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FP6

NR4A2 TARGETS Résumé de rapport

Project ID: 517970
Financé au titre de: FP6-MOBILITY
Pays: Greece

Final Activity Report Summary - NR4A2 TARGETS (NR4A2 target genes important in Parkinson's Disease')

The aetiology of Parkinson's disease (PD) is unknown, but recently discovered gene mutations have provided new insights and have enhanced our understanding of the pathophysiology of the disease. Even though these mutations account for a small fraction of the total PD cases, understanding the function of the mutations can help us identify pathways that are important for the survival of the dopaminergic (DAergic) neurons. One gene that has been associated with PD is NR4A2 (Nurr1), a ligand-independent nuclear receptor that can act either as a monomer or as a heterodimer with RXR to modulate transcription of downstream genes.

NR4A2 appears to have a neuroprotective role. NR4A2 deletion in mice results in death after birth, which is associated with the selective agenesis of midbrain DAergic neurons (Zetterstrom 1997). In addition, NR4A2 appears to be required for the survival of the DAergic neuron precursors (Saucedo-Cardenas 1998). The function of NR4A2 continues apparently beyond development as it is highly expressed in adult midbrain DAergic neurons. During aging in humans NR4A2 mRNA steady state levels decrease (Chu 2002). This decrease is even more pronounced in Parkinson disease patients when compared to age matched controls (Chu 2006) and it appears to be physiologically significant since dopamine neurons from NR4A2 +/- mice have reduced survival in vitro (Eells, 2002). In addition NR4A2 +/- mice as they age display features in both rotarod performance and locomotor activities consistent with parkinsonism (Jiang 2005). Most importantly, genetic analysis of the NR4A2 gene in PD patients has revealed mutations in familial and sporadic PD cases, providing a potential link between lack of neuroprotection and the development of adult-onset PD (Le 2003, Hering 2004, Healy 2006, Grimes 2006). Most of the mutations have been identified in the 5' untranslated region of the gene and thus do not affect the protein primary structure but result in the decrease of NR4A2 steady state mRNA levels that, in turn, affect tyrosine hydroxylase expression levels (Le 2003, Healy 2006 and our unpublished data). One point mutation S125C has also been identified in a sporadic individual that uncoupled ERK1/2-dependent phosphorylation of NR4A2 and attenuated transcriptional activation of the human TH promoter (Jacobsen 2008). Possibly the transcription levels of other genes that may be neuroprotective is also affected by reduced NR4A2 expression levels or reduced activity.

The neuroprotective effects of NR4A2 have been demonstrated in several experiments and it has been shown that its action in DAergic cells requires heterodimerisation with RXR? (Wallen-Mackenzie, 2003). This is verified by the fact that NR4A2 dim, a point mutant that cannot heterodimerise with RXR, does not function in midbrain DAergic neurons (Wallen-Mackenzie, 2003). Activation of NR4A2/RXR? heterodimers by natural or the synthetic ligands increases the survival of primary Ventral Midbrain (VMB) DAergic neurons (Wallen-Mackenzie, 2003). Also, NR4A2 +/- mice show increased susceptibility to MPTP-induced nigral injury (Le 1999). Thus, it is speculated that NR4A2 controls the expression of neuroprotective factors.

We have shown that NR4A2/RXR? heterodimers control the expression of a neuroprotective network and we have established a cellular sysytem where this function can be analysed. We have shown that controlled and reversbla overexpression of NR4A2/RXR? heterodimers can be achieved and that transintly these two trancription factors can protect from MPTP toxicity. MPTP or MPP+ causes Parkinson Disease like symptoms in people and experimental animals. We have additionally explored the efficacy of specific compounds that have the potential to activate the neuroprotective network in animals. In addition we have enerated a novel way to mark the dopaminergic neurons while at the same time to monitor in real time the efficacy of novel compounds to activate NR4A2 expression.

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VASSILATIS DEMETRIOS
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