Filippo Rossi

Proinflammatory profile of cytokine production by human monocytes and murine microglia stimulated with β-amyloid[25–35]

Growing evidence indicates that amyloid (A beta) deposition and phagocyte activation participate in inflammatory reactions in the brain during the course of Alzheimers disease. To further investigate the effects of A beta-phagocyte interaction, we examined the production of proinflammatory (IL-1beta, IL-6), chemotactic (MIP-1alpha, IP-10) and inhibitory (IL-1Ra, IL-10 and TGFbeta1) cytokines by cultured human monocytes and mouse microglial cells upon stimulation with A beta[25-35]. Northern blot analysis and specific immunoassays demonstrated that A beta[25-35] triggers mRNA expression and release of IL-1beta, IL-1Ra and MIP-1alpha but not of IL-6, IL-10, TGFbeta1 and IP-10 from human monocytes. Similar results were obtained by examining the production of IL-1beta, IL-6 and IL-10 from mouse microglial cells in the same experimental conditions. Taken together, these data indicate that A beta-phagocyte interaction can drive a different response towards cytokine production by monocytes and microglia, with a particular proinflammatory trend, and further support a role for A beta deposition as a triggering factor of inflammatory events in Alzheimers disease.

Gamma interferon is able to enhance the oxidative metabolism of human neutrophils.

The oxidative metabolism of human neutrophils has been studied after incubation of the cells with recombinant interferon-y. Neutrophils incubated for 2-4 hours with 2-50 U/ml recombinant interferon-y undergo a higher respiratory burst measured both as Oz consumption and Oz- production when stimulated with formyl-methionyl-leucyl-phenylalanine, Concanavalin A or phorbol myristate acetate. The potentiating effect of interferon-y requires more than one hour of incubation, is optimal at 20-50 U/ml and depends on the presence of serum in the incubation medium. The interferon effect depends on new protein synthesis. Cycloheximide at doses which do not alter the respiratory response of normal cells completely prevents the potentiating effect of interferon.

Role of p75 Neurotrophin Receptor in the Neurotoxicity by β-amyloid Peptides and Synergistic Effect of Inflammatory Cytokines

The neurodegenerative changes in Alzheimers disease (AD) are elicited by the accumulation of β-amyloid peptides (Aβ), which damage neurons either directly by interacting with components of the cell surface to trigger cell death signaling or indirectly by activating astrocytes and microglia to produce inflammatory mediators. It has been recently proposed that the p75 neurotrophin receptor (p75NTR) is responsible for neuronal damage by interacting with Aβ. By using neuroblastoma cell clones lacking the expression of all neurotrophin receptors or engineered to express full-length or various truncated forms of p75NTR, we could show that p75NTR is involved in the direct signaling of cell death by Aβ via the function of its death domain. This signaling leads to the activation of caspases-8 and -3, the production of reactive oxygen intermediates and the induction of an oxidative stress. We also found that the direct and indirect (inflammatory) mechanisms of neuronal damage by Aβ could act synergistically. In fact, TNF-α and IL-1β, cytokines produced by Aβ-activated microglia, could potentiate the neurotoxic action of Aβ mediated by p75NTR signaling. Together, our results indicate that neurons expressing p75NTR, mostly if expressing also proinflammatory cytokine receptors, might be preferential targets of the cytotoxic action of Aβ in AD.

Phosphatidic acid and not diacylglycerol generated by phospholipase D is functionally linked to the activation of the NADPH oxidase by FMLP in human neutrophils

It is widely accepted that the activation of the NADPH oxidase of phagocytes is linked to the stimulation of protein kinase C by diacylglycerol formed by hydrolysis of phospholipids. The main source would be choline containing phospholipid via phospholipase D and phosphatidate phosphohydrolase. This paper presents a condition where the activation of the respiratory burst by FMLP correlates with the formation of phosphatidic acid, via phospholipase D, and not with that of diacylglycerol. In fact: 1) in neutrophils treated with propranolol, an inhibitor of phosphatidate phosphohydrolase, FMLP plus cytochalasin B induces a respiratory burst associated with a stimulation of phospholipase D, formation of phosphatidic acid and complete inhibition of that of diacylglycerol. 2) The respiratory burst by FMLP plus cytochalasin B lasts a few minutes and may be restimulated by propranolol which induces an accumulation of phosphatidic acid. 3) In neutrophils stimulated by FMLP in the absence of cytochalasin B propranolol causes an accumulation of phosphatidic acid and a marked enhancement of the respiratory burst without formation of diacylglycerol. 4) The inhibition of the formation of phosphatidic acid via phospholipase D by butanol inhibits the respiratory burst by FMLP.

Induction of Functional IL-8 Receptors by IL-4 and IL-13 in Human Monocytes

IL-8 and related Glu-Leu-Arg (ELR+) CXC chemokines are potent chemoattractants for neutrophils but not for monocytes. IL-13 and IL-4 strongly increased CXCR1 and CXCR2 chemokine receptor expression in human monocytes, macrophages, and dendritic cells. The effect was receptor- and cell type-selective, in that CCRs were not increased and no augmentation was seen in neutrophils. The effect was rapid, starting at 4 h, and concentration dependent (EC50 = 6.2 and 8.3 ng/ml for CXCR1 and CXCR2, respectively) and caused by new transcriptional activity. IL-13/IL-4-treated monocytes showed increased CXCR1 and CXCR2 membrane expression. IL-8 and related ELR+ chemokines were potent and effective chemotactic agents for IL-13/IL-4-treated monocytes, but not for untreated mononuclear phagocytes, with activity comparable to that of reference monocyte attractants, such as MCP-1. In the same cells, IL-8 also caused superoxide release. Macrophages and dendritic cells present in biopsies from Omenn’s syndrome and atopic dermatitis patients, two Th2 skewed pathologies, expressed IL-8 receptors by immunohistochemistry. These results show that IL-13 and IL-4 convert IL-8 and related ELR+ chemokines, prototypic neutrophil attractants, into monocyte chemotactic agonists, by up-regulating receptor expression. Therefore, IL-8 and related chemokines may contribute to the accumulation and positioning of mononuclear phagocytes in Th2-dominated responses.

Activation of nuclear factor-κB by β-amyloid peptides and interferon-γ in murine microglia

Abstract An increasing body of evidence suggests that amyloid- β (A β ) peptides and microglia are crucially involved in the pathogenesis of Alzheimers disease. In an effort to further elucidate the biological effects of A β towards microglia, we investigated the ability of A β peptides to activate nuclear factor (NF)- κ B in the N9 murine microglial cell line. Co-stimulation of microglia with suboptimal concentrations of A β (25–35) and 100 U/ml IFN γ resulted in the detection of a specific NF- κ B DNA-binding activity in nuclear extracts, as determined in gel mobility shift assays. This response required at least 120 min to be evident and supershift experiments revealed that the NF- κ B complex contains both RelA and p50. Accordingly, immunoblot experiments showed that amongst NF- κ B/Rel proteins, RelA and p50 are mobilized to the nucleus following microglial cell stimulation with A β (25–35) plus IFN γ . Higher concentrations of A β (25–35) were effective by themselves in inducing NF- κ B activation, both in the N9 microglial cell line and in rat primary microglia, as well as in human monocytes. For purposes of comparison, microglia were also stimulated with bacterial LPS, a known NF- κ B inducer. As expected, LPS strongly induced the formation of two NF- κ B DNA-binding activities, one of which was identified as RelA/p50. The LPS response was also more rapid, as it was already evident by 40 min and remained sustained for up to 3 h. Collectively, these findings indicate that NF- κ B activation might constitute one of the mechanisms underlying the inducible expression of κ B-dependent genes in microglia stimulated by A β peptides and IFN γ , or by LPS.

Neurotrophin p75 Receptor Is Involved in Neuronal Damage by Prion Peptide-(106–126)

In this work we have investigated the molecular basis of the neuronal damage induced by the prion peptide by searching for a surface receptor whose activation could be the first step of a cascade of events responsible for cell death. By using a human neuroblastoma cell line lacking all the neurotrophin receptors and derived clones expressing the full-length or truncated forms of the low affinity neurotrophin receptor (p75NTR), we have been able to demonstrate that the neuronal death induced by the prion protein fragment PrP-(106–126) is an active process mediated by a) the binding of the peptide to the extracellular region of p75NTR, b) the signaling function of the intracytoplasmic region of the receptor, and c) the activation of caspase-8 and the production of oxidant species.

Phagocytosis of Opsonized Yeast Induces Tumor Necrosis Factor‐α mRNA Accumulation and Protein Release by Human Polymorphonuclear Leukocytes

In this report we show that phagocytosis of yeast particles opsonized with IgG (Y‐IgG) by human polymorphonuclear cells (PMN) results in the selective induction of tumor necrosis factor (TNF‐α) messenger RNA (mRNA) and release of its mature protein. Lipopolysaccharide (LPS) was also found able to induce TNF‐α secretion by PMN, but was a less potent stimulus compared with Y‐lgG. There was no evidence of interleukin‐6 (IL‐6) gene expression in PMN after phagocytosis of Y‐lgG or in response to LPS, whereas IL‐6 mRNA expression and secretion were induced by either stimulus in monocytes. These findings demonstrate that a physiological function such as phagocytosis modulates the gene expression for a cytokine in PMN and shed new light on the understanding of the pathogenesis of the inflammatory process.

Protein kinase C phosphorylates a component of NADPH oxidase of neutrophils

NADPH oxidase Cytochrome b−245 Phosphorylation Protein kinase Neutrophil activation Respiratory burst

Mechanisms of expression of NADPH oxidase components in human cultured monocytes: role of cytokines and transcriptional regulators involved

Human blood monocytes lose their capability to produce microbicidal oxidants during culture. We report that this process is associated with decreased gp91phox, p22phox and p47phox expression, release of PU.1 and CP‐1 from gp91phox promoter, and PU.1 from p47phox promoter. However, in presence of IFN‐γ or TNF‐α, the superoxide anion (O  2– ) production, the p47phox, gp91phox and p22phox expression, and the binding of PU.1 and CP‐1 to DNA are maintained at the high levels observed in blood monocytes. To clarify the role of PU.1 in the expression of NADPH oxidase components, oligonucleotides competing for PU.1‐DNA binding were added to cultured monocytes. These oligonucleotides abrogated the maintenance of gp91phox and p22phox expression by IFN‐γ and TNF‐α, but did not inhibit the effect of these cytokines on p47phox expression and O  2– production. Our results indicate that in monocytes the IFN‐γ‐ and TNF‐α‐induced expression of gp91phox and p22phox, but not p47phox, requires the binding of PU.1 to gp91phox promoter. However, the preservation of O  2– production by IFN‐γ and TNF‐α is unrelated to their effect on gp91phox and p22phox expression.