Nanostructured TiO 2 surfaces promote polarized activation of microglia, but not astrocytes, toward a proinflammatory profile Silvia De Astis,† abc Irene Corradini,† abc Raffaella Morini, bd Simona Rodighiero, a Romana Tomasoni, bd Cristina Lenardi, ae Claudia Verderio, df Paolo Milani ae and Michela Matteoli * bd Activation of glial cells, including astrocytes and microglia, has been implicated in the inflammatory responses underlying brain injury and neurodegenerative diseases including Alzheimer's and Parkinson's diseases. The classic activation state (M1) is characterized by high capacity to present antigens, high production of nitric oxide (NO) and reactive oxygen species (ROS) and proinflammatory cytokines. Classically activated cells act as potent effectors that drive the inflammatory response and may mediate detrimental effects on neural cells. The second phenotype (M2) is an alternative, apparently beneficial, activation state, more related to a fine tuning of inflammation, scavenging of debris, promotion of angiogenesis, tissue remodeling and repair. Specific environmental chemical signals are able to induce these different polarization states. We provide here evidence that nanostructured substrates are able, exclusively in virtue of their physical properties, to push microglia toward the proinflammatory activation phenotype, with an efficacy which reflects the graded nanoscale rugosity. The acquisition of a proinflammatory phenotype appears specific for microglia and not astrocytes, indicating that these two cell types, although sharing common innate immune responses, respond differently to external physical stimuli. Introduction Activation of glial cells, i.e. astrocytes and microglia, has been implicated in the inammatory responses underlying brain injury and neurodegenerative diseases, including multiple sclerosis, Alzheimer's and Parkinson's diseases. Astrocytes and microglia are two distinct types of glial cells in the central nervous system, and, although they are clearly distinct in embryonic origin, morphology and functional properties, they share some properties of immune active and supportive cells. 1 Also, microglia and astrocytes have the ability to either secrete soluble mediators triggering neural repair and contributing to the creation of an environment conducive to regeneration or release of neurotoxic cytokines and reactive oxygen species that regulate immune cell entry into the central nervous system (CNS) and are deleterious to the CNS. Under resting conditions, microglia are highly ramied cells, with a cell body fairly motionless, and long branches constantly moving and surveying the surrounding brain parenchyma. 2–4 Like macro- phages, microglia are able to react to tissue insults by a rapid differentiation process, consisting of thickening and retraction of branches, up to taking a large, ameboid shape, which is accompanied by the elaboration and release of an array of immune mediators, including reactive oxygen and nitrogen species, chemokines, and inammatory cytokines. 5 Microglia activation is related to the canonical host-defense mechanisms, consisting of the enhancement of phagocytic properties and secretion of trophic factors, which may contribute to neuro- protection and repair. In chronic neuroinammation, however, microglia remain activated for an extended period, during which the production of inammatory mediators is sustained longer than usual, thus exacerbating the neural damage. 6 This is particularly evident in neurodegenerative diseases, such as Alzheimer's disease where activated microglia surround extra- cellular deposits of beta-amyloid and maintain an inammatory milieu through the secretion of inammatory cytokines, thus possibly contributing to neuronal death. 7 The contribution of astrocytes to inammatory processes is much less recognized. However, recent evidence suggests that astrocytes, like a Fondazione Filarete, viale Ortles 22/4, 20139 Milano, Italy b Department of Biotechnology and Translational Medicine, University of Milano, Via Vanvitelli 32, 20129 Milano, Italy. E-mail: michela.matteoli@unimi.it; Fax: +39 02 503 17132 c Center of Excellence for Neurodegenerative Diseases, University of Milano, Milan, Italy d Humanitas Clinical and Research Center, via Manzoni 56, 20089 Rozzano, Italy e CIMAINA and Dipartimento di Fisica, Universit` a di Milano, via Celoria 16, I-20133 Milano, Italy f CNR-Institute of Neuroscience, via Vanvitelli 32, 20129 Milan, Italy † Double rst authors. Cite this: Nanoscale, 2013, 5, 10963 Received 10th July 2013 Accepted 26th August 2013 DOI: 10.1039/c3nr03534d www.rsc.org/nanoscale This journal is ª The Royal Society of Chemistry 2013 Nanoscale, 2013, 5, 10963–10974 | 10963 Nanoscale PAPER Published on 24 September 2013. Downloaded by Universita Studi di Milano on 30/10/2013 20:47:26. View Article Online View Journal | View Issue