Post-transcriptional regulation of alpha-synuclein by leucine-rich repeat kinase 2 and micro-RNAs with implications for Parkinson's disease
Boon, Joon Ying
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One of the major hallmarks of Parkinson’s disease (PD) is the deposition of intracellular Lewy body inclusions. α-Synuclein is a small protein that accumulates and aggregates to form Lewy bodies. Recent studies uncovered variation of α-synuclein mRNA 3’ untranslated region (UTR), but the role of this region in regulating the α-synuclein expression is poorly understood. 3’UTR is a target region for RNA binding proteins and microRNAs (miRs) in regulating protein translation from the mRNA transcript. Leucine-rich repeat kinase 2 (LRRK2) is a key regulator of miR-mediated translational repression and is frequently mutated and causally associated with PD. We hypothesize that LRRK2 regulates α-synuclein expression post-transcriptionally via binding of miR to α-synuclein mRNA’s 3’UTR. We have found that α-synuclein mRNA with short 3’UTR has similar protein expression level to that of long 3’UTR in the absence of LRRK2 in both HEK-293 FT cells and primary hippocampal neurons. However, LRRK2 wild-type and disease mutant G2019S increased α-synuclein protein expression. In particular, an increase of 2-fold was observed for the short 3’UTR transcript, which is significantly greater than the increase for the long isoform. These data suggest differential effects of LRRK2 on α-synuclein depending on the length of 3’UTR. The short 3’UTR of the α-synuclein transcript has a binding site for miR-7; whereas, that of the long isoform has binding sites for miR-7 and miR-153. We discovered that these differential effects of LRRK2 on α-synuclein are dependent on the binding of miR-7 and miR-153 to the 3’UTR of the isoforms. Specifically, miR-7 is a stronger mediator in regulating α-synuclein translation compared to miR-153, leading to an approximately 30% inhibition of α-synuclein protein expression. Our studies have also shown that the effects of LRRK2 on regulating α-synuclein protein expression are dependent on LRRK2 kinase activity. Gain-of-kinase-function mutation, G2019S, leads to a greater increase of α-synuclein protein expression compared to wild-type; whereas, inhibition of LRRK2 kinase function decreases its effect on α-synuclein protein expression. These findings highlight novel mechanisms regulating the expression of α-synuclein involving LRRK2, miRs-7 and -153. These results highlight miRs as potential targets for reducing levels of α-synuclein in PD.