Animal Models for Neurodegenerative Diseases (Morbus Parkinson)
Few conditions are more feared than degenerative neurological diseases, i.e. Parkinson´s disease (PD). Slowly, patients suffer progressive loss of muscle and/or mental function. However, despite being able to attenuate symptoms of PD for some time there is no definitive cure. In order to increase our understanding of the molecular mechanisms underlying the aetiology and progression of the disease the PD team generates genetic mouse models carrying deletions or mutations in the genes known to be associated with early onset PD. We have by now generated different animal models for PINK1, DJ-1 and LRRK2 and are analysing these animal models by a wide array of morphological, histological, molecular/cell biological and biochemical, and behavioural analyses, to pursue the search for molecular mechanisms underlying the aetiology of the disease. We also expose these animals to different environmental stressors in order to determine the effect of the environment on the development and progession of the disease, specifically since it became apparent that the single dysfunctions of PD associated genes is not sufficient to elicit the disease phenotype in our animal models – possibly due to neuroprotective compensatory mechanisms. The knowledge of the observed molecular and systemic phenotype as well as the compensatory mechanism may form the basis for new and better therapies of PD.
Funding:
Our research is funded by
Most important publications:
Piccoli, G., S. B. Condliffe, M. Bauer, F. Giesert, K. Boldt, S. De Astis, A. Meixner, H. Sarioglu, D. M. Vogt-Weisenhorn, W. Wurst, C. J. Gloeckner, M. Matteoli, C. Sala, and M. Ueffing (2011), "LRRK2 controls synaptic vesicle storage and mobilization within the recycling pool", J Neurosci 31 (6):2225-2237.
Pham, T. T., F. Giesert, A. Röthig, T. Floss, M. Kallnik, K. Weindl, S. M. Hölter, U. Ahting, H. Prokisch, L. Becker, T. Klopstock, M. Hrabé de Angelis, K. Beyer, K. Görner, P. J. Kahle, D. M. Vogt Weisenhorn, and W. Wurst (2010), "DJ-1-deficient mice show less TH-positive neurons in the ventral tegmental area and exhibit non-motoric behavioural impairments", Genes, Brain and Behavior 9 (3): 305-17.
Aron, L., P. Klein, T. T. Pham, E. R. Kramer, W. Wurst, and R. Klein (2010), "Pro-survival role for Parkinson's associated gene DJ-1 revealed in trophically impaired dopaminergic neurons", PLoS Biol 8 (4):e1000349.
Lutz, A. K., N. Exner, M. E. Fett, J. S. Schlehe, K. Kloos, K. Laemmermann, B. Brunner, A. Kurz-Drexler, F. Vogel, A. S. Reichert, L. Bouman, D. Vogt-Weisenhorn, W. Wurst, J. Tatzelt, C. Haass, and K. F. Winklhofer (2009), "Loss of parkin or PINK1 function increases DRP1-dependent mitochondrial fragmentation", J Biol Chem. 284 (34): 22938-51
Morais, V. A., P. Verstreken, A. Roethig, J. Smet, A. Snellinx, M. Vanbrabant, D. Haddad, C. Frezza, W. Mandemakers, D. Vogt-Weisenhorn, R. Van Coster, W. Wurst, L. Scorrano, and B. De Strooper (2009), "Parkinson's disease mutations in PINK1 result in decreased Complex I activity and deficient synaptic function", EMBO Mol Med 1 (2):99-111.
Mouse model of Pink1 deficiency
We generated mice deficient in Pink1 as a genetic model to study the mechanisms underlying disease development. In analogy to other genetic loss-of-function mouse models, morphological analysis of our Pink1-/- mice did not reveal any alterations in the dopaminergic system. However, we found a significant reduction in the density of 5-HT positive fibers in the glomerular layer of the olfactory bulb, and a trend towards reduction in layer I of the agranular insular cortex. Behaviorally, subtle gait abnormalities and impairments in several olfactory functions could be detected, both phenotypes resembling early pre-motoric symptoms of the disease. On cellular level, analysis of primary neuronal cultures revealed fragmentation of mitochondria after acute lentiviral knock-down of Pink1, which was, however, compensated over time. Accordingly, in vivo in brain slices from Pink1-/- mice no fragmentation was observed. This observation together with the subtle premotor phenotypes indicate that compensatory mechanisms may impede the onset of full blown disease phenotypes under unchallenged baseline conditions and render these mice valuable models for early phases of Parkinson´s disease and the discovery of relevant biomarker for the long presymptomatic phase. Here we are specifically investigating the role of the metabolome and the influence of increased oxidative stress.
- Mitochondrial fragmentation induced by acute deficiency of Pink1 is compensated over time and in vivo. Note that 3 days after transduction of neuronal cultures significant more fragmented and less intermediate mitochondria are observed (middle). This phenotype has vanished 5 days after transduction (right). In contrast, significantly less fragmented and more intermediate mitochondria are observed in vivo (left).
Mouse model of DJ-1 deficiency
Loss-of-funcion mutations in the DJ-1 gene have been associated with familial Parkinson´s Disease. In order to evaluate on the molecular function of DJ-1 in the pathoetiology of PD we generated a mouse line deficient of DJ-1 using the genetrap technology. The analysis of this mouse line revealed that loss DJ-1 function results in the occurrence of non-motor symptoms of PD, such as cognitive deficits and reduced explorative behaviour, whereas the major motor-symptoms are not reproduced in this mouse model. This is supported by the fact that no obvious neurodegeneration could be observed, suggesting that the loss of DJ-1 function may be compensated in vivo. Indeed at least one neuroprotective pathway seems to be activated in these mice. Furthermore in collaboration with a research group at the MPI for Neurobiology (Prof. Klein) we could show that in order elicit the neurodegenerative process in these mice they have to be challenged with other factors, in this case age and reduced neurotrophic support. In conclusion, the research on this genetic animal model for PD revealed that PD-associated genes have pleiotropic functions and contribute to pre-motor symptoms of PD rendering them valid models for the pre-motor (clinical) phase of PD. Furthermore it is obvious that the loss of the function of a single gene is not sufficient to elicit the neurodegenerative phenotype rather several factors have to act in concert. Thus we are concentrating our work in this animal model on the impact of environmental stressors i.e. nutrition and inflammation.
- DJ-1 deficient male mice exhibit a subtle but significant cognitive phenotype in the object recognition test (bottom right panel)
LRRK2 mouse models
In order to determine the function of LRRK2 in health and disease we generated a knock-down model of LRRK2 by RNAi technology and a mouse model harbouring the disease-associated point mutation R1441C in the GTPase domain of the endogenous murine Lrrk2 gene, respectively. In both models no overt motor dysfunction or pathological signs of neurodegeneration can be observed both in young and fully aged animals (Giesert et al. in preparation) In addition, both mouse models have been used as a source to investigate the cellular functions of Lrrk2. Both mouse embryonic fibroblasts (MEF) and primary hippocampal neurons have been utilized in this regard. We could provide hints for a role of the protein in cytoskeleton organisation as well as synaptic transmission, albeit the constitutive expression of pathogenic LRRK2 on an endogenous level seems to be compensated to a large extend (Giesert et al, in preparation). If we compare the results of the two lines, it is remarkable that on the functional level, altered LRRK2 function in the R1441C line rather leads to opposing effects compared to the loss of the protein, but strikingly on the behavioural level both lines performed in a similar manner and did show a very high overlap in regard to the identified phenotypes. This might indicate that LRRK2 dysfunction and loss of LRRK2 alters distinct cellular processes in a contrary way, but the general impairment of these processes results in a similar dysfunction on the systemic level. Further studies are aimed at unravelling the precise underlying molecular mechanisms with specific focus on dysfunctional cytoskeleton.
- The expression of Lrrk2 in the basal ganglia circuitry is highly dynamic during postnatal development. In the striatum, mRNA levels increase markedly in comparison to the cortex during postnatal development. On the contrary, the substantia nigra in the midbrain depicts constantly a quite low degree of expression