Human R1441C LRRK2 regulates the synaptic vesicle proteome and phosphoproteome in a Drosophila model of Parkinson’s disease

<span class="paragraphSection"><div class="boxTitle">Abstract</div>Mutations in <span style="font-style:italic;">leucine-rich repeat kinase 2</span> (<span style="font-style:italic;">LRRK2</span>) cause late-onset, autosomal dominant familial Parkinson`s disease (PD) and variation at the <span style="font-style:italic;">LRRK2</span> locus contributes to the risk for idiopathic PD. LRRK2 can function as a protein kinase and mutations lead to increased kinase activity. To elucidate the pathophysiological mechanism of the R1441C mutation in the GTPase domain of LRRK2, we expressed human wild-type or R1441C LRRK2 in dopaminergic neurons of <span style="font-style:italic;">Drosophila</span> and observe reduced locomotor activity, impaired survival and an age-dependent degeneration of dopaminergic neurons thereby creating a new PD-like model. To explore the function of LRRK2 variants <span style="font-style:italic;">in vivo</span>, we performed mass spectrometry and quantified 3,616 proteins in the fly brain. We identify several differentially-expressed cytoskeletal, mitochondrial and synaptic vesicle proteins (SV), including synaptotagmin-1, syntaxin-1A and Rab3, in the brain of this LRRK2 fly model. In addition, a global phosphoproteome analysis reveals the enhanced phosphorylation of several SV proteins, including synaptojanin-1 (pThr1131) and the microtubule-associated protein futsch (pSer4106) in the brain of R1441C hLRRK2 flies. The direct phosphorylation of human synaptojanin-1 by R1441C hLRRK2 could further be confirmed by <span style="font-style:italic;">in vitro</span> kinase assays. A protein–protein interaction screen in the fly brain confirms that LRRK2 robustly interacts with numerous SV proteins, including synaptojanin-1 and EndophilinA. Our proteomic, phosphoproteomic and interactome study in the <span style="font-style:italic;">Drosophila</span> brain provides a systematic analyses of R1441C hLRRK2-induced pathobiological mechanisms in this model. We demonstrate for the first time that the R1441C mutation located within the LRRK2 GTPase domain induces the enhanced phosphorylation of SV proteins in the brain.</span>

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