Janus-faced microglia: beneficial and detrimental consequences of microglial phagocytosis
- 1Achucarro—Basque Center for Neuroscience, Zamudio, Spain
- 2Department of Neuroscience, University of the Basque Country EHU/UPV, Leioa, Spain
- 3Ikerbasque—Basque Foundation for Science, Bilbao, Spain
- 4Neural Reconstruction Group, Institute of Reconstructive Neurobiology, University of Bonn, Bonn, Germany
Microglia are the resident brain macrophages and they have been traditionally studied as orchestrators of the brain inflammatory response during infections and disease. In addition, microglia has a more benign, less explored role as the brain professional phagocytes. Phagocytosis is a term coined from the Greek to describe the receptor-mediated engulfment and degradation of dead cells and microbes. In addition, microglia phagocytoses brain-specific cargo, such as axonal and myelin debris in spinal cord injury or multiple sclerosis, amyloid-β deposits in Alzheimer's disease, and supernumerary synapses in postnatal development. Common mechanisms of recognition, engulfment, and degradation of the different types of cargo are assumed, but very little is known about the shared and specific molecules involved in the phagocytosis of each target by microglia. More importantly, the functional consequences of microglial phagocytosis remain largely unexplored. Overall, phagocytosis is considered a beneficial phenomenon, since it eliminates dead cells and induces an anti-inflammatory response. However, phagocytosis can also activate the respiratory burst, which produces toxic reactive oxygen species (ROS). Phagocytosis has been traditionally studied in pathological conditions, leading to the assumption that microglia have to be activated in order to become efficient phagocytes. Recent data, however, has shown that unchallenged microglia phagocytose apoptotic cells during development and in adult neurogenic niches, suggesting an overlooked role in brain remodeling throughout the normal lifespan. The present review will summarize the current state of the literature regarding the role of microglial phagocytosis in maintaining tissue homeostasis in health as in disease.
Keywords: microglia, phagocytosis, apoptosis, synapses, debris, myelin, amyloid, inflammation
Citation: Sierra A, Abiega O, Shahraz A and Neumann H (2013) Janus-faced microglia: beneficial and detrimental consequences of microglial phagocytosis. Front. Cell. Neurosci. 7:6. doi: 10.3389/fncel.2013.00006
Received: 10 October 2012; Paper pending published: 11 November 2012;
Accepted: 09 January 2013; Published online: 30 January 2013.
Edited by:Marie-Eve Tremblay, Université Laval, Canada
Reviewed by:Marcel Leist, University of Konstanz, Germany
Rafael Linden, Federal University of Rio de Janeiro, Brazil
Copyright © 2013 Sierra, Abiega, Shahraz and Neumann. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Amanda Sierra, Achucarro—Basque Center for Neuroscience, Laida Bidea, Building 205, Bizkaia Technological Park, 48170 Zamudio, Spain. e-mail: firstname.lastname@example.org
Harald Neumann, Neural Reconstruction Group, Institute of Reconstructive Neurobiology, University Bonn, Sigmund-Freud-Str. 25, 53127 Bonn, Germany. e-mail: email@example.com