Functional proteomics of mutant LRRK2 induced Parkinson's Disease
Final Report Abstract
Parkinson’s disease (PD) is the second most common neurodegenerative disorder and causes progressive motor dysfunction as the result of dopaminergic neuron loss in the substantia nigra. Degenerating neurons undergo “dying back”, in which distal axons degenerate prior to cell bodies. LRRK2 G2019S is the most common genetic mutation known to cause PD. PD patients with LRRK2 resemble sporadic PD and contain aggregates of α-Synuclein. Because LRRK2 G2019S causes increased kinase activity, small molecule inhibitors are being developed as possible PD therapeutics. However, the mechanism of pathogenesis is not known, making drug discovery very difficult. To better understand the mechanism of LRRK2 pathogenesis, we performed quantitative phosphoproteomics of neurons differentiated from induced pluripotent stem cells (iPSCs) with and without a LRRK2 kinase inhibitor. We found that phosphorylation of TAU is LRRK2 dependent. This is significant because TAU has been previously linked to PD pathology. Since TAU is an axonal protein, we assessed axonal trafficking and found that neurons with LRRK2 G2019S showed profound defects in the transport of lysosomes and mitochondria in the distal axon, but not in the proximal axon. This was the first striking read out for the direct role that LRRK2 plays in degeneration. Axonal trafficking defects were caused by a gain-of-function by LRRK2 G2019S as shown by amelioration of defects by a LRRK2 knockout as well as by LRRK2 inhibition. Ablation of a TAU phosphorylation site partially rescued axonal transport. α-Synuclein pathology is a hallmark of PD, and we found that neurons with LRRK2 G2019S contained more α- Synuclein protein and spread aggregation more efficiently compared to isogenic WT neurons. Significantly, we demonstrated that spreading of α-Synuclein aggregation in neurons with LRRK2 G2019S required phosphorylated TAU. Taken together, these results demonstrate that LRRK2 G2019S induced dying back pathology and α-Synuclein via increased TAU phosphorylation.
Publications
- Distinct Neurodegenerative Changes in an Induced Pluripotent Stem Cell Model of Frontotemporal Dementia Linked to Mutant TAU Protein. Stem Cell Reports. 2015 Jul 14;5(1):83-96
Ehrlich M, Hallmann AL, Reinhardt P, Araúzo-Bravo MJ, Korr S, Röpke A, Psathaki OE, Ehling P, Meuth SG, Oblak AL, Murrell JR, Ghetti B, Zaehres H, Schöler HR, Sterneckert J, Kuhlmann T, Hargus G
(See online at https://doi.org/10.1016/j.stemcr.2015.06.001)
