhibitor IV; 3microg). Phosphorylated Akt was found exclusively in neurons in grey matter and in oligodendrocytes in white matter. Interestingly, this increase was seen first in superficial dorsal horn and alpha-motor neurons (peak 45min) and later (peak 2h post-injection) in deep dorsal horn neurons. Akt and GluR1 phosphorylation, AMPA receptor trafficking and mechanical allodynia were all TNF dependent. Whether phosphorylation of Akt and of GluR1 are in series or in parallel or upstream of pain behavior remains to be determined. Certainly, TNF-mediated GluR1 trafficking appears to play a major role in inflammatory pain and TNF-mediated effects such as these could represent a path by which glia contribute to neuronal sensitization (spinal LTP) and pathological pain.