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

Accumulation of aggregated alpha-synuclein (-syn) is believed to play a pivotal role in the pathophysiology of Parkinsons disease (PD) and other synucleinopathies. -Syn is a key constituent protein of Lewy pathology, and -syn phosphorylated at serine-129 (pS129) constitutes more than 90% of -syn in Lewy bodies and hence, it is used extensively as a pathological marker for the aggregated form of -syn. However, the exact role of pS129 remains controversial as well as the kinase(s) responsible for the phosphorylation. In this study, we investigated the effect of Polo-like kinase 2 (PLK2) inhibition on formation of pS129 using ex-vivo organotypic brain slice model of synucleinopathy. Our data demonstrated that PLK2 inhibition has no effect on -syn aggregation, pS129 or inter-neuronal spreading of the aggregated -syn seen in the organotypic slices. Instead, PLK2 inhibition reduced the soluble nuclear pS129 level confined in the nuclei. The same finding was replicated in an in-vivo mouse models of templated -syn aggregation and human dopaminergic neurons, suggesting that PLK2 is more likely to be involved in S129 phosphorylation of soluble non-pathology related fraction of -syn. We also demonstrated that reduction of nuclear pS129 but not the aggregates specific pS129 following PLK2 inhibition for a short time before sample collection improves the signal to noise ratio when quantifying pS129 aggregate pathology.