Genetic deletion of Polo-like kinase 2 reduces alpha-synuclein serine-129 phosphorylation in presynaptic terminals but not Lewy bodies

Abstract

Phosphorylation of alpha-synuclein at serine-129 is an important marker of pathologically relevant, aggregated forms of the protein in several important human diseases, including Parkinson’s disease, Dementia with Lewy bodies, and Multiple system atrophy. Although several kinases have been shown to be capable of phosphorylating alpha-synuclein in various model systems, the identity of the kinase that phosphorylates alpha-synuclein in the Lewy body remains unknown. One member of the Polo-like kinase family, PLK2, is a strong candidate for being the Lewy body kinase. To examine this possibility, we have used a combination of approaches, including biochemical, immunohistochemical, and in vivo multiphoton imaging techniques to study the consequences of PLK2 genetic deletion on alpha-synuclein phosphorylation in both the presynaptic terminal and preformed fibril-induced Lewy body pathology in mouse cortex. We find that PLK2 deletion reduces presynaptic terminal alpha-synuclein serine-129 phosphorylation, but has no effect on Lewy body phosphorylation levels. Serine-129 mutation to the phosphomimetic alanine or the unphosphorylatable analog aspartate does not change the rate of cell death of Lewy inclusion-bearing neurons in our in vivo multiphoton imaging paradigm, but PLK2 deletion does slow the rate of neuronal death. Our data indicate that inhibition of PLK2 represents a promising avenue for developing new therapeutics, but that the mechanism of neuroprotection by PLK2 inhibition is not likely due to reducing alpha-synuclein serine-129 phosphorylation and that the true Lewy body kinase still awaits discovery.

A β-Wrapin Targeting the N-Terminus of α-Synuclein Monomers Reduces Fibril-Induced Aggregation in Neurons

“…In our paradigm, the tight correlation between DN and (i) degeneration of dopaminergic axon terminals in the striatum (Figure 5F), (ii) degeneration of dopaminergic dendrites in the SNr (Figure 5G), and (iii) astrogliosis (Figure 6G) suggests that the DN pathology is responsible for these observed effects. The functional importance of aSyn pathology in neuronal processes is consistent with the finding of presynaptic aSyn microaggregates in the absence of somatic inclusions (Spinelli et al, 2014), earlier aSyninduced oxidative stress in the synaptic terminals than in the soma (Szegő et al, 2019;Schaser et al, 2020), and the observation that presynaptic aSyn is a primary target for phosphorylation (Weston et al, 2021). As noted above, however, neuritic aSyn pathology often precedes somatic pathology, and cortical neurons with aSyn inclusions degenerate over time (Osterberg et al, 2015).…”

“…The extent of early PFF-induced aSyn pathology was determined by staining for phospho-aSyn 24 and 72 h after seeding ( Figures 1A,C ). Phosphorylation of aSyn is widely used to quantify seeded aSyn pathology ( Mahul-Mellier et al, 2020 ; Weston et al, 2021 ).…”

Polo-like kinase 2 inhibition reduces serine-129 phosphorylation of physiological nuclear alpha-synuclein but not of the aggregated alpha-synuclein

“…In contrast, PLK2 inhibition reduced the RIPA-soluble fraction of pS129 and elevated the level of soluble α-syn, corroborating earlier data reported where PLK2 inhibition led to increased α-syn level by affecting transcription an/or autophagy [10,23]. Our data are in line with a recently published study using GFP-α-syn mice crossed with PLK2 knock-out mice and another study from the same group that opted for pharmacological inhibition of PLK2 in zebra fish, demonstrating that PLK2 deletion or inhibition had no influence on aggregate-formation even though they demonstrated a slight reduction in pS129 at the studied synaptic terminals [41,42].…”

Tyrosine 136 phosphorylation of α-synuclein aggregates in the Lewy body dementia brain: involvement of serine 129 phosphorylation by casein kinase 2

“…The results suggest that S129 can be phosphorylated by multiple kinases in vivo. Moreover, PLK2 KO has been reported to have no effect on pS129 in LB but not presynaptic terminals in mice [ 36 ]. Therefore, it is likely that other, non-PLK kinases, including CK2, mediate phosphorylation of S129 of αSyn aggregates in vivo.…”