Modeling LRRK2-associated Parkinson's Disease in C. Elegans

Download or read book Modeling LRRK2-associated Parkinson's Disease in C. Elegans written by Chen Yao and published by . This book was released on 2012 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt: Parkinson's disease (PD) is a common neurodegenerative disease characterized initially by prominent motor symptoms resulting from the loss of dopaminergic neurons in the midbrain. Later in the course of disease, cognitive, behavioral and other symptoms may arise with the involvement of other brain regions. The etiology of PD remains elusive. Nevertheless, PD is believed to be triggered by aging, as well as environmental and genetic factors. Several genes have been identified as genetic factors associated with PD, which include parkin, PINK-1, DJ-1, alpha-synuclein and Leucine-rich repeat kinase 2 (LRRK2). Mutations in LRRK2 are thus far the most frequent genetic cause of autosomal dominant and idiopathic PD. LRRK2 is a multi-domain structure protein containing a Roc GTPase domain and a kinase domain, surrounded by several protein interaction domains. Two prevalent PD-linked mutations G2019S and R1441C/G occur within the LRRK2 kinase and GTPase domains respectively. To better understand the pathogenesis of LRRK2 in vivo, we have generated transgenic C. elegans overexpressing two most common LRRK2 disease-mutants G2019S and R1441C, as well as LRRK2 wildtype (WT) and K1347A GTPase-dead mutant in dopamine (DA) neurons. Overexpression of LRRK2 WT, G2019S and R1441C all caused age-dependent DA neurodegeneration, behavioral deficits, and locomotion changes accompanied by a reduction of DA level in C. elegans. In comparison, R1441C and G2019S mutants induced earlier and more severe disease phenotypes than WT LRRK2. These observations suggest that WT LRRK2 over-expression and the PD-linked mutants are all toxic to C. elegans DA neurons. Notably, over-expression of K1347A GTPase dead mutant did not cause any PD-like phenotypes, suggesting an essential role of enzymatic activity in LRRK2 linked PD. These observations also suggest that LRRK2-linked toxicity is likely from protein "gain of function". Our LRRK2 transgenic C. elegans model will be useful for studying pathogenesis of LRRK2-linked PD and for development of potential therapeutics. Small molecule kinase inhibitors have been developed as potential therapeutics for PD. However, it remains to be established whether they can mitigate neurodegeneration caused by different pathogenic mutations such as G2019S and R1441C located within and outside of the LRRK2 kinase domains, respectively. By taking advantage of our previously established LRRK2 transgenic C. elegans models, we have characterized two potent LRRK2 kinase inhibitors, TTT-3002 and LRRK2-IN1, in our worm models that allows for robust analysis of their efficacy and mechanism of action against R1441C- and G2019S-induced neurodegeneration. TTT-3002 and LRRK2-IN1 dose-dependently rescued behavioral deficit in transgenic C. elegans expressing human R1441C and G2019S LRRK2 in dopamine neurons with nanomolar to low micromolar potency at both pre- and post-symptomatic stages. Temporal treatments of TTT-3002 and LRRK2-IN1 before and after the onset of behavioral symptoms also led to long-lasting prevention and rescue of neurodegeneration in these C. elegans models of R1441C- and G2019S-linked PD. TTT-3002 and LRRK2-IN1 were ineffective against neurodegenerative phenotype in transgenic R1441C and G2019S worms with an additional inhibitor-resistant A2016T mutation, suggesting that TTT-3002 and LRRK2-IN1 specifically target LRRK2 in vivo for their observed neuroprotective effects. Our study indicates the power of the combined pharmacological and genetic approaches in the investigation of LRRK2-linked pathogenesis. Our findings indicate that kinase activity is critical for neurodegeneration caused by different LRRK2 mutations, and suggest that pharmacological inhibition of LRRK2 may represent a promising strategy for treating PD. In summary, our studies demonstrate the power of the model organism C. elegans in the investigation of LRRK2-linked PD pathogenesis and in the early development of potential PD therapeutics.