Polo-like kinase 2 regulates selective autophagic α-synuclein clearance and suppresses its toxicity in vivo

Abstract

An increase in α-synuclein levels due to gene duplications/triplications or impaired degradation is sufficient to trigger its aggregation and cause familial Parkinson disease (PD). Therefore, lowering α-synuclein levels represents a viable therapeutic strategy for the treatment of PD and related synucleinopathies. Here, we report that Polo-like kinase 2 (PLK2), an enzyme up-regulated in synucleinopathy-diseased brains, interacts with, phosphorylates and enhances α-synuclein autophagic degradation in a kinase activity-dependent manner. PLK2-mediated degradation of α-synuclein requires both phosphorylation at S129 and PLK2/α-synuclein complex formation. In a rat genetic model of PD, PLK2 overexpression reduces intraneuronal human α-synuclein accumulation, suppresses dopaminergic neurodegeneration, and reverses hemiparkinsonian motor impairments induced by α-synuclein overexpression. This PLK2-mediated neuroprotective effect is also dependent on PLK2 activity and α-synuclein phosphorylation. Collectively, our findings demonstrate that PLK2 is a previously undescribed regulator of α-synuclein turnover and that modulating its kinase activity could be a viable target for the treatment of synucleinopathies.adeno-associated virus | animal model | serum inducible kinase P arkinson disease (PD) is a neurodegenerative disorder characterized by the progressive neuronal loss in different brain regions, including the dopaminergic (DA) neurons of the substantia nigra pars compacta (SNc) (1, 2). Pathologically, PD is characterized by the presence, in surviving DA neurons, of intracellular inclusions called Lewy Bodies (LBs) and Lewy Neurites (LNs) (3). These fibrillar aggregates are mainly composed of the presynaptic protein α-synuclein (α-syn) (4). Converging evidence from pathologic, genetic, biochemical, and biophysical studies supports the hypothesis that α-syn accumulation and misfolding play a central role in the pathogenesis of PD and related disorders, which are altogether referred to as synucleinopathies (5).Although α-syn is constitutively phosphorylated at low levels (<4%) at S129 (pS129) in normal brains (6-8), a clear accumulation of pS129 (>90%) is found in LBs (8, 9) and in the brain of animal models of synucleinopathies (7,(10)(11)(12). The roles of this major posttranslational modification in regulating α-syn physiology and LB formation and/or neurodegeneration in PD remain elusive.Recently, our group and others (13-15) demonstrated that Pololike kinase 2 (PLK2), a serine/threonine kinase playing a central role in cell division, oncogenesis, and synaptic regulation in the adult brain (16-19), efficiently phosphorylates α-syn, with an exclusive preference for the S129 site. Unlike other kinases that were reported to partially phosphorylate α-syn at S129, PLK2 phosphorylates α-syn with quantitative conversion in vitro (>95%) and in mammalian cell lines (13-15).Interestingly, PLK2 expression levels are significantly up-regulated in the midbrain of aged monkeys and correlate with increased pS129 levels in dopaminer...

α-Synuclein interacts with the switch region of Rab8a in a Ser129 phosphorylation-dependent manner

“…However, the relevance of αS phosphorylation at S129 for neurotoxicity and disease remains controversial (Basso et al, 2013). While some reports report a beneficial effect (Kuwahara et al, 2012;Oueslati et al, 2013), others identified deleterious consequences (Chen and Feany, 2005;Sato et al, 2011). A separate study found no effects of this posttranslational modification (McFarland et al, 2009).…”

Silencing synuclein at the synapse with PLK2

“…Because the phosphorylation of S129 appeared to have no consistent effect on α-syn function in the cell, it has been unclear whether the process does anything more than reflect the magnitude of total α-syn levels in diseased neurons. In their article in PNAS, Oueslati et al (6) now reveal a unique and unexpected effect coupled to S129 phosphorylation.…”

“…Although this may at first appear irrelevant to α-syn, which is mostly located at presynaptic terminals in neurons, it should be noted that increased synaptic activity promotes α-syn secretion from neurons, and that phosphorylated α-syn is enriched in the secreted fraction of some cell types (15,16). Given the suggestion that α-syn secretion is a key step in a prion-like cell-to-cell transfer of α-syn pathology and thereby contributes to progression of PD symptoms (17), the findings by Oueslati et al (6) suggest that PLK2 might influence transmission of misfolded α-syn variants.…”

“…Oueslati et al (6) show that the phosphorylation of S129 of α-syn is no exception. This is because the kinase of interest, polo-like kinase 2 (PLK2), not only phosphorylates α-syn, but also escorts modified α-syn into the autophagy pathway for degradation.…”

“…Oueslati et al (6) demonstrate that after phosphorylating α-syn at S129, PLK2 binds α-syn via this polo-box domain and escorts it into a degradation pathway, most likely of autophagy/lysosomal origin (Fig. 1).…”