rAAV-based brain slice culture models of Alzheimer's and Parkinson's disease inclusion pathologies.

It has been challenging to produce ex vivo models of the inclusion pathologies that are hallmark pathologies of many neurodegenerative diseases. Using three-dimensional mouse brain slice cultures (BSCs), we have developed a paradigm that rapidly and robustly recapitulates mature neurofibrillary inclusion and Lewy body formation found in Alzheimer's and Parkinson's disease, respectively. This was achieved by transducing the BSCs with recombinant adeno-associated viruses (rAAVs) that express α-synuclein or variants of tau. Notably, the tauopathy BSC model enables screening of small molecule therapeutics and tracking of neurodegeneration. More generally, the rAAV BSC "toolkit" enables efficient transduction and transgene expression from neurons, microglia, astrocytes, and oligodendrocytes, alone or in combination, with transgene expression lasting for many months. These rAAV-based BSC models provide a cost-effective and facile alternative to in vivo studies, and in the future can become a widely adopted methodology to explore physiological and pathological mechanisms related to brain function and dysfunction.

Identification of compounds that inhibit the kinase activity of leucine-rich repeat kinase 2.

Mutations in leucine-repeat rich kinase 2 (LRRK2) are the most common known cause of late-onset Parkinson's disease. In this study, a novel system to purify active recombinant LRRK2 expressed in mammalian cells was generated. This recombinant enzyme was used to characterize the specificity of LRRK2 and identify small compounds that can inhibit the kinase activity. Recombinant LRRK2 was shown to autophosphorylate and phosphorylate MBP and a peptide (LRRKtide) corresponding to the T558 [corrected] site in moesin. A series of well-characterized kinase peptide substrates was not modified by LRRK2 demonstrating remarkable specificity. G2019S, the most common disease-causing mutation in LRRK2, increased kinase activity more dramatically than previously appreciated ( approximately 10-fold). Several small molecules sharing a basic indolocarbazole structure (Gö6976, K-252a, and staurosporine) where identified as potent inhibitors of LRRK2 kinase activity. These findings provide important insights and tools to study the mechanisms of LRRK2 pathobiology, and could lead to therapeutic applications.

Reversible inhibition of alpha-synuclein fibrillization by dopaminochrome-mediated conformational alterations.

Previous studies demonstrated that alpha-synuclein (alpha-syn) fibrillization is inhibited by dopamine, and studies to understand the molecular basis of this process were conducted (Conway, K. A., Rochet, J. C., Bieganski, R. M., and Lansbury, P. T., Jr. (2001) Science 294, 1346-1349). Dopamine inhibition of alpha-syn fibrillization generated exclusively spherical oligomers that depended on dopamine autoxidation but not alpha-syn oxidation, because mutagenesis of Met, His, and Tyr residues in alpha-syn did not abrogate this inhibition. However, truncation of alpha-syn at residue 125 restored the ability of alpha-syn to fibrillize in the presence of dopamine. Mutagenesis and competition studies with specific synthetic peptides identified alpha-syn residues 125-129 (i.e. YEMPS) as an important region in the dopamine-induced inhibition of alpha-syn fibrillization. Significantly, the dopamine oxidation product dopaminochrome was identified as a specific inhibitor of alpha-syn fibrillization. Dopaminochrome promotes the formation of spherical oligomers by inducing conformational changes, as these oligomers regained the ability to fibrillize by simple denaturation/renaturation. Taken together, these data indicate that dopamine inhibits alpha-syn fibrillization by inducing structural changes in alpha-syn that can occur through the interaction of dopaminochrome with the 125YEMPS129 motif of alpha-syn. These results suggest that the dopamine autoxidation can prevent alpha-syn fibrillization in dopaminergic neurons through a novel mechanism. Thus, decreased dopamine levels in substantia nigra neurons might promote alpha-syn aggregation in Parkinson's disease.

The E46K mutation in alpha-synuclein increases amyloid fibril formation.

The identification of a novel mutation (E46K) in one of the KTKEGV-type repeats in the amino-terminal region of alpha-synuclein suggests that this region and, more specifically, Glu residues in the repeats may be important in regulating the ability of alpha-synuclein to polymerize into amyloid fibrils. It was demonstrated that the E46K mutation increased the propensity of alpha-synuclein to fibrillize, but this effect was less than that of the A53T mutation. The substitution of Glu(46) for an Ala also increased the assembly of alpha-synuclein, but the polymers formed can have different ultrastructures, further indicating that this amino acid position has a significant effect on the assembly process. The effect of residue Glu(83) in the sixth repeat of alpha-synuclein, which lies closest to the amino acid stretch critical for filament assembly, was also studied. Mutation of Glu(83) to a Lys or Ala increased polymerization but perturbed some of the properties of mature amyloid. These results demonstrated that some of the Glu residues within the repeats can have significant effects on modulating the assembly of alpha-synuclein to form amyloid fibrils. The greater effect of the A53T mutation, even when compared with what may be predicted to be a more dramatic mutation such as E46K, underscores the importance of protein microenvironment in affecting protein structure. Moreover, the relative effects of the A53T and E46K mutations are consistent with the age of onset of disease. These findings support the notion that aberrant alpha-synuclein polymerization resulting in the formation of pathological inclusions can lead to disease.