Acid sphingomyelinase actively triggers microparticle release from glia cells

CNR Institute of Neuroscience and Department of Medical Pharmacology, University of Milano, Milano, Italy.
The EMBO Journal (Impact Factor: 10.43). 04/2009; 28(8):1043-54. DOI: 10.1038/emboj.2009.45
Source: PubMed


We have earlier shown that microglia, the immune cells of the CNS, release microparticles from cell plasma membrane after ATP stimulation. These vesicles contain and release IL-1beta, a crucial cytokine in CNS inflammatory events. In this study, we show that microparticles are also released by astrocytes and we get insights into the mechanism of their shedding. We show that, on activation of the ATP receptor P2X7, microparticle shedding is associated with rapid activation of acid sphingomyelinase, which moves to plasma membrane outer leaflet. ATP-induced shedding and IL-1beta release are markedly reduced by the inhibition of acid sphingomyelinase, and completely blocked in glial cultures from acid sphingomyelinase knockout mice. We also show that p38 MAPK cascade is relevant for the whole process, as specific kinase inhibitors strongly reduce acid sphingomyelinase activation, microparticle shedding and IL-1beta release. Our results represent the first demonstration that activation of acid sphingomyelinase is necessary and sufficient for microparticle release from glial cells and define key molecular effectors of microparticle formation and IL-1beta release, thus, opening new strategies for the treatment of neuroinflammatory diseases.

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Available from: Roberto Furlan, Oct 07, 2015
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    • "Microparticles containing ␤-actin are released from vascular endothelial cells stimulated by inflammatory mediators [29] [30] [31] [32]. However, reported released vesicles and microparticles are generally much smaller in size than the cofilin rods seen here in AD brain [29] [30]. Nevertheless, these mechanisms could point to cofilin rods/aggregates as potential markers of microglial activation and/or inflammation. "
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    • "It has been suggested that these micMP may be a rapid and specific way for the brain to relay its immune status to not only its own resident microglial population, but also to the systemic circulation (Bianco et al., 2009). MicMP and astrocytic MP are frequently found to contain IL-1b and have been shown to release it upon stimulation by ATP (Bianco et al., 2009). Since ATP is often associated with neuroinflammation , it is therefore reasonable to assume that the release of ATP from damaged neurons may be a way of rapidly activating microglia and opening MP pores for swift dissemination of IL-1b and other proinflammatory cytokines. "
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    • "The real-time temporal kinetics of microparticle production has not before been studied in neutrophils. Static measurements of microparticle number have been made using aliquots of cerebral vascular endothelial cell line supernatant taken and tested by flow cytometry29 or by spectrophotometric analysis of the supernatants of adherent glial cells stimulated with an ATP mimetic30. During glial cell culture, stimulation with ATP induced a plateau of microparticle production after 20 minutes, and with time-lapse microscopy, microparticle shedding could be observed (but not quantified) 1–2 minutes after stimulation30. "
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