Lucia Meda

Glial activation in Alzheimer’s disease: the role of Aβ and its associated proteins

A common feature of Alzheimers disease (AD) pathology is the abundance of reactive astrocytes and activated microglia in close proximity to neuritic plaques containing amyloid-beta protein (Abeta). The relationship between glial activation and neurodegeneration remains unclear, although several cytokines and inflammatory mediators produced by activated glia have the potential to initiate or exacerbate the progression of neuropathology. Assuming that glial activation plays a central role in the development and progression of AD, a prominent feature is to understand which stimuli drive this activation in senile plaques and to define their effects in vitro. There is a growing body of evidence to suggest that deposition of Abeta and expression of its associated molecules represent important trigger factors in glial activation leading to an inflammatory reaction in the brain. Thus, unraveling the mechanisms by which these proteins exert their effect on glial cells may provide significant insight into the pathophysiology of AD, and may lead to the identification of new strategies for AD treatment.

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.

The human astrocytoma cell line U373MG produces monocyte chemotactic protein (MCP)-1 upon stimulation with β-amyloid protein

Astrocytes associated with beta-amyloid (Abeta) accumulate in senile plaques of Alzheimers disease (AD). To investigate the biological effects of Abeta/astrocyte interaction, we examined chemokine production by the human astrocytoma cell line U373MG stimulated with Abeta peptides. Northern blot analysis and specific immunoassays demonstrate that Abeta [1-42] and Abeta [25-35] induce mRNA expression and release of monocyte chemotactic protein (MCP)-1 but not of gamma-interferon inducible protein (IP)-10 by U373MG cells. The observation that Abeta induces astrocyte production of the potent microglia chemoattractant MCP-1 contributes to understanding mechanism of damage exerted by Abeta in AD senile plaques.

β-Amyloid(25–35) induces the production of interleukin-8 from human monocytes

In an effort to unravel some of the cellular actions of beta-amyloid protein (A beta), we investigated its effects on interleukin-8 (IL-8) production from human monocytes. Supernatants harvested from cultured monocytes stimulated with the neurotoxic fragment 25-35 of beta-amyloid [A beta(25-35)] contained significant amounts of IL-8. Northern blot analysis demonstrated that A beta(25-35) also induced IL-8 mRNA accumulation. The effect of A beta(25-35) on IL-8 mRNA accumulation and secretion was not mimicked by a scrambled A beta(25-35) peptide, and was not affected by polymyxin B sulphate, which, on the other hand, almost completely abolished the effect of lipopolysaccharide. Our results uncover a new biological action of beta-amyloid: that of stimulating the production of a chemokine from monocytes.

Priming of monocyte respiratory burst by β-amyloid fragment (25–35)

Abstract In the present study we have examined the ability of the β-amyloid peptide (Aβ(25–35)) to modulate the respiratory burst activity of human monocytes in vitro. Incubation of the cells for 24 h with Aβ(25–35) as well as with Aβ(1–42) resulted in an enhanced production of reactive oxygen radicals (ROI) in response to phorbol 12-myristate 13-acetate (PMA). Such effect was additively increased by coincubation with interferon-γ (IFNγ), and was paralleled by modulation of gene and protein expression of some components of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system. Since the effects of Aβ(25–35) were also reproduced in primary rat microglia, our findings indicate that Aβ(25–35) can potentiate the ability of mononuclear phagocytes to produce ROI, and add further insights into its biological effects.

Production of IL-6 by human myoblasts stimulated with Aβ Relevance in the pathogenesis of IBM

Objective: To determine whether amyloid-β protein (Aβ) can induce the production of proinflammatory cytokines by cultured normal muscle cells. Background: Sporadic inclusion body myositis (IBM) is characterized by the presence of rimmed vacuoles and fibrillary inclusions of Aβ in muscle fibers, and often inflammatory cells. Endomysial expression of proinflammatory molecules has suggested an ongoing immune process, but the site of sensitization and the mechanisms that trigger an inflammatory reaction is unknown. Method: The authors used Northern blot analysis and specific immunoassays to study the expression and secretion in cell-free supernatants of tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6) by purified human myoblasts and C2C12 mouse skeletal muscle cells incubated with Aβ[1-42] or Aβ[25-35] peptides. Results: Nonstimulated muscle cells produced detectable IL-6, whereas secretion of IL-1β and TNFα was absent. Incubation with Aβ peptides increased IL-6 production, whereas TNFα and IL-1β levels remained undetectable. Northern blot analysis of Aβ-stimulated human myoblasts revealed an increase in IL-6 mRNA expression. Conclusions: Cultured muscle cells increase the constitutive production of IL-6 in response to local deposition of Aβ in sporadic IBM. IL-6 could be a CD8+ proliferation and differentiation agent, an autocrine proteolysis-inducing factor of damaged myotubes, and a proliferation-stimulating agent for satellite cells to replace the destroyed myofibers in IBM.

Heparan sulfate proteoglycan induces the production of NO and TNF-α by murine microglia

BackgroundA common feature of Alzheimers disease (AD) pathology is the abundance of activated microglia in neuritic plaques containing amyloid-beta protein (Aβ) and associated molecules including heparan sulfate proteoglycan (HSPG). Besides the role as pathological chaperone favouring amyloidogenesis, little is known about whether or not HSPG can induce microglial activation. Cultures of primary murine microglia were used to assess the effect of HSPG on production of proinflammatory molecules that are known to be present in neuritic plaques of AD.ResultsHSPG stimulated up-regulation of tumor necrosis factor-alpha (TNF-α), production of inducible nitric oxide synthase (iNOS) mRNA and accumulation of TNF-α protein and nitrite (NO2-) in a time- and concentration-dependent manner. The effects of HSPG were primarily due to the property of the protein core as indicated by the lack of microglial accumulation of TNF-α and NO2- in response to denaturated HSPG or heparan sulfate GAG chains (HS).ConclusionThese data demonstrate that HSPG may contribute to chronic microglial activation and neurodegeneration seen in neuritic plaques of AD.

Cultured human monocytes release proinflammatory cytokines in response to myelin basic protein

In human cultured monocytes we examined the ability of myelin basic protein (MBP) to induce the production of proinflammatory cytokines potentially involved in inflammatory demyelination. Northern blots and specific immunoassays demonstrated that monocytes incubated with optimal doses of MBP showed increased mRNA expression and release of tumor necrosis factor (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), interleukin-8 (IL-8) but not of interleukin-12/p40 (IL-12/p40). We also showed that cytokine production by MBP-stimulated monocytes was abrogated by incubation with Dexamethasone. These data suggest that interaction of mononuclear phagocytes with MBP may participate in the regulatory process of cytokine production during inflammatory demyelination and support the beneficial role of corticosteroids therapy in aberrant immune responses to the myelin sheath.