Loss of Prion Protein in a Transgenic Model of Amyotrophic Lateral Sclerosis Luc Dupuis, Corinne Mbebi, Jose ´-Luis Gonzalez de Aguilar, Fre ´de ´rique Rene, Andre ´ Muller, Marc de Tapia, and Jean-Philippe Loeffler 1 Laboratoire de Signalisations Mole ´culaires et Neurode ´ge ´ne ´rescence, EA 3433 Faculte ´ de Me ´decine, Universite ´ Louis Pasteur, 11 rue Humann, 67085 Strasbourg, France Amyotrophic lateral sclerosis (ALS) is a motor neuron degenerative disorder caused in a proportion of cases by missense mutations in the gene encoding Cu/Zn super- oxide dismutase (Cu/Zn-SOD) which result in unknown, lethal enzymatic activity. Based on a differential screening approach, we show here that the gene encoding the cel- lular prion protein (PrP C ) was specifically repressed in a transgenic model of ALS overexpressing the mutant G86R Cu/Zn-SOD. Analysis by Northern blot, semiquantitative RT–PCR, and Western blot revealed that PrP C down-reg- ulation, which appeared early in the asymptomatic phase of the pathology, occurred preferentially in those tissues primarily affected by the disease (spinal cord, sciatic nerve, and gastrocnemius muscle). This down-regulation was not accompanied by refolding of the aberrant PrP Sc isoform, the agent which causes transmissible spongi- form encephalopathies. Furthermore, modification of PrP C expression was specifically linked to the presence of the G86R mutant since no changes were observed in transgenic mice overexpressing wild-type Cu/Zn-SOD. PrP C has been shown to play a role in the protection against oxidative stress, and we therefore propose that its down-regulation may contribute at least in part to ALS pathogenesis. INTRODUCTION Amyotrophic lateral sclerosis (ALS) is a lethal neuro- logical disorder affecting middle-aged individuals. It appears as a weakness and muscle atrophy of the ex- tremities, caused by the selective loss of large motor neurons in the spinal cord, brainstem, and motor cortex (Mulder et al., 1986). The precise mechanisms underly- ing motor neuron degeneration remain unclear, and multiple factors have been proposed to be involved. Many studies agree that oxidative stress plays an im- portant role in the pathogenesis of the disease (refer to Robberecht, 2000). It was observed by Rosen et al. (1993) that a subset of patients, with autosomal dominantly inherited ALS, harbor point mutations in the gene en- coding Cu/Zn superoxide dismutase (Cu/Zn-SOD), which is a free radical scavenging enzyme. Overexpres- sion of ALS-linked Cu/Zn-SOD in transgenic mice al- lows the development of a neurological disorder that resembles human ALS without affecting SOD enzy- matic activity. This strongly suggests that mutations confer an unknown gain of function to the enzyme (Gurney, 1994; Ripps et al., 1995; Wong et al., 1995). How this deleterious enzymatic activity provokes neu- ronal degeneration is a matter of controversy. Some studies have proposed that the mutant Cu/Zn-SOD is able to generate highly toxic hydroxyl radicals that can damage essential cellular constituents (Wiedau-Pazos et al., 1996). Alternatively, another hypothesis has emerged from the observation that Cu/Zn-SOD catalyzes peroxynitrite radicals to form a nitronium-like intermedi- ate, which in turn induces nitration of tyrosine residues and subsequent cell injury (Beckman, 1996). The cellular prion protein (PrP C ) is a glycophosphati- dylinositol-anchored glycoprotein that binds copper and possesses SOD activity (Brown et al., 1997, 1999). However, its precise physiological role remains elusive. Studies involving PrP C knockout mice (Prnp 0/0 ) support a protective role in the cellular resistance to oxidative stress (Brown and Besinger, 1998) and to apoptosis (Kuwahara et al., 1999). In addition, its expression seems to influence, through modulation of copper traf- 1 To whom correspondence and reprint requests should be ad- dressed. Fax: +33-(0)3-90-243065. E-mail: loeffler@neurochem.u- strasbg.fr. doi:10.1006/mcne.2001.1049, available online at http://www.idealibrary.com on Molecular and Cellular Neuroscience 19, 216–224 (2002) MCN 1044-7431/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved. 216