RAGE down-regulation: An early event in the striatal dysfunction in a mouse model of Parkinson´s disease

SD Viana1, AM Silva1, CC Portugal1,2, R Socodato1,2, SF Ali3, CA Fontes Ribeiro1, FC Pereira1. 1Faculty of Medicine, University of Coimbra, Pharmacology and Experimental Therapeutics/Biomedical Institute for Research on Light and Image (IBILI), Coimbra, Portugal, 2Institute of Biology, Fluminense Federal University, Department of Neurobiology and Program of Neurosciences, Niterói, RJ, Brazil, 3Division of Neurotoxicology, National Center for Toxicological Research, Food and Drug Administration (NCTR/FDA), Neurochemistry Laboratory, Jefferson, Arkansas, USA

Introduction: Recent studies have invoked inflammation and oxidative stress as major contributors to the striatal dopaminergic denervation in idiophatic Parkinson’s disease (PD)(1). Receptors for advanced glycation end products (RAGE), due to its ability to convert a transient pro-inflammatory response into perpetuated cellular dysfunction, have been involved in several neurodegenerative disorders(2). Even though RAGE overexpression has already been reported in human SN and cortex of PD brains(3), the role of RAGE in PD striatal degeneration is unknown. The aim of this work was to characterize RAGE axis in early stages of striatal dysfunction induced by the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP). Material and methods: Male C57BL/6 mice (26±2g; 10-14 weeks old) were submitted to an acute MPTP protocol (4x20 mg.kg-1 i.p. 2 h-apart), an established PD model. Control animals received 0,9% saline solution (n=11). Mice were killed by cervical dislocation in a fume hood and striata were dissected 3 h (post-first MPTP injection; n=4), 12 h (n=4) and 7 days (n=4) post-acute MPTP protocol. Pro-oxidant/inflammatory setting (4-HNE and TNF-α levels) and RAGE and S100B (RAGE agonist) levels were assessed during the first 12 h of MPTP protocol. Dopaminergic homeostasis (DA, DOPAC, HVA and TH total contents) and astrogliosis (GFAP levels) were analyzed in all studied time-points. Monoamines were evaluated by HPLC-ED and protein contents were assessed by Western blot. Results were expressed as mean ± S.E.M. Statistical differences were evaluated by ANOVA followed by post-test Bonferroni’s multiple comparison and P<0.05 was considered significant. Animals were maintained with pelleted diet and water supplied ad libitum and all experiments were conducted in controlled environment (12 h light/dark cycle, at room temperature 21 ± 1º C) under the rules of the European Convention on Animal Care. Safety MPTP-handling guidelines were implemented. Results: MPTP imposed a severe striatal dopaminergic denervation (DA and TH depletion; increase in DA turnover; p<0.001) and astrogliosis (GFAP upregulation; p<0.001) 7 days after MPTP administration, thus validating the model. Focusing on the early stages of neurodegeneration where TH levels are still normal, a robust RAGE down-regulation (p<0.001) was observed as early as 3h after the first MPTP administration that kept down-regulated at 12 h after MPTP protocol. An increase in both TNF-α and 4-HNE levels (p<0.05 and p<0.001, respectively) was detected no sooner than 12 h and accompanied a mild DA and its metabolites depletion (p<0.05) at 12 h No differences were observed in S100B levels in any studied time-point. Conclusions: An early loss of striatal RAGE levels is observed prior to a dopaminergic homeostasis disruption and pro-inflammatory/oxidant features invoked by MPTP. Although the pathophysiological meaning of these observations will be subject of future studies, RAGE down-regulation definitely represents an early cellular response triggered by MPTP. Unraveling RAGE dynamics may open new insights into successful biomarkers of striatal dysfunction, a paramount topic in PD clinic.

1- Luchtman DW et al., (2009) Physiol Behav 98: 130-138; 2- Alexiou P et al., (2010) Curr Med Chem 17: 2232-2252; 3- Dalfo E et al., (2005) J Neuropathol Exp Neurol 64: 816-830. (This research was supported by PEst-C/SAU/UI3282/2011).