Glimepiride reduces CD14 expression and cytokine secretion from macrophages

Victoria Ingham,Alun Williams,Clive Bate

doi:10.1186/1742-2094-11-115

Victoria Ingham, Alun Williams + Show 1 more

Open Access

https://doi.org/10.1186/1742-2094-11-115

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Abstract

BackgroundActivated microglia are associated with deposits of aggregated proteins within the brains of patients with Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases. Since the cytokines secreted from activated microglia are thought to contribute to the pathogenesis of these neurodegenerative diseases, compounds that suppress cytokine production have been identified as potential therapeutic targets. CD14 is a glycosylphosphatidylinositol (GPI)- anchored protein that is part of a receptor complex that mediates microglial responses to peptides that accumulate in prion disease (PrP82-146), AD (amyloid-β (Aβ)42) and PD (α-synuclein (αSN)). As some GPI-anchored proteins are released from cells by treatment with glimepiride, a sulphonylurea used for the treatment of diabetes, the effects of glimepiride upon CD14 expression and cytokine production from cultured macrophages were studied.MethodsRAW 264 cells and microglial cells were treated with glimepiride or phosphatidylinositol (PI)-phospholipase C (PLC) and the expression of cell receptors was analysed by ELISA and immunoblot. Treated cells were subsequently incubated with Aβ42, αSN, PrP82-146 or lipopolysaccharide (LPS) and the amounts of Toll-like receptor (TLR)-4, tumour necrosis factor (TNF), interleukin (IL)-1 and IL-6 measured.ResultsGlimepiride released CD14 from RAW 264 cells and microglial cells. Pre-treatment with glimepiride significantly reduced TNF, IL-1 and IL-6 secretion from RAW 264 and microglial cells incubated with LPS, Aβ42, αSN and PrP82-146. Glimepiride also reduced the LPS, Aβ42, αSN and PrP82-146-induced translocation of TLR-4 into membrane rafts that is associated with cell activation. These effects of glimepiride were also seen after digestion of RAW 264 cells with PI-phospholipase C (PLC). In addition, the effects of glimepiride were blocked by pharmacological inhibition of GPI-PLC. The cytokine production was CD14-dependent; it was reduced in microglia from CD14 knockout mice and was blocked by antiserum to CD14.ConclusionsRAW 264 and microglial cell responses to Aβ1–42, αSN, PrP82-146 and LPS are dependent upon CD14 expression. Glimepiride induced the shedding of CD14 from cells by activation of GPI-PLC and consequently reduced cytokine production in response to Aβ42, αSN, PrP82-146 and LPS. These results suggest that glimepiride acts as a novel anti-inflammatory agent that could modify the progression of neurodegenerative diseases.

Highlights

Activated microglia are associated with deposits of aggregated proteins within the brains of patients with Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases
While multiple receptors have been reported to be involved in macrophage responses to aggregated neurotoxic proteins [20], including scavenger receptors [21] and CD40 [22], other studies implicate CD14, a protein that is highly expressed on myeloid cells including microglia [23], as a key component of the receptor complex that mediates cytokine secretion induced by fibrillar Aβ peptides [16], prion-damaged neurons [24] and lipopolysaccharide (LPS) [25,26]
Cells were pre-treated with test compounds including glimepiride, glipizide, p-chloromercuriphenylsulphonate (p-CMPS), polymyxin B or phosphatidylinositol (PI)-phospholipase C (PLC) derived from Bacillus cereus, or with antibodies to CD14 (goat polyclonal IgG anti-mouse CD14 (R&D Systems, www.rndsystems.com), cellular prion protein (PrPC) or CD55 for one hour before the addition of LPS (Sigma, www.sigmaaldrich.com), PrP82146, αSN or Aβ42

Summary

Introduction

Activated microglia are associated with deposits of aggregated proteins within the brains of patients with Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases. The deposition of aggregated proteins within the brain is a common feature of neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases These aggregates are often surrounded by activated microglial cells, the resident macrophage-like cells of the brain [1,2,3] and, in vitro aggregated forms of disease-associated peptides stimulate cytokine secretion. While multiple receptors have been reported to be involved in macrophage responses to aggregated neurotoxic proteins [20], including scavenger receptors [21] and CD40 [22], other studies implicate CD14, a protein that is highly expressed on myeloid cells including microglia [23], as a key component of the receptor complex that mediates cytokine secretion induced by fibrillar Aβ peptides [16], prion-damaged neurons [24] and lipopolysaccharide (LPS) [25,26]. Such observations suggest that either a reduction of cell-associated CD14, or an increase in soluble CD14 in extracellular fluids, can reduce cytokine secretion from macrophages

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