Norepinephrine promotes microglia to uptake and degrade amyloid beta peptide through upregulation of mouse formyl peptide receptor 2 and induction of insulin-degrading enzyme.

Locus ceruleus (LC) is the main subcortical site of norepinephrine synthesis. In Alzheimer's disease (AD) patients and rodent models, degeneration of LC neurons and reduced levels of norepinephrine in LC projection areas are significantly correlated with the increase in amyloid plaques, neurofibrillary tangles, and severity of dementia. Activated microglia play a pivotal role in the progression of AD by either clearing amyloid beta peptide (Abeta) deposits through uptake of Abeta or releasing cytotoxic substances and proinflammatory cytokines. Here, we investigated the effect of norepinephrine on Abeta uptake and clearance by murine microglia and explored the underlying mechanisms. We found that murine microglia cell line N9 and primary microglia expressed beta(2) adrenergic receptor (AR) but not beta(1) and beta(3)AR. Norepinephrine and isoproterenol upregulated the expression of Abeta receptor mFPR2, a mouse homolog of human formyl peptide receptor FPR2, through activation of beta(2)AR in microglia. Norepinephrine also induced mFPR2 expression in mouse brain. Activation of beta(2)AR in microglia promoted Abeta(42) uptake through upregulation of mFPR2 and enhanced spontaneous cell migration but had no effect on cell migration in response to mFPR2 agonists. Furthermore, activation of beta(2)AR on microglia induced the expression of insulin-degrading enzyme and increased the degradation of Abeta(42). Mechanistic studies showed that isoproterenol induced mFPR2 expression through ERK1/2-NF-kappaB and p38-NF-kappaB signaling pathways. These findings suggest that noradrenergic innervation from LC is needed to maintain adequate Abeta uptake and clearance by microglia, and norepinephrine is a link between neuron and microglia to orchestrate the host response to Abeta in AD.

Resveratrol differentially modulates inflammatory responses of microglia and astrocytes.

BACKGROUND: Inflammatory responses in the CNS mediated by activated glial cells play an important role in host-defense but are also involved in the development of neurodegenerative diseases. Resveratrol is a natural polyphenolic compound that has cardioprotective, anticancer and anti-inflammatory properties. We investigated the capacity of resveratrol to protect microglia and astrocyte from inflammatory insults and explored mechanisms underlying different inhibitory effects of resveratrol on microglia and astrocytes. METHODS: A murine microglia cell line (N9), primary microglia, or astrocytes were stimulated by LPS with or without different concentrations of resveratrol. The expression and release of proinflammatory cytokines (TNF-alpha, IL-1beta, IL-6, MCP-1) and iNOS/NO by the cells were measured by PCR/real-time PCR and ELISA, respectively. The phosphorylation of the MAP kinase superfamily was analyzed by western blotting, and activation of NF-kappaB and AP-1 was measured by luciferase reporter assay and/or electrophoretic mobility shift assay. RESULTS: We found that LPS stimulated the expression of TNF-alpha, IL-1beta, IL-6, MCP-1 and iNOS in murine microglia and astrocytes in which MAP kinases, NF-kappaB and AP-1 were differentially involved. Resveratrol inhibited LPS-induced expression and release of TNF-alpha, IL-6, MCP-1, and iNOS/NO in both cell types with more potency in microglia, and inhibited LPS-induced expression of IL-1beta in microglia but not astrocytes. Resveratrol had no effect on LPS-stimulated phosphorylation of ERK1/2 and p38 in microglia and astrocytes, but slightly inhibited LPS-stimulated phosphorylation of JNK in astrocytes. Resveratrol inhibited LPS-induced NF-kappaB activation in both cell types, but inhibited AP-1 activation only in microglia. CONCLUSION: These results suggest that murine microglia and astrocytes produce proinflammatory cytokines and NO in response to LPS in a similar pattern with some differences in signaling molecules involved, and further suggest that resveratrol exerts anti-inflammatory effects in microglia and astrocytes by inhibiting different proinflammatory cytokines and key signaling molecules.

Sodium oligomannate therapeutically remodels gut microbiota and suppresses gut bacterial amino acids-shaped neuroinflammation to inhibit Alzheimer's disease progression.

Recently, increasing evidence has suggested the association between gut dysbiosis and Alzheimer's disease (AD) progression, yet the role of gut microbiota in AD pathogenesis remains obscure. Herein, we provide a potential mechanistic link between gut microbiota dysbiosis and neuroinflammation in AD progression. Using AD mouse models, we discovered that, during AD progression, the alteration of gut microbiota composition leads to the peripheral accumulation of phenylalanine and isoleucine, which stimulates the differentiation and proliferation of pro-inflammatory T helper 1 (Th1) cells. The brain-infiltrated peripheral Th1 immune cells are associated with the M1 microglia activation, contributing to AD-associated neuroinflammation. Importantly, the elevation of phenylalanine and isoleucine concentrations and the increase of Th1 cell frequency in the blood were also observed in two small independent cohorts of patients with mild cognitive impairment (MCI) due to AD. Furthermore, GV-971, a sodium oligomannate that has demonstrated solid and consistent cognition improvement in a phase 3 clinical trial in China, suppresses gut dysbiosis and the associated phenylalanine/isoleucine accumulation, harnesses neuroinflammation and reverses the cognition impairment. Together, our findings highlight the role of gut dysbiosis-promoted neuroinflammation in AD progression and suggest a novel strategy for AD therapy by remodelling the gut microbiota.

RNA interference as a novel and powerful tool in immunopharmacological research.

RNA interference (RNAi), as an evolutionarily conserved mechanism for silencing gene expression, is realized through the actions of both small interference RNA (siRNA) and microRNA. Since its discovery, siRNA has been rapidly deployed not only for the elucidation of gene function, but also for identification of drug targets and as a powerful therapeutic approach for a variety of diseases. In this review, we briefly introduce the mechanisms of RNAi, methods of siRNA design and delivery, and summarized recent researches on the therapeutic potential of RNAi for immune diseases.

Biologically active peptides interacting with the G protein-coupled formylpeptide receptor.

Leucocytes accumulate at sites of inflammation and microbial infection in response to locally produced chemotactic factors. N-formylpeptides produced by Gram negative bacteria were among the first chemotactic factors structurally defined which signal through G protein-coupled formylpeptide receptor (FPR) and FPR-like 1 (FPRL1) expressed by phagocytic leukocytes in human and in mouse homogogues mFPR and mFPR2. During the past few years, a number of pathogen- and host-derived agonists/antagonists for FPR, FPRL1 and another FPR variant FPR-like 2 (FPRL2) have been identified. Activation of formylpeptide receptors (FPRs) in phagocytic leukocytes by agonists results in increased cell chemotaxis, phagocytosis, and release of pro-inflammatory mediators. Peptide agonists for FPRs have also been shown to possess immune adjuvant activity when injected in mice. In addition, FPR aberrantly expressed on highly malignant human glioblastoma cells promotes tumor cell migration, proliferation and production of vascular endothelial growth factor in response to agonists released by necrotic tumor cells. Therefore, formylpeptide receptor ligands, by interacting with FPRs, play important roles in host defense and in the rapid progression of human glioblastoma.

The immunopharmacological properties of transforming growth factor beta.

Transforming growth factor-beta (TGF-beta) family members are multifunctional molecules, which play pivotal roles in regulating cell proliferation, differentiation, migration, development, tissue remodeling and repair. These events are closely associated with host immune responses and inflammation. Despite some controversies on their function in controlling dendritic and T regulatory cell development and activity, the importance of TGF-betas in the progress of autoimmunity and inflammatory diseases has been well appreciated and new aspects of their contribution continue to be recognized. Since one of the major biological properties of TGF-betas is its capacity to potently suppress immune responses, they are considered as candidates for the development of therapeutic agents to fend off undesirable damage associated with immune and inflammatory conditions.

Chemoattractants and receptors in Alzheimer's disease.

Chemoattractants, including classical chemoattractants and chemokines, are mediators of leukocyte trafficking in physiological immunosurveillance as well as recruitment of leukocyte to the sites of inflammation and injury. Besides their well-established role in the immune system, recent researches have demonstrated that chemoattractants and their receptors are also involved in brain development and in the maintenance of normal brain homeostasis. Evidence is emerging that chemoattractants and their receptors play important roles in neuroinflammation, neuronal death and hence neurodegenerative diseases. In this review, we summarize recent progress regarding the involvement of chemoattractants and their receptors in Alzheimer's disease and their potential as therapeutic targets.

Amyloid deposition and inflammation in APPswe/PS1dE9 mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by amyloid plaques and neurofibrillary tangles associated with chronic inflammation. APPswe/PS1dE9 is an AD mouse model bearing mutant transgenes of amyloid precursor protein and presenilin-1. Amyloid deposition is present in this mouse model at early stage of life. However, the progression of inflammation and its relationship with amyloid deposition have not been characterized. Here we showed that amyloid plaques were present at 4 months of age and increased with age. CD11b-positive microglia clusters appeared in hippocampus and neocortex at 4 months of age and increased with age. Clustered glial fibrillary acidic protein (GFAP)-positive astrocytes were observed in hippocampus and cortex after 6 months of age and increased with age. Double staining with CD11b/GFAP antibody and thioflavin S showed clustered microglia and astrocytes were in close association with amyloid plaques. Expression of TNF-alpha was detected at 8 months of age, while IL-1 beta, IL-6 and MCP-1 at 10 months. These cytokines increased with age. Double immunostaining of cell specific marker and cytokine indicated TNF-alpha, IL-1 beta, IL-6 and MCP-1 were expressed by activated microglia and a small part of activated astrocytes. MCP-1 was also expressed by neurons, which support recent finding that MCP-1 expression was increased in neurons of AD patient. These results demonstrate amyloid plaques and its associated inflammatory response developed at early stage of life and progressively increased with age, both activated glia and neurons are involved in chronic inflammation in AD. APPswe/PS1dE9 model provides a mean for studying the mechanisms and novel therapeutics for AD.

The green tea polyphenol (-)-epigallocatechin-3-gallate inhibits leukocyte activation by bacterial formylpeptide through the receptor FPR.

Although green tea polyphenol catechin is considered as a potential anti-inflammatory agent, its effect on bacterial component-induced inflammation has been poorly investigated. We examined the capacity of epigallocatechin gallate (EGCG) to regulate leukocyte responses to bacterial chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLF), which is recognized by a human G protein-coupled receptor FPR on phagocytic leukocytes. Pretreatment of human monocytic cells or FPR-transfected rat basophilic leukemia cells (ETFR cells) with EGCG significantly inhibited fMLF-induced chemotaxis. Intraperitoneal administration of EGCG in mice suppressed fMLF-induced leukocyte infiltration into the air pouch created in the skin. Mechanistic studies revealed that EGCG dose-dependently suppressed fMLF-induced calcium flux in monocytic cells and ETFR cells. fMLF-induced ETFR cell migration was significantly inhibited by a specific MEK1/2 inhibitor, PD98059, which was associated with reduction in fMLF-induced ERK1/2 phosphorylation. These results suggest that EGCG inhibits FPR-mediated leukocyte activation thus is a promising anti-inflammatory compound.