Frizzled-1 Is Involved in the Neuroprotective Effect of Wnt3a Against Ab Oligomers MARCELO A. CHACO ´ N, LORENA VARELA-NALLAR, AND NIBALDO C. INESTROSA * Centro de Regulacio´n Celular y Patologı ´a ‘‘Joaquı´n V. Luco’’ (CRCP), Instituto Milenio (MIFAB), Facultad de Ciencias Biolo´gicas, Pontificia Universidad Cato´lica de Chile, Santiago, Chile The activation of the canonical Wnt signaling pathway protects hippocampal neurons against the toxicity of Alzheimer’s amyloid-b-peptide (Ab), however, the role played by the Wnt receptors Frizzleds, has not been studied. We report here that Frizzled-1 mediates the activation of the canonical Wnt/b-catenin pathway by Wnt3a in PC12 cells. In addition, the protective effect of Wnt3a against the toxicity of Ab oligomers was modulated by Frizzled-1 expression levels in both PC12 cells and hippocampal neurons. Over-expression of Frizzled-1 significantly increased cell survival induced by Wnt3a and diminished caspase-3 activation, while knocking-down Frizzled-1 expression by antisense oligonucleotides decreased the Wnt3a protection. Over-expression of wild-type b-catenin, but not a transcriptionally inactive mutated version, prevented the toxicity of Ab suggesting that the transcription of Wnt target genes may be involved in these events. This was confirmed by co-transfecting both Frizzled-1 and the inactive form of b-catenin, which does not elicited protection levels similar to those showed with endogenous b-catenin. Our results indicate that Wnt3a protects from Ab-oligomers toxicity by activating the canonical Wnt signaling pathway through the Frizzled-1 receptor, suggesting a therapeutic potential for this signaling pathway in the treatment of Alzheimer’s disease. J. Cell. Physiol. 217: 215–227, 2008. ß 2008 Wiley-Liss, Inc. Wnt signaling regulates several fundamental development processes including cell fate, proliferation, differentiation and survival (Moon et al., 2002, 2004). At least three different Wnt pathways have been described downstream Frizzled (Fz) receptor: the Wnt/b-catenin pathway (known as the canonical pathway) and the non-canonical pathways Wnt/Ca 2þ and the Wnt/planar cell polarity (Logan and Nusse, 2004; Gordon and Nusse, 2006). Wnt signaling pathway plays a role in the maintenance of neuronal function and homeostasis (Patapoutian and Reichardt, 2000; Ciani and Salinas, 2005) and it has been involved in neurodegenerative processes, including bipolar disorder (Gould and Manji, 2002), schizophrenia (Miyaoka et al., 1999; Yang et al., 2003; Ftouh et al., 2005) and Alzheimer’s disease (AD) (De Ferrari and Inestrosa, 2000; Mudher and Lovestone, 2002; Caricasole et al., 2004). AD is the most common neurodegenerative disorder characterized by the presence of amyloid plaques and neurofibrillary tangles in specific brain regions. The amylod-b-peptide (Ab), the major plaque component, induces neuronal cell loss and synaptic failure (Selkoe, 2002). Accumulation of Ab in the brain seems to be crucial for the neurodegenerative events in AD, being Ab oligomers the most important players in the neurotoxicity observed in this pathology (Ferreira et al., 2007; Haass and Selkoe, 2007). Several studies have provided evidence that AD is related to Wnt signaling. Cultured neurons exposed to Ab show an increased GSK-3b activity (Takashima et al., 1996, 1998), the enzyme involved in tau hyperphosphorylation (Pei et al., 1997), and the loss of the microtubule network (Busciglio et al., 1995). A recent study shows that the phosphorylation of tau, the major component of neurofibrillary tangles, antagonizes the apoptosis by stabilizing b-catenin (Li et al., 2007), the effector protein of the canonical Wnt signaling pathway. Moreover, we have previously demonstrated that the activation of the canonical Wnt signaling pathway prevents Ab-induced neurotoxicity (Garrido et al., 2002; De Ferrari et al., 2003; Farias et al., 2004; Quintanilla et al., 2005), although the Wnt receptor participating in this event has not been identified. In mammals, Fz genes have been implicated in a variety of developmental processes, including axonal outgrowth and guidance in the central nervous system (Wang et al., 2002; Lyuksyutova et al., 2003), the survival of cerebellar neurons (Wang et al., 2001), hippocampal and visuospatial learning (Zhao et al., 2005) and the control of the neural tube closure (Wang et al., 2006). Rat Fz1 and Fz2 have been studied in greatest detail and provide the best discrimination of the Wnt pathways referred as Wnt/b-catenin pathway (Sancho et al., 2004; Moon, 2005) versus the Wnt/Ca 2þ pathway (Kuhl et al., 2000; Wang and Malbon, 2004). An exhaustive study of the possible combinations between the known 19 Wnt ligands and the 10 Fz has not been carried out, although some pairs seem to work (Karasawa et al., 2002; Caricasole et al., 2003), including human Fz1 and Wnt3a (Gazit et al., 1999). Although Wnt signaling pathway and Fz receptors have been shown to participate in the development and maintaining of the nervous system, little is known about the expression of Fz in the mammalian brain. We report here that the Wnt3a ligand activates the Wnt signaling pathway in PC12 cells and it prevents Ab oligomer-induced cell death, caspase-3 activation and b-catenin degradation; these Wnt3a effects are potentiated by Contract grant sponsor: FONDAP; Contract grant number: 13980001. Contract grant sponsor: FONDECYT; Contract grant number: 3070017. Contract grant sponsor: CONICYT; Contract grant numbers: 102025, 4040214. *Correspondence to: Nibaldo C. Inestrosa, CRCP Biomedical Center, P. Universidad Cato ´lica de Chile, Alameda 340, Santiago, Chile. E-mail: ninestrosa@bio.puc.cl Received 5 March 2008; Accepted 16 April 2008 DOI: 10.1002/jcp.21497 ORIGINAL ARTICLE 215 Journal of Journal of Cellular Physiology Cellular Physiology ß 2008 WILEY-LISS, INC.