LRRK2 impairs autophagy by mediating phosphorylation of leucyl‐tRNA synthetase

Abstract

Leucine‐rich repeat kinase 2 (LRRK2) is a causal gene of Parkinson disease. G2019S pathogenic mutation increases its kinase activity. LRRK2 regulates various phenotypes including autophagy, neurite outgrowth, and vesicle trafficking. Leucyl‐tRNA synthetase (LRS) attaches leucine to tRNALeu and activates mTORC1. Down‐regulation of LRS induces autophagy. We investigated the relationship between LRRK2 and LRS in regulating autophagy and observed interaction between endogenous LRRK2 and LRS proteins and LRS phosphorylation by LRRK2. Mutation studies implicated that T293 in the LRS editing domain was a putative phosphorylation site. Phospho‐Thr in LRS was increased in cells overexpressing G2019S and dopaminergic neurons differentiated from induced pluripotent stem (iPS) cells of a G2019S carrier. It was decreased by treatment with an LRRK2 kinase inhibitor (GSK2578215A). Phosphomimetic T293D displayed lower leucine bindings than wild type (WT), suggesting its defective editing function. Cellular expression of T293D increased expression of GRP78/BiP, LC3B‐II, and p62 proteins and number of LC3 puncta. Increase of GRP78 and phosphorylated LRS was diminished by treatment with GSK2578215A. Levels of LC3B, GRP78/BiP, p62, and α‐synuclein proteins were also increased in G2019S transgenic (TG) mice. These data suggest that LRRK2‐mediated LRS phosphorylation impairs autophagy by increasing protein misfolding and endoplasmic reticulum stress mediated by LRS editing defect. Significance of the study Leucine‐rich repeat kinase 2 (LRRK2) is the most common genetic cause of Parkinson disease (PD), and the most prevalent pathogenic mutation, G2019S, increases its kinase activity. In this study, we elucidated that leucyl‐tRNA synthetase (LRS) was an LRRK2 kinase substrate and identified T293 as an LRRK2 phosphorylation site. LRRK2‐meidated LRS phosphorylation or G2019S can lead to impairment of LRS editing, increased ER stress, and accumulation of autophagy markers. These results demonstrate that LRRK2 kinase activity can facilitate accumulation of misfolded protein, suggesting that LRRK2 kinase might be a potential PD therapeutic target along with previous studies.

Protein Kinase C Isozymes and Autophagy during Neurodegenerative Disease Progression

“…p62 has a binding site at the N-terminal region of LRRK2, and overexpression of p62 affects the autophagic degradation of LRRK2 [106]. Comparably similar studies showed that LRRK2 interacts with different targets as leucyl-tRNA synthetase [107], nicotinic acid adenine dinucleotide phosphate [108], dynamin-like protein 1 [109] and activation of MEK/ERK pathway by MAPK/ERK kinases phosphorylation [110]. Wild-type α-synuclein protein in Parkinson's disease is efficiently degraded by CMA.…”

The Vicious Cycle Between α‐Synuclein Aggregation and Autophagic‐Lysosomal Dysfunction

“…Mutations on LRRK2 are the most common known genetic causes for PD. The most prevalent pathogenic mutation, G2019S, increases LRRK2 kinase activity and impairs the autophagy process, leading to a significant accumulation of α‐syn, as assessed by in in vitro and in vivo experiments …”

Induced pluripotent stem cell‐based modeling of mutant LRRK2‐associated Parkinson's disease

“…LRRK2 is pivotally involved in regulating proteostasis by its effect on (at least) two major proteostatic mechanisms: on the one hand, it regulates macroautophagy by affecting the phosphorylation status of the key autophagy protein Beclin‐1 (Manzoni et al., ) and the mammalian target of rapamycin (mTOR) regulator Leucyl‐tRNA synthetase (LRS) (Ho et al., ). On the other hand, LRRK2 is under normal conditions degraded via both proteasomal and lysosomal pathways.…”

“…() found that the LRRK2 variant I2020T, too, is associated with increased LC3‐II levels. In a recent study, Ho and colleagues used several cell models including iPSC‐derived mesDA neurons from G2019S carriers to demonstrate that the mTOR regulator leucyl‐tRNA synthetase (LRS) is phosphorylated by LRRK2 in a genotype‐dependent way, and that G2019S‐associated hyperphosphorylation was linked to impairment of the autophagic system (Ho et al., ). These data suggest that LRRK2 may affect macroautophagy at several levels, including phosphorylation of LRS and Beclin‐1 (Manzoni et al., ).…”

“…A major limitation of the iPSC technology is posed by the fact that reprogramming of somatic cells into the pluripotent state resets not only the cell's identity but also erases its age-associated epigenetic memory (Horvath, 2013). Consequently, iPSCs exhibit embryonic-like epigenetic profiles with only very weak residual aging signatures (Lo Sardo et al, 2017), thus posing a severe limitation for modeling age-related pathologies.…”