Microglial/macrophage GRK2 determines duration of peripheral IL-1β-induced hyperalgesia: Contribution of spinal cord CX3CR1, p38 and IL-1 signaling

Chronic pain associated with inflammation is a major clinical problem, but the underlying mechanisms are incompletely understood. Recently, we reported that GRK2^+/− mice with a ∼50% reduction of GRK2 develop prolonged hyperalgesia following a single intraplantar injection of the pro-inflammatory cytokine interleukin-1β (IL-1β). Here we show that spinal microglia/macrophage GRK2 is reduced during chronic inflammation-induced hyperalgesia. Next, we applied CRE-Lox technology to create mice with low GRK2 in microglia/macrophages/granulocytes (LysM-GRK2^f/+), or sensory neurons or astrocytes. Only mice deficient in microglial/macrophage/granulocyte GRK2 display prolonged IL-1β-induced hyperalgesia that lasts up to 8 days. Two days after intraplantar IL-1β, increased microglial/macrophage activity occurs in the lumbar but not thoracic spinal cord of GRK2-deficient mice. Intrathecal pre-treatment with minocycline, an inhibitor of microglia/macrophage activation, accelerates resolution of hyperalgesia independent of genotype and prevents transition to chronic hyperalgesia in GRK2^+/− mice. Ongoing hyperalgesia in GRK2^+/− mice is reversed by minocycline administration at days 1 and 2 after IL-1β injection. Similarly, IL-1β-induced hyperalgesia in LysM-GRK2^f/+ mice is attenuated by intrathecal administration of anti-CX3CR1 to abrogate fractalkine signaling, the p38 inhibitor SB239063 and the IL-1 antagonist IL-1ra. These data establish that chronic inflammatory hyperalgesia is associated with reduced GRK2 in microglia/macrophages and that low GRK2 in these cells is sufficient to markedly prolong hyperalgesia after a single intraplantar injection of IL-1β. Ongoing hyperalgesia is maintained by spinal microglial/macrophage activity, fractalkine signaling, p38 activation and IL-1 signaling. We propose that chronic inflammation decreases spinal microglial/macrophage GRK2, which prevents silencing of microglia/macrophage activity and thereby contributes to prolonged hyperalgesia.     

西妥昔对脂多糖诱导的小胶质细胞活化和迁移的影响

目的:研究表皮生长因子受体(EGFR)的特异性单克隆抗体西妥昔(Cetuximab)对小胶质细胞活化及迁移的影响.方法:细菌脂多糖(LPS)诱导活化原代培养的大鼠脊髓小胶质细胞,给予西妥昔干预,免疫荧光法观察小胶质细胞形态及磷酸化EGFR表达水平的变化,Transwell法检测细胞的迁移.结果:与对照组相比,LPS诱导...     

Prostaglandin signaling suppresses beneficial microglial function in Alzheimer’s disease models

Microglia, the innate immune cells of the CNS, perform critical inflammatory and noninflammatory functions that maintain normal neural function. For example, microglia clear misfolded proteins, elaborate trophic factors, and regulate and terminate toxic inflammation. In Alzheimer’s disease (AD), however, beneficial microglial functions become impaired, accelerating synaptic and neuronal loss. Better understanding of the molecular mechanisms that contribute to microglial dysfunction is an important objective for identifying potential strategies to delay progression to AD. The inflammatory cyclooxygenase/prostaglandin E2 (COX/PGE₂) pathway has been implicated in preclinical AD development, both in human epidemiology studies and in transgenic rodent models of AD. Here, we evaluated murine models that recapitulate microglial responses to Aβ peptides and determined that microglia-specific deletion of the gene encoding the PGE₂ receptor EP2 restores microglial chemotaxis and Aβ clearance, suppresses toxic inflammation, increases cytoprotective insulin-like growth factor 1 (IGF1) signaling, and prevents synaptic injury and memory deficits. Our findings indicate that EP2 signaling suppresses beneficial microglia functions that falter during AD development and suggest that inhibition of the COX/PGE₂/EP2 immune pathway has potential as a strategy to restore healthy microglial function and prevent progression to AD.     

The Role of Glia and the Immune System in the Development and Maintenance of Neuropathic Pain

Neuropathic pain refers to a variety of chronic pain conditions with differing underlying pathophysiologic mechanisms and origins. Recent studies indicate a communication between the immune system and the nervous system. A common underlying mechanism of neuropathic pain is the presence of inflammation at the site of the damaged or affected nerve(s). This inflammatory response initiates a cascade of events resulting in the concentration and activation of innate immune cells at the site of tissue injury. The release of immunoactive substances such as cytokines, neurotrophic factors, and chemokines initiate local actions and can result in a more generalized immune response. The resultant neuroinflammatory environment can cause activation of glial cells located in the spinal cord and the brain, which appear to play a prominent role in nociception. Glial cells, also known as neuroglia, are nonconducting cells that modulate neurotransmission at the synaptic level. Glial cells can be subdivided into two primary categories: microglia and macroglia, which include astrocytes and oligodendrocytes. Astrocytes and microglia are known to play a role in the development, spread, and potentiation of neuropathic pain. Following peripheral nociceptive activation via nerve injury, microglia become activated and release pro‐inflammatory cytokines such as tumor necrosis factor‐α, interleukin‐1β, and interleukin‐6, thereby initiating the pain process. Microglia propagate the neuroinflammation by recruiting other microglia and eventually activating nearby astrocytes, which prolongs the inflammatory state and leads to a chronic neuropathic pain condition. Our review focuses on the role of glia and the immune system in the development and maintenance of neuropathic pain.     

Interleukin‐6 induces microglial CX3CR1 expression in the spinal cord after peripheral nerve injury through the activation of p38 MAPK

Peripheral nerve injury leading to neuropathic pain induces the upregulation of interleukin (IL)‐6 and microglial CX3CR1 expression, and activation of p38 mitogen‐activated protein kinase (MAPK) in the spinal cord. Here, we investigated whether IL‐6 regulates CX3CR1 expression through p38 MAPK activation in the spinal cord in rats with chronic constriction injury (CCI) of the sciatic nerve. Similar temporal changes in the expression of IL‐6, phosphorylated p38 MAPK and CX3CR1 were observed following CCI. The increases in CX3CR1 expression, p38 MAPK activation and pain behavior after CCI were suppressed by blocking IL‐6 action with a neutralizing antibody, while they were enhanced by supplying exogenous recombinant rat IL‐6 (rrIL‐6). rrIL‐6 also induced increases in spinal CX3CR1 expression, p38 MAPK activation and pain behavior in naïve rats without nerve injury. Furthermore, treatment with the p38 MAPK‐specific inhibitor, SB203580, suppressed the increase in CX3CR1 expression induced by CCI or rrIL‐6 treatment. Finally, blocking CX3CR1 or p38 MAPK activation prevented the development of mechanical allodynia and thermal hyperalgesia induced by CCI or rrIL‐6 treatment. These results suggest a new mechanism of neuropathic pain, in which IL‐6 induces microglial CX3CR1 expression in the spinal cord through p38 MAPK activation, enhancing the responsiveness of microglia to fractalkine in the spinal cord, thus playing an important role in neuropathic pain after peripheral nerve injury.     

Dynamic motility of microglia:Purinergic modulation of microglial movement in the normal and pathological brain

小神经胶质细胞具有高分支且可以动态移动的细胞突起,在生理条件下监控脑的活动。在病理刺激下,小神经胶质细胞表现出形态学变化,向损伤部位迁移,并在此处的炎性反应和神经元损伤中发挥重要作用。在脑损伤发生的数分钟内,小神经胶质细胞突起很快延伸至损伤部位。这种趋化作用为损伤部位的ATP释放和随之发生的小神经胶质细胞嘌呤能受体-P2Y12R活化所触发。除嘌呤能信号之外,大量神经元信号分子正向或负向调控小神经胶质细胞的移动,这对调节病理条件下的小神经胶质细胞功能性活化起重要作用。本综述重点讨论小神经胶质细胞的动态移动过程,并描述几种在正常和病理脑组织中调节小神经胶质细胞移动的重要信号分子及其作用。     

Role for CD4(+) CD25(+) regulatory T cells in reactivation of persistent leishmaniasis and control of concomitant immunity

Reactivation of dormant infections causes an immense burden of morbidity and mortality in the world at large. Reactivation can occur as a result of immunosuppression, environmental insult, or aging; however, the cause of reactivation of such infections is often not clear. We have previously shown that persistence of the parasite Leishmania major is controlled by endogenous CD4(+) CD25(+) regulatory T (T reg) cells. In this report, we show that despite efficient parasite clearance at secondary sites of infection, Leishmania superinfection can cause disease reactivation at the primary site. Our results strongly suggest that T reg cells, whose numbers increase in sites of reactivation, are directly responsible for such reactivation. Depletion of CD25(+) cells at the time of secondary challenge prevented disease reactivation at the site of persistent infection while strengthening the expression of immunity at the site of secondary challenge. Finally, transfer of T reg cells purified from infected mice into chronically infected mice was sufficient to trigger disease reactivation and prevent the expression of an effector memory response. Our results demonstrate that after persistence is achieved, an equilibrium between T reg cells and effector lymphocytes, which can be disturbed by superinfection, controls the efficiency of recall immune responses and disease reactivation.     

Functional MR imaging in pediatrics

Functional magnetic resonance (fMR) imaging can show neuronal structures underlying specific perceptual and cognitive processes. With the aid of fMR imaging, the development of brain functions can be followed, and deviation from the normal pattern can be established quickly. This article discusses the unique issues of fMR imaging in the pediatric population (e.g., the occurrence of a negative blood oxygenation-level dependent [BOLD] signal during visual stimulation in the age group in whom the synaptic density is the highest; in older children, when synaptic pruning has proceeded, the BOLD signal takes on the positive characteristics seen in adults). fMR imaging also suggests prospectively important applications in the diagnostic workup of children: an early diagnosis of functional deficit can reduce residual deficits to a minimum because remediation, such as specialized training, can be started at an early stage.     

Methylation-dependent gene silencing induced by interleukin 1beta via nitric oxide production

Interleukin (IL)-1beta is a pleiotropic cytokine implicated in a variety of activities, including damage of insulin-producing cells, brain injury, or neuromodulatory responses. Many of these effects are mediated by nitric oxide (NO) produced by the induction of NO synthase (iNOS) expression. We report here that IL-1beta provokes a marked repression of genes, such as fragile X mental retardation 1 (FMR1) and hypoxanthine phosphoribosyltransferase (HPRT), having a CpG island in their promoter region. This effect can be fully prevented by iNOS inhibitors and is dependent on DNA methylation. NO donors also cause FMR1 and HPRT gene silencing. NO-induced methylation of FMR1 CpG island can be reverted by demethylating agents which, in turn, produce the recovery of gene expression. The effects of IL-1beta and NO appear to be exerted through activation of DNA methyltransferase (DNA MeTase). Although exposure of the cells to NO does not increase DNA MeTase gene expression, the activity of the enzyme selectively increases when NO is applied directly on a nuclear protein extract. These findings reveal a previously unknown effect of IL-1beta and NO on gene expression, and demonstrate a novel pathway for gene silencing based on activation of DNA MeTase by NO and acute modification of CpG island methylation.     

Complement-dependent Proinflammatory Properties of the Alzheimer's Disease β-Peptide

Large numbers of neuritic plaques (NP), largely composed of a fibrillar insoluble form of the β-amyloid peptide (Aβ), are found in the hippocampus and neocortex of Alzheimer''s disease (AD) patients in association with damaged neuronal processes, increased numbers of activated astrocytes and microglia, and several proteins including the components of the proinflammatory complement system. These studies address the hypothesis that the activated complement system mediates the cellular changes that surround fibrillar Aβ deposits in NP. We report that Aβ peptides directly and independently activate the alternative complement pathway as well as the classical complement pathway; trigger the formation of covalent, ester-linked complexes of Aβ with activation products of the third complement component (C3); generate the cytokine-like C5a complement-activation fragment; and mediate formation of the proinflammatory C5b-9 membrane attack complex, in functionally active form able to insert into and permeabilize the membrane of neuronal precursor cells. These findings provide inflammation-based mechanisms to account for the presence of complement components in NP in association with damaged neurons and increased numbers of activated glial cells, and they have potential implications for the therapy of AD.