Interleukin-19 Acts as a Negative Autocrine Regulator of Activated Microglia

Activated microglia can exert either neurotoxic or neuroprotective effects, and they play pivotal roles in the pathogenesis and progression of various neurological diseases. In this study, we used cDNA microarrays to show that interleukin-19 (IL-19), an IL-10 family cytokine, is markedly upregulated in activated microglia. Furthermore, we found that microglia are the only cells in the nervous system that express the IL-19 receptor, a heterodimer of the IL-20Rα and IL-20Rβ subunits. IL-19 deficiency increased the production of such pro-inflammatory cytokines as IL-6 and tumor necrosis factor-α in activated microglia, and IL-19 treatment suppressed this effect. Moreover, in a mouse model of Alzheimer’s disease, we observed upregulation of IL-19 in affected areas in association with disease progression. Our findings demonstrate that IL-19 is an anti-inflammatory cytokine, produced by activated microglia, that acts negatively on microglia in an autocrine manner. Thus, microglia may self-limit their inflammatory response by producing the negative regulator IL-19.     

Norepinephrine Modulates the Motility of Resting and Activated Microglia via Different Adrenergic Receptors

Microglia, the resident immune cells of the central nervous system (CNS), monitor the brain for disturbances of tissue homeostasis by constantly moving their fine processes. Microglia respond to tissue damage through activation of ATP/ADP receptors followed by directional process extension to the damaged area. A common feature of several neurodegenerative diseases is the loss of norepinephrine, which might contribute to the associated neuroinflammation. We carried out a high resolution analysis of the effects of norepinephrine (NE) on microglial process dynamics in acute brain slices from mice that exhibit microglia-specific enhanced green fluorescent protein expression. Bath application of NE to the slices resulted in significant process retraction in microglia. Analysis of adrenergic receptor expression with quantitative PCR indicated that resting microglia primarily express β₂ receptors but switch expression to α_2A receptors under proinflammatory conditions modeled by LPS treatment. Despite the differential receptor expression, NE caused process retraction in both resting and LPS-activated microglia cultured in the gelatinous substrate Matrigel in vitro. The use of subtype-selective receptor agonists and antagonists confirmed the involvement of β₂ receptors in mediating microglial process dynamics in resting cells and α_2A receptors in activated cells. Co-application of NE with ATP to resting microglia blocked the ATP-induced process extension and migration in isolated microglia, and β₂ receptor antagonists prolonged ATP effects in brain slice tissues, suggesting the presence of cross-talk between adrenergic and purinergic signaling in microglia. These data show that the neurotransmitter NE can modulate microglial motility, which could affect microglial functions in pathogenic situations of either elevated or reduced NE levels.     

The Effect of Annexin A1 as a Potential New Therapeutic Target on Neuronal Damage by Activated Microglia

Brain disease is known to cause irrevocable and fatal loss of biological function once damaged. One of various causes of its development is damage to neuron cells caused by hyperactivated microglia, which function as immune cells in brain. Among the genes expressed in microglia stimulated by various antigens, annexin A1 (ANXA1) is expressed in the early phase of the inflammatory response and plays an important role in controlling the immune response. In this study, we assessed whether ANXA1 can be a therapeutic target gene for the initial reduction of the immune response induced by microglia to minimize neuronal damage. To address this, mouse-origin microglial cells were stimulated to mimic an immune response by lipopolysaccharide (LPS) treatment. The LPS treatment caused activation of ANXA1 gene and expression of inflammatory cytokines. To assess the biological function in microglia by the downregulation of ANXA1 gene, cells were treated with short hairpin RNA-ANXA1. Downregulated ANXA1 affected the function of mitochondria in the microglia and showed reduced neuronal damage when compared to the control group in the co-culture system. Taken together, our results showed that ANXA1 could be used as a potential therapeutic target for inflammation-related neurodegenerative diseases.     

Evidence Group I mGluR Drugs Modulate the Activation Profile of Lipopolysaccharide-Exposed Microglia in Culture

Metabotropic glutamate receptors (mGluRs) may play a role in modulating microglial activation, but group I mGluRs have received little attention. This study aimed to investigate the effects of group I mGluR selective ligands, (S)-3,5-dihydroxyphenylglycine ((S)-3,5-DHPG) and (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA), in lipopolysaccharide (LPS; 50 ng/ml)-activated rat microglial cultures. (S)-3,5-DHPG (150 μM) significantly reduced (approximately 20–60%) the LPS-mediated production of nitrite (NO₂ ⁻), tumour necrosis factor alpha (TNF-α), and l-glutamate (Glu) at 24 and 72 h. Image analysis revealed increases in both cell area and number, with larger amoeboid microglia (with retracted processes) formed following 2 h LPS exposure. This cellular population was absent after addition of (S)-3,5-DHPG, an effect antagonised by AIDA, and a concomitant reduction in cell area was also found. Taken together, these biochemical and morphological observations suggest that (S)-3,5-DHPG reduces microglial activation, indicating a role for group I mGluRs in modulating microglial function.     

Lauric Acid Alleviates Neuroinflammatory Responses by Activated Microglia: Involvement of the GPR40-Dependent Pathway

In several neurodegenerative diseases such as Alzheimer’s disease (AD), microglia are hyperactivated and release nitric oxide (NO) and proinflammatory cytokines, resulting its neuropathology. Mounting evidence indicates that dietary supplementation with coconut oil (CNO) reduces the cognitive deficits associated with AD; however, the precise mechanism(s) underlying the beneficial effect of CNO are unknown. In the present study, we examined the effects of lauric acid (LA), a major constituent of CNO, on microglia activated experimentally by lipopolysaccharide (LPS), using primary cultured rat microglia and the mouse microglial cell line, BV-2. LA attenuated LPS-stimulated NO production and the expression of inducible NO synthase protein without affecting cell viability. In addition, LA suppressed LPS-induced reactive oxygen species and proinflammatory cytokine production, as well as phosphorylation of p38-mitogen activated protein kinase and c-Jun N-terminal kinase. LA-induced suppression of NO production was partially but significantly reversed in the presence of GW1100, an antagonist of G protein-coupled receptor (GPR) 40, which is an LA receptor on the plasma membrane. LA also decreased LPS-induced phagocytosis, which was completely reversed by co-treatment with GW1100. Moreover, LA alleviated amyloid-β-induced enhancement of phagocytosis. These results suggest that attenuation of microglial activation by LA may occur via the GPR40-dependent pathway. Such effects of LA may reduce glial activation and the subsequent neuronal damage in AD patients who consume CNO.     

Predominant Functional Expression of Kv1.3 by Activated Microglia of the Hippocampus after Status epilepticus

Background

Growing evidence indicates that the functional state of microglial cells differs according to the pathological conditions that trigger their activation. In particular, activated microglial cells can express sets of Kv subunits which sustain delayed rectifying potassium currents (Kdr) and modulate differently microglia proliferation and ability to release mediators. We recently reported that hippocampal microglia is in a particular activation state after a status epilepticus (SE) and the present study aimed at identifying which of the Kv channels are functionally expressed by microglia in this model.

Methodology/Principal Findings

SE was induced by systemic injection of kainate in CX3CR1^eGFP/+ mice and whole cell recordings of fluorescent microglia were performed in acute hippocampal slices prepared 48 h after SE. Microglia expressed Kdr currents which were characterized by a potential of half-maximal activation near −25 mV, prominent steady-state and cumulative inactivations. Kdr currents were almost abolished by the broad spectrum antagonist 4-Aminopyridine (1 mM). In contrast, tetraethylammonium (TEA) at a concentration of 1 mM, known to block Kv3.1, Kv1.1 and 1.2 subunits, only weakly reduced Kdr currents. However, at a concentration of 5 mM which should also affect Kv1.3 and 1.6, TEA inhibited about 30% of the Kdr conductance. Alpha-dendrotoxin, which selectively inhibits Kv1.1, 1.2 and 1.6, reduced only weakly Kdr currents, indicating that channels formed by homomeric assemblies of these subunits are not important contributors of Kdr currents. Finally, agitoxin-2 and margatoxin strongly inhibited the current.

Conclusions/Significance

These results indicate that Kv1.3 containing channels predominantly determined Kdr currents in activated microglia after SE.     

The Multifaceted Associations of Hepatobiliary Disease and Diabetes

ObjectiveTo investigate the association of diabetes and hepatobiliary disease.MethodsWe performed a MEDLINE search of the English-language literature published between January 1980 and January 2007 for studies in which diabetes was associated with liver diseases.ResultsThrough its association with the insulin resistance syndrome, type 2 diabetes is associated with nonalcoholic fatty liver disease, nonalcoholic steatohepatitis (NASH), NASH-cirrhosis, and NASH-cirrhosis-related hepatocellular carcinoma. Because of the association with insulin resistance, insulin sensitizers may slow or even arrest the progress of these diseases. Type 2 but not type 1 diabetes is associated with hepatitis C virus but not hepatitis B viral infection. This association is likely due to hepatitis C viral infection of the pancreatic β-cells. Early detection and antiviral therapy can decelerate the development of diabetes. Type 1 diabetes is associated with hemochromatosis and autoimmune hepatitis. Because of the presence of autonomic neuropathy, cholelithiasis but not cholecystitis is more common in patients with diabetes than in the general population. Therefore, asymptomatic cholelithiasis in patients with diabetes no longer warrants a cholecystectomy. In patients with advanced liver disease of any cause, insulin resistance and diabetes have an increased frequency of occurrence and can be reversed with liver transplantation. Rarely, medications used to treat type 2 diabetes have been associated with drug-induced hepatitis.ConclusionThe prevalence of hepatobiliary diseases is increased in patients with diabetes. Early recognition and treatment of these conditions can prevent, stabilize, or even reverse hepatic damage and prevent the development of hepatic carcinoma and liver failure. (Endocr Pract. 2007;13:300-312)     

小胶质细胞在神经病理性疼痛中的作用

神经病理性疼痛对患者的生理和心理健康都有着极大的影响。近几年来的研究表明,外周神经炎症或损伤激活的小胶质细胞通过表达及释放一系列介质分子,在神经病理性疼痛的产生和传递通路中发挥重要的调制作用。激活的小胶质细胞与神经元之间信息交互传递从而影响痛敏行为的这一崭新模式极大地推进了人们对于疼痛的理解。同时也为以小胶质细胞作为靶点,开辟镇痛药物治疗的新方法提供了理论依据。     

Neuroprotective Effect of 6-Paradol in Focal Cerebral Ischemia Involves the Attenuation of Neuroinflammatory Responses in Activated Microglia

Paradols are non-pungent and biotransformed metabolites of shogaols and reduce inflammatory responses as well as oxidative stress as shogaols. Recently, shogaol has been noted to possess therapeutic potential against several central nervous system (CNS) disorders, including cerebral ischemia, by reducing neuroinflammation in microglia. Therefore, paradol could be used to improve neuroinflammation-associated CNS disorders. Here, we synthesized paradol derivatives (2- to 10-paradols). Through the initial screening for anti-inflammatory activities using lipopolysaccharide (LPS)-stimulated BV2 microglia, 6-paradol was chosen to be the most effective compound without cytotoxicity. Pretreatment with 6-paradol reduced neuroinflammatory responses in LPS-stimulated BV2 microglia by a concentration-dependent manner, which includes reduced NO production by inhibiting iNOS upregulation and lowered secretion of proinflammatory cytokines (IL-6 and TNF-α). To pursue whether the beneficial in vitro effects of 6-paradol leads towards in vivo therapeutic effects on transient focal cerebral ischemia characterized by neuroinflammation, we employed middle cerebral artery occlusion (MCAO)/reperfusion (M/R). Administration of 6-paradol immediately after reperfusion significantly reduced brain damage in M/R-challenged mice as assessed by brain infarction, neurological deficit, and neural cell survival and death. Furthermore, as observed in cultured microglia, 6-paradol administration markedly reduced neuroinflammation in M/R-challenged brains by attenuating microglial activation and reducing the number of cells expressing iNOS and TNF-α, both of which are known to be produced in microglia following M/R challenge. Collectively, this study provides evidences that 6-paradol effectively protects brain after cerebral ischemia, likely by attenuating neuroinflammation in microglia, suggesting it as a potential therapeutic agent to treat cerebral ischemia.     

Multifaceted mammalian transcriptome

Despite surprisingly a small number of protein-coding gene in mammalian genomes, a large variety of different RNAs is being produced. These RNAs are amazingly different in their number, size, cell localization, and mechanism of actions. Although new classes of short RNAs (sRNAs) are being continuously discovered, it is not yet obvious how many of the sRNAs are originated. Altogether, the research in the recent few years has identified an unexpectedly rich variety of mechanisms by which noncoding RNAs act, suggesting that we have identified probably only few of the many potential functional mechanism and more investigation will be needed to comprehensively understand the complex nature and biology of mammalian RNAome. Here, we focus on various aspects of the diversity of the biological role of these nonprotein-coding RNAs (ncRNAs), with emphasis on functional mechanisms recently elucidated.     

The Multifaceted Benefits of Protein Co-expression in Escherichia coli

We report here that the expression of protein complexes in vivo in Escherichia coli can be more convenient than traditional reconstitution experiments in vitro. In particular, we show that the poor solubility of Escherichia coli DNA polymerase III ε subunit (featuring 3’-5’ exonuclease activity) is highly improved when the same protein is co-expressed with the α and θ subunits (featuring DNA polymerase activity and stabilizing ε, respectively). We also show that protein co-expression in E. coli can be used to efficiently test the competence of subunits from different bacterial species to associate in a functional protein complex. We indeed show that the α subunit of Deinococcus radiodurans DNA polymerase III can be co-expressed in vivo with the ε subunit of E. coli. In addition, we report on the use of protein co-expression to modulate mutation frequency in E. coli. By expressing the wild-type ε subunit under the control of the araBAD promoter (arabinose-inducible), and co-expressing the mutagenic D12A variant of the same protein, under the control of the lac promoter (inducible by isopropyl-thio-β-D-galactopyranoside, IPTG), we were able to alter the E. coli mutation frequency using appropriate concentrations of the inducers arabinose and IPTG. Finally, we discuss recent advances and future challenges of protein co-expression in E. coli.     

The Multifaceted Roles of TAM Receptors during Viral Infection

■yro3, ■xl, and ■ertk(TAM) receptors play multiple roles in a myriad of physiological and pathological processes,varying from promoting the phagocytic clearance of apoptotic cells, sustaining the immune and inflammatory homeostasis,maintaining the blood-brain barrier(BBB) integrity and central nervous system(CNS) homeostasis, to mediating cancer malignancy and chemoresistance. Growth arrest-specific protein 6(Gas6) and protein S(Pros1) are the two ligands that activate TAM receptors. Recently, TAM receptors have been reported to mediate cell entry and infection of multitudinous enveloped viruses in a manner called apoptotic mimicry. Moreover, TAM receptors are revitalized during viral entry and infection, which sequesters innate immune and inflammatory responses, facilitating viral replication and immune evasion.However, accumulating evidence have now proposed that TAM receptors are not required for the infection of these viruses in vivo. In addition, TAM receptors protect mice against the CNS infection of neuroinvasive viruses and relieve the brain lesions during encephalitis. These protective effects are achieved through maintaining BBB integrity, attenuating proinflammatory cytokine production, and promoting neural cell survival. TAM receptors also regulate the programmed cell death modes of virus-infected cells, which have profound impacts on the pathogenesis and outcome of infection. Here, we systematically review the functionalities and underlying mechanisms of TAM receptors and propose the potential application of TAM agonists to prevent severe viral encephalitis.     

Serotonin Acts as a Radical Scavenger and Is Oxidized to a Dimer During the Respiratory Burst of Activated Microglia

Abstract: Serotonin (5-HT) is known to be readily oxidized and to act as a scavenger of reactive oxygen species produced, e.g., in the presence of peroxidase and H₂O₂ or during the respiratory burst of phagocytes. One major oxidation product formed under these conditions, the 5-HT dimer 5,5'-dihydroxy-4,4'-bitryptamine (DHBT), was suggested to have neurotoxic properties and to contribute to neuronal damage in neurodegenerative disorders. It is shown in the present study that the luminol-enhanced chemiluminescence signal measured after stimulation of the respiratory burst activity of cultivated rat microglial cells by the addition of phorbol 12-myristate 13-acetate is suppressed by 5-HT in a dose-dependent manner. During this process, 5-HT is oxidized to DHBT. Neither the intraventricular injection of DHBT nor the addition of DHBT to cultured astrocytes, neurons, or PC-12 cells was found to cause measurable cytotoxic effects. It is concluded that extracellular 5-HT locally released from platelets and 5-HT nerve endings at sites of brain damage or inflammation, through its suppressant effect on the release of reactive oxygen species during the respiratory burst of activated microglia, may contribute to attenuate secondary tissue damage in the CNS.