CNR - Institute of Neuroscience CNR
Institute of Neuroscience
 

Project

Cell-to-cell signalling in brain

Background

Resident microglia are CNS immune effector cells, which are normally present in the brain parenchima in a resting state and are characterized by the ability to promptly respond to any alterations of the microenviroment. Under pathological conditions, they change their morphology, up-regulate a number of surface molecules and acquire the features of cytotoxic, phagocytic cells. A significative microglia activation is present in neurodegenerative and neuroinflammatory disorders and factors released by these cells are belived to contribute to the demyelination and progressive axonal loss. However, activation of microglial cells is not necessarily detrimental to the CNS. These cells can, in fact, counteract the brain lesions by providing neurotrophic or immunosuppressive factors. Recent studies indicate that microglial cells .can even promote neurogenesis, by inducing neuronal and oligodendroglial differentiation from adult neural precursor cells. Identifying the key signals governing the interactions between microglial cells and their surroundings is of paramount importance for understanding both the normal and pathological functioning of the nervous system. Calcium-mediated intercellular communication is a mechanism by means of which astrocytes communicate with each other and modulate the activity of adjacent cells, including neurons and oligodendrocytes. Few years ago we provided evidence that microglial cells can be involved in this calcium-mediated communication network. By analyzing calcium dynamics in Fura 2-loaded co-coltures of astrocytes and microglia we found that increases in [Ca2+]i in astrocytes induce the release of ATP, which is in turn responsible for triggering a delayed [Ca2+]i response in microglial cells. (Verderio and Matteoli, J Immunol, 2001). This ATP-mediated mechanism of intercellular communication between astrocytes and microglia may be involved in controlling the number and the function of microglial cells under pathophysiological CNS conditions.

P2X7-induced microvesicle shedding from glial cells

To characterize atrocyte-to-microglia communication pathway, we studied the mechanisms of ATP release in primary astrocytes and demonstrated the existence of a regulated non-lytic pathway of ATP secretion in these cells (Coco et al, JBC 2003). We then focused on the functional consequences that P2X7 activation induces in microglial cells and demonstrated that astrocyte-derived ATP induces the formation and shedding of microvesicles (MVs) from the plasmamembrane. These MVs store and release IL1-beta, a critical cytokine in neuroiflammatory as well in neurodegenerative disorders (Bianco et al, J Immunol 2005).

 

More recently we have characterized the molecular mechanisms which mediate MV shedding downstream the activation of the P2X7 receptor, and performed a morphological and biochemical characterization of MVs, which represent a population of extracellular vesicles distinct from exosomes. Upon activation of the P2X7 receptor, MV shedding is associated with rapid activation of acid sphingomyelinase, which translocates to plasma membrane outer leaflet.

Activation of the enzyme downstream P2X7 receptor is necessary for MV shedding and IL-1beta release, given both processes are markedly reduced by inhibition of acid sphingomyelinase, and completely blocked in glial cultures from acid sphingomyelinase knock-out mice (Bianco et al, EMBO J 2009). MVs released from microglia cells demand, however, further characterization as they represent new, still unexplored, organelles potentially contributing to the complex web of interactions among microglia and the other brain cells, especially during inflammation or neurodegeneration. At inflammatory lesions, where ATP accumulates extracellularly, MVs released from reactive microglia could, indeed, mediate cell-to-cell transfer of proteins, lipid components or mRNAs/microRNAs as well as influence neuronal transmission. In this respect, proteomic analysis and microRNA profiling of MVs released from resting and reactive microglia will allow to clarify whether MVs reflect the activation state of microglial cells from which they originate. One of the most relevant aspects we would like to evaluate is the possibility that MV amount may increase in diseases characterized by microgliosis, reflecting the development of the inflammatory plaque, in neuroinflammatory diseases, or progressive neurodegeneration.

Prospects for the future

To verify the existence of glial MVs in vivo.

To characterize the protein/lipid composition and mRNA/microRNA content of shed MVs with the goal to identify components involved in intercellular signalling.

To evaluate whether glial MVs influence neuronal responsiveness.

Publications

  • Bianco F, Perrotta C, Novellino L, Francolini M, Riganti L, Menna E, Saglietti L, Schuchman EH, Furlan R, Clementi E, Matteoli M, Verderio C (2009) Acid sphingomyelinase activity triggers microparticle release from glial cells. EMBO J. 28:1043-54.
  • Schenk U, Westendorf AM, Radaelli E, Casati A, Ferro M, Fumagalli M, Verderio C, Buer J, Scanziani E, Grassi F (2008) Purinergic control of T cell activation by ATP released through pannexin-1 hemichannels. 1:ra6.
  • Bianco F, Pravettoni E, Colombo A, Schenk U, Möller T, Matteoli M, Verderio C (2005) Astrocyte-derived ATP induces vesicle shedding and IL-1 beta release from microglia. J. Immunol. 174:7268-77.
  • Coco S, Calegari F, Pravettoni E, Pozzi D, Taverna E, Rosa P, Matteoli M, Verderio C (2003) Storage and release of ATP from astrocytes in culture. J. Biol. Chem. 278:1354-62.
  • Verderio C, Matteoli M (2001) ATP mediates calcium signaling between astrocytes and microglial cells: modulation by IFN-gamma. J. Immunol. 166:6383-91.

Grants

European Community Integrated Project (EUSynapse) 2005-2009

FISM 2003/R35 (2004-2006)

FISM 2007/R/20 (2008-2010)

Fondazione Cariplo, Project 2004.1419 (2005-2007)

Fondazione Cariplo, Project 2006.0882 (2007-2008)

Italian Ministry of University and Research (PRIN 2005)

Telethon Italia, GGP07032 (2007-2008)

Collaborations

  • M. P. Abbracchio, Department of Pharmacological Sicences, Università degli Studi di Milano, Milan, Italy.
  • F. Di Virgilio, Dipartimento di Medicina Sperimentale e Diagnostica, Ferrara, Italy.
  • Roberto Furlan, Clinical Neuroimmunology Unit, DIBIT, San Raffaele Scientific Institute, Milano, Italy.
  • E. Clementi, Department of Preclinical Science, LITA-Vialba University of Milano, Milano, Italy.
  • A. Urbani, European Centre for Brain Research, Fondazione Santa Lucia, Roma.
  • F. Grassi, Institute for Research in Biomedicine, Bellinzona, Switzerland.

 

PI photo

Claudia Verderio

Contact information

email  E-mail

email  +39 02 5031 7097

Participating staff
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