The pathogenic LRRK2 R1441C mutation induces specific deficits modeling the prodromal phase of Parkinson's disease in the mouse.

The aim of the present study was to further explore the in vivo function of the Leucine-rich repeat kinase 2 (LRRK2)-gene, which is mutated in certain familial forms of Parkinson's disease (PD). We generated a mouse model harboring the disease-associated point mutation R1441C in the GTPase domain of the endogenous murine LRRK2 gene (LRRK2 R1441C line) and performed a comprehensive analysis of these animals throughout lifespan in comparison with an existing knockdown line of LRRK2 (LRRK2 knockdown line). Animals of both lines do not exhibit severe motor dysfunction or pathological signs of neurodegeneration neither at young nor old age. However, at old age the homozygous LRRK2 R1441C animals exhibit clear phenotypes related to the prodromal phase of PD such as impairments in fine motor tasks, gait, and olfaction. These phenotypes are only marginally observable in the LRRK2 knockdown animals, possibly due to activation of compensatory mechanisms as suggested by in vitro studies of synaptic transmission. Thus, at the organismal level the LRRK2 R1441C mutation does not emerge as a loss of function of the protein, but induces mutation specific deficits. Furthermore, judged by the phenotypes presented, the LRRK2-R1441C knock-in line is a valid preclinical model for the prodromal phase of PD.

Loss of DJ-1 impairs antioxidant response by altered glutamine and serine metabolism.

The oncogene DJ-1 has been originally identified as a suppressor of PTEN. Further on, loss-of-function mutations have been described as a causative factor in Parkinson's disease (PD). DJ-1 has an important function in cellular antioxidant responses, but its role in central metabolism of neurons is still elusive. We applied stable isotope assisted metabolic profiling to investigate the effect of a functional loss of DJ-1 and show that DJ-1 deficient neuronal cells exhibit decreased glutamine influx and reduced serine biosynthesis. By providing precursors for GSH synthesis, these two metabolic pathways are important contributors to cellular antioxidant response. Down-regulation of these pathways, as a result of loss of DJ-1 leads to an impaired antioxidant response. Furthermore, DJ-1 deficient mouse microglia showed a weak but constitutive pro-inflammatory activation. The combined effects of altered central metabolism and constitutive activation of glia cells raise the susceptibility of dopaminergic neurons towards degeneration in patients harboring mutated DJ-1. Our work reveals metabolic alterations leading to increased cellular instability and identifies potential new intervention points that can further be studied in the light of novel translational medicine approaches.

A differential interaction of putative ?-selective agonists with opiate binding sites in rat brain.

The availability of tritium-labelled sufentanil ([(3)H]SUF) allowed for a further radioligand analysis of opiate binding sites in rat brain. A comparison of the binding characteristics of [(3)H]SUF and [(3)H]dihydromorphine ([(3)H]DHM) revealed a very similar potency in their mutual displacement by unlabelled analogues. Furthermore, a series of putative ?-opiate agonists displayed equal potencies in displacing either [(3)H]SUF and [(3)H]DHM, the only striking exception being the highly ?-selective opioid peptide morphiceptin which was 33 times less potent in inhibiting [(3)H]SUF as compared to [(3)H]DHM binding. Additional experiments revealed further pronounced differences in [(3)H]SUF and [(3)H]DHM binding characteristics: the total amount of binding sites for [(3)H]SUF was 4 times higher than that for [(3)H]DHM and the regional distribution within particular brain areas displayed considerable differences. Furthermore, the binding of [(3)H]SUF was differentially modulated by sodium and GTP as compared to [(3)H]DHM binding. These data suggest that in rat brain, [(3)H]SUF interacts both with ?-opiate sites recognizing [(3)H]DHM and another type of opiate site, which cannot be equated with any of the, as yet, described ?- or ?-binding sites, and rather, represents a subclass of ?-opiate receptor sites. These experiments, thus, support the notion of subclasses (isoreceptors) for different types of opiate receptors.