TISSUE-SPECIFIC STEM CELLS ADAM-17/Tumor Necrosis Factor-a-Converting Enzyme Inhibits Neurogenesis and Promotes Gliogenesis from Neural Stem Cells CARMEN ROMERO-GRIMALDI, a MARIBEL MURILLO-CARRETERO, b MIGUEL ANGEL LO ´ PEZ-TOLEDANO, b MANUEL CARRASCO, b CARMEN CASTRO, b CARMEN ESTRADA b a Ciber of Mental Health (CIBERSAM), Instituto de Salud Carlos III, Madrid, Spain; b A ´ rea de Fisiologı ´a, Facultad de Medicina, Universidad de Ca ´diz, Ca ´diz, Spain Key Words. Astrocytes • Epidermal growth factor receptor • Metalloproteases • Neural precursor cells • Neuroblasts • Transforming growth factor-a ABSTRACT Neural precursor cells (NPCs) are activated in central nervous system injury. However, despite being multipoten- tial, their progeny differentiates into astrocytes rather than neurons in situ. We have investigated the role of epi- dermal growth factor receptor (EGFR) in the generation of non-neurogenic conditions. Cultured mouse subventric- ular zone NPCs exposed to differentiating conditions for 4 days generated approximately 50% astrocytes and 30% neuroblasts. Inhibition of EGFR with 4-(3-chloroanilino)- 6,7-dimethoxyquinazoline significantly increased the number of neuroblasts and decreased that of astrocytes. The same effects were observed upon treatment with the metalloprotease inhibitor galardin, N-[(2R)-2-(hydroxamido- carbonylmethyl)-4-methylpentanoyl]-L-tryptophan methyl- amide (GM 6001), which prevented endogenous transforming growth factor-a (TGF-a) release. These results suggested that metalloprotease-dependent EGFR- ligand shedding maintained EGFR activation and favored gliogenesis over neurogenesis. Using a disintegrin and metalloprotease 17 (ADAM-17) small interference RNAs transfection of NPCs, ADAM-17 was identified as the metalloprotease involved in cell differentiation in these cultures. In vivo experiments revealed a significant upreg- ulation of ADAM-17 mRNA and de novo expression of ADAM-17 protein in areas of cortical injury in adult mice. Local NPCs, identified by nestin staining, expressed high levels of ADAM-17, as well as TGF-a and EGFR, the three molecules necessary to prevent neurogenesis and promote glial differentiation in vitro. Chronic local infu- sions of GM6001 resulted in a notable increase in the number of neuroblasts around the lesion. These results indicate that, in vivo, the activation of a metalloprotease, most probably ADAM-17, initiates EGFR-ligand shedding and EGFR activation in an autocrine manner, preventing the generation of new neurons from NPCs. Inhibition of ADAM-17, the limiting step in this sequence, may contrib- ute to the generation of neurogenic niches in areas of brain damage. STEM CELLS 2011;29:1628–1639 Disclosure of potential conflicts of interest is found at the end of this article. INTRODUCTION Neural precursor cells (NPCs) have been isolated from several regions of the adult central nervous system (CNS), including the subventricular zone (SVZ) of the lateral ventricles [1], dentate gyrus subgranular zone (SGZ) of the hippocampus [2], cerebral cortex [3, 4], striatum [5], or spinal cord [6, 7]. Despite their ubiquity, physiological generation of new neu- rons from NPCs has only been demonstrated in the SGZ and the SVZ (reviewed in [8, 9]). When NPCs from rodent SVZ are transplanted to the SVZ of host animals, they give rise to neuroblasts, which become integrated in the olfactory bulb as mature neurons; however, these same cells transplanted to other brain regions do not generate neurons, but differentiate into astrocytes [10–12]. These results indicate that two requi- sites are necessary for neurogenesis to occur in a specific brain area: the existence of NPCs and their location within a neurogenic niche providing the adequate molecular and cellu- lar environment for neuronal differentiation and survival [13]. In brain lesions of different origins, such as transient global [14] or focal [15, 16] ischemia, seizures [17], or apo- ptosis induction [3], a moderate number of new neurons appear in the injured area. The newly generated neurons result from further differentiation and maturation of migrating neu- roblasts which arrive from the neurogenic areas, where the proliferation rate of NPCs increases upon brain injury [18, 19] An alternative or complementary mechanism is the activa- tion of local quiescent NPCs by molecules upregulated in the damaged tissue [20]. However, the capacity of neuronal Author contributions: C.R-G. and M.A.L.-T.: collection and assembly of data, data analysis and interpretation; M.M.-C: conception and design, collection and assembly of data, data analysis and interpretation; M.C. and C.C.: collection and assembly of data; C.E.: conception and design, financial support, data analysis and interpretation, manuscript writing. C.R.-G. and M.M.-C. contributed equally to this article. Correspondence: Carmen Estrada, M.D., Ph.D., A ´ rea de Fisiologı ´a, Facultad de Medicina, Universidad de Ca ´diz, Plaza Falla 9, E-11003 Ca ´diz, Spain. Telephone: 34-95-601-5252; Fax: 34-95-601-5251; e-mail: carmen.estrada@uca.es Received January 5, 2011; accepted for publication July 21, 2011; first published online in STEM CELLS EXPRESS August 11, 2011. V C AlphaMed Press 1066-5099/2009/$30. 00/0 doi: 10.1002/stem.710 STEM CELLS 2011;29:1628–1639 www.StemCells.com