The endocannabinoid system modulates a transient TNF pathway that induces neural stem cell proliferation Ana Rubio-Araiz a , Ángel Arévalo-Martín a , Oscar Gómez-Torres a , Beatriz Navarro-Galve a , Daniel García-Ovejero a , Philipp Suetterlin b , Elena Sánchez-Heras b , Eduardo Molina-Holgado a, ⁎, Francisco Molina-Holgado b, ⁎ a Laboratory of Neuroinflammation, Unidad de Neurología Experimental (Research Unit associated to the Instituto Cajal, CSIC, Madrid), Hospital Nacional de Parapléjicos (SESCAM), 45071 Toledo, Spain b The Wolfson Centre for Age-Related Diseases, King's College London, Hodgkin Building, Guy's Campus, London SE1 1UL, UK ABSTRACT ARTICLE INFO Article history: Received 17 December 2007 Revised 14 March 2008 Accepted 28 March 2008 Available online 10 April 2008 Evidence is emerging that the tumour necrosis factor (TNF-α) is a potent signal that induces neural stem cell proliferation and migration. We show that NSC self-renewal is controlled by bi-directional cross-talk between the endocannabinoid system and the TNF signalling pathway. By blocking endogenous TNF-α activity, we demonstrate that the TNF system is critical for the proliferation of NSC. Furthermore, we show that pharmacological blockade of the CB1/CB2 cannabinoid receptors dramatically suppresses TNF-α-induced NSC proliferation. Interestingly, we found that CB1 or CB2 agonists induce NSC proliferation coupled to a significant increase in both TACE/ADAM 17 and TNF-α levels. Overall these data suggest a novel mode of action for the endocannabinoid system in NSC proliferation that is coupled to TNF signalling and that may be of therapeutic interest in the emerging field of brain repair. © 2008 Elsevier Inc. All rights reserved. Introduction It has long been accepted that our brain tissue is incapable of regenerating and that from birth, neurodegeneration is a long trip towards senility. However, in the adult mammalian brains some dis- crete regions do retain the capacity to generate functional neurons, such as the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus. In these regions adult neural stem cells (NSC) continue to proliferate, differentiate, and undergo neuro- genesis (Alvarez-Buylla and Lim, 2004). Recent reports suggest that there is a synergy between the im- mune system and NSC to promote functional recovery, since immune cells help to maintain neurogenesis in germinal centres of the adult CNS even under non-pathological conditions (Ziv et al., 2006a; 2006b; Butovsky et al., 2006). Similarly, there is substantial evidence that neural stem cell proliferation in the SVZ is modulated in various neu- rodegenerative diseases (Curtis et al., 2007). Therefore, some cross- talk between elements involved in the neuroinflammatory response and those that interact with NSC might occur and to some extent, may activate endogenous brain repair (Rolls et al., 2007). The pleiotropic cytokine, TNF-α, is a key part of the inflammatory response that modulates the proliferation of neural progenitors in the subventricular zone of the adult rat brain, acting through two dif- ferent receptor subtypes, TNF-RI and TNF-RII (Wu et al., 2000; Allan and Rothwell, 2001). Indeed, evidence from TNF receptor knock-out (KO) mice suggests that signalling through TNF-RI suppresses neural progenitor proliferation and neurogenesis in vivo, while signalling through TNF-RII enhances neurogenesis under basal conditions or in neurodegenerative disorders (Iosif et al., 2006). More recent studies confirmed that under pathological conditions such as stroke, ac- tivity of the TNF-α-converting enzyme (TACE/ADAM 17) protease induces neural progenitor proliferation in the SVZ (Katakowski et al., 2007). In the brain, the endocannabinoid system is composed of two well characterized lipid mediators, N-arachidonoylethanolamine (ananda- mide) and 2-arachidonoylglycerol (2-AG), ligands of the CB1 and CB2 cannabinoid receptors (Di Marzo et al., 2004). Both cannabinoid receptors are expressed by NSC/precursor cells in the SVZ, and impaired neurogenesis has been found in mice that lack the CB1 receptor (Arevalo-Martin et al., 2007; Jin et al., 2004). Two closely related sn-1 diacylglycerol lipases α and β (DAGL α and β) are responsible for the synthesis of 2-AG from diacylglycerol (DAG), (Bisogno et al., 2003; Williams et al., 2003). Notably, DAGL α is expressed in NSC and en- docannabinoids are produced by neurospheres in culture (Molina- Holgado et al., 2007; Aguado et al., 2005). Moreover, TNF-α induces the rapid and transient production of DAG, the substrate for DAGL α and β, Molecular and Cellular Neuroscience 38 (2008) 374–380 ⁎ Corresponding authors. E-mail addresses: eduardom@sescam.jccm.es (E. Molina-Holgado), francisco.molina-holgado@kcl.ac.uk (F. Molina-Holgado). 1044-7431/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.mcn.2008.03.010 Contents lists available at ScienceDirect Molecular and Cellular Neuroscience journal homepage: www.elsevier.com/locate/ymcne