ORIGINAL RESEARCH REPORT The Matrix Metalloproteinase Inhibitor Marimastat Promotes Neural Progenitor Cell Differentiation into Neurons by Gelatinase-Independent TIMP-2-Dependent Mechanisms Maddalena Sinno, 1 Stefano Biagioni, 1 Maria Antonietta Ajmone-Cat, 2 Irene Pafumi, 1 Pasquale Caramanica, 1 Virginia Medda, 3 Gaetana Tonti, 3 Luisa Minghetti, 2 Ferdinando Mannello, 3 and Emanuele Cacci 1,4 Metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs), produced in the brain by cells of non- neural and neural origin, including neural progenitors (NPs), are emerging as regulators of nervous system development and adult brain functions. In the present study, we explored whether MMP-2, MMP-9, and TIMP- 2, abundantly produced in the brain, modulate NP developmental properties. We found that treatment of NPs, isolated from the murine fetal cerebral cortex or adult subventricular zone, with the clinically tested broad- spectrum MMP inhibitor Marimastat profoundly affected the NP differentiation fate. Marimastat treatment allowed for an enrichment of our cultures in neuronal cells, inducing NPs to generate higher percentage of neurons and a lower percentage of astrocytes, possibly affecting NP commitment. Consistently with its pro- neurogenic effect, Marimastat early downregulated the expression of Notch target genes, such as Hes1 and Hes5. MMP-2 and MMP-9 profiling on proliferating and differentiating NPs revealed that MMP-9 was not expressed under these conditions, whereas MMP-2 increased in the medium as pro-MMP-2 (72 kDa) during differentiation; its active form (62 kDa) was not detectable by gel zymography. MMP-2 silencing or adminis- tration of recombinant active MMP-2 demonstrated that MMP-2 does not affect NP neuronal differentiation, nor it is involved in the Marimastat proneurogenic effect. We also found that TIMP-2 is expressed in NPs and increases during late differentiation, mainly as a consequence of astrocyte generation. Endogenous TIMP-2 did not modulate NP neurogenic potential; however, the proneurogenic action of Marimastat was mediated by TIMP-2, as demonstrated by silencing experiments. In conclusion, our data exclude a major involvement of MMP-2 and MMP-9 in the regulation of basal NP differentiation, but highlight the ability of TIMP-2 to act as key effector of the proneurogenic response to an inducing stimulus such as Marimastat. Introduction N eural stem cells (NSCs) persistently generate new neurons that are destined to the olfactory bulb and the hippocampal granular cell layer throughout lifespan [1]. The regulation of neurogenesis under physiological and patho- logical conditions involves a wide spectrum of instructive signals from the microenvironment in which NSCs reside, the so-called neurogenic niche. Many aspects of the neurogenic and gliogenic programs during embryonic development and at adulthood are regulated by a multiplicity of extrinsic fac- tors. Among them, matrix metalloproteinases (MMPs), a broad family of endopeptidases, are emerging as critical regulators of cell proliferation, migration, differentiation, survival, neurite outgrowth, and plasticity [2]. MMP’s family comprises more than 25 enzymes able to process a multiplicity of substrates, including extracellular matrix components, chemokines, growth factors, cell surface receptors, and cell– cell adhesion molecules [3–5]. MMPs, synthesized as inactive zymogenes, can be activated by other proteases [6,7], and are tightly regulated by 4 endogenous inhibitors, namely tissue inhibitors of metalloproteinases (TIMPs) [8,9]. Among MMPs, MMP-2 and MMP-9, referred as to gelatinases for their ability to degrade gelatin besides other substrates, have been 1 Department of Biology and Biotechnology ‘‘Charles Darwin,’’ Sapienza, University of Rome, Rome, Italy. 2 Department of Cell Biology and Neuroscience, Istituto Superiore di Sanita ` , Rome, Italy. 3 Section of Clinical Biochemistry, Unit of Cell Biology, Department of Biomolecular Sciences, University ‘‘Carlo Bo,’’ Urbino, Italy. 4 Department of Biology and Biotechnology ‘‘Charles Darwin,’’ Istituto Pasteur-Fondazione Cenci Bolognetti, Sapienza, University of Rome, Rome, Italy. STEM CELLS AND DEVELOPMENT Volume 00, Number 00, 2012 Ó Mary Ann Liebert, Inc. DOI: 10.1089/scd.2012.0299 1